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The study was aimed at a better understanding of the corrosion behaviour of silicon nitride ceramics under environmental conditions relevant to the petrochemical and coal gasification industries. Experiments were carried out in air, H(2) and H(2)S-H(2) environments with variable amounts of H(2)O (up to 3 v/o) at temperatures between 900 and 1600 C for exposure periods up to 450 hours. Whilst in air, silicon nitride undergoes passive oxidation resulting in the formation of a silicate layer whose integrity depends on both the temperature and the composition of the material. In low oxygen potential environments, the corrosion of Si(3)N(4) involves the formation of volatile species which lead to rapid material losses. The rate of loss in turn depends critically on the water vapour pressure in the gas. The results can be understood by consulting a volatility diffusion map which takes mass transport phenomena as well as thermodynamic equilibria into account. Provided that the amount of water vapour is sufficiently high to form a SiO(2)-rich layer, the resulting material recession rates (0.2 - 0.4 mm/year at 1300 C) may be quite acceptable for many industrial applications.

Additional information

Bibliographic Reference: EUR 14571 EN (1992) 280 pp., FS, free of charge
Availability: Available from Joint Research Centre, Publication Department, I-21020 Ispra (Va.) (IT)
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