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High temperature reactions within SiC–Al2O3 composites

Published online by Cambridge University Press:  31 January 2011

Ahmed Gadalla*
Affiliation:
Chemical Engineering Department, Texas A&M University, College Station, Texas 77843-3122
Mohamed Elmasry*
Affiliation:
Chemical Engineering Department, Texas A&M University, College Station, Texas 77843-3122
Paisan Kongkachuichay
Affiliation:
Chemical Engineering Department, Texas A&M University, College Station, Texas 77843-3122
*
a)Author to whom correspondence should be addressed.
b)Now with Nuclear Energy Organization, Cairo, Egypt.
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Abstract

Composites of SiC–Al2O3 and SiC–mullite are unstable at high temperatures. The reactions occurring within the composites between 1700 and 1850 °C in stagnant inert atmospheres were characterized. Gaseous products cause excessive weight losses which cannot be attributed to passive oxidation. These losses can be successfully retarded by processing under high pressures. Compatible phases were determined by x-ray analysis for mixtures lying in the section SiC–Al4C3−Al2O3−SiO2. The reactions produced condensed phases of Al2OC and Al4O4C as well as gaseous SiO and CO. The condensed phases have high vapor pressures above 1700 °C. The effect of these reactions on densification of composites by firing at different temperatures for various periods under different pressures was studied. Dense materials prepared under high pressures at 1825 °C were tested at 1700 °C under normal pressure in argon, where active oxidation is expected, and weight losses were insignificant.

Type
Articles
Copyright
Copyright © Materials Research Society 1992

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