The powder and the method for producing the same thing.

Abstract

DEPCT6720 / 08 / 2567 Zirconia powder containing 2% by mol or more and 8% by mol or Less than that of the stabilizing element and 50 ppm or less of titanium (Ti) and containing Activation energies of 225 kJ / mol or more, and 300 kJ / mol or less, are provided. There is at least one zirconia powder that can produce sintered objects with high transparency. By using pressureless sintering, a method suitable for industrial production, the following can be employed: Zirconia powder production: methods for manufacturing calcined objects using zirconia powder and techniques. For the production of sintered objects using zirconia powder, the powder is desirablely manufactured by: The method involves the following steps: adjusting the pH of the raw material solution containing the source. Zirconium and its stabilized sources are at 3.5% or higher and 5.5% or lower. Heating the raw material solution to produce zirconia sol solution; mixing the zirconia solution. And alkaline solutions for co-sludge production and heat treatment of the co-sludge;

Description

Powder and its manufacturing method

[0001] The present disclosure relates to a powder having a zirconia matrix, a method for producing the same, and a calcined body and a sintered body using the same.

[0002] Zirconia (zirconium oxide; ZrO ２ Zirconia sintered bodies are used in a wide range of applications, including pulverization, optical applications, decorative applications, and dental applications. Zirconia has a translucent appearance (so-called translucency) in addition to its mechanical properties, so its application to dental and decorative applications is being widely investigated. Furthermore, manufacturing methods and raw material powders suitable for these applications are being investigated.

[0003] For example, it has been disclosed that a sintered body having high total light transmittance can be obtained from commercially available zirconia powder by sintering using hot isostatic pressing (HIP) (Patent Document 1). In contrast, it has been disclosed that a sintered body having high total light transmittance can be obtained by atmospheric sintering using a powder in which the rate of sintering shrinkage is controlled to a relative density of 70% to 90% during atmospheric sintering (Patent Document 2). Furthermore, it has been disclosed that a sintered body having relatively high light transmittance can be obtained by atmospheric sintering using nanozirconia particles with a primary particle diameter of less than 30 nm (Patent Document 3).

[0004] International Publication No. 2008 / 013099 Japanese Patent Application Laid-Open No. 2010-150064 Japanese Patent Application Laid-Open No. 2016-060687

[0005] In Patent Document 1, HIP treatment is required to impart translucency, so although inexpensive powder can be used, the manufacturing cost tends to be high as a manufacturing method for a translucent sintered body. Furthermore, the powder in Patent Document 2 can be used to obtain a sintered body with high translucency by atmospheric sintering, but precise control of manufacturing conditions is required to manufacture such powder industrially and stably. Furthermore, the nano-zirconia in Patent Document 3 requires special manufacturing equipment called supercritical drying, which increases the manufacturing cost and makes it unsuitable from the viewpoint of industrial manufacturing.

[0006] An object of the present disclosure is to provide at least one of a zirconia powder that can produce a sintered body having high translucency even when sintered under atmospheric pressure and that is suitable for industrial production, a method for producing the same, a method for producing a calcined body using the same, and a method for producing a sintered body using the same.

[0007] In this disclosure, we have investigated industrial zirconia powder suitable as a raw material powder for translucent zirconia sintered bodies and a method for producing the same. As a result, we have discovered a powder that can produce a sintered body with higher translucency even when sintered under atmospheric pressure by focusing on the state of the powder, particularly its composition and energy state. At the same time, we have discovered that by improving a part of the production process, such a powder can be produced without requiring special production equipment or precise control of production conditions.

[0008] That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows. [1] Zirconia powder containing 2 mol% to 8 mol% of a stabilizing element and 50 ppm or less of titanium (Ti), and having an activation energy of 225 kJ / mol to 300 kJ / mol. [2] The powder according to [1] above, in which the stabilizing element is one or more selected from the group consisting of yttrium, calcium, and magnesium. [3] The powder according to [1] or [2] above, containing chlorine. [4] The powder according to [3] above, in which the chlorine content is 100 ppm to 500 ppm. [5] A powder having a BET specific surface area of ​​6 m ２ / g or more, 15m ２ / g or less. [6] The powder according to any one of [1] to [4] above, having a primary particle diameter of 80 nm or more and 150 nm or less. [7] The powder according to any one of [1] to [6] above, containing an actinide element. [8] A method for producing a zirconia powder according to any one of [1] to [7] above, comprising the steps of adjusting the pH of a raw material solution containing a zirconium source and a stabilizing element source to 3.5 or more and 5.5 or less, heating the raw material solution to obtain a zirconia sol solution, mixing the zirconia solution with an alkaline solution to obtain a coprecipitate, and heat-treating the coprecipitate. [9] The method according to [8] above, wherein the raw material solution contains ammonium chloride.

[10] A method for producing a calcined body using the powder according to any one of [1] to [7] above.

[11] A method for producing a sintered body using the powder according to any one of [1] to [7] above.

[0009] The present disclosure makes it possible to provide at least one of a zirconia powder that can produce a sintered body having high translucency even when sintered under atmospheric pressure and that is suitable for industrial production, a method for producing the same, a method for producing a calcined body using the same, and a method for producing a sintered body using the same.

[0010] The powder of the present disclosure will be described below by showing an example of an embodiment.

[0011] This embodiment is a zirconia powder containing 2 mol % to 8 mol % of a stabilizing element and 50 ppm or less of titanium (Ti), and having an activation energy of 225 kJ / mol to 300 kJ / mol.

[0012] This embodiment relates to zirconia powder. The zirconia powder in this embodiment (hereinafter also referred to as "zirconia powder") is zirconia (ZrO ２ The zirconia powder of the present embodiment may be a powder containing zirconia as a matrix (main component), and is not limited to a powder consisting of zirconia alone. Furthermore, the zirconia in the zirconia powder of the present embodiment may be a partially stabilized zirconia.

[0013] The powder of this embodiment contains a stabilizing element. The stabilizing element is an element that has the function of stabilizing the crystal structure of zirconia, and is preferably an element that stabilizes the crystal structure of zirconia without coloring the zirconia. Specific examples of the stabilizing element include one or more elements selected from the group consisting of yttrium (Y), calcium (Ca), and magnesium (Mg), and further yttrium.

[0014] The content of the stabilizing element is the amount at which the zirconia crystal phase is stabilized by a crystal phase containing tetragonal crystals, and is 2 mol% to 8 mol%. Preferred contents of the stabilizing element (hereinafter also referred to as the "stabilizing element amount", and when the stabilizing element is yttrium or the like, also referred to as the "yttrium amount") include more than 2 mol%, 2.5 mol% to 3 mol%, and 7 mol% or less, 6 mol% or less, 4.5 mol% or less, or 4 mol% or less. Further, more than 2 mol% to 7 mol%, 2.5 mol% to 6 mol%, 3 mol% to 4.5 mol%, or 3 mol% to 4 mol%.

[0015] The amount of the stabilizing element in this embodiment is the molar ratio [mol %] of the stabilizing element calculated as an oxide to the total of the stabilizing element and zirconia calculated as an oxide. Furthermore, the amount of the stabilizing element in the powder containing titanium is TiO ２ The molar ratio [mol %] of the stabilizing element converted into an oxide to the total of titanium converted into an oxide, the stabilizing element converted into an oxide, and zirconia. ２ O ３ Calcium may be CaO and magnesium may be MgO.

[0016] The powder of this embodiment contains 50 ppm or less (50 mass ppm or less) of titanium (Ti). It is known that 2000 ppm (0.2 mass%) or more of titanium is added to zirconia to promote grain growth of the crystal grains of the sintered body. In contrast, the powder of this embodiment contains titanium (i.e., the titanium content is greater than 0 ppm (greater than 0 mass ppm)), and contains an amount that does not substantially promote grain growth of the crystal grains of the sintered body. By containing such a small amount of titanium and having the activation energy described below, sintering during heat treatment in a relatively high temperature range during the sintering process is more likely to be promoted. This is thought to result in a sintered body with high translucency, even with normal atmospheric sintering. It is more preferable that the titanium contained in the powder of this embodiment is titanium derived from the raw materials, which makes it easier to obtain the activation energy of the powder of this embodiment. The powder of this embodiment contains titanium at or above the detection limit (for example, more than 0 ppm, or even more than 5 ppm, or even more than 10 ppm), preferably 10 ppm or more or more than 20 ppm, and preferably contains 40 ppm or less or 30 ppm or less of titanium, such as more than 0 ppm by mass and less than 50 ppm by mass, more than 5 ppm by mass and less than 40 ppm by mass, or more than 10 ppm by mass and less than 30 ppm by mass.

[0017] The titanium content (hereinafter also referred to as "titanium amount") in this embodiment is TiO ２ TiO relative to the total of titanium converted, stabilizing elements converted into oxides, and zirconia ２ The mass percentage of titanium (ppm) calculated as an oxide is expressed as the mass percentage of titanium in the powder of the present embodiment, where the powder contains alumina or the like. ２ TiO relative to the total of titanium converted, stabilizing elements converted into oxides, and zirconia ２ It is sufficient if it is the converted mass percentage of titanium [ppm].

[0018] The amount of titanium can be measured by ICP mass spectrometry using a general ICP mass spectrometer (for example, NexION300S, manufactured by Perkin Elmer).

[0019] The powder of this embodiment can be sintered under atmospheric pressure to obtain a sintered body having high translucency even if it does not contain alumina. ２ O ３ The alumina content may be 0% by mass or more or more than 0% by mass, and may be 0.5% by mass or less, 0.3% by mass or less, 0.25% by mass or less, less than 0.25% by mass, less than 0.1% by mass, or less than 0.05% by mass. Examples of the alumina content include 0% by mass or more and 0.5% by mass or less, 0% by mass or more and 0.25% by mass or less, 0% by mass or more and 0.25% by mass or less, 0% by mass or more and 0.1% by mass or less, more than 0% by mass but less than 0.25% by mass, or more than 0% by mass but less than 0.05% by mass. From the viewpoint of increasing the strength of the obtained sintered body, the alumina content may be 0.1% by mass or more and 3% by mass or more, or even 0.1% by mass or more and 0.5% by mass or less.

[0020] The content of alumina in this embodiment (hereinafter also referred to as "alumina amount") is Al ２ O ３ Al relative to the total of aluminum converted, metal elements converted into oxides, stabilizing elements converted into oxides, and zirconia ２ O ３ This is the converted mass percentage of aluminum [mass %].

[0021] In measuring the amount of the stabilizing element and the amount of alumina, the stabilizing element and aluminum may be measured by ICP emission spectrometry using a general ICP mass spectrometer (for example, device name: 7300DV, manufactured by Perkin Elmer).

[0022] The powder of this embodiment contains hafnia (HfO ２ The hafnia content varies depending on the raw zirconia ore and its processing method. In this embodiment, when calculating values ​​based on the composition such as density, hafnia can be considered as zirconia.

[0023] The powder of this embodiment may be composed of zirconia containing a stabilizing element, titanium, and optionally alumina, but may also contain an actinide element in a sufficiently small amount. Examples of actinide elements that may be contained in the powder of this embodiment include one or more selected from the group consisting of actinium (Ac), thorium (Th), and protactinium (Pa), and may further include thorium. Actinide elements originate from raw material ores such as zircon sand, and their presence in the powder is thought to affect the activation energy of the powder.

[0024] When an actinide element is contained, the content thereof (hereinafter also referred to as "actinide amount", and when the actinide is thorium or the like, also referred to as "thorium amount", etc.) is equal to or greater than the detection limit (for example, 0 mass ppb or more, more than 0 mass ppb, more than 100 mass ppb, 200 mass ppb or more, or 400 mass ppb or more) and is, for example, 700 mass ppb or less or 500 mass ppb or less, such as 0 mass ppb or more to 700 mass ppb or less, 0 mass ppb or more to 500 mass ppb or less, more than 0 mass ppb to 700 mass ppb or more, or more than 0 mass ppb to 500 mass ppb or less.

[0025] The amount of actinide in this embodiment is the mass ratio [ppb] of actinide (element) to the mass of powder.

[0026] In measuring the amount of actinides, actinides may be measured by ICP mass spectrometry using a general ICP mass spectrometer (device name: NexION300S, manufactured by Perkin Elmer).

[0027] The powder of this embodiment may contain chlorine (Cl). The chlorine content of the powder of this embodiment can be, for example, 0 ppm by mass or more, more than 0 ppm by mass, or 100 ppm by mass or more, and 500 ppm by mass or less, 300 ppm by mass or less, or 250 ppm by mass or less, and can also be 0 ppm by mass or more and 500 ppm by mass or less, or more than 0 ppm by mass and 300 ppm by mass or less.

[0028] The amount of chlorine in this embodiment is the mass ratio (ppm) of chlorine to the powder mass, determined by fluorescent X-ray diffraction.

[0029] For example, when the powder of this embodiment is a zirconia powder containing yttrium, thorium, titanium, and alumina, the amount of yttrium [mol %] is ２ O ３ [mol] / (Y ２ O ３ + ZrO ２ ) [mol], the titanium content [ppm] is calculated as TiO ２ [g] / (Y ２ O ３ + ZrO ２ + TiO ２ +ThO ２ +Al ２ O ３ ) [g] and the alumina content [ppm] is Al ２ O ３ [g] / (Y ２ O ３ + ZrO ２ + TiO ２ +ThO ２ +Al ２ O ３ ) [g].

[0030] In addition, the amount of actinide in the powder is calculated by dividing the mass of actinide (element) by the mass of powder (ppb), and similarly, the amount of chlorine, a nonmetallic element, is calculated by dividing the mass of chlorine (Cl) by the mass of powder (ppm). The mass of the powder used to calculate the amount of actinide and the amount of chlorine is the Ig. Loss mass, which is the mass of the powder after treatment in air at 1000°C for 1 to 2 hours (preferably 2 hours).

[0031] The powder of this embodiment is a zirconia powder having an activation energy of 225 kJ / mol to 300 kJ / mol. The powder contains a stabilizing element and a trace amount of titanium, preferably titanium derived from the raw materials, and has such an activation energy, which promotes sintering at high temperatures. As a result, densification is facilitated prior to grain size growth. The activation energy is preferably 225 kJ / mol to 240 kJ / mol or 260 kJ / mol, and 300 kJ / mol to 290 kJ / mol or 270 kJ / mol. Examples of activation energies include 225 kJ / mol to 300 kJ / mol, 240 kJ / mol to 290 kJ / mol, 260 kJ / mol to 290 kJ / mol, or 260 kJ / mol to 270 kJ / mol.

[0032] In this embodiment, the activation energy is determined from an Arrhenius plot of the sample length (hereinafter also referred to as "sample length") of a measurement sample, which is a molded powder, when the temperature is increased.

[0033] The sample length was measured under the following conditions.

[0034] Measurement sample: rectangular parallelepiped molded body measuring 4 mm length x 4 mm width x 5 mm length Temperature increase / decrease atmosphere: air Temperature increase rate: 5°C / min Maximum temperature reached: up to 1500°C Measurement interval of sample length: ΔT = 5°C intervals Temperature decrease rate: 5°C / min The temperature increase and decrease of the measurement sample may be performed using a general thermal dilatometer (for example, TD5020SE, manufactured by NETZSCH).

[0035] The measurement sample was prepared by weighing out 1.25±0.01 g of the powder of this embodiment, uniaxially pressing it at a molding pressure of 20 MPa, and then cold isostatically pressing it at 200 MPa (hereinafter also referred to as "CIP treatment") to form a rectangular solid measuring 4 mm in length, 4 mm in width, and 5 mm in length, which was then fired in an air atmosphere at 500°C for 1 hour.

[0036] The measured value of the sample length during the temperature rise (L ＴThe value of the sample length (L ′) includes the effect of thermal expansion. Ｔ ) is the measured value (L Ｔ The corrected value is obtained by correcting the measured value with the thermal expansion coefficient, and the correction with the thermal expansion coefficient can be performed by a known method depending on the thermal dilatometer used, such as a method using a standard sample.

[0037] The sample length before heating (L ０ ) to the corrected sample length (L Ｔ The corrected sample length (L) at the temperature T obtained for the change (ΔL) in the range of 0% to 4% Ｔ ) and temperature T, as ３／５ ・△(1-L Ｔ / L ０ ) / ΔT], and the activation energy can be determined from the slope of the linear approximation obtained from the plot.

[0038] The Arrhenius plot above corresponds to the left side of the following equation, and the activation energy can be determined by analyzing the plot with the equation on the right side. That is, the slope of the linear approximation obtained from the plot corresponds to Q / RT in the following equation, and Q can be determined from this.

[0039]

[0040] In the above equation, β is the frequency factor, Q is the activation energy [kJ / mol], R is the gas constant (= 8.31 [J / (mol·K)]), T is the temperature [K], L ０ is the sample length before heating [mm], L Ｔ is the corrected sample length at temperature T [mm] and ΔT is 5 [K].

[0041] The BET specific surface area of ​​the powder of this embodiment is 6 m ２ / g or more or 7m ２ / g or more, and ２ / g or less, 12m ２ / g or less or 10m ２ / g or less, and ２ / g or more 15m ２ / g or less, 7m２ / g or more 12m ２ / g or less, or 7m ２ / g or more 10m ２ / g or less.

[0042] In this embodiment, the BET specific surface area is a value measured by a quantitative method in accordance with JIS R 1626, and may be measured by a general automatic specific surface area measuring device (for example, Tristar 3000, manufactured by Micromeritics) and a five-point method using nitrogen as the adsorption gas. Prior to the measurement, the sample may be pretreated by degassing in air at 550°C for 30 minutes.

[0043] The primary particle diameter of the powder of this embodiment is 80 nm or more or 100 nm or more, and may be 150 nm or less, 135 nm or less, 125 nm or less, or 120 nm or less, and may be 80 nm or more and 150 nm or less, 80 nm or more and 135 nm or less, 100 nm or more and 135 nm or less, 100 nm or more and 125 nm or less, or 100 nm or more and 120 nm or less.

[0044] The average primary particle diameter in this embodiment is the average value of primary particle diameters observed with a transmission electron microscope (so-called TEM diameter), and is the average value of the circle-equivalent diameters of 300 particles extracted from an observation image obtained using a transmission electron microscope and the circle-equivalent diameters of each extracted particle determined using image analysis software (e.g., ImageJ).

[0045] The powder of this embodiment preferably has little aggregation, and the average secondary particle size is preferably 0.7 μm or less, 0.5 μm or less, or 0.45 μm or less. The average secondary particle size may be equal to or greater than the average primary particle size, for example, 0.15 μm or more, 0.2 μm or more, or 0.3 μm or more. Preferred average secondary particle sizes are in the range of 0.15 μm to 0.7 μm, 0.2 μm to 0.5 μm, or 0.3 μm to 0.45 μm.

[0046] The average secondary particle size in this embodiment is the median size (D50) in the volume particle size distribution of the powder measured by a wet method, and can be measured using a general device (for example, MT3300EXII, manufactured by Microtrac-Bell Co., Ltd.). The measurement sample may be a powder that has been heat-treated in the air at 400 to 600°C, and then subjected to a dispersion treatment such as ultrasonic treatment to remove slow agglomerates, and then made into a slurry.

[0047] The monoclinic rate of the powder of this embodiment is 0% or more, or 3% or more, and may be 10% or less, 6% or less, or 5% or less, and may be 0% or more and 10% or less, or 3% or more and 5% or less.

[0048] In this embodiment, the monoclinic ratio is the ratio of monoclinic zirconia to the zirconia crystal phase. The monoclinic ratio can be calculated from the powder X-ray diffraction (hereinafter also referred to as "XRD") pattern of the powder using the following formula: ｍ = {I ｍ (111) + I ｍ (11-1)} / [I ｍ (111) + I ｍ (11-1) + I ｔ (111) + I ｃ (111)] × 100

[0049] In the above formula, f ｍ is the monoclinic crystal ratio (%), I ｍ (111) and I ｍ (11-1) are the integrated intensities of the XRD peaks corresponding to the (111) and (11-1) planes of monoclinic zirconia, respectively, and I ｔ (111) is the area intensity of the XRD peak corresponding to the (111) plane of tetragonal zirconia, and I ｃ (111) is the integrated intensity of the XRD peak corresponding to the (111) plane of cubic zirconia.

[0050] Radiation source: CuKα radiation (λ=0.15418 nm) Measurement mode: Continuous scan Scan speed: 4° / min Step width: 0.02° Measurement range: 2θ=26° to 33° The following conditions can be mentioned as conditions for measuring the XRD pattern.

[0051] In the above-mentioned XRD pattern measurement, preferably, the XRD peaks corresponding to the respective crystal planes of zirconia are measured as peaks having peak tops at the following 2θ angles:

[0052] XRD peak corresponding to the (111) plane of monoclinic zirconia: 2θ = 31 ± 0.5° XRD peak corresponding to the (11-1) plane of monoclinic zirconia: 2θ = 28 ± 0.5° The RD peaks corresponding to the (111) planes of tetragonal zirconia and cubic zirconia were measured in duplicate, and the 2θ of the peak tops was 2θ = 30 ± 0.5°.

[0053] The integrated intensity of the XRD peak of each crystal plane can be determined by separating each XRD peak using the calculation program "PRO-FIT" according to the method described in H. Toraya, J. Appl. Crystallogr., 19, 440-447 (1986).

[0054] The powder of this embodiment can be used in a method for producing at least one of a calcined body and a sintered body, and can be used as a precursor for the calcined body and the sintered body.

[0055] Any method for producing a calcined body using the powder of this embodiment may be used, as long as it includes a step of calcining a molded body (hereinafter also referred to as a "calcining step").

[0056] The molded body is a compact of the powder of this embodiment, and can be obtained by molding the powder of this embodiment by a known method, for example, at least one method selected from the group consisting of uniaxial pressing, CIP treatment, slip casting, and injection molding, preferably at least one method selected from the group consisting of uniaxial pressing, CIP treatment, and injection molding.

[0057] The calcination may be carried out by heat treating the compact (compressed powder) at a temperature lower than the sintering temperature, and the calcination conditions include the following: Calcination atmosphere: air Calcination temperature: 800°C or higher but lower than 1200°C

[0058] Any method for producing a sintered body using the powder of this embodiment may be used, as long as it includes a step of sintering at least one of a molded body and a calcined body containing the powder of this embodiment (hereinafter also referred to as the "sintering step").

[0059] Sintering may be carried out by any known sintering method, for example, one or more selected from the group consisting of pressure sintering, vacuum sintering, and atmospheric sintering, preferably atmospheric sintering and pressure sintering, and more preferably atmospheric sintering. Preferred sintering conditions include the following: Sintering method: atmospheric sintering Sintering atmosphere: air Sintering temperature: 1200°C or higher or 1350°C or higher, and 1600°C or lower or 1550°C or lower

[0060] In this embodiment, atmospheric sintering refers to a method of sintering by heating an object to be sintered (such as a compact or a calcined body) without applying an external force.

[0061] The sintered body obtained from the powder of this embodiment is preferably a sintered body obtained by atmospheric sintering, that is, a so-called atmospheric sintered body.

[0062] The sintered body obtained from the powder of this embodiment preferably has a total light transmittance (hereinafter simply referred to as "total light transmittance") of 38.5% or more, and more preferably 40% or more, measured on a sample with a thickness of 1 mm in accordance with JIS K 7361-1. The higher the total light transmittance, the higher the translucency, but examples of the total light transmittance include 50% or less or 46% or less. Examples of the range of the total light transmittance include 38.5% or more and 50% or less, 40% or more and 50% or less, or 40% or more and 46% or less.

[0063] In this embodiment, the total light transmittance can be measured by a method conforming to JIS K 7361-1. The total light transmittance may be measured using a disk-shaped sintered body having a thickness of 1 mm and a surface roughness Ra of 0.02 μm or less on both sides as a measurement sample, and using a haze meter equipped with a D65 light source as a measurement device (for example, a haze meter NDH4000 manufactured by Nippon Denshoku Industries Co., Ltd.).

[0064] The calcined body and sintered body obtained from the powder of this embodiment can be used as components containing them in the same applications as known zirconia sintered bodies. For example, the calcined body can be used as a biomaterial such as a dental material, and the sintered body can be used as a structural material such as a grinder component, a precision machine component, or an optical connector component, a biomaterial such as a dental material, or an exterior material such as a decorative component or an exterior component for an electronic device.

[0065] Next, a method for producing the powder of this embodiment will be described.

[0066] The powder of this embodiment can be obtained by a production method comprising the steps of: adjusting the pH of a raw material solution containing a zirconium source and a stabilizing element source to 3.5 or more and 5.5 or less; heating the raw material solution to obtain a zirconia sol solution; mixing the zirconia solution with an alkaline solution to obtain a coprecipitate; and heat-treating the coprecipitate.

[0067] The powder production method of this embodiment includes a step of adjusting the pH of a raw material solution containing a zirconium source and a stabilizing element source to 3.5 or more and 5.5 or less (hereinafter also referred to as a "precipitation step"). In the powder production method of this embodiment, a zirconium sol is obtained by so-called hydrothermal synthesis. In the precipitation step, by controlling the pH of the raw material solution prior to hydrothermal synthesis, metal elements present in trace amounts in the zirconium source are selectively precipitated, while precipitation of metal elements derived from the starting materials that are present in excess can be prevented. As a result, in the subsequent step of heating the raw material solution to obtain a zirconia sol solution, a zirconium sol containing metal elements, such as titanium, that can contribute to improving the properties of zirconia can be obtained.

[0068] The zirconium source used in the precipitation step may be any zirconium-containing salt (zirconium salt). The zirconium salt may be any industrially used zirconium salt, preferably a zirconium salt obtained from natural ores, or even zirconium salt obtained from zircon sand. Such zirconium salts contain sufficient amounts of titanium, and in some cases titanium and actinide elements. While high-purity zirconium salts such as reagents can also be used as the zirconium source, it is not necessary to use such excessively pure zirconium salts from the viewpoint of production costs.

[0069] Specific examples of zirconium salts include one or more selected from the group consisting of zirconium nitrate, zirconium sulfate, and zirconium oxychloride, with zirconium oxychloride being preferred, and zirconium oxychloride obtained from zircon sand being more preferred.

[0070] The stabilizing element source is a compound or salt containing the stabilizing element, and examples thereof include one or more selected from the group consisting of oxides, hydroxides, oxyhydroxides, halides, sulfates, nitrates, and acetates containing the stabilizing element, one or more selected from the group consisting of oxides, hydroxides, and chlorides containing the stabilizing element, and even chlorides containing the stabilizing element. When the stabilizing element is yttrium, the stabilizing element source (hereinafter, when the stabilizing element is yttrium or the like, each will be referred to as an "yttrium source" or the like) is preferably at least one of yttrium oxide (yttria) and yttrium chloride.

[0071] The raw material solution containing the zirconium source and the stabilizing element source preferably contains ammonium chloride, since this makes it difficult for the primary particles of the resulting powder to aggregate.

[0072] The solvent of the raw material solution is arbitrary, and examples thereof include at least one of water and alcohol, and further includes water.

[0073] The zirconium concentration of the raw material solution may be 0.05 mol / L or more or 0.1 mol / L or more, and may be 1 mol / L or less or 0.5 mol / L or less, and may be 0.05 mol / L or more and 1 mol / L or less, or 0.1 mol / L or more and 0.5 mol / L or less. The stabilizing element concentration of the raw material solution may be an amount that results in the desired stabilizing content of the powder, and may be, for example, 0.003 mol / L or more or 0.005 mol / L or more, and may be 0.02 mol / L or less or 0.05 mol / L or less, and may be 0.003 mol / L or more and 0.02 mol / L or less, or 0.005 mol / L or more and 0.05 mol / L or less.

[0074] In the precipitation step, the pH of the raw material solution is adjusted to 3.5 or more and 5.5 or less, preferably 4 or more and 5 or less. As long as the pH of the raw material solution falls within this range, any method can be used, but it is preferable to mix the raw material solution with an alkaline solution, and examples of such methods include adding an alkaline solution to the raw material solution and adding the raw material solution to an alkaline solution. A specific method is to add an alkaline solution to the mixed solution so that the pH is 4±0.5, preferably 4.5±0.5.

[0075] The alkaline solution used in the precipitation step is preferably an alkaline solution that does not contain metal cations, and examples thereof include aqueous ammonia.

[0076] The method for producing a powder according to this embodiment includes a step of heating a raw material solution to obtain a zirconia sol solution (hereinafter also referred to as the "sol step"). This produces a zirconia sol. The heating conditions for the raw material solution may be appropriately set depending on the amount of raw material solution used, the type and characteristics of the heating equipment, and the like, and examples thereof include the following conditions: Heating temperature: 120°C to 250°C Heating time: 30 minutes to 100 hours Heating state: Stirring state or static state, preferably stirring state

[0077] The method for producing the powder of this embodiment includes a step of mixing the zirconia sol solution with an alkaline solution to obtain a coprecipitate (hereinafter also referred to as a "coprecipitation step"). The coprecipitation step results in zirconia sol with the stabilizing element uniformly dispersed therein being precipitated as a coprecipitate.

[0078] The alkaline solution used in the coprecipitation step (hereinafter also referred to as "coprecipitation alkaline solution") may be the same as or different from the alkaline solution used in the precipitation step (hereinafter also referred to as "precipitation alkaline solution"), but is preferably ammonia water.

[0079] The method for mixing the zirconia sol solution and the coprecipitating alkaline solution may be any method that produces a coprecipitate in a practical yield. Examples include adding the coprecipitating alkaline solution to the zirconia sol solution and adding the zirconia sol solution to the coprecipitating alkaline solution. Since the pH of the zirconia sol solution tends to be lower than the pH of the raw material solution used in the precipitation process, the coprecipitate is produced by adding the coprecipitating alkaline solution to increase the pH. To produce the coprecipitate more efficiently, the mixing method is preferably a method in which the coprecipitating alkaline solution is added to the zirconia sol solution so that the pH of the zirconia sol solution is 5 or more and 6.5 or less, and more preferably 5 or more and 6 or less. A specific example of such a method is a method in which the coprecipitating alkaline solution is added to the zirconia sol solution so that the pH is 5±0.5, preferably 5.5±0.5.

[0080] In the method for producing a powder of this embodiment, it is preferable that at least one of the zirconium source, the stabilizing element source, the precipitating alkaline solution, and the coprecipitating alkaline solution contains a chloride salt.

[0081] The method for producing a powder according to this embodiment includes a step of recovering the coprecipitate (hereinafter also referred to as the "recovery step"). The recovery step may involve recovering the coprecipitate, washing it, and drying it. The recovery, washing, and drying methods may be any methods applicable to the method for producing zirconia powder. For example, the method for recovering the coprecipitate may include at least one of filtration, ultrafiltration, filter press, centrifugation, and sedimentation, and further at least one of ultrafiltration and filter press. An example of a method for washing the coprecipitate is to pass a sufficient amount of pure water through the coprecipitate. The drying conditions may be any conditions that remove the moisture physically adsorbed on the coprecipitate, and the coprecipitate may be dried in the air at 100°C to 200°C.

[0082] The method for producing the powder of this embodiment includes a step of heat-treating the coprecipitate (hereinafter also referred to as the "heat treatment step"). The powder of this embodiment is obtained by the heat treatment step. The heat treatment conditions can be exemplified as follows, and may be set appropriately depending on the amount of coprecipitate to be subjected to the heat treatment and the characteristics of the heat treatment furnace. Heat treatment atmosphere: air atmosphere Heat treatment temperature: 800°C or higher or 900°C or higher, and 1100°C or lower or 1050°C or lower Heat treatment time: 30 minutes or higher or 1 hour or higher, and 24 hours or lower or 12 hours or lower

[0083] The method for producing a powder according to this embodiment may include a step of pulverizing the heat-treated powder (hereinafter also referred to as the "pulverization step"). This allows the average particle size and BET specific surface area of ​​the powder to be adjusted. The pulverization method may be at least one of wet pulverization and dry pulverization, with wet pulverization being preferred, and pulverization using at least one of a ball mill and a vibration mill being more preferred. When subjected to wet pulverization, the powder content of the slurry containing the powder (hereinafter also referred to as the "solid content concentration") can be, for example, 40% by mass or more and 60% by mass or less.

[0084] When the powder of this embodiment contains alumina, it is preferable to mix zirconia powder with an alumina source in the pulverization step.

[0085] The alumina source is at least one of alumina powder and sol, preferably alumina powder and more preferably α-alumina powder. The amount of the alumina source added may be the same as the amount of alumina in the target zirconia powder.

[0086] To improve operability (handling), the powder manufacturing method of this embodiment may include a step of granulating the powder (hereinafter also referred to as a "granulation step"). A known method can be used for the granulation method. The granulation method may involve forming a slurry from the powder and spray-drying the slurry. For example, when wet pulverization is performed in the pulverization step, the slurry from the pulverization plant may be spray-dried as is, or after adjusting the powder content (solid content concentration) in the slurry as necessary. An organic binder may also be used to adjust the viscosity of the slurry to be granulated. The organic binder may be appropriately selected depending on the viscosity of the slurry and the spray dryer used to achieve the desired yield, and examples thereof include acrylic binders. The content of the organic binder may be appropriately changed depending on the viscosity of the slurry, and may be, for example, 0.1% by mass or more and 5% by mass or less relative to the mass of the slurry.

[0087] The present embodiment will be specifically described below with reference to examples, but the present embodiment is not limited to these examples.

[0088] (Activation Energy) 1.25±0.01 g of powder was weighed out, and this was uniaxially press-molded at a molding pressure of 20 MPa, and then subjected to CIP treatment at 200 MPa to form a rectangular solid-shaped body having dimensions of 4 mm length × 4 mm width × 5 mm length, which was then fired in an air atmosphere at 500°C for 1 hour to prepare a measurement sample.

[0089] The length of the sample measured with a micrometer before heating (L ０ After measuring the thickness [μm], the measurement sample was heated and cooled using a thermal dilatometer (device name: TD5020SE, manufactured by NETZSCH) under the following conditions: Heating and cooling atmosphere: air Heating rate: 5°C / min Maximum temperature reached: up to 1500°C Measurement interval of sample length: ΔT = 5°C intervals Heating rate: 5°C / min

[0090] The sample length before heating (L ０ ) to the corrected sample length (L Ｔ ) change (ΔL / L ０) in the range of 0% to 4%. Ｔ ) and temperature T, as ３／５ ・△(1-L Ｔ / L ０ An Arrhenius plot was made in the form of [(kJ / mol)] / (ΔT)]. Based on the above formula, the activation energy (Q [kJ / mol]) was calculated from the slope of the linear approximation obtained from the plot. Ｔ ') is the thermal expansion coefficient (9.3 × 10) calculated from the relationship between temperature and sample length at ΔT = 5°C intervals during cooling. －６ [ / °C]) was used for correction.

[0091] (BET Specific Surface Area) The BET specific surface area of ​​the powder sample was measured using a general automatic specific surface area measuring device (device name: Tristar 3000, manufactured by Micromeritics) and nitrogen as an adsorption gas. Prior to the measurement, the powder sample was pretreated by degassing in air at 550°C for 30 minutes.

[0092] (Monoclinic Crystal Ratio) An XRD pattern of the powder sample was obtained using a general X-ray diffractometer (device name: MiniFlex 600, manufactured by Rigaku Corporation). The conditions for the XRD measurement were as follows: Radiation source: CuKα radiation (λ = 0.15418 nm) Measurement mode: Continuous scan Scan speed: 1° / min Step width: 0.02° Measurement range: 2θ = 26° to 33°

[0093] Monoclinic ratio f ｍ was calculated from the above formula.

[0094] (Average primary particle diameter) 300 particles were extracted from a TEM image obtained using a transmission electron microscope. The extracted particles were analyzed using image analysis software (software name: ImageJ) to determine the circle-equivalent diameter of each particle, and the average value thereof was used as the average primary particle diameter.

[0095] (Average secondary particle diameter) The volume particle diameter distribution curve of the powder was measured using a Microtrac particle size distribution analyzer (device name: MT3300EXII, manufactured by Microtrac Bell) in HRA mode, and the median diameter (D50) was taken as the average secondary particle diameter. Prior to the measurement, the powder was heat-treated at 550°C in an air atmosphere, suspended in pure water, and dispersed for 10 minutes using an ultrasonic homogenizer to remove slow aggregation.

[0096] (Chlorine Amount) The chlorine amount of the powder was determined by a calibration curve method using a scanning X-ray fluorescence analyzer (device name: ZSX Primus IV, manufactured by Rigaku).

[0097] (Total Light Transmittance) The total light transmittance was measured using a haze meter (device name: NDH4000, manufactured by Nippon Denshoku Industries Co., Ltd.) and a D65 light source according to a method in accordance with JIS K 7361-1.

[0098] The measurement sample used was a disk-shaped sintered body having a thickness of 1 mm, which had been polished on both sides so as to have a surface roughness Ra≦0.02 μm.

[0099] (Bending strength) The bending strength was measured by a three-point bending test in accordance with JIS R 1601. The measurement was performed using a columnar sintered body sample with a support distance of 30 mm, a width of 4 mm, and a thickness of 3 mm, and the bending strength was calculated by averaging 10 measurements.

[0100] (Deterioration test) A deterioration test was performed by immersing a sintered body sample in hot water at 140°C for 24 hours. After the deterioration test, the sintered body sample was cut and the cross section was observed under an SEM. A structure containing many cracks confirmed on the surface of the sintered body in the SEM observation was regarded as a deteriorated layer, and the thickness of the deteriorated layer was measured.

[0101] <Preparation of Powder> Example 1 Zircon sand was melted in a sodium hydroxide aqueous solution and then decomposed with hydrochloric acid to obtain a zirconium oxychloride solution. Ammonium chloride, yttrium chloride pure water, and the obtained zirconium oxychloride were mixed to obtain a raw material aqueous solution having a zirconium oxychloride concentration of 0.3 mol / L, an ammonium chloride concentration of 0.5 mol / L, and an yttrium chloride concentration of 0.0064 mol / L. While the raw material aqueous solution was being stirred, ammonia water (NH ) with an ammonia concentration of 0.1 mol / L was added to the raw material aqueous solution while measuring the pH so that the pH of the raw material aqueous solution was 4.5±0.5. ４ OH) was added dropwise. After the dropwise addition of the aqueous ammonia, the raw material aqueous solution was heated at 130°C for 50 hours to generate a zirconia sol, thereby obtaining a zirconia sol solution. Ammonia water with an ammonia concentration of 0.1 mol / L was added to the obtained zirconia sol solution to obtain a coprecipitate. The aqueous ammonia was added while stirring the reaction solution, and the addition rate was appropriately adjusted so that the pH of the reaction solution was 5 to 6. The obtained coprecipitate was filtered, washed with water, and dried to obtain a dry powder. The dry powder was then heat-treated in an air atmosphere at 1010°C for 2 hours.

[0102] The heat-treated powder was mixed with pure water to obtain a slurry with a solids concentration of 50% by mass, which was then processed in a ball mill for 8 hours. Zirconia balls with a diameter of 10 mm were used as grinding media for the ball mill. 3.5% by mass of an acrylic binder was added to the processed slurry, and the resulting slurry was spray-dried to obtain a granular powder, which was used as the powder of this example.

[0103] The powder of this example has a BET specific surface area of ​​11.2 m ２ / g, the average primary particle size was 115 nm, the average secondary particle size was 0.44 μm, and the monoclinic crystal ratio was 6%.

[0104] Example 2 The powder and sintered body of this example were obtained in the same manner as in Example 1, except that the yttrium chloride concentration in the raw material aqueous solution was set to 0.0114 mol / L and the calcination heat treatment temperature was set to 1050°C.

[0105] The powder of this example has a BET specific surface area of ​​9.2 m ２ / g, the average primary particle size was 116 nm, the average secondary particle size was 0.44 μm, and the monoclinic crystal ratio was 0%.

[0106] Example 3 A powder (powder 1) obtained by heat treatment in the same manner as in Example 1, except that the calcination temperature was 1,050°C, and a powder (powder 2) obtained by heat treatment in the same manner as in Example 3 were mixed in a mass ratio of calcined powder 1:calcined powder 2 of 49:51 to obtain a mixed powder. The powder of this example was obtained in the same manner as in Example 1, except that the obtained mixed powder was used.

[0107] The powder of this example has a BET specific surface area of ​​9.8 m ２ / g, the average primary particle size was 123 nm, the average secondary particle size was 0.44 μm, and the monoclinic crystal ratio was 3%.

[0108] Example 4 The powder of this example was obtained in the same manner as in Example 1, except that the heat treatment temperature was set to 1100°C, and the heat-treated powder, 0.24 mass% of alumina powder, and pure water were mixed together to prepare a slurry with a solid content of 50 mass%, which was then treated in a ball mill.

[0109] The powder of this example has a BET specific surface area of ​​8.1 m ２ / g, the average primary particle size was 130 nm, the average secondary particle size was 0.47 μm, and the monoclinic crystal ratio was 7%.

[0110] Comparative Example 1 Commercially available zirconia powder containing 3 mol % yttrium (product name: TZ-3YSB-E, manufactured by Tosoh Corporation) was used as the powder in this comparative example.

[0111] Comparative Example 2: Titania (TiO) was added to commercially available zirconia powder containing 3 mol% yttrium (product name: TZ-3YS, manufactured by Tosoh Corporation) so that the titanium content was 45 ppm. ２ ) were mixed.

[0112] The results of these examples and comparative examples are shown in the table below.

[0113]

[0114] Examples 5 to 8 The powder of Example 5 was obtained in the same manner as in Example 1, except that spray drying was performed without using an acrylic binder. The powder of this example had an activation energy of 280 kJ / mol and a BET specific surface area of ​​11.2 m ２ / g, the average primary particle size was 115 nm, the average secondary particle size was 0.44 μm, and the monoclinic crystal ratio was 6%, confirming that the composition and these physical properties were not affected by the binder.

[0115] Powders of Examples 6, 7 and 8 were obtained in the same manner as in Examples 2, 3 and 4, respectively, except that spray drying was carried out without using an acrylic binder. The results are shown in the table below.

[0116]

[0117] From the above table, it can be seen that the composition, activation energy, BET specific surface area, average primary particle size, average secondary particle size, and monoclinic crystal ratio are not affected by the binder.

[0118] <Preparation of Calcined and Sintered Bodies> Examples 9 to 13 and Comparative Examples 3 and 4 The powders obtained in Examples 1 to 4 and 8 and Comparative Examples were each molded using a die press at a molding pressure of 20 MPa, and then isostatically pressed at a molding pressure of 200 MPa to obtain a compact. This compact was heated at a rate of 50°C / hour and calcined at 1000°C for 2 hours to obtain a calcined body. Thereafter, the temperature was raised at a rate of 600°C / hour and sintered at the sintering temperature shown below for 2 hours to obtain a sintered body.

[0119]

[0120] All of the sintered bodies of the Examples had a high total light transmittance of more than 35%, and furthermore, the total light transmittance of the sintered bodies of Examples 9 to 11, which did not contain alumina, was 39% or more. Furthermore, it can be confirmed from Examples 12 and 13 that the presence or absence of a binder has almost no effect on the total light transmittance, bending strength, and thickness of the deteriorated layer.

[0121] The entire contents of the specification, claims and abstract of Japanese Patent Application No. 2021-192672, filed on November 29, 2021, are hereby incorporated by reference as the disclosure of the specification of the present disclosure.

Claims

DEPCT6720 / 08 / 25671. Zirconia powder incorporating 2% by mol or more and 8% by mol or less of a stabilizing element and 50 ppm or less of titanium (Ti) and having an activation energy of 225 kJ / mol or more and 300 kJ / mol or less.

2. Powder according to Reputation 1 in which the stabilizing element is one or more elements selected from a group consisting of yttrium, calcium and magnesium.

3. Powder according to Reputation 1 or 2 incorporating chlorine.

4. Powders under Reputation 3 where the chlorine content is 100 ppm or more and 500 ppm or less.

5. Powders under Reputation 1 to 4 where the specific surface area of ​​BET is 6 m² / g or more and 15 m² / g or less.

6. Powders under Reputation 1 to 5 where the primary particle size is 80 nm or more and 150 nm or less.

7. Powders under Reputation 1 to 6 that contain actinoid elements. 8.A method for the production of zirconia powder under any one of claims 1 through 7 that includes the following steps: adjusting the pH of the raw material solution containing the zirconium source and the stabilizing element source to 3.5 or higher and 5.5 or lower; heating the raw material solution to produce zirconia sol solution; mixing the zirconia solution and the alkaline solution to produce the coprecipitate; and heat conditioning of the coprecipitate.

9. A production method under claim 8 where the raw material solution contains ammonium chloride.

10. A method for the production of calcined material using any one of the powders under claims 1 through 7.

11. A method for the production of sintered material using any one of the powders under claims 1 through 7.