Chemistry Reference
In-Depth Information
The solubility of silica tends to increase with increasing temperature and pres-
sure. Increasing pressure on the solution increases the concentration of water molecules
around and thus increases the amount of time that water molecules are in the
most stable configuration.
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At silica concentrations less than 2mM, the stable form is
the monomer, whereas at dissolved silica concentrations greater than about 2 mM, poly-
mers of dissolved silica become important.
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The presence of other dissolved constituents can affect silica solubilities. Some
solutes react with to form complexes and others interact with water molecules
to change the hydration energy of It has been reported that the affinity of
various ionic species in solutions for reaction with decreases in the order:
The solubility is also a function of radius
of curvature of the surface described as follows:
where
B
is a geometric factor, the surface free energy,
V
the volume of the solid,
C
the solubility of curved surface, the bulk solubility,
R
the gas constant, and
T
the
temperature. As shown in Fig. 2.6, the solubility of convex surfaces (positive radius of
curvature) increases with decreasing particle size so that for radii less than
particles have an increased solubility. On the other hand, the solubility at concave sur-
faces (negative radius of curvature) decreases with decreasing radius of curvature,
the
which causes silica to precipitate at the tips of cracks.
In HF solutions,
dissolves by forming highly stable complex fluorosilicates
according to
