NON-CALCINED COKE QUALITY CRITERIA FOR PRODUCING STRONG
FINE-GRAINED GRAPHITE WITH IMPROVED HOMOGENEITY
N. A. Lobastov
and A. N. Chernyavets
Translated from Novye Ogneupory, No. 12, pp. 28 – 31, December, 2006.
Original article submitted March 31, 2006.
The results of studying variations of different properties of the filler, coke-pitch composite, and the target
graphite depending on their heat treatment temperature in a wide temperature range are considered. These re
sults are used to issue recommendations for producing strong close-grained defect-free graphite based on
non-calcined coke. The probable reasons for the higher strength of graphite based on non-calcined coke com
pared to analogous materials based on calcined coke are discussed.
Several grades of strong close-grained construction
graphite are currently produced on the basis of non-calcined
coke proceeding from different origins: pitch, shale, and oil
coke [1 – 3]. In all cases the properties of target graphite are
significantly unsteady . For instance, its compressive
strength varies from 63 to 163 MPa, apparent density from
1600 to 1900 kg/m
, volatile substance yield 1.82 – 6.46%,
and mechanical abrasion strength 4.3 – 10.0%. The abrada-
bility and the volatile yield most fully reflect the properties
of coke determining its behavior (when used without addi-
tional heat treatment) in the technological process and affect
ing the properties of target graphite [4, 5]. The practice of
producing strong close-grain graphite lacks justified criteria
for estimating the suitability of non-calcined coke with re
spect to the considered parameters. Abradability and yield of
volatile materials from coke primarily depend on its coking
degree, i.e., on the process temperature and the duration of
its impact on the coking material [5, 6]. Non-calcined coke
used as a filler in coke-pitch composites is produced within a
sufficiently wide temperature interval from 450 to 700°C.
There are several opinions regarding the effect of the filler
production temperature on the properties of graphite [7, 8],
which do not offer a convincing interpretation of significant
instability of properties in this class of materials.
In our opinion, to stabilize the properties of such graphite
one needs a filler produced at a temperature T
close to the
temperature of the transformation of the binder pitch into
Such filler ensures an adequate change of pro
perties under joint shrinkage of the components of the
coke-pitch composite in coking. When the composite con
tains a filler produced at a temperature above some critical
which is higher than T
), there is no joint shrink-
age of the components under heat treatment. As the tempera-
ture grows to a level above the temperature of semicoke for-
mation from pitch, its further shrinkage takes place.
The thermal expansion of the filler impedes the shrink-
age of the pitch semicoke. As a result, shrinkage stresses
arise in the pitch semicoke: the greater the resistance of the
filler to this semicoke in shrinking, the higher the stresses.
Upon reaching a critical level of shrinkage stresses, defects
(microcracks) arise in the pitch semicoke, decreasing the
strength of the preform. When the composite contains a filler
produced at the admissible temperature, stresses in the pitch
semicoke do not reach the critical level due to joint shrinking
of the components and do not produce structural defects in
the material. Therefore, the strength of the latter composite is
higher than the strength of the composite based on the filler
produced at a temperature above the admissible level. The
admissible filler production temperature, which leads to the
formation of a material free of structural defects in the pitch
brichges, can be analytically presented as follows:
+ DT, (1)
where DT is the temperature interval in which deformation å
reaches a limiting value (å = å
) in the course of pitch semi
coke shrinking. This interval is determined from the formula
DT = å
where á is the coefficient of linear temperature contraction
of pitch semicoke.
Refractories and Industrial Ceramics Vol. 47, No. 6, 2006
1083-4877/06/4706-0359 © 2006 Springer Science+Business Media, Inc.
NIIgrafit Federal State Company, Russia.