Reactions and Phase Relations of the System Si₃N₄-SiC-ZrC-ZrN at 1650°C under 1atm N₂

Abstract

Reactions among Si₃N₄, SiC, ZrC, ZrN and C were investigated under 1 atm N₂ at 1650°C. Compatibility relations among the compounds coexisting with 1 atm N₂ in the system Si-Zr-C-N were determined. Equilibrium states were confirmed by the fact that reaction products obtained from nitridation reactions were identical with those from decomposition of nitrides and by thermochemical calculation. The reaction products obtained from the starting sample of ZrC-Si₃N₄ were zirconium carbonitride and SiC, and those from ZrN-SiC were zirconium carbonitride and Si₃N₄. The lattice parameter of the zirconium carbonitride varied with the composition of the starting sample. The isobaric and isothermal section of the system Si-Zr-C-N includes 2 three-phase triangles: the area [I] ZrC_xN_1-x (x=0.43)+C+SiC, the area [III] ZrC_yN_1-y (y=0.32)+SiC+Si₃N₄ and 2 two-phase regions: the area [II] ZrC_1-bN_b (0.32<1-b<0.43)+SiC, the area [IV] ZrC_cN_1-c (0≤c<0.32)+Si₃N₄. On the assumption that zirconium carbonitride might be a regular solution between ZrC and ZrN, the interaction parameter of zirconium carbonitride was estimated to be -6--10kcal/mol from thermochemical calculation.