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Nucleation and Growth of MoSi2 Pest During Low Temperature Oxidation

Published online by Cambridge University Press:  01 January 1992

T. C. Chou  and
T. G. Nieh
T. C. Chou
Affiliation:
Lockheed Research and Development Division, O/93-60, B/204, Palo Alto, CA 94304
T. G. Nieh
Affiliation:
Lawrence Livermore National Laboratory, L-350, P. O. Box 808, Livermore, CA 94550
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Abstract

The phenomenon of “MoSi2 pest” has been studied in detail by low temperature oxidation of various polycrystalline MoSi2 monoliths and composites. Single crystalline samples were studied to address the nucleation and growth of pest reaction. Pest of MoSi2 was observed to occur at temperatures between 375 and 500°C. Samples after pest reactions yielded to powdery reaction products of MoO3 whiskers, SiO2 clusters, and residual MoSi2 particles. Although all the samples showed complete disintegration after sufficient oxidation durations were rendered, the kinetics of pest disintegration varied among different samples. By performing interrupted oxidation tests, pest reaction was found to consist of nucleation and growth stages, with the former stage acung as the rate-limiting step. Furthermore, the nucleation of pest reaction was found to be closely related to the formation of MoO3, which was preferentially formed at such defect sites as intergranular boundaries and cracks. Mechanisms leading to the pest disintegration of MoSi2 are discussed in light of the nucleation and growth of pest reaction.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 288: Symposium L – High-Temperature Ordered Intermetallic Alloys V , 1992 , 965
Copyright
Copyright © Materials Research Society 1995

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