| abstract |
Finely divided precipitated silica for use as a delustering agent with high structure and a -BET surface (DIN 66 132) of 150 to 350 m2/g -Stamping density (DIN 53 194) between 60 and 120 g/l -DBP absorption number between 3.0 and 4.0 ml/g -Particle size distribution at least 70% from 1 to - 6 mu m - can be prepared by heating a mixture of water and sodium silicate under agitation to a temperature of 70 DEG to 80 DEG C., adding concentrated sulfuric acid into this mixture until half of the alkali present has been neutralized, shearing the reaction mixture and optionally raising the temperature at the same time to 86 DEG +/-5 DEG C. Concentrated sulfuric acid is added after a period of 30 to 120 minutes at a rather high rate until the pH of the silica suspension produced is 3.0 to 3.5. The resulting silica suspension is ultimately filtered off by known filter devices, the silica filter cake washed free of sulfate, and a dry product is ultimately obtained. |