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EC number: 215-710-8
CAS number: 1344-95-2
The surface of silica may be
covered by a partial hydrolysed gel layer when in contact with water (p.
4389). This layer is in equilibrium with the outer aqueous phase and
constitutes a diffusion barrier for ions and water.
It is known and generally
recognised that proton and hydroxide ion promoted dissolution plays a
more prevailing role in the dissolution process than a simple hydrolysis
of siloxane bridges (p. 4390).
The experimental part showed that
there was a distinct pH dependence in the rate of dissolution,
increasing with the pH increasing. However, the free dissolved SiO2
reached a maximum independent of the pH (Report, Table 1, Fig.. 4). It
is concluded that the total amount of silica dissolved is relatively
constant in a broad range of pH (1.1 < pH < 8.9) (p. 4393).
The level of maximum solubility
was about 2.7 mmol SiO2/L (here: Monosphere, see also 4.8 Water
The degree of hydrolysis that may
be involved in the dissolution process could not yet be solved.
It is not possible to quantify the very limited hydrolysis involved in
the dissolution of silicates in water.
Based on the results of the study performed with silicon dioxide, it can
be stated that although ion exchange processes are possible, depending
on the surrounding environment, the degree of hydrolysis involved in the
dissolution of silicates in water is very limited and not quantifiable.
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