The single hot thermocouple technique (SHTT) and image analysis program were applied to study synthetic slag's crystallization behaviors under different temperatures and cooling rates. In order to get crystallization mechanism

the crystallization kinetics parameters in isothermal process were calculated. Crystalline phases also were predicted by FactSage. In isothermal process

as temperature decreases

crystallization time decreases at first and increases later

and the crystals get smaller. At the same time

crystallization proportion increases at first

keeps stable later and decreases finally. There is saltation of crystallization proportion because of different crystalline phases at different temperature ranges. With increase of cooling rates

initial crystallization temperature declines and crystal turn from bulks to grains. Crystallization proportion remains unchanged

then decreases. Several stable areas of crystallization proportion appear owing to different crystalline phases under changing cooling rates. There is no crystal when cooling rate is large enough

and slag is totally solidified in glassy state. The heat curve of slag's crystallization measured by DSC fits well with the result of SHTT.