Fused periclase is finding increasing use for the production of refractories and powders, and also as an electrical insulating material in electrical engineering and certain other industries.The main criteria of the quality of this material are the magnesia concentration and the impurity oxide content. High demands are placed on the chemical composition of electricalengineering periclase in which the main-component concentration (MgO) for various grades (GOST 13236-73) is 95-98% and above. Metallurgists use powdered fused periclase containing 93-97% MgO. The behavior of refractories in electric-insulating materials in service is also determined by their fine structure and degree of crystal defectiveness, the mineral and spatial form of impurity distribution, and other factors.Fused periclase is produced from magnesite from the Satkinsk, Talsk and Kirgiteisk deposits, Kul'dursk brucites, and calcined magnesia from the production of Soviet and foreign chemical factories. Electrlcal-engineering periclase of high quality is obtained from chemically beneficiated magnesites [i, 2].The chemical composition and electrical properties of fused periclase (Table i) show that the quality of the product largely depends on the chemical composition of the materials ( Table 2). The chemical composition of brucite and magnesite may be improved by crushing before fusing to obtain lumps less than 60 mm in size, followed by screening off the grains below i0 mm in which the largest amounts of impurities are concentrated. The magnesia content is thereby raised by 1-1.5%.Experimental studies and practical work at Bogdanovich have established that the high purity of the periclase (with regard to chemical composition) is not always the factor determining the best electrical properties. For example, periclase fused from chemically pure magnesia corresponds to class-3 in terms of electrical resistance (GOST 13236-73). At the same time, periclase obtained from Satkinsk magnesite with a high content of Fe203 in some cases meets class-2 demands for electrical resistance.The original materials undergo complex physicochemical changes during melting. The growth of periclase crystals is accomplished in different sections of the block as a result of five basic processes (Fig. i, l-V). The block thus acquires a zonal structure [3]. Due to the irregular temperature field, disparate growth of crystals with thedifferent mechanisms and the action of gravitation as the periclase melts, there is marked differentiation in the melt's components, and the various zones of the block are enriched with magnesia, while the impurities accumulate in a skin, the central zone, and the melter dust. Most redistribution in the block is experienced by the calcium oxide and the silica, and the least by the iron and aluminum oxides [3].Trial industrial meltings with various materials showed that the block structure, the nature of the zones, and the amount of impurities in the periclase can be regulated through batch feed, melting rates, and cooling rates. For example, per...

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