... 2) Hard materials: carborundum, brown corundum, superfine cement, zirconium sand, and fire-proof materials, etc.(3) High purity materials: ... quartz, feldspar, α-alumina, glass fine bead, etc.(4) Metal powders: zinc powder, aluminum powder, ... self-diffluent classifiers. And then the relatively coarse and fine powders will be separated. Qualified powders will be collected; ...