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In situ formation of MoSi2–SiC through reaction of SiO2 or Si3N4 with Mo and carbon

Published online by Cambridge University Press:  31 January 2011

R. V. Krishnarao
Affiliation:
Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad-500058, India
V. V. Ramarao
Affiliation:
Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad-500058, India
Y. R. Mahajan
Affiliation:
Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad-500058, India
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Abstract

Composite powders of molybdenum silicide–SiC were synthesized by reacting mixtures of (Mo–SiO2 –C), (Mo–Si3N4 –C), and (Mo–SiO2 –Si3N4 –C) powders at 1300 °C. In the (Mo–SiO2 –C) system Mo5Si3 and Mo3Si formed predominantly. MoSi2 formed the major constituent of the reaction product from powder mixtures containing Si3N4. Vapor-solid SiC whiskers formed in the (Mo–SiO2 –C) system. Vapor-liquid-solid whiskers of SiC and Mo5Si3C formed in (Mo–SiO2 –Si3N4–C) and (Mo–Si3N4 –C) systems, respectively. The mechanism of formation of the VLS whiskers and molybdenum silicides was identified as follows: initially a thin layer of Mo2C forms on Mo particle; the Si vapor from thermal decomposition of Si3N4 deposits on the Mo2C surface and forms a droplet of ternary “Nowotny phase” Mo<5Si3C<1; an SiC/Mo5Si3C whisker forms by nucleation and growth from the supersaturated ternary phase; after reaction with the Mo2C layer, the SiO/Si vapor further reacts with Mo particle to form bulk silicides.

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Articles
Copyright
Copyright © Materials Research Society 1997

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