| 摘要 |
Precipitated silica which has a BET surface area of 10-130 m2/g, a CTAB surface area of 10-70 m2/g, an average particle diameter of 5-20 .mu.m, a Cu abrasion value in a 10% glycerol dispersion of 4-50 mg and thickening behavior in a CMC solution (20% dispersion) of 300-3500 mPa.s, is produced by this invention. The process comprises simultaneously adding alkali metal silicate (weight modulus SiO2:alkali metal oxide = 2.5-3.9:1) and a mineral acid to an initial amount of water which has been adjusted to a pH value of 7.0 to 9.9 or 10.0 to 10.7 by the addition of water glass (sodium silicate). The pH value is held constant between 7.0 to 9.9 or 10.0 to 10.7 during addition of the alkali metal silicate and mineral acid. The initial precipitation temperature is 50.degree.-90.degree. C. and an increase in viscosity occurs after at most 25% of the duration of precipitation. The pH value is adjusted to ~ 6, preferably 3.5, once a silica content of greater than 120 g/l or greater than 150 g/l, preferably ~ 160 g/l to 240 g/l, has been reached. The solid is separated by filtration, washed, dried and ground. The precipitated silica may be used as an abrasive and/or thickening component in toothpastes.
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