RU2753672C1 - Method for producing bismuth germanate bi12geo20 by casting - Google Patents

Abstract

FIELD: material technology.SUBSTANCE: invention relates to the technology of a material with high photoconductive and photorefractive properties. The method for obtaining bismuth germanate Bi12GeO20includes preliminary mechanical mixing of the initial powders of bismuth oxide Bi2O3and germanium oxide GeO2, heating the resulting mixture in a platinum crucible to 1060-1160°C with holding in this temperature range for 15-60 minutes, after which the resulting melt is poured onto a platinum substrate.EFFECT: pure bismuth germanate of the composition Bi12GeO20is obtained, while this technology requires much less time for synthesis compared to the known ones, which significantly reduces not only time, but also economic costs. Moreover, the method makes it possible to obtain Bi12GeO20by casting, which contributes to the economy of expensive crucibles used in the synthesis and destroyed during the extraction of the finished material.1 cl, 5 dwg

Description

The method relates to the field of chemistry and can be used: as an initial charge for growing, defect-free single crystals; in optical processing and information recording; to create promising reversible recording materials for real-time holography and image processing; has high piezoelectric properties; can be used in electro- and magneto-optics, as well as as a material with high photoconductive and photorefractive properties.

The authors of the work [Senlin Fu, Hiroyuki Ozoe. Reaction Pathways in the Synthesis of Photorefractive g-Bi12MO20 (M = Si, Ge, or Ti). // J. Am. Ceram. Soc, 80 [10] 2501-509 (1997)] a synthesis method is proposed in which bismuth oxide Bi ₂ O ₃ (purity 99.99%, monoclinic structure) and germanium oxide GeO ₂ (purity 99.99%, hexagonal structure) was thoroughly mixed in a stoichiometric ratio of 6: 1, and then mixed with about 5 wt. % deionized water at room temperature. After that, the resulting mass was pressed into a cylindrical rod with a diameter of 6.5 mm and a length of 68 mm. Next, the rod was dried for one day at room temperature and sintered at a temperature of 865.5 ° C (reaction time not indicated).

However, using this method does not achieve:

1. fast acquisition of the desired phase, because the specified method is not only more laborious, in view of the greater number of operations to obtain the desired phase, but also more time-consuming;

2. The use of additional equipment in the analogue complicates and increases the cost of the process of obtaining the Bi ₁₂ GeO ₂₀ compound.

Also known works:

1. HS Horowitz, AJ Jacobson, JM Newsam, J.T. Lewandowski, ME Leonowicz. Solution synthesis and characterization of sillenite phases Bi ₂₄ M ₂ 0 ₄₀ (M = Si, Ge, V, As, P). // Solid State Ionics 32/33 (1989) 678-690;

2. M.F. Carrasco, S.K. Mendiratta, L. Marques, A.S.B. Sombra. Properties of nanoparticles of Bi12GeO20 (BGO) obtained by ball milling. // Journal of materials science letters 21, 2002, 963-965;

3. GS Suleimenova, VM Skorikov. Studies on the process of Bi ₁₂ MO ₂₀ (M = Ti, Ge, Si) formation from oxides. // Journal of Thermal Analysis, Vol. 38 (1992) 835-841.

4. Sam Chehab, Pierre Conflant, Michel Drache, Jean-Claude Boivin, George McDonald. Solid-state reaction pathways of Sillenite-phase formation studied by high-temperature X-ray diffractometry and differential thermal analysis. // Materials Research Bulletin 38 (2003) 875-897;

5. Matjaz Valant and Danilo Suvorov. Processing and Dielectric Properties of Sillenite Compounds Bi ₁₂ MO _20-δ (M = Si, Ge, Ti, Pb, Mn, B _1/2 P _1/2 ) // J. Am. Ceram. Soc. 84 [12] 2900-904 (2001).

General conclusion by analogs: the indicated analogs, for the most part, require a large number of technological operations using additional reagents and equipment, and are also very time-consuming. This entails high costs, greatly complicates and increases the cost of obtaining the desired phase Bi ₁₂ GeO ₂₀ , and also significantly increases the risk of contamination of the resulting material.

Closest to the claimed method is the prototype, which is described in [Xing-Hua Ma, Sang-Hyo Kweon, Sahn Nahm, Chong-Yun Kang, Seok-Jin Yoon, Young-Sik Kim, and Won-Sang Yoon. Microstructural and Microwave Dielectric Properties of Bi ₁₂ GeO ₂₀ and Bi ₂ O ₃ -Deficient Bi ₁₂ GeO ₂₀ Ceramics // J. Am. Ceram. Soc., 99 [7] 2361-2367 (2016)]. In it, the starting components Bi ₂ O ₃ and GeO _{2 were} mixed and ground in a nylon container with ZrO ₂ beads for 24 hours. Then the resulting mixture was dried and calcined at a temperature of 700 ° C for 5 hours. Thereafter, the resulting powders were milled for 24 hours and dried to obtain fine powders. Next, the resulting material was pressed into cylindrical tablets and sintered at a temperature of 825 ° C for 3 hours in an air atmosphere.

However, using this method does not achieve:

1. fast acquisition of the desired phase, because the specified method is more laborious and requires a lot of time spent on synthesis;

2. The use of grinding devices in the synthesis significantly increases the risk of contamination of the finished product not only by grinding components (balls), but also by the material of the vessel in which grinding itself takes place.

To achieve this task, the claimed "Method for producing bismuth germanate Bi ₁₂ GeO ₂₀ by casting" contains the following set of essential features similar to the prototype:

1.the need for heating the initial components;

2. the use of the same initial reagents (pure oxides of bismuth and germanium).

In relation to the claimed method, the specified prototype has the following distinctive features and disadvantages:

1.The long duration of the synthesis time significantly increases the cost of manufacturing the finished product in view of the huge time costs;

2. intermediate stages of grinding also complicates the synthesis process and lengthens it in time, and also significantly increases the risk of contamination of the finished product.

There is the following causal relationship between the distinctive features and the problem being solved:

1. the use of higher heating temperatures in the claimed method helps to significantly reduce the time required for synthesis and, accordingly, significantly reduces the cost of manufacturing the finished product. The use of the casting method also significantly accelerates the synthesis of the Bi ₁₂ GeO ₂₀ compound, because in this case, much less time is spent on cooling than if the material was cooled in a crucible;

2. When the starting reagents melt, the intermediate stages of prolonged grinding of the starting reagents with each other lose their meaning, which again contributes to the acceleration of the synthesis process.

1. The choice of the boundary parameters of the temperature of the beginning of the cooling of the melt (from 1060-1160 ° C) is due to the high-temperature regions of the melt, each of which has its own, special structure. It is known that on the phase diagram of the Bi ₂ O ₃ - GeO _{2 system,} the melt region can be divided into 3 temperature zones A, B and C (Fig. 1) [Zhereb VP, Skorikov VM Metastable States in Bismuth-Containing Oxide Systems // Inorganic Materials. 2003. Vol. 39. Suppl. 2. P. S121-S145]. Zone "C" has a number of indisputable advantages favorable for preliminary heat treatment of the melt: low viscosity, high mobility of atoms, fine structural features of the melt. At the same time, a very important factor is that in the Bi ₂ O ₃ -GeO _{2 system, the} solubility of platinum decreases with increasing temperature [Voskresenskaya E.N. Interaction of platinum with molten bismuth-containing oxides // Abstract of the thesis ... Ph.D. - Moscow: Academy of Sciences of the USSR, Order of Lenin Institute of General and Inorganic Physics. N.S., Kurnakova. 1983. - 24 S.], therefore, synthesis at relatively low temperatures of overheating of the melt can lead to increased dissolution of platinum, and, consequently, to greater wear of the crucible and greater contamination of the resulting material with platinum. Heating above the upper limit of the temperature range is possible, but is impractical due to higher energy costs.

The choice of the boundary parameters of exposure at a given temperature range (15-60 minutes) should ensure complete mutual dissolution of the initial components in each other, and also ensure the transition of the melt into a homogeneous and fluid state.

The choice of the substrate material (pure platinum) is due to the fact that Bi ₂ O _{3 is an} extremely reactive compound in a liquid state and very quickly interacts with almost all known materials, except for pure platinum. Therefore, it is the use of pure platinum that ensures the production of a pure Bi ₁₂ GeO ₂₀ phase, without the risk of contamination by the substrate material.

The method is illustrated graphically, where:

FIG. 1 - Temperature zones 1 in the region of the melt on the phase diagram of stable equilibrium 2 of the Bi ₂ O ₃ - GeO _{2 system} . FIG. 1 shows a double diagram of the stable equilibrium of the Bi ₂ O ₃ -GeO _{2 system} containing the temperature zones of the melts. It is known that on the phase diagram of the Bi ₂ O ₃ - GeO _{2 system,} the melt region can be divided into 3 temperature zones A, B, and C.

FIG. 2 - Results of microstructural analysis of the sample, composition 6: 1 mol. % (system Bi ₂ O ₃ - GeO ₂ ), obtained by the claimed method, increase - 50 times;

FIG. 3 - Results of microstructural analysis of the sample, composition 6: 1 mol. % (system Bi ₂ O ₃ - GeO ₂ ), obtained by the claimed method, increase - 200 times;

FIG. 4 - Results of X-ray phase analysis of a sample with a composition of 6: 1 mol. % (system Bi ₂ O ₃ - GeO ₂ ) obtained by the claimed method.

FIG. 5 - Results of macrostructural analysis of the sample, composition 6: 1 mol. % (system Bi ₂ O ₃ - GeO ₂ ), obtained by the claimed method, an increase of 1.25 times;

The essence of the invention is illustrated by the diagram, as well as the results of X-ray phase, macro- and microstructural analysis.

We have found that heating the initial components to a temperature range of 1060-1160 ° C, holding it for 15-60 minutes and casting the resulting melt onto a platinum substrate ensures reliable production of bismuth germanate with the formula Bi ₁₂ GeO ₂₀ . This is explained by the fact that the process of nucleation of this composition, when casting onto a solid surface, contributes to the formation of a stable phase with the formula Bi ₁₂ GeO ₂₀ .

The data obtained are confirmed by microstructural analysis (Figs. 2-3), which clearly shows the single-phase structure of the obtained material in the form of grains grown and elongated along the direction of heat removal. The existence of a single-phase region with the formula Bi ₁₂ GeO ₂₀ is also confirmed by the X-ray phase analysis shown in Fig. 4. The macrostructure (Fig. 5) shows the finished material crystallized on a platinum plate, immediately after casting.

Based on the analysis results shown in FIG. 2-4, it can be concluded that the decisive role in the synthesis of the Bi ₁₂ GeO ₂₀ phase is played by the cooling method (casting onto a platinum substrate).

The inventive method "Method for producing bismuth germanate Bi1 ₂ GeO ₂₀ by casting" can be implemented using the following material objects:

1. furnace - a heating device with a working chamber, which provides heating of the material to a predetermined temperature in the range of up to 1160 ° C;

2. platinum crucible;

3. platinum plate (crucible, bowl or other platinum container).

An example of a specific implementation:

1. as the initial components, we take powders of bismuth oxide (Bi ₂ O ₃ ) and germanium dioxide (GeO ₂ ) in a ratio of 6: 1 mol. %;

2. the initial reagents are placed in a platinum crucible and mixed with a platinum spatula or a metal spoon;

3. Heat the resulting mixture to 1160 ° C;

4. keep at this temperature for 60 minutes;

5. Pour the resulting melt onto a platinum plate.

As shown by the results of the pilot test, when using the proposed method, the following results are achieved:

1. Pure bismuth germanate with the formula Bi ₁₂ GeO _{20 was} obtained;

2. The inventive method requires much less time for synthesis than all known modern analogs and the prototype given above, which significantly reduces not only time, but also economic costs;

3. One of the reasons for the emergence of a huge number of solid-phase, hydrothermal mechanochemical synthesis methods was precisely the difficulty in extracting the resulting material from the crucible. The inventive method makes it possible to obtain Bi ₁₂ GeO _{20 by} casting, which is of great importance, first of all, for saving expensive crucibles used in the synthesis and destroyed during the extraction of the finished material.

Claims (1)

A method for producing bismuth germanate Bi ₁₂ GeO ₂₀ by casting, including preliminary mechanical mixing of the initial powders of bismuth oxide Bi ₂ O ₃ and germanium oxide GeO ₂ , heating the resulting mixture in a platinum crucible to a predetermined temperature, characterized in that heating is carried out to 1060-1160 ° With holding in this temperature range for 15-60 minutes, after which the resulting melt is poured onto a platinum substrate.

Images