Dense Refractories Made from Carbidized Granules

Abstract

The process of obtaining dense refractory materials based on carbidized granules of kyanite ore is examined. The materials are tested in a multilayered lining on an experimental unit. Relations are found for the dependence of the temperature of the cold surface of the lining on its thickness and the dependence of the heat-flux indices and equivalent thermal conductivity on the thickness of the granular layer composed of mullite-cordierite thermal insulation.Low-grade and hard-to-concentrate ores of complex material composition are now being industrially processed for commercial use. However, their extraction and beneficiation is costly, the quantities of useful components that are recovered are small, and the resulting mineral concentrates do not always satisfy the technical prerequisites and requirements of modern industry. Studies we performed previously [1 -5] have shown that it is possible to use low-grade low-plasticity alumosilicate-based natural raw materials from the Murmansk region and industrial waste products to create a number of new materials. The results obtained from studies of the carbidization of the alumosilicate matrix show that refractories made from these resources are likely to be strong and resistant to heat and oxidation.The notion of creating a refractory based on granules of carbon and loamy clays was conceived by researchers D. Cölle, C. G. Aneziris, W. Schärfl, and S. Dudczig in 2007 [6 -15]. The loamy clays that were used were natural mixtures of quartz and clay-based minerals composed of fine fractions of microscopic kaolin particles and submicroscopic alumosilicate-based amorphous phases. The binder of the refractory was carbonaceous resin that has a high melting point and forms oriented graphite-like structures after coking. The carbon-bearing alumosilicate composites which are produced today are characterized by densities of up to 2200 kg/m 3 , values up to 20% for open porosity, and ultimate compressive strengths higher than 30 MPa, depending on the chosen heat treatment. These materials have undergone testing not only in the sintering zones of shaft furnaces but also as monolithic and shaped refractory products for use in the metallurgical industry [6 -15].The goals of the investigation being discussed here were to develop refractories of different compositions based on carbidized granules of kyanite raw materials from the Murmansk region and study the use of these materials and previously developed materials in a multilayered lining.For the pseudo-closed system Al 2 O 3 -SiO 2 -C, the occurrence of carbothermic reactions in a reducing medium leads to the formation of SiC. The carbidization process necessarily entails the reduction of silicon dioxide, which is present in the ore as a impurity and is precipitated during the mullitization process. Thermodynamic calculations show that reactions of SiO 2 with carbon can lead to the formation of silicon carbide. This process is affected by the sizes of the particles, their proximity to one another, and the type of carbon-bearing re...