| 摘要 |
The finely divided high-structure precipitated silica, which has a… BET surface area (DIN 60132) of between 150 and 350 m<2>/g… a compacted bulk density (DIN 53194) of between 60 and 120 g/l… a DBP number of between 3.0 and 4.0 ml/g… a particle size distribution of at least 70 % of 1 to 6 mu m. …<??>It can be prepared by heating a mixture of water and sodium silicate to a temperature of 70 to 80 DEG C with stirring, metering into this mixture concentrated sulphuric acid until half of the alkali present is neutralised, treating the reaction mixture by means of a shearing unit and, if desired, simultaneously increasing the temperature to 86 +/- 5 DEG C, adding concentrated sulphuric acid after a period of 30 to 120 minutes at a higher speed until the pH of the silica suspension formed is 3.0 to 3.5, diluting, if desired, the silica suspension with water, separating off, if desired, the coarse portion by means of a centrifugal pump and a hydrocyclone, filtering off the silica using a known filtering device, washing the silica filter cake free of sulphate, redispersing the silica filter cake with the addition of water and using a stirrer to give a suspension having a solids content of 80 +/- 10 g/l, adding to this suspension, if desired, alkyldimethylbenzylammonium chloride, spray drying the suspension thus obtained and, if desired, milling the dried product. …<??>The precipitated silica can be used as matting agents in paints either in uncoated or coated form. |
