Microsilica condensed silica fume

A comparative study of microsilicas from 18 sources showed considerable variation in composition and properties, one of those examined containing as little as 23% of SiOj and having a specific surface area of only 7.5 m g (A21). The same study showed that in most of the samples the diffuse XRD peak from the glass accounted for 98-99.5% of the total diffracted intensity and that it peaked at the value of 0.405 nm characteristic of vitreous silica. The commonest crystalline impurities detected were KCl, quartz, metallic iron and iron silicide, and pozzolanic reactivity was found to depend more on the chemical composition and nature of impurities than on the fineness or SiOj content. A surface layer of carbon, if present, greatly decreased reactivity. 

Viewed as a mineral addition in concrete, microsilica is characterized by its small particle size and high pozzolanic activity. In the absence of a water- 

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Microsilica, also called silica fume or condensed siiica fume, is a by-product in the production of silicon metal, ferrosilicone, and some other silicone alloys in a submerged-arc electric furnace. Here it condenses from the gaseous phase in the form of very small spherical particles with a mean diameter in the range 0.1-0.2 pm and with a specific surface area between about 10 and 20 m /g (BET). 

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