... - 450kg /m3,granularity diameter is about 1 mm , Hollow glass micropheres is a hollow ball collected from coal powder,its coloure is ... light grey,thin wall,hollow,light weight.Volume weighs is 250----450kg /m3,granularity ... castable production and oil wells.The chemical composition of the hollow galss microsphaeres mainly contains SiO2 and Al2O3, with fine particles ...