NATURAL GRAPHITES USED AS ADDITIONS AND THEIR EFFECT
ON THE PERFORMANCE OF CARBON-CONTAINING REFRACTORIES
S. I. Borovik,
N. V. Pykhova,
G. A. Lysova,
and T. V. Yarushina
Translated from Novye Ogneupory, No. 10, pp. 49 – 51, October, 2003.
Natural graphites as additions to periclase-carbon refractory materials are considered. The effect of ash com
ponents and natural graphites with different specific surface on the oxidizability, mechanical strength, and slag
resistance of the refractory material are studied. Low-ash natural graphites with low specific surface are rec
ommended for production of periclase-carbon refractories.
Periclase-carbon refractories for ferrous metallurgy
should display physicomechanical and thermophysical pro-
perties that allow their use under the conditions of an oxidiz-
ing medium, at high temperatures, and in direct contact with
molten metal and slag.
Adding carbon to the mixture enhances substantially the
service properties of periclase-carbon refractories . The
use of carbon is aimed at improving the thermal stability of
the refractory (owing to the high thermal conductivity and
low thermal linear expansion coefficient of graphite), pre-
venting infiltration of slag into the refractory (owing to the
low wettability of graphite by slag), and increasing the vis
cosity and melting point of slag (by reducing iron oxides in
the slag) .
The wear resistance of carbon-containing refractories
used in thermal power units is mainly controlled by the car
bon oxidation rate which, in turn, depends on the phase and
chemical composition, structure, and dispersity of the carbon
component . For this reason, the extended service life of
periclase-carbon refractories of composition MgO – C is di
rectly related to preventing carbon from oxidation. The use
of natural graphite provides a route to solving this problem.
We have studied the effect of specific surface S
oxidation, mechanical strength, and slag resistance of peri-
clase-carbon refractories using low-ash (K-grade) and ash
-grade) graphites (both available from a Chinese manu-
facturer). The chemical composition of the ash, fractional
composition and specific surface of the graphites are given in
Tables 1 and 2.
Natural graphites varying in ash content and specific sur-
face were tested for oxidation in the temperature range of
700 – 1000°C. Test specimens with specific surfaces of
1700, 5000, and 10,000 cm
/g were prepared using a labora
tory attritor. The fineness of grinding was controlled using a
As was established, the oxidation of graphites increases
with degree of grinding over the temperature range consi
dered (Fig. 1). Within 700 – 800°C, the ash content produced
no visible effect on oxidation of graphites. It may be pre
sumed that in this low-temperature range, dispersity is the
main factor that controls oxidation of the material.
In the range of 800 – 900°C, the oxidation rate and de
gree of oxidation are observed to increase. The ash graphites
are more susceptible to oxidation, possibly due to the cata
lytic properties of the ash and to the partial oxidation of ash
impurities (see Fig. 1).
Refractories and Industrial Ceramics Vol. 44, No. 6, 2003
1083-4877/03/4406-0383$25.00 © 2003 Plenum Publishing Corporation
Ural Electrode Institute Joint-Stock Co., Russia; Kombinat Mag
nezit Joint-Stock Co., Satka, Chelyabinsk Region, Russia.
TABLE 1. Ash Characteristics of Natural Graphites
S FeSiAlMg Cu Ca B
K 1.4 0.01 0.05 0.13 0.01 0.0003
4.8 ´ 10
2.0 0.1 0.45 1.70 0.60 0.30 – 0.25 – 0.2 7.30