Russian Journal of Applied Chemistry, 2009, Vol. 82, No. 5, pp. 832−835.
Pleiades Publishing, Ltd., 2009.
Original Russian Text
N.A. Shabanova, M.N. Sergeeva, 2009, published in Zhurnal Prikladnoi Khimii, 2009, Vol. 82, No. 5, pp. 778−781.
OF SYSTEMS AND PROCESSES
Over many decades silica hydrosols have aroused
an ever-growing interest, which became especially
pronounced in recent years owing to the development
of sol-gel synthesis of materials used for various
purposes. The sol-gel technology is the most suitable
for silica-based materials. Readily accessible precursors
of nanotechnology are solutions of alkali metal silicates
and sols. Synthesis of silica sols from sodium silicate
solutions is well known . The processes proceeding
in silica hydrosols in the presence of alkali metal
hydroxides to form aqueous polysilicates or silicates
have been studied to a lesser extent. Aging of silica in
aqueous solutions at рН > 9, consisting in its intense
dissolution and formation of singly charged anions
and a reverse order of the alkali metal cations
with respect to the sorption ability of silica gel at high
pH values are well known [2, 3].
Subject under discussion is maximum on the zeta-
potential vs. pH dependence , including that at small
ionic strength (0.3 mmol l
KCl), and the shift of the
isoelectric point (IEP) toward pH 5.0 for various types of
silica, caused by speciﬁ c effect of Cs
, or K
[5, 6]. These ﬁ ndings show that the Cs
, and K
are adsorbed non-speciﬁ cally (non-electrostatically).
Among theories explaining a specific effect of
cations on the amorphous silica properties, a concept
 postulating formation of a gel layer upon silica
depolymerization deserves a special attention [8, 9].
Virtually all aspects of the sol-gel technology of
silica-based materials are determined by silica reactivity.
Generalization of the above data suggests that interaction
of alkali metal hydroxides with amorphous silica particles
changes the structure of both a gel layer and a conjugate
aqueous solution. In particular, presence of the Si−O−Si
and Si−OH conjugated bonds affects kinetics of the
colloid-chemical processes at various stages of passage
of the sol to polysilicates or silicate solutions.
This study is concerned with the dissolution of
colloidal silica particles in strongly alkaline solutions of
lithium, sodium, and potassium hydroxides. The study
was performed with the means of colorimetric analysis.
Objects of study were silica hydrosols (Ludox AS-40
and Ludox HS-30) with the average particle size of 16
and 12 nm, respectively. The surface of sol particles was
charged negatively. Ludox AS-40 was stabilized with
ammonia; counterions in a double electric layer were
ammonium ions and a minor amount of sodium ions. As a
stabilizer of Ludox HS-30 served sodium hydroxide. The
sols were diluted to a concentration of 41.02 g l
tests. The study was performed at the molal ratio (modulus
O = 3, where M is alkali metal cation
, or Li
). Solutions of alkali metal hydroxides
(chemically pure grade) were introduced into the sol
upon agitation at a temperature of 298 K, which was
Regularities of the Change in Colloid-Chemical Properties
of Silica Hydrosols in the Presence of Alkali Metal Hydroxides
N. A. Shabanova and M. N. Sergeeva
Mendeleev Russian University of Chemical Engineering, Moscow, Russia
Received September 18, 2008
Abstract—The effect exerted by type of alkaline hydroxide additive on the change in turbidity and on the
formation of silica hydrosol spatial structures was studied. Silica depolymerization in an alkaline solution to form
active silicic acids was studied depending on the aging time of the system, size of sol particles, and the type of
alkaline hydroxide additive.