Better Upscaling and Optimization of Nanoparticle and Nanostructure Production by Means of Electrical Discharges

Información del proyecto

BUONAPART-E

Identificador del acuerdo de subvención: 280765

Proyecto cerrado

Fecha de inicio 1 Febrero 2012

Fecha de finalización 31 Enero 2016

Financiado con arreglo a

• Specific Programme "Cooperation": Nanosciences, Nanotechnologies, Materials and new Production Technologies

Coste total € 10 423 897,40

Aportación de la UE € 7 799 929,00

Coordinado por

UNIVERSITAET DUISBURG-ESSEN
Germany

Final Report Summary - BUONAPART-E (Better Upscaling and Optimization of Nanoparticle and Nanostructure Production by Means of Electrical Discharges)

Executive Summary:
The BUONAPART-E project demonstrated that a physical nanoparticle synthesis process can be economically scaled up to yield a production rate of several kg/day. The process is simple, versatile, and reliable. It avoids chemical precursors and solvents, while fully recycling the necessary inert carrier gas, resulting in a minimal impact on the environment. The main goal of BUONAPART-E was to increase the production rate of a single set of electrodes, which evaporate the raw material by electric means by a factor of 10 to 100 and to implement necessary monitoring and collecting tools to ensure high quality product delivery. Production rates of 36 g/h (Zn), 4.4 g/h (Cu) and 1.0 g/h (Ag) have been obtained for a single unit, leading to a specific electricity consumption of 12, 179 and 6807kWh/kg.

The developed process is a major step forward in the availability of high-purity metallic nanoparticles (NPs) with high-process throughput (guaranteed by the concept of parallelisation of simple single units), low product costs and high energy-efficiency, with minimal impact on the environment. A major advantage of the process is the possibility of producing NPs with nanostructures and sizes on customer demands with a simple process route that can be applied to multiple variants. Several process variations using electrical discharges have been developed (low-cost DC arc discharge, glow discharge, high-frequency spark discharge) which have a high degree of innovativeness and can be chosen according to the requirements of the application targeted, such as the required primary particle size. The arc discharge has the highest production rate and applies a low-cost power supply (200 EUR/kW, commercial plasma power supplies cost 8000 EUR/kW), whereas the spark discharge can produce smaller primary particles.

The motivation behind the choice of an electrical discharge as a synthesis platform stems from the experience of BUONAPART-E consortium that this technology is cost-efficient to implement and easy to use, while still allowing for rapid process optimization. As the basic unit is just a pair of electrodes and a large number of these pairs can be placed in a single housing, it is evident that a cost-effective scaling-up strategy include the use of multiple units in parallel. This strategy is analogous to supercomputers based on low-cost graphic cards from the consumer market. The main input is electric power for the electric discharges. Pilot plants with up to 16 individual electrode sets have been developed and shown to have the same product quality, production rate and energy consumption per kg product as the single unit but at reduced cost, thereby showing the soundness of this scaling-up approach. The process is designed for enabling low workplace exposure to nanoparticles. It avoids complicated and expensive safety measures, as quasi-atmospheric inert gas is used as transport medium and hazardous chemicals are avoided. All these factors make this process a clear example of a green and sustainable synthesis process.

The availability of a simple and low-cost nanoparticle generation system which is precursor-free means that it is possible to integrate the synthesis step into another process which requires nanoparticles for integration in the final product. This is demonstrated by several applications in the BUONAPART-E consortium, in which a nanoparticle generator is used for direct feeding of the process with gas-carried nanoparticles or for direct deposition of freshly synthesized nanoparticles on intermediate or final products. This direct integration is especially relevant for metallic nanoparticles, as these are often oxidation-sensitive and a transport or storage of the intermediate product nanoparticles presents risks for the application as well as the working place or the environment. The versatility of the synthesis process was demonstrated by means of six very different applications requiring nanoparticles and having various requirements for which the synthesis unit was optimized. Here either the nanoparticle product quantity is crucial or the nanoparticle quality and effectiveness of the integration strategy.

Project Context and Objectives:
The BUONAPART-E project aimed at demonstrating that a physical nanoparticle synthesis process can be economically scaled up to yield a production rate of several kg/day. The process is simple, versatile, and reliable. It avoids chemical precursors and solvents, while fully recycling the necessary inert carrier gas, resulting in a minimal impact on the environment. The process does not necessitate external heating of the inert gas, thereby keeping electricity consumption low. The main goal of BUONAPART-E was to increase the production rate of a single basic unit in which the evaporation of the raw material is done by electric means by a factor of 10 to 100 and to implement necessary monitoring and collecting tools to ensure high quality product delivery.

The challenge addressed in BUONAPART-E was to obtain an increase in the production rate, while retaining energy efficiency. The process allows for the synthesis of different materials using the same production platform. The basic evaporation unit (called hereafter the Optimal Single Unit or ‘OSU’) is a set of electrodes (Fig. 1).

The scaling-up strategy is basically numbering-up the basic electrode pair. A large number of these units can be placed in a single housing, contributing to the cost-effectiveness of the process. The use of many single production units in parallel, which can be thoroughly optimized and tested on a lab scale for a given material, ensures that a highly-effective scale-up of the synthesis process in terms of cost and electricity consumption is possible. Further equipment, such as pumps, power supply to the OSUs and the particle collection unit, can be scaled up as single units leading to additional cost benefits (Fig. 2).

In order to reach these objectives, the project was structured into 8 work packages (Fig. 3), which enabled step-wise progression of the scaling up of the synthesis process, while integrating specifications from technology developers and end-users of nano-technologies.

The main objective of the Fundamental work package (WP1) was to understand the underlying mechanisms that result in NP formation in atmospheric pressure discharge generators, more specifically arc and spark discharges, and to develop theoretical models to describe these processes. These goals were achieved by using a combination of in-situ optical and electrical measurements, particle sampling and computer simulations. Beyond enabling us to explain the relationships between process parameters and particle properties the research performed supported the design of an efficient NP generator and provided the scientific basis for the development of in-situ monitoring technologies, namely DENSMO and DIMON, which are essential for the robust operation of the multi-unit pilot plant.

The scientific work was divided in the following three tasks:
1.1 Plasma diagnostics of electrical discharges
1.2 Particle formation model development and validation
1.3 Investigation of the OSU by diagnostic measurements and modelling

The objective of WP2 (OSU and core technology development) was to establish an optimized single-electrode pair unit (OSU) and to determine the optimal process parameters for both the strongly pulsed (spark) and the continuous (miniarc and arc) operation modes. We achieved a maximized production rate, control of the particle size with large variability and stable operation. Preparation for scaling up with multi-electrode systems was another goal achieved. Finally, we delivered limited amounts of material, produced under adapted process conditions, to the end-users (WP5).
The overall aim of WP3 (Supporting Technology) was to provide the supporting technology necessary to apply the generated NP in various target products (within WP5). This included downstream technologies between the OSU and subsequent product manufacturing steps as well as the technology needed to integrate the OSU (the NP production itself) into the production processes of the target applications. Therefore, a number of objectives were defined:
Product flow pre-treatment steps were developed to enable further application of the particles, when special requirements have to be fulfilled. This includes the exclusion of too large particles (which might occur from splashing), the tailoring of particle size and shape and the narrowing of the width of the size distribution, the adjustment of particle charge, and the passivation of reactive particles by a controlled oxidation of an outer shell for safe handling.
Particle collection techniques were developed and adopted for collection of powder products and for wet and dry deposition of particle layers, especially targeting the applications in WP5. A dry powder collection device for larger production of metallic NP in an upscaled demonstration plant (multi-OSU arrangement in WP4) with special regard to system inertisation and safe handling of pyrophoric NP, including necessary cleaning procedures had to be developed. Also, different dry and wet routes (including the production of stable NP suspensions) for applying particle films, patterns and coatings on different substrates, such as textile fibres, or ceramic or semiconductive substrates were developed and compared.
The development of suitable monitoring devices for the proper operation of the arc or spark generators, but also for the suitable quality of the produced particles is an additional aim of WP3. On one side, this is needed for the reliable continuous long-time operation of multi-generator units for high production rates.
On the other hand, these devices allow for the integration of the particle production into manufacturing lines; for some applications, it is necessary to directly use the generated airborne NP without collection, so the integration of the particle production into the process line is a key requirement here. For these applications, the monitoring devices have to be affordable and easy to use, especially for technical personnel not experienced in aerosol measurements or plasma diagnostics.

The production rate of a single OSU was successfully optimized within WP2, but for further increase in production, it is evident that a cost-effective scaling-up strategy includes the use of multiple units in parallel. The single housing containing 8 OSUs is called the multiple-OSU (mOSU), and is the basis for scaling-up. In Work package 4 (Scaling-up) we demonstrated the efficient parallelisation in pilot plant up to 16 OSUs in a closed-loop carrier gas recycling system in a production facility yielding 1.6 kg Cu nanopowder/day, using established up-scaling technologies for all utilities, such as pumps and power supply. The pilot plants were designed while laying a strong emphasis on safety for human health and the environment. It was also shown that the product quality as produced by the multiple parallel OSUs and the single unit are identical. The feasibility of a further scale-up to a 100 kg/day production facility was assessed to be feasible as well.

In Work package 5 (Feasibility studies and cost benefit analysis for sample potential applications), six end-users from different industries contributed to the evaluation of the nanoparticles and at the same time incited the core technology developers from WP2 as well as the supporting technology developers from WP3 to come to a versatile and flexible process. The possibility to introduce an electrical discharge unit in aerotaxy® growth tools was evaluated and recommendations given to the OSU design team. The integration of nanoparticles in various textiles and composites for antibacterial / biocide / flavour modifier / flame retardant or conductive properties were investigated. A new concept of fabrication of a photonic sensor chips was explored. In addition, the use of nanoparticles to improve cooling of a blast furnace and to enhance the catalytic properties of a membrane reactor were evaluated.

Work package 6 (Efficiency, Risk and Economical Assessment) assessed feasibility, economic viability and potential risks to workers and the environment when taking the BUONAPART-E concept into large-scale use, with many process units (OSU) operated in parallel. While operating OSU and later mOSU setups, measurements related to environment, health and safety (EHS) involved the production stage with emphasis on removing the NP product from the production unit, risks of handling metallic NP and later use in commercial products. Pyrophoricity is one important feature here. Energy use evaluation addressed spark versus arc systems, producing diverse NP sizes with varying production rates and energy use (electricity). However, electricity costs contribute a minor part to the total, and for the environmental footprint the wider approach of life cycle assessment (LCA) addressed, besides energy, the impact on human health, natural resources and the ecosystem, using a commercial software. This was extended to commercial products that contain metallic NP, assessing the relative life cycle impact (LCI) with respect to the “bulk” material it is mixed with. The feasibility and economics of scale-up to large production rates was evaluated based on comparing the results of OSU and mOSU setups, showing how production costs for NP production decrease when scaling up by parallelization of OSU.

Work Package 7 deals with Training, exploitation and dissemination, whereas Work Package 8 takes care of the Administrative and financial management.

Project Results:
WP1: FUNDAMENTALS

Arc and spark discharges can be transformed into each other by changing the experimental conditions, therefore their operation is interrelated. Still, since the two discharge regimes are of major interest for the BUONAPART-E project, they have been investigated separately and the scientific results achieved will also be presented in two separate parts below. There were also similarities in the approaches used in the arc- and spark-based scientific works. First, the scientific challenges of electrical discharge based NP synthesis were tackled by using theoretical and experimental approaches in synergy for devising fundamental understanding of processes leading to NP formation. Second, the scientific toolbox of experimental techniques was, to a large extent, also common, namely electrical and optical (i.e. imaging and spectroscopic) information were acquired, since these observations are non-invasive and allow for studying the discharge and NP formation processes without the need to alter the electrode geometry and other conditions of the discharge gap. Third, the use of different modelling routes, ranging from first principle to engineering calculations, was also essential in order to cover the many orders of magnitude time-scale and the plethora of processes that contribute to NP production.

Spark discharge:
The fundamental processes occurring in a spark discharge are less understood and more difficult to access both experimentally and theoretically due to its strong transient nature. Therefore the prerequisite of studying the spark process was to design and build a spark discharge generator for the fundamental investigations and develop a modelling toolbox for describing the elemental processes leading to NP generation.
The experimental efforts were naturally centred around the OSU design, but needed to address several unique issues which are specific to the fundamental measurements. Examples to these include:
• For the temporal characterisation of spark events, devising a reproducible way of triggering for the data acquisition was a must. Various potential trigger signal sources (i.e. optical (photodiode based) and electrical (voltage and current) signals) were studied in depth. It was found that the voltage waveform signal is the most appropriate for general triggering use.
• Strong electromagnetic interference (EMI) was detected around the spark gap, which was characterised thoroughly. It was concluded that optical signal connections should be preferred and/or extensive EM shielding of the spark generator must be implemented to trust any collected data.
From the modelling point of view it was essential to develop a multi-scale physical model (Fig. 4), which consists of a three-stage plasma discharge model that handles i) streamer formation and propagation between the electrodes, ii) streamer-to-spark transition and hence plasma formation, and iii) electrode processes like Joule heating and electrode erosion. The plasma discharge model is complemented by a NP formation module, which uses the amount of metal flux ejected from the electrode as a key input parameter.

The early stages of the spark process were studied in detail. This was achieved experimentally by fast (ns-scale) time-resolved spectroscopic, electrical and imaging measurements and theoretically by using and fine-tuning/refining the modules of the multi-scale NP formation model. Our most important achievements in these fields include the followings:
• The fundamental investigation of sparking was done using various (Cu, Ni, Ag and Au) electrodes, in N2, as well as Ar atmosphere under a wide range of other experimental conditions (e.g. electrode geometry, gas flow rate, spark frequency and spark energy).
• The acquired time resolved emission spectra proved the presence of atomic and ionized species of both the carrier gas and the electrode material. We proved that right after the ignition of the discharge, the emission of doubly charged ions of the carrier gas peaks first at very early times (ca. 100 ns), while the emission of singly charged and neutral species follow suit later, typically on the sub-µs timescale and exhibiting broader peaks. Emission from the species of the electrode material starts in the µs-range and lasts significantly longer (10-12 µs in duration). We found no significant difference in the temporal behaviour of the four electrode metals studied (Fig. 6).
• Key plasma diagnostic parameters, such as temperature, electron concentration and degree of ionization were all derived from spectroscopic data.
o The Boltzmann method was used for both carrier gas and electrode material species to derive information on the temperature of the species in the spark gap. The temporal variation of the temperature is consistent and proves that i) the momentary temperature of the spark plasma drops from above 20000 Kelvins to 8000-10000 K in 10 µs and ii) the atoms of the electrode material cool slower in Ar, as compared to N2.
o We found that the electron concentration drops from values around 3·1018 cm-3 (Ar spark) and 1·1018 cm-3 (N2 spark) to values around 2·1017 cm-3 during the first 4 µs of a Cu spark discharge and decreases further down to ~1·1016 cm-3 by 20 µs.
• We collected imaging data on the time evolution of the morphology of the spark channel. Apart from the expansion of the plasma plume these data also revealed that i) the shape of the light emitting cloud varies in time and ii) a hot spot exists in the spark plasma during the time period in which the current is ringing and that iii) the axial position of this hot spot oscillates over time in synchron with the polarity changes occurring in the gap voltage.
• The gas atmosphere (Ar or N2) has a dramatic effect on the time evolution of the concentration of electrode material in the gap. In N2, the concentration of electrode material in the discharge monotonously increases until the end of the electrical oscillations, while in Ar, the electrode material persists in the discharge gap several µs after the electrical oscillations ceased (Fig. 6).
• Our plasma diagnostic investigations proved that the characteristics of consecutive sparks (in accordance with the normal operating conditions in a spark OSU) are not independent from each other. Preceding sparks always influence the characteristics of follow up sparks in the train, even at spark frequencies below 10 Hz.
• Combining electrical and imaging data, we showed that the emitted light signal correlates well with the instantaneous power dissipated in the plasma and it has been found that the ca. 80% of the energy of the plasma is dissipated in the first ca. 2 µs of the plasma lifetime.
• We employed simplified phenomenological, detailed numerical and computational modelling for the theoretical description of the NP formation. First, the main physical processes involved in spark discharge were identified and their time scales estimated. Then the processes of streamer formation, streamer propagation and streamer-to-spark transition were studied.
• Gas temperature in plasma channel during electric current, adiabatic expansion and cooling due to thermal conductivity changes were evaluated. The temperature values and temporal evolution agreed well with experimental values measured under similar conditions.
• The contributions of Joule heating, ion bombardment and thermal conduction to the increase of the temperature of the electrode surface were calculated and the role of evaporation and sputtering in electrode erosion was investigated. The calculated electrode mass loss values showed good agreement with the measured ones.
• The role of experimental parameters such as gap size, inductance of the discharge loop, and roughness of electrode surface were elucidated modelling-wise. It was shown that i) there is an optimal energy where energy absorption by the cathode is maximum (~0.5 J for Cu in N2) and ii) it is preferable to use cables with low inductance.

The other focus of the fundamental activities was related to the spark electrodes. Beyond the efforts devoted to the determination of electrode temperature, the study of the electrode erosion with microscopic and chemical analysis was also carried out.
• Modelling results backed up the experimental finding that in spite of the thousands of Kelvin local transient temperatures existing at the plasma channel entry point on the surface of the electrode, the equilibrium temperature of the electrode hardly increases by 10-15 K above room temperature.
• Computer modelling demonstrated that thermal evaporation, due to electrode heating, and sputtering, caused by ion bombardment, can play role in electrode material removal though we found that evaporation dominates the erosion process.
• Gravimetric data on electrode erosion was also used in modelling and allowed the calculation of the fraction of the spark energy actually resulting in electrode material evaporation.
• The morphological and compositional changes of micro-polished electrode surfaces subjected to single and multiple oscillatory spark discharges were used to document three erosion features, figuratively described as dentritic, undulated and crater-like regions. Our results indicate that the erosion process is highly complex, and involves concurrent evaporation/sputtering, material deposition and hydrodynamic sub-processes.
• Electrode erosion experiments also brought important findings. It was found that when the spark generator is run for an extended period of time (e.g. hours), periodic surface structures (arranged protrusions) emerge on the facing surfaces of the cylindrical electrodes. The morphological investigations proved that the protrusions are a few 100 µm in diameter and typically less than 10 µm in height. The experimental data excluded that the pattern formation would be chemically driven or would stem from pre-existing surface structures due to machining. The detailed explanation of this pattern formation is still under study.
In order to gain insight into the early stages of the NP growth process i) sampling the particle population in the vicinity of the discharge and ii) the morphological analysis of the collected NPs were also performed.
• A thermophoretic sampler for collecting NPs on TEM grids in the proximity of the electrodes was constructed. The sampler was used to investigate the production of metal NP around different discharges. Thermophoretic sampling of Au NP was carried out and particle properties were compared to those of aggregated nanoparticles sampled by an electrostatic precipitator downstream of the SDG.
• Systematic measurements have been done on the primary particles of gold. The particles have been sampled downstream of the OSU and subsequently analysed using TEM imaging. It has been found that the particles are perfectly spherical and their characteristic size is smaller than 5 nm. The primary particle size can be adjusted in a range of 2.5 nm to 5 nm by changing the dilution flow rate.

The formation of primary particles was described both via first principle and semi-empirical models.
• Both models predict similar size distribution of the NP that observed experimentally, though useful for different purposes. While first principle modelling assists in finding a balanced, i.e. non-oversimplified description of the nucleation, growth, NP collision, coagulation and aggregation processes (and e.g. was used to prove the existence of self-preserved nanoparticle size distribution), the semi-empirical model more easily predicts the size evolution of primary NP as a function of process parameters, such as gas flow rate and energy per spark.
• The first principle NP formation model proved that plasma column expansion and cooling of the ejected electrode material play essential role in the formation of primary NPs by homogeneous nucleation. Both electrode evaporation and sputtering mechanisms for electrode erosion were considered. Gas motion was described by hydrodynamic equations and accounted for particle nucleation and growth in the model. Finally, secondary particle formation, originating from the primary ones via coagulation, agglomeration and/or sintering on much longer timescales, when the vapour cools down due to diffusion in the carrier gas. Also, particle loss to the reactor surfaces decreases the particle concentration in the gas and hence the NP yield. We identified that the rates of these processes depend on parameters such as electrical charge of particles, particle number concentration, gas temperature and gas flow conditions. As a result, the NP size distribution is investigated as a function of potentially relevant experimental conditions. The effect of plasma parameters on the mean size, size dispersion and morphology of NP assemblies was examined.
• The semi-empirical model yields the size of perfectly coalesced, so called singlet particles and is applicable to cases, where the particles are small and clean enough to coalesce completely into spheroids, e.g. for Au or Ag NP smaller than 5 nm at room temperature. This analytical model, that neglected the diffusional losses and assumed a constant coagulation kernel, was refined to a numerical model which is able to describe the particle size as a function of primary process parameters (Fig. 7).

Arc discharge:
When investigating the arc, measurements were done with Cu, Ag and Zn metals in both N2 and Ar atmospheres under different electric currents, input powers and gas flow rates. Moreover, the geometry of the arc source was extensively studied until an optimized design was achieved.

The experimental investigation of the arc, with least disturbance to the NP generation process, was achieved by analysing the emitted light of the gap via spectroscopy and imaging. Our major findings are the followings:
• Spatially and temporally averaged emission spectra were collected under different discharge conditions. The arc spectrum is characterized by a strong atomic emission of the evaporated electrode material, as well as a strong continuous emission from the electrodes. We found that the major constituent present in the arc gap is not the atomic or molecular background gas, but the metal vapour extracted from the cathode.
• Species concentrations were also assessed by spectroscopic measurements. It was found that the plasma is mainly composed of neutral species of the electrode, with no significant traces of metal ions.
• The spectroscopic methods resulted in, ca. 2700 K electrode temperature and 3500-18000 K gas temperatures, depending on the metal and input power used.
• The main trends in the change of plasma parameters as a function of the most important process parameters were found to be the followings:
o An increase in power and lateral flow produces a wider arc flame.
o The input power and lateral flow has minor effect on the average gas temperature for Cu and Ag. However, a clear rise in average temperature with power is observed for Zn arc.
o We have observed how the gas temperature rises with the arc power and how it decays as the distance from the cathode tip is increasing. It was also observed that arcs produced in Ar show no atomic metal vapor emission and that the gas temperature is higher than the one obtained in N2.
o The metallic emission (similar to metal vapour concentration) increase strongly with an increasing electrical power, while its behaviour with gas flow depends on the particular metal.

Proximity sampling of the NP population, accompanied with the dimensional and structural analysis of the stabilized particles, collected downstream of the OSU was also carried out. Computer modelling assisted the understanding, optimization and the control of the arc-based NP generation process. With regards to this, our major observations were the followings:
• Proximity sampling was used to determine the evolution of NP size in the vicinity of the arc. The analysis of primary particles is performed at different positions around the crucible. Particles are successfully sampled at three different characteristic moments during primary particle growth; shortly after nucleation, during common growth processes and when growth of primary particles has been finished. A sample insertion directly into the arc discharge shows a high concentration of singular particles with a mean number weighted particle size of 29 nm (surface weighted 42 nm). Further sampling around the arc revealed a common formation of agglomerates with primary particle sizes in the range of 42-60 nm. Here, heterogeneous nucleation and coagulation still contribute to the particle growth. A decreasing trend of primary particle size and standard deviation are found towards the particle formation zone and towards the diagonal axis with which the arc stream aligns itself.
• Ex-situ TEM, BET and SMPS/ELPI measurements enabled analysis of particles and agglomerates collected downstream of the generator. Primary particle sizes upwards from 84-88 nm were found.
• It was found that the particle growth is almost completed at a distance of 2 cm from the particle formation zone.
• Both computational fluid dynamics (CFD) and first-principle Monte Carlo (MC) simulation models were elaborated and iteratively refined to describe NP condensation, aggregation and growth.
• Particle dynamics and transport in the carrier gas flow for the arc discharge generator was modelled by CFD. A system of aerodynamic equations based on the moments of the size distributions integrated in a CFD environment is solved together with gas flow, temperature and metallic vapour concentration fields in 3D. The electrode surface temperature and the outwards flux of atoms from the electrodes, both determined experimentally, serve as boundary conditions to the model.
• Temperature and metal vapour concentration data from 3D simulations of trajectories of fluid particles served as inputs for the simulations of the particle size distribution by MC methods.
• A highly efficient MC code was developed using low-cost graphic cards (GPUs) for describing the aggregation and the concomitant morphology evolution of NPs.
• The MC simulation shows that the N2 arc produces bigger particles than the Ar arc. The number concentration of particles is approximately the same for both aerosols. However, due to the increased mean size in the N2 arc, its mass output is much higher. The Ar arc results in less sintered particles, i.e. agglomerates formed in Ar are therefore expected to contain more particles with smaller sizes.
• The calculations are validated by comparing the results of the models to the experimentally found particle results. It can be concluded that the models i) describe the particle formation properly, e.g. for all metals predicts that both the production rate and the particle size increase with power and starts to level off at material specific threshold powers, ii) clearly distinguishes the NP formation in Ar and N2 in terms of particle size and the experimentally found difference observed in the mass output.

The 3D simulation data was not only used to describe and understand particle dynamics but was also extensively used for the optimization of the OSU geometry.
• The simulations and the experiments reveal that thermophoretic particle losses can be minimised by adding a graphite tube covering the area from the discharge to the outlet of the OSU. This can be attributed to the decrease of thermal gradients in the vicinity of the walls.
• Condensation of vapour to the crucible edges was found to be the dominant loss mechanism in the “hood” type geometry and takes about 10% of the total evaporated material.
• To better capture the experimental production rates and temperatures a simplified electrodynamics model (EDM) of the plasma was introduced in the CFD arc model (Fig. 8). The overall effect of the inclusion of EDM is that the modified arc CFD model matches the experimentally measured temperatures and production rates better.
• All in all, the final design of the arc-OSU was achieved in not less than 8 iterative steps, including substantial modifications such as adding a “hood” placed above the cathode crucible in order to minimize particle losses.

WP2: OSU AND CORE TECHNOLOGX DEVELOPMENT

A low-cost standardized multipurpose reactor chamber was developed to allow arc as well as spark operation, and ensured compatibility between participants, thereby allowing easy connection of measurement instruments, particle collection units, etc. It was used for reactor optimization, (as different electrode designs, gas inlets and production flow outlets can be hosted), instrument testing and diagnostic studies. It was also delivered to scientists performing diagnostics, developers of supporting technology (such as size narrowing, monitoring and filtering), and end-users, allowing them to perform feasibility studies of exemplary nanostructured applications. The design is also such that it is suitable for multi-electrode operation, essential for scaling-up.

Arc-OSU:
The possibility of using an electric arc for producing nanoparticles is well known, however obtaining a sufficient evaporation rate and arc stability over an extended time period has been a major problem thereby limiting commercial exploitation. Extensive engineering and optimization efforts have been conducted in BUONAPART-E to solve these problems. A cheap high-current, low-voltage power supply (which can be procured at local home improvement and equipment stores) was found to be the most suitable power source for the liquid electrode arc. Melting of the consumable electrode occurs at currents >10A for copper. A graphite crucible is used to hold the pool of molten metal at high-current operation (10-100 A), and tungsten serves as the counter electrode. Seven different crucible designs have been tested. One design is in use for high-rate production and one design is more suitable for low-rate production leading to smaller particle sizes. A rising axial gas flow around the crucible with a much smaller flow around the tungsten cathode placed in an angle of 90° to the axis leads to the highest production rates, mainly due to smaller particle losses in the reactor. The carrier gas has the strongest influence on the production rate, nitrogen was found to be the most effective gas and is to be preferred for non-nitride forming metals (Fig. 9a). For the four most relevant metals, production rates of 36 g/h (Zn), 4.4 g/h (Cu), 1.0 g/h (Ag) and 0.03 g/h (Al) were found, leading to a specific electricity consumption of 12, 179, 6807 and 32025 kWh/kg, respectively. However, the evaporation rates are a factor 3-4 higher than the effective production rate, as a result of particle losses in the reactor as well as the lines. The smaller the production rate, the smaller the primary particle size obtained. In general the primary particle sizes of the arc –OSU were larger than 50 nm. By reducing the electric current, the production rate could be decreased, so that smaller primary particles could be obtained. A further reduction (as well as precise tuning) of primary particle size is possible by adding argon to the carrier gas (Fig. 9b). It was shown that 50% reduction in the average primary particle size could be achieved for the same electric current and processing gas, by using centrally downward focused gas injection from the electrode to the graphite crucible during the arc discharge operation. This allows the use of high electric current such as 80A, giving an extremely high evaporation rate of 71g/hr, while keeping the average primary particle size to 58nm.

Due to the high evaporation rates, refilling the crucible is required after a relatively short time (typically every 10-30 minutes). UDE has developed and tested a simple device for feeding spherical shots into the crucible, which delivers a known amount of feedstock when externally triggered. Uninterrupted operation over 8 hours is thereby now possible. Similarly, MNL has applied a commercially available gas assisted powder feed system to refill the crucible with coarse powdered material during the stable arc discharge operation between single electrode pair over a period of time.
At effective currents intermediate between spark and arc operation, a glow discharge regime was found (typically <1A, 300 V). The power input is larger than that of a classic spark and comparable with the high-frequency spark (see below). Aerosols produced by glow (0.05-0.15 A) had smaller mass production rates (<1 mg*h-1) but larger agglomerate size (dg ~ 20 nm) as compared to spark discharge in the same setup. Experiments on glow discharge and arc discharge (6 A) conducted with solid copper rods as cathode and nitrogen as carrier gas resulted in aerosol mass production rates in the interval of 20 to 400 mg*h-1 . However, the cost of the required HV power supply makes solid electrode operation unattractive for commercial use.

Spark-OSU:
In spark ablation of the electrodes, short sparks of several microseconds duration, with variable energy and repetition rate are performed in a variable inert gas flow. This process is associated with extremely fast quenching of the vapor, which leads to formation of very small particles, typically 5 nm in diameter. Another consequence of the high quenching rate is the possibility of mixing different materials on an atomic scale (forming alloys). The great potential of this feature is generating great interest in the spark method for various high-tech applications. The main objective of the work on the spark-OSU was to maximize the mass production rate, while keeping the particle size small.
A high-production-rate spark-OSU with complete control over particle size has been developed. Basically, the mass production rate can be increased by increasing the energy per spark and the spark frequency. Two limiting effects were encountered: (i) If the energy per spark is chosen too high, a “splashing” effect occurs, producing some large particles of several 100 nm in diameter or larger, and (ii) for effective quenching to occur between sparks, the time between sparks must be substantially longer than the spark duration. Regarding the first effect, splashing is tolerable for a spark energy of about 35 mJ. Regarding the second effect, a maximum frequency of 9 kHz guaranteed sufficient quenching to keep the particle size smaller than 10 nm at a moderate flow rate of 15 L/min. With regard to these limitations, it became clear that for spark production the originally targeted mass production rate of 5 kg/day is not feasible within BUONAPART-E for high-quality sub-10 nm particles. Regarding the potential of these particles, e.g with regard to their superiority to large ones regarding their large specific surface area, and the demand within BUONAPART-E itself, the objective of producing sub-10 nm particles was maintained. The mass production rate was increased by almost a factor of 100 with respect to the classical circuit by a respective increase of the frequency in a high-frequency (HF) spark. It uses a newly designed switching circuit to replace the conventional one, which superimposes high energy pulses and a low-power, continuous discharge (Fig. 10a). The continuous component enabled magnetic deflection of the spark position, so that successive sparks do not hit the same point. We showed that this reduced the occurrence of the “splashing particles” formed by local liquification, thus the quality of the nanoparticulate product was further enhanced. It was repeatedly shown for frequencies below 4 kHz that the mass production rate linearly increases with the frequency, where different materials show different slopes. Between 4 and 9 kHz, the slope increases due to the effect of electrode heating, as shown in Fig. 10b. The maximum production rate achieved under stationary conditions is 280 mg/h for aluminum, if an estimated 20% contribution of large particles due to splashing is subtracted. According to relations between mass production rates for different materials (see Fig. 12), this corresponds to a similar rate for Cu and about 1500 mg/h for gold. Numbering up for higher production is easily possible, as demonstrated in WP4. This performance makes the HF-spark commercially interesting.

The connection between process parameters and the mass production rate as well as the particle size and concentration was empirically derived and summarized in a semi-empirical model (see WP 1). In particular, this enables complete control over the particle size, as the size distribution was shown to resemble the so-called self-preserving distribution with a geometric standard deviation of 1.35 similar to the case of glow discharge described above. This value is considered as “monodisperse” for many applications.
Stable long-term operation of spark discharges requires control over interelectrode distance as well as the electrode shape. Stability of the produced metallic NP output depends very much on the exact geometry and flow conditions in and around the gap zone. While the influence of gap distance on production rate and size spectrum is known, the displacement between gap and quench gas flow had to be investigated for the specific geometric arrangement in the OSU. Experimental results as well as simulations showed a significant drop of the gap gas velocity to 50 % of the optimal values for displacements of a few mm, which already influences particle production rate. A motorized high precision electrode position system and an electronic control loop system, based on the measurement of the breakdown voltage for spark frequencies up to 1 kHz was developed and integrated into the generator setup. The system is able to feed solid rods of a joint length of 240 mm before electrode replacement is necessary. Compared to the only existing commercial rod feed system of a spark discharge particle generator from PAL, this extends the continuous operating time of the spark discharge particle generator by a factor of more than 20 reducing the replacement costs and increasing the continuous operating time significantly. Results show a stable particle production rate and size distribution over weeks after an initial phase, were the shape of the electrode tips converted from flat-end rods or tubes to a stable (mainly rounded) shape (Fig. 11), and, depending on material, distinct surface patterns.
Production rates and corresponding agglomerate mobility diameters were measured for a low frequency spark generator under constant operating conditions. Production rates in good agreement with a semi-empirical model by Llewellyn Jones et al. were found for all BUONAPART-E materials except for Zn (Fig. 12). This allows extrapolation to practically any metal. As Zn is the metal with the lowest boiling point, we presume that the discrepancy is due to the phenomenon of splashing, which can be avoided by reducing the spark energy.

Adoption of OSU to specific endusers’ demands:
One of the project goals was to show experimentally that the same synthesis platform can be used for producing a variety of materials and applications by simply changing the electrode material. Therefore, four specific particle production studies were carried out, based on End-User’s Demands. The functionality of the obtained materials were assessed in WP5.

The first application required particles deposited on a catalyst substrate (SINTEF and CoorsTek). A single arc-OSU was optimized to allow production, collection or deposition of nickel nanoparticles on ceramic tubes for testing catalytic activity. Homogeneous deposition of nanoparticles smaller than 10nm was achieved. After heat treatment, they formed isolated catalyst nanoparticles mainly between 10 to 30 nm in diameter. Successful operation of the user showed that the operation of this OSU is simple and can be easily adopted for research purposes aiming at specific applications by un-experienced users. For the same purpose, spark-produced particles with sizes down to the atomic cluster size range were deposited on substrates. At room temperature or under increased temperature, these particles self-organize to form non-agglomerated (catalytic) nanoparticles. The desired particle size can be controlled by the deposited mass per unit area. Alternatively, a somewhat different approach was developed, in which agglomerated particles were reshaped to the desired spherical shape in a tube oven before deposition on the tube. Monodisperse alloyed CuNi particles of defined (and adjustable) composition with sizes below 20 nm were produced this way. Optimization of the composition can be used to reduce coking on the catalyst surface and to attain the optimal catalytic activity.

The second application dealt with nanofinishing of textiles. A new method for preparing fabrics with antibacterial activities was developed by passing the aerosol coming from the spark or arc OSU through the textile, which acts as a filter with respect to the nano-sized particles. This dry, one-step procedure does not involve any toxic chemicals and leads to improved antibacterial properties with respect to conventional methods.

The third application concerned gold nanoparticles to be used as seeds in the Aerotaxy® process of SOL. Gold particles (<150 nm) were prepared using a low frequency spark-OSU and passing them through a tube oven to reshape agglomerates into compact particles (singlets). After extracting a narrow size interval in an electrostatic size classifier, the task was to deposit these particles onto substrates and for them to serve as catalysts for the growth of nanowires in the Aerotaxy® process. The nanowires had the desired crystalline properties for solar cell fabrication. The deposition onto specific areas on pre-patterned samples (inside or outside of the patterns) was controlled by applying charged particles and electric fields. For diameters as large as 150-200 nm, the spark-OSU was replaced by an arc-OSU. The particle generation using aerosol technology was calibrated and optimized. The arc source is now part of the SOL aerotaxy® setup.

The fourth application required silver particles production for the fabrication of nanoparticulate LSPR (Localized Surface Plasmon Resonance) sensors to be tested by DAS. Very small (7 - 30 nm), non-agglomerated nanoparticles were produced by a spark-OSU. A special nanoparticle collector that can be placed inside the OSU was fabricated for efficient deposition. The residence times are so short that freshly formed nanoparticles do not have time to form agglomerates, and singlets are deposited. This solution avoids the use of high gas flow rates, which are required, if the aerosol is passed through a large volume before reaching the substrate. This implies lower process and environmental costs.

WP3: SUPPORTING TECHNOLOGY

The concept of WP3 is to provide the supporting technologies needed for product and process integration between the OSU-based generation and the spectrum of target applications in WP5. The topic of the different tasks and their integration into the other work packages are shown in Fig. 13.
In the first task, different pretreatment techniques (prior to particle application/integration in WP5 target applications) were developed and scaled to dimensions suitable for the high flow rates (and high particle concentrations) coming from the particle generation.
Arc and spark generators are used in the project to produce specific nanoparticles. While the majority of the produced particles are nano-scaled, a certain fraction of micron-sized particles are generated by so-called splashing. These large particles need to be removed from the product flow to ensure that the final aerosol contains only the desired nanoparticles. Hence a suitable inertia-based preseparator was needed. Literature studies identified a specific cyclone design, which was suitable for the desired flow rate range and cut size. A dimensioning model based on the method of effective turns was adapted to the existing efficiency data of the cyclone and then used to scale the cyclone inlet dimensions to the exact flow rates and cut sizes needed for a multi-OSU generator system (mOSU). The design was further modified for adaption to the tubing of the mOSU, for vacuum tightness and to allow for easy adaption of the inlet geometry to various flow rates.
Some end-user applications (especially for plasmon resonance sensors) need highly unipolar charged particles in the product aerosol, e.g. for the deposition of regular patterns on substrates by electrostatic deposition. Therefore, a unipolar charging device was developed for diffusion charging by mixing the aerosol flow with a flux of unipolar ions produced by a corona discharge in a separate volume and flushed to the product aerosol flow. The design allows for the attachment of multiple vacuum-tight corona modules to adopt the ion concentration to the flow rate of product aerosol.
Reshaping of as-produced agglomerates into spheres by annealing is important e.g. for seeding particles for aerotaxy®. One aim for the aerotaxy® process is to increase aerosol flow rates for higher production rates of VLCs. This requires the upscaling of the annealing zone for higher flow rates. Therefore, a two-step approach is used. Firstly, the necessary residence time and annealing temperature was derived for different initial and target particle sizes based on a sintering model from WP1 and data on sintering of gold spheres from literature, and limitations on sintering temperature were identified by the detrimental thermionic charging effect at very high wall temperatures, observed in additional measurements. Secondly, CFD calculations of different tube geometries using commercial codes (Fluent, Comsol multiphysics) were performed which allow for the selection of appropriate dimensions of the anealing zone.
Metallic NP produced in inert atmosphere will react with oxygen if exposed to air, either accidentally during handling/packaging or intentionally during further processing or in the final product. To avoid uncontrolled reactions of pyrophoric particles and to protect the metallic core, the addition of a thin passivation layer onto non-noble NP by controlled oxidation is investigated. In initial experiments, the pyrophobicity of different NP (depending on material and particle size) was investigated to determine which products need passivation for safe handling. Ni particles were found to be especially reactive, if their primary particle size is below 20 nm. For Zn and Al NP, no self-ignition was observed, which was explained by the larger particle sizes, and still calls for passivation of smaller particles. Passivation by oxidation at low O2 partial pressures is proved to be efficient and recommended as an effective measure to minimize the risk of ignition by exposure to air of high purity metallic powders in the up-scaled facilities in BUONAPART-E (Fig. 14).

The second task aimed at fractionating a narrow size range from the broader size spectrum coming from NP generators. While instruments based on bipolar charging and electrical mobility classification in a DMA are available for low aerosol flow rates since decades, these devices are not suited for high product flow rates. In a first step, a bipolar charger based on a soft X-ray source was designed, built and tested. It has been found that the system successfully neutralizes charged aerosols produced by means of a glow-OSU setup for aerosol flow rates of up to 50 lpm to equilibrium, and concepts were developed for neutralising higher flow rates by increasing Ion concentration and residence time in the neutraliser. In a second step, a cylindrical high flow DMA (HFDMA) for aerosol flow rates up to 200 lpm and target particle sizes of 100 nm was designed and built with variable length of the classification zone, and later on, an additional medium flow DMA for intermediate flow rates up to 50 lpm was constructed. Both devices were tested and optimised (Fig. 15), based on practical experience and corresponding CFD simulations to improve flow distribution and to reduce NP deposition in the inlet section, thus increasing classification results (monodispersity) and operational time (limited by blockage / demand for cleaning) at high concentrations.

The third task deals with suitable particle collection and deposition techniques. For powder collection from high production rate mOSU gnerators, the design of a matching filtration system was a key aim. Therefore, data from an overview of commercially available filter media, from manufacturer’s information, and mainly from experimental results gained by small-scale filtration tests at existing NP generation setups within BUONAPART-E were collected. These measurements included the determination of values of specific cake resistance for different particle materials and generation conditions, testing of filter efficiencies, differential pressure and cleanability both with wet and dry cleaning. Based on the collected database, dimensioning, design and operational recommendations for the filter system to be used in conjunction with the mOSU design were given. Based on these recommendations, a detailed concept for the filter system for a 5 kg/day production facility was developed (Fig. 16), and all necessary components were either selected from the market or specified and designed for customised construction. Finally, all necessary operating procedures for start, stop and continuous operation (e.g. filtration, regeneration, powder passivation and bagging, and cleaning for maintenance) were defined and documented. Based on these works, a vacuum-tight, inertisable, safe, continuously operated filter system for pyrophoric metallic NP was constructed in WP4.

Besides pure powder collection, techniques for dry and wet coating of substrates by particle layers and structured deposition patterns have been adopted for the specific applications in WP5, and suitable deposition devices have been constructed and integrated in the NP production line. Suspensions containing Ni or Ag NP have been prepared for wet coating of ceramic substrates and textiles, respectively, and their stability has been optimized. In parallel, alternative techniques were applied for dry deposition on ceramics (using diffusional deposition mainly for sub-10 nm particles, and electrostatic precipitation for larger NP) and on textiles, using a diffusional filtration step. The later represents a novel textile finishing step which can replace traditional multi-step batch wet finishing procedures for deposition of functional metallic NP.
The fourth task in WP3 aims at different monitoring techniques for product quality of the generated metallic NP and for process control, in particular for the large scale facilities which use multiple generators in parallel (mOSU). SAXS/WAXS instrumentation initially intended for offline powder sample analysis was extended by a single stage multi-orifice low-pressure impactor system (SS-MOLPI) for rapid sample collection from the product aerosol flow. With this combined system (quasi-online SWAXS, qo-SWAXS), sampling time for the typical concentration range within the BUONAPART-E product spectrum was down to around 5 min or less for the SWAX signal (Fig. 17a), allowing for quasi-online monitoring of NP product morphology, based on primary particle size, fractal dimension, diffuse interface layer thickness. With higher sampling times in the order of 20 to 40 min, also crystalline phase information is accessible.
A second instrument (DENSMO) was developed, which combines an aerosol diffusion charger, a mobility analyser, a low-pressure impactor stage and a filter stage within a Faraday cup electrometer. The charging characteristics and the penetration efficiencies for the individual components were determined, and the corresponding deconvolution routines were developed and integrated in a monitoring device, which allows for online determination of particle concentration, mobility and aerodynamic diameter, and effective density. After calibration with monodisperse liquid aerosols, the instrument was tested with mono- and polydisperse aerosols containing agglomerated and fully sintered metal NP from various sources, including NP from OSU (Fig. 17b), and results were compared to appropriate reference methods.
Based on demands from end-users in WP5 for very simple monitoring of constant product generation from the OSU integrated in the process lines, an additional, less sophisticated – and less expensive – instrument (Bmini) was developed, which yields particle concentration and which is suitable for inserting into a single OSU output line (costs ~1 k€).

The last task in WP3 aimed at the development of a device for monitoring the proper operation of the electrical discharge process. For that, fundamental information from the plasma diagnosis experiments for arc and spark discharges, performed in WP2, was used to select the most effective parameters for monitoring, and the technically feasible, flexible and cost effective means were identified. For spark operation, emission spectroscopy and optically determined spark repetition rate was chosen, whereas for arc, emission spectroscopy and imaging by electronic cameras are most promising for monitoring.
Based on these data, the conceptional design, construction and adaption (to the OSU) of a functional and robust, yet portable low-cost optical sensor assembly (DIMON, Fig. 18a) was completed, which provides an efficient and flexible means of monitoring the operation of single or multiple discharge generators. The system uses (near) real-time evaluation of collected optical data; by referencing the current data to previously acquired “normal” values (generated during an initial learning phase), a binary “health” indicator can be provided. Using optical multiplexing, the system is able to monitor each generator in a mOSU setup individually. The device was successfully tested by collecting long-term monitoring data from a single spark OSU (Fig. 18b), and from different mOSU arc and spark systems with up to 4 OSU generators monitored in parallel (limitation in number of simultaneously monitored OSU caused only by the number of channels in the optical multiplexer).

WP4: SCALING-UP

This Work package dealt with design, construction and performance testing of production facilities enabling the production of metallic nanopowders in kg/day quantities, as well as an operational study of handling the production facilities including collection, product quality and stability tests. Two central pilot line facilities basing on the arc-OSU were set up, one at UDE and one at MNL. The facility at UDE contains 2 mOSU (each with 8 electrode pairs), gas recirculation system including cooling, vacuum pumps and gas lines, and individual power supplies. The optimized crucible and feeder design from WP2 was adopted for the mOSU. A large filtration facility based on advice from WP3 has been constructed. It has two PTFE filter units which can alternately been used so that a filter and cleaning cycle allows the continuous operation over extended period of time. The system incorporates pulse jet and wet cleaning facilities, of which the latter are also used for clean-in-place operation (CIP) in order to enhance workplace safety. Particles may be passivated on the filter elements directly after collection and are subsequently transferred to a novel bagging system designed by UDE. The optimized crucible and feeder design from WP2 was adopted for the mOSU. (Fig. 19a) The facility at MNL contains 8 arc-OSUs, uses a powder feed mechanism to replenish evaporated feedstock instead of the granule feed system of UDE, and operates with a metal filter in batch mode with cleaning and collection in glove box. (Fig. 19b).

Also a mOSU applying a fourfold high-frequency spark-OSU has been constructed. For Cu, the spark produces about 10-7 g/J equivalent to 5 g/day with a 500 W unit. Producing 5 kg/day would thus require a mOSU consisting of 1000 electrode pairs. However, the spark-OSU can produce nanomaterials having smaller primary particle sizes than the arc-OSU spark’s and its’ production rate with respect to surface area is comparable to the arc. In order to demonstrate the scalability of the spark principle a spark-mOSU consisting of 4 electrode pairs was constructed at TUD. It is designed to supply endusers with high surface area material. With respect to surface area the spark’s production rate is comparable to the arc. (Fig. 19c)

Specific hazards are created by use of high voltages, potential flammability of small metallic nanoparticles and nanoparticle exposure at the working place due to leaks or during powder removal. The facilities were designed in close collaboration with WP6 to minimize health, safety and environment (HSE) risks. Dedicated tests of the effectiveness of these measures were performed in cooperation with WP6. Aerosol monitors were used for monitoring the particle concentration in the working environment of the mOSU facility. Electromagnetic Interference (EMI) measurements were done, including conducted and radiated electromagnetic emissions for several power supply units, leading to advices how to minimize these potential disturbances to other (nearby) electrical equipment.
It is important that the system is able to deliver the particles having the same properties with the process parameters determined in a single OSU. It was found that the primary particle size in the large facility did not increase in comparison to the single OSU. Furthermore, the production rate of the facility containing N OSUs has to be N times that of the OSU at identical process parameters. Mass production rate and primary particle size were measured and their stability over time verified in experiments of up to 4 h duration. It has been proven that the mass production rate rises linearly with the number of electrode pairs simultaneously operating, and that the specific electricity consumption did not change significantly when increasing the number of electrode pairs (Fig. 20). For Cu, the measured production rate is 67 g/hr (1.6 kg/day), for Ag this would be 14 g/hr (0.35 kg/day), for Zn 356 g/hr (8.5 kg/day).

Extensive operation experience has been gained. As a result, a number of operative problems have been recognized, mainly relating to keeping the electrode distance constant, feeder problems, necessity of having monitoring systems for arc operation/size/housing temperatures, particle deposition in the chamber, short circuits and insufficient optical access. The continuous filter system was also operated for weeks continuously, applying dry pulse-jet cleaning. While this method was effective in the initial weeks of filter operation, residual pressure drop increased to levels of 40 to 80 mbar later on, and pulse cleaning was less effective. The main reason for this is seen in probably too high face velocity as well as too high gas inlet temperature. These experiences will be very helpful when further exploiting the production facilities.

The facilities also offer a platform to test to functionality of the diverse monitoring strategies developed in WP3. The newly developed low-cost production line monitoring sensor BMini shows a good correlation with total current of the ELPI (a 80 k€ aerosol monitoring instrument, whereas the BMini costs are approximately in order of 1000€.), which allows to monitor the particle concentration Therefore, the BMini is shown to be an appropriate low-cost tool to monitor the stability of the arc OSU particle production. Optical monitoring experiments were performed on both the spark-mOSU and the arc-mOSU by the Discharge Monitor (DIMON) system. The mOSUs were monitored simultaneously allowing to test the multi-channel and HF capabilities of DIMON, as well as to collect “first-look” diagnostic information on the operational stability of the system. The DIMON is capable of indicating when any of the generators stop operating or improper gas and/or electrode material is present in the spark chamber. It is also shown that the spectroscopically derived data is robust enough and provides useful information on the stability of the discharge operation. Another indicator relates to the temperature in the spark gap. It is also straightforward to detect whether the arc hits the anode metal (as under normal operation) or spreads partly over to the crucible (which is undesired). Deviation in the arc power (investigated by varying the arc current) can also be followed by optical means.

WP5: FEASIBILITY STUDIES AND COST BENEFIT ANALYSIS FOR SAMPLE POTENTIAL APPLICATIONS

In Work package 5, six end-users applications have evaluated the use of the nanoparticles produced within the project. Various materials were produced in the project and assessed for the following applications:

• Aerotaxy® growth of nanowire for generation of highly efficient solar cells (Ag, Au)
• Antibacterial activity for advance textile (Ag)
• Composite polymer with improved properties such as biocide, conductivity, flame retardant, flavour modifier (Ag, Zn, Cu)
• Plasmonic resonance sensor for chemicals or biomolecules (Ag)
• Nanofluids for cooling of blast furnace (Cu, FeCr)
• Catalyst in a membrane reactor for steam methane reforming (Ni, NiCu)

Aerotaxy® growth of nanowires for generation of highly efficient solar cells:
An OSU-based arc discharge reactor was evaluated as a potential aerosol source suitable for Aerotaxy® wire growth (Fig. 21). For this purpose, an arc discharge generator was built to fulfil several requirements so that it can be integrated in the Aerotaxy® line in terms of aerosol density, particle size, carrier flow and continuous operation.
In combination to the arc source development, a sintering furnace, an aerosol neutraliser and a radial DMA (RDMA) were integrated to the line to meet the requirements of the aerotaxy® process. In addition, in-situ cleaning has been implemented for the RDMA, allowing uninterrupted operation over extended time.
The arc-OSU developed within BUONAPART-E has enabled an upscaling of approximately 30 times of the Aerotaxy® process, calculated from the increase in carrier flow and particle concentration.

Antibacterial activity for advanced textile:
In order to assess the antibacterial activity of silver nanoparticles on textiles, wet and gas phase deposition were investigated with both arc or spark discharge as nanoparticles sources. Wet deposition required dispersions of Ag nanoparticles in binder solutions used in the textile industry (padding or coating) whereas gas phase deposition consists of depositing the nanoparticles directly onto the textile from the aerosol phase. For both deposition techniques, several parameters were investigated such as the fabrics or binder type, wet coating technique, aerosol flow rate and deposition time. Industry standards were used to determine the antibacterial activity of fabrics treated with Ag NPs by both deposition techniques and their resistance to washing. The main achievements are as follows:
• Textiles with durable and strong bactericidal property have been attained by applying Ag NPs generated by electrical discharges in gases by using standard wet routes as well as by aerosol filtration. To our knowledge, this is the first time that aerosol filtration is attempted to functionalize textiles by directly depositing NPs from the gas stream on textile fabrics.
• The arc discharge has been proven for mass production of metal NPs in the gas phase. Nonetheless, collecting NPs by gas filtration and handling, and packaging and delivery of large amounts of bulk metallic powders raise issues with regard to environment, human health and safety (EHS) and in relation with the quality of the final powders supplied to the end-users; in particular, their suitability for wet nanofinishing of textiles. These issues are beyond the scope of this project and therefore remain unsolved.
• The aerosol filtration is a much simpler route to nanofinishing of textiles, which minimizes most problems related to wet routes and is also sustainable.
• With regard to the synthesis of Ag NPs for use as antimicrobial agents in textiles, both spark and arc sources need to be further optimized. In particular, splashing particles and large particle agglomerates must be prevented, since their contribution to the antibacterial activity of the textiles treated by aerosol filtration is negligible, as compared to NP and nanoclusters, but they mostly contribute to the release of Ag from the textiles into the wash water.
• The antibacterial activity of textiles treated with Ag particles by means of aerosol filtration may be to a large extent determined by the load of Ag in the textiles. In general, textiles containing 50ppm of Ag attained a high antibacterial activity of 5, regardless of the fabric type and particle size. Furthermore, increasing the load of Ag above 50ppm does not result in increased bactericidal activity. Finally, the treated fabrics maintain high antibacterial activity up to at least 10 washes.
• The variation of the antibacterial activity with the load of Ag below 50ppm was not discerned in this work. Nonetheless, there are evidences that loads of Ag in the order of 15ppm or even less could also impart significant bactericidal property to textiles. Further effort is needed to clarify this issue. Furthermore, the load of Ag affects properties such as the colour and hand touch of textiles, which are relevant to consumer acceptation of textile products
• Although the particle size seems not to have a significant impact on the bactericidal activity of the textiles, it determines to a large extent the release of Ag to the wash water. Nanoclusters adhere stronger to the textile fibers than large NPs, thereby reducing the EHS impact associated to Ag in wash water.

Composite polymer with improved properties such as biocide, conductivity, flame retardant, flavour modifier:
The properties of various composite polymers where nanoparticles like silver, coper and zinc where integrated were assessed. Main results achieved are as follows:
• Cu NPs in polymers show strong catalytic activity, resulting in highly efficient removal of sulfur compounds in production. The pre-industrial phase has been completed and samples have been tested by various customers with 100% positive results. There is currently no alternative product in the market.
• Synergetic effects of Zn NPs with NPs produced by wet chemistry route lead to epoxy-Zn nanocomposites with outstanding flame retardancy, as demonstrated by using flammability industry standards (V0 classification).
• PVC plastisol doped with extremely low loads of Cu NPs exhibit superior electrical conductivity.
• Thermal conductivity, bactericidal property and sensing behaviour of nanocomposites with metal NPs as additives have been exhaustively investigated as well. For these properties, results were only partially successful.

Plasmonic resonance sensor for chemicals or biomolecules:
Plasmonic resonance sensors allow the detection of chemicals or biomolecules by converting the presence of the analyte into a readable signal by transducing local refractive index changes into a wavelength shift. The fabrication method of nanostructured SPR sensors were investigated and optimised. It relies on controlled deposition of small size-selected Ag NP generated in a spark-OSU onto non-patterned (SiO2) and patterned (PMMA-SiO2) substrates. The latter is fabricated by using e-beam lithography.
Two types of nanostructures were achieved:
• disorderly distributed non-agglomerated NPs with a narrow size distribution and adjustable surface coverage.
• periodically patterned structures with nanodisks or nanocrosses. They were formed by deposition and accumulation of NPs in the originally empty circles and crosses of the patterned substrate. The shape and dimensions of the motives and the separation (pitch) between consecutive motives were selected based on the results of analytical calculations and numerical simulations undertaken. Heat treatment was applied to the substrates in order to obtain dense homogeneous nanocircles and nanocrosses matching the dimensions of the original motives.

Both simulated and experimentally measured (FTIR) absorption/transmission spectra confirmed both types of nanostructures exhibit plasmonic resonance in the expected wave length range. Then, the substrates were functionalized and their capability as chemisensors and biosensors was proven to detect ethylenediamine (ED) and bovin serum albumin (BSA) protein, respectively (Fig. 22). In terms of the figure of merit for sensors (a relationship between sensitivity and specificity), the NP-based nanostructured SPR sensors perform similarly to SPR sensors currently found in the market.
A cost/benefit analysis showed that the production cost of the spark-generated nanostructures (nanodisks, nanocrosses) is cheaper than that of conventional fabrication methods, such as metal evaporation. The reason is that the spark-discharge process is more material and energy efficient, while the cost of the required equipment and its maintenance is lower. In the case of nanoparticles, the spark-OSU production cost is similar to that of conventional fabrication routes, such as chemical synthesis. However, the former is greener, as no chemical waste is generated. For the cost of the full sensor chip, by employing low-cost large-scale methods, such as nanoimprint, the overall cost has been estimated to be below the targeted 1€ per sensor chip. Further effort need to be made to improve the quality of the nanostructures in terms of definition, homogeneity, compaction, mechanical resistance, etc.

Nanofluids for cooling of blast furnace:
The addition of nanoparticles in cooling water of a blast furnace for improving the cooling capacity was investigated, so that less cooling water (water velocity) or less pumping power is needed.
A full-scale heat exchanger with recirculating nanofluids for cooling a copper plate (150 kg) was constructed. The fluid volume is 20 litres and the required amount of nanoparticles (Cu) is about 5 kg for a nanofluid with 3%vol. nanoparticles content. The physical properties of the nanofluid (thermal conductivity, heat capacity, density and viscosity) were measured in dependence of the nanoparticles concentration.
Higher density and higher viscosity of nanofluids compared to distilled water have negative influence on pumping power, which increases with increasing nanoparticles concentration. Due to the increase of electricity consumption of the pump used to circulate the nanofluids and despite the improved cooling shown in the 1:1 model, no benefit was found of using nanofluids as cooling agent for their blast furnace.

Catalyst in membrane reactor for steam methane reforming
In order to assess the enhancing performance of the integrated nanocatalyst in a catalytic membrane reactor for steam methane reforming, several tasks were carried out within the project and results both in fabrication and testing were achieved.
• A fabrication route for a ceramic composite consisting a mixture of two mixed protonic-electronic conductors was developed. Open and closed-end tubular gas tight membranes of length up to 15 cm were fabricated by extrusion of the support and dip coating of a membrane layer. Sealing technology comprising glass-ceramics and methods was successfully transferred to these membrane tubes.
• The pure hydrogen evolution rate of the asymmetric tubes was measured to a maximum of 0.05 mL min-1cm-2 under non-optimized conditions. Ni NPs deposited on the membrane increase the hydrogen evolution as compared to a non-coated surface (Fig. 23).
• The catalytic activity of Ni NPs directly deposited from arc and spark discharge were tested. A rather low methane conversion was observed at 820 °C for the NPs deposited from arc discharge. For a tube covered with Ni NPs from spark discharge, a methane conversion of 3.4 % was determined at a GHSV of 400 L h-1 g-1 and at 820 °C. This was benchmarked against a commercial catalyst, which under similar conditions converted 74 % of methane. Because of the low conversion of methane, it was not possible to determine the impact of particle size on the formation of filamentous carbon during SMR.
• Techno-economic aspects of a catalytic membrane reactor concept where a different protonic conductor material is used to produce pressurized hydrogen were investigated by ASPEN modelling and benchmarked with state-of-art technologies. Based on forecasts of crucial reactor parameters, the overall efficiency of the entire process was modelled to be 82.3 %. Both in terms of energy efficiency and operating cost, this process has the potential of being highly attractive for production of pure and pressurized hydrogen from natural gas.
• The results of the catalytic experiments points towards that the coverage of Ni NPs is too low to compete with commercial catalysts when deposited directly onto the tubes. Further efforts should focus on depositing NPs into a porous three-dimensional network on the membrane to enhance the concentration of catalyst in the reactor.

In addition, a range of metal (e.g. Cu, Ag, Zn) nanoparticles were generated in larger quantities using m-OSU facility in arc discharge operation for subsequent evaluation of its performance in fire retandant and antimicrobial textiles, as well as the pyrophoricity behaviour.

WP6: EFFICIENCY, RISK AND ECONOMICAL ASSESSMENT

A major task of this WP was the assessment of the energy use and energy efficiency of metallic NP production using arc/spark discharges, and expand this to a wider analysis of the environmental impact using life cycle assessment (LCA). Since data on the use and end-of-life treatment of NP-containing products is practically non-existing a partial, or cradle-to-gate LCA was conducted. For most of the metals, a comparison could be made with “conventional” production routes for the NP. This contributed to the studies on feasibility of a production unit with a capacity of 100 kg/day NP by parallelization of OSU, and on how NP prices would drop as a result of scale-up. Eventually this determines whether the BUONAPART-E concept can be competitive with other routes for metallic NP production further supported by the benefit of using (relatively cheap) electricity instead of complex chemical mixtures. Most progress was made with the three metals Ag, Cu and Zn when it comes to NP production and scale up, the use in commercial products, and the studies involving energy use, life cycle impact assessment (LCI) and process economy during scale-up.
Energy use evaluation addressed both spark and arc systems, which produce diverse NP sizes, have very different production rates and varying energy use (electricity). Production data reported by project partners, was used for this, allowing not only for comparing spark and arc systems but also similar setups operated by several partners, the use of N2 or Ar as carrier gas, and the influence of scale-up from OSU to mOSU. To be able to make energy efficiency assessment, the exergy concept (based on the second law of thermodynamics) was expanded to the production of NP, taking into account the changing thermodynamic properties of NP especially for sizes < 50 nm. This showed that the energy input needs are partly the result of increased surface energy of the NP compared to the starting metal, and partly the result of the fact that melting and evaporation of the metallic material occurs at higher temperatures than the condensation and solidification of the NP material. The specific electricity consumption (SEC) in practise is 2-3 orders of magnitude higher, pointing to an energy efficiency of < 1%. (n this respect the spark systems perform better than arc systems; results with the TUD high frequency spark indicate still better results.) Indeed a set of experiments on energy use and equipment temperatures at the 2x8 mOSU arc unit at UDE revealed that most of the electricity needed for powering the arc and circulating the carrier gas eventually leaves the production unit as cooling heat and heat released to the surroundings. Clearly, integration with a heat recovery system can lower the energy penalty of this NP production method.
However, electricity contribute a minor part to the total costs, and for the environmental footprint the wider approach offered by LCA is used that addresses not only the effects of energy use but also the impact on human health, natural resources and the ecosystem. A commercial software tool (SimaPro) combined with database (Ecoinvent 2.2) information (in a few cases extended with data from external sources) was used for this. Four life cycle impact (LCI) categories were considered, being Resources depletion, Climate change, Ecosystem quality and Human health. The three most important LCI factors were the production of metal from metal ore, the production of electricity for driving the NP production process, and the production of the carrier gas (N2 or Ar, assuming 99.5% recyclability), respectively. Clear differences were found between spark and arc systems. For Au and Ag the production of metal from ore gives a much larger environmental footprint than NP production, while for Cu, Ni and Zn the electricity production gives the largest footprint. Comparison with more “conventional” production routes showed that for Ag a “wet” route will have a smaller footprint than an arc/spark process while for Cu and Zn an arc/spark can be preferable over a “wet” route if production efficiencies (metal NP out vs. metal in) can be raised to 80-90%. This puts emphasis on systems for removing the produced NP from the production unit.
The LCA work was extended to three commercial product scenarios, being Ag NP used in textile, Zn NP mixed in polymers like polypropylene (PP) and Cu NP mixed with water to give a nanofluid coolant. For the Ag application the amounts used are so small that the textile determines the LCI outcome (see Fig. 24), for Zn in PP the contribution of the Zn becomes significant at mass fractions above 1%-wt, while for Cu NP in water the electricity for NP production gives the main LCI contribution. Overall, the LCA method is a mature tool for assessments like this, although limited database information is still a problem (as also concluded at the BUONAPART-E Workshop dedicated to this - see Deliverable 6.4) making it impossible to consider e.g. Ni NP production.

For the scale-up from OSU to mOSU to an eventual 100 kg/day production unit (prOSU) it was found that production rates, (primary) NP sizes and SEC were similar for OSU and separate mOSU arcs, for Cu NP. Thus, the LCI, being primarily determined by the impact of electricity use and carrier gas make-up show now significant difference between one arc of a mOSU and an OSU. As reported below (UDE), the costs of NP production drop by a factor of 2 (1€/g → 0.40-0.45 €/g) for 80 nm Cu NP when moving from a 2x8 mOSU to a 192 unit prOSU, for 10 nm particles (almost 3000 €/g mOSU production costs) this factor of 2 becomes very significant.

Also a detailed life cycle analysis with investigations on the possible release of product particles during their whole life cycle as well as possible hazards stemming from these particles was carried out. Derived from these investigations recommendations in view of safe production, handling and products had to be developed. The focus was set to in-depth analysis for the copper NP as the first case study. A life cycle analysis was also conducted for silver and zinc NP, two completely different nanoparticles with quite different applications.
During the course of the project pyrophoricity was identified as one major point of concern and a safety relevant property especially for the metallic NPs. The study of this material characteristic was not foreseen in the Description of Work but anyhow investigated, since it is essential for safe production and further processing phases of the particles. Proper passivation of the particles is addressed within the production unit at all partners to effectively inhibit self-ignition after collection of the product particles in the filtration unit. The copper and zinc nanopowders as produced by the Consortium were tested after passivation for pyrophoricity by testing the impact of mechanical shock and determining the self-ignition temperature. Both powders were found to be safe as tested for further processing with regard to the foreseen applications, namely the use as cooling agent additive and as additive within polypropylene for cable coatings. Theoretical investigations as well as collaboration with a partner of the EU Project MARINA (J. Bouillard, INERIS) were conducted, identifying critical parameters for the produced NPs. For Cu and Zn nanoparticles we recommend safe handling and passivation for particle sizes below 100 nm for Cu and 300 nm for Zn. It is, nevertheless, clear that specific safety measures have to be in place when metallic powders are used even when passivated by an oxide layer.
One area of concern is the production phase of these powders. Special safety measures have to be in place to prevent fires or even explosions. Thus, several measures were addressed during the installation of mOSU unit. The use of closed vessels without oxygen is mandatory, but also proper passivation procedures for the whole production unit have to be foreseen. Together with the project partners first operating procedures for normal operation were conceived. Several emergency scenarios, rated by their potential impact, were identified and possible countermeasures were described. These scenarios are applicable also for other production facilities and form a basis for future safety assessments of the (m)OSU.
During production of copper NPs workplace measurements were conducted at the mOSU according to the tiered approach developed in other projects. The measurements gave valuable input how to place the different measurement devices, especially with regards to screening measurements during operation. Also data analysis and presentation were improved during the course of the project. These improvements will be used for future workplace measurements within research projects and for contractual work.

The life cycle analysis (looking at scientific issues beyond the regulatory issues) provided theoretical and also practical insights into the main release pathways of the different materials. A mass balance was established for the three case studies showing similarities and differences between the nanopowders. During the production phase a possible release, besides accidental scenarios, can usually be neglected due to the use of closed vessels and also due to proper recycling of the materials involved. Minor material losses leading to a possible exposure can be expected for the further processing stage. But since this takes place within controlled environments appropriate measures can prevent any exposure in case of a release, e.g. during preparation of suspensions. The use and recycling phase is quite different for the different scenarios: in case of copper NPs in cooling agent no major release during the whole life cycle is expected, with a higher uncertainty for the end-of-life phase and the possible recycling after usage. In case of silver NPs applied to medical clothes some release is expected during the use phase due to wearing and washing. In case of zinc NPs as an additive within cable coatings no release should occur during the use phase, but the end-of-life phase is unclear. Overall, it can be concluded that a mass balance has to be evaluated on a case by case basis. Nevertheless, similarities during production, processing and use phase can be applied to simplify future analyses. Based on the literature review on potential environmental and health impacts of Cu, Ag and Zn NPs a summary table was produced (Deliverable D6.5) and further detailed information collected where seen as relevant. D6.5 can be used as a starting point to assess the potential impact for the use phase of these particles.

An economic evaluation was made on the basis of the costs incurred for the pilot plant having 16 OSUs, as well as the measured production rates and specific electricity consumption. A facility of 192 OSU in a three-level lay-out 3x8x8 OSU should be up to the task of 100 kg/day NP. The 3D CAD-based system layout for the prOSU is shown in the Figure 26.

Potential Impact:
SUMMARY OF THE IMPACT OF THE PROJECT

Many future products will be contain nanomaterials or will be more efficiently produced with processes containing nanomaterials or nanotechnology. However, especially metallic nanoparticles are still rather expensive and are only supplied at a small scale, so that the use of metallic nanomaterials in practical applications is still rather limited. The processes developed or improved within BUONAPART-E will allow to:
• Supply metallic nanoparticles at lower prices, due to reduction of process and energy costs
• Increase the supply of metallic nanoparticles due to the development of efficient scaling-up technology which has a low scaling-up uncertainties,
• Estimate the production cost of a metallic nanopowder at a given primary particle size rather precisely by performing some rapid laboratory tests,
• Improve the product quality on demand in case of high-added value products, as very high-quality nanoparticles (size dispersion within +/- 10 %, spherical shape) can be supplied at any desired sizes between 5 and 160 nm,
• Improve and monitor the process stability and product quality by online monitoring tools adopted to this process

The motivation behind the choice of an electrical discharge as a synthesis platform stems from the experience of BUONAPART-E consortium that this technology is cost-efficient to implement and easy to use, while still allowing for rapid process optimization. As the basic unit is just a pair of electrodes and a large number of these pairs can be placed in a single housing, it is evident that a cost-effective scaling-up strategy include the use of multiple units in parallel. This strategy as analogous to supercomputers based on low-cost graphic cards from the consumer market.

The project demonstrated that it is possible to use the same synthesis platform in a whole range of different applications, ranging from mass power production to high-tech applications where only amounts of nanoparticles are necessary to yield the desired product. The project led to several pilot plant facilities, having production rates between 1 and 10 kg/day, mainly depending on the type of metal. An engineering study of a 100 kg/day facility showed the feasibility of such constructing such a production facility.

The versatility of the synthesis process is demonstrated by means of six very different applications requiring nanoparticles having various requirements for which the synthesis unit was optimized. Here either the nanoparticle product quantity is crucial or the nanoparticle quality and effectiveness of the integration strategy. Optimization of synthesis parameters as well as dedicated deposition strategies were performed based on feedback from six endusers coming from application fields as various as blast furnaces for steel production, solar cells, textiles, catalysts for membrane reactor, nanocomposites and plasmonic sensors:
o Integration of arc-OSU in aerotaxy® production line for solar cells
o Direct deposition of nanoparticles on textiles
o Nanocomposites showing flame retardancy
o Deposition of nanoparticles within periodic arrays of nanocrosses for photonics
o Higher heat transfer with nanoparticle dispersions
o Direct deposition of catalytic nanoparticles on membrane structures

The process has been developed in such a way that possible impact on the environment is minimal. The process is designed as a closed loop system that avoids the use of hazardous precursors, solvents and stabilizers. The main input is electric power for the electric discharges, for this a new quantification tool has been proposed: the Specific Electricity Consumption (SEC, expressed in kWh/kg product). The process is designed for having a low possibility of workplace exposure to nanoparticles. It avoids complicated and expensive safety measures, as quasi-atmospheric inert gas is used as transport medium and hazardous chemicals are avoided. All these factors make this process a clear example of green and sustainable synthesis process, and will thereby contribute to increase the level of acceptance of nanotechnology in society.

A more extensive analysis of the impact is detailed below

1) IMPACT ON INDUSTRY

a) Impact on production of nanoparticles

Before the start of BUONAPART-E, precursor-free nanoparticle production processes for metallic nanoparticles had following drawbacks:
- Conventional plasma reactors potentially allowing metallic nanoparticle synthesis are offered on the market, however the setups are very costly (at least 2 M€) and require personnel experienced with dedicated plasma power supplies. Furthermore, the size and complexity of these setups is such that they cannot be easily integrated as nanoparticle source in an industrial system
- DC-arc discharge systems which are simpler and can be powered by simple high-current power supplies have been described in the literature, but are either notoriously instable and not able to run for more extended periods, or have a low production rate.
- Small-scale spark discharge systems are well known as potentially suitable for the production of sub-20 nm primary (metallic and alloyed) particles and commercially offered as simple aerosol generators, but have production rates not surpassing a few mg/hr due to the low frequency used.
In BUONAPART-E, the arc-discharge method has been developed into a stable and low-cost process having production rates in the order of g/h per electrode and not requiring expensive power supplies. Three patent applications for the most efficient, stable and productive version of the arc-OSU has been filed in Germany, Europe and US, thereby effectively protecting the IP. The spark-discharge process has been made more productive by developing a high-frequency power supply, which allows frequencies up to 9 kHz instead of a few hundreds Hz, at the same time keeping the primary particle size small.

The developed arc-based process presents a major step forward in the availability of high-purity metallic nanoparticles (NPs) with high-process throughput (guaranteed by the already realized parallelisation of simple single units), low product costs and high energy-efficiency, with minimal impact on the environment. A major advantage of the process is the possibility of producing NPs with nanostructures and sizes on customer demands with a simple process route that can be applied to multiple variants. The process is designed in an environmentally friendly way as a closed loop system that avoids the use of hazardous precursors, solvents and stabilizers. The main input is electric power for the electric discharges. The process is designed for having a low possibility of workplace exposure to nanoparticles. It avoids complicated and expensive safety measures, as quasi-atmospheric inert gas is used as transport medium and hazardous chemicals are avoided. All these factors make this process a clear example of green and sustainable synthesis process. The motivation behind the choice of an electrical discharge driven by low-cost welding power supplies stems from the experience that this technology is cost-efficient to implement and easy to use, while still allowing for rapid process optimization.
The availability of a simple and low-cost nanoparticle generation system which is precursor-free means that it is possible to integrate the synthesis step in another process which requires nanoparticles for integration in the final product. This is demonstrated by several applications in the BUONAPART-E consortium, in which a nanoparticle generator is used for direct feeding of the process with gas-carried nanoparticles or for direct deposition of freshly synthesized nanoparticles on intermediate or final products. This direct integration is especially relevant for metallic nanoparticles, as these are often oxidation-sensitive and a transport or storage of the intermediate product nanoparticles presents risks for the application as well as the working place or the environment.
A single OSU produces between 0.2 and 36 g/h nanoparticles in the arc mode (3 g/h for copper), a feeding system allows continuous operation. The energy efficiency for production is ~200 kWh/kg for copper nanoparticles in the arc mode, it is independent of the arc current. The production rate and thus the energy efficiency depends strongly on the metal used. The primary particle size can be varied by means of the arc current. The approach chosen here has clear economic advantages, as the power supply for a single DC arc power supply costs only 200 EUR/kW. The power supply of commercial large-scale plasma power supplies cost 8000 EUR/kW. The reason for this is that cheap power supplies from the consumer market are being used.
The impact for the commercial metal nanoparticle producer involved in the project is following:
• Increased 1 Full-time staff and 4 part-time staff in the company.
• Increased the choices of metal nanoparticles (e.g. Cu, Zn, Ag) production at larger quantities.
• Potential increased sales from the supply of Zn NPs to AIT for fire retardant composites after the project.
• Adaption of m-OSU concept to our existing arc discharge in liquid process will be planned after the project.

The HF spark-OSU developed within BUONAPART-E gives easy access to an enormous variety of metallic nanoparticles. This is unique and due to the mixing feature of the spark method. For the future, possible applications are not only in catalysis. Other domains, where spark-produced particles have already proven to be useful include chemical sensor production, efficiency enhancement of solar cells and solar water splitting, hydrogen storage and special magnetic materials. In the future, 3-D printing of micro-devices using nanoparticles is within the possibilities presently discussed.

During the duration of BUONAPART-E, the usefulness and therefore the need of very small particles (diameter smaller than 10 nm or even 5 nm) became more evident than ever, also with respect to the users within BUONAPART-E. The HF-Spark is opening doors to new disruptive technologies including catalysis, textile finishing, chemical sensors and very impressive work has recently been completed by TUD outside of BUONAPART-E, which uses spark-produced plasmonic particles for increasing the efficiency in water splitting and photovoltaics.

b) Impact on technology related to the production of nanoparticles

Post-processing technology:
The developed size classification systems and the filter system allow for much higher production rate of metal NP from discharge systems, compared to the previous state of discharge-based NP generators, because they can operate at higher aerosol flow rates, which come from the scaled-up multi-electrode systems that use many discharges in parallel. At the same time, these systems allow for closed-loop operation, which minimises the consumption of inert gas and, thus, reduces the operational costs. Additionally, the price for the developed systems does scale less than proportional with the aerosol flow rate, further reducing the (relative) investment costs. The developed systems are not limited to the type of NP generation processes investigated within BUONAPART-E, but can also applied to other NP generation systems which need post-generation equipment, especially for critical materials that require special handling (closed system, inert gas atmosphere, passivation, internal cleaning etc.).

Process monitoring systems:
The novel monitoring systems, both for the produced NP aerosol as well as for the discharge process itself, allow for better process control, thus reducing the risk of producing large amounts of particles (and final products) that do not match the specifications. This reduces energy and raw material consumption and waste generation, and thus improves the environmental friendliness and energy efficiency of the process.
The dry routes, developed as an alternative to conventional wet multi-step batch processes, simplify the production of different end products, thus potentially reducing process and product costs.

c) Impact on products and processes enabled by nanoparticles

Possibilty of nanoparticles being offered at lower prices:
Currently, some metallic nanoparticles are being offered on the market, however the prices are high and the availability of larger amounts is still problematic, thereby limiting their application in products and processes requiring metallic nanoparticles. The process developed within BUONAPART-E will allow lower prices, when the process is commercialized. The estimated price ranges from 0.58 €/g for Zn particles with a size of 210 nm to 2928 €/g for Ag particles with a size of 12 nm. The price decreases significantly with increasing particle size and hence mass output. Analysis shows that the fixed costs compose the main part of the costs. With increasing size respectively an increased mass output there is an increase in feedstock costs noticeable, as more material is needed. The costs for the electricity are quite low and decrease with increasing particle size. Thus, optimization in terms of costs has to be performed in terms of the fixed costs, such as maintenance, unscheduled costs or personnel costs. A comparison of the estimated particle prices with prices for commercially available nanopowders with similar attributes show that the estimated prices are competitive. Especially larger amounts of smaller sized particles are commercially almost not available. The production facility is able to cover the demand of smaller particles. Silver particles of a size of 120 nm can be produced in terms of costs in the same range than from other distributors. The copper nanoparticles (80 nm) can be sold cheaper than they are available at the moment. For zinc, only the production of larger particles (210 nm) is profitable. When exemplarily comparing the cost for 80 nm Cu, the price resulting from the existing pilot plant, at 1.04 €, would drop to 0.43 € with pilot plant containing 192 OSUs, mainly due to lower personnel and depreciation costs. The fixed costs (mainly personnel and depreciation) decrease when the particle size increases and the feedstock costs increase.

Solar cells:
With the mission to improve the efficiency of solar energy capture and generation using nanowires grown from the Aerotaxy®, the arc-OSU source concept and DMA development that was undertaken within the BUONAPART-E has enabled to reach a particle size distribution and concentration, which led to an increase of the production capability of 30x of nanowires grown from nanoparticles. By adding SolFilm™ on crystalline silicon modules it is possible to convert today’s average panel of 15.5 percent conversion efficiency to go beyond the silicon limits of 23-24 percent. That is more than a 50 percent improvement in performance creating a lower levelized cost of energy for the users.

Advanced textiles:
The results of the project can have an important impact, due to the growing demand of antimicrobial functionality for textile materials applications such as:
• Filter materials, Filtech. Applications: water filtration and cleaning, food and liquid production, air filtration, etc. In the latter, there are often problems with mould formation and bacterial growth, e.g. leading to the sick building syndrome.
• Medical and hygienic materials, Medtech: dressing materials, artificial limbs, orthoses, wound applications, implants, artificial vessels, tapes, and hernia meshes.
• Transportation materials, Mobiltech: seat covers, safety belts, interiors for the automotive, train and aviation industries.
• Domestic materials, Hometech: furniture coverings, filler materials, ceiling, wall and floor coverings, etc.
• Footwear and clothing, Clotech:smell reduction and increased durability (filler/lining materials, insoles, waterproofing and stain resistant...).

With the future development of the technology for direct production – application of nanoparticles for fabrics, from the economic point of view of the industrial production, there will be a direct benefit for industries implied. That will take the form of costs reduction and entire respect of environmental and safety legislation. We can estimate that the current processes costs will be cut of 14%, and functionalities improvements will be obtained. The future development of this technology can have an impact in European SMEs, because according to EURATEX, in 2013 the turnover of the textile and clothing industry in the EU rose to 156.000 million EURO thanks to nearly 172.600 enterprises. More than 90% of the textile companies are SMEs, employing more than 1.800.000 workers, in total. These SMEs are relatively small (textile: 13 workers; clothing: 9 workers, as average), but very flexible and willing to adapt to the needs of their clients. Note that the sector has increased by 35% from the period 2010 to 2013. This shows that this sector is becoming resilient and more competitive.

Composite polymers:
Cu nanoparticles (Cu Quality A) produced using arc discharge will have a huge potential impact. They can be used as raw material enabling to produce our new product to eliminate mercaptans. This new product has a huge potential of exploitation because there is not any other method and no other Cu NPs commercially available to reduce mercaptans. The fact that it is the only product in the sector for this application makes it attractive for customers, so it would have a very good acceptance in the market. For that reason, this product present a real interest as it is completely new in this sector.

In addition, Zn particles produced also by arc discharge, for use as fire retardant additive to polymers is of interest. End-user and nanoparticle producers from the project are in discussion to determine which quantity of Zn powder can be produced in the scaled up process and also to arrange a reasonable price for the application.

With these nanoparticles, the targets defined at the beginning of the project, related with the development of new added-value nanocomposite products with improved properties are reached.

Plasmonic sensors:
The small-sized non-agglomerated nanoparticles obtained with modified OSU has proven very useful for fabrication of LSPR sensors and is expected to have a high impact in this field. Photonic applications in other fields of science are to be anticipated, because singlet nanoparticles exhibit an outstanding behaviour in their interaction with light, and the interaction with molecules as well as the influence of environmental factors like temperature changes their properties on a small time scale.
The capability of producing NP-based localized surface plasmon resonance sensors (LSPR) would place the project partner (and potentially other SMEs) in a very competitive position in the market thanks to the low cost of the raw material (metallic NPs) and required equipment (spark discharge generator instead of expensive metal evaporators). Moreover, since the sensors can be produced on site due to the simplicity of the production tool (as opposed to the complexity and cost of a standard CMOS production line), the project partner will be in control of the fabrication chain and have a great advantage when providing added value sensors to its customers. This technology represents a solution to clients that are looking for new, cheap, fast, energy-efficient and user-friendly chemical and bio sensors for applications such as food chain safety or environmental pollution monitoring, with a high potential societal and economic impact. Just as an example, LSPR sensors could detect different chemical contaminants, toxins and bacterial pathogens responsible for a variety of foodborne illnesses, which only in the United States result in medical and lost productivity costs of up to $22 billion annually.

Catalytic membrane reactor:
The catalytic tests of the Ni NPs deposited onto the membranes showed that the conversion of methane into hydrogen was too low for being commercially interesting.

Techno-economic aspects of a catalytic membrane reactor concept where pressurized hydrogen is produced were investigated by modelling and benchmarked with state-of-art technologies. By forecasting crucial reactor parameters, this process was modelled to being highly attractive for production of pure and pressurized hydrogen from natural gas, both in terms of production costs and energy efficiency.

2) IMPACT ON SCIENCE

The project had a relevant impact in the scientific community as can be shown through the relatively large number of scientific papers in refereed journal as well as conference talks and poster presentations (which will be demonstrated later in the dissemination section), see Fig. 27. Major scientific results are related to the fundamentals of spark and arc-based electrical discharges relevant for nanoparticle synthesis and handling technology and development of models which can be used for understanding and optimization the processes as well as predicting the production rate and expected particle size of other materials.

The impact of scientific publications is traditionally measured in terms of their citation impact. As it is still too early to analyze the impact of the BUONAPART-E publications themselves, in Fig. 28 the impact factors of journals where the project publications have appeared are shown. It can be seen that most of the publications appeared in relatively high-impact factor journals (>2).

BUONAPART-E also had a decisive influence on the education of future scientists that may play a role in the real life application of the project’s results, as eight PhD Thesis are or will be dedicated to topics originating from research conducted within BUONAPART-E:
• Matthias Stein (UDE): Synthesis and Application of Metal Nanoparticles (defended in Sep 2015)
• Linus Ludvigsson (ULUND): Optimization and characterization of the spark discharge process, for production of nanoparticles with tailored properties
• Jicheng Feng (TUD): Advances of spark produced nanoscopic building blocks with composition, size and shape control (submitted March 2016)
• Anssi Arffman (TUT): Numerical and experimental study on inertial impactors (defended in February, 2016)
• Attila Kohut (USZ): Plasma diagnostic measurements in a spark discharge nanoparticle generator
• Andrey Voloshko (CNRS-UJM): Numerical study of spark discharge at atmospheric pressure: Application for nanoparticle formation (defended in October 2015)
• Martin Slotte (AAU): Energy efficiency and LCA of process scale-up (June 2016)
• Matthias Stadlbauer (TKSE-UDE): Investigation on heat transfer characteristics by using nanofluids in heat exchanger installations (June 2016)

3) IMPACT ON SOCIETY AND THE ENVIRONMENT

a) Minimal environmental footprint of nanoparticle production and nanomaterials based on the produced nanoparticles
Features such as the efficiency of material and energy use and the environmental footprint of the BUONAPART-E concept for NP production will affect economic feasibility and market potential. This was assessed by studying how the energy (electricity) used for the different operation modes (arc or spark discharge) compares to what is theoretically needed for converting the metal into NP, the remainder being converted into (waste) heat to be removed by cooling. For this assessment, the thermodynamic concept of exergy was expanded to metallic NP and the arc/spark discharge process used: this was published in the open literature. (This tool was then used to evaluate production data from the project partners.)
Electricity being relatively cheap and aiming at a wider view in order to be able to compare results with more “conventional” routes for metallic NP production, a life cycle impact assessment (LCA) was made that addresses also the impact on human health, natural resources and the ecosystem, using a commercial software tool. Clear differences were identified for the different metals but also for arc vs. spark systems and the primary NP size. Comparison with more “conventional” production routes showed that the BUONAPART-E concept is favourable if production efficiencies (metal NP out vs. metal in) can be raised to 80-90%. (This puts emphasis on systems for removing the produced NP from the production unit.) Although limited by information available in databases used in LCA it showed to be a useful tool that also could be used for calculating the environmental footprint of commercial products that contain metallic NP (e.g. Ag, Cu, Zn), as well as the changes during scale-up, revealing more than economic benefits of larger scale of production.
The newly developed dry deposition process for direct deposition of nanoparticles on textiles have the following benefits from an environmental point of view:
• Reduction of chemicals involved in textile finishing processes.
• Reduction of water used in textile finishing processes.
• Reduction of energy used for finishing (drying/curing steps).
• Reduction of wastes and emissions generated at the end of the finishing process.
• Reduction of the pollutant charge received by Waste Water Treatment Plants (WWTP).

b) Healthy working place environment as a result of safe by design process development
Safety aspects during production and further use of metallic NP play a major role for the acceptance of this technology. Thus, the conducted work with regard to the potential release during the production of the particles, their further processing into products and the possible release during the use and end-of-life phase are essential parts of the life cycle analysis. Also the pyrophoricity of some of the metallic particles has a high impact on the foreseen production and use scenarios and was therefore analysed in detail. Due to the conducted work the “safety by design” approach was further elaborated for the metallic NPs produced within BUONAPART-E. With regard to planning and building of NP synthesis reactors valuable information was obtained and will be used for future facilities. It is important to notice that practical experiences were obtained with a pilot plant in a university surroundings, so that the information gathered will be published in accessible literature. Also, the already existing tiered approach for workplace measurements with regard to particle release was further refined, especially with regard to data gathering and analysis. This will be used for measurements within future projects or for contracted work by industry partners.

4) IMPACT ON VARIOUS STAKEHOLDERS

By communication of the results and collaboration with different stakeholders (e.g. industry, public bodies) also a contribution to the sustainability of nanomaterials was made. We were able to demonstrate that all aspects of possible concerns (health and safety of workers, the public and the environments) are dealt with in a life-cycle-analysis and that measures are developed, recommended and implemented to ensure a safe use of this new technology.

DISSEMINATION ACTIVITIES

The work performed during BUONAPART-E (48 months) resulted in a very active website (both the public and restricted area), many different publications and in other dissemination activities, which are summarized in the following text.

Website
The project’s Website and emailing lists were well-established in the first period of the project. They were valuable instruments for internal and external communication and were regularly updated.

Publications in peer reviewed Journals
Until Mid-March 2016, 25 peer-reviewed scientific papers have been published (6 of which are open access), some 16 more have been submitted or are in preparation. A full listing is therefore here not possible, so a selection is given, thematically ordered:
WP1, Fundamentals:
• Palomares J M, Kohut A, Galbacs G, Engeln R, Geretovszky Zs, A time-resolved imaging and electrical study on a high current atmospheric pressure spark discharge, Journal of Applied Physics 118, 233305, 2015, http://dx.doi.org/10.1063/1.4937729
• Wagner M, Kohut A, Geretovszky Zs, Seipenbusch M, Galbács G, Observation of fine-ordered patterns on electrode surfaces subjected to extensive erosion in a spark discharge, Journal of Aerosol Science 93, 16-20, 2016, http://dx.doi.org/10.1016/j.jaerosci.2015.11.008
• Feng J, Huang L, Linus L, Messing M E, Maisser A, Biskos G, Schmidt-Ott A, A general approach to the evolution of singlet nanoparticles from a rapidly-quenched point source, Journal of Physical Chemistry C 120, 621-630, 2016, http://dx.doi.org/10.1021/acs.jpcc.5b06503
WP2, OSU and core technology development
• Meuller B O, Messing M E, Engberg D L J, Jansson A M, Johansson L I M, Norlén S M, Tureson N, Deppert K, Review of spark discharge generators for production of nanoparticle aerosols (review paper), Aerosol Science and Technology 46, 1256-1270, 2012 (open source)
• Hontañón E, Palomares J M, Stein M, Guo X, Engeln R, Nirschl H, Kruis F E, The transition from spark to arc discharge and its implications with respect to nanoparticle production, Journal of Nanoparticle Research15, Article no. 1957 (19 pp) 2013 http://dx.doi.org/10.1007/s11051-013-1957-y
• Pfeiffer T V, Feng J, Schmidt-Ott A, New developments in spark production of nanoparticles (invited review paper), Advanced Powder Technology 25, 56-70, 2014, http://dx.doi.org/10.1016/j.apt.2013.12.005
• Jicheng Feng, George Biskos , Andreas Schmidt-Ott, Toward industrial scale synthesis of ultrapure singlet nanoparticles with controllable sizes in a continuous gas-phase process, Nature Scientific Reports 5, Article number: 15788 (2015), doi:10.1038/srep1578
WP3, Supporting technology
• X. Guo, A. Gutsche, M. Wagner, M. Seipenbusch, H. Nirschl, Simultaneous SWAXS study of metallic and oxide nanostructured particles, Journal of Nanoparticle Research, 15, Article No. 1559, 2013
• X. Guo, A. Gutsche, H. Nirschl, SWAXS investigations on diffuse boundary nanostructures of metallic nanoparticles synthesized by electrical discharges, Journal of Nanoparticle Research, 15, Article No. 2058, 2013
• E. Hontañón, M. Rouenhoff, A. Azabal, E. Ramiro, F.E. Kruis, Assessment of a cylindrical and a rectangular plate differential mobility analyzer for size fractionation of nanoparticles at high aerosol flow rates, Aerosol Science and Technology, 48, 333-339, 2014 (open source)
• X. Guo, M. Wagner, A. Gutsche, J. Meyer, M. Seipenbusch, H. Nirschl, Laboratory SWAXS combined with a low-pressure impactor for quasi-online analysis of nanoparticles generated by spark discharge, Journal of Aerosol Science, 85,17-29, 2015
WP4, Scale-up
• M. Stein, D. Kiesler, F.E. Kruis, Effect of carrier gas composition on transferred arc metal nanoparticle synthesis, Journal of Nanoparticle Research Volume 15 Issue 1 Article No. 1400, 2013, http://dx.doi.org/10.1007/s11051-012-1400-9
WP5, Feasibility studies and cost benefit analysis for sample potential applications
• J.M. Polfus, W. Xing, M L. Fontaine, C. Denonville, P.P. Henriksen, R. Bredesen, Hydrogen membranes based on dense ceramic composites in the La27W5O55.5-LaCrO3 system, Journal of Membrane Science, 479, 39-45, 2015
• E. Hontañón, J. Meyer, M. Blanes, X. Guo, M. Masuhr, A. Muntean , L. Santos, A sustainable route for antibacterial nanofinishing of textile, International Journal of Theoretical and Applied Nanotechnology, (under review)
WP6, Efficiency, Risk and Economical Assessment
• R. Zevenhoven and A. Beyene, Exergy of nanoparticulate materials, International Journal of Applied Thermodynamics, Volume 17 Issue 3, 145-151, 2014, open source.
• M. Slotte, G. Metha and R. Zevenhoven, Life cycle indicator comparison of copper, silver, zinc and aluminium nanoparticle production through electric arc evaporation or chemical reduction, International Journal of Energy and Environmental Engineering, Volume 6 Issue 3, 233-243, 2015, open source

Publications for conference proceedings and oral or poster presentation at conferences
In total, 129 presentations of project results at scientific conferences were given in form of oral (95) or poster (34) presentations, among which:
• European Aerosol Conference EAC 2012 (Granada, Spain), 2013(Prague, Czech Republic), and 2015(Milan, Italy)
• International Aerosol Conference, Busan, South Korea, 2014
• ProcessNet2013 (Cottbus, Germany), 2014 (Würzburg, Germany) and 2015 (Magdeburg, Germany)
• International Congress on Particle Technology PARTEC 2013, Nürnberg, Germany
• 42nd Seminar on Nanomaterials and Polymeric Nanocomposites 2013, Logrono, Spain
• 10th International Conference on Nanosciences and Nanotechnologies NN13, Thessaloniki, Greece
• 26th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems ECOS 2013, Guilin, China
• AIChe Annual Meeting 2013, San Francisco, USA
• 7th World Congress on Particle Technology WCPT7, Bejing, China
• Aerosol Technology Conference 2014, Karlsruhe, Germany, and 2015, Tampere, Finland
• International Aerosol Conference IAC 2014, Busan, South Korea
• ECHA Topical Scientific Workshop on Regulatory Challenges in Risk Assessment of Nanomaterials 2014, Helsinki, Finland
• Materials Research Society Fall Meeting (Symposium HH) MRS 2014 , Boston, USA
• 4th International conference on Multifunctional, Hybrid and Nanomaterials, 2015, Sitges, Spain
• 8th International Conference for Conveying and Handling of Particulate Solids CHoPS2015, Tel Aviv, Israel

BUONAPART-E was present twice at the EuroNanoForum conference, in 2015 the project was selected for the FutureFlash! Best Project Competition: BUONAPART-E as one of the 10 very best of all the over 1000 projects launched under the EU Funding Instruments in the field of nanotechnologies and advanced materials, allowing to present in an exhibition booth the project to the European nano-community and policy makers.

Dissemination activities to a wider public
11 presentations presenting the project to a general audiences were given, 8 times the project was presented at exhibitions. 2 press releases were released and 2 times the project appeared in the non-scientific press.

Organization of Workshops
A number of public workshops were organized by the Consortium. The workshops brought together students, scientists, technologists and industrial end-users to discuss about the optimization of nanoparticle synthesis and practical applications of nanoparticles, but also the Environmental, Health and Safety aspects and Life Cycle Evaluation and energy use.
The lecturers were selected from the Consortium, but also lecturers from other EU projects or from industry were invited to facilitate the exchange of knowledge and experiences. These workshops were:
• Workshop, titled „Environmental, Health and Safety Aspects of Nanomaterial Use and Production“, was held in collaboration with SafeNano Norway on January 21st, 2013 at the Forskningsparken conference center in Oslo, Norway. Topics: various nano-EHS aspects of general interest, including the release of and exposure to nanomaterials, their toxicology as well as energy aspects of the nanoparticle production. 55 people attended this workshop.
• BUONAPART-E Summer School, Valencia, Spain, 10-12 June 2014. Topics. Gas-phase synthesis of metal nanoparticles by means of electrical discharges, Modeling of gas-phase particle synthesis, Online monitoring techniques: Electrical discharge and plasma, Online monitoring techniques: Aerosols, Offline characterization techniques for nanoparticles, Nanoparticle collection and handling, Applications of metal nanoparticles, Visits to nanotechnology-related facilities :NTC cleanroom for micro- and nanofabrication and AITEX textile research institute. 22 people attended this workshop.
• Workshop on “Life cycle evaluation and energy use for different production processes of Nanomaterials”, Turku, Finland, 15-16 April 2015. Topics: comparison of production routes and NP-based products, the use of energy and the efficiency of that during NP-based material production and, for a wider perspective, life cycle assessment (LCA) , economic factors this will allow for ranking NP production routes and NP-based materials based on both sustainability and economic viability. 33 people attended this workshop.
• Final Workshop “Symposium on Synthesis of functional nanomaterials: fundamental understanding, scale-up, and design for applications“, Duisburg, Germany, 20-21 January 2016. Topics: Optimization and scaling-up of nanoparticle synthesis, Measurement, modeling and diagnostics, Post-treatment, functionalization and deposition technology, Sustainable technology and policies, Applications of nanoparticles. In this two-day international symposium, the relevant scalable nanoparticle synthesis processes such as plasma synthesis and flame synthesis have been presented, with an emphasis on recent innovations, scaling-up strategies and methods for evaluating the sustainability of these processes. The Symposium was organized in cooperation with the DFG research unit FOR2284 “Model-based scalable gas-phase synthesis of complex nanoparticles” and CENIDE, the Centre for Nano-integration, located at the University Duisburg-Essen. This cooperation consolidated the local experiences but also strongly gained benefit regarding scientific and networking aspects. 98 people attended this workshop.

EXPLOITATION OF RESULTS

An Intellectual Property (IP) Directory was created describing the contribution of all project partners to the project Background and Foreground. An Exploitation Strategy Seminar (ESS) was held following the 2nd General Assembly meeting (Delft, January 2014), led by an experienced innovation consultant appointed by the EU. Within the ESS, the focus was predominantly on non-technical issues related to the BUONAPART-E project. This includes exploitable results, risks, recommendations, IPR issues, and issues related to working together in an international consortium of both commercial and scientific project partners. The seminar and the resulting documents (the Exploitation Strategy Seminar Report, ESSR, and the Plan for Using and Disseminating Foreground, PUDF) were deemed to be very useful by the consortium. During the ensuing meetings, more exploitable results were proposed and discussed. Finally, 13 exploitable results having the best prospects for exploitation were selected:
• Optimal Single Unit (OSU) in arc mode
• Optimal Single Unit (OSU) in high frequency spark mode
• Synthesis facility containing N Optimal Single Units
• Optical discharge monitoring equipment
• Real-time low-cost aerosol quality monitoring equipment
• Scaled-up Differential Mobility Analyser (DMA) for high throughput size-selected nanoparticles
• Improvement of blast furnace cooling by the use of nanofluids
• Nanocomposites with improved funcionalities
• Low-cost energy-efficient SPR chemical- and biosensors based on clusters of metallic nanoparticles
• Protonic membrane reformer for on-site hydrogen production
• Electrode rod feed system with stepping motor and control circuit
• Electronic for spark discharge mode with control of each single spark
• Dry deposition of nanoparticles onto textile fibers by passing aerosol through the fabrics

Some of partners protected their exploitable results by means of patent applications. Four patents were filed:” Lichtbogenreaktor und Verfahren zur Herstellung von Nanopartikeln” (DE 102014220817.3) „Arc reactor and process for the production of nanoparticles” (US 14875310), “Arc reactor and process for the production of nanoparticles” (EP 151188763.5) and “Kühlkreislauf für ein Kühlmedium mit Nanopartikeln” (DE 102015211050.8)

List of Websites:
www.buonapart-e.eu

Beneficiaries:

1. UDE, University Duisburg-Essen, Faculty of Engineering, Institute of Technology for Nanostructures,
Bismarckstr. 81, 47057 Duisburg, Germany

Prof. Dr.-Ing. Einar Kruis (Coordinator)
[e-mail]
phone: [phone]
fax: [phone]

Dr. Maria Gies (Project Management)
[e-mail]

2. ULUND, Lund University, Knut Deppert
3. TUD, Delft University of Technology, Andreas Schmidt-Ott
4. TUT, Tampere University of Technology, Jorma Keskinen
5. a) KIT-S, Karlsruher Institut für Technologie, Jörg Meyer
b) KIT-N, Karlsruher Institut für Technologie, Herrmann Nirschl
6. USZ, University of Szeged, Zsolt Geretovszky
7. AAU, Åbo Akademi University, Ron Zevenhoven
8. CNRS, Centre National de la Recherce Scientifique, Tatiana Itina
9. TU/e, Technische Universiteit Eindhoven, Richard Engeln
10. IUTA, Institut für Energie- und Umwelttechnik e.V. Thomas Kuhlbusch
11. TKSE, ThyssenKrupp Steel Europe AG, Jörg Bergmann
12. RAMEM, RAMEM S.A. Daniel Fuentes Calero
13. MNL, Metal Nanopowders Ltd., Isaac Chang
14. SOL, Sol Voltaics AB, Linda Johansson
15. FOMENTEX, Fundación para el Fomento del Sector Textil de la Comunidad Valenciana, Felipe Carrasco Torres
16. PAL, Palas GmbH, Maximilian Weiß
17. AIT, Avanzare Innovación Tecnológica SL, Julio Gómez
18. SINTEF, Stiftelsen SINTEF, Christelle Denonville
19. CoorsTek, CoorsTek Membranes AS, Harald Malerød-Fjeld
20. UPLVC, Universidad Politécnica de Valencia, David Ortiz de Zárate Díaz
21. DAS, DAS Photonics SL, Carlos García