Final Report Summary - AERSUS (Aerogel European Supplying Unit for Space Applications)
Executive Summary:
The purpose of the AerSUS project is to create a European Supplying Unit for one of the critical space technologies for European strategic non-dependence: advanced thermal control materials.
The main objective of AerSUS is to provide aerogels, develop their manufacturing technology and aerogel insulation systems prototypes that are suitable for specific Space applications. Aerogels are considered to be the next generation of thermal insulation in Space and are regarded as the materials with the greatest potential to substitute multi-layer insulation (MLI) and other materials used for the thermal insulation of spacecraft. This is because of their very low density, very high thermal insulation efficiencies, and their ability to provide thermal insulation as a single material that can be industrially produced and tailored to different applications.
The consortium provides a wide variety of know-how that has been integrated into the project, covering research and aerogel development at laboratory scale; the design and construction of semi-industrial equipment for aerogels manufacturing; and the design, integration and qualification of thermal insulation materials in-space applications. This consortium-wide effort creates excellent synergies to place Europe as a key supplier of aerogels which are projected to be the future of thermal insulation in Space.
Towards these efforts, a fully integrated project programme was carried out. The AerSUS programme, broken down into 10 Work Packages, included the development of a preliminary study (WP1); the identification of the technical specifications for the aerogels’ synthesis methods, the development and operation of the manufacturing technology, and the requirements of aerogel insulation for use on space applications (WP2), the actual development of the aerogels by three project partners (WP3); the design and building of aerogel manufacturing technology (WP4); the up-scaling of the developed aerogels (WP5); the development of aerogel insulation systems (WP6); the development of prototypes using the developed aerogels and validation of their performance (WP7); the dissemination and exploitation of the project (WP8); the implementation of long-term commitment activities (WP9); and the management of the project (WP10).
From the project, several results emerged. The most significant were the development of the aerogels by the three manufacturing partners: RF aerogel – silica aerogel composites I, organically modified silica based aerogels derived from MTMS with and without PEG additive, and Silica/organic hybrid aerogels. Based on the developed aerogels, another result was the design of semi-industrial scale equipment adapted to the AerSUS aerogels. This resulted in fully automated equipment for large scale aerogels. From the aerogels developed at lab scale and using the manufacturing technology, partners developed aerogels at an industrial scale: RF – silica gel composites II, Organically modified silica based gels derived from MTMS, and Silica/organic hybrid gels II. Using an aerogel encapsulation process developed in the project, the industrial-scale aerogels were encapsulated, and later evaluated through depressurization and vibration testing. The encapsulating procedure proved to be successful, and was later used to develop additional encapsulated aerogel panels. The developed aerogels were also subjected to thermal testing with a simulated ‘real-environment’ – a Mission to Mars – providing insight on the optimal configuration for the instruments to work optimally. Lastly, long-term commitment activities were set in motion, including additional developments on aerogels: RF aerogel – silica aerogel composites III, Organically modified silica based aerogels derived from MTMS with BTMSH/BTMSE/ODS additives, and Silica/organic hybrid aerogels III. Lastly, the possible target applications for the develop aerogels were revised, where the main applications for the developed aerogels are thermal insulation of manned compartments, in unmanned compartments in ascent/reentry vehicle and cargo modules, as well as in a Mars environment.
The multitude of project results suggests that AerSUS has successfully contributed to strengthening Europe’s strategic non-dependence for advanced thermal control materials. While improvements on the developed aerogels will have to be put in motion, the consortium has set the foundation for the next generation of thermal insulation for Space applications.
Project Context and Objectives:
The main purpose of the AerSUS project is to create a European supplying unit for one of the critical space technologies for European strategic non-dependence: advanced thermal control materials.
Currently, thermal protection of spacecraft hardware is assured by underlying advanced thermal control materials, commonly Multi-Layer Insulations (MLI). Most of the MLI materials are procured from non-European sources and often under access restrictions. Furthermore, one of the basic materials for MLI, the Kapton, is used in several thermal control applications and easily falls under access restrictions, such as ITAR. On this basis, advanced thermal control materials have been included in the Critical Space Technologies for European Strategic Non-Dependence [Excerpt from Critical Space Technologies for European Strategic Non-Dependence", List of Urgent Actions 2010/2011, EC-ESA-EDA, September 2010.]. Finding alternative solutions to MLI was also addressed in the ESA's roadmap, including ESA funded initiatives that have similar aims (e.g. “Proof of Concept for Aerogel Applications”, “Aerogel Thermal Insulations Systems”, “Adaptation of Aerogel Materials for Thermal Insulation”).
Aerogels are the lightest solid materials in the world and are composed over 90% of air. Due to their unique properties, such as low density and low thermal conductivity, aerogels have emerged as the best alternative to MLI. Before the AerSUS project, many of the project consortium partners worked on the development of thermal insulation systems based on aerogels that could meet space requirements. Despite these efforts, the main difficulties found by the space industry at the time, and concerning the use of aerogels, were the lack of reproducibility of their properties and the absence of an entity that could guarantee the continued supply on a long-term basis for an aerogel product with a high TRL and with tailored properties. As a result of this necessity, the AerSUS project emerged within the outlined context.
The AerSUS project has collaborated on the development of aerogels, their manufacturing technology and aerogel insulation systems prototypes for specific space applications where, due to the presence of atmosphere, MLI are not efficient. These applications include, for example, (re)-entry vehicles, Mars rovers, and pressurized compartments.
The combination of know-how of the entities involved in the project, covering research and development of aerogels at a laboratory scale; the design and construction of semi-industrial equipment for aerogels manufacture; and the design, integration and qualification of thermal insulation materials in-space applications, created excellent synergies to put Europe as a supplier of aerogel materials for the aforementioned space applications.
Project Results:
Within the context of the AerSUS project, the partnership has developed the following main S&T results/foregrounds.
1.1.1. Aerogels Development
One of the main project activities was to develop aerogel materials that are suitable for thermal insulation purposes in different space applications. This work was based mainly on the thermal insulation requirements previously defined for space applications. The development activities performed by the various research organisations included in this project resulted in the following foregrounds:
>>RF aerogel – silica aerogel composites I (DLR)
Aerogel-aerogel composites consisting of highly insulating hydrophobic granular silica aerogel were fabricated by industry and RF aerogel as the matrix were synthesized with a standard RF-recipe from DLR. During sol-gel process of the RF solution granular silica aerogel can be mixed with RF without phase separation when the viscosity of RF reminds of milk pudding. This stadium of viscosity is reached close to the gel point. After mixing and aging the gel can be subcritically or supercritically dried. The volume fraction and the grain size of silica in the composite influences the properties of the material significantly. Best results were obtained with 60 vol.-% of silica aerogel and 1-2 mm grain size since the use of these parameters is the best compromise concerning values of mechanical, thermal and structural properties. Typical values obtained are E=2.3 MPa, λ=0.024-0.035 W/m.K and ρ=0.18 g/cm³. Concerning the requirements for space application samples need further improvement. Reinforcement with cellulose fibres was attempted by adding fibres (untreated or pretreated with sodium hydroxide to swell or dissolve) into the RF solution during synthesis. A reinforcing effect occurs regarding compressive strength (up to +53%) but density and thermal conductivity can increase as well.
>>Organically modified silica based aerogels derived from MTMS with and without PEG additive (UC)
UC researched possible improvements in the insulation/density properties of the MTMS-derived aerogels, to widen their possible Space applications. Aerogels were prepared with a two-step acid-base catalysed sol-gel synthesis, followed by aging and drying steps. Considering the relevant factors found in a first screening, the strategies used were: i) change of synthesis conditions and the solvent/precursor molar ratio; ii) addition of a pore templating agent - polyethylene Glycol (PEG), to tailor the porous network. The operating conditions of the Low Temperature Supercritical Drying (LTSCD) method were optimized to obtain the best properties of the aerogels, including washing and drying steps.-Based on this work, two aerogels with good properties to achieve the targets of the AerSUS project were obtained: a) one with an S of 35 and Ca of 0.01 without PEG; b) a second with the same synthesis conditions, but a PEG/MTMS molar ratio of 0.01. The second aerogel had a bulk density of 41.7 kg/m3, thermal conductivity (RT) of 0.036 W/(m.K) contact angle of 145.8o and Young’s modulus of 3.14 kPa, showing the better overall properties for thermal insulation and also high flexibility and hydrophobicity. The first aerogel showed slightly higher values for these properties. The gel confinements were changed from test tubes to Petri dishes, requiring a new optimization of conditions.
>> Silica/organic hybrid aerogels (ARMINES)
ARMINES developed new hybrid organic-inorganic super insulating materials. These aerogels are based on a blanket route coupled with “one-pot” methods. Amongst the different chemical combinations and the associated results, materials elaborated with PET unwoven fibrous network, resorcinol, formaldehyde and APTES as silica source can be emphasized. Synthesis appears to be rapid and easy to handle. Resulting RF-silica hybrids present a certain degree of flexibility, very low thermal conductivity in room conditions (down to 0.019 W m^-1K^-1) and rather standard apparent density (down to 0.05 g/cm3).
1.1.2. Aerogels Thermal Analysis
In addition to aerogel development, further activities were performed to characterize, via testing and evaluation, the thermal analysis the performances and the possible field of application and best target application for aerogel materials developed in AerSUS. This work has resulted in the following foregrounds:
>> Aerogels thermal conductivity measurement (3-Omega method)
The 3-Omega method (3ω) was used to analyse aerogels thermal conductivity measurement. Within the context of AerSUS, the implementation of the 3ω method involved the fixing of a wire heater/temperature sensor on the aerogel or embedding it within the specimen. Specifically, aerogel samples consisting of two pieces of at least 7cm were placed in a dish. A copper heater wire of diameter 60 micrometers was placed between the two pieces. Low resistance lead-wires were soldered to the ends of the heater wire in pairs to allow for 4-wire resistance measurements for high precision resistance determination.
During the tests, a total of four aerogel samples were tested: samples A131 and A132 supplied by ARMINES; sample 396 supplied by the University of Coimbra and RC1500-020 supplied by DLR. The samples were tested at atmospheric pressure and at 10mBar vacuum pressure, not controlling for the temperature (lab temperature ca. 20-23°C). The measurements taken at 10mBar were used for the simulations of the Martian lander application, with conductivity values obtained in the range of 12 to 23mW/m.K. At atmospheric pressure, values were obtained ranging from 29 to 42 mW.
The performed thermal conductivity measurements demonstrated the value of the 3-Omega method, and showed good agreement with measurements using more traditional methods, but achieving total measurement uncertainty, including lower statistical and systematic errors.
Regarding thermal conductivity, uncertainties as low as a few per cent were achieved and a total uncertainty on the diffusivity as low as 7–10% was achieved. Relative errors, in general, can be reduced by using a longer sample (and heating wire), thus making the errors negligible in its length and resistance which can be measured to an accuracy of about 0.3 mm and 0.001 Ω respectively.
In general, the performed thermal tests showed an excellent agreement with other measurements over a wide dynamic range of conductivities and diffusivities, with repeatability on the order of a few per cent even while changing the applied heating power by a factor of 2, 3 or even 4 without the need for thermal models to correct for convection losses, radiation losses or rising temperature of the sample.
Furthermore, the minimum aerogel sample size is significantly smaller with this method than with many other measurement techniques and sample preparation is shown to be simple and low cost. Lastly, since these measurements can be performed in 20 to 30 minutes, multiple measurements can easily be quickly performed to reduce statistical uncertainty. These tests demonstrate the great success and advantages of this technique as a measurement method, especially for very low conductivity samples.
>> Thermal analysis of aerogels
Regarding the implemented thermal analysis of aerogels, the performed tests showed that the materials tested have a wide range of properties (i.e. density, specific heat, conductivity), all with different values and results.
As such, different results can be foreseen, comparing them on the same thermal model. The differences in terms of thermal conductivity, specific heat, and other variables are quite large, in particular considering together the specific heat and the density (volumetric heat capacity). The strongest differences were between the first aerogel prototype (DLR) and the remaining. This may have been related to the way in which these different materials were synthetized by the partners, based on different processes or objectives. This suggests that the materials evaluated via the currently used model can be quite hard to be compared between each material type. Furthermore, this also suggested that different materials would be more interesting/suitable for different applications than others.
In general, the obtained results vary significantly after a comparison of the aerogels’ physical properties, especially in the overall insulation mass and the heating power necessary to switch ON the Electronic box used in testing and for reaching the minimum temperature requirement. For this tested application, the best mass saving material is ARMINES A132, while the best heating power saving material is the DLR Aerogel.
However, no single best material for this tested application can be identified. All the other materials represent a good compromise between limiting the mass and limiting the heater power. The selection of a proper material for the thermal analysis case can only be evaluated taking into account the specific requirements of the mission. In particular, different materials can apply to the best mass saving configuration (ARMINES A132), best heat power saving configuration (DLR RC1500-020) and the one with the smallest volume (UC396) for the insulation layer or thickness for configuration constraints (ARMINES A131, ARMINES A132, UC396).
>> Aerogel thermal performance in air and CO2
Due to test facility availability at STFC, the thermal testing was completed after the submission of Deliverable 5.1 – Semi-industrial scale aerogels manufacturing. Therefore, the testing process was described in Deliverable 9.1 – Long-term commitment activities. The thermal conductivity of three samples of aerogel, from the three manufacturers, were tested in air and in an approximately 10 mBar CO2 environment. The conductivity was measured using a guarded hot-plate at five nominal test temperatures (between +20 °C and +90 °C in air; between -35 °C and +120 °C in the CO2¬¬). The in-air results measured by STFC showed a good agreement with the results obtained earlier in the project (WP 3.6). The CO2 environment results were also in line with what would be expected based on the in air and vacuum results obtained, and showed reasonable correlation to the results obtained by AST-DE within WP 3.6.
1.1.3. Technology for aerogel manufacturing
One of the main project activities was the design and building of an innovative and tailored technology for manufacturing aerogels developed for space applications. As part of this work, the following new foregrounds were produced:
>> Autoclave fluids flow simulation
In order to establish optimal conditions of operation, simulations of both diffusion within aerogel and flow through the vessel considering supercritical CO2 was performed. This work involved three complementary steps.
First, some parameters were estimated considering a small, axisymmetric vessel and a qualitative study of the influence of aerogel physical properties on the drying process was developed, utilizing a simplified geometry. Then, the drying process was modelled considering the autoclave designed by SPX. In addition, several configurations were simulated, namely 3 inlets instead of a single inlet as well as a modified geometry with specific constraints with 1 or 3 inlets. The configuration that optimizes the drying time is a geometry with constraints/barriers and 3 inlets. The results of this task are described in detail in Deliverable D4.2 – Description of results that were obtained by simulation of supercritical fluids flow.
>> Design and manufacturing equipment
A plant for manufacturing equipment was designed, assembled and installed at SEPAREX facilities. Additional systems such as CO2 storage tanks, ventilation systems, chiller and hot utilities were also attached to the equipment. Internal structures to hold the samples during drying were design in order to use self-supporting samples (vertical disposition) and non-self-supporting samples (horizontal disposition). The structure has been designed in stainless steel and is able to host ca. 40 samples of 35x35x1 cm³ per batch.
A security protocol plan has also been filled in order to prevent all the issues of the process relative to the high quantity of organic solvent to be used. In order to validate the operational function of the equipment some tests at working conditions were carried out. Parameters such as working temperature, working pressure, facility temperature, and others were validated.
1.1.4. Semi-industrial scale aerogel manufacturing
Following the development of laboratory scale aerogels, the synthesis of semi-industrial scale aerogels was implemented, as well as the supercritical drying of these materials. As part of this work, the properties of specific aerogel samples were also optimized at a laboratory scale. These activities resulted in the following foregrounds:
>> Optimised CO2 drying process
The time and energy required for each material depends on the organic solvent and structure of the aerogel: less time is required for macroporous aerogels and methanol-based solvents, and more narrow microporous aerogels and ethanol-based solvents. Drying conditions depend on the organic solvent used, but generally the temperature for the materials used by the partners it stays over 40 – 50 °C.
Calculations showed that to use several layers of material to achieve a performance per thickness is more efficient than to directly process the final thickness. It was also observed that the extra configuration for the ARMINES A132 sample would extremely reduce the production cost since the capacity can be highly increased. Therefore, it is supported that further developments be made on this material.
It can be appreciated that production cost is highly reduced (up to 40%) by increasing capacity for the same procedure. For high manufacturing volume, Separex can propose several solutions depending on the material to further decrease the cost if it would be needed.
>> RF – silica gel composites II (DLR)
Aerogel-aerogel composites from RF aerogel and granular silica aerogel can be synthesized in any size and shape. The up-scaling process is similar to the lab-scale process but with increased volume of both components to reach higher total volume (VRF + Vsilica). The sample box which gives the material a shape has to be adapted to the new total volume and can be made of PP or PMMA. In case the sample box is flexible (PP), the material can be removed easily by careful pressing. In case of a rigid box (PMMA) a filter paper on the box ground can help to lift the material out of the vessel after aging process.
The equipment (e.g. oven) which is used for the aging process has a size limiting effect. Plates with a maximum dimension of 24 x 24 cm² can be easily produced but a bigger oven is required to enable the synthesis of samples with a higher area otherwise the synthesis takes weeks up to months.
Samples from semi-industrial process have similar properties compared to samples from lab-scale process. But it was noticed that the amount of air bubbles in the composite material which occur during the mixing procedure increase with the dimension of the composite. The existence of air bubbles can be avoided by applying a vacuum or sufficient underpressure during synthesis.
>> Organically modified silica based gels derived from MTMS – synthesis, washing and molding/unmolding scale-up conditions and apparatus (UC)
UC synthesized large organically modified silica based gels derived from MTMS, firstly using Petri dishes and then larger moulds as confinements. The moulds consist of large glass or metallic trays, with grid baskets inside designed by UC. The baskets allow an easy unmoulding of the gels from the trays. Some monolithic and very large aerogel samples were obtained from these gels, using the Separex drying facility. The larger samples obtained have densities of 55-70 kg/m3 and thermal conductivities of 0.034-0.037 W/(m K). The aerogels produced at semi-industrial scale have high hydrophobicity (> 140o), high flexibility, specific surface area of ~400 m2g-1 and average pore size included in the size range of mesopores (5-6 nm). Thinner samples and a horizontal position in the autoclave gave the best results in terms of aerogels properties. The absence of the washing step in the drying system leads to the presence of residual solvents/catalyst in the aerogels, but this can be corrected by conditioning the resultant aerogels samples in an oven (several hours at 100oC).
>> Silica/organic hybrid gels II
The sol-gel processing route developed at lab-scale by ARMINES was simple to up-scale to synthesize samples with significant larger characteristics dimensions. Following this “one-pot” hybridization route it is possible to obtain monolithic 35×35×0.5 cm3 wet gels presenting similar characteristics than their smaller counterparts (some cm3).
1.1.5. Aerogel insulation systems development
Using the aerogels manufactured as a semi-industrial scale, thermal insulation systems were developed. This work resulted in the following foregrounds:
>>Aerogels encapsulation system
STFC developed a procedure for manufacturing a completed insulation system using the aerogel materials. This process involves encapsulating the aerogel materials, since the level of particulate generation and fragility of the current aerogel materials means that they are not compatible with the high cleanliness levels required for space applications in their as manufactured state. A method for encapsulation of the aerogel materials from all three consortium partners was successfully developed. This encapsulation process uses standard Multi-Layer Insulation (MLI) materials (with good space heritage) and standard MLI manufacturing tools to fully encapsulate the aerogel material. This encapsulation process was described in Deliverable 6.2 – Development of aerogel thermal insulation systems.
STFC assessed the encapsulated samples through depressurisation and vibration testing. The three aerogel panels did not demonstrate gross changes in their structure as a result of this testing, although all three panels demonstrated at least some contamination release from the encapsulated panel. The materials were therefore all shown to be compatible with a launch environment, but do present a risk of contamination. These tests were also described within Deliverable 6.2 – Development of aerogel thermal insulation systems.
>> Thermal correlations
Six individual blankets for each aerogel tested – developed by AST/UC, DLR and ARMINES – were manufactured and installed on an aluminum box equipped with heaters. The box with aerogel blankets was placed within thermal vacuum chamber in TAS-I facilities for thermal vacuum testing.
In the case of AST/UC aerogel blankets, almost all temperature values were correlated. In the case of ARMINES and DLR blankets, the correlation results obtained are slightly inferior. This situation may have been created by the uncertainties present in the test set-up and the design of the test article: as the aerogel blanket and the foils around were not glued to each other, a non-uniform and uncontrolled contact is present.
Therefore, it was possible that some parts of the foil could have slightly moved and lost contact with the blanket and change the temperature values measured, making them more difficult to correlate. However, in case of the ARMINES and DLR blankets, most of the temperatures measured on the aluminum box or internal foil were correlated.
1.1.6. Aerogel insulation systems prototypes manufacturing
Based on the experience developed on the best method to encapsulate aerogels, aerogel insulation systems prototypes were manufactured. This resulted in the following foreground:
>> Manufacturing of prototypes based on aerogel
STFC were responsible for the manufacture of prototype insulation panels to be used for the thermal efficiency evaluation tests in WP7.3. As part of this work, the encapsulation procedure developed within WP6.2 was further developed based upon the results of the testing completed for WP6.3. These developments were focussed upon improving the venting characteristics, and reducing the contamination release from the aerogel panels. These revised encapsulation techniques were successfully used for the encapsulation of six aerogel panels each from three consortium partners required for the WP7.3 activities (18 panels in total). This prototype manufacture process is described in detail within Deliverable 7.1 – Thermal insulation prototypes.
1.1.7. Long-term commitment activities
As part of the long-term commitment activities of AerSUS, additional lab-scale aerogels were synthesised with the aim of improving specific properties. Additionally, the potential use of selected aerogels available in the market for thermal insulation in space applications was performed, by applying thermal models to predict the effectiveness of such insulation in target applications. These activities resulted in the following foregrounds:
>> Thermal analysis of aerogels
The thermal analysis of aerogels and corresponding objective of assessing their performance in a real environment required a preliminary analysis. The defined ‘real environment’ was a mission to Mars, with an instrument (part of a bigger lander) on its surface. This was considered the most interesting application for aerogels, taking into account the bad performances of MLI in cases with presence of atmosphere. An instrument, named “EXO 1”, is part of this lander and is the main recipient of the insulation application. The lander was analysed in a realistic Mars environment with solar fluxes, sky temperature, dust effect and convection modelled. The insulation of the internal electronic box is evaluated using different materials, in order to fulfill the mission requirements.
This analysis was done taking into consideration the newly developed materials, and using the Thermal Mathematical Model described in Deliverable 6.3 – Thermal correlations from space environment tests, where 6 different scenarios (with different latitudes and altitudes and therefore different solar fluxes) of Martian conditions are considered and two of them are chosen for being the most extreme in terms of temperature values: one hot and one cold case were chosen (“Maximum Day” and “Maximum Night”), taking into account the influence of the solar fluxes (depending on seasonal changes), the apparent temperature of the sky and the ground temperature, dust-storm effect. The system is evaluated in the hot case taking into account only the temperatures during the day, while in the cold case, taking into account only those during the night
The thermal analysis aims to select a configuration (i.e. type and thickness of the insulation) that allows the boards of the instrument to operate at maximum dissipation and in the warmest conditions without damage and, at the same time, to reduce as much as possible the heating power needed during the coldest conditions. The outputs of the analysis used to evaluate the different insulations were: (1) thickness, volume and mass of the insulation layer (chosen to fulfill the requirements of the hot case); (2) heater power dissipation (to fulfil the cold case requirement).
The newly developed aerogel materials demonstrated similar performances, where the biggest difference was related to the mass of the insulation needed, which directly depends on the density of the material used. It was verified that the best mass-saving material was the DLR Cellulose, which showed a good compromise between the mass and heater power needed amongst all aerogels.
When compared to previously developed and analysed aerogels, similar conclusions can be drawn: DLR material still offers the best heat power saving material, even with a bit worse performance than the previously developed material. However, it allows to save almost 2/3 of the necessary insulation mass, making it very similar to the ARMINES A131 aerogel.
>> RF aerogel – silica aerogel composites III
An attempt was made to optimize the RF aerogel – silica aerogel composites based on the production procedure and the values of thermal conductivity and of density. The mixing procedure of the granular material with the matrix was improved by applying a vacuum or sufficient underpressure during synthesis resulting in materials without air bubbles and with a better reproducibility. Furthermore, a change of the granular material by using hydrophobic granular silica aerogel from different manufacturer was applied but with no significant effect. A change of the matrix was performed by using a different recipe for the RF aerogel. The new RF recipe was developed at DLR containing a two-step synthesis route in which the solution is initially catalysed by a base and after a certain time the catalyst is changed to an acid one. The new recipe causes lower production time of RF aerogels and the composites and additionally decreases the density of the composite (0.17 g/cm³). Thermal conductivity of the new composite is still >0.03 W/m.K.
Another approach was tested in which both the granular material and the matrix was changed. New aerogel-aerogel composites consisting of hydrophilic granular silica aerogel and of a cellulose aerogel matrix were synthesized. Thermal conductivity still reached values >0.03 W/m.K but the density obtained is reduced and is between 0.03-0.16 g/cm³.
>>Organically modified silica based aerogels derived from MTMS with BTMSH/BTMSE/ODS additives
Different additives were added to the MTMS-derived aerogels with the objective of trying to improve the mechanical integrity of aerogels and reduce particle shedding:
-- 1,6-bis(trimethoxysilyl)hexane (BTMSH) acts as a bridging organic ligand and was tested to check its effect on the connectivity of the silica network. BTMSH enhanced the gelation process and very cohesive gels were obtained in less than 2h. Moreover, it gave rise to aerogels with less release of powders when compared to the aerogel without additive.
-- 1,2-bis(trimethoxysilyl)ethane (BTMSE), with a shorter ligand group, was also tested. The addition of BTMSE did not add any improvement on the MTMS-based aerogels.
-- Trimethoxy(octadecyl)silane (ODS), with a large alkyl substituent group on the trimethoxysilane, was also studied. The 18C long chain was expected to act as a very small fibre, improving the aerogels network connectivity/resistance. In fact, the ODS contributed to an improvement of flexibility of the aerogels and gave rise to samples with the lowest particle shedding. The presence of the non-polar chain (ODS) slightly increases the hydrophobic character of the aerogels.
The synthesis conditions for the first two additives were the same as for MTMS-derived aerogels without additives. For ODS, a one-step base catalysed synthesis process was developed. The optimum percentage of Si derived from the additive in the system was found to be 2% for all cases. Although the density increased to near 60 kg/m3, BTMSH and ODS improved slightly the insulation performance of the aerogels, due the decrease of the proportion of large pores to smaller pores.
>>Silica/organic hybrid aerogels III
Based on the results obtained with reference to the RF-silica hybrid materials (previously presented regarding “Aerogel development”), ARMINES studied the improvement of the characteristics of the so-obtained hybrids by using silanes technologies. For this purpose, methyltriethoxysilane (MTES) as well as trimethoxy(methyl)silane (MTMS) were used as silica co-precursors with APTES. “One pot” processing route performed with APTES, MTES (or MTMS), resorcinol and formaldehyde allows to significantly improve the flexibility of the hybrids while decreasing dramatically apparent density (0.03 g/cm3) while maintaining low level of effective thermal conductivity (0.027 W m-1K-1 in room conditions).
>> Aerogel Thermal Insulation Systems for Space
The activities undertaken by STFC through the project provided valuable insight into how thermal insulation systems using aerogel should be developed further for space flight application. Several areas for improvement of the aerogel materials and the encapsulation method were identified which, from the point of view of a manufacturer or user of insulation panels, would improve the viability of the materials for use as a space insulation product. These areas were reviewed during WP9 and preliminary ideas, based upon STFC experience of developing thermal design solutions for scientific space instruments, were developed and reported.
Potential Impact:
Reducing the dependence on critical technologies and capabilities from outside Europe was one of the driving forces behind the AerSUS project.
The objective of AerSUS was to create a European supply unit capable of providing aerogel materials and aerogel thermal insulation systems for specific space applications. Such aerogels, their manufacturing technology and aerogel thermal insulation systems were successfully produced in this project. The aerogel materials and insulation systems resulting from AerSUS are suitable particularly in environments where atmosphere is present, including space applications such as (re)-entry vehicles, Mars rovers, and pressurized compartment. The relevant technology, materials and insulation systems deriving from AerSUS will allow an unrestricted access by the European space community to this new space technology, therefore reducing their dependence on technologies from non-European sources.
The dissemination activities carried out in the project targeted a wider community. However, a majority of the stakeholders reached throughout the project belonged to European space and space/non-space scientific communities. It is relevant to highlight that a stakeholder consultation event was also organized in 2013 as part of AerSUS, and hosted representatives of major players of the European space industry, especially in what concerns large space system integrators and small system manufacturers. This event aimed to collect feedback from stakeholders on the lab-scale aerogel materials developed previously in the project so that further project developments could be tailored according to the received inputs. The participation of AerSUS in the ESA Industry Space Days 2014 also aimed to increase the proximity towards relevant European stakeholders.
Concrete steps were also implemented in order to prepare the commercial exploitation of some of the aerogels developed throughout the project AerSUS. The different project foregrounds were discussed and mapped internally. This resulted in a specific foreground table that was updated as necessary during the year.
For the different project foregrounds, partners identified the ownership regime as sole ownership. An exception was verified on the ‘selected aerogels of UC optimised by AST’, where the UC and AST are both foreground owners. Regarding ‘selected aerogels of DLR/ARMINES optimised by AST’, by the end of the project, discussions on foreground ownership were still not concluded. Therefore, discussions have been held regarding joint ownership agreements between AST and other project partners (UC, ARMINES and DLR). License agreements between Active Aerogels/DLR and Active Aerogels/ARMINES were also discussed, but later delayed due to the fact they address aerogels that were still in development at a later stage of the project. Currently, partners are continuing to define the details of the agreements to be implemented. Active Aerogels and UC have a license agreement process related to the exploitation of results generated by UC in the AerSUS project. At the time of this report, partners are continuing to define the details of the agreements. Active Aerogels, a spin-off company of Active Space Technologies (scientific coordinator of AerSUS), has already formed rights to manufacture some of the AerSUS aerogels for commercial purposes in the future. Active Aerogels already commercializes aerogel materials for applications such as launchers and rockets; spacecraft and re-entry probes; rovers and landers for planetary exploration; stratospheric balloons; cryogenic tanks and helium storage.
The access to aerogel materials for space applications and aerogel thermal insulation systems from European sources, will also increase the overall competitiveness of European space industry satellite vendors on the worldwide market. The aerogels resulting from this project will also target non-European space missions in addition to the European ones.
The participation/dissemination of AerSUS in international trade fairs, including the International Astronautical Congresses in 2012 (Naples, Italy), 2013 (Beijing, China) and 2014 (Toronto, Canada) and the ILA Berlin Air Show in 2012 had the objective of reaching out to the larger international space community that could have interest in the products developed within AerSUS.
By contributing to the creation of a European supply unit of aerogels and aerogel insulation systems for space applications, AerSUS has contributed to enhancing the European economic growth, employment and European SME policy. AerSUS will leverage the sales of European made products in the fields of thermal insulation and will help the economic development of European companies, contributing thus to the recruitment of new employees. In addition, AerSUS involved 4 SMEs in the partnership. Their collaboration with research organisations and end users of space technologies allowed these ‘smaller’ companies to improve their technical capabilities, make long-term relationships and create future opportunities benefiting their future business activities.
Furthermore, AerSUS technologies are likely to be used as thermal insulation systems for applications that are related especially to scientific exploration in space. Beyond the wider general impacts of space activities on society (including technology development, educational stimulation, and expansion of communication technologies), scientific space activities have an outstanding role in our knowledge development of the worlds that surround us and through this of our own world. AerSUS intends to contribute to this evolution.
In addition to the above socio-economic impacts, it is important to refer the impacts that the project has in scientific terms. The following refers to the new know-how AerSUS brings to the academic world:
|| Know-how (KH) / Benefits to whom (BtW) ||
1.
KH: Synthesis of aerogels from different chemical systems/Large-scale synthesis of gels/Optimization of synthesis and drying conditions to tailor aerogels properties.
BtW: Aerogels scientific community, Aerogels manufacturers, Aerogels end-users.
2.
KH: Scale up of sc CO2 drying of aerogel to 220L scale.
BtW: Insulation industry (building, Space industry) that can tests on bigger insulation plate (35*35cm) and start implementation.
3.
KH: Development of new super insulating organic-inorganic hybrid aerogel blanket-type materials based on silica / resorcinol-formaldehyde chemical systems.
BtW: Scientific community.
4.
KH: Development of process permitting the facile and rapid realization of large and monolithic super insulating hybrid blanket-type gels ready for supercritical CO2 drying.
BtW: Scientific community and aerogels industry.
5.
KH: Manufacture of aerogel-aerogel composites.
BtW: Scientific community, industrial companies.
6.
KH: Production of large-scale ambient dried composite materials.
BtW: Scientific community, industrial companies.
7.
KH: Two step synthesis of resorcinol-formaldehyde aerogels.
BtW: Scientific community, industrial companies.
Several activities were implemented during the course of AerSUS to disseminate and exploit the scientific results of the project. These were mainly the presentation of outcomes at scientific events, such as:
> 1st AEROCOINs Workshop, France 2012
> 6th International Conference on Advanced Computational Engineering and Experimenting - ACE-X Conference, Turkey 2012
> AEROGELS Properties-Manufacture-Applications SEMINAR, France, 2012
> International Astronautical Congress (IAC) 2012, Italy, 2012
> 43rd International Conference on Environmental Systems, U.S. 2013
> XVII International Sol-Gel Conference, Spain, 2013
> International Astronautical Congress (IAC) 2013, China, 2013
> Aero-ORMOSIL Seminar, Portugal, 2014
> Journées Industrielles Nanomatériaux 2014, France, 2014
> 14th European Meeting on Supercritical Fluids, France, 2014
> International Astronautical Congress (IAC) 2014, Canada, 2014
> International Seminar on Aerogels 2014, Germany, 2014
> 3rd Cycle of Interdisciplinary Conferences & Debate of IIIUC, Portugal, 2014
Publications in scientific journals are an optimal way to transfer scientific results to relevant public. Results from AerSUS were sent for publication in the following journals:
> Effect of Additives on the Properties of Sílica Based Aerogels Synthesized from Methyltrimethoxysilane (MTMS). Durães, L., Maia, A., Portugal, A., in Proceedings of the International Seminar on Aerogels-2014: Properties-Manufacture-Applications, International Society for Advancement of Supercritical Fluids (ISASF), 2014, p.33-43.
> Influence of sol-gel conditions on the key properties of silica based aerogels for thermal insulation in Space. Maia, A., Portugal, A., Durães, L., in Book of Abstracts of the XVII International Sol-Gel Conference, Instituto de Ciencia de Materiales de Madrid (ICMM) & Consejo Superior de Investigaciones Científicas (CSIC) & Sol-Gel Group (SGG) & Ministerio de Economía y Competitividad & International Sol-Gel Society (ISGS), Madrid, 2013, p.454.
>The 3 omega transient line method for thermal characterization of Superinsulator materials developed for spacecraft thermal control. Dalton, M. et al., in Acta Astronautica.
Furthermore, other publications are in development and should be published during 2015.
In addition to scientific publications and congresses/events, dissemination was also established through other traditional strategies, including the project website, newsletters, brochures and press releases.
List of Websites:
http://www.spi.pt/aersus
The purpose of the AerSUS project is to create a European Supplying Unit for one of the critical space technologies for European strategic non-dependence: advanced thermal control materials.
The main objective of AerSUS is to provide aerogels, develop their manufacturing technology and aerogel insulation systems prototypes that are suitable for specific Space applications. Aerogels are considered to be the next generation of thermal insulation in Space and are regarded as the materials with the greatest potential to substitute multi-layer insulation (MLI) and other materials used for the thermal insulation of spacecraft. This is because of their very low density, very high thermal insulation efficiencies, and their ability to provide thermal insulation as a single material that can be industrially produced and tailored to different applications.
The consortium provides a wide variety of know-how that has been integrated into the project, covering research and aerogel development at laboratory scale; the design and construction of semi-industrial equipment for aerogels manufacturing; and the design, integration and qualification of thermal insulation materials in-space applications. This consortium-wide effort creates excellent synergies to place Europe as a key supplier of aerogels which are projected to be the future of thermal insulation in Space.
Towards these efforts, a fully integrated project programme was carried out. The AerSUS programme, broken down into 10 Work Packages, included the development of a preliminary study (WP1); the identification of the technical specifications for the aerogels’ synthesis methods, the development and operation of the manufacturing technology, and the requirements of aerogel insulation for use on space applications (WP2), the actual development of the aerogels by three project partners (WP3); the design and building of aerogel manufacturing technology (WP4); the up-scaling of the developed aerogels (WP5); the development of aerogel insulation systems (WP6); the development of prototypes using the developed aerogels and validation of their performance (WP7); the dissemination and exploitation of the project (WP8); the implementation of long-term commitment activities (WP9); and the management of the project (WP10).
From the project, several results emerged. The most significant were the development of the aerogels by the three manufacturing partners: RF aerogel – silica aerogel composites I, organically modified silica based aerogels derived from MTMS with and without PEG additive, and Silica/organic hybrid aerogels. Based on the developed aerogels, another result was the design of semi-industrial scale equipment adapted to the AerSUS aerogels. This resulted in fully automated equipment for large scale aerogels. From the aerogels developed at lab scale and using the manufacturing technology, partners developed aerogels at an industrial scale: RF – silica gel composites II, Organically modified silica based gels derived from MTMS, and Silica/organic hybrid gels II. Using an aerogel encapsulation process developed in the project, the industrial-scale aerogels were encapsulated, and later evaluated through depressurization and vibration testing. The encapsulating procedure proved to be successful, and was later used to develop additional encapsulated aerogel panels. The developed aerogels were also subjected to thermal testing with a simulated ‘real-environment’ – a Mission to Mars – providing insight on the optimal configuration for the instruments to work optimally. Lastly, long-term commitment activities were set in motion, including additional developments on aerogels: RF aerogel – silica aerogel composites III, Organically modified silica based aerogels derived from MTMS with BTMSH/BTMSE/ODS additives, and Silica/organic hybrid aerogels III. Lastly, the possible target applications for the develop aerogels were revised, where the main applications for the developed aerogels are thermal insulation of manned compartments, in unmanned compartments in ascent/reentry vehicle and cargo modules, as well as in a Mars environment.
The multitude of project results suggests that AerSUS has successfully contributed to strengthening Europe’s strategic non-dependence for advanced thermal control materials. While improvements on the developed aerogels will have to be put in motion, the consortium has set the foundation for the next generation of thermal insulation for Space applications.
Project Context and Objectives:
The main purpose of the AerSUS project is to create a European supplying unit for one of the critical space technologies for European strategic non-dependence: advanced thermal control materials.
Currently, thermal protection of spacecraft hardware is assured by underlying advanced thermal control materials, commonly Multi-Layer Insulations (MLI). Most of the MLI materials are procured from non-European sources and often under access restrictions. Furthermore, one of the basic materials for MLI, the Kapton, is used in several thermal control applications and easily falls under access restrictions, such as ITAR. On this basis, advanced thermal control materials have been included in the Critical Space Technologies for European Strategic Non-Dependence [Excerpt from Critical Space Technologies for European Strategic Non-Dependence", List of Urgent Actions 2010/2011, EC-ESA-EDA, September 2010.]. Finding alternative solutions to MLI was also addressed in the ESA's roadmap, including ESA funded initiatives that have similar aims (e.g. “Proof of Concept for Aerogel Applications”, “Aerogel Thermal Insulations Systems”, “Adaptation of Aerogel Materials for Thermal Insulation”).
Aerogels are the lightest solid materials in the world and are composed over 90% of air. Due to their unique properties, such as low density and low thermal conductivity, aerogels have emerged as the best alternative to MLI. Before the AerSUS project, many of the project consortium partners worked on the development of thermal insulation systems based on aerogels that could meet space requirements. Despite these efforts, the main difficulties found by the space industry at the time, and concerning the use of aerogels, were the lack of reproducibility of their properties and the absence of an entity that could guarantee the continued supply on a long-term basis for an aerogel product with a high TRL and with tailored properties. As a result of this necessity, the AerSUS project emerged within the outlined context.
The AerSUS project has collaborated on the development of aerogels, their manufacturing technology and aerogel insulation systems prototypes for specific space applications where, due to the presence of atmosphere, MLI are not efficient. These applications include, for example, (re)-entry vehicles, Mars rovers, and pressurized compartments.
The combination of know-how of the entities involved in the project, covering research and development of aerogels at a laboratory scale; the design and construction of semi-industrial equipment for aerogels manufacture; and the design, integration and qualification of thermal insulation materials in-space applications, created excellent synergies to put Europe as a supplier of aerogel materials for the aforementioned space applications.
Project Results:
Within the context of the AerSUS project, the partnership has developed the following main S&T results/foregrounds.
1.1.1. Aerogels Development
One of the main project activities was to develop aerogel materials that are suitable for thermal insulation purposes in different space applications. This work was based mainly on the thermal insulation requirements previously defined for space applications. The development activities performed by the various research organisations included in this project resulted in the following foregrounds:
>>RF aerogel – silica aerogel composites I (DLR)
Aerogel-aerogel composites consisting of highly insulating hydrophobic granular silica aerogel were fabricated by industry and RF aerogel as the matrix were synthesized with a standard RF-recipe from DLR. During sol-gel process of the RF solution granular silica aerogel can be mixed with RF without phase separation when the viscosity of RF reminds of milk pudding. This stadium of viscosity is reached close to the gel point. After mixing and aging the gel can be subcritically or supercritically dried. The volume fraction and the grain size of silica in the composite influences the properties of the material significantly. Best results were obtained with 60 vol.-% of silica aerogel and 1-2 mm grain size since the use of these parameters is the best compromise concerning values of mechanical, thermal and structural properties. Typical values obtained are E=2.3 MPa, λ=0.024-0.035 W/m.K and ρ=0.18 g/cm³. Concerning the requirements for space application samples need further improvement. Reinforcement with cellulose fibres was attempted by adding fibres (untreated or pretreated with sodium hydroxide to swell or dissolve) into the RF solution during synthesis. A reinforcing effect occurs regarding compressive strength (up to +53%) but density and thermal conductivity can increase as well.
>>Organically modified silica based aerogels derived from MTMS with and without PEG additive (UC)
UC researched possible improvements in the insulation/density properties of the MTMS-derived aerogels, to widen their possible Space applications. Aerogels were prepared with a two-step acid-base catalysed sol-gel synthesis, followed by aging and drying steps. Considering the relevant factors found in a first screening, the strategies used were: i) change of synthesis conditions and the solvent/precursor molar ratio; ii) addition of a pore templating agent - polyethylene Glycol (PEG), to tailor the porous network. The operating conditions of the Low Temperature Supercritical Drying (LTSCD) method were optimized to obtain the best properties of the aerogels, including washing and drying steps.-Based on this work, two aerogels with good properties to achieve the targets of the AerSUS project were obtained: a) one with an S of 35 and Ca of 0.01 without PEG; b) a second with the same synthesis conditions, but a PEG/MTMS molar ratio of 0.01. The second aerogel had a bulk density of 41.7 kg/m3, thermal conductivity (RT) of 0.036 W/(m.K) contact angle of 145.8o and Young’s modulus of 3.14 kPa, showing the better overall properties for thermal insulation and also high flexibility and hydrophobicity. The first aerogel showed slightly higher values for these properties. The gel confinements were changed from test tubes to Petri dishes, requiring a new optimization of conditions.
>> Silica/organic hybrid aerogels (ARMINES)
ARMINES developed new hybrid organic-inorganic super insulating materials. These aerogels are based on a blanket route coupled with “one-pot” methods. Amongst the different chemical combinations and the associated results, materials elaborated with PET unwoven fibrous network, resorcinol, formaldehyde and APTES as silica source can be emphasized. Synthesis appears to be rapid and easy to handle. Resulting RF-silica hybrids present a certain degree of flexibility, very low thermal conductivity in room conditions (down to 0.019 W m^-1K^-1) and rather standard apparent density (down to 0.05 g/cm3).
1.1.2. Aerogels Thermal Analysis
In addition to aerogel development, further activities were performed to characterize, via testing and evaluation, the thermal analysis the performances and the possible field of application and best target application for aerogel materials developed in AerSUS. This work has resulted in the following foregrounds:
>> Aerogels thermal conductivity measurement (3-Omega method)
The 3-Omega method (3ω) was used to analyse aerogels thermal conductivity measurement. Within the context of AerSUS, the implementation of the 3ω method involved the fixing of a wire heater/temperature sensor on the aerogel or embedding it within the specimen. Specifically, aerogel samples consisting of two pieces of at least 7cm were placed in a dish. A copper heater wire of diameter 60 micrometers was placed between the two pieces. Low resistance lead-wires were soldered to the ends of the heater wire in pairs to allow for 4-wire resistance measurements for high precision resistance determination.
During the tests, a total of four aerogel samples were tested: samples A131 and A132 supplied by ARMINES; sample 396 supplied by the University of Coimbra and RC1500-020 supplied by DLR. The samples were tested at atmospheric pressure and at 10mBar vacuum pressure, not controlling for the temperature (lab temperature ca. 20-23°C). The measurements taken at 10mBar were used for the simulations of the Martian lander application, with conductivity values obtained in the range of 12 to 23mW/m.K. At atmospheric pressure, values were obtained ranging from 29 to 42 mW.
The performed thermal conductivity measurements demonstrated the value of the 3-Omega method, and showed good agreement with measurements using more traditional methods, but achieving total measurement uncertainty, including lower statistical and systematic errors.
Regarding thermal conductivity, uncertainties as low as a few per cent were achieved and a total uncertainty on the diffusivity as low as 7–10% was achieved. Relative errors, in general, can be reduced by using a longer sample (and heating wire), thus making the errors negligible in its length and resistance which can be measured to an accuracy of about 0.3 mm and 0.001 Ω respectively.
In general, the performed thermal tests showed an excellent agreement with other measurements over a wide dynamic range of conductivities and diffusivities, with repeatability on the order of a few per cent even while changing the applied heating power by a factor of 2, 3 or even 4 without the need for thermal models to correct for convection losses, radiation losses or rising temperature of the sample.
Furthermore, the minimum aerogel sample size is significantly smaller with this method than with many other measurement techniques and sample preparation is shown to be simple and low cost. Lastly, since these measurements can be performed in 20 to 30 minutes, multiple measurements can easily be quickly performed to reduce statistical uncertainty. These tests demonstrate the great success and advantages of this technique as a measurement method, especially for very low conductivity samples.
>> Thermal analysis of aerogels
Regarding the implemented thermal analysis of aerogels, the performed tests showed that the materials tested have a wide range of properties (i.e. density, specific heat, conductivity), all with different values and results.
As such, different results can be foreseen, comparing them on the same thermal model. The differences in terms of thermal conductivity, specific heat, and other variables are quite large, in particular considering together the specific heat and the density (volumetric heat capacity). The strongest differences were between the first aerogel prototype (DLR) and the remaining. This may have been related to the way in which these different materials were synthetized by the partners, based on different processes or objectives. This suggests that the materials evaluated via the currently used model can be quite hard to be compared between each material type. Furthermore, this also suggested that different materials would be more interesting/suitable for different applications than others.
In general, the obtained results vary significantly after a comparison of the aerogels’ physical properties, especially in the overall insulation mass and the heating power necessary to switch ON the Electronic box used in testing and for reaching the minimum temperature requirement. For this tested application, the best mass saving material is ARMINES A132, while the best heating power saving material is the DLR Aerogel.
However, no single best material for this tested application can be identified. All the other materials represent a good compromise between limiting the mass and limiting the heater power. The selection of a proper material for the thermal analysis case can only be evaluated taking into account the specific requirements of the mission. In particular, different materials can apply to the best mass saving configuration (ARMINES A132), best heat power saving configuration (DLR RC1500-020) and the one with the smallest volume (UC396) for the insulation layer or thickness for configuration constraints (ARMINES A131, ARMINES A132, UC396).
>> Aerogel thermal performance in air and CO2
Due to test facility availability at STFC, the thermal testing was completed after the submission of Deliverable 5.1 – Semi-industrial scale aerogels manufacturing. Therefore, the testing process was described in Deliverable 9.1 – Long-term commitment activities. The thermal conductivity of three samples of aerogel, from the three manufacturers, were tested in air and in an approximately 10 mBar CO2 environment. The conductivity was measured using a guarded hot-plate at five nominal test temperatures (between +20 °C and +90 °C in air; between -35 °C and +120 °C in the CO2¬¬). The in-air results measured by STFC showed a good agreement with the results obtained earlier in the project (WP 3.6). The CO2 environment results were also in line with what would be expected based on the in air and vacuum results obtained, and showed reasonable correlation to the results obtained by AST-DE within WP 3.6.
1.1.3. Technology for aerogel manufacturing
One of the main project activities was the design and building of an innovative and tailored technology for manufacturing aerogels developed for space applications. As part of this work, the following new foregrounds were produced:
>> Autoclave fluids flow simulation
In order to establish optimal conditions of operation, simulations of both diffusion within aerogel and flow through the vessel considering supercritical CO2 was performed. This work involved three complementary steps.
First, some parameters were estimated considering a small, axisymmetric vessel and a qualitative study of the influence of aerogel physical properties on the drying process was developed, utilizing a simplified geometry. Then, the drying process was modelled considering the autoclave designed by SPX. In addition, several configurations were simulated, namely 3 inlets instead of a single inlet as well as a modified geometry with specific constraints with 1 or 3 inlets. The configuration that optimizes the drying time is a geometry with constraints/barriers and 3 inlets. The results of this task are described in detail in Deliverable D4.2 – Description of results that were obtained by simulation of supercritical fluids flow.
>> Design and manufacturing equipment
A plant for manufacturing equipment was designed, assembled and installed at SEPAREX facilities. Additional systems such as CO2 storage tanks, ventilation systems, chiller and hot utilities were also attached to the equipment. Internal structures to hold the samples during drying were design in order to use self-supporting samples (vertical disposition) and non-self-supporting samples (horizontal disposition). The structure has been designed in stainless steel and is able to host ca. 40 samples of 35x35x1 cm³ per batch.
A security protocol plan has also been filled in order to prevent all the issues of the process relative to the high quantity of organic solvent to be used. In order to validate the operational function of the equipment some tests at working conditions were carried out. Parameters such as working temperature, working pressure, facility temperature, and others were validated.
1.1.4. Semi-industrial scale aerogel manufacturing
Following the development of laboratory scale aerogels, the synthesis of semi-industrial scale aerogels was implemented, as well as the supercritical drying of these materials. As part of this work, the properties of specific aerogel samples were also optimized at a laboratory scale. These activities resulted in the following foregrounds:
>> Optimised CO2 drying process
The time and energy required for each material depends on the organic solvent and structure of the aerogel: less time is required for macroporous aerogels and methanol-based solvents, and more narrow microporous aerogels and ethanol-based solvents. Drying conditions depend on the organic solvent used, but generally the temperature for the materials used by the partners it stays over 40 – 50 °C.
Calculations showed that to use several layers of material to achieve a performance per thickness is more efficient than to directly process the final thickness. It was also observed that the extra configuration for the ARMINES A132 sample would extremely reduce the production cost since the capacity can be highly increased. Therefore, it is supported that further developments be made on this material.
It can be appreciated that production cost is highly reduced (up to 40%) by increasing capacity for the same procedure. For high manufacturing volume, Separex can propose several solutions depending on the material to further decrease the cost if it would be needed.
>> RF – silica gel composites II (DLR)
Aerogel-aerogel composites from RF aerogel and granular silica aerogel can be synthesized in any size and shape. The up-scaling process is similar to the lab-scale process but with increased volume of both components to reach higher total volume (VRF + Vsilica). The sample box which gives the material a shape has to be adapted to the new total volume and can be made of PP or PMMA. In case the sample box is flexible (PP), the material can be removed easily by careful pressing. In case of a rigid box (PMMA) a filter paper on the box ground can help to lift the material out of the vessel after aging process.
The equipment (e.g. oven) which is used for the aging process has a size limiting effect. Plates with a maximum dimension of 24 x 24 cm² can be easily produced but a bigger oven is required to enable the synthesis of samples with a higher area otherwise the synthesis takes weeks up to months.
Samples from semi-industrial process have similar properties compared to samples from lab-scale process. But it was noticed that the amount of air bubbles in the composite material which occur during the mixing procedure increase with the dimension of the composite. The existence of air bubbles can be avoided by applying a vacuum or sufficient underpressure during synthesis.
>> Organically modified silica based gels derived from MTMS – synthesis, washing and molding/unmolding scale-up conditions and apparatus (UC)
UC synthesized large organically modified silica based gels derived from MTMS, firstly using Petri dishes and then larger moulds as confinements. The moulds consist of large glass or metallic trays, with grid baskets inside designed by UC. The baskets allow an easy unmoulding of the gels from the trays. Some monolithic and very large aerogel samples were obtained from these gels, using the Separex drying facility. The larger samples obtained have densities of 55-70 kg/m3 and thermal conductivities of 0.034-0.037 W/(m K). The aerogels produced at semi-industrial scale have high hydrophobicity (> 140o), high flexibility, specific surface area of ~400 m2g-1 and average pore size included in the size range of mesopores (5-6 nm). Thinner samples and a horizontal position in the autoclave gave the best results in terms of aerogels properties. The absence of the washing step in the drying system leads to the presence of residual solvents/catalyst in the aerogels, but this can be corrected by conditioning the resultant aerogels samples in an oven (several hours at 100oC).
>> Silica/organic hybrid gels II
The sol-gel processing route developed at lab-scale by ARMINES was simple to up-scale to synthesize samples with significant larger characteristics dimensions. Following this “one-pot” hybridization route it is possible to obtain monolithic 35×35×0.5 cm3 wet gels presenting similar characteristics than their smaller counterparts (some cm3).
1.1.5. Aerogel insulation systems development
Using the aerogels manufactured as a semi-industrial scale, thermal insulation systems were developed. This work resulted in the following foregrounds:
>>Aerogels encapsulation system
STFC developed a procedure for manufacturing a completed insulation system using the aerogel materials. This process involves encapsulating the aerogel materials, since the level of particulate generation and fragility of the current aerogel materials means that they are not compatible with the high cleanliness levels required for space applications in their as manufactured state. A method for encapsulation of the aerogel materials from all three consortium partners was successfully developed. This encapsulation process uses standard Multi-Layer Insulation (MLI) materials (with good space heritage) and standard MLI manufacturing tools to fully encapsulate the aerogel material. This encapsulation process was described in Deliverable 6.2 – Development of aerogel thermal insulation systems.
STFC assessed the encapsulated samples through depressurisation and vibration testing. The three aerogel panels did not demonstrate gross changes in their structure as a result of this testing, although all three panels demonstrated at least some contamination release from the encapsulated panel. The materials were therefore all shown to be compatible with a launch environment, but do present a risk of contamination. These tests were also described within Deliverable 6.2 – Development of aerogel thermal insulation systems.
>> Thermal correlations
Six individual blankets for each aerogel tested – developed by AST/UC, DLR and ARMINES – were manufactured and installed on an aluminum box equipped with heaters. The box with aerogel blankets was placed within thermal vacuum chamber in TAS-I facilities for thermal vacuum testing.
In the case of AST/UC aerogel blankets, almost all temperature values were correlated. In the case of ARMINES and DLR blankets, the correlation results obtained are slightly inferior. This situation may have been created by the uncertainties present in the test set-up and the design of the test article: as the aerogel blanket and the foils around were not glued to each other, a non-uniform and uncontrolled contact is present.
Therefore, it was possible that some parts of the foil could have slightly moved and lost contact with the blanket and change the temperature values measured, making them more difficult to correlate. However, in case of the ARMINES and DLR blankets, most of the temperatures measured on the aluminum box or internal foil were correlated.
1.1.6. Aerogel insulation systems prototypes manufacturing
Based on the experience developed on the best method to encapsulate aerogels, aerogel insulation systems prototypes were manufactured. This resulted in the following foreground:
>> Manufacturing of prototypes based on aerogel
STFC were responsible for the manufacture of prototype insulation panels to be used for the thermal efficiency evaluation tests in WP7.3. As part of this work, the encapsulation procedure developed within WP6.2 was further developed based upon the results of the testing completed for WP6.3. These developments were focussed upon improving the venting characteristics, and reducing the contamination release from the aerogel panels. These revised encapsulation techniques were successfully used for the encapsulation of six aerogel panels each from three consortium partners required for the WP7.3 activities (18 panels in total). This prototype manufacture process is described in detail within Deliverable 7.1 – Thermal insulation prototypes.
1.1.7. Long-term commitment activities
As part of the long-term commitment activities of AerSUS, additional lab-scale aerogels were synthesised with the aim of improving specific properties. Additionally, the potential use of selected aerogels available in the market for thermal insulation in space applications was performed, by applying thermal models to predict the effectiveness of such insulation in target applications. These activities resulted in the following foregrounds:
>> Thermal analysis of aerogels
The thermal analysis of aerogels and corresponding objective of assessing their performance in a real environment required a preliminary analysis. The defined ‘real environment’ was a mission to Mars, with an instrument (part of a bigger lander) on its surface. This was considered the most interesting application for aerogels, taking into account the bad performances of MLI in cases with presence of atmosphere. An instrument, named “EXO 1”, is part of this lander and is the main recipient of the insulation application. The lander was analysed in a realistic Mars environment with solar fluxes, sky temperature, dust effect and convection modelled. The insulation of the internal electronic box is evaluated using different materials, in order to fulfill the mission requirements.
This analysis was done taking into consideration the newly developed materials, and using the Thermal Mathematical Model described in Deliverable 6.3 – Thermal correlations from space environment tests, where 6 different scenarios (with different latitudes and altitudes and therefore different solar fluxes) of Martian conditions are considered and two of them are chosen for being the most extreme in terms of temperature values: one hot and one cold case were chosen (“Maximum Day” and “Maximum Night”), taking into account the influence of the solar fluxes (depending on seasonal changes), the apparent temperature of the sky and the ground temperature, dust-storm effect. The system is evaluated in the hot case taking into account only the temperatures during the day, while in the cold case, taking into account only those during the night
The thermal analysis aims to select a configuration (i.e. type and thickness of the insulation) that allows the boards of the instrument to operate at maximum dissipation and in the warmest conditions without damage and, at the same time, to reduce as much as possible the heating power needed during the coldest conditions. The outputs of the analysis used to evaluate the different insulations were: (1) thickness, volume and mass of the insulation layer (chosen to fulfill the requirements of the hot case); (2) heater power dissipation (to fulfil the cold case requirement).
The newly developed aerogel materials demonstrated similar performances, where the biggest difference was related to the mass of the insulation needed, which directly depends on the density of the material used. It was verified that the best mass-saving material was the DLR Cellulose, which showed a good compromise between the mass and heater power needed amongst all aerogels.
When compared to previously developed and analysed aerogels, similar conclusions can be drawn: DLR material still offers the best heat power saving material, even with a bit worse performance than the previously developed material. However, it allows to save almost 2/3 of the necessary insulation mass, making it very similar to the ARMINES A131 aerogel.
>> RF aerogel – silica aerogel composites III
An attempt was made to optimize the RF aerogel – silica aerogel composites based on the production procedure and the values of thermal conductivity and of density. The mixing procedure of the granular material with the matrix was improved by applying a vacuum or sufficient underpressure during synthesis resulting in materials without air bubbles and with a better reproducibility. Furthermore, a change of the granular material by using hydrophobic granular silica aerogel from different manufacturer was applied but with no significant effect. A change of the matrix was performed by using a different recipe for the RF aerogel. The new RF recipe was developed at DLR containing a two-step synthesis route in which the solution is initially catalysed by a base and after a certain time the catalyst is changed to an acid one. The new recipe causes lower production time of RF aerogels and the composites and additionally decreases the density of the composite (0.17 g/cm³). Thermal conductivity of the new composite is still >0.03 W/m.K.
Another approach was tested in which both the granular material and the matrix was changed. New aerogel-aerogel composites consisting of hydrophilic granular silica aerogel and of a cellulose aerogel matrix were synthesized. Thermal conductivity still reached values >0.03 W/m.K but the density obtained is reduced and is between 0.03-0.16 g/cm³.
>>Organically modified silica based aerogels derived from MTMS with BTMSH/BTMSE/ODS additives
Different additives were added to the MTMS-derived aerogels with the objective of trying to improve the mechanical integrity of aerogels and reduce particle shedding:
-- 1,6-bis(trimethoxysilyl)hexane (BTMSH) acts as a bridging organic ligand and was tested to check its effect on the connectivity of the silica network. BTMSH enhanced the gelation process and very cohesive gels were obtained in less than 2h. Moreover, it gave rise to aerogels with less release of powders when compared to the aerogel without additive.
-- 1,2-bis(trimethoxysilyl)ethane (BTMSE), with a shorter ligand group, was also tested. The addition of BTMSE did not add any improvement on the MTMS-based aerogels.
-- Trimethoxy(octadecyl)silane (ODS), with a large alkyl substituent group on the trimethoxysilane, was also studied. The 18C long chain was expected to act as a very small fibre, improving the aerogels network connectivity/resistance. In fact, the ODS contributed to an improvement of flexibility of the aerogels and gave rise to samples with the lowest particle shedding. The presence of the non-polar chain (ODS) slightly increases the hydrophobic character of the aerogels.
The synthesis conditions for the first two additives were the same as for MTMS-derived aerogels without additives. For ODS, a one-step base catalysed synthesis process was developed. The optimum percentage of Si derived from the additive in the system was found to be 2% for all cases. Although the density increased to near 60 kg/m3, BTMSH and ODS improved slightly the insulation performance of the aerogels, due the decrease of the proportion of large pores to smaller pores.
>>Silica/organic hybrid aerogels III
Based on the results obtained with reference to the RF-silica hybrid materials (previously presented regarding “Aerogel development”), ARMINES studied the improvement of the characteristics of the so-obtained hybrids by using silanes technologies. For this purpose, methyltriethoxysilane (MTES) as well as trimethoxy(methyl)silane (MTMS) were used as silica co-precursors with APTES. “One pot” processing route performed with APTES, MTES (or MTMS), resorcinol and formaldehyde allows to significantly improve the flexibility of the hybrids while decreasing dramatically apparent density (0.03 g/cm3) while maintaining low level of effective thermal conductivity (0.027 W m-1K-1 in room conditions).
>> Aerogel Thermal Insulation Systems for Space
The activities undertaken by STFC through the project provided valuable insight into how thermal insulation systems using aerogel should be developed further for space flight application. Several areas for improvement of the aerogel materials and the encapsulation method were identified which, from the point of view of a manufacturer or user of insulation panels, would improve the viability of the materials for use as a space insulation product. These areas were reviewed during WP9 and preliminary ideas, based upon STFC experience of developing thermal design solutions for scientific space instruments, were developed and reported.
Potential Impact:
Reducing the dependence on critical technologies and capabilities from outside Europe was one of the driving forces behind the AerSUS project.
The objective of AerSUS was to create a European supply unit capable of providing aerogel materials and aerogel thermal insulation systems for specific space applications. Such aerogels, their manufacturing technology and aerogel thermal insulation systems were successfully produced in this project. The aerogel materials and insulation systems resulting from AerSUS are suitable particularly in environments where atmosphere is present, including space applications such as (re)-entry vehicles, Mars rovers, and pressurized compartment. The relevant technology, materials and insulation systems deriving from AerSUS will allow an unrestricted access by the European space community to this new space technology, therefore reducing their dependence on technologies from non-European sources.
The dissemination activities carried out in the project targeted a wider community. However, a majority of the stakeholders reached throughout the project belonged to European space and space/non-space scientific communities. It is relevant to highlight that a stakeholder consultation event was also organized in 2013 as part of AerSUS, and hosted representatives of major players of the European space industry, especially in what concerns large space system integrators and small system manufacturers. This event aimed to collect feedback from stakeholders on the lab-scale aerogel materials developed previously in the project so that further project developments could be tailored according to the received inputs. The participation of AerSUS in the ESA Industry Space Days 2014 also aimed to increase the proximity towards relevant European stakeholders.
Concrete steps were also implemented in order to prepare the commercial exploitation of some of the aerogels developed throughout the project AerSUS. The different project foregrounds were discussed and mapped internally. This resulted in a specific foreground table that was updated as necessary during the year.
For the different project foregrounds, partners identified the ownership regime as sole ownership. An exception was verified on the ‘selected aerogels of UC optimised by AST’, where the UC and AST are both foreground owners. Regarding ‘selected aerogels of DLR/ARMINES optimised by AST’, by the end of the project, discussions on foreground ownership were still not concluded. Therefore, discussions have been held regarding joint ownership agreements between AST and other project partners (UC, ARMINES and DLR). License agreements between Active Aerogels/DLR and Active Aerogels/ARMINES were also discussed, but later delayed due to the fact they address aerogels that were still in development at a later stage of the project. Currently, partners are continuing to define the details of the agreements to be implemented. Active Aerogels and UC have a license agreement process related to the exploitation of results generated by UC in the AerSUS project. At the time of this report, partners are continuing to define the details of the agreements. Active Aerogels, a spin-off company of Active Space Technologies (scientific coordinator of AerSUS), has already formed rights to manufacture some of the AerSUS aerogels for commercial purposes in the future. Active Aerogels already commercializes aerogel materials for applications such as launchers and rockets; spacecraft and re-entry probes; rovers and landers for planetary exploration; stratospheric balloons; cryogenic tanks and helium storage.
The access to aerogel materials for space applications and aerogel thermal insulation systems from European sources, will also increase the overall competitiveness of European space industry satellite vendors on the worldwide market. The aerogels resulting from this project will also target non-European space missions in addition to the European ones.
The participation/dissemination of AerSUS in international trade fairs, including the International Astronautical Congresses in 2012 (Naples, Italy), 2013 (Beijing, China) and 2014 (Toronto, Canada) and the ILA Berlin Air Show in 2012 had the objective of reaching out to the larger international space community that could have interest in the products developed within AerSUS.
By contributing to the creation of a European supply unit of aerogels and aerogel insulation systems for space applications, AerSUS has contributed to enhancing the European economic growth, employment and European SME policy. AerSUS will leverage the sales of European made products in the fields of thermal insulation and will help the economic development of European companies, contributing thus to the recruitment of new employees. In addition, AerSUS involved 4 SMEs in the partnership. Their collaboration with research organisations and end users of space technologies allowed these ‘smaller’ companies to improve their technical capabilities, make long-term relationships and create future opportunities benefiting their future business activities.
Furthermore, AerSUS technologies are likely to be used as thermal insulation systems for applications that are related especially to scientific exploration in space. Beyond the wider general impacts of space activities on society (including technology development, educational stimulation, and expansion of communication technologies), scientific space activities have an outstanding role in our knowledge development of the worlds that surround us and through this of our own world. AerSUS intends to contribute to this evolution.
In addition to the above socio-economic impacts, it is important to refer the impacts that the project has in scientific terms. The following refers to the new know-how AerSUS brings to the academic world:
|| Know-how (KH) / Benefits to whom (BtW) ||
1.
KH: Synthesis of aerogels from different chemical systems/Large-scale synthesis of gels/Optimization of synthesis and drying conditions to tailor aerogels properties.
BtW: Aerogels scientific community, Aerogels manufacturers, Aerogels end-users.
2.
KH: Scale up of sc CO2 drying of aerogel to 220L scale.
BtW: Insulation industry (building, Space industry) that can tests on bigger insulation plate (35*35cm) and start implementation.
3.
KH: Development of new super insulating organic-inorganic hybrid aerogel blanket-type materials based on silica / resorcinol-formaldehyde chemical systems.
BtW: Scientific community.
4.
KH: Development of process permitting the facile and rapid realization of large and monolithic super insulating hybrid blanket-type gels ready for supercritical CO2 drying.
BtW: Scientific community and aerogels industry.
5.
KH: Manufacture of aerogel-aerogel composites.
BtW: Scientific community, industrial companies.
6.
KH: Production of large-scale ambient dried composite materials.
BtW: Scientific community, industrial companies.
7.
KH: Two step synthesis of resorcinol-formaldehyde aerogels.
BtW: Scientific community, industrial companies.
Several activities were implemented during the course of AerSUS to disseminate and exploit the scientific results of the project. These were mainly the presentation of outcomes at scientific events, such as:
> 1st AEROCOINs Workshop, France 2012
> 6th International Conference on Advanced Computational Engineering and Experimenting - ACE-X Conference, Turkey 2012
> AEROGELS Properties-Manufacture-Applications SEMINAR, France, 2012
> International Astronautical Congress (IAC) 2012, Italy, 2012
> 43rd International Conference on Environmental Systems, U.S. 2013
> XVII International Sol-Gel Conference, Spain, 2013
> International Astronautical Congress (IAC) 2013, China, 2013
> Aero-ORMOSIL Seminar, Portugal, 2014
> Journées Industrielles Nanomatériaux 2014, France, 2014
> 14th European Meeting on Supercritical Fluids, France, 2014
> International Astronautical Congress (IAC) 2014, Canada, 2014
> International Seminar on Aerogels 2014, Germany, 2014
> 3rd Cycle of Interdisciplinary Conferences & Debate of IIIUC, Portugal, 2014
Publications in scientific journals are an optimal way to transfer scientific results to relevant public. Results from AerSUS were sent for publication in the following journals:
> Effect of Additives on the Properties of Sílica Based Aerogels Synthesized from Methyltrimethoxysilane (MTMS). Durães, L., Maia, A., Portugal, A., in Proceedings of the International Seminar on Aerogels-2014: Properties-Manufacture-Applications, International Society for Advancement of Supercritical Fluids (ISASF), 2014, p.33-43.
> Influence of sol-gel conditions on the key properties of silica based aerogels for thermal insulation in Space. Maia, A., Portugal, A., Durães, L., in Book of Abstracts of the XVII International Sol-Gel Conference, Instituto de Ciencia de Materiales de Madrid (ICMM) & Consejo Superior de Investigaciones Científicas (CSIC) & Sol-Gel Group (SGG) & Ministerio de Economía y Competitividad & International Sol-Gel Society (ISGS), Madrid, 2013, p.454.
>The 3 omega transient line method for thermal characterization of Superinsulator materials developed for spacecraft thermal control. Dalton, M. et al., in Acta Astronautica.
Furthermore, other publications are in development and should be published during 2015.
In addition to scientific publications and congresses/events, dissemination was also established through other traditional strategies, including the project website, newsletters, brochures and press releases.
List of Websites:
http://www.spi.pt/aersus