Objective The aim of the work is to further develop amorphous protective layers based on SiO2 to improve their mechanical properties and increase the temperature at which the amorphous layer is stable, thereby enhancing its effectiveness as a diffusion carrier. It is planned to investigate plasma assisted chemical vapour deposition (PACVD), laser chemical vapour deposition (LCVD) and laser fusion methods for production of the coatings, and to develop coating systems containing an interlayer to reduce the incidence of solid/solid reactions between the ceramic coating and the substrate.It has been established that amorphous silica coatings deposited by plasma assisted chemical vapour deposition (PACVD) are excellent barriers to ingress of aggressive species at temperatures up to 450 C for 16000 hours and 750 C up to 8000 hours. Increased stability of these layers was achieved by incorporating a titanium nitride (TiN) interlayer to prevent solid/solid reactions between the silica and the substrate steel (Incoloy 800H and 2.25 chromium (Cr) ferritic and thereby maintain the amorphous nature of the silica layer. Silica coatings have been deposited by laser chemical vapour deposition (LCVD) and laser fusion. In the former case it has been demonstrated that the protective properties of the silica can be modified by deposition conditions, and in this way a strain tolerant coating has been produced. Laser fusion processes have been developed to allow independent control of powder and substrate temperature in a single laser beam so that substrate heating is minimised. Optimised coatings using the PACVD system have been produced on a gas turbine blade and a laser fusion coated boiler tuber is currently undergoing a trial in a power station boiler.Amorphous silica coatings, produced by plasma assisted chemical vapour deposition (PACVD), laser chemical vapour deposition (LCVD) and laser fusion, were deposited on various metallic materials and then exposed in air and simulated coal gasification atmospheres (CGA) for periods of up to 2 years at 450 C to 1000 C. In some case interlayers of titanium nitride and silicon were used to promote adhesion and to reduce interdiffusion between the coating and the substrate.The results indicate that PACVD silica deposited onto Incolog 800 H provided outstanding protection at 450 C. At 750 C, however, interaction with the substrate was observed which was reduced by the presence of a titanium nitride interlayer. Silica coatings would not adhere to the surface of 2.25 chromium steel in the absence of a titanium nitride interlayer. In contrast protection at 450 C in the CGA using the LCVD coatings was highly dependent upon coating density, the presence of interlayers and silica thickness in the range 0.35 to 3.5 um (adhesion of the silica layer to the substrates was good without the use of interlayers).Novel methods were developed for deposition of silica coatings by laser depostion in which overheating of the substrate was avoided by the use of inclined substrates. Coaxial feeding of the powder was also successfully used to minimize substrate heating.The industrial potential of the optimized coatings was evaluated for application in gas turbines, coal fired power plant, coal gasification systems and nuclear reactors.THE OBJECTIVE OF THE PROJECT IS TO DEVELOP IMPROVED COATINGS FOR SERVICE IN AGGRESSIVE ENVIRONMENTS AT HIGH TEMPERATURES. CURRENT PRACTICE IS TO USE ALLOYS OR METALLIC COATINGS THAT FORM PROTECTIVE OXIDE LAYERS OF POLYCRYSTALLINE CR2O3 OR AL2O3. THESE OXIDE LAYERS ARE REQUIRED TO BE GOOD DIFFUSION BARRIERS AND TO BE MECHANICALLY AND CHEMICALLY STABLE IN THE ENVIRONMENT. HOWEVER, SINCE GRAIN BOUNDARY DIFFUSION PROCESSES DOMINATE IN THE TECHNICALLY IMPORTANT TEMPERATURE RANGE UP TO 1000 C, THE POLYCRYSTALLINE NATURE OF THESE OXIDES GREATLY REDUCES THEIR EFFECTIVENESS AS DIFFUSION BARRIERS AND THEIR MECHANICAL STABILITY IS OFTEN POOR WHEN THERMAL CYCLES ARE IMPOSED, DUE TO THE LARGE DIFFERENCES IN EXPANSION COEFFICIENT RELATIVE TO THE SUBSTRATE. TO OVERCOME MANY OF THE DIFFICULTIES NOW ENCOUNTERED, IT IS INTENDED TO DEVELOP AMORPHOUS PROTECTIVE OXIDE LAYERS WITH MATCHING THERMAL EXPANSION COEFFICIENT IN THE OXIDE AND SUBSTRATE. THE RESEARCH PART OF THE STUDY WILL BE CARRIED OUT IN 3 PHASES : - COATING PRODUCTION USING PAVD, LCVD AND LASER FUSION TECHNIQUES. THE EFFECTS OF ADDITIVES TO EXTEND THE PROTECTION OF SILICA WILL BE INVESTIGATED IN THIS PHASE. - COATINGS EVALUATION INCLUDING LAYER CHARACTERISATION AND ADHESION AND THERMAL TESTS. - INDUSTRIAL TRIALS ON GAS TURBINES, DIESELS AND BOILER TUBING AS WELL AS HIGH PRESSURE AUTOCLAVES FOR NUCLEAR FUEL COMPONENTS. Fields of science natural scienceschemical sciencesinorganic chemistrytransition metalsengineering and technologyenvironmental engineeringenergy and fuelsfossil energycoalengineering and technologyother engineering and technologiesnuclear engineeringengineering and technologymaterials engineeringcoating and filmsnatural sciencesphysical sciencesopticslaser physics Programme(s) FP1-EURAM - Research programme (EEC) on materials (raw materials and advanced materials) - Advanced materials (EURAM) -, 1986-1989 Topic(s) Data not available Call for proposal Data not available Funding Scheme CSC - Cost-sharing contracts Coordinator National Physical Laboratory (NPL) EU contribution No data Address Queen's Road TW11 0LW Teddington United Kingdom See on map Total cost No data Participants (8) Sort alphabetically Sort by EU Contribution Expand all Collapse all BILLITON RESEARCH BV (SHELL) Netherlands EU contribution No data Address See on map Total cost No data CENTRO LASER DE NAVARRA Spain EU contribution No data Address See on map Total cost No data Harwell Laboratory United Kingdom EU contribution No data Address Harwell Didcot See on map Total cost No data IBERDUERO SA Spain EU contribution No data Address See on map Total cost No data National Power plc United Kingdom EU contribution No data Address See on map Total cost No data UNIVERSITY OF LISBON Portugal EU contribution No data Address LISBOA See on map Total cost No data UNIVERSITY OF LIVERPOOL United Kingdom EU contribution No data Address LIVERPOOL See on map Total cost No data UNIVERSITY OF VIGO (FORMERLY SANTIAGO) Spain EU contribution No data Address VIGO See on map Total cost No data
