process for preparing a filler in finely dispersed calcium silicate

摘要

Finely divided calcium silicate having a molar ratio of SiO2: CaO of 1.2-3: 1 and a disturbed tobermorite-like structure (as defined) is made by mixing with intense stirring freshly precipitated hydrated calcium silicate having SiO2: CaO of 1: 1 and the above structure, with an aqueous solution of an alkali metal silicate and a calcium halide, hydrohalic acid or mixture thereof. The calcium silicate of 1: 1-SiO2: CaO ratio may be made from milk of lime, hydrochloric acid or calcium chloride, and water glass. Calcium chloride may be used in the form of spent lye containing sodium chloride from the Solvay soda process. The reactants may be added separately or simultaneously. The product mau be ground in a pin mill to form a voluminous filler. The invention also comprises a finely divided calcium silicate filler comprising leaf-shaped primary particles and also particles of spherical form showing the strongest 4-7 interferences of the tobermorite X-ray diagram, the molar ratio of SiO2: CaO being 1.2-3: 1, and having a specified surface area and sedimentation volume.