RESISTANT CORUNDUM-GRAPHITE MATERIALS FOR METALLURGY
G. D. Semchenko,
L. A. Angolenko, I. N. Opryshko,
and A. V. Dunikov
Translated from Novye Ogneupory, No. 8, pp. 35 – 37, December, 2002.
Corundum-graphite materials are of importance for manufacturing components intended for steel-teeming
technology. Heat- and corrosion-resistant corundum-graphite nozzles for continuous casting of steel have
been developed at the laboratory for structural ceramics and refractories of the NTU-KPI and tested success
fully under industrial conditions. The refractoriness of nozzles is provided by corundum-graphite matrices
self-reinforced by whisker crystals and by the use of layered materials and coatings preventing fouling of the
nozzle channels and oxidation of the refractory material.
Refractories play an extremely important role in modern
metallurgical technologies. Refractories, depending on the
service requirements placed on them, must be slag- and
metal-resistant and possess specified density, porosity, and
structure — factors that determine their stability in service.
The tendency to use a larger number of pours per heat (by the
so-called “heat-on-heat” method in the jargon of technolo-
gists) and to expand the range of steel grades employing con-
tinuous-casting techniques places stringent requirements on
the performance of refractories.
As is known, corundum-graphite nonswirl nozzles and
submersible nozzles used in the continuous casting techno
logy are prone to fouling. To prevent this undesired effect,
the inner surface of the nozzle is usually thinly lined with a
material (for example, BN-based) which does not readily en
ter into reaction with Al
-containing deposits and is not
wetted by them. The lining and glazing of nozzles is a costly
and labor intensive procedure.
In the foreseeable future, carbon-containing refractories
will prevail in the steelmaking industry owing to their supe
rior operational properties [1, 2]. As was emphasized in ,
major problems with their manufacture lie in the sphere of
economy and in the development of synthetic materials with
low heat conductivity.
To resolve environmental problems and to decrease heat
conductivity of corundum-graphite (C/G) refractories, ef
forts at the NTU-KPI were directed at the development of a
self-reinforcing C/G matrix . The main objective was
(i) to use binding agents that would bind environmentally
hazardous, carcinogenic products of thermal destruction in
volved in the synthesis of whisker crystals of b-SiC and
mullite, and (ii) develop a technique for making layered
All-round hydrostatic compression for molding mixtures
based on self-curing sol-gel binders makes it possible to pro-
duce a layered structure in the C/G material. The layers in
question differ in phase composition and thermoelastic prop-
erties. Self-reinforcement of the matrix and the layered struc-
turing cause heat conductivity of a C/G material to decrease.
Directional control over the phase composition of the
binding agent in C/G refractories is effected by using com-
posite carbon-filled binders, for example, pitch-ethyl silicate
binders. Properly converted via a physicochemical mecha
nism, they allow synthesis of oxygen-free compounds with
tailored phase properties.
A technology was developed [3 – 5] in which the mix
tures were prepared using a composite pitch-ethyl silicate
binder  without heating. Here a peculiar feature was that
the binder, subjected to thermal degradation, produces car
bon nanoparticles and an ultradisperse SiO
. In a reducing
medium during calcination as the pitch undergoes degrada
tion and carbonization, SiO
converts to SiO and Si, with the
resulting synthesis of silicon carbide in the form of nano
particles and whisker crystals. A higher yield in b-SiC and a
lower temperature of synthesis can be reached through a uni
form distribution of ultradisperse SiO
from the ethyl silicate binder) and coked pitch particles and
through increasing the surface for interaction between com
ponents of the composite binder. The b-SiC crystals may be
3–5mm in size or larger; frequently, the synthetic b-SiC oc
curs as whisker crystals or crystalline felt sandwiched be
tween layers formed by the finely ground mixture of the C/G
filler and the binder.
Refractories and Industrial Ceramics Vol. 44, No. 1, 2003
1083-4877/03/4401-0059$25.00 © 2003 Plenum Publishing Corporation
Kharkov Polytechnical Institute National Technical University
(NTU–KPI), Kharkov, Ukraine.