SYNTHESIS OF â-SiC IN THE INTERMEDIATE LAYER
OF CORUNDUM COATINGS BASED ON A SOL-GEL BINDER
FOR PROTECTING GRAPHITE OBJECTS FROM OXIDATION
G. D. Semchenko,
I. Yu. Shuteeva,
M. I. Ryshchenko,
M. A. Panasenko,
and Yu. I. Ryabkov
Translated from Novye Ogneupory, No. 12, pp. 23 – 27, December 2010.
Original article submitted September 3, 2010.
A coating is developed for protecting graphite from oxidation at 2023 – 2223 K. The efficiency of the protec
tive action of a corundum coating based on a sol-gel binder increases due to creating a dense intermediate
layer between the graphite substrate and the coating as a result of its self-reinforcement with fibers of mullite
crystals and b-SiC nanoparticles. Components of a modifier and sol-gel binder, but not carbon of the graphite
substrate, provide synthesis of b-SiC.
Keywords: graphite oxidation protection, corundum coatings, silicon carbide, mullite, self-reinforcement,
dense intermediate layer.
Reliable use of graphite at high temperature is possible in
an inert gas atmosphere or in a vacuum. Objects made of
graphite and refractory graphite-containing materials often
serve at elevated temperature in an oxidizing atmosphere.
Under normal conditions graphite is very inert, but above
673 K it oxidizes with oxygen from air to CO, and above
773 K to CO
. Operation in an oxidizing atmosphere is ac
companied by a reduction in material strength. There is an
increase in pore volume and growth of permeability. With an
increase in temperature there is an increase in oxidation rate
as a result of an increase in graphite material porosity. The
CO and CO
gases formed are removed from the surface of
an article, promoting further graphite oxidation and burning
of it. Burning rate depends to a considerable extent on tem
perature and the rate of oxygen influx.
If the surface of a graphite component is not protected
from oxidation during firing, then at about 1573 K the graph
ite burns by 10 – 15 mm . A reduction in graphite strength
during its oxidation is connected with development of poros
ity , and development of porosity leads to a reduction in
strength. Failure of graphite proceeds through the coke of a
binder, which reacts with oxygen. Bridges, which form the
coke binder between filler grains are oxidized, burn away,
and this leads to marked loss of strength with a significant
material weight loss .
Due to a collection of valuable physicochemical proper-
ties graphite is used in many branches of industry. The high
heat resistance gives rise to use of graphite in many domestic
refractory objects, including those used in rocket construc-
tion, and as a result of chemical graphite is used in chemical
engineering as a structural material; the low friction coeffi
cient of graphite makes it possible to employ it for
antifriction components, and high electrical conductivity
makes it possible to use it as an electrical engineering mate
rial and components, heaters, electrodes, etc. It is well
known that graphite is used in nuclear technology and other
Graphite is used in rocket building for manufacturing lin
ings for rocket nozzles, operating on solid fuel, nose cones
and other components. The nozzle for a solid fuel rocket
should operate in an oxidizing atmosphere for 35 sec in all. It
is necessary to guarantee travel of a rocket into a near-earth
orbit, providing a ten- to fifteen-fold life of nozzle material.
Artificial graphite machines well, although the field of its ap
plication is limited by a tendency towards oxidation and ero
sion at high temperature. Therefore the question of protect
ing carbon materials is urgent and its solution is an important
Several methods exist for protecting carbon materials
from oxidation. Particular attention is devoted to protective
Refractories and Industrial Ceramics Vol. 51, No. 6, March, 2011
1083-4877/11/5106-0443 © 2011 Springer Science+Business Media, Inc.
National Technical University “Khar’kov Polytechnic Institute,
Institute of Chemistry of the KomiNTs, Uro RAN, Syktyvkar,