Microsilica or Silica Fume, is amorphism dusty Silicon Dioxide. When melting the Ferrosilicon Or the industrial Silicon, the Silicon steam is expelled from the flue and is oxidized and become Silicon Dioxide then it is collected by special equipment. The average size of Microsilica is Between 0.1-015um, which is smaller than 1% of cement's radius. Its B.E.T Fineness is 15-27m2/g.