PROTECTION OF GRAPHITE
AND GRAPHITE-CONTAINING MATERIALS FROM OXIDATION
G. D. Semchenko,
I. Yu. Shuteeva,
O. N. Slepchenko,
and L. A. Angolenko
Translated from Novye Ogneupory, No. 7, pp. 25 – 33, July, 2005.
The results of a comprehensive study of newly synthesized single-layer and multiple-layer coatings based on
modified corundum for protection of graphite from oxidation are reported.
Graphite is chemically inert at high temperatures and
does not enter into a reaction with acids, alkalis, and with ba
sic and acid slags; it undergoes no deformation, and its
strength tends to increase somewhat with temperature.
Graphite displays an exceptionally high thermal stability; its
elastic modulus is two orders of magnitude smaller than that
of sintered ceramics. The structural features of graphite are
reflected in its unique properties, in particular, electric con-
duction, which permits its use for fabricating electrodes.
Graphite, owing to its structural zonality and granular com-
position, is an attractive material for use in the production of
corundum-graphite, magnesia-carbon and other refractory
An intriguing property of graphite is that it improves its
strength with temperature; this behavior may be explained by
the enhancement of intercrystalline bonding on heating and
by the reorientation of grains in a loading direction, also by
the reduced internal stress generated because of the reduction
of the anisotropy of thermal expansion of the crystalline
graphite. Another benefit of graphite is that it can be used as
an antifriction material capable of operating without a lubri
cant. Under the service conditions of an electric vacuum fur
nace, it is only lubricants with a high vaporization tempera
ture and low vapor pressure that are capable long-term per
formance. Antifriction properties of graphite come from its
layered structure: under shear forces applied, the graphite
layers undergo mutual displacements since the interlayer
bonding in graphite is much weaker than the interatomic
bonding within the layer.
Graphite materials at high temperatures can effectively
be used only on condition that no chemical reaction occurs
between the graphite-mating parts (coatings among them).
Another important concern is the eventual interaction be
tween graphite and the burning furnace environment, or dur
ing the service of graphite components. Reliable high-tem
perature service of graphite is possible in an inert atmosphere
or under vacuum. In the high-temperature technology, artifi-
cial graphite is typically used that is prepared by a thermal
graphitization method [2, 3].
Components made of graphite and refractory graph-
ite-containing materials are frequently in tended for service
at elevated temperatures in an oxidizing medium. Under nor-
mal conditions, graphite behaves as an inert material. Graph-
ite is oxidized by the atmospheric oxygen to CO at tempera-
tures above 673 K, and to CO
— at above 773 K. Graphite,
when operating in an oxidizing medium, loses some strength,
concomitant with an increase in pore volume and permeabil
ity. The increase in porosity accelerates the oxidation of
graphite material with temperature. The gases CO and CO
as they are removed from the surface of a component, pro
mote the oxidation and burnout of graphite. The burnout rate
is mainly controlled by the temperature and flow rate of oxygen.
The more perfect the crystal structure of graphite, the
higher the oxidation onset temperature. The oxidation is ac
celerated in the presence of Fe, V, Na, Cu and some other
metals; by contrast, Cl
, phosphorus and boron compounds
produce an inhibitory effect. Halogen atoms are capable of
incorporating into the crystal lattice of graphite to form in
clusion compounds that are stable in neutral media or under
vacuum when heated to 1473 – 1773 K. Graphite is virtually
inert towards the nitrogen molecules, and graphite compo
nents can operate in a nitrogen atmosphere at temperatures
up to 2773 K. Graphite enters into a reaction with gaseous
hydrogen at 573 – 1273 K to form methane.
In a graphite component whose surface is not protected
from oxidation, the graphite materials burns out to a depth of
Refractories and Industrial Ceramics Vol. 46, No. 4, 2005
1083-4877/05/4604-0260 © 2005 Springer Science+Business Media, Inc.
National Technical University, Kharkov Polytechnical Institute,