SCIENTIFIC RESEARCH AND DEVELOPMENTS
A PHYSICOCHEMICAL STUDY OF PROPERTIES
OF INTEGRATED HIGH-TEMPERATURE HEAT-INSULATING MATERIALS
S. A. Suvorov
and V. V. Skurikhin
Translated from Novye Ogneupory, No. 2, pp. 18 – 24, February, 2004.
Results of a study of properties of integrated high-temperature heat-insulating materials based on expanded
vermiculite are reported. These materials combining low heat conductivity and high strength, have a potential
for use as lining refractories in thermal power units with operating temperatures not exceeding 1100°C.
Introduction of a porous filler into a material is a method
widely used in industry for achieving a porous structure in
the material. The expanded vermiculite exhibits a range of
unique properties such as a low bulk density (80 –
), low heat conductivity (0.04 – 0.12 W/(m × K)),
and relatively high melting point (1240 – 1430°C); further-
more, it is chemically inert, durable, and environmentally
safe . All these properties show that the expanded vermicu-
lite can be a promising candidate for use as the porous filler
for fabrication of high-temperature heat-insulating materials.
Heat-insulating vermiculite-based products are com
posed of an expanded vermiculite (porous filler), a refractory
clay, possibly containing additives (the bond), and a
nonplastic refractory material — chamotte, dust collected in
electric filters (refractory filler). At the Borovichi Refractory
Kombinat (BRK) JSC, the so-called integrated high-temper
ature heat-insulating materials (ITOM-grade) based on the
above vermiculite-based formulation have been developed
[2, 3]. Each of the ITOM ingredients was selected for a spe
cialized function: disperse refractory fillers jointly with a
plastic mineral binder (refractory clay, kaolin) form, when
calcined, a refractory matrix, which improves the mechanical
strength and refractoriness of the product; the expanded ver
miculite allows achievement of superior heat-insulating
properties and thermal stability.
To study processes involved in the sintering of ITOM
green preforms, compositions were selected that included a
refractory clay with additives, expanded vermiculite, and re-
fractory fillers (electric filter dust and chamotte) taken in
varying proportions. The characteristics of precursor materi-
als and finished products are given in Table 1.
The test spec-
imens were prepared by a method in . The dried (not cal-
cined!) specimens were ground in a porcelain mortar and
pestle and analyzed on a Mettler Toledo derivatograph.
pical ITOM derivatogram (composition 2 ) is shown in Fig. 1.
The physicochemical processes involved in the ITOM
heat treatment can be formulated in the following way:
– removal of physical moisture in the temperature range
of 60 – 160°C (an endo-effect peak for different composi
tions was recorded at 114 – 134°C);
– removal of the loosely held chemically bound water in
the hydrous layers sandwiched between micaceous vermicu
lite packets, in the range 160 – 290°C (an endo-effect peak at
218 – 265°C);
– removal of the crystallohydrate water from the hy
drous vermiculite layer at 260 – 480°C co-current with the
burnout of organic plasticizer CMC (carboxymethyl cellu
lose), with an exo-thermal effect markedly superior to the
endo-thermal effect of vermiculite dehydration (exo-effect
peak at 297 – 373°C);
– decomposition of kaolinite in the range of 315 – 825°C
(endo-effect peak at 526 – 537°C);
Refractories and Industrial Ceramics Vol. 45, No. 3, 2004
1083-4877/04/4503-0165 © 2004 Plenum Publishing Corporation
St. Petersburg State Technological Institute (Technical Univer
sity), St. Petersburg, Russia; Borovichi Refractory Kombinat
Joint-Stock Co., Borovichi, Novgorod Region, Russia.
Work was done with participation of N. N. Klopova and
V. M. Skvortsova, Center for Improvement of Technology and
Production (CITP), Borovichi Refractory Kombinat JSC.
Differential thermal analysis was carried out by S. D. Stepanova,
Physical Chemistry Department, CITP.