Bauxite concentrate is a promising raw material for producing high-alumina refractories that are used in the ladles designed for out-of-furnace treatment of steels [i].The purpose of this work is to study the structure and the properties of the fused refractories made from a bauxite concentrate obtained by hydrochloric acid treatment [2].Mullite-based solid solutions (having a basicity >1.5) constitute the main crystalline phase of the refractories obtained from bauxite and its concentrate [2][3][4]. The phase diagram of the AI203-SiO2 system gives an approximate phase constitution of the aluminosilicate refractories (including the fused refractories) as a functionof the chemical composition. According to this diagram, mullite is the only aluminosilicate that is stable at high temperatures. It was established [5][6][7][8][9][10][11][12][13] that the solid solutions of mullite whose composition changes from 3A1203"2Si02 up to 2A!203"Si02 are obtained as a result of a heterovalent substitution 2Si~++C~--~-~2AI~++ 0.In sillimanite, the type (i) substitution leads to a mullite structure having a statistical (random) distribution of oxygen vacancies [] [8, 9, 13]. The following structural formula of mullite was previously suggested [Ii]:where AIVI and AIIV indicate the coordination~ (sites) of aluminum atoms in the octahedral and tetrahedral positions, respectively; and x is the number of oxygen atoms lost per unit structural cell of sillimanite. Cameron [10][11][12] noted that sucha scheme of isomorphous substitution does not restrict the extent of mullitic solid solutions right up to sillimanite [14] on one hand and up to aluminum oxide [15][16][17][18] on the other.The possibility of obtaining mullites of variable composition by electromelting alumina and silica was shown earlier [19].Electromelting of bauxite concentrate and the compositions of the Al2Os-bauxite concentrate-SiO 2 system was carried out in a 'Kristall' unit using a cold crucible having an internal diameter of 65 mm. In order to melt (cast) the specimens of this system, we used high purity (99.99%) aluminum oxide and silica. Electromelting was carried out in air by successive fusion of AI203 and the mixtures of A1203, bauxite concentrate, and silica and an ingot measuring approximately 600 mm in length was obtained. Samples were cut out from the external region of the ingot using a diamond tool. The ingot was subjected to the maximum cooling rate (10-20~ Phase analysis of aluminosilicate refractories is difficult because not only chemical, but also crystallographic transformations occur during the process of their production. In view of this, the methods of rational chemical and x-ray phase analysis are of limited use because chemical analysis requires corrections for the solubility of the phase being analyzed as a function of the particle size, the temperature, and the duration of acid treatment; and x-ray phase analysis needs corrections for the degree of crystallinity of the phases. These facts prompted the application of infrared spectroscopy.Qu...
