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The development of the electronic and semiconductor branches of industry --the creation of various design elements for the new technology --has extended the field of use of single leucosapphire crystals, which have a wide range of transmission in the UV, visible, and IR regions of the spectrum combined with excellent thermomechanical properties.The large crystals were zone-grown from a melt of aluminum oxide blanks in special boats [i, 2].In order to obtain large single crystals of high purity, the aluminum oxide blanks must have a sufficiently high density and a minimum amount of impurity.The concentration of A1203 in the blanks should be not less than 99%.* The use for this purpose of sintered corundum plates made from microlite (TsM-332) measuring 7•215 mm, whose production method has been described in [8], does not meet the increasing demand from industry; it requires a significant amount of manual labor to stack them in a container and in several cases leads to the boiling of the melt when the crystals are grown.Therefore, the aim of the present study was to develop the manufacturing technology for corundum plates from 7 to 35-40 mm thick as the blanks for growing single crystals of leucosapphire of a size equal to that of the container.Corundum, deep-purified from alkalis, was used to produce the high-purity corundum [3].For this purpose, technical alumina, grade G-00, containing 99.64% of A1203, 0.02% of SiO2, 0.01% of TiO2, 0.01% of CaO, 0.01% of MgO, 0.03% of Fe203, and 0.28-0.33% of Na20, were mixed together in a ball mill with an addition of MgCI2"6H20 calculated as 0.2% of MgO [4]; the materials were fired in a batch or tunnel furnace under pilot-plant and industrial conditions. During the firing the density of the alumina increased from 3.665 to 3.95-3.99 g/cm 3 while the concentration of A1203 grew from 99.74-99.75% with a reduction in the amount of impurity Fe203 to 0.02% and of Na20 to 0.007-0.04%; the concentration of MgO in the corundum varied between 0.14-0.16%.Since the deep-purified corundum in the form of aqueous suspensions has been used up to the present time after milling and washing in HCI with seven decantations for products cast in gypsum molds [5], we studied the milling kinetics of corundum; the hammering on of iron; and the effect of these on the sintering of pressed products (no washing) and also on the concentration of impurity iron oxide in the products.The study of the milling kinetics of the deep purified corundum (dry method) in a laboratory vibromill (capacity i0 liter) showed that intense dispersion continues for ~ 4 h and the number of fractions of < 1 or 1-2 Dm increases significantly) the concentration of fractions of 2-5, 5-10, and 10-20 ~m is reduced (Fig. i). With prolonged milling for > 4 h, the concentration of all grains and, correspondingly, the specific surface and average diameter do not change (Fig. 2).Here and elsewhere mass fractions are given.

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Sialons have recently been obtained abroad from compounds in the system Si--AI--O-N [1-5]; they combine the main outstanding physicoehemical properties of oxides [6][7][8][9] and nonoxygen compounds* [10][11][12][13][14].Sialons are very resistant to oxidation and to the action of the metals Fe, AI, Cu, Zn, steels and also to sulfur, sulfuric acids, and alkalis.According to [15] the use of sialon for storing and transporting molten metals, including steel, is a very important application area.Abroad, sialons are synthesized mainly from AI=O~, Si3N~ and AIN [1][2][3][4], and in some cases nitrided mixtures of SiO2 and AI are used [5].Since sialons are essentially silicates or aluminosilicates in which the oxygen is partialiy replaced by nitrogen, the present authors synthesized sialon from various natural aluminosilicate materials whose compositions are shown in Table i. The carbon constituent consisted of graphite grade GL-3 (GOST 5279-74).Aluminosilicate material was mixed in a ball millwith the appropriate quantity of graphite calculated to obtain sialon with the composition 8i6_xAlxOxN6_ x , where x = 3~ The batch was used to make specimens (briquettes) at pressures of 30 and i00 MPa in the form of cylinders, 20 mm in length and diameter.The specimens and also the nonbriquetted batch (filling) were fired in an industrial muffle furnace at the Semiluksk refractories factory at 1450~ in a nitrogen atmosphere, purified to remove moisture and oxygen, at a pressure of 196 Fa. Firing was done in an open setting and also in graphite crucibles.The degree of synthesis in the sialon was evaluated on the basis of x-ray and petrographic investigations.Measurements were made of the intensity of the most typical lines with interplane distances of 0.270 and 0.331 nm (with an index of 200) for B'-sialon, and 0.362 nm for l-sialon.It was established that the sialon is synthesized from all the aluminosilicate materials studied.Judging from the intensity of the lines on the x-ray patterns corresponding to 8t and l-sialons, it is formed particularly actively in mixtures of Novoselitsk kaolin and carbon (Table 2), and furthermore with a reduction in the ratio of A1203:Si02 in the aluminosilicate materials we observe a reduction in the height of the lines for sialon (Fig. i). Firing in graphite crucibles speeds up the synthesis of sialon.The concentration of sialon expressed by the height of the line on the x-ray patterns is proportional to the amount of bonded nitrogen in the batch (Fig. 2).According to petrographic and x-ray data, in addition to sialon, all the specimens contained silicon oxynitride, residues of unreacted graphite, and glass. The sialon and silicon oxynitride have a fine-grained structure; their crystal sizes are not more than 3-8 ~m. The average refractive index of silicon oxynitride is 1.760• for the sialon it varies from 1.855 to 1.897, which indicates the variable composition of the compound.It is also established that during the nitriding of briquetted mixtures the amount of synthesized sialon is reduced, an...