Appeal No. 95-2237
Application 08/067,308
1. A continuous process for the preparation of aqueous
alkaline silica sols which contain non-aggregated,
spherical Si0 particles with an average diameter of 27-72
2
nm, from an acidic fresh sol which contains 4-8% by
weight of Si0 in the form of particles having an average
2
particle diameter of about 2 nm at a pH value of 2-4 and
which has been prepared by mixing an alkali silicate
solution with a cation exchanger resin in the H-form,
this acidic fresh sol is added to a starting medium
containing an aqueous, alkaline, colloidal silica sol
solution having a pH value of >8, a Si0 content of 2-20%
2
by weight and an average particle size of 14-27 nm,
alkaline agents are added to this medium at temperatures
near the boiling point thereof in such quantities that
the pH value does not fall below 8 during the whole
process, and the addition of acidic fresh sol and
alkaline agents is continued until the particles have an
average diameter of 27-72 nm and the aqueous, alkaline
silica sols thus prepared are concentrated, characterised
(sic)in that
a) the acidic fresh sol is continuously
introduced into the reactors of a multi-stage
reaction cascade, in which the first stage
contains the starting medium and each successive
reactor of the cascade is supplied with overflow
from the preceding reactor, and the pH value in
the reactors must not fall below 8,
b) alkaline agents, preferably alkaline sodium
silicate solution, alkaline potassium silicate
solution, sodium hydroxide solution, potassium
hydroxide solution, are continuously introduced
into the first reactor or into the first
reactors in such a quantity that a pH value of 8
2
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Last modified: November 3, 2007