Effects of Chlorine and Alkali Chlorides on Corrosion of Silicon Carbide BasedCeramics in Combustion Environments. Topical Report, June 1, 1987-May 31, 1992

摘要

High temperature corrosion of SiC based ceramics in oxidizing gas mixturescontaining chlorine and chloride compounds has been characterized. SiC based ceramics can be subject to rapid active oxidation in gases where the ratio of chlorine to oxygen is greater than one. A passive film will form at sufficiently high temperatures or oxygen contents. The conditions under which a passive film forms are affected by the sintering aids used in the manufacture of the ceramic. Silicon nitride is resistant to this type of attack, but the silicon nitride in nitride bonded SiC does not protect the SiC grains in this material. At temperatures above 1200 deg. C, oxidation of SiC can be accelerated by penetration of chlorine containing environments, the alkali produces the attack by fluxing the silica film to liquid alkali silicate. This type of attack is accelerated by water vapor and inhibited by HC1 or chlorine.