SU1723211A1 - Method of bismuth oxide monocrystals preparation - Google Patents

Abstract

The invention relates to methods for producing single crystals of bismuth oxide and can be used in the chemical industry to create superconducting materials, as well as in piezoelectric engineering and acousto-optics. It provides an increase in the size of the crystals, increasing their output and simplifying the process. The process is conducted from equally mixed aqueous solutions of hydrochloric and nitric acids with a concentration of 2.3-3.5% by weight at 150-180 ° C, a pressure of 15-20 atm and a temperature difference. The ratio of the volumes of solid and liquid phases (1.2-16): (4.3-55). Crystals were obtained in sizes up to 5.6 mm with a yield of -98%. Reduced process temperature. 1 hp f-ly. yo

Description

The invention relates to methods for producing single crystals of bismuth oxide and can be used in the chemical industry to create superconducting materials, as well as in piezoelectric engineering and acousto-optics.

A known method for producing single crystals of bismuth oxide under hydrothermal conditions in aqueous solutions of NaOH (KOH) with a concentration of up to 80 wt.% At temperatures above 350 ° C and pressures above 150 atm. In the presence of a temperature difference, bismuth oxide is formed in the cold part of the autoclave.

The disadvantages of this method are the insignificant yield of the final product and the high temperature and pressure of the process. The sizes of single crystals of bismuth oxide are insignificant and are 0.2-2.3 mm at a sufficiently high process temperature.

The known method of hydrothermal production of single crystals of bismuth oxide during crystallization of compounds with the structure of stibiotantalite in the В1аО-Nb2 (Ta2) Os systems and in aqueous solutions of KHF2 and H2202 with a concentration of 0-50 and 0-12 wt.%, Respectively, at a temperature of 450-600 ° С, pressure 1000 -1500 atm and temperature difference in the height of the autoclave 2-12 ° С. Single crystals of bismuth oxide are formed as a side phase and their yield is 5-10 wt.% Of the output of the single crystal BINb04, BlTa04, the dimensions of the single crystals obtained are 0.5-1 mm.

The disadvantages of this method is the owner - a slight yield, small size

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single crystals of bismuth oxide and a high process temperature.

The purpose of the invention is to increase the size of the crystals, increase their yield and simplify the process.

This goal is achieved in that according to the method of producing single crystals of bismuth oxide by hydrothermal methods from an aqueous solution with a mixture containing bismuth oxide at high temperatures and pressures in the presence of a temperature differential, the process is carried out from equal mixed hydrochloric and nitric acid solutions of a concentration of 2 , 5-3.5 wt.%, Respectively, at a temperature of 150-180 ° C, a pressure of 15-20 atm, a temperature difference of 20-30 ° C. Mainly the process is carried out at a ratio of the volumes of the solid and liquid phase VTB.:Vx (1.2-1.6) :( 413-5.5).

The method is carried out as follows.

A standard batch of autoclave, lined with Teflon, is charged with bismuth oxide grade osch. An aqueous solution of HCI and HNOZ of a given concentration in a volume ratio of 3: 1 and with a strictly defined ratio of solid and liquid phases is poured into the autoclave loaded with the mixture, which creates an optimal mobility of the hydrothermal solution to saturation, in which the nutrient material is continuously transported to form and grow single oxide crystals bismuth. In the autoclave, a partition is placed to create a temperature differential, then the autoclave is hermetically sealed with a special machine and placed in a resistance furnace, where it is heated to a predetermined temperature. Preliminary experiments showed that the optimum temperature at which the process of dissolution of bismuth oxide and its mass transfer to the crystallization zone occurs is 150 ° C, the pressure of the liquid medium is 15 atm, and the temperature difference is 2-20 ° C.

When the temperature of the process and pressure decreases, the solubility of the initial mixture decreases sharply, which directly adversely affects the duration of the crystallization process and the yield of the bismuth single crystal. So, for example, at a temperature of about 145 ° C and a pressure of 14 atm, the yield of single crystals of bismuth oxide is only 75% of the initial charge in the autoclave and the process lasts more than 450 hours, at a temperature of 130 ° C the yield of single crystals drops to 60%. At temperatures above 180 ° C, the reactivity of hydrochloric acid is increased due to the more active decomposition of HCI into the constituent H and CI ions, which leads to the partial formation of the by-phase BiOCI. The appearance of this phase reduces the yield of bismuth oxide.

Therefore, temperature parameters are essential in terms of obtaining the maximum yield of single crystals of bismuth oxide. The value of the temperature difference is also significant from the point of

in view of achieving the goal of the invention. A decrease in the temperature difference (AT at 20 ° C) leads to a decrease in the supersaturation necessary for the growth of crystals, and consequently, to an increase in the duration

process for producing single crystals of bismuth oxide. An increase in the value of the temperature difference (DT 30 ° C) contributes to the intensive mass transfer of the initial charge (V1203) to the upper zone of the reaction

autoclave space. This circumstance leads to a high rate of nucleation compared with the growth of crystals that are small in size. For example, when DT 32 ° C and

ceteris paribus, the size of single crystals of bismuth oxide is no more than 2.2 mm, and at T 37 ° C - 2 mm.

The concentration of aqueous solutions of HCI v. NMO3 is 2.5-3.5 wt.%, Which is quite

it is sufficient to completely dissolve bismuth oxide and transfer it into solution in oxidation state (III). At lower concentrations of HCi and HN03 (2 v-ac.%), The solubility of BiaOs decreases, which limits the yield

single crystals of bismuth oxide, and a higher concentration of HCI and HN03 leads to the formation of a phase of BiOCI composition, which does not allow to obtain the optimal yield of the final product.

The process of obtaining single crystals of bismuth oxide occurs according to the following scheme: dissolution of the starting bismuth oxide reactant in aqueous solutions of HCI and HNOZ, mass transfer of dissolved forms of oxide

bismuth followed by crystallization in the form of single crystals in the reaction zone of the autoclave due to supersaturation of the solution created by the temperature difference in the height of the autoclave.

Example 1. A teflon-lined, standard batch autoclave was charged with 120 g of bismuth oxide. Then, an aqueous solution of HCI and HN03 with a concentration of 2.5 wt.% Is poured into the autoclave at

the ratio of solid and liquid phases of 1.2: 4.3. In the autoclave, a partition is placed to create a temperature difference, then the autoclave is hermetically closed and placed in a resistance furnace, where

heated to 150 ° C (dissolution zone) with a temperature difference of 20 ° C. Due to the expansion of the liquid phase, a pressure of 15 atm is created in the autoclave when heated. The holding time of the autoclave in stationary mode is 6 days. The initial charge is dissolved with simultaneous mass transfer of the dissolved forms of bismuth oxide and its subsequent crystallization in the form of single crystal UHW. The yield of single crystals of bismuth oxide is 95.2% of the initial amount of bismuth oxide, sizes 4.0-4.3 mm.

Example 2. A batch of fluoride lined in a batch autoclave, charged with 1.20 g of bismuth oxide. Then, an aqueous solution of hydrochloric and nitric acids with a concentration of 2.5% by weight is poured at a solid-to-liquid ratio of 1.2: 4.3. A partition is placed in the autoclave, then it is closed and placed in a resistance furnace, where it is heated to 150 ° C, as a result of which a pressure of 17 atm is created in it due to expansion of the liquid phase. The temperature difference between the dissolution zone and the crystallization zone is 25 ° C. According to the scheme described in example 1, crystallization of single crystals of bismuth oxide occurs, the yield of which reaches 96.2%, the size of 4.4-4.6 mm.

EXAMPLE 3. The process is carried out in a similar manner. Operating parameters: temperature 150 ° С, pressure 17 atm, temperature difference 30 ° С, concentration of aqueous solutions of hydrochloric and nitric acids 3.5 wt.%, Respectively, the ratio of solid and liquid phases 1.6: 5.5, the amount of bismuth oxide 120 In these technological conditions, the yield of single crystals is 97.0%, and their dimensions are 4.6-5.0 mm.

PRI me R 4. The operating parameters of crystallization: temperature 180 ° C, pressure

18 atm, a temperature difference of 30 ° C, a concentration of aqueous solutions of HCI and HM03 of 2.5 and 2 wt.%, Respectively, the ratio of solid and liquid phases is 1.6: 5.5, the amount of bismuth oxide is 120 g. The yield of single crystals is 97.3 %, and their sizes up to 5.3 mm:

PRI me R 5. The operating parameters of crystallization: temperature 180 ° C, pressure

19 atm, a temperature difference of 30 ° C, a concentration of aqueous solutions of HCI and IMO3 of 3 wt.%, The ratio of solid and liquid phases is 1.2: 4.3, the amount of bismuth oxide is 120 g. The yield of single crystals is 97.8%. 5, their sizes are up to 5.4 mm.

PRI me R 6. The operating parameters of crystallization: temperature 180 ° С, pressure 20 atm, temperature difference 30 ° С, concentration of aqueous solutions of HCI and HN03 03 wt.%, The ratio of solid and liquid phases 1.4: 4.9 . The yield of single crystals of bismuth oxide is 98.1%, and their sizes are up to 5.6 mm.

The use of the proposed method 5 for producing single crystals of bismuth oxide provides the following advantages as compared with known methods.

The yield increases and the single crystal size of bismuth oxide increases. 0 Thus, the yield reaches 98.1%, and the size of single crystals is 5.6 (in the known methods, the yield is small, and the size of single crystals is up to 2.3 mm).

The process temperature is lowered, 5 which simplifies the technology for producing bismuth oxide from the point of view of safety engineering and durability of using expensive autoclaves.

The method is characterized by reliable reproducibility and efficiency, technological prospects for implementation in the chemical industry.

Claims (2)

Invention Formula 5 1. A method of producing single crystals of bismuth oxide under hydrothermal conditions from an aqueous solution of a mixture containing bismuth oxide at high temperatures and pressures and in the presence of a temperature difference between the dissolution zone of the charge and the growth zone, characterized in that in order to increase the size of the crystals , increasing their output and simplifying the process; it is derived from equally mixed water 5 solutions of hydrochloric and nitric acids with a concentration of 2.5-3.5 wt.% At a temperature of 150-180 ° C, a pressure of 15-20 atm and a temperature differential of 20-30 ° C. 2. The method according to p. 1, about tl and h a y i and with 0 by the fact that the process is carried out at the ratio of the volumes of the solid and liquid phases (1.2-1.6): (4.3-5.5).