Final Report Summary - CR FREE EPAINT (Development of a non chromated, Reach’s compliant anodic electropaint, with very low volatile organic compounds, for high protection against electrochemical corrosion of pickled aluminium alloys used) Executive Summary:This project was designed to help prove anodic Ecoat technology for Aerospace at an industrial pilot scale. Some elements of the background science were examined in order to validate the technology and understand underlying mechanisms.It has been shown that the electrodeposition process is viable in terms of both the the process viability and cost, that high integrity coating are produced which give outstanding levels of performance when compared with other chrome replacement technologies and we belive the work herein has helped establish this process as a strong option for adoption by OEM's and component suppliersThe consortium consisted of PPG Aerospace who are the original developers of this technology and Dassault Aviation who are a potential end user with an interest in being an early adopter. The Uniiversity of Lille were engaged as a project partner to provide a range of sophisticated surface analytical techniques used for probing the structure of surface layers from which we were able to determine some mechanistic detail and understand the effects of process variablesThe main objective of the project was to further develop a promising chromium replacement technology by gaining information on product performance, characterisation of the deposited layers and the effect of process variables. The final stage of the project was to show feasibility of the process on a demonstrator unit that is intermediate in scale between lab experiments and full industrial scale Project Context and Objectives:Context and ObjectivesIt remains a major objective of the Aerospace industry to replace chromium containing paints and pre-treatments. Chromium (especially in oxidation state 6 commonly referred to as Chrome VI) is known to be a carcinogen by inhalation and it is a persistent toxin in the environment. Therefore replacement of Chromium has the benefits of eliminating worker exposure to a dangerous and toxic material, elimination of the resulting environmental impact, reduced requirements for waste containment and safe disposal, and reduced decommissioning costs. Furthermore, use of chromium VI is scheduled to be discontinued under REACh legislation with a sunset date of January 2019 although Authorisation for continued use had been requested and we await the outcome.Airframe manufacturers and MRO organisations are actively searching for replacement technologies of which anodic electrodeposition is a candidate technology. Many potential replacement technologies have been explored with limited success. A major obstacle faced by airframe manufacturers is how to guarantee extended service lifetime of say 30 years based on laboratory tests. For conventional Chrome VI containing products there is a high degree of confidence but this is based on decades of in-service field data and no comparable history exists so far for any replacement technologyPPG has a long history of innovation within the field of Ecoat technology and is a market leader within several market sectors where Ecoat technology is used such as Automotive OEM, Industrial, etc. This technology represented a paradigm shift in the Automotive sector when it was first introduced, and is the main reason why modern car bodies are much more resistant to corrosion than before. Both anodic and cathodic technologies have been developed in which the piece to be coated is either the anode or the cathode respectively.PPG Aerospace began exploring the application of Ecoat technology in Aerospace applications some years before the start of this project. Amongst the technical challenges was the need to balance the long term corrosion requirements with low temperature cure as commonly used Aerospace aluminium grades undergo morphological changes above 120oC resulting in a loss of tensile strength and increased susceptibility to fatigue cracking. Furthermore, it was found that anodic systems performed better on aluminium substrates compared to cathodic systems and this was attributed to growth of a protective Al2O3 layer in the anodic process. The current project was focussed on the parameters that are important in an industrial process environment, in particular we wanted to answer the questions how robust is the process, what are the tolerances associated with critical process parameters and to examine how variations can affect the quality of the oxide film and the deposited Ecoat layer. A second focus was to understand some of the mechanisms and science behind the electrodeposition process and the growth of the oxide layer The project was structured into the following work packages1. Product designed and optimised2. Testing versus Major OEM Specifications3. Technology Characterised4. Electrodeposition Process Parameters defined5. DemonstratorIt was originally planned that WP5 would include some trials where real parts were coated and mounted on in-service aircraft. However, it was decided that this would not be good use of time within the project for the following reasons: practicality of identifying a suitable aircraft and logistics of getting a part coated and fitted, insufficient time to allow ageing of the part preventing generation of meaningful new information, risk in the vent of failure. It was therefore agreed that this element would be excluded from WP5 and that we would focus on defining process parameters using the pilot scale mini-coater. As a final element we have demonstrated that the process is viable from a cost viewpointProject Results:Foreground and Main ResultsWP1Work on optimization of the resin system has been achieved via modifications to the polymer composition, several variants were generated each allowing for a curing temperature of 110°C which is essential in order to guarantee that no structural and/or morphological changes occur in the aluminium substrate during the heating cycle. Non chromate inhibitive pigments (NCCI) have been incorporated into these formulations. It has been confirmed that the anodic ecoat baths obtained are stable and that the VOC does not exceed 100g/l. For the generation of coated parts, we have mainly focused on Al2024 clad and unclad aluminium panels which were prepared as follows prior to deposition of Aerocron:• Alkaline degreasing• Hot water cleaning• Acid pickling• Deionized water cleaningThe following describes a typical lab process used to obtain a 20 micron deposit of Aerocron:• Ramp up phase = 30 seconds• Application duration (ramp up included) = 2 minutes• Bath temperature = 25°C• Ratio cathode/anode (surface to be painted) = ¼• Bare 2024-T3 substrate: Tension = 120VThe bath is ultrafiltrated prior to electrodeposition in order to eliminate undesirable soluble species (such as residual low molecular weight molecules). The coated panels are then cured at 110°C for 30 mins in a conventional oven.Critical tests have been launched on various electrocoated panels and significant results havebeen obtained. In standard tests we have shown that the performance of Aerocron 2200 when compared to other known chrome-free products is exceptional, offering a performance level similar to that of chromated products (Note: Normal test duration is 1000hours for filiform corrosion test and 3000 hours for the Salt Spray corrosion test). In some cases we ran tests for longer durations and still found excellent performance at 3000 hours filifiorm and 6000 hours Salt Spray, similar to results obtained with a conventional chromated epoxy primer used as a control.Most of the other critical tests have also been done on Al-2024 clad and bare metal panels, such as resistance to hydraulic fluid, adhesion after water immersion etc. Aerocron passes all these testsAn important feature of our new concept is that it does not require any anodizing pre-treatment. As the aluminium part is held at anodic potentials, an oxide layer is formed at the surface concomitant with the paint electrodeposition. This layer makes an important contribution to the finalperformance of the coating. It is the role of our University partner "EcoleNationale Supérieure de Chimie de Lille" (France) to characterize it using sophisticated microscopy and analytical methods. WP2Previous work within this project has shown the validity of the electrodeposition concept on 2024 aluminium at laboratory scale, and has shown the exceptional performance of Aerocron in conventional laboratory tests, in particular laboratory corrosion testing has shown that performance is similar to chrome VI coating systems. During this reporting period, the main focus was on testing of Aerocron 2200 to standard customer specifications. Obviously it is impractical to test versus all relevant specifications so the tests have focussed on typical standard protocols unless otherwise stated.The main elements of the work carried out in WP2 is as follows:• Influence of Ecoat application parameters on growth of oxide layer• Influence of surface preparation• Study of bath ageingSecondary objectives were to carry out preliminary assessments of:• Throw-power• Sealant adhesion• Resistance of cured films to fungal growth• Resistance of cured films to chemical fluidsEffect of Process VariablesWhilst some variations in corrosion as measured in the salt spray test were observed, there is a lot of variability from various sources and the results are not considered to be conclusive. In this study we found slightly improved corrosion performance from panels prepared using the minimum ramp up time but these results are opposed to results from PPG’s in-house studies so we tend to conclude that ramp up time is not an influential factor in determining corrosion performanceThere appears to be a rough correlation between increasing applied voltage and oxide film thickness (data points at 120, 140, 160 and 180V applied). The Coulomb count is approximately constant throughout all applications. However, it is probable that the vast majority of the coulombic consumption is not associated with either oxide growth or Ecoat deposition. There appears to be an inverse correlation between ramp-up time and oxide film thickness, increasing ramp-up time at a fixed applied voltage results in decreased film thicknessIt is difficult to draw significant conclusions from this data as the corrosion results seem to indicate that corrosion protection is insensitive to any of these process variables. Effect of Surface PreparationAlkaline cleaning solutions of 3 different compositions have been looked at for effect on Ecoat deposition. A test protocol has been developed in which panels are alkaline degreased followed by acid etch (Soccosurf 10), the Ecoat is then applied, cured and stripped and the bare panel is then subjected to salt spray for 4 hours. No real differences have been noticed. A series of test panels have been subjected to salt spray to find out if any effects of surface cleaning are discernible via the salt spray test.Bath Ageing StudyAs the bath gets used, there is an accumulation of amine, a decrease in total solids (loss of Ecoat via deposition) and an increase in conductivity. Whilst it is clear that numerical values are dependent on surface area throughput and will vary from one bath configuration to the next, we have observed the following (using number of standard panels coated as a measure of surface area)• Conductivity rises from an initial value of 975 µS/cm to approx. 1200 µS/cm after roughly 100 panels, after which it stabilises for the rest of the study (~280 panels)• Amine build up appears to be approximately linear over the same series of experiments• Solids content appears to have an approximately inverse relationship with conductivityFrom this data it will be possible to work out the quantitative requirements for ultrafiltrationThrowpower DeterminationThrowpower is the relative ability of the Ecoat bath to deposit under specific conditions of applied voltage and the ability to deposit in occluded spaces. Throwpower is formulation dependent and in this study we have found that formulations containing added adhesion promoter (examined in WP1) have enhanced throwpower related to higher conductivity. However throwpower of standard formulation Aerocron 2200 is consider acceptable for scale-up and no further work has been carried out.Sealant AdhesionAdhesion tests have been carried out to establish which sealant types adhere best to Aerocron. Whilst sealant adhesion to conventional chromated epoxy appears to be better than the Ecoat samples tested in this series, adhesion to Aerocron was generally considered acceptable. Also we note that addition of adhesion promoters can enhance adhesion. However, there are significant variations depending on choice of sealant and this is considered to be an issue at implementation with individual customers. Resistance to Fungal GrowthA basic settlement test has been carried out (subcontractor laboratory) using the fungus Hormoconis Resinae in which coated panels are immersed in a medium containing the fungus and optionally jet fuel also. The tests show that there is no significant fungal settlement and no differences were noted between Aerocon and a chromated epoxy standard.Chemical ResistanceResistance to the following fluids has been confirmed:• Deicing fluid• Cleaning fluid• Kerosene at 80oC• Kerosene at 23oC• Turbine oil at 60oC• Toilet fluid at 23oC• Hydraulic fluid at 23oC• Skydrol LD4• Hydraunicol FH2 and FH51WP3During this reporting period, the work focussed on characterisation of the oxide layer formed during anaphoretic deposition of Aerocron™. Surface analysis has been done by project subcontractors Unité Matériaux et Transformations (UMET) – UMR-CNRS 8207, Equipe Ingénierie des Systèmes Polymères, Groupe Traitement des Surface, Ecole National Supérieure de Chemie de Lille (ENSCL) BP 90108Substrate cleaning and deposition parameters used were as reported previously:• Substrate 2024-T3• Alkaline degrease• Hot water wash• Acid pickling• DI water rinseVoltage ramp-up 30 secondsTotal deposition timeBath temperature 25oCSurface area cathode:anode 1:4Applied voltage 120VTechniques that have been used to characterise the oxide film include FEG-SEM (field emission gun scanning electron microscopy), TEM (transmission electron microscopy) and ToF SIMS (time of flight secondary ion mass spectroscopy). The ToF SIMS technique has been shown to be particularly useful for the characterisation of the oxide film. The oxide film has been shown to consist of 2 distinct regions: 1) a dense layer of Al2O3 in contact with the Al substrate of about 100 nm, and 2) a filamentous layer, the filaments of Al2O3 penetrating into the deposited paint layer to about 100 nm. The interpenetrating filament structure explains the excellent adhesion of cured Aerocron films to aluminium substrates.The corrosion resistance given by the combined oxide/Aerocron film has been characterised using conventional laboratory test methods as reported in the periodic report. It is a stated objective of the next work package to characterise the protective contribution of the oxide layer, at this stage it is not clear how to isolate the oxide layer and carry out meaningful tests on it. A further objective of WP4 is to examine the effect on the thickness and morphology of the oxide layer of variations in the process parameters (applied voltage, ramp time, bath temperature and composition, other variables if relevant). If the oxide film is shown to be insensitive to process variations, then it may not be necessary to further characterise the protective qualities of the isolated oxide layer.WP4The main focus of WP4 was aimed at defining and establishing process variables at pilot scale. The main elements and new conclusions from the work carried out in WP4 are as follows:• effects of pre-treatment stages, degreasing and deoxidation, effect of contact time with pre-treatment chemicals (no effect on film thickness was seen, or on results of filiform corrosion tests)• ultrafiltration (removal of amine, pH control) was found to influence the appearance and smoothness of the coated surface• voltage ramp-up time was found to have an inverse relationship with film thickness, faster ramp up gives lower film thickness• current-voltage curves indicate optimum deposition conditions, higher film thicknesses are obtained at higher applied voltages up to the "rupture" voltage above which excessive gassing from electrolysis of water causes defects in the film• obviously film thickness increases with increasing time but this is specific to each bath design and the process is self-limiting so there is no benefit in extended process times• higher temperatures give higher film thicknesses• A bath ageing study has been carried out leading to recommendations for maximum amine concentration, replenishment and ultrafiltration capacity• Resistance to Hormoconis Resinae has been confirmed in a basic settlement test• Resistance to the following fluids has been confirmed (De-icing fluid, Cleaning fluid, Kerosene at 80oC and 23oC, Turbine oil at 60oC, Toilet fluid at 23oC, Hydraulic fluid at 23oC, Skydrol LD4, Hydraunicol FH2 and FH51)WP5This Work Package (WP5 – Demonstrator) was designed to show that the process is viable at an intermediate scale between lab experiments and full scale industrial scale. An intermediate scale pilot coater was used to study various practical aspects of process operation in a realistic industrial environment. Real parts were coated and the process has been shown to be viable. Pilot scale feasibility has been demonstrated by construction of a mobile coater with bath volume of 500 ltr. This represents an intermediate scale, big enough to coat some real parts and obtain coatings representative of full scale quality, but relatively small by comparison to what we envisage for a full scale large facility. This unit is capable of giving real-time demonstrations of the technology and is in principle mobile so it can be used in different locationsThe construction of a “mini-coater” has enabled us to explore some of the practical aspects of running the Ecoat process in a realistic environment and using realistic operational parameters:• Use of various pretreatment processes• Production of a further test panels and some special parts with specific properties (form - tubular parts, real production parts ; pretreatment – cleaning, deox, chemical conversion in different combinations; substrates – different aluminium alloys). • Live demonstrationsDetails are reported in the WP5 Deliverable which cover the following elements:• Mini-coater design• Installation, preparation, clean-down, waste disposal• Hanging of pieces• Pre-treatment• Electrodeposition parameters• Curing• Results on complex shapes and real pieces• Cost modelFurther explanation of the results from the application of the cost model is required. We have deliberately not run any modelling using real customer data as part of the project because cost information is confidential. However, general conclusions from our experience with real analyses shows that the process is viable from a cost point of view and that there are significant cost benefits associated with greatly improved utilisation, elimination of toxic waste, minimisation of process waste streams and reduced labour content. There is a small increase in energy costs mainly associated with the curing process but the cost balance is favourable to the Ecoat processPotential Impact:It remains a major objective of the Aerospace industry to replace chromium containing paints and pre-treatments. Chromium (especially in oxidation state 6 commonly referred to as Chrome VI) is known to be a carcinogen by inhalation and it is a persistent toxin in the environment. Therefore replacement of Chromium has the benefits of eliminating worker exposure to a dangerous and toxic material, elimination of the resulting environmental impact, reduced requirements for waste containment and safe disposal, and reduced decommissioning costs. Furthermore, use of chromium VI is scheduled to be discontinued under REACh legislation with a sunset date of January 2019 although Authorisation for continued use had been requested and we await the outcome.Airframe manufacturers and MRO organisations are actively searching for replacement technologies of which anodic electrodeposition is a candidate technology. Many potential replacement technologies have been explored with limited success. A major obstacle faced by airframe manufacturers is how to guarantee extended service lifetime of say 30 years based on laboratory tests. For conventional Chrome VI containing products there is a high degree of confidence but this is based on decades of in-service field data and no comparable history exists so far for any replacement technologyPPG has a long history of innovation within the field of Ecoat technology and is a market leader within several market sectors where Ecoat technology is used such as Automotive OEM, Industrial, etc. This technology represented a paradigm shift in the Automotive sector when it was first introduced, and is the main reason why modern car bodies are much more resistant to corrosion than before. Both anodic and cathodic technologies have been developed in which the piece to be coated is either the anode or the cathode respectively.PPG Aerospace began exploring the application of Ecoat technology in Aerospace applications some years before the start of this project. Amongst the technical challenges was the need to balance the long term corrosion requirements with low temperature cure as commonly used Aerospace aluminium grades undergo morphological changes above 120oC resulting in a loss of tensile strength and increased susceptibility to fatigue cracking. Furthermore, it was found that anodic systems performed better on aluminium substrates compared to cathodic systems and this was attributed to growth of a protective Al2O3 layer in the anodic process. Since the start of this project PPG have commercialised the first version of this technology but at the time of writing there are only a few small industrial scale baths operating worldwide and these are being used to produce pieces for pre-qualification test programs and demonstrator projects. The technology does not yet have an OEM qualification. Given that this technology is at the beginning of its life it has not had great societal impact so far. However it promises a genuine high performance alternative to chrome containing primers and therefore offers the societal benefits of reduced worker exposure with elimination of chromium related diseases, elimination of chromium from waste streams giving reduced containment costs, and elimination of environmental effects. The industry is cautious about making the switch and this will be driven by regulatory pressure in the form of REACh. There is a lobby to extend the use of chromium beyond the nominal sunset date in 2019 and an Authorisation has been applied for. There is also a growing trend for aircraft manufacturers to base their operations globally, and it is conceivable that European legislation would incentivise manufacturers to shift operations involving chrome based paints to sites outside Europe in order to continue using these products legally. It can therefore be argued that this technology is helping towards keeping the associated jobs based in Europe
