A STUDY OF EFFECTIVE THERMAL CONDUCTION
IN LIGHTWEIGHT FOAM CORUNDUM REFRACTORIES
B. S. Skidan
and S. A. Borisov
Translated from Novye Ogneupory, No. 10, pp. 13 – 15, October, 2003.
Thermal conduction of lightweight foam corundum refractories is studied by a hot-wire method. Empirical re
lations for the thermal conductivity as a function of temperature (20 – 1100°C) and porosity (79 – 93%) are
derived. The thermal conductivity at higher temperature is less dependent on porosity because of the increased
role of radiation in the heat conduction process.
Thermal conduction is a major property of refractory ma
terials closely related to most characteristics of thermal pro
cesses. Knowledge of the thermal conductivity of refractory
materials, in particular, high-temperature lightweight heat in-
sulators, and its dependence on various factors is important
for practical applications and design of thermal power units.
A literature survey showed a high scatter in experimental
thermophysical properties of refractories close in chemical
composition and porosity, from 30 to 100% or even more,
which is much higher than the measurement error of methods
used. Much of the scatter comes from the ambiguous charac-
terization of specimens and specific features of the experi-
mental method and the instrumentation used. Assessing the
reasons for the scatter of literature data in quantitative terms
is an arduous task in view of the incomplete information
available and the as yet poor understanding of the mecha
nisms that determine effective thermophysical characteristics
In this work, we have studied the effective thermal con
ductivity of lightweight corundum refractories as a function
of porosity. The effective thermal conductivity is an impor
tant characteristic of heat insulating materials that can be de
termined uniquely and with sufficient accuracy.
The materials examined were lightweight corundum heat
insulators of different porosities; they were prepared by
foaming an a-Al
aqueous suspension followed by drying
and calcination at 1600°C (commercially available from the
Termokeramika Joint-Stock Co., Moscow).
Thermal conductivity was determined by a nonstationary
hot-wire method (cross-array) in conformance with the ISO
8894–1 international standard. A detailed description of this
method and the experimental setup used can be found in .
The accuracy of measurement was within 8%. The relative
random error in the determination of thermal conductivity
varied from 2 to 15% depending on thermophysical proper-
ties, shape, and size of the specimen, on the boundary condi-
tion effects, etc.
The porosity of materials was determined by the method
of hydrostatic weighing  to an accuracy of 0.1%. Relevant
data are given in Table 1.
The microstructure of materials was examined by mi-
croscopy using a MIN-8 polarization microscope (´ 600,
transmitted light). The petrographic analysis revealed an iso-
tropic highly porous structure typical of corundum-type ma-
terials. Most pores are of closed type, spherical in shape, 150
to 500 mm across, occasionally oblongate, with rounded
edges; aggregates composed of two-three clustered pores are
also encountered. The maximum pore size is 1 mm, and the
minimum 40 – 50 mm. The solid phase is composed of fine
crystalline corundum grains5–10to20–30mm across.
Data on the thermal conductivity of corundum materials
in the temperature range of 20 – 1100°C were obtained. The
results of measurement were processed on a computer using
a least-squares technique and empirical relationships for
thermal conductivity as a function of temperature and poros
ity were derived; they are given in Figs. 1 and 2.
Refractories and Industrial Ceramics Vol. 44, No. 6, 2003
1083-4877/03/4406-0355$25.00 © 2003 Plenum Publishing Corporation
D. I. Mendeleev Russian Chemical Engineering University, Mos
TABLE 1. Porosity of Corundum Materials
Foam corundum-0.3 0.27 93.0
Foam corundum-0.5 0.49 91.8
Foam corundum-0.7 0.65 83.3
Foam corundum-0.9 0.86 79.4