Phase relations of a silicide/silica reaction couple at 2273 K

Abstract

The phase relations of a zirconium silicide/silica reaction couple have been investigated at 2273 K in air. After annealing times from 4 to 49 hours, the reaction couples, created by encapsulating zirconium disilicide in a quartz ampule, developed an interdiffusion zone and an inner core consisting of solidified zirconium silicide. The interdiffusion zone consisted of a silica layer, zirconia precipitates, and prior liquid silicide globules dispersed in prior liquid silica. Zirconia precipitates formed from the oxidation of the silicide melt between the protective silica layer and the two liquid regions of silicide and silica, as a result of oxygen diffusion. At 2273 K, the inner core consisted of liquid zirconium silicide (ZrSi)L, although the microstructure analysis indicated formation of proeutectic ZrSi2 and a eutectic microstructure of ZrSi2 and Si upon solidification. A constant oxygen potential developed within the interdiffusion zone and protected the silicide from oxidation even after 49 hours at temperature.