Zirconium oxide powder and method for producing same

Abstract

The present invention addresses the problem of providing: a zirconium oxide powder obtained by reducing the particle diameter of secondary particles; and a method for producing the same. A zirconium oxide powder according to the present invention has: a crystal phase consisting solely of monoclinic crystals; and a unimodal particle size distribution. A method for producing the zirconium oxide powder according to the present invention comprises: a reaction step in which heated ammonium peroxodisulfate is added to heated zirconium oxychloride to obtain a basic zirconium sulfate slurry; a dehydration step in which the basic zirconium sulfate slurry is neutralized by adding ammonia water thereto to obtain a zirconium hydroxide slurry, and then a solvent is removed to obtain a zirconium hydroxide cake; a repulp washing step in which the zirconium hydroxide cake is subjected to repulp washing using ammonia water; a firing step in which the zirconium hydroxide cake is fired in a furnace using superheated steam to obtain zirconium oxide; and a crushing step in which the zirconium oxide is crushed to obtain a zirconium oxide powder.

Description

Zirconium oxide powder and method for producing the same

[0001] This invention relates to zirconium oxide and a powder for producing the same.

[0002] In recent years, zirconia-based powder materials, primarily composed of zirconium oxide, have attracted attention as additives that improve the properties of electronic materials.

[0003] Patent Document 1 discloses a zirconia-based powder material, which is said to be easily obtained as fine particles through a simple crushing process.

[0004] Japanese Patent Publication No. 2023-142376

[0005] With the advancement of electrification in automobiles, the number of electronic devices installed in vehicles is increasing. As a result, the production of multilayer ceramic capacitors (MLCCs) is also increasing. MLCCs are becoming even smaller and more multilayered to meet the demands of miniaturization in electronic devices. Therefore, the dielectric calcium zirconate powder, which is the main raw material, needs to be made into finer particles, and furthermore, the zirconium oxide powder, which is a raw material for dielectric calcium zirconate, needs to have smaller secondary particle sizes.

[0006] In view of the above circumstances, the present invention aims to provide zirconium oxide with reduced particle size as secondary particles, and a method for producing the same.

[0007] The present inventors have diligently investigated methods for reducing the particle size of secondary particles of zirconium oxide powder. As a result, they have found that the particle size of secondary particles of zirconium oxide powder can be reduced by a manufacturing method that includes a calcination treatment using superheated steam. The present invention has been made by further investigation and includes the following embodiments.

[0008] (1) Zirconium oxide powder having a crystalline phase consisting only of monoclinic crystals and a unimodal grain size distribution.

[0009] (2) The particle size distribution is (D 90 -D 10 ) / D 50 The zirconium oxide powder of (1) that satisfies ≤ 3.00.

[0010] (3) Specific surface area of ​​20.0 to 100.0 m 2 The zirconium oxide powder of (1) or (2) described above, in a quantity of / g.

[0011] (4) A method for producing zirconium oxide powder, comprising: a reaction step of adding heated ammonium peroxodisulfate to heated zirconium oxychloride to obtain a basic zirconium sulfate slurry; a dehydration step of adding ammonia water to the basic zirconium sulfate slurry to neutralize it and obtain a zirconium hydroxide slurry, then removing the solvent to obtain a zirconium hydroxide cake; a repulping wash step of repulping the zirconium hydroxide cake with ammonia water; a calcination step of calcining the zirconium hydroxide cake in a furnace using superheated steam to obtain zirconium oxide; and a crushing step of crushing the zirconium oxide to obtain zirconium oxide powder.

[0012] (5) The method for producing zirconium oxide powder according to (4), characterized in that the maximum temperature of the furnace atmosphere in the firing step is 250 to 800°C.

[0013] (6) The method for producing zirconium oxide powder according to (5), characterized in that the firing step includes the steps of: loading a zirconium hydroxide cake into a furnace; raising the furnace atmosphere to the maximum temperature at a heating rate of 5°C / min or more; starting the circulation of superheated steam at 200 to 650°C into the furnace while the furnace atmosphere is being heated or after the furnace atmosphere has reached the maximum temperature; holding the zirconium hydroxide cake for 0 to 2 hours; stopping the circulation of the superheated steam; and lowering the furnace atmosphere to a temperature of 100°C or lower at a cooling rate of 5°C / min or more.

[0014] The present invention also includes the following embodiments.

[0015] (A) The crystalline phase consists only of monoclinic crystals, the grain size distribution is monomodal, and D 90 Zirconium oxide powder satisfying the requirement of ≤0.650 μm.

[0016] (B) The particle size distribution is D 100The zirconium oxide powder of (A) satisfying ≦ 5.00 μm.

[0017] (C) The particle size distribution is (D 90 - D 10 ) / D 50 The zirconium oxide powder according to (A) or (B) satisfying ≦ 3.00.

[0018] (D) The specific surface area is 20.0 to 100.0 m 2 / g of any of the zirconium oxide powders of (A) to (C).

[0019] According to the present invention, it is possible to provide a zirconium oxide powder with reduced secondary particle size and a method for producing the same.

[0020] It is a diagram showing an outline of a firing apparatus using superheated steam. It is a diagram showing an example of an X-ray diffraction pattern in an example. It is a diagram showing an example of a particle size distribution in an example.

[0021] <Zirconium Oxide Powder> The zirconium oxide powder of the present invention consists only of a monoclinic crystal phase and has a unimodal particle size distribution.

[0022] (Crystal Phase) The zirconium oxide powder of the present invention consists only of a monoclinic crystal phase. The fact that the crystal phase consists only of a monoclinic crystal means that there are few impurities. As the main raw material during the synthesis of calcium zirconate dielectric, in zirconium oxide particles composed only of monoclinic crystals, Ca 2+ It is considered that the diffusion of metal ions proceeds uniformly. That is, there is an advantage that the dielectric calcium zirconate can be stably obtained with easy reaction control and reduced defect rate. The fact that the crystal phase consists only of a monoclinic crystal can be confirmed by an X-ray diffraction method. As the X-ray diffractometer, for example, MiniFlex600 manufactured by Rigaku Corporation can be used.

[0023] (Particle Size Distribution) The zirconium oxide powder of the present invention has a unimodal particle size distribution. The particle size distribution is a histogram with the particle size on the horizontal axis and the frequency on the vertical axis. A unimodal particle size distribution means that the distribution has one peak, that is, a distribution with a single peak (extreme value), and both sides of the peak are monotonically increasing or monotonically decreasing. The fact that the particle size distribution is unimodal means that there are no coarse particles in the zirconium oxide powder and the particle sizes are uniform.

[0024] Since the zirconium oxide powder of the present invention has the above characteristics, it can contribute to the stabilization of product quality and is suitable as a raw material for calcium zirconate dielectrics.

[0025] The particle size distribution is (D 90 - D 10 ) / D 50 The sharpness defined by is preferably 3.00 or less. Here, D n (n is a real number greater than 0 and less than or equal to 100) indicates the particle size at the point where the cumulative curve of the particle diameter becomes n% when the cumulative curve of the particle diameter is obtained with the entire powder population as 100%. That is, D 90 is the particle size at the point where the cumulative curve of the particle diameter becomes 90% when the cumulative curve of the particle diameter is obtained with the entire powder population as 100%.

[0026] The zirconium oxide powder, the main raw material for the synthesis of dielectric calcium zirconate, is solid-phase mixed with compound powders such as calcium carbonate. When the sharpness is 3.00 or less, the zirconium oxide powder is composed of more uniform secondary particle sizes, resulting in a more homogeneous mixture of zirconium oxide particles and calcium carbonate, etc., and a tendency to synthesize a high-precision zirconium oxide powder. On the other hand, when the sharpness exceeds 3.0, the particle size distribution becomes broad. Such a distribution means that there is a wide variety of particle sizes, and many particles that deviate significantly from the average. Therefore, when mixing zirconium oxide particles with particles that have a different particle size distribution, uniform mixing becomes difficult, and it is quite possible that the mixing of, for example, calcium carbonate and zirconium oxide particles will become more non-uniform. As a result, the physical properties of the mixture (e.g., density, fluidity, compressibility, etc.) tend to be non-uniform, and because particles of different sizes are mixed together, it is difficult to obtain a mixture with consistent properties overall, and there is a possibility that the mixture will have a lot of segregation. The sharpness may be 2.80 or less, 2.60 or less, 2.50 or less, 2.40 or less, or 2.30 or less. The sharpness may be 1.20 or more, 1.30 or more, 1.40 or more, or 1.50 or more.

[0027] The particle size distribution is D 90 The condition ≤0.650 μm may also be satisfied. D 90 The particle size may be 0.600 μm or less, 0.550 μm or less, 0.500 μm or less, or 0.450 μm or less. Also, the particle size distribution is D 100 The condition ≤ 5.00 μm may also be satisfied. D 100 The particle size may be 4.50 μm or less, 4.00 μm or less, or 3.50 μm or less. It is generally known that the particle size distribution of the zirconium oxide powder, which is the main raw material during the synthesis of dielectric calcium zirconate, is inherited by the particle size distribution after the synthesis of dielectric calcium zirconate. D 90 ≤0.650 μm, D 100 If the particle size is ≤5.00 μm, the likelihood of uniform thin-layer coating being hindered by coarse particles is low.

[0028] The particle size distribution can be measured, for example, using an MT3300EXII manufactured by Microtrac and by the laser diffraction / scattering method.

[0029] (Specific surface area) The zirconium oxide powder of the present invention preferably has a specific surface area of 20.0 to 100.0 m 2 / g. When the specific surface area is 20.0 m 2 / g or more, it is preferable because the contact area becomes large during the production of calcium zirconate dielectric. When the specific surface area is 100.0 m 2 / g or less, it is possible to suppress the aggregation of zirconium oxide powder, which is preferable. When the specific surface area is less than 20.0 m 2 / g, the primary particles become larger, and the diffusion distance of Ca 2+ metal ions increases, making it difficult to obtain particles in which Ca 2+ metal ions are uniformly solid-dissolved. It is also conceivable that the increase in the size of the primary particles reduces the activity of the zirconium oxide particles, requiring heat treatment at a temperature above a predetermined reaction temperature. When the specific surface area exceeds 100.0 m 2 / g, the contact area becomes large, and the reactivity increases due to the high activity of the zirconium oxide particles, making it easier to react. On the other hand, re-aggregation of fine primary particles also occurs, and it is considered that the sharpness of the particle size distribution increases. Therefore, the specific surface area may be 25.0 m 2 / g or more, or 30.0 m 2 / g or more. The specific surface area may be 95.0 m 2 / g or less, 90.0 m 2 / g or less, 85.0 m 2 / g or less, or 80.0 m 2 / g or less.

[0030] The specific surface area can be measured by the gas adsorption method (BET single point method). As the measuring device, for example, a gas adsorption type pore size distribution measuring instrument NOVA-2000 (manufactured by Yuasa Ionics) can be used.

[0031] <Method for producing zirconium oxide powder>

[0032] Hereinafter, a method for producing the zirconium oxide powder of the present invention will be described.

[0033] The present invention provides a method for producing zirconium oxide powder, comprising: a reaction step of adding heated ammonium peroxodisulfate to heated zirconium oxychloride to obtain a basic zirconium sulfate slurry; a dehydration step of neutralizing the solute solvent with ammonia water, then removing the solvent to obtain the solute; a repulping wash step of performing repulping wash with ammonia water on the solute to obtain zirconium hydroxide powder; a calcination step of performing calcination on the zirconium hydroxide using superheated steam to obtain zirconium oxide; and a crushing step of performing a crushing treatment on the zirconium oxide to obtain zirconium oxide powder. Each step will be described below.

[0034] (Reaction Step) In the reaction step, heated ammonium peroxodisulfate is added to a heated zirconium oxychloride solution and mixed and aged to produce a precipitate, thereby obtaining a basic zirconium sulfate slurry.

[0035] The heating temperature of the zirconium oxychloride solution may be 60 to 95°C. The heating temperature of the zirconium oxychloride solution may be 65°C or higher, 70°C or higher, 75°C or higher, or 80°C or higher. The heating temperature of the zirconium oxychloride solution may be 94°C or lower, 93°C or lower, or 92°C or lower.

[0036] The heating temperature of ammonium peroxodisulfate may be 55 to 70°C. The heating temperature of ammonium peroxodisulfate may be 56°C or higher, 58°C or higher, or 60°C or higher. The heating temperature of ammonium peroxodisulfate may be 68°C or lower, 66°C or lower, or 65°C or lower.

[0037] The amount of ammonium peroxodisulfate added may be 0.23 mol to 0.45 mol per mol of zirconium oxychloride. The amount of ammonium peroxodisulfate added may be 0.25 mol or more, 0.27 mol or more, or 0.30 mol or more per mol of zirconium oxychloride. The amount of ammonium peroxodisulfate added may be 0.42 mol or less, 0.40 mol or less, or 0.38 mol or less per mol of zirconium oxychloride.

[0038] Normally, when producing zirconium sulfate from zirconium salts, a sulfated agent such as ammonium sulfate is used; however, in the production method of the present invention, ammonium peroxodisulfate is used.

[0039] After being added to the reaction system, ammonium peroxodisulfate undergoes a decomposition reaction, supplying reaction materials (sulfate rhizates) for the production of basic zirconium sulfate. During the process leading up to this decomposition reaction, ammonium peroxodisulfate diffuses sufficiently into the reaction system, and as a result, the sulfated reaction with zirconium oxychloride proceeds uniformly within the system. Because the reaction proceeds uniformly, particle nucleation occurs almost simultaneously, which is thought to result in a uniform particle size for basic zirconium sulfate. Furthermore, sintering during heat treatment can be suppressed, and the cleavability of zirconium oxide is expected to improve.

[0040] (Dehydration process) In the dehydration process, the obtained basic zirconium sulfate slurry is neutralized with ammonia water to obtain a zirconium hydroxide slurry. The solvent is then removed by filtration, and the slurry is washed with water to obtain a zirconium hydroxide cake from which most of the impurities such as sulfate ions and chloride ions have been removed. A filter press, centrifuge, etc., which are commonly used in industry, may be used for filtration and washing.

[0041] (Repulping and Washing Process) In the repulping and washing process, the zirconium hydroxide cake is repulped and washed with ammonia water to remove any remaining contaminating ions from the dehydration process. A carboxylic acid solution or an ammonia carboxylic acid solution may be used instead of, or in conjunction with, ammonia water. Formic acid, acetic acid, oxalic acid, etc., may be used as the carboxylic acid.

[0042] (Casturing Process) In the calcination process, the zirconium hydroxide cake is calcined in a furnace to produce zirconium oxide. In the method for producing zirconium oxide of the present invention, it is important to calcine the zirconium hydroxide in a superheated steam atmosphere. Superheated steam refers to water vapor heated to 100°C or higher, and further heated to the saturation steam temperature (approximately 100°C) under normal pressure, and is a colorless, transparent water vapor (H2O) gas.

[0043] Referring to Figure 1, the outline of firing in a superheated steam atmosphere will be described. Figure 1 is a schematic diagram of a firing apparatus 1 using superheated steam. The zirconium hydroxide cake is placed in a cylindrical furnace 101. The furnace 101 is equipped with a furnace tube 101a and a tubular heating device 101b arranged around it, and can be heated by the heating device 101b. Distilled water 11 is sent to an evaporator 202 by a pump 201, and is heated in the evaporator 202 to become superheated steam. The superheated steam is sent to the furnace tube 101a, and the zirconium hydroxide cake 21 placed in the furnace tube 101a is fired. At this time, it is preferable not to use any carrier gas other than superheated steam. Furthermore, a thermocouple 111 may be provided to measure the temperature inside the furnace tube. In addition, a lid such as a silicone rubber stopper 121 may be provided to prevent gases other than superheated steam from entering the furnace.

[0044] The maximum temperature of the furnace atmosphere during the firing process may be 250 to 800°C. The maximum temperature of the furnace atmosphere during the firing process may be 280°C or higher, 300°C or higher, 320°C or higher, or 350°C or higher. The maximum temperature of the furnace atmosphere during the firing process may be 750°C or lower, 700°C or lower, 650°C or lower, 600°C or lower, or 550°C or lower.

[0045] The zirconium hydroxide cake 21 placed on the alumina boat 301 is charged into the furnace, and then the furnace atmosphere is heated to the maximum temperature. The heating rate may be 5°C / min or more, 8°C / min or more, or 10°C / min or more. After reaching the maximum temperature, the circulation of superheated steam may be started, and the zirconium hydroxide cake 21 may be held at the maximum temperature. The superheated steam may be heated to 200 to 650°C and sent to the furnace tube 101a. The heating temperature of the superheated steam may be 250°C or more, 300°C or more, or 350°C or more. The heating temperature of the superheated steam may be 600°C or less, 550°C or less, or 500°C or less. The holding time may be 0 to 2 hours. The superheated steam may be circulated after the furnace atmosphere reaches the maximum temperature, or it may be circulated from the heating process of the furnace atmosphere. The zirconium hydroxide cake 21 placed on the alumina boat 301 may be charged into the furnace during the heating process, or it may be inserted into the furnace from the point of maximum temperature. After maintaining the maximum temperature, the furnace atmosphere is cooled to a temperature of 100°C or lower, and the alumina boat 301 with the zirconium hydroxide cake 21 on it is removed from the furnace. The cooling rate may be 5°C / min or higher, 8°C / min or higher, or 10°C / min or higher.

[0046] The specific firing process and furnace details shown in Figure 1 are merely examples, and it goes without saying that the specific equipment configuration is not limited when firing is performed in a superheated steam atmosphere.

[0047] (Disintegration process) The obtained zirconium oxide is subjected to a disintegration process to obtain zirconium oxide powder. The zirconium oxide powder of the present invention can be obtained by disintegrating the zirconium oxide obtained by the above means, and the specific disintegration method is not limited. For example, dry disintegration may be performed using a mortar and pestle, or a bead mill or roller mill may be used. Alternatively, wet disintegration may be performed in which the zirconium oxide is disintegrated in a solvent using a bead mill or the like. Examples of solvents that can be used include acetone, ethanol, isopropanol, ether, acetonitrile, etc.

[0048] By the above manufacturing method, zirconium oxide powder with reduced particle size of secondary particles can be produced.

[0049] The present invention will be described below using specific examples. The conditions in the examples are just one example of conditions adopted to confirm the feasibility and effectiveness of the present invention. The present invention is not limited to this one example of conditions. The present invention can adopt various conditions as long as they do not depart from the spirit of the invention and achieve the objectives of the present invention.

[0050] <Example of Invention 1> A basic zirconium sulfate slurry was obtained by adding ammonium peroxodisulfate heated to 63°C to an aqueous solution of zirconium oxychloride heated to 92°C, mixing, reacting, and aging the mixture. The amount of ammonium peroxodisulfate added was 0.24 mol per 1 mol of zirconium oxychloride.

[0051] Next, the obtained slurry was added to aqueous ammonia and neutralized to obtain a zirconium hydroxide slurry. The zirconium hydroxide slurry was filtered to obtain the solute, zirconium hydroxide cake.

[0052] Subsequently, repulp washing was performed using ammonia water.

[0053] Furthermore, the zirconium hydroxide cake, after repulping and washing, was calcined in a superheated steam atmosphere to obtain zirconium oxide powder. More specifically, during calcination, 10 g of zirconium hydroxide cake, placed on a small calcination board, was placed in the furnace at room temperature, and then the temperature was increased at a rate of 5°C / min. As soon as the furnace temperature reached the maximum temperature of 450°C, superheated steam at 200°C was circulated into the furnace at a flow rate of 1 mL / min, and the furnace temperature was maintained at 450°C for 2 hours. After that, the flow of superheated steam was stopped, and the temperature was allowed to cool naturally. The rate of natural cooling was 6°C / min. After confirming that the temperature had cooled naturally to room temperature, the small calcination board was removed from the furnace.

[0054] The obtained zirconium oxide was dry-crushed in a mortar to obtain zirconium oxide powder.

[0055] <Examples 2-3 of Invention> Zirconium oxide powder was obtained in the same manner as in Example 1, except that the maximum temperature in the firing process was replaced with that listed in Table 1.

[0056] <Comparative Example 1> Zirconium oxide powder was obtained in the same manner as in Invention Example 1, except that the atmosphere in the firing process was an atmospheric atmosphere (without circulating superheated steam) and the maximum temperature was changed to 350°C.

[0057] <Comparative Example 2> Zirconium oxide powder was obtained in the same manner as in Invention Example 1, except that the additive in the reaction step was changed to ammonium sulfate heated to 63°C at a concentration of 0.48 mol per 1 mol of zirconium oxychloride.

[0058] <Comparative Example 3> Zirconium oxide powder was obtained in the same manner as in Invention Example 1, except that the additive in the reaction step was ammonium sulfate heated to 63°C at a concentration of 0.48 mol per 1 mol of zirconium oxychloride, and the atmosphere in the calcination step was changed to an atmospheric atmosphere (without circulating superheated steam).

[0059] (Crystalline Phase) For each of the obtained zirconium oxide powders, the X-ray diffraction pattern was measured using a Rigaku MiniFlex 600 to confirm whether the crystalline phase consisted solely of monoclinic crystals. The measurement conditions were as follows.

[0060] X-ray: Cu Kα Detector: 1D detector D / tex Ultra II Sample holder: ASC non-reflective sample plate Measurement conditions: Voltage 40kV, current 15mA Measurement range (2θ) 10-90° Scan step 0.01° Scan speed 0.2° / min

[0061] Figure 2 shows the X-ray diffraction pattern of Invention Example 1 as an example of the measurement results. The lines for monoclinic ZrO2 and tetragonal ZrO2 shown at the bottom of Figure 2 indicate the positions of their respective diffraction lines. In the X-ray diffraction pattern of Invention Example 1 in Figure 2, a peak pattern similar to that of monoclinic ZrO2 was observed. On the other hand, the tetragonal ZrO2 peak around 30° was not observed. Therefore, it was determined that Invention Example 1 consists only of monoclinic material. Although not shown, Invention Examples 2 and 3 were also determined to consist only of monoclinic material using a similar method.

[0062] (Particle Size Distribution) To measure the particle size distribution of the obtained zirconium oxide powder, the pretreatment of the powder to be measured and the method for measuring the particle size distribution of the measurement slurry obtained from the pretreatment are described below. A particle size distribution analyzer (MT3300EXII) and an external ultrasonic homogenizer (Nippon Seiki Seisakusho Co., Ltd. US-300AT) were used for the particle size distribution measurement.

[0063] The details of the preparation of slurry samples for measurement and the measurement of particle size distribution are as follows.

[0064] [1] 0.20 g of the sample was weighed and placed in a 100 mL beaker. Then, the sample was immersed in a 0.2% sodium hexametaphosphate solution while washing away any sample adhering to the sides of the beaker until the total volume was 80 mL.

[0065] [2] The tip of the ultrasonic transducer (tip) was placed on the sample stage of the ultrasonic disperser so that it was approximately 15 mm above the bottom of the beaker, and dispersion treatment was performed with an external ultrasonic homogenizer with an amplitude of (13 μm × 2 min) + (23 μm × 6 min) to obtain a slurry sample for measurement.

[0066] [3] The slurry sample obtained in [2] is placed into a Microtrac particle size distribution analyzer (MT3300EXII) so that the concentration index (DV value) is within the range of DV = 0.00185 ± 0.0005, and the volume-based particle size distribution is measured by laser diffraction and scattering (measurement conditions: transparency: transmitted, spherical particles: non-spherical, refractive index (particles): 2.17, refractive index (solvent): 1.333, number of measurements: 30), D 10 , D 50 , D 90 , D 100 The desired result was obtained. Note that the built-in ultrasound function of the MT3300EXII was not used during the measurement.

[0067] Figure 3 shows two examples of particle size distribution measurement results: (a) the particle size distribution of Invention Example 2, and (b) the particle size distribution of Comparative Example 1. It was confirmed that the particle size distribution of Invention Example 2 (a) is a unimodal particle size distribution with one peak. On the other hand, the particle size distribution of Comparative Example 1 (b) has two peaks.

[0068] (Specific Surface Area) The specific surface area was measured using the gas adsorption method (BET single-point method) with a gas adsorption type pore distribution analyzer NOVA2000 (manufactured by Yuasa Ionics). The measurement range was 0.01 m. 2 The concentration was set to / g or less, and N2, Ar, and CO2 were used as adsorbent gases. In addition, vacuum degassing and heating (up to 250°C) was performed as a pretreatment.

[0069] The evaluation results are shown in Table 1. In Table 1, "XRD Monoclinic Single Phase" indicates that the crystalline phase was determined to consist solely of monoclinic crystals based on the X-ray diffraction pattern measurement results, and "×" indicates that the crystalline phase was determined not to consist solely of monoclinic crystals. In Table 1, "Unimodal Type" indicates that the grain size distribution is unimodal, and "×" indicates that the grain size distribution has multiple peaks other than unimodal. In this example, if "XRD Monoclinic Single Phase" is "○" and "Unimodal Type" is "○", it was determined that the secondary particles have been reduced in size and the problem of the present invention has been solved.

[0070]

[0071] As shown in Table 1, it was confirmed that the method for producing zirconium oxide powder of the present invention can yield zirconium oxide powder of the present invention with reduced secondary particle size.

[0072] 1. Firing apparatus 11. Distilled water 21. Zirconium hydroxide cake 101. Furnace 101a. Furnace tube 101b. Heating device 111. Thermocouple 121. Silicone rubber stopper 201. Pump 202. Evaporator 301. Alumina boat

Claims

1. Zirconium oxide powder having a crystalline phase consisting solely of monoclinic crystals and a unimodal grain size distribution.

2. The particle size distribution is (D 90 -D 10 ) / D 50 The zirconium oxide powder according to claim 1, satisfying ≤ 3.

00.

3. Specific surface area of ​​20.0 to 100.0 m² 2 The zirconium oxide powder according to claim 1 or 2, wherein the amount is / g.

4. A method for producing zirconium oxide powder, comprising: a reaction step of adding heated ammonium peroxodisulfate to heated zirconium oxychloride to obtain a basic zirconium sulfate slurry; a dehydration step of neutralizing the basic zirconium sulfate slurry with ammonia water to obtain a zirconium hydroxide slurry, then removing the solvent to obtain a zirconium hydroxide cake; a repulping wash step of repulping the zirconium hydroxide cake with ammonia water; a calcination step of calcining the zirconium hydroxide cake in a furnace using superheated steam to obtain zirconium oxide; and a crushing step of crushing the zirconium oxide to obtain zirconium oxide powder.

5. The method for producing zirconium oxide powder according to claim 4, characterized in that the maximum temperature of the furnace atmosphere in the firing process is 250 to 800°C.

6. The method for producing zirconium oxide powder according to claim 5, characterized in that the firing step includes the steps of: charging a zirconium hydroxide cake into a furnace; raising the furnace atmosphere to the maximum temperature at a heating rate of 5°C / min or more; starting the circulation of superheated steam at 200 to 650°C into the furnace while the furnace atmosphere is being heated or after the furnace atmosphere has reached the maximum temperature; holding the zirconium hydroxide cake for 0 to 2 hours; stopping the circulation of the superheated steam; and lowering the furnace atmosphere to a temperature of 100°C or lower at a cooling rate of 5°C / min or more.

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