PROCESS FOR PREPARING FUMED SILICA DISPERSIONS

摘要

Process for preparing an aqueous dispersion of fumed silica having a pH of 9 to 11.5, the silica having a BET surface area of 30 to 400 m<SUP>2</SUP>/g and being present in the dispersion at 20% < 40% by weight, characterized in that - water is circulated and via a feed means, and with a rotor/stator machine running, fumed silica powder is introduced in an amount such as to result in a preliminary dispersion having a silica content of between 25% and 70% by weight, and, after all of the silica powder has been added, - the feed means is closed and, at a pH of 2 to 4 and a temperature of 10 to 50°C, shearing is carried out with a shear rate of 10 000 to 30 000 s<SUP>-1</SUP>, - dilution is carried out with water until the desired silica content is exceeded by 0.1% to 10%, and - subsequently, under the same shearing conditions, an aqueous base is added in an amount and concentration such that the amount needed to attain the desired solids content is reached and a pH of 9 to 11.5 results.