DEPENDENCE OF THE SERVICE PROPERTIES OF CARBON-BEARING
MATERIALS ON THE PROCESSES OF SPINEL FORMATION
THAT OCCUR IN THE STRUCTURE OF REFRACTORY IN SERVICE
I. D. Kashcheev,
L. V. Serova,
and E. V. Chudinova
Translated from Novye Ogneupory, No. 12, p. 65, December, 2007.
The process of steel making requires the use of
refractories that can withstand the aggressiveness of slag and
metal and durable residence of metal in the teeming ladle.
The refractories wear due to impregnation with metal and
slag, chemical interaction, mechanical wear, and heat shocks.
Producers and consumers of refractories face the problem of
predicting their properties depending on the conditions of
steel making and creating what are known as combined lin-
ings. In combined linings refractories with specified quality
parameters are used in different zones with allowance for the
process used for steel making and for the processes that
occur in the refractory material in operation. In order to form
a strong carbon skeleton in a refractory material it is neces-
sary to use a complex carbon-constituting system that usu-
ally consists of a combination of carbon-bearing materials,
i.e., natural graphite, artificial carbon-bearing materials
having a tendency to be less oriented during pressing, and
high-temperature pitch. The antioxidant in periclase-carbon
refractories is a metal, most frequently metallic aluminum.
Initially, the idea to use metallic aluminum was based on the
fact that a metal possessing a higher tendency to oxidation
should promote preservation of the carbon phase. However,
the results of numerous tests in a range of 700 – 1600°C
show that the formation of Al2O3 is accompanied by the ap
pearance of new phases such as the Al
carbide and the
spinel. Powdered metallic aluminum (for example,
PAP-2 aluminum dust) introduced into the charge does not
oxidize fully under the given conditions, remains inside the
articles in an unreacted condition until 800 – 1000°C, and
serves as a source spinel formation. The reaction can occur at
a temperature exceeding 800°C, and spinel can form both on
the surface and inside the articles. In addition, the reaction
resists growth in the open porosity in the articles, which ap-
pears due to removal of the volatile components of the pitch
during oxidation of carbon and reduction of MgO.
Thus, the producers have to choose materials that acce-
lerate the process of spinel formation and ensure formation
of a strong carbon-bearing skeleton. It should be noted that
spinel continues to form at a higher temperature, which is
confirmed by the change in the sizes of the articles at a tem-
perature exceeding 1200°C.
As a result of checking of the quality parameters of
periclase-carbon articles of various producers after heating to
1000°C in an inert medium it has been established that the
ultimate compressive strength of the articles decreases on the
average by 50% and the open porosity increases by 70%.
The quality parameters of articles, the charge for which has
been developed with the use of spinel formation, remain vir
tually unchanged; in some cases their ultimate compressive
strength increases by 20%. When spinel-carbon articles are
used, the change in the quality parameters is the same as in
Refractories and Industrial Ceramics Vol. 48, No. 6, 2007