Precipitated silica is a silica (SiO2) produced by precipitation from a solution containing silicate salts. In 1999, more than 1M tons/y were produced, mainly for use in tires and shoe soles.
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Production
The production of precipitated silica starts with the reaction of an alkaline silicate solution with a mineral acid. Sulfuric acid and sodium silicate solutions are added simultaneously with agitation to water. Precipitation is carried out under alkaline conditions. The choice of agitation, duration of precipitation, the addition rate of reactants, their temperature and concentration, and pH can vary the properties of the silica. The formation of a gel stage is avoided by stirring at elevated temperatures. The resulting white precipitate is filtered, washed and dried in the manufacturing process.
Na2(SiO2)7 + H2SO4 + O → 7 SiO2 + Na2SO4 + H2O Na2SiO3 + H2SO4 → SiO2 + Na2SO4 + H2OProperties
The particles are porous. Primary particles with a diameter of 5 - 100 nm, and specific surface area 5-100 m2/g. Agglomerate size is 1 - 40 µm with average pore size is > 30 nm. Density: 1.9 - 2.1 g/cm3.