RU2104946C1 - Method for production of barium tetratitanate bati4o9 - Google Patents

Abstract

FIELD: manufacturing of high grade super high frequency ceramics. SUBSTANCE: preliminary thread-like crystals of titanium dioxide are treated by sulfuric acid, its quantity being 0.25-0.5 dm³H₂SO₄ per 1 kg of titanium dioxide. Then mixing with oxygen-containing barium compound having melting point lower than 650 C is carried out. Thus prepared mixture is affected by heating within 3-6 h at 1050-1160 C. Ratio of said barium compound and titanium dioxide is 0.5-0.8 as calculated for BaO. Thus high grade single phase thread-like crystals of barium tetratitanate are obtained. EFFECT: improved efficiency of the method, improved quality of desired product. 2 tbl

Description

 The invention relates to methods for producing semiconductor, piezoelectric and ferroelectric materials with the required properties, in particular barium tetratitanate, which is a promising material for producing high-quality microwave ceramics, which is used for elements in microwave integrated circuits and for substrates on which circuit elements are performed.

A known method of producing barium tetratitanate, including the preparation of a mixture of titanium dioxide and an oxygen-containing barium compound, for example, barium oxide, its heating, aging, cooling and separation of crystals. However, in this way it is impossible to obtain BaTi ₄ O ₉ in the form of high purity whiskers, which is used in microwave ceramics.

The aim of the invention is to obtain single-phase whiskers (for microwave ceramics barium tetratitanate BaTi ₄ O ₉ with high quality factor).

This goal is achieved in that, in contrast to the known method, including the preparation of a mixture of titanium dioxide TiO ₂ and an oxygen-containing barium compound, its heating, aging, subsequent cooling and isolation of crystals, in the proposed method, the initial TiO _{2 is} taken in the form of whiskers and pre-treated sulfuric acid in an amount of 0.25-0.5 dm ³ per 1 kg of TiO ₂ , it is used as an oxygen-containing barium compound with a melting point of not higher than 650 ^o C, which is taken in an amount with respect to TiO ₂ equal to 0 , 5 - 0.8 in terms of BaO, and heating is carried out at 1050-1150 ^o C for 3 to 6 hours

The purity of TiO ₂ whiskers used can be improved by transferring impurities to a soluble state. For this, treatment with sulfuric acid with a density of 1.18-1.25 g / dm ^{3 is} preferred with a ratio of: 1 kg of TiO ₂ 0.25-0.5 dm ³ H ₂ SO ₄ . Moreover, at lower ratios, the dissolution of impurities proceeds much worse, and at the same wash water flow rates, the filtrate contains an order of magnitude less SO ions $\genfrac{}{}{0ex}{}{\text{2-}}{\text{4}}$ . At large ratios, the dissolution of TiO ₂ begins, i.e. loss of productive phase. Other acids either inefficiently dissolve impurities and react with TiO ₂ (HCL, HNO ₃ ) or simply form insoluble compounds with impurity ions. With a duration of less than 15 minutes, the SOI contains after washing the ions of SO $\genfrac{}{}{0ex}{}{\text{2-}}{\text{4}}$ less than the established norm, with a duration of more than 35 min, the TiO ₂ phase begins to dissolve.

Another, most important effect that is achieved after acid treatment is the etching of the surface of the crystals and the appearance of channels between the octahedra in the TiO ₂ structure, along which the diffusion of Ba ^2– ions occurs. It is this effect, ceteris paribus, that the reaction proceeds with the formation of the BaTi ₄ O ₉ phase. So, when carrying out the reaction between TiO ₂ whiskers that were not subjected to acid treatment, and, for example, Ba (NO ₃ ) ₂ , the output of the BaTi ₄ O ₉ phase is not more than 60 wt%, the remaining 40% are BaO, TiO phases ₂ , BaTiO ₃ . Thus, the acid treatment of TiO ₂ whiskers plays an essential role in achieving this goal.

It was established that the reaction proceeds between the components most fully in the desired direction, if, before the temperature of the onset of interaction, the oxygen-containing barium compound impregnates the TiO ₂ structure and after impregnation, intense diffusion of Ba ^2– ions into the TiO ₂ structure begins. This process is feasible in the presence of sufficient porosity, which is achieved as a result of acid treatment and subject to the transformation of the oxygen-containing barium compound into the liquid phase to the decomposition temperature. In addition, as follows from theoretical assumptions, the diffusion process begins to occur intensively at temperatures of 600 - 800 ^o C. Therefore, to achieve the goal, it is necessary that the oxygen-containing barium compound melts at a temperature below 650 ^o C. When using an oxygen-containing barium compound with a melting point above 650 ^o C it is not possible to obtain pure barium tetratitanate. The resulting product in this case has a phase composition: BaCO ₃ , BaTi ₄ O ₉ , BaTiO ₃ , BaO, TiO ₂ .

 Another important factor in the process is the mandatory excess of oxygen-containing barium compounds in relation to the stoichiometrically necessary. The ratio of oxygen-containing barium compound (in terms of BaO): titanium dioxide should be 0.5 - 0.8. Below 0.5 - the ratio is close to stoichiometric, more than 0.8 - is not economically feasible, because there is an increased consumption of barium compounds and a large consumption of water for washing the product.

Thus, this method allows to obtain barium tetratitanate BaTi ₄ O ₉ in the form of single-phase whiskers of high purity.

 Table 1 shows the characteristics of the starting reagents with a detailed description of the synthesis modes.

The proposed method is as follows. The titanium dioxide whiskers of any structural modification, prepared by any method, are subjected to grinding and hydroclassification, if necessary, and then treated with sulfuric acid with a density of 1.18-1.25 g / dm ³ at a ratio of: 1 kg TiO ₂ - 0.25-0 5 dm ³ H ₂ SO ₄ for 15-35 minutes Then, the TiO ₂ nanocrystals are filtered, washed with distilled water to obtain a filtrate containing traces of H ₂ SO ₄ in an amount of <0,0003 kg / dm ³ . The resulting product is mixed with an oxygen-containing barium compound having a melting point below 650 ^o C, in the ratio of an oxygen-containing barium compound (in terms of BaO): titanium dioxide = 0.5-0.8, and then the resulting mixture is heated for 3-6 hours at a temperature of 1050-1150 ^o C. Annealing product is repulpated with distilled water, filtered, washed with distilled water to obtain a filtrate with a barium ion content <0,0003%. The solid precipitate of BaTi ₄ O ₉ nanocrystals is dried at a temperature of 200-300 ^o C. The phase composition of the product is determined using x-ray phase analysis on a DRON-2 diffractometer in Cu-K _α radiation at a tube voltage of 35 kV and a current of 30 mA. Graphite is a monochromator, which provides good resolution of lines in diffractograms. The size of the crystals and their morphology are studied using a UEM-100 electron microscope. The crystals are tested for strength (tensile strength) using an IKAN-2 apparatus. The dielectric constant is determined by the standard method.

Example 1. 1000 g of titanium dioxide in the form of whiskers prepared according to technology 1 (table. 1), with average sizes: l = 1 μm, d = 1.5 μm, l / d = 66 served in a quartz glass reactor with a volume of 5 l equipped with a stirrer. At the same time, a sulfuric acid solution with a density of 1.18 g / dm ³ in an amount of ₄ l is supplied to the reactor, which is the ratio of TiO ₂ : H ₂ SO ₄ = 1: 0.5. The acid treatment is carried out for 35 minutes with constant stirring. The resulting suspension is filtered on a drum vacuum filter with a working surface of 0.5 m ² equipped with a filter cloth Canar, and in an amount of 0,00025 kg / DM ³ . After washing, the moisture content of the solid precipitate is 10-12%. Accordingly, the amount of solid mass, taking into account humidity, is 1114.4 g. The resulting product is fed into a stainless steel paddle mixer having a steam jacket and heated with steam with a pressure of 0.25 MPa (2.5). In the working area of the mixer maintain a temperature of 95-98 ^o C. At the same time as the product is fed into the paddle mixer, a second reagent Ba (NO ₃ ) ₂ with a melting point of 595 ^o C in the amount of 1365 g, which is the ratio of BaO: TiO ₂ = 1: 0.5. The components are stirred for 1 hour. The resulting mixture is a granule (pellet) of 3-8 mm in size. After that, the resulting mixture is annealed for 6 hours at a temperature of 1150 ^o C in a rotating electric furnace (the speed of the furnace is 0.5 rpm, the diameter is 0.4 m, the length is 2 m, the muffle is made of corundum). The annealing product is treated with distilled water in a quartz reactor with a capacity of 25 l with constant vigorous stirring. Water consumption with a temperature of 96 ^o C per mass of the obtained product is 45 l, the processing of the solid mass is carried out in three cycles, in each cycle the volume of water is 15 l. In the final filtrate, the content of barium ions is 0.0001%. After the last filtration, a solid precipitate is obtained in an amount of 1184 g, including 12% H ₂ O, i.e. the target product in terms of dry was 1042 g. Then, the solid precipitate is fed into a paddle dryer, where it is dried to constant weight at a temperature of 200 ^o C. The result is a solid product in an amount of 1042.2 g

The resulting product is identified on a DRON-2 diffractometer. As a result, peaks characteristic of BaTi ₄ O ₉ were obtained on the diffractogram. Microscopic analysis shows that the particles are whiskers close to the praederite structure with an axial ratio l / d ≈50. The size distribution of crystals obeys the random distribution law - the Gauss law. The predominant crystal size is l = (15 ± 1) μm, d = (3 ± 0.2) μm. The tensile strength of the crystals is 150 kg / mm ² .

 In tab. 2 are examples illustrating the effectiveness of the method in the claimed parameters and when going beyond them. In all examples, the equipment and sequence of operations are similar.

Claims (1)

A method of producing barium tetratitanate BaTi ₄ O ₉ , comprising preparing a mixture of TiO ₂ and an oxygen-containing barium compound, heating it, aging, subsequent cooling and isolation of crystals, characterized in that, in order to obtain single-phase whiskers for microwave ceramics, the initial TiO ₂ taken in the form of whiskers and pre-treated with sulfuric acid in an amount of 0.25 0.5 dm ³ / kg of TiO ₂ as an oxygen compound of barium is used a compound thereof having a melting point not higher than 650 ^o C, which taken in coli ETS respect to TiO ₂ of 0.5 to 0.8 in terms of BaO, and heating was carried out at 1050 -1150 ^o C within 3 6 hours.

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