Community Research and Development Information Service - CORDIS

Amorphous silica coatings on metallic materials

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.

Reported by

National Physical Laboratory (NPL)
Queen's Road
TW11 0LW Teddington
United Kingdom
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