Synthesis of MgAl 2 O 4 from a stoichiometric mixture of aluminum and magnesium nitrates by its burning with urea, glycine, sugar, and mixtures of these as a fuel was studied.A transparent ceramic based on MgAl 2 O 4 is a good alternative to the expensive and diffi cultly reproducible single-crystal MgAl 2 O 4 spinel. Optical applications of the transparent ceramic includes IR windows and inert laser shutters [1]. It is known that good properties of a ceramic result from the adequate choice of synthesis method and sintering conditions, being also determined by favorable properties of the starting powder. It is impossible to obtain a good, homogeneous, pore-free ceramic suitable for optical applications without using a highly active, pure, and unagglomerated powder.It was shown in [2, 3] that the burning method is promising for production of highly pure homogeneous crystalline powders of the aluminomagnesium spinel at comparatively low temperatures with lower energy expenditure. In addition, powders produced by this method retain their nanostructure even upon sintering, which is highly important for fabrication of superelastic materials.A study of MgAl 2 O 4 synthesis in an electric furnace at 500°C in the course of 5 min with urea [2] demonstrated that parameters of the powder synthesized depend on the charge of the starting substances. For example, with the mass of the fi nal product raised from 2 to 100 g, the specifi c surface area of the powder decreases from 126 to 8.1 m 2 g -1 . This can be attributed to the high adiabatic temperature generated as a result of increasing accumulation of heat at larger single-portion charges.The goal of our study was to obtain Mg Al 2 O 4 by the burning method. EXPERIMENTALAs starting materials served magnesium nitrite Mg(NO 3 ) 2 ·6H 2 O, aluminum nitrite Al(NO 3 ) 3 ·9H 2 O, urea, glycine (all of analytically pure grade), and sugar. A mixture of the starting components to obtain 5-10 g of MgAl 2 O 4 was prepared by mixing of stoichiometric amounts of Al(NO 3 ) 3 ·9H2O and Mg(NO 3 ) 2 ·6H 2 O and a prescribed amount of the fuel in a Tefal household blender. The mixture was thermally treated in singleor double-stage modes: (1) by calcination in alundum crucibles in a muffl e furnace heated at a rate of 15 deg min -1 to 800°C in the course of 1 h and (2) by preliminary drying in glass vessels in a drying box at 300°C for 1 h, mixing in a blender, and calcination in a muffl e furnace under the same conditions.The phase composition of the powders was determined by X-ray phase analysis on a DRON-12 diffractometer (Cu Kα radiation and graphite monochromator), with a counter motion rate of 2 deg min -1 . The phases were identifi ed using the JCPDS database. The specifi c surface area of MgAl 2 O 4 powder samples was determined by the method of thermal desorption of nitrogen on a FlowSorb II 2300 laboratory electronic specifi c-surface-area and porosity meter. The average crystallite size was calculated by the Debye-Scherrer formula d = 0.94λ/ βcos θ, where λ for Cu K is 0.15406 nm;...

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Reactions of crushed wastes from lithium tantalate (niobate) production with lithium carbonate were studied by thermal and X-ray analyses. Conditions for their most complete conversion into lithium orthotantalate (orthoniobate) were determined.In modern production of lithium metatantalate (metaniobate) single crystals, which are widely used in electronics, large amounts (70 380% in many cases) of the rare metals pass into wastes. Because of shortage and high cost of tantalum and niobium raw materials, and also of a substantial demand for the products of their conversion, development of the methods for the waste regeneration is an urgent problem.Lithium metatantalate and metaniobate are very stable compounds, and their breakdown is a complex problem. In contrast to LiNbO 3 , lithium orthoniobate was found [1] to react easily with H 2 SO 4 , HCl, and HNO 3 ; in the process, lithium passes into a solution and niobium is converted to complex compounds. Their calcination yields amorphous niobium pentoxide. However, the degree of Li 3 NbO 4 decomposition depends not only on the acid in use, but also on the degree of LiNbO 3 conversion into Li 3 NbO 4 by the reaction of LiNbO 3 with Li 2 CO 3 . At present, procedures for preparing lithium orthotantalate and its properties have not been adequately studied. At the same time, this problem is important for the technology of compound production and waste processing.In this work we studied of the mechanism of the solid-state reaction between lithium tantalate (niobate) and lithium carbonate with the aim to find conditions of their most complete conversion into other less stable compounds.We studied the Li 2 CO 3 3LiTaO 3 and Li 2 CO 3 3 LiNbO 3 systems by differential thermal (DTA), differential thermal gravimetric (DTG), and thermal gravimetric analyses (TG), and also by X-ray diffraction and crystal-optics methods.We studied the sintering process on an MOM Q-1500D derivatograph (Hungary) in platinum crucibles. We used calcined Al 2 O 3 as a reference. The temperature was measured with a platinum/platinum3 rhodium thermocouple. The heating rate was 10 and 20 deg min 31 .We performed the X-ray analysis of the reaction products on a DRON-2 diffractometer with CuK a radiation.As starting substances we used predried ultrapure grade lithium carbonate; crushed wastes of LiNbO 3 and LiTaO 3 with particle size less than 160 mm (d > 50 mm, 40%; d < 50 mm, 60%), and also the 30 3 60-mm fractions.The melting points of Li 2 CO 3 reported by numerous researchers are inconsistent, because in the vicinity of the melting point of the compound (or simultaneously with melting) it starts to dissociate to give Li 2 O. The following melting points are given for Li 2 CO 3 in different papers: 618, 699, 710, 720, and 723oC. Plyushchev and Stepin [2] believe that these results are underestimated and the value of 735oC recommended in the handbook [3] and confirmed in numerous studies is the most reliable. The data characterizing the range of temperatures at which the dissociation of Li 2 CO 3 star...