GB783712A - Alkaline earth metal silicates - Google Patents

Abstract

<PICT:0783712/III/1> Alkaline earth metal silicates having a surface area of at least 89 m.2/g. and an average particle size of 300 or less are obtained by reacting solutions of an alkali metal silicate and an alkaline earth metal chloride under vigorous stirring with shearing stresses above 100 per second, by means of a stirring device arranged in a reaction vessel filled with an aqueous medium comprising the resultant alkaline earth metal silicate which is continually sucked into said device. The surface area is that of the ultimate particles determined by a specified method. The desired reaction conditions may be obtained in colloid mills and high-speed mixers, for example in a "Kotthoff" mill in which a rotor rotating at, e.g., 2800 r.p.m., imparts a high tangential velocity to the reaction material and a stator which preferably closely surrounds the rotor suddenly deflects it into a radial direction. Preferably one, or in the case of continuous processes both, reactants are fed to the central part of the stirrer. It is preferred to use sodium silicate in which the Na2O/SiO2 ratio is from 1/3 to 1/4, generally 1/3.3, in 0.1-0.7 molar concentration with respect to Na2O, and to produce the calcium silicate which corresponds approximately in formula (e.g. CaO(SiO2)3.3.nH2O) to the sodium silicate in a 0.05-0.4, preferably 0.2-0.3 molar concentration. A higher concentration of sodium silicate may, however, be used (e.g. 1.7 mols. Na2O per litre) provided the calcium chloride is diluted so that the precipitate will still flow. Increasing the ratio of sodium silicate to calcium chloride and increasing the Na2O/SiO2 ratio in the silicate, increases the particle size, and finest particles are obtained if the concentration of the reaction solutions are such as to produce a final mixture which is just flowable: 0.4 molar reactant solutions are suitable for discontinuous operation. Lower viscosities may be achieved by means of a sodium chloride-containing solution of calcium chloride. The examples describe both continuous and discontinuous processes using a Kotthoff mill, the calcium silicate being subsequently filtered, dried at 110 DEG or 120 DEG F. and ground in a high-speed pin-mill. In one case it has a particle size below 250 .