THERMOPHYSICAL PROPERTIES OF COMPOSITE MATERIALS
IN THE Si
– BN SYSTEM
N. I. Ershova
and I. Yu. Kelina
Translated from Novye Ogneupory, No. 10, pp. 47 – 49, October, 2004.
Original article submitted August 20, 2004.
The results of a study of the thermophysical properties (thermal diffusivity, heat capacity, heat conductivity,
and coefficient of linear thermal expansion) of Si
– BN hot-pressed composite (with BN concentration
varying from 10 to 60 wt.%) in the temperature range of 20 – 900°C are reported.
Ceramic materials intended for service under heavy-duty
conditions — high temperatures (up to 1300 – 1500°C) and
high mechanical loads — must necessarily be tested for
thermophysical properties. Knowledge of heat conductivity,
heat capacity, thermal diffusivity, and coefficient of linear
thermal expansion (CLTE) is of utmost importance for con-
ducting analysis of the structural design and chemical com-
position of the material under specific conditions of thermal
and mechanical loading .
Our goal in this work was to study the thermophysical
properties of Si
– BN composite ceramic of variable
composition which is prepared by hot pressing technology
and is intended for operation under heavy-duty conditions.
These composites combine advantageously superior proper
ties of ceramic materials such as high strength, thermal sta
bility, and good fabricability [2, 3]. The ceramic matrix was
prepared using ultradisperse powders of composition
(MgO); the filler was hexagonal BN. The mass
fraction of BN varied within 10 – 60% .
– BN composite specimens containing 10, 30, 40,
and 60% BN were tested to determine thermal diffusivity,
heat capacity, and heat conductivity. Different methods were
used to measure heat capacity and thermal diffusivity for ce
ramic materials: the former was measured in air within the
temperature range of 20 – 900°C, and the latter was mea
sured using a rapid method. In this way, the accuracy of de
termination could be improved considering that materials of
this class are insulators at room temperature, while at tem
peratures above 500°C they develop semiconducting proper
ties. Since the heat capacity and thermal diffusivity are
known from independent measurements, one can construct a
temperature curve for heat conductivity:
l = aC
where l is heat conductivity, W/(m × K); a is thermal
is heat capacity, kJ/(kg × K); r is den-
We consider materials whose density does not change
with temperature and which undergo no phase transition on
heating. Otherwise, the use of formula (1) may lead to erro-
neous results. The method by which the thermal diffusivity
Refractories and Industrial Ceramics Vol. 46, No. 1, 2005
1083-4877/05/4601-0012 © 2005 Springer Science+Business Media, Inc.
Tekhnologiya Research and Production Enterprise (Tekhnologiya
RPE), Obninsk, Kaluga Region, Russia.
Thermal diffusivity , 10 m seca
0 200 400 600 800 1000
Fig. 1. Thermal diffusivity a plotted as a function of temperature t
for materials with varying BN concentration (numerals at curves in
dicate BN concentration, wt.%).