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.
