Periclase-lime refractories with increased concentration of carbon

Abstract

The lining of steel-melting converters which operate on oxygen blow involves the use of unfired refractories based on periclase, lime-periclase powders, and mixtures of these. The bond consists of presteamed coal tar or medium-temperature pitch, as a result of which during the coking process the refractories contain from 2.5 to 2.8% carbon [i, 2]. The resistance of the lining in the converters made with these refractories is largely determined by the rate of their decarbonization in service, since the presence in the refractory of carbon prevents damage from thermal shock, and reduces the wettability by metal and slag [2, 3]. In connection with this, in preparing unfired converter refractories we try to use a bond with ahigher coking number.In Soviet practice, the coke residue of the presteamed coal tar at the present time has reached 48%, and for the pitch up to 56%. With the use of coal tar pitch as the bond, in the production of converter refractories we can ensure a highquality product; and the resistance of the linings in the converters using such refractories, as a rule, is 10-.15% higher than that of linings made from refractories with a tar bond [3].Thus, to increase the resistance of the lining of the converters it is necessary to boost the concentration of residual carbon in the refractory.However, it is impossible to achieve this by increasing the concentration of bond, since this leads to a reduction in the green strength, and also causes deformation in the unfired brick.During the coking of such articles we observe an increase in the open porosity, due to the separation of a large amount of volatiles from the bond.In order to improve the working factors of the refractory and increase the life of the lining in service, work is being done on the incorporation into the body composition of carbon-containing additives for the production of refractories [4, 5]. Thus, experience with the production of periclase-carbon refractories, which is becoming popular indicates that the most effective additive is crystalline graphite containing more than 90% carbon [6]. Its amount is determined by the purpose for which the refractory is intended and the service conditions.It is known that crystalline graphite, ensuring the necessary effect, is a scarce raw material, and its use in mass-produced refractories at the present time is not possible.In conncection with this, for ordinary refractories based on lime-periclase powders we tried additions of inexpensive and readily available materials for the carbonaceous bond: lew grade cryptocrystalline graphite with carbon concentrations of 80.8%, and high-temperature (softening point 173~ modified pitch with a coking number of 72.4%. In the investigation of the influence of these additives on the product quality we used lime-periclase and periclase powders whose properties are shown in Table i. and the bonds -presteamed coal tar with a coke number of 47.6 and a viscosity of Ci~ 150 sec.Since the increase in the concentration of carbon bond in the refractory bodies is accompan...

Investigation of Taimyrsk graphites for producing periclase-carbon ladle refractories

“…It is possible to use cryptocrystalline graphite [6,7]. With an increase in the carbon content in the graphite, the resistance of the periclase increases [4][5][6].…”