Microsilica or Silica Fume, is powdery dusty Silicon Dioxide. When melting the Ferrosilicon Or the industrial Silicon, the Silicon steam is expeled from the flue and is oxidized and become Silicon Dioxide then it is collected by special equipment. The average size of Microsilica is from 0.1 to 015μm, which is smaller than 1% of cement's radius. so many sellers on internet .we are compelled to give you better price .welcom to vist our company .after autoptical we must build good cooperate.if yu bnsy ,we can offer 500g sample for free ,pls feel free to contact us .thank you sir !