INCREASE IN THE REFRACTORINESS OF CARBON COMPOSITE
MATERIALS WITH USE OF HEAT-RESISTANT CERAMIC COATINGS
G. A. Kravetskii,
V. V. Rodionova,
S. A. Kolesnikov,
and A. N. Gordeev
Translated from Novye Ogneupory, No. 7, pp. 50 – 55, July 2008.
Original article submitted April 21, 2008.
The main directions are considered for increasing the refractoriness of structural graphite materials,
carbon-carbon composite materials (CCCM), and structures made of them. Practical examples are proposed
for increasing the refractoriness of materials based on carbon in the application temperature range from 1200
to 1700°C. Results are provided for experimental study of four types of increased refractoriness. It is
demonstrated that the contemporary direction of domestic work for increasing the refractoriness of structural
graphite materials and CCCM agrees on the whole with a series of overseas achievements in this field.
The increase in the cost of industrial energy resources
has a marked effect on the cost of a most energy-consuming
producing that relates to structural graphite materials,
including carbon-carbon composite materials (CCCM).
Therefore the task of determining the endurance of these
materials during operation acquires even more importance.
Graphite materials and CCCM are related to the most heat
resistant structural materials, but their refractoriness in
oxidizing atmospheres is inadequate.
An increase in the operating capacity of structural
graphite materials in high-temperature oxidizing atmo
spheres is the theme of an ever increasing stream of research.
A comparatively more complex problem is provision of
refractoriness for CCCM in a high-temperature oxidizing
atmosphere. This is connected with the more marked dif
ference in thermophysical, elastic and deformation properties
of isotropic heat-resistant coatings and anisotropic surface
layers for CCCM.
The most important problem is increasing refractoriness
of graphite materials and CCCM above 1500°C, when
structural steels and heat-resistant alloys are not efficient or
short-lived. Starting from these temperatures carbon material
are oxidized by oxygen, water vapor, carbon dioxide, by a
so-called diffusion mechanism . Here reaction with an
oxidizing agent proceeds not only over the surface of a
component with a specific surface of about 0.5 m
also through the porous volume of a component with a spe
cific surface up to2–8m
Simulation of oxidation material of the composition
C–SiC  is based on passage of a gas- oxidizing agent
through a porous solid, a reduction in oxidizing agent con-
centration over the length of a pore as a result of its
consumption in reaction with the carbon surface, and the
effect of temperature on these processes. Considerable
hindering of these processes is achieved by volumetric and
surface siliciding of carbon material due to a reduction in the
transport pore diameter . However, in layers of a coating,
due to a difference in thermophysical properties of the
coating and carbon material, cracks form that in turn “pass”
the oxidizing agent towards the inner surface of the pore
volume of carbon material, and the overall oxidation rate is
not markedly reduced . Here the wider the cracks in a
coating, the greater is the maximum carbon material weight
loss and the lower the temperature for the maximum
oxidation rate . The main developments for refractory
materials based on graphite is suppression of cracking for
silicon carbide coatings.
Oxidation of carbon materials with coatings of silicon
carbide alone, due to its cracking or discontinuities at the
surface is observed up to 900°C, which is accompanied by
weight loss and a change in the physicomechanical
properties and electrical conductivity of graphite . Most
resistant to oxidation and carbon nanotubes with a coating of
SiC after 3 h exposure in air at 770°C and they retain about
60% of the original weight .
A mechanical method for increasing the operating
efficiency of protective coatings may be an attempt to reduce
the thickness of an SiC-coating to a level with which it has
the least internal stresses, and also creation of coatings with
Refractories and Industrial Ceramics Vol. 49, No. 4, 2008
1083-4877/08/4904-0309 © 2008 Springer Science+Business Media, Inc.
FGUP NIIgrafit, Institute of Mechanics of the Russian Academy
of Sciences, Russia.