PHASE-RELATIONS OF A SILICIDE SILICA REACTION COUPLE AT 2273 K/

The phase relations of a zirconium silicide/silica reaction couple hav e been investigated at 2273 K in air. After annealing times from 4 to 49 hours, the reaction couples, created by encapsulating zirconium dis ilicide in a quartz ampule, developed an interdiffusion zone and an in ner core consisting of solidified zirconium silicide. The interdiffusi on zone consisted of a silica layer, zirconia precipitates, and prior liquid silicide globules dispersed in prior liquid silica. Zirconia pr ecipitates formed from the oxidation of the silicide melt between the protective silica layer and the two liquid regions of silicide and sil ica, as a result of oxygen diffusion. At 2273 K, the inner core consis ted of liquid zirconium silicide (ZrSi)(l), although the microstructur e analysis indicated formation of proeutectic ZrSi2 and a eutectic mic rostructure of ZrSi2 and Si upon solidification. A constant oxygen pot ential developed within the interdiffusion zone and protected the sili cide from oxidation even after 49 hours at temperature.