RU2598728C1 - Method of producing nanostructured powder of zirconium tungstate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of nanostructured powder of zirconium tungstate ZrW₂O₈. Synthesis of ZrW₂O₇(OH,Cl)₂·2H₂O precursor is carried out from a mixture of solutions of zirconium oxychloride, sodium tungstate and hydrochloric acid in distilled water, taken in stoichiometric ratio Zr : W=1:2, method then comprises thermal decomposition of obtained precursor in air atmosphere at temperature of 700-900 K for 0.75-1.5 hours at a rate of heating to said temperature not exceeding 100 K/h. Method prevents agglomeration and reduces time for ageing powder. Obtained nano-powder of zirconium tungstate has average size of elongated particles in transverse direction of not more than 15 nm, in longitudinal direction of not more than 0.5 mcm.

EFFECT: disclosed is a method of producing nanostructured powder of zirconium tungstate ZrW₂O₈.

3 cl, 2 dwg

Description

The invention relates to methods for producing nanostructured ceramic oxide (composite) powders, which can be, in particular, used for the manufacture of wear-resistant ceramic materials (or products) with a coefficient of thermal linear expansion of zero.

Known work of E.S. Dedova et al. Obtaining and properties of zirconium tungstate with anomalous characteristics. // Bulletin of the Tomsk Polytechnic University. Chemistry. - 2014. - T. 324 - No. 3, S. 22-25. As the starting components for the preparation of the precursor, we used: Na ₂ WO ₄ · 2H ₂ O (analytical grade), ZrOCl ₂ -8H ₂ O (chemical grade) and HCl (chemical grade). The hydrothermal reaction was carried out at a temperature of 160 ° C for 36 hours. To obtain a monophasic ZrW ₂ O ₈ powder, the synthesized precursor was annealed at a temperature of 570 ° С for 1 hour in air.

The main disadvantages of the known technical solutions are:

- long aging of the precursor (up to 3 weeks),

- powder agglomeration.

The closest in technical essence is the method of producing nanostructured zirconium tungstate powder by the hydrothermal method described in the article: Kozy, L.С. Particle size and morphology control of the negative thermal expansion material cubic zirconium tungstate / LC Kozy, MN Tahir // J. Mater. Chem. - 2009. - V. 19. - P. 2760-2765. Zirconium tungstate hydroxide hydrate was prepared hydrothermally in acidic media. In the experiment, solutions of 0.240 g of ZrOCl ₂ · H ₂ O (0.80 mmol) and 0.330 g of Na ₂ WO ₄ 2H ₂ O (1.00 mmol) and 1.6 ml of water are poured simultaneously into a container with a Teflon insert, and a white gel-like precipitate. A mixture of 6.1 ml of concentrated HClO ₄ / 2.98 g of NaCl (0.05 mol) was prepared and 0.9 ml of water was added to the first mixture and stirred for several minutes. The final concentrations of the starting materials were 0.08 M ZrOCl ₂ · H ₂ O, 0.1 M Na ₂ WO ₄ 2H ₂ O, 7 M HClO ₄ and 5 M NaCl. After the container is placed in a preheated oven at 130 ° C for 72 hours. After cooling, the white precipitate is centrifuged and washed several times with water.

The main disadvantage of this method is the agglomeration of the final powder.

The task of the invention is to develop a method for producing nanostructured powder of zirconium tungstate (ZrW ₂ O ₈ ).

The technical result of the proposed method for producing nanostructured powder of zirconium tungstate (ZrM ₂ O ₈ ) is the absence of agglomeration and a decrease in the aging time of the powder.

The specified technical result is achieved by the fact that the method for producing a nanostructured zirconium tungstate powder involves the synthesis of a precursor (ZrW ₂ O ₇ (OH, Cl) ₂ · 2H ₂ O), then its thermal decomposition, and a mixture of solutions of zirconium and sodium is used to synthesize the precursor tungstate and hydrochloric acid in distilled water, taken at a stoichiometric ratio of elements Zr: W = 1: 2, and the thermal decomposition of the precursor (ZrW ₂ O ₇ (OH, Cl) ₂ · 2H ₂ O) is carried out in air at a temperature of 800-900 K within 0.75-1.5 hours, moreover the heating rate to the specified temperature should not exceed 100 K / h.

The precursor is synthesized in an autoclave with an air atmosphere at a pressure of 2-3 atm, a temperature of 400-450 K for 10-12 hours, then cooled to room temperature and subjected to repeated washing of the precursor at room temperature in air, followed by drying at a temperature of 375-400 TO.

The obtained nanostructured zirconium tungstate powder has an average elongated particle size: not more than 15 nm in the transverse direction, not more than 0.5 μm in the longitudinal direction

The invention consists in the following.

It is known that the synthesis of nanostructured zirconium tungstate powder is possible in several ways. The most preferred is the hydrothermal method, allowing to obtain monophasic zirconium tungstate at relatively low temperatures. The main advantages compared to other methods of “soft chemistry” are the absence of agglomeration and the reduction of the aging time of the powder.

The hydrothermal synthesis parameters determine the properties of the final powders.

The main stages of the proposed hydrothermal method are:

- precursor synthesis;

- thermal decomposition of the precursor to the compound of zirconium tungstate.

The acidity of the solution, the type of acid and the duration of the heat treatment play a decisive role in the morphology of the powder.

When synthesizing zirconium tungstate under hydrothermal synthesis, it is most effective to use hydrochloric acid as the starting acid, which provides the best crystallization of the powder compared to other acids. Also, the type of acid determines the morphology of the powder. For example, the morphology of zirconium tungstate obtained using HCl is represented by elongated particles. The average size of elongated particles in the transverse direction did not exceed 15 nm, in the longitudinal - 0.5 μm.

The particle size of the powder directly depends on the acidity of the solution: the higher the acidity, the smaller the particle size of the precursor. High powder homogeneity and distribution uniformity are determined by the duration of the hydrothermal reaction. Due to the solubility of the precursor at low pH of the solution, recrystallization of ZrW ₂ O ₇ (OH) ₂ · 2H ₂ O is observed, which determines the uniformity of the powder.

The hydrothermal method allows to lower the crystallization temperature of zirconium tungstate in comparison with other chemical methods. ZrW ₂ O ₈ single crystals crystallize already at 573 K.

The main advantages of obtaining zirconium tungstate under conditions of hydrothermal synthesis include:

- high homogeneity of the precursor;

- low crystallization temperatures of zirconium tungstate single crystals.

Nanocrystalline zirconium tungstate powder is made according to the following formulation:

- zirconium oxychloride,

- sodium tungstate 2 water,

- hydrochloric acid.

The following sequence of technological operations is proposed. First, a precursor (ZrW ₂ O ₇ (OH, Cl) ₂ · 2H ₂ O) is prepared under the conditions of the hydrothermal method.

The synthesis of the precursor (ZrW ₂ O ₇ (OH, Cl) ₂ · 2H ₂ O) is carried out from a stoichiometric mixture of Zr: W = 1: 2. As the starting components, solutions of zirconium oxychloride and sodium tungstate and hydrochloric acid in distilled water are used. An aqueous solution of Na ₂ WO ₄ · 2H ₂ O in an amount of 25 ml (0.5 M) is mixed with 25 ml of ZrOCl ₂ · 8H ₂ O (0.25 M), then 25 ml of a solution of hydrochloric acid of various concentrations (0.4 M, 0.7 M) are gradually added. , 1.4 M, 2.5 M).

The freshly prepared solution is thoroughly mixed at room temperature under normal atmospheric pressure.

The resulting suspension is placed in a steel autoclave with a Teflon liner and placed in a furnace for hydrothermal reaction. Heating is carried out in an air atmosphere at a temperature of 400-450 K in a furnace with lanthanum chromite heaters. The duration of the hydrothermal reaction is 10-12 hours.

After turning off the furnace, the steel autoclave is cooled to room temperature. The resulting precursor is subjected to filtration using filtered paper of various densities, then repeatedly washing with distilled water and drying at room temperature in air at a temperature of 375-400 K.

Then, a nanocrystalline zirconium tungstate powder (ZrW ₂ O ₈ ) is synthesized from the obtained precursor by thermal decomposition of the precursor (ZrW ₂ O ₇ (OH, Cl) ₂ · 2H ₂ O). Thermal decomposition of the precursor is carried out in an air atmosphere at a temperature of 800-900 K in a furnace with lanthanum chromite heaters. The duration of isothermal exposure is 0.75-1.5 hours, the heating rate to the temperature of thermal decomposition does not exceed 100 K / hour.

In FIG. Figures 1 and 2 show images of zirconium tungstate powders obtained at different thermal decomposition temperatures, respectively 700 K and 900 K.

Case Studies

Example 1

As the starting components, solutions of zirconium oxychloride and sodium tungstate and hydrochloric acid in distilled water are used. An aqueous solution of Na ₂ WO ₄ · 2H ₂ O in an amount of 25 ml (0.5 M) is mixed with 25 ml of ZrOCl ₂ · 8H ₂ O, then 25 ml of a solution of hydrochloric acid of various concentrations (0.4 M, 0.7 M, 1.4 M, 2.5 M).

A freshly prepared solution in a volume of 150 ml is thoroughly mixed at room temperature under normal atmospheric pressure, while the stoichiometric ratio of elements Zr: W = 1: 2 is observed.

The resulting suspension is placed in a steel autoclave with a Teflon liner and placed in a furnace for hydrothermal reaction. Heating is carried out in an air atmosphere at a pressure of 2 atm, a temperature of 400 K in a furnace with lanthanum chromite heaters. The duration of the hydrothermal reaction is 12 hours. After turning off the furnace, the steel autoclave is cooled to room temperature. The resulting precursor is subjected to filtration using filtered paper of various densities, then repeatedly washing with distilled water and drying at room temperature in air at a temperature of 375 K.

Then, the nanocrystalline zirconium tungstate powder (ZrW ₂ O ₈ ) is synthesized from the obtained precursor by thermal decomposition of the ZrW ₂ O ₇ (OH, Cl) ₂ · 2Н ₂ О precursor in an air atmosphere at a temperature of 900 K in furnaces with lanthanum chromite heaters. The duration of isothermal exposure 0.75 hours, the heating rate to a temperature of thermal decomposition of 100 K / hour.

Example 2

As the starting components, solutions of zirconium oxychloride and sodium tungstate and hydrochloric acid in distilled water are used. An aqueous solution of Na ₂ WO ₄ · 2H ₂ O in an amount of 25 ml (0.5 M) is mixed with 25 ml of ZrOCl ₂ · 8H ₂ O (0.25 M), then 25 ml of a solution of hydrochloric acid of various concentrations (0.4 M, 0.7 M) are gradually added. , 1.4 M, 2.5 M).

A freshly prepared solution in a volume of 150 ml is thoroughly mixed at room temperature under normal atmospheric pressure.

The resulting suspension is placed in a steel autoclave with a Teflon liner and placed in a furnace for hydrothermal reaction. Heating is carried out in an air atmosphere at a pressure of 3 atm and a temperature of 450 K in a furnace with lanthanum chromite heaters. The duration of the hydrothermal reaction is 10 hours.

After turning off the furnace, the steel autoclave is cooled to room temperature. The resulting precursor is filtered, then washed repeatedly with distilled water and dried at room temperature in air at a temperature of 385 K.

Then, the nanocrystalline zirconium tungstate powder (ZrW ₂ O ₈ ) is synthesized from the obtained precursor by thermal decomposition of the ZrW ₂ O ₇ (OH, Cl) ₂ · 2H ₂ O precursor in air at a temperature of 700 K in furnaces with lanthanum chromite heaters. The duration of isothermal exposure is 1.5 hours, the heating rate to the temperature of thermal decomposition is 90 K / hour.

Example 3

As the starting components, solutions of zirconium oxychloride and sodium tungstate and hydrochloric acid in distilled water are used. An aqueous solution of Na ₂ WO ₄ · 2H ₂ O in an amount of 25 ml (0.5 M) is mixed with 25 ml of ZrOCl ₂ · 8H ₂ O (0.25 M), then 25 ml of a solution of hydrochloric acid of various concentrations (0.4 M, 0.7 M) are gradually added. , 1.4 M, 2.5 M).

A freshly prepared solution in a volume of 150 ml is thoroughly mixed at room temperature under normal atmospheric pressure.

The resulting suspension is placed in a steel autoclave with a Teflon liner and placed in a furnace for hydrothermal reaction. Heating is carried out in an air atmosphere at a pressure of 2 atm and a temperature of 430 K in a furnace with lanthanum chromite heaters. The duration of the hydrothermal reaction is 11 hours.

After turning off the furnace, the steel autoclave is cooled to room temperature. The resulting precursor is subjected to filtration, then repeatedly washing with distilled water and drying at room temperature in air at a temperature of 400 K.

Then, the nanocrystalline zirconium tungstate powder (ZrW ₂ O ₈ ) is synthesized from the obtained precursor by thermal decomposition of the ZrW ₂ O ₇ (OH, Cl) ₂ · 2Н ₂ О precursor in an air atmosphere at a temperature of 800 K in furnaces with lanthanum chromite heaters. The duration of isothermal exposure 1.0 hour, the heating rate to a temperature of thermal decomposition of 95 K / hour.

The obtained nanostructured zirconium tungstate powder has an average elongated particle size in the transverse direction not exceeding 15 nm, in the longitudinal - 0.5 μm.

Claims (3)

1. A method of producing a nanostructured zirconium tungstate powder, including the synthesis of the ZrW ₂ O ₇ (OH, Cl) ₂ · 2H ₂ O precursor and its thermal decomposition to obtain zirconium tungstate powder, characterized in that the precursor is synthesized from a mixture of solutions of zirconium oxychloride, sodium tungstate and hydrochloric acid in distilled water, taken at a stoichiometric ratio of elements Zr: W = 1: 2, and the thermal decomposition of the resulting precursor is carried out in air at a temperature of 700-900 K for 0.75-1.5 hours at a heating rate va to 100 K / hour this temperature not higher. 2. The method according to p. 1, characterized in that the precursor synthesis is carried out in an autoclave with an air atmosphere at a pressure of 2-3 atm, a temperature of 400-450 K for 10-12 hours, followed by cooling to room temperature, repeated washing at room temperature temperature in air and subsequent drying at a temperature of 375-400 K. 3. The method according to p. 1, characterized in that the obtained zirconium tungstate powder has an average size of elongated particles in the transverse direction of not more than 15 nm, and in the longitudinal direction of not more than 0.5 microns.

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