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Reaction between niobium and silicon carbide at 1373 K

Published online by Cambridge University Press:  31 January 2011

D. L. Yaney  and
A. Joshi
D. L. Yaney
Affiliation:
Lockheed Missiles and Space Company, Inc., Research and Development Division, O/93-10, B/204, 3251 Hanover Street, Palo Alto, California 94304
A. Joshi
Affiliation:
Lockheed Missiles and Space Company, Inc., Research and Development Division, O/93-10, B/204, 3251 Hanover Street, Palo Alto, California 94304
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Abstract

The reaction zone formed between niobium and silicon carbide during heating for 4 h at 1373 K was examined by transmission electron microscopy (TEM) and Auger electron spectroscopy (AES). The typical reaction layer sequence is SiC/Nb5Si4C/Nb5Si3/Nb2C/NbO/Nb. However, in one area of the specimen, the first reaction layer was NbC rather than Nb5Si4C. The high oxygen and carbon concentrations near the outer surface were shown by AES depth profiling to result from carbon and oxygen contamination from the vacuum system during annealing. In order to determine if the observed reaction layer sequence is consistent with conditions of local thermodynamic equilibrium, the quaternary Nb–Si–C–O phase diagram was calculated from available thermodynamic data. A minimum (most negative) free energy of formation for the ternary compound Nb5Si4C of −582 kJ/mole was estimated assuming that the equilibrium between NbSi2 and SiC observed experimentally at 1573 K1 also exists at 1373 K. Except for the region immediately adjacent to the substrate, the observed reaction layer sequence was in agreement with the calculated quaternary phase diagram. However, it was noted that agreement with the quaternary phase diagram would be obtained if a thin layer of either SiO2 or NbC were present at the substrate surface.

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Articles
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Journal of Materials Research , Volume 5 , Issue 10 , October 1990 , pp. 2197 - 2208
Copyright
Copyright © Materials Research Society 1990

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