EFFECT OF STRUCTURE AND MINERALOGICAL FEATURES
OF SILICA RAW MATERIAL ON PHASE CHANGES DURING HEATING
T. V. Vakalova,
V. M. Pogrebenkov,
and N. P. Shlayeva
Translated from Novye Ogneupory, No. 1, pp. 18 – 22, January 2009.
Original article submitted March 10, 2008.
It is established that the sequence and intensity of polymorphic transformations of silica raw material on heat
ing in the range 1000 – 1200°C are explained by features of its chemical and phase composition. Differences
in structure and phase changes determine the different degree of activity for this raw material during synthesis
of silicate compounds.
Keywords: wollastonite, solid-phase synthesis, natural and technogenic silica raw material, phase formation,
polymorphic transformations, reaction activity.
The main tendencies of contemporary development of
science and technology suggest the use of ceramic materials
with a high level of functional properties. Of particular im-
portance are calcium silicate ceramics with a wollastonite
crystalline phase due to its good mechanical properties, low
thermal conductivity, high heat resistance, etc. The ceramics
may be used in nonferrous metallurgy, mainly for preparing
primary aluminum, in special radio ceramic technology,
glazed pottery, porcelain, building and heat insulation ceram
ics, sanitary objects, etc.
Synthesis of wollastonite and its use in ceramic technol
ogy in recent years has received considerable attention. The
known synthesis methods are very varied: hydrothermal syn
thesis, solid-phase reaction in the presence of a liquid phase,
crystallization from a melt, dehydration of hydrosilicates,
etc. Of particular scientific and practical interest is
solid-phase synthesis of wollastonite by ceramic technology
from a mixture of silica and lime raw materials of natural and
technogenic occurrence. It is well known that the rate of in
tensity of reaction in the solid phase depends on numerous
factors, of which the main ones are the condition (degree of
perfection) of the crystal lattice of mixture components, sur
face defects of reagent grains, fineness of the components, etc.
In nature and in commercial products silica raw material
is encountered both in amorphic and crystalline states, which
undoubtedly affects its activity during synthesis of
wollastonite and other silicate materials. In addition, the
most widespread quartz sands and vein quartz are known and
other forms of natural silica-containing material, in particular
tripolite, i.e. a soft porous rock composed of very fine
(0.005 – 0.020 mm) weakly-bonded grains of amorphous sil-
ica (opal) of volcanic occurrence; diatomite (kieselgur, rock
flour), i.e. light, porous, weakly-cemented sedimentary rock
formed from the residues of microscopic radiolaria; opoka, a
light porous, but distinguished from diatomite and tripolite,
densely-cemented silica rock formed by opal microspherulite
material; marshallite (powdery or dusty quartz), i.e.
finely-dispersed loose weakly-compacted sedimentary rock
consisting mainly of grains of powdery quartz and some
times with a mixture of chalcedony.
In this work as a silica raw material for synthesizing
wollastonite natural rocks have been studied in the form of
diatomite and opoka of the Inzensk deposit (Ul’yanovsk re
gion), marshallite of the Elbashevsk deposit (Novosibirsk re
gion) and also commercial products, i.e. analytical grade an
hydrous silicic acid and microsilica that is a waste product of
crystalline silicon and ferrosilicon of the Novekuznetsk
According to electron microscope data opoka is com
posed of isometric particles with a size of 0.8 – 1.5 mm; ag
gregates with sizes up to 10 – 15 mm (Fig. 1) are encoun
tered. For diatomite at the macrolevel there is presence
mainly of unbroken cladding and folds of diatomite algae,
and also radiolaria and spicules of sponges with a size from
10 to 20 mm (Fig. 2). As far as marshallite is concerned, then
is composed of powdery angular, unrounded quartz grains
with a size from 1 – 3 to 10 – 15 mm (Fig. 3). The macro
Refractories and Industrial Ceramics Vol. 50, No. 1, 2009
1083-4877/09/5001-0017 © 2009 Springer Science+Business Media, Inc.
Tomsk Polytechnic University, Tomsk, Russia.