Final Report Summary - PARTICOAT (New multipurpose coating systems based on novel particle technology for extreme environments at high temperatures)
Executive Summary:
The objective of the project is to develop a novel and cost efficient multipurpose high temperature coating system on the basis of particle processing of metallic source materials. It shall possess multi-functionality that will comprise thermal barrier effect, oxidation and corrosion protection, anti-adhesion effect, electrical insulation at elevated temperatures and fire protection.
The concept of this novel approach is a coating consisting of micro-scaled metal particles with a defined size range, deposited by spraying, brushing, dipping or sol-gel. During the heat treatment, the binder is expelled, bonding to the substrate surface is achieved, the metallic particles sinter and oxidise completely resulting in hollow oxide spheres that form a quasi-foam structured topcoat. Simultaneously, a diffusion layer is formed below the topcoat serving as a corrosion protection layer and as bond coat for the topcoat. The structure of the coating system is adjusted by parameters like selection of source metal/alloy, particle size, substrate, binder and a defined heat treatment.
The main objectives in High temperature protection have been the development of coating designs, the production and characterisation of the source particles, the research on coating manufacturing procedures, investigation on the performance and the understanding of the degradation mechanisms as well as life cycle assessment. For the Fire protection the objectives were coating design, coating deposition on composites, measurement of the thermal insulation and study of fire protection performance. For the High temperature electrical insulation the coatings were designed, a suitable deposition processes was found and the performance and degradation mechanisms were studied.
High temperature protection
Multi-size spherical Al particles in the range of 1-20 µm were found as mostly suitable for forming the coating structures according to the concept. In the case of the austenitic steels, additions of boron and silicon demonstrated a beneficial effect on the adhesion of the topcoat and on the sintering of the Al particles to each other. On both austenitic steels as well as on Ni-based alloys coatings were produced that withstand scratch tests subjected to 4 kg and showed adhesion strength up to 7 MPa. Experiments demonstrated that the topcoat effectuates as thermal barrier by gas phase insulation reducing the temperature up to 50% with a coating thickness of 170 µm. The coatings were subjected to application relevant temperatures under isothermal and cyclic conditions showing stability within the investigated times.
Fire protection
Hollow alumina spheres were produced by oxidising µm-Al particles on laboratory scale. Using these particles for an inner layer and implanting other µm-particles in an outer flame retardant layer two different coating structures were designed and produced. The coatings can easily be produced also at industrial level and a production procedure was designed. Both coatings were tested against flame resistance and heat insulation. On flame subjection, both coating concepts keep the backside temperature of a 5 mm thick composite sample below 100°C for 60 min and have great potential for flame retardant and heat protection for composites.
High temperature electrical insulation
Electrical conductors for high temperature heating elements, such as in metallurgy, are often from copper. Three coating approaches were developed: i) Al particles with Si-O semi-polymer as bonding material, ii) Cu-Sn-A2O3 “PARTICOAT” systems and iii) Potassium Silicate emulsion with “PARTICOAT” particles. Scratch tests and adhesion strength tests according to ASTM 4541, particle erosion tests, flame tests and the measurement of the electrical resistivity as well as of the break-down voltage were performed. The concept i) fulfilled all the requirements and yields electrical resistance in the range of GΩ. It was selected for in field testing.
Project Context and Objectives:
Objectives:
- To develop a new alternative for high temperature resistant coatings based on property tailoring by particle size processing of metallic source materials, resistant to oxidizing and corrosive environments and aggressive media integrating a wide spectrum of industrial applications (Month 48). - Achieved, basis for industrial exploitation provided
- To investigate the optimum source metal composition and particle size for achieving the coating structures suitable for the addressed application fields (Milestone M1). - Achieved
- To investigate the appropriate coating deposition procedures and heat treatment processes for the formation of the desired coating structure tailored for the addressed environment (Milestone M2). - Achieved
- To find the appropriate binders and achieve maximum adherence of the top coat on the substrate (Milestone M2). - Achieved
- To investigate the thermal barrier effect and corrosion protection performance as well as the potential for a high temperature lotus effect by adequate material and particle size selection under the targeted extreme environmental conditions (Milestone M3). - Thermal barrier effect and corrosion protection achieved, HT lotus effect not found but protection of YPZ TBC against CMAS is possible.
- To investigate the mechanical performance regarding the targeted applications (Milestone M3). Achieved
- To elaborate the approach for fire protection of composite materials in construction, including conversion of source metal particles to hollow spheres in a prior process, deposition and performance under fire conditions (Milestones M4 und M5). - Achieved
- To investigate a procedure for application of the coating as electrical insulator at elevated temperatures (Milestones M6 and M7). - Achieved
- Experimentation and modelling for an advanced understanding of the ageing and degradation mechanisms of the complete coating system (Month 45). - Achieved
- To explore and assess the potential and limitations of the new coating systems in the targeted application fields. Especially, upper temperature limits, corrosion resistance, mechanical tolerance and finally, a lifetime assessment (Milestone M8). - Achieved
Main scientific/technical achievements
The overall objective of the project was to develop a novel, unconventional and cost efficient type of multipurpose high temperature coating systems on the basis of property tailoring by particle size processing of metallic source materials. It shall possess multi-functionality that will comprise thermal barrier effect, oxidation and corrosion protection, anti-adhesion effect, electrical insulation at elevated temperatures and fire protection.
The concept of the novel approach to protection of surfaces is a coating consisting in its initial state of micro-scaled metal particles with a defined size range, deposited by spraying, brushing, dipping or sol-gel. During the heat treatment, the binder is expelled, bonding to the substrate surface is achieved, the metallic particles sinter and oxidize completely resulting in hollow oxide spheres that form a quasi-foam structured topcoat. Simultaneously, a diffusion layer is formed below the topcoat serving as a corrosion protection layer and as bond coat for the topcoat. The structure of the coating system is adjusted by parameters like selection of source metal/alloy, particle size, substrate, binder and a defined heat treatment.
The flexibility of the new coatings integrates a wide field of application areas, such as gas and steam turbines in electric power generation and aero-engines, combustion chambers, boilers, steam generators and super-heaters, waste incineration, fire protection of composite materials in construction as well as reactors in chemical and petrochemical industry. The project is divided into three sub-projects: 1) High temperature protection, 2) fire protection and 3) electrical insulation at high temperatures.
The main objectives in High temperature protection have been the development of coating designs, the production and characterization of the source particles, the research on appropriate coating manufacturing procedures, investigation on the performance of the new coatings and the understanding of the degradation mechanisms as well as life cycle assessment. For the Fire protection the objectives were coating design, coating deposition on composites, measurement of the thermal insulation effect and to study the fire protection performance. For the High temperature electrical insulation the appropriate coatings had to be designed, a suitable deposition processes had to be found and the performance and degradation mechanisms under application relevant conditions are being studied.
High temperature protection:
The austenitic steels AISI 321, 347 and 446, the nickel-based alloys IN738, CM247, René N5, PWA1483 and the model alloys Ni/Ni20Cr were selected as substrates for coating. Coating manufacturing procedures were developed for the selected substrates yielding homogeneous, stable and adherent top coats demonstrating the viability of the concept. Multi-size spherical Al particles in the range of 1-20 µm were found as mostly suitable for forming the coating structures according to the concept. In the case of the austenitic steels, additions of boron and silicon demonstrated a beneficial effect on the adhesion of the topcoat and on the sintering of the Al particles to each other. Water based binders such as PVA as well as organic binders e.g. PEG400 were successfully used. During the heat treatment, which may be performed in air or in argon, the Al particles oxidize to hollow alumina spheres and are sintered to each other and the diffusion zone is formed.
On both austenitic steels as well as on Ni-based alloys coatings were produced that withstand scratch tests subjected to 4 kg and showed adhesion strength up to 7 MPa. Experiments demonstrated that the topcoat effectuates as thermal barrier by gas phase insulation reducing the temperature up to 25% with a coating thickness of 170 µm. The coatings were subjected to application relevant temperatures under isothermal and cyclic conditions showing stability within the investigated times.
With producing a topcoat from hollow alumina spheres according to the PARTCIACOAT concept on thermal barrier coatings from yttria partially stabilized zirconia, a reduction of CMAS attack is achieved. Such a topcoat acts as a sacrificial coating yielding the Al for reaction of the CMAS to anorthite. The latter is crystalline and does not infiltrate the TBC.
Additionally to the PARTICOAT concept, special industrial applications were identified and appropriate coatings were designed using micro and nano sized source particles. In first experiments, these coatings show interesting potential under cyclic conditions compared to reference coating.
Fire protection:
Hollow alumina spheres were produced by oxidizing µm-Al particles on laboratory scale. Using these particles for an inner layer and implanting other µm-particles in an outer flame retardant layer two different coating structures were designed and produced. The coatings can easily be produced also at industrial level and a production procedure was designed.
Both coatings were tested against flame resistance and heat insulation. The temperatures as a function of time during flame exposure were determined on the flame and the back side by a specially developed experimental set-up using NIR spectroscopy for the temperature measurement. On flame subjection, both coating concepts keep the backside temperature of a 5 mm thick composite sample below 100°C for 60 min and have great potential for flame retardant and heat protection for composites.
High temperature electrical insulation:
Electrical conductors for high temperature heating elements, such as in metallurgy, are often from copper. Coatings using source different particles and procedures for their deposition were designed. Three approaches have been developed: i) Al particles with Si-O semi-polymer as bonding material, ii) Cu-Sn-A2O3 “PARTICOAT” systems and iii) Potassium Silicate emulsion with “PARTICOAT” particles. Scratch tests and adhesion strength tests according to ASTM 4541, particle erosion tests, flame tests and the measurement of the electrical resistivity as well as of the break-down voltage were performed. The concept i) fulfilled all the requirements and yields electrical resistance in the range of GΩ. It was selected for in field testing.
Conclusions
- PARTICOAT developed an innovative concept for thermal barrier coatings, where in one single thermal treatment step a combined bond coat / topcoat system is formed. This is achieved by the use of spherical nano- / micro-scale aluminium particles. They serve as a reservoir for the formation of the Al-rich bond coat and are converted into hollow alumina spheres by oxidation providing thermal barrier by gas phase insulation.
- Flame and heat protection was achieved by a coating keeping the backside temperature of a 5 mm thick composite sample below 100°C for 60 min of flame subjection.
- Electrical insulation at high temperatures can be achieved by the designed coatings.
- The results at the end of the project demonstrate the viability of the PARTICOAT concept.
Contribution to the State of the Art
High temperature protection
- Concept for low cost coatings offering oxidation protection at high temperatures and thermal barrier effect.
- Approach to surface protection of YSZ TBCs to reduce CMAS attack using the concept of micro-sized Al particle based coatings.
Fire protection
- Coating to protect composite materials for construction against fire – both heat and flames.
High temperature electrical insulation
- Coating with electrical insulation properties at high temperatures to protect electrolytic copper conductors in metallurgy against spark damage at high temperatures.
Project Results:
See attached file.
Potential Impact:
Outcome from Sub-Project 1: Novel cost efficient and easy to apply high temperature coatings for Ni- and Fe-based alloys. Application areas: Siemens identified potential areas of interest for PARTICOAT: (i) auxiliary pipes and burner hub in the pre-combustion area, where Fe-based materials are attacked by H2S and (ii) hot gas area with need to get better protection against SO2 attack. WIP Prague identified the thermocouple tubing as one of the areas of interest for PARTICOAT in a waste incineration plant.
Impact from Sub-Project 1: Coatings according to the PARTICOAT concept would yield to a significant cost reduction in regard to state-of-the-art coatings and would provide the socio-economic impact described in detail in the Description of Work.
Outcome from Sub-Project 2: Heat and flame resistant coating for composite materials. Application: construction of buildings.
Impact from Sub-Project 2: Acciona is evaluating the potential of the proposed coating for application in buildings. This would enable the construction industry to use composites in buildings yielding all the impact described in detail in the DoW.
Outcome from Sub-Project 3: Flame resistant coating for electrical insulation of copper. Application: High voltage electrical conductors in nickel metallurgy.
Impact from Sub-Project 3: LARCO is performing in field testing for evaluation of the coating’s performance under practice relevant condition. A successful application is expected to bring all the socio-economic impact described in the DoW.
Important milestones to achieve the impact described in section 3 of the Description of Work were accomplished. A mechanically stable and adherent topcoat from hollow alumina spheres providing good thermal barrier effect is available for austenitic and Ni-based alloys and suitable coatings for both fire protection as well as for electrical insulation at high temperatures were found.
For dissemination, results from the project were reported to the scientific community on several scientific conferences and selected results were published in scientific journals, according to the consortium agreement, see core report. Young scientists were involved in the project at all five research organisations thus contributing to increasing S&T attractiveness to young people and to a high level education in Europe.
List of Websites:
www.particoat.eu
