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The production of KP-95 corundum files [1, 2] involves certain laborious and energy-consuming processes in obtaining kaolinized corundum chamotte, including dry pressing the finely milled mixture of alumina and kaolin, replacing the briquet on kil cars, drying it, and firing in a tunnel kiln at 1520-1580~The Semiluksk factory has developed and implemented a method for the production of high-grade tiles for gate valves, which involves replacing the kaolinized corundum chamotte by a more economical material. It is best to use m~lite--corundum chamotte obtained at the Semiluksk factory, using the normal methods.The water absorption of the mullite--eorundum ehamotte is not more than 2%, * A1203 content not less than 85%, Fe203 not more than 0.5%, and SiO 2 9-10%. The main requirement in changing from kaolinized corundum ehamotte (not less than 95% A1203, not more than 0.5% Fe203 and 1.8-2% SiO2) to a material with a lower refractoriness was the preservation, together with the high density, of adequately high-temperature strength and corrosion resistance, which ensure the stable operation of the tiles.It is known that the high-temperature strength and also the resistance to the action of molten slags and metal by aluminosilicate refractories of a granular structure depend on the composition and structure of the * Here and subsequently parts by weight.

Speeding up processes in ferrous metallurgy has placed new demands on refractories. Thus, when metal is being cast from ladles using gate valves, the refractory plate, which is part of the valve design, in addition to the usual properties required of refractories (high density, strength, spalling resistance, metal and slag resistance), should possess properties typical of construction materials (constant dimensions, abrasion resistance, and stability of the strength characteristics during operation).The combination of the above propertiescan be realized in corundum refractories, whose structure, phase composition, and technical factors can be varied in wide limits by introducing various oxide additives.The question of the role of oxides of Mg, Ti, Fe, Si, Cr, and other elements for producing articles from corundum has been widely discussed [1][2][3].It is known, for example, that the addition of magnesia suppresses the growth of corundum crystals and thereby contributes to the formation of a fine-grained structure, ensuring densification and strengthening of the material, and increasing its hardness [4,5].Additions of titanium dioxide on the other hand activate recrystallization of corundum, and considerably reduce the sintering temperature [4,5].Chromium oxide retards the recrystallization of A1203; its presence in the corundum in amounts of up to 3%* in the form of a solid solution leads to a tenfold increase in the hardness of the material [4][5][6].The question of the combined action of oxides on the structure and properties of corundum refractories has been less thoroughly investigated. As shown by experiments, with the addition of magnesia, titania, and chromium oxide in various combinations, titanium dioxide preserves the strong mineralizing action, magnesia retards the growth of the crystals, while Cr203 in the presence of MgO and TiO2 acts as an indifferent oxide [4,5].Existing information relates completely to the finely dispersed compositions of the oxides AI--Mg(Cr, Ti), whose sintering is accompanied by a high linear shrinkage, as a rule, equal to 15-18%. Moreover, modern metallurgical processes require large refractory articles, often of very complex shape. The linear shrinkage of such articles should not exceed 5%. Therefore, in developing high-grade corundum refractories we should be disposed toward preliminary sintering of corundum with additions, followed by milling and the use of various fractions of the resulting material.In this case, it must be considered that the structure of the grains of sintered corundum used as the filler have a marked effect on the structure, technical properties, and operational behavior of the refractory as a whole, since to a large degree it determines the nature of the sintering of the goods, the resistance to thermal stresses, and impregnation by molten metal and slags.The present article deals with a study of the effect of magnesia, titania and chromium oxide and also mixtures of these on the structure of sintered corundum and articles made from it.The structure ...