| 摘要 |
Granules based on silicon dioxide and having the properties : Average grain size: 10 to 120 Vm BET surface area: 40 to 400 m^2/g Pore volume: 0. 5 to 2.5 ml/g Pore size distribution: less than 5 % of the total pore volume exists of pores with a diameter < 5 nm, rest meso-and macropores pH value: 3.6 to 8.5 Tapped density: 220 to 700 g/1 They are prepared by dispersing silicon dioxide in water, spray drying, optionally heating and/or silanising. Whereas a pyrogenic silicon dioxide powder with a BET surface area of 30 to 90 m^2/g, a DBP index of 80 or less, a mean aggregate area of less than 25000 nm^2 and a mean aggregate circumference of less than 1000 nm, wherein at least 70% of the aggregates have a circumference of less than 1300 nm or a high-purity pyrogenically prepared silicon dioxide having metal contents of less than 0.2 Vg/g is prepared by reacting a silicon tetrachloride having a metal content of less than 30 ppb by means of flame hydrolysis is used. |
