ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 5, pp. 909!911. + Pleiades Publishing, Ltd., 2008.
Original Russian Text + Ya.I. Vakhula, I.V. Lutsyuk, I.D. Borshchishin, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81, No. 5,
Effect of pH and Reagent Concentrations on Gelation
of Magnesium!Silicate Aqueous Systems
Ya. I. Vakhula, I. V. Lutsyuk, and I. D. Borshchishin
ka Politekhnika National University, Lviv, Ukraine
Received August 23, 2007
Abstract-The rate of gelation of the maghesium3silicate aqueous systems was studied in relation to pH
and concentration of particular magnesium salts. The magnesium and silicate ions were found to interact
in solutions at low temperature.
Forsterite ceramics are formed at low sintering
temperature (normally as low as 1400 oC) and are
widely used in various branches of modern engineer-
ing, primarily in electronic devices. To prepare
highly homogeneous ceramics, mechanical mixing of
the components is insufficient.
The sol3gel process is one of the most effective
modern techniques for preparing highly dispersed
powders. This technique allows preparation of
ultradispersed uniform multicomponent powders
suitable for preparing ceramics at reduced sintering
temperature, with controlled morphology and phase
composition of the product. These advantages are
reached owing to uniform distribution of ceramic
precursor throughout the system.
The significant contribution to study of sol3gel
processes involving the effect of particular com-
ponents of sol on the temperature of forsterite for-
mation was made by researchers of the Mendeleev
Russian University of Chemical Engineering [1, 2]. It
was found that, in the case of precursors based on
magnesium chloride, sulfate, citrate, and, particular-
ly, nitrate, the synthesis of forsterite is decelerated
and proceeds at lower temperature than for mag-
nesium acetate. The kind of the initial magnesium
salt and silicon-containing gelling agent considerably
affects the course of solid-phase reactions, size distri-
bution of crystals, their shape, and degree of dis-
persion of the forsterite powder.
In this study, the gelation rate in the system
O was examined in relation to par-
ticular magnesium salt and the initial ratio of com-
ponents. The physicochemical processes accompany-
ing the gelation were also analyzed.
The initial uniform sols were prepared by adding
tetraethoxysilane (TEOS) hydrolyzate (HCl) as gel-
ling agent to aqueous magnesium salt (chloride
O, acetate Mg(CH
O) or anhydrous MgSO
TEOS hydrolyzate is widely used for gelation of
metal-containing aqueous solutions . Apart from
TEOS, other gelling agents, e.g., white black or silica
sol, are used [1, 2]. However, we used TEOS to
compare our results with other published data on
The initial magnesium salt was dissolved in dis-
tilled water at room temperature. In all the experi-
ments the concentration of magnesium salt was 1 M.
Fifteen minutes after completion of the dissolu-
tion of the magnesium salt, pH of the mixture was
measured. Table 1 shows that, except for magnesi-
um acetate, the initial solutions were weakly acidic
or neutral (pH 5.837.6). The aqueous magnesium
acetate solution was weakly alkaline (pH 8.6).
The initial sols were prepared by adding TEOS
hydrolyzate to aqueous magnesium salt in a pre-
scribed ratio. This mixture was stirred and its pH
was measured. As seen from Table 1, in all the
systems pronounced acidification was observed. This
effect was expected, since pH of TEOS hydrolyzate
was approximately 2 by itself.
After addition of TEOS hydrolyzate, all the mix-