... silica fume is gray.Microsilica in refractory is a highly effective pozzolanic material, the functions of adding ... .0Al2O3,%≤1.01.01.5----Fe2O3,%≤1.01.02.0----CaO+MgO, %≤1.01.52.0----K2O+Na2O,%≤1.01.52.0----C, %≤1.02 ... .02.02.53.0NaOH, %≤1. ... 8.5Specific surface,m2/g%≥15Moisture, %≤1.02.02.53.03.0 Good quality of Microsilica SF90