Zg. Zhou et Gc. Stangle, KINETICS OF A NONCATALYTIC GAS-SOLID CHEMICAL-REACTION UNDER SHS-LIKECONDITIONS, Journal of Materials Science, 30(12), 1995, pp. 3256-3264
Nitration of metallic tantalum under self-propagating high-temperature
synthesis (SHS) conditions (i.e. rapid heating rates 2000-3000 K s(-1
), and short heating periods 2-100 s) has been studied. Phase analysis
and microstructural characterization have been performed. A two-phase
mixture region of solid solution TaNx and tantalum subnitride, namely
Ta2N, was observed in the nitrided tantalum at temperatures of 1600-2
600 K and a pa rtial nitrogen pressure of 0.1-0.8 MPa. It was also fou
nd that tantalum subnitride phase formed before the formation of Ta-N
solid solution throughout the sample during nitration. A theoretical s
tudy was conducted in order to determine the intrinsic reaction kineti
cs of a typical combustion synthesis reaction. A new model was develop
ed to explain all experimental observations. The computer simulation r
esults are in good agreement with experimental data. The results indic
ate that at sufficiently large heating rates the product layer does no
t necessarily act as a diffusion barrier that prevents further uptake
of nitrogen. The results are helpful in developing an understanding of
the mechanism of powder-based SHS.