Monotectic crystallization of melts in the ZrO2-Al2O3 system

The morphology of the crystalline phases prepared at different cooling rates, temperatures, and compositions of melts in the ZrO2-Al2O3 system is investigated. It is established that both the quenched and slowly crystallized samples containing 35-70 wt % ZrO2 have a submicron structure. Outside this concentration range, the ingots have a zonal structure: the peripheral region is formed by large baddeleyite crystals (at a ZrO2 content higher than 70 wt %) or corundum crystals (at a ZrO2 content lower than 30 wt %). This character of the crystallization confirms the presence of the phase separation (liquid immiscibility) region in melts of this system. A variant is proposed for the phase diagram of the system under investigation.