... ,thin wall,hollow,light weight. 2)Volume weighs is 250 - 450kg /m3,granularity diameter ... ball collected from coal powder,its coloure is light grey,thin wall,hollow,light weight.Volume weighs is 250----450kg /m3,granularity ... a good refractory insulation .It is widely used in the light castable production and oil wells.The chemical composition of the ...