HIGHLY HEAT-RESISTANT MULLITE-SILICON CARBIDE MATERIALS
O. A. Belogurova
and N. N. Grishin
Translated from Novye Ogneupory, No. 11, pp. 44 – 46, November 2008.
Original article submitted June 6, 2008.
Cross-linking additions of silicon carbide and waste material from ferroalloy production make it possible to
increase the heat-resistance index for mullite-containing refractories. For briquette specimens based on a
charge containing aluminum powder it reaches 45 thermal cycles (1300°C – water).
The possibility of describing the thermal conductivity of
refractories, proposed by non-equilibrium thermodynamics
together with methods of statistical physics, makes it possi
ble to break into the mechanism of the heat transfer phenom-
enon as a non-equilibrium process, and to establish the ana-
lytical dependences for thermal conductivity on ceramic ma-
In the thermodynamic model developed in this article by
the authors for thermal conductivity it shown that the heat re-
sistance of refractories is governed on one hand by heat
transfer conditions in the ceramic matrix, and on the other
hand by the capacity of its structure to generate non-destruc-
tive thermal stresses with presence of a temperature gradient.
Elements are developed on the basis of this model for pro-
ducing thermally stable forsterite-containing refractories
[1 – 3].
The theoretical model of heat resistance provides a sys
tematic nature to the particular results obtained and it is pos
sible to transfer it to mullite-containing material elements al
ready developed. Creation of new forms of highly heat-resis
tant aluminosilicate ceramics is possible due to development
of composites based on high-alumina raw material with
non-traditional additions of technogenic waste materials.
The aim of this work is a study of the effect of non-equi
librium processes on formation of the structures of
mullite-silicon carbide refractories, and the role of modifying
additions and charge composition on heat-resistance index.
High alumina raw material, i.e. kyanite is used in order to
prepare refractories. In the North-West part of the Kola Pen
insula there are large deposits of kyanite shales, i.e. Keivy.
Here 27 deposits have been discovered and eight explored,
and 23 of them are placed on the state balance. The largest
are the Novaya Shuururta, Tyapsh Manyuk and Chervurta
deposits. The predicted reserve of kyanite ore is two billion
The starting components of the charge are: briquettes
made of kyanite (without additions, with addition of alumi-
num powder or with aluminum hydroxide calcined at
800°C), silicon carbide, ferrosilicon production waste mate-
rial. A charge was mixed with a temporary binder (polyvinyl
alcohol), and compacted specimens were placed in a carbu-
For mullite there is typical anisotropy of thermal expan-
= 5.2 × 10
= 7.1 × 10
= 2.4 × 10
at 298 – 1098 K), and thermal conductivity l = 3.0 – 3.5 W(m × K).
The different linear thermal expansion coefficients (LTEC)
over crystallographic axes lead to the occurrence within the
volume of the material of thermal stresses with unidirec
tional heating or cooling. An increase in heat resistance in
dex is obtained as a result of improving heat transfer and re
ducing the thermal gradient due to a higher value of thermal
conductivity for silicon carbide (65 W(m × K)) at 500°C,
42 W(m × K) at 875°C) and the low values of LTEC
(a = 3.6 × 10
), and also absence of anisotropy com
pared with mullite.
Sintering additions are important in structure formation.
For example, in preparing highly heat-resistant forster
ite-containing materials it was established that the efficiency
of the cross-linking action of silicon carbide increases on
combined introduction with ferrosilicon production waste
material whose main component is silicon. During firing silicon
reacts with CO of a reducing atmosphere and silicon carbide
is obtained as a reaction product: 2Si + 2CO®2SiC + O
In addition, it is possible for a reduction reaction of SiO
silicon to occur: SiO
+Si® 2SiO. The reaction products
Refractories and Industrial Ceramics Vol. 49, No. 6, 2008
1083-4877/08/4906-0466 © 2008 Springer Science+Business Media, Inc.
I. V. Tananaev Institute of Chemistry and Technology of Rare
Elements and Mineral Raw Material, Kola Scientific Center, Rus
sian Academy of Sciences, Apatity, Murmansk Region, Russia.