RU2600400C1 - Method of producing nanoscale powder of stabilized zirconium dioxide - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to methods of producing nanosized powder of stabilized zirconium dioxide and can be used to make a vacuum-tight nanostructured ceramic: solid electrolytes, sensors of fuel combustion completeness, membranes for solid oxide fuel cells; nano-modified organic and inorganic materials; powder coating on metals. Method of producing nano-sized stabilized zirconium dioxide was created, it includes combined deposition of initial reagents in the form of solution of oxynitride zirconium and metal nitrate-stabilizer with ammonia solution, amorphous filtering deposit gel hydroxides, fast freezing of these hydroxides and dehydration of the frozen gel with the help of freeze drying with formation of nanosized xerogel. This xerogel is annealed at 500-1,000 °C and ground in a planetary mill.

EFFECT: method allows to product nano-sized powders of zirconium dioxide with fluorite structure, upon that the powder is characterised by low degree of agglomeration.

1 cl, 5 ex, 3 dwg

Description

The invention relates to methods for producing nanoscale powdered stabilized zirconia and can be used in aircraft and rocket engineering, engine building, space technology for the manufacture of nanostructured ceramic materials, nanomodified organic and inorganic materials, powder coatings on metals, nanostructured solid electrolytes operating under elevated conditions thermal loads and in corrosive environments.

The use of stabilized zirconia in a nanoscale low agglomerated state allows one to lower the temperature of formation of fluorite-like zirconia, increase the vacuum density of the final ceramic, and also reduce the resistance of grain boundaries in the final ceramic material.

A known method of producing nanodispersed powders of metal dioxides, namely 3d metal oxides and 4e metals [1], including continuous interaction, in a flow mode, of metal nitrates with urea in a molar ratio of 2 mol of nitrate groups to 1 mol of urea, while the reaction mixture is exposed microwave radiation. The invention allows to obtain nanodispersed powders with a grain size of not more than 30 nm. However, the known method does not allow to control the degree of agglomeration and the phase composition of the obtained nanodispersed oxides.

Known methods for producing nanoscale zirconium dioxide from an aqueous solution in the gas phase. The invention [2] describes a method comprising spraying an aqueous solution of a salt of a desired metal in a nitrogen stream and contacting the resulting particles with a circulating stream of an aqueous solution under pH control. The particles obtained in the manner described are in the form of fibers. Subsequent processing includes calcination, sonication and evaporative drying. However, sonication of the powder and evaporative drying contribute to a significant enlargement of the agglomerates in the nanosized zirconia powder.

There is also a method of producing zirconium dioxide [3], which includes pyrohydrolysis in the gas phase of fluorine-containing zirconium salts in the presence of water vapor. The invention allows to obtain a high-purity zirconia powder, while the particle size of the powder does not exceed 0.1 microns.

Common disadvantages of the described methods are their multi-stage, energy consumption, as well as low yield.

There is also a known method of manufacturing ceramics based on zirconium dioxide [4], which includes the following stages:

- mixing zirconium dioxide with yttrium oxide is carried out by co-precipitation from salt solutions;

- at the time of precipitation, sodium and potassium fluorides in an amount of 0.5-1.0 weight are added to salt solutions. %;

- conduct heat treatment of the mixture at 1250-1300 ° C;

- sintering is carried out at a temperature of 1600-1700 ° C;

- cooling is carried out to a temperature of 1270-1300 ° C.

The invention allows to obtain ceramic products based on zirconium dioxide with improved thermomechanical properties and operating under conditions of increased thermomechanical loads. However, the introduction of additional components increases the intergranular component of the ceramic resistance.

A significant drawback of the described technical solution is that the heat treatment of the mixture at 1250-1300 ° C contributes to the sintering of the particles of the dispersed phase with the formation of strong, not breakable agglomerates.

A known method of producing a powder of stabilized zirconia [5] from a solution of zirconium salt and a stabilizing agent (stabilizing agent), which includes the preparation of the initial solution, its transformation into an intermediate product by spray drying at 120-350 ° C. The resulting intermediate product is subjected to subsequent grinding and calcination in the range from 400 to 1300 ° C.

The disadvantage of this method is the high degree of agglomeration of the powder due to the production of large durable agglomerates at the stage of high-temperature spray drying due to the occurrence of condensation processes. In this case, strong oxygen bridges are formed between the particles and, thus, the initial structure and dispersion of the gel are violated after sol-gel synthesis.

There is also a method of freeze drying to obtain a catalyst based on zirconium dioxide with a high surface area and high porosity [application US 2006/0183955 A1 from August 17. 2006]. The invention is directed to a catalyst comprising a step of freeze drying an intermediate product. The proposed technical solution describes the possibility of using freeze drying to obtain a catalyst with a high surface area and porosity. As the catalyst material, any Group IV metal oxides, including zirconium dioxide, can be used. However, the method does not allow to obtain nanosized ceramic powder with a low degree of agglomeration, suitable for the manufacture of vacuum-tight nanoceramics, anion-conducting solid electrolytes and powder coatings on metals.

A known method of producing ceramics based on stabilized zirconia for restoration dentists [RU 2536593 C1 from December 27. 2014], closest to the claimed invention in the production of nanoscale precursor powders. The described method is adopted as a prototype of the claimed invention. In common with the claimed method is the stage of formation of xerogels, which in the known method is achieved by freezing the gels, and in the claimed method by freeze drying.

The known method includes a sequence of stages of co-precipitation of hydroxides, the precipitation of which is filtered and frozen at a temperature of -20-25 ° C, which is subjected to a crystallization process at a temperature of from 500 to 600 ° C. The method provides the production of nanocrystalline powders with the required dimensional uniformity and chemical purity of the composition, while the temperature of synthesis and sintering of the product is reduced, the duration of the phase formation stage is reduced.

However, the slow freezing of gel-like precipitates (at -20-25 ° С) does not allow eliminating the diffusion of dispersion phase particles during movement of the freezing front into the gel, which violates the initial structure of the precipitate. Subsequent drying under atmospheric conditions contributes to irreversible agglomeration due to the approach of the particles of the dispersed phase and the formation of strong oxygen bridges between them. In addition, the known method provides for the production of tetragonal zirconium dioxide, which does not have the necessary physicochemical characteristics for the manufacture of nanostructured ceramic materials, nanomodified organic and inorganic materials, powder coatings on metals, nanostructured solid electrolytes operating under high thermal loads and in corrosive environments .

The disadvantages of the known method for producing a stabilized zirconia powder powder are also a high degree of agglomeration of the obtained nanosized powders, the presence of large, strong agglomerates and the low vacuum density of ceramics made from such a powder.

The basis of the known invention is the development of a simple and technologically advanced method for producing nanosized powdered zirconia with a fluorite structure, consisting of unstable agglomerates for the manufacture of nanostructured ceramic materials, nanomodified organic and inorganic materials, powder coatings on metals, nanostructured solid electrolytes operating under conditions of high thermal loads and in corrosive environments.

The technical result of the claimed invention consists in reducing the degree of agglomeration of the obtained nanosized powders, thermal stresses, corrosion of the medium due to a fundamentally new approach to the method of producing nanosized powdered zirconium dioxide, which consists in the joint deposition of the starting reagents in the form of a solution of zirconium nitrate and metal stabilizer nitrate with ammonia solution; wherein the hydroxide precipitate is filtered and washed to a neutral pH; the resulting hydroxide gel is frozen at high speed and subjected to dehydration by freeze drying to form powdery xerogels, which are milled and calcined from 500 to 1000 ° C.

The specified technical result according to the claimed method is achieved by the fact that to reduce the degree of agglomeration, gel freezing is carried out at temperatures from -196 to -50 ° C, since at such temperatures the speed of movement of the freezing front is at least 1 ° C / s and exceeds the diffusion rate of particles dispersed phase in the gel, which prevents the agglomeration of nanosized powder at the stage of freeze drying

In addition, the specified technical result according to the claimed method is achieved by the fact that dehydration is carried out by freeze drying at a pressure of 0.018-0.036 mm Hg. within 18-24 hours, since in this case the dispersion medium is removed directly from the solid phase into the gas, bypassing the liquid phase, which ensures the production of nanosized powders of the required dispersion and characterized by a low degree of agglomeration.

In addition, the specified technical result according to the claimed method is achieved by the fact that nitrates, sulfates, chlorides, zirconyl oxalates and a metal stabilizer can act as starting reagents, and metal cations of the second group of the main subgroup (calcium, magnesium can act as a stabilizer metal cation) , strontium), transition metals of 3, 4, 5 groups (scandium, yttrium, cerium, lanthanum) in an amount of 5-15 mol. %, since the addition of these stabilizers ensures the stability of the fluorite-like modification of zirconium dioxide in the required temperature range, for the manufacture of working under high thermal loads and in corrosive environments, in particular, sensors for monitoring the completeness of fuel combustion

In addition, the specified technical result according to the claimed method is achieved by the fact that mechanical activation in planetary mills is carried out with an acceleration of not less than 8 g, since with these accelerations a greater degree of transfer of the mechanical energy of destruction to agglomerates of nanosized powder of stabilized zirconia is achieved.

The invention is confirmed by FIG. 1-3, where in FIG. Figure 1 shows the distribution of the average size of agglomerates in size before and after ultrasonic treatment in powdery xerogels with a total composition of 9 mol. % CaO - 91 mol. % ZrO ₂ after freeze drying, and in FIG. 2 - micrograph of powdered xerogels of the final composition of 9 mol. % CaO - 91 mol. % ZrO ₂ after freeze drying.

The claimed method is implemented as follows.

The synthesis of nanodispersed powders was carried out by the method of co-precipitation of zirconium and calcium hydroxides. As initial reagents, aqueous solutions of zirconium oxy nitrate ZrO (NO ₃ ) ₂ * 2H ₂ O, metal stabilizer nitrate, and aqueous ammonia were selected. The starting reagents were taken in quantities sufficient to obtain the final nanoscale zirconia powder with fluorite structure. The synthesis flow chart is shown in FIG. 1. A mixture of salt solutions in a predetermined stoichiometric ratio was added to the ammonia solution. To obtain a precipitate with a higher dispersion, dilute solutions of zirconyl nitrate and calcium nitrate salts (~ 0.05-0.2 M) were used to reduce the coagulation of the deposited particles, which occurs during their collisions as a result of Brownian motion and promotes the formation of agglomerates. To reduce agglomeration, the deposition process was carried out at an ice bath temperature of 0-2 ° C and a minimum deposition rate of 0.5 ml / s with vigorous stirring of the obtained hydroxides using an overhead mechanical stirrer. The gel-like precipitates were filtered using a water-jet pump, a Buchner funnel, and a Bunsen flask to a neutral pH and were frozen at a rate of at least 1 ° C / s at temperatures from -196 to -50 ° C. Frozen gels were transferred to a freeze-drying chamber and subjected to dehydration by sublimation at a pressure of 0.018-0.036 mm Hg. at a temperature of 18-25 ° C for 18-24 hours with the formation of nanoscale powdery xerogels. Using X-ray nanotomography, it was found that the average size of the agglomerates in the powders is ~ 250 nm, which corresponds to the size of the agglomerates in the initial gel-like precipitate and confirms the preservation of the structure of the substance during freeze drying. Using scanning electron microscopy, it was found that the particle size of the dispersed phase constituting the powder agglomerates is 26-38 nm. To form a fluorite-like modification of zirconium dioxide, complete recrystallization and deagglomeration processes, the powder was calcined in the range of 500-1000 ° C. A nanosized zirconia powder with a fluorite structure was milled and mechanically activated in a planetary mill lined with agate, silicon carbide or corundum balls of the same material as the lining to obtain the required dispersion. The grinding mode was chosen from 350 to 450 rpm, 10-20 reverse shifts lasting 4-8 minutes and the optimal ratio (350/11/5).

The claimed method was tested at St. Petersburg State University in real time and in real modes. The results of laboratory tests are given in specific examples of implementation.

Example 1. As described above, was synthesized nano-sized powder of zirconia stabilized with calcium oxide final composition 9CaO-91ZrO ₂ (mol.%). The obtained powder was systematically studied by the methods of synchronous thermal analysis (CTA), x-ray phase analysis (XRD) and laser sedimentography (PSD). According to CTA, the phase transition temperature was 494 ° C. According to XRD, a single-phase zirconia powder with a fluorite structure was obtained in the range 400–1300 ° C. Agglomerates after freeze drying are fragile and are easily destroyed by ultrasound or by subsequent heat treatment, as can be seen from FIG. 1. The average size of the agglomerates in the powder after calcination at 1000 ° C was 180 nm (see Fig. 1). In FIG. 2 presents the data of scanning electron microscopy, according to which the agglomerates are composed of particles of a dispersed phase with a size of 26-38 nm.

Example 2. As described above, was synthesized nanosized powder of zirconia stabilized with calcium oxide, the final composition of 12CaO-88ZrO ₂ (mol.%). The obtained powder was systematically studied by the methods of synchronous thermal analysis (CTA), x-ray phase analysis (XRD) and laser sedimentography (PSD). According to CTA, the phase transition temperature was 513 ° C. According to XRD, a single-phase zirconia powder with a fluorite structure was obtained in the range of 500-1000 ° C. The average size of the agglomerates in the powder was 190 nm. Agglomerates are fragile and easily broken by ultrasound.

Example 3. As described above, a nanosized zirconia powder stabilized with calcium oxide of the final composition 8Y ₂ O ₃ -92ZrO ₂ (mol%) was synthesized. The obtained powder was systematically studied by the methods of synchronous thermal analysis (CTA), x-ray phase analysis (XRD) and laser sedimentography (PSD). According to CTA, the phase transition temperature was 485 ° C. According to XRD, a single-phase zirconia powder with a fluorite structure was obtained in the range of 500-1000 ° C. The average size of the agglomerates in the powder was 230 nm. Agglomerates are fragile and easily broken by ultrasound.

Example 4. A nanosized powder of zirconia stabilized with calcium oxide, the final composition of 9CaO-91ZrO ₂ (mol.%) Was obtained by co-precipitation of the starting reagents in the form of a solution of zirconium oxy nitrate and a metal stabilizer nitrate with ammonia solution, the precipitate of hydroxides was filtered and washed to neutral pH; the resulting hydroxide gel was frozen at a temperature of -196 ° C and dried at room temperature. According to CTA, the phase transition temperature was 524 ° C. The resulting powder was calcined at 500-1000 ° C. According to XRD, a single-phase zirconia powder with a fluorite structure was obtained in the range of 500-1000 ° C. After synthesis, large agglomerates were obtained, the average size of which was 950 nm. From FIG. Figure 3 shows that the size distribution of agglomerates is extremely heterogeneous, which does not satisfy the requirements for nanosized zirconia powders.

Example 5. A nanosized powder of zirconia stabilized with calcium oxide, the final composition of 9CaO-91ZrO ₂ (mol%) was obtained by co-precipitation of the starting reagents in the form of a solution of zirconium oxynitrate and a metal stabilizer nitrate with ammonia solution, the precipitate of hydroxides was filtered and washed to neutral pH; the resulting hydroxide gel was frozen at −5 ° C. and dried at room temperature. The size of the obtained agglomerates in the powder was 1500 nm. Under the influence of ultrasound, the average size of agglomerates decreased to 1220 nm, however, this particle size of the dispersed phase does not satisfy the requirements for nanosized zirconia powders.

Thus, the problem facing the authors of this invention has been solved - a simple and technologically advanced method for producing nanosized zirconia powder with a fluorite structure consisting of unstable agglomerates for the manufacture of vacuum-tight ceramic materials operating under high thermal loads and in corrosive environments, in particular, has been developed in sensors for monitoring the completeness of fuel combustion.

The claimed method for producing nanosized powders of stabilized zirconia has a number of obvious advantages compared with the prior art and the prototype - a significant reduction in the degree of agglomeration, which allows you to save the original structure of the original gel-like precipitate; provides nanoscale powders of the required dispersion, consisting of unstable agglomerates; provides stability of fluorite-like solid solution in the temperature range 500-1000 ° C.

List of references

1. Patent (RU) No. 2223929 (IPC C04B 35/486)

2. Patent (US) No. 6162130 (IPC C04B 35/624)

3. Patent (RU) No. 2539581 C1 (IPC G25 / 02)

4. Patent (RU) No. 2194028 C2 (IPC C04B 35/486)

5. Patent (US) No. 6982073 B2 (IPC G25 / 02).

Claims (2)

1. The method of obtaining nanoscale powdered stabilized zirconium dioxide, which consists in the co-precipitation of the starting reagents in the form of a solution of zirconium oxy nitrate and metal stabilizer nitrate with an ammonia solution, filtering the resulting hydroxide precipitate to form a gel, dehydrating this gel to form a powder xerogel, which is subjected to grinding and calcination at 500-1000 ° C, characterized in that yttrium and calcium nitrates in amounts of ve 8-12 mol.%, the hydroxide precipitate is frozen at temperatures from -196 to -50 ° C with a freezing rate of at least 1 ° C / s, and dehydration is carried out using freeze drying at a pressure of 0.018-0.036 mm Hg for 18-24 hours, after which the powder xerogel is calcined and mechanical activation is carried out with an acceleration of at least 8 g. 2. The method according to p. 1, characterized in that the mechanical activation is carried out in planetary mills.

Images