Microsilica, also known as silica fume, condensed silica powder, is a mineral composed of highly purified ultra-fine amorphous spheres of silicon dioxide (SiO2). It is collected by environmental protection equipment from the flue gas during the smelting of silicon or ferrosilicon.
Microsilica is a very ultrafine powder with amorphous SiO2 as main components. Its average diameter is about 0.10～0.20μm and the specific surface area is about 1 5～2 7 m²/g. It is about 80～100 times smaller than cement and 50~70 times smaller than fly-ash in fineness and specific surface area, with good pozzolanic effect. Since the silica fume is made by combustion of silicon tetrachloride in the hydrogen-oxygen flame, it has smooth spherical shape and 85％～95％ of it are active glassy state SiO2.
Silica fume is characterized by fine particles, high activity, big specific surface area, and great pozzolanic and particle filling effect. Thus it has become an indispensable additive in high-performance and high strength concrete and been widely applied to railways, bridges, tunnels, hydropower stations, oil wells, offshore platforms, and amorphous refractories, etc. By combining silica fume with other materials, it will turn into new composite materials with special performance which can be utilized in special fields.
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