RU2714452C1 - Method of producing powders of zirconium dioxide with a spheroidal shape of particles - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to sol-gel technology for production of zirconium dioxide-based materials with spheroidal shape of particles. It can be used in production of powders for plasma sputtering, hot and cold pressing, laser sintering. Aqueous solution of water-soluble zirconium salts is prepared, water-soluble salts of metals selected from among scandium, yttrium, lanthanum and lanthanides are added to form a common solution of metal salts. Prepare solution-precipitant by dissolving hydroxides of alkali metals or ammonia in water, depositing hydrated zirconium oxide by dosing total solution of metal salts into reaction volume, in which mixing and constant pH from range of values from 4 to 6 inclusive is maintained due to controlled introduction of settling solution. Formed residue is separated, dried and thermally treated.

EFFECT: obtaining narrow-fractionated powder materials at reduction of process steps.

7 cl, 3 dwg, 7 ex

Description

FIELD OF THE INVENTION

The invention relates to a technology for producing oxide materials, in particular to a technology for producing powders based on zirconium dioxide with a spheroidal particle shape, which can be used to produce ceramics, coatings, sorbents and catalysts.

BACKGROUND OF THE INVENTION BACKGROUND OF THE INVENTION

Zirconia is widely used in the creation of ceramics and coatings, sorbents and catalysts. Particle shape is an important characteristic of powder materials, often determining the possibility of their use in various fields of technology. The correct particle shape close to spherical determines the high flowability of powder materials, high bulk density, as well as low hydro- and aerodynamic drag of particles, therefore, the task of forming zirconia powders with the correct particle shape is very important.

A known technological approach for the formation of zirconia particles with the correct shape is to granulate a zirconium sol by dispersing it into a liquid medium. So the known method [Patent SU 1491561, prior. from 10.20.1987, publ. 07/07/1989, IPC B01J20 / 06] for producing a sorbent based on zirconium hydroxide, including mixing a solution of zirconium with urotropine and urea, dropping dispersing the solution into a layer of water-insoluble organic liquid at a temperature of 85-95 ⁰ C, washing the obtained spherical granules of the hydrogel and their subsequent heat treatment . The disadvantages of the method are the necessity of using expensive organic substances heated to a high temperature in the technological process, as well as the difficulty of obtaining powders with a narrow particle size distribution at the level of 10-60 microns.

The known method [Patent RU 2235686, prior. dated January 4, 2003, publ. 09/10/2004, IPC C01G25 / 02, C25B1 / 00, B01J20 / 06] for producing spherical granular materials based on zirconium hydroxide and zirconium oxide, including electrolysis of an aqueous solution based on zirconium chloride at a temperature of 50-100 ° C to obtain a zirconium hydroxide sol, dispersing a sol into a gelling medium, separation of the formed gelsfer, their washing, drying and heat treatment. An advantage of the described method is the ability to use aqueous ammonia or alkali solution as a gelling medium, which is ensured by obtaining a highly viscous zirconium sol at the stages of carbonate dissolution and electrolysis of the solution. Significant disadvantages of the method are the complexity and multi-stage process, the need to work with hydrochloric acid, which necessitates a thorough washing of the obtained helspheres from residual chlorine ions, as well as the difficulty of obtaining powders with a narrow particle size distribution at the level of 10-60 microns.

An alternative approach for the formation of zirconia particles with the correct shape is the electrofusion of zirconia particles. The known method [Patent US6893994, prior. from 08.13.2002, publ. 02/19/2004, IPC C23C-004/10] the formation of chemically homogeneous particles of zirconium dioxide, including the electrofusion of zirconium dioxide, cooling of zirconium dioxide and heat treatment of the obtained powder. The technical result is the formation of predominantly spherical hollow particles with a size of less than 200 microns. The advantage of the proposed method is the ability to obtain hollow particles. Significant disadvantages of the method are the difficulty of obtaining powders with a narrow particle size distribution at the level of 10-60 microns and high energy costs for melting zirconium dioxide.

Another technological approach for the formation of zirconia particles with the correct shape is spray drying of suspensions containing zirconia particles as a solid phase and, if necessary, particles of stabilizing additives. The spherical shape of the particles is given by spraying a suspension of particles, followed by removal of the solvent and the formation of aggregated powders. The known method [Patent JP5932072, prior. from 02/12/2015, publ. 05/13/2016, IPC C23C-004/10] for producing particles by spray drying and a method for using these particles to create heat-protective coatings by gas thermal spraying. The method includes the steps of forming a suspension with a solids content in the range of 75 to 85% by mass, feeding the suspension to a disk atomizer, controlling the speed of release of the suspension particles from the disk atomizer in the range of 60 to 90 m / s by adjusting the disk rotation speed drying the particles of the suspension with the formation of powder and finishing to obtain a powder in which 50% of the mass particles are in the range from 40 to 100 microns. The advantage of the method is the ability to increase the heat resistance of coatings by inhibiting crack growth. Significant disadvantages of the method are the high energy costs for drying and the difficulty of obtaining powders with a narrow particle size distribution at the level of 10-60 microns.

Thus, the technical problem facing the authors of the present invention is the complexity and multi-stage process for producing materials based on zirconium dioxide with a spheroidal particle shape, as well as the difficulties in obtaining powders with a narrow particle size distribution of 10-60 microns when using existing synthesis methods.

SUMMARY OF THE INVENTION

The technical result achieved by the implementation of the invention is to significantly reduce the number of operations of the process for producing zirconium oxide with a spheroidal particle shape, as well as to obtain powders with a narrow particle size distribution at the level of 10-60 microns.

The claimed method for producing materials based on zirconium dioxide with a spheroidal particle shape includes:

- preparation of an aqueous solution of zirconium salts;

- introduction of a metal salt of group 3 of the Periodic Table of Chemical Elements D.I. Mendeleev (PSHE D.I. Mendeleev) selected from scandium, yttrium, lanthanum and lanthanides into an aqueous solution of zirconium salts with the formation of a common solution of metal salts;

- preparation of a precipitating solution by dissolving alkali metal or ammonia hydroxides in water;

- introduction of an aqueous medium into the reaction volume;

- precipitation of hydrated zirconium oxide by dosing a total solution of metal salts in the reaction volume in which stirring and a constant pH value from a range of values from 4 to 6, inclusive due to the controlled introduction of a precipitating solution, are maintained;

- separation of the formed precipitate, drying and heat treatment.

The claimed technical result is achieved due to the formation of aggregates of particles of hydrated zirconium oxide with a spheroidal shape and with a narrow controlled size distribution of aggregates at the stage of hydrolysis of a solution of zirconium salts by maintaining a constant pH of the hydrolysis process at the pH of the isoelectric point of hydrated zirconium oxide.

The inventors proceeded from the fact that the particles of hydrated zirconium oxide formed during hydrolysis interact with the dispersion medium to form a double electric layer. The formation of a double electric layer is caused by predominant adsorption on the surface of particles of hydroxyl ions or hydroxonium ions and, in turn, is determined by the pH level of the dispersion medium. The double electric layer provides electrokinetic stabilization of particles, prevents their growth and aggregation during the deposition process. The organization of the process of hydrolysis of zirconium salts at a pH close to the pH of the isoelectric point of hydrated zirconium oxide leads to the formation of particles with a weakly pronounced double electric layer. Such particles are unstable, they are characterized by processes of aggregation growth during hydrolysis of salts, which, during the process of hydrolysis in solution due to layer-by-layer growth, leads to the formation of aggregates with a regular shape close to spherical. Due to the fact that the formation of hydrated zirconia aggregates during the implementation of the claimed method occurs due to layer-by-layer particle growth, it becomes possible to obtain aggregates with an adjustable size. Subsequent heat treatment of hydrated zirconium oxide aggregates leads to the formation of particles of zirconium oxide with a spheroidal shape and with a narrow particle size distribution.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by figures, which depict

- figure 1 is a table of parameters of the distribution of particle sizes of samples,

- figure 2 is a graph of the distribution of particle sizes for the sample obtained in example 1,

- figure 3 is an optical photograph of the particles of the sample according to example 1.

DETAILED DESCRIPTION OF THE INVENTION

At the first stage of obtaining materials based on zirconium dioxide with a spheroidal particle shape, a solution of a zirconium salt in water is prepared. As the zirconium salt, water-soluble salts of inorganic acids can be used, in particular zirconium nitrate, chloride or sulfate. The nature of the salt anion does not significantly affect the feasibility of the invention, the main criteria for selection are sufficient solubility in water and the stability of zirconium salts to hydrolysis in an aqueous solution. In order to prepare a solution of zirconium salt, the corresponding zirconium salt is dissolved in water. It is also possible to prepare a solution of the zirconium salt by dissolving the zirconium compounds in the corresponding inorganic acid. According to a preferred embodiment of the invention, basic zirconium carbonate and nitric acid are used to prepare the zirconium salt solution.

In the second stage of obtaining materials based on zirconium dioxide

in an aqueous solution of zirconium salts add an additive of metal salts of 3 groups of PSHE D.I. Mendeleev, selected from scandium, yttrium, lanthanum and lanthanides with the formation of a common solution of metal salts. As metal salts of the 3rd group PSHE D.I. Mendeleev can be used water-soluble inorganic salts, primarily nitrates, chlorides or sulfates of the corresponding metals. The nature of the salt anion does not significantly affect the feasibility of the invention, the main criteria for selection are sufficient solubility in water and the stability of metal salts of the 3rd group of PSE D.I. Mendeleev, selected from scandium, yttrium, lanthanum and lanthanides, to hydrolysis in an aqueous solution. The addition of metal salts of group 3 PSHE D.I. Mendeleev can be performed both by dissolving metal salts of the 3rd group of PSHE D.I. Mendeleev in a solution of zirconium salts in water, and by introducing an aqueous solution of metal salts of the 3rd group of PSHE D.I. Mendeleev's zirconium salt solution. Preferably, the addition of a compound of Group III metals may comprise from 0 to 20% by weight of the composition, calculated as oxides. With an increase in the amount of the additive of the compound of metals of the 3rd group Mendeleev above 20% of the mass may not fully coprecipitate metals of the 3rd group of PSE DI Mendeleev selected from the group of lanthanum, yttrium or lanthanides with zirconium, however, this does not affect the possibility of obtaining materials based on zirconium dioxide with a spheroidal particle shape when using the claimed method.

In the third stage, a precipitating solution is prepared. As the precipitating solution, an aqueous solution of alkali metal or ammonia hydroxides with a hydrogen index of more than 7, including an aqueous solution of ammonia, sodium hydroxide, or potassium, can be used. In a preferred embodiment of the invention, aqueous ammonia is used to precipitate hydrated zirconia.

In the fourth stage of obtaining a material based on zirconium dioxide with a spheroidal particle shape, an aqueous medium is introduced into the reaction volume. An aqueous medium is necessary for the distribution of reagents and reaction products in the reaction volume at the initial stage of deposition, as well as to ensure pH control. The amount of aqueous medium introduced into the reaction volume is not critical. In the General case, in order to reduce the volume of the apparatus, the minimum amount of aqueous medium necessary to ensure pH control and the distribution of reagents and reaction products due to mixing is introduced into the reaction volume. As the aqueous medium, distilled water or aqueous solutions of inorganic salts can be used. In the general case, the type of cations and anions of salts does not significantly affect the implementation of the invention, however, the addition of salts having a buffer capacity, such as ammonium salts, leads to an increase in the inertia of the reaction volume and facilitates the maintenance of a constant pH value in the reaction volume at the precipitation stage. Preferably, distilled water or an aqueous solution of ammonium nitrate or ammonium chloride with a concentration of from 0 to 5 mol / L inclusive is used as the liquid medium.

At the fifth stage of obtaining a material based on zirconium dioxide with a spheroidal particle shape, hydrated zirconia is precipitated by dosing a common solution of metal salts obtained in the second stage, into which reaction volume is maintained during the entire deposition process and mixing at a constant pH from a range of 4 to 6 units inclusive, and even better from a range of values from 4.5 to 5.5 units inclusive due to the controlled introduction of the precipitating solution obtained in the third hundred diy. Hereinafter, a constant pH value during the entire deposition process is understood to mean a value that does not differ from the selected one by more than 0.1 units, while in the first minutes of precipitation, the deviation of the pH from the set value may exceed 0.1 due to the low inertia of the reaction volume. The inertia of the reaction volume during the deposition process depends on a large number of factors, primarily on the composition of the initial aqueous medium, on the type and concentration of the precipitating solution used, on the acidity and total concentration of salts in the total solution of metal salts, on the ratio of the reaction volume and the rates of introduction of the components . For this reason, the duration of establishing a constant pH in the reaction volume varies to a large extent depending on the selected conditions for the organization of the deposition process. In the General case, in the framework of the proposed method of synthesis, the pH during the deposition process is considered constant if the period of establishing a constant pH in the reaction volume does not exceed one tenth of the total duration of the deposition process. A constant pH value during the deposition process is ensured by controlled independent dosing of a common solution of metal salts having a pH value of less than 7, and a precipitating solution having a pH value of more than 7. Adjustable independent dosing of solutions can be performed using peristaltic pumps, diaphragm pumps, pumps direct dosing, centrifugal pumps with variable speed, as well as other methods. The pH of the reaction volume is monitored throughout the deposition process using pH meters with ion-selective electrodes or other pH detection systems in solution.

After the completion of the precipitation step (supplying the entire volume of the total salt solution), the resulting suspension is held under stirring. In the case of using metals of the 3rd group of PSHE D.I. Mendeleev yttrium, lanthanum or lanthanides, to achieve complete precipitation of these components after the suspension is kept, it is necessary to ensure a smooth increase in the pH of the suspension to a value of 9 units. To achieve high uniformity of distribution of metal compounds of the 3rd group PSHE D.I. Mendeleev in the sediment operation, an increase in pH must be carried out at a rate of not more than 1 unit of pH / hour.

After exposure to hydrated zirconium oxide, the operation of filtering, drying and calcining the precipitate is carried out. Preferably, the precipitate is dried at a temperature of from 30 to 120 ° C to constant weight. Sediment firing can be carried out at temperatures from 300 to 1300 ° C, while the main impurities of salts sublimate or decompose.

Example 1

This example relates to a composition of 93% by weight zirconia and 7% yttrium oxide.

620 ml of distilled water and 442.9 grams of zirconium carbonate are introduced into a beaker with stirring (the content of zirconium oxide in zirconium carbonate is 42% by weight). To the resulting suspension was added 187 ml of concentrated nitric acid (mass concentration 71.6%). After complete dissolution of zirconium carbonate, 60.2 grams of yttrium hexahydrate Y (NO ₃ ) ₃ ⋅ 6H ₂ O are introduced into the solution. After complete dissolution of yttrium nitrate, the solution volume is adjusted to 2000 ml using a volumetric flask. The resulting solution was kept under stirring for 2 hours before precipitation. In parallel with the preparation of a common solution of metal salts, a precipitating solution is prepared. To do this, 350 ml of concentrated ammonia solution (mass concentration of 24%) and 438 ml of distilled water are introduced into a beaker.

To carry out the deposition of hydrated zirconia with a spheroidal particle shape, 200 ml of distilled water are introduced into a reactor equipped with a stirrer and a pH sensor. Then, with the help of peristaltic pumps, a controlled dosed introduction of a total solution of metal nitrates and an aqueous solution of ammonia into the reaction volume is carried out with stirring, and the pH in the reaction volume is maintained constant at 5.0 ± 0.1 units. due to balancing the rates of introduction of both solutions. After the introduction of the entire volume of the total solution of metal nitrates, the resulting suspension is maintained at pH = 5.0 ± 0.1 units within 2 hours. Next, the suspension is filtered, the precipitate is placed in an oven, and the precipitate is dried at a temperature of 100 ⁰ С for 12 hours. After that, the precipitate is fired in a muffle furnace at a temperature of 1000 ⁰ C for 2 hours.

After firing, the particle size distribution is measured using an Analisetta 22 nanotech laser diffractometer using a green and infrared laser. The particle shape is examined using optical microscopy. The particle size distribution is characterized by a set of different parameters, including D90 - the conditional particle diameter, that 90% of the powder particles will have a diameter less than or equal to this value, D [4,3] - the average volume diameter of the particles, the size dispersion is a parameter characterizing the spread particle size of the material, determined by the ratio (D90-D10) / D50. The described parameters of the particle size distribution of the samples for all examples are presented in figure 1. The particle size distribution for the sample obtained in example 1 is presented in figure 2, an optical photograph of the particles of the sample in example 1 is shown in figure 3.

Example 2

This example relates to a composition of 82% by weight zirconia and 13% yttrium oxide and 5% scandium oxide.

620 ml of distilled water and 390.5 grams of zirconium carbonate are introduced into a beaker with stirring (the content of zirconium oxide in zirconium carbonate is 42% by weight). 165 ml of concentrated nitric acid are added to the resulting suspension. After complete dissolution of zirconium carbonate, 88.1 grams of yttrium hexahydrate Y (NO ₃ ) ₃ ⋅ 6H ₂ O and 33.5 g of scandium nitrate Sc (NO ₃ ) ₃ are introduced into the solution _. After complete dissolution of the salts, the solution volume is adjusted to 2000 ml s using a volumetric flask. The resulting solution was kept under stirring for 2 hours before precipitation. In parallel with the preparation of a common solution of metal salts, a precipitator solution is prepared. To do this, 350 ml of concentrated ammonia solution (mass concentration of 24%) and 438 ml of distilled water are introduced into a beaker. Precipitation is carried out at a constant pH value of 5.5 ± 0.1. After the introduction of the entire volume of the total solution of metal nitrates, the resulting suspension is maintained at pH = 5.5 ± 0.1 units. within 2 hours. Next, a slow introduction of the precipitating solution into the suspension is carried out until a pH value of 9 is reached, and the pH growth rate is 1 unit. pH / hour After that, the suspension is kept under stirring for another 2 hours, the suspension is filtered. Next, the precipitate is placed in an oven, drying the precipitate is carried out at a temperature of 100 ° C for 12 hours. After that, the precipitate is fired in a muffle furnace at a temperature of 1000 ° C for 2 hours.

Example 3

This example relates to a composition of 93% by weight zirconia and 7% yttrium oxide.

620 ml of distilled water and 442.9 grams of zirconium carbonate are introduced into a beaker with stirring (the content of zirconium oxide in zirconium carbonate is 42% by weight). 258.5 ml of concentrated hydrochloric acid (mass concentration of 36.2%) was added to the resulting suspension. After complete dissolution of zirconium carbonate, 37.4 grams of yttrium chloride hexahydrate YCl ₃ ⋅ 6H ₂ O is introduced into the solution. After complete dissolution of yttrium chloride, the solution volume is adjusted to 2000 ml using a volumetric flask. The resulting solution was kept under stirring for 2 hours before precipitation. In parallel with the preparation of a general solution of metal salts, a precipitating solution is also prepared as described in Example 1. To precipitate hydrated zirconium oxide with a spheroidal particle shape, 200 ml of distilled water and 53 grams of ammonium chloride are introduced into a reactor equipped with a stirrer and a pH sensor. which corresponds to a concentration of ammonium chloride in the reaction volume of 5 mol / L. Precipitation, drying and firing of the precipitate are carried out as described in example 1.

Example 4

This example relates to a composition of 98% by weight zirconia and 2% yttrium oxide.

620 ml of distilled water and 466.7 grams of zirconium carbonate are introduced into a beaker with stirring (the content of zirconium oxide in zirconium carbonate is 42% by weight). To the resulting suspension was added 197 ml of concentrated nitric acid (mass concentration 71.6%). After complete dissolution of zirconium carbonate, 13.6 grams of yttrium hexahydrate Y (NO ₃ ) ₃ ⋅ 6H ₂ O is introduced into the solution. After complete dissolution of yttrium nitrate, the solution volume is adjusted to 2000 ml using a volumetric flask. The resulting solution was kept under stirring for 2 hours before precipitation. The precipitating solution is prepared as follows: 52.8 g of anhydrous sodium hydroxide and 400 ml of distilled water are introduced into a beaker. By mixing, complete dissolution of sodium hydroxide is achieved. After complete dissolution of sodium hydroxide, the solution volume was adjusted to 500 ml using a volumetric flask. Precipitation is carried out as described in example 1.

Example 5

This example relates to a composition of 90% by weight zirconia and 10% ytterbium oxide.

620 ml of distilled water and 390.5 grams of zirconium carbonate are introduced into a beaker with stirring (the content of zirconium oxide in zirconium carbonate is 42% by weight). 165 ml of concentrated nitric acid are added to the resulting suspension. After complete dissolution of zirconium carbonate, 31.6 grams of ytterbium sulfate of eight-water Yb ₂ (SO ₄ ) ₃ ⋅ 8H ₂ O is introduced into the solution. After complete dissolution of the salt, the solution volume is adjusted to 2000 ml using a volumetric flask. The resulting solution was kept under stirring for 2 hours before precipitation. Precipitation is also carried out as described in example 1, only at a constant pH of 4. Precipitation, drying and firing of the precipitate are carried out in the same manner as described in example 1.

Example 6 (comparative).

This example relates to a composition of 93% by weight zirconia and 7% yttrium oxide.

A general solution of metal salts and a precipitating solution are prepared in the same manner as in Example 1. Precipitation of hydrated zirconium oxide is carried out in a direct manner, i.e. an ammonia solution is introduced into the total solution of metal nitrates with stirring until the pH is equal to 9. After that, the precipitate is kept for 2 hours with stirring, filtered, washed with 1000 ml of distilled water on the filter, dried and calcined in the same way as described in example 1 .

Example 7 (comparative).

In this case, they do the same as described in example 6, only the precipitation of hydrated zirconium oxide is carried out by the reverse method, i.e. a common solution of metal nitrates is added dropwise to an ammonia solution with stirring.

Thus, from the above examples it follows that the deposition of hydrated zirconium oxide with a different content of metals of the 3rd group of PSCE D.I. Mendeleev (examples 1, 2, 4, 5) from solutions of various water-soluble inorganic salts (examples 1,3) at a constant pH in the reaction volume from a range of values from 4 to 6 (examples 1, 3, 5), when used as precipitating solution of an aqueous solution of ammonia and alkali metal hydroxides (examples 1, 2, 3, 4 and 5) leads to the formation of spheroidal particles, while direct deposition (example 6) and reverse deposition (example 7) do not lead to the formation of particles spheroidal shape. The samples obtained in examples 1, 2, 3, 4 and 5 are characterized by a low value of the volumetric average diameter, as well as the dispersion of particle sizes in comparison with samples 6 and 7. Thus, the proposed synthesis method ensures the achievement of the claimed technical result.

Claims (7)

1. A method of obtaining materials based on zirconia with a spheroidal particle shape, characterized in that an aqueous solution of a water-soluble inorganic zirconium salt is prepared, water-soluble inorganic metal salts of the 3rd group of the Periodic system of chemical elements selected from scandium, yttrium are introduced into the aqueous solution of a water-soluble inorganic zirconium salt , lanthanum and lanthanides with the formation of a common solution of metal salts, a precipitating solution is prepared by dissolving alkali metal or ammonium hydroxides aka in water and injected into the reaction volume of the aqueous medium, after which hydrated zirconium oxide is precipitated by dosing a total solution of metal salts in the reaction volume, in which stirring is carried out and a constant pH value is maintained from a range of 4 to 6 inclusive due to the controlled introduction of the solution precipitator, the precipitate formed is separated and drying and heat treatment are carried out. 2. The method according to claim 1, characterized in that during the deposition of hydrated zirconia maintain a constant pH value from a range of values from 4.5 to 5.5 inclusive. 3. The method according to claim 1, characterized in that the concentration of metal salts of group 3 in the total solution of metal salts is from 0 to 20% by weight of the composition in terms of oxides. 4. The method according to claim 1, characterized in that the concentration of zirconium in the total solution of metal salts is from 0.1 to 4 mol / L. 5. The method according to claim 1, characterized in that before the deposition begins, distilled water is introduced into the reaction volume. 6. The method according to claim 1, characterized in that before the deposition begins, an aqueous solution of ammonium nitrate or ammonium chloride with a concentration of from 0 to 5 mol / L, inclusive, is introduced into the reaction volume. 7. The method according to claim 1, characterized in that after the completion of the deposition at a constant pH value, a smooth increase in the pH of the suspension to a value of 9 units is carried out. at a rate of not more than 1 pH / hour unit.

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