On the basis of establishing the control model of fine particle size, effectively controls and optimizes the particle size distribution. Meanwhile it makes phase change and surface modification to own small crystal grain size and crystal-like, spherical-like properties.   Activated calcined alumina is the national project achievement and has passed the national technical appraisal. It uses a unique process and possesses the characteristics of high activity, small grains and high conversion rate. It is the main raw material for the high quality refractory products, as well as fine ceramics and polishing products.