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High‐Temperature Mixed Oxidation of Nitride‐Bonded Silicon Carbide in Oxidizing Gas Mixtures Containing 2% Cl 2
Author(s) -
Park Chan,
McNallan Michael J.
Publication year - 1995
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1995.tb08415.x
Subject(s) - oxidizing agent , silicon carbide , materials science , silicon nitride , nitride , chlorine , chemical engineering , ceramic , carbide , silicon , layer (electronics) , ceramic matrix composite , atmospheric temperature range , inorganic chemistry , metallurgy , composite material , chemistry , organic chemistry , engineering , physics , meteorology
Nitride‐bonded silicon carbide ceramics have lower processing costs than many other SiC‐based ceramics and adequate properties for use as high‐temperature heat exchangers in oxidizing environments. Silicon nitride has much better resistance to attack by chlorine at temperatures above 900°C than silicon carbide. When nitride‐bonded silicon carbide ceramics are exposed to gas mixtures containing 2% Cl 2 and small amounts of oxygen in this temperature range, the SiC is selectively chlorinated, leaving behind a porous matrix of silicon nitride. The rate of corrosion is controlled by a combination of interfacial kinetics at the surfaces of the SiC grains and transport of volatile species through the silicon nitride skeleton. In more oxidizing environments, the rate of chlorination is suppressed by the formation of a protective SiO 2 film. In highly oxidizing environments at temperatures in excess of 1200°C, the formation of volatile chloride reaction products at the interface between the SiC and the passivating SiO 2 layer causes bubbles to form in the SiO 2 , which accelerates the oxidation.