Powder and production method therefor

Abstract

To provide: a zirconia powder from which sintered objects having high light-transmitting properties are obtained even by ordinary-pressure sintering and which is suitable for industrial manufacturing; a method for producing the zirconia powder; and a method for producing a calcined object from the zirconia powder and / or a method for producing a sintered object therefrom.SOLUTION: A zirconia powder contains 2 mol% or more and 8 mol% or less of a stabilizing element and 50 ppm or less of titanium (Ti) and has an activation energy of 225 kJ / mol or more and 300 kJ / mol or less. Such powder is preferably obtained by a production method comprising a step in which the pH of a raw-material solution containing a zirconium source and a stabilizing element source is regulated to 3.5 or more and 5.5 or less, a step in which the raw-material solution is heated to obtain a zirconia sol solution, a step in which the zirconia solution is mixed with an alkali solution to obtain a coprecipitation product, and a step in which the coprecipitation product is subjected to a heat treatment.SELECTED DRAWING: None

Description

[Technical Field]

[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. [Background technology]

[0002] Zirconia (zirconium oxide; ZrO2) 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, research is being conducted on manufacturing methods and raw material powders suitable for these applications.

[0003] For example, it has been disclosed that a sintered body with 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 with 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 with relatively high light transmittance can be obtained by atmospheric sintering by using nanozirconia particles with a primary particle diameter of less than 30 nm (Patent Document 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2008 / 013099 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-150064 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-060687 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, HIP treatment is required to impart translucency, which allows the use of inexpensive powder, but the manufacturing cost tends to be high for a method of manufacturing 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 in a stable manner. Furthermore, the nano-zirconia in Patent Document 3 requires special manufacturing equipment called supercritical drying, which increases the manufacturing cost and makes it unsuitable for 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. [Means for solving the problem]

[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% or more and 8 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] The powder according to [1] above, wherein 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, which contains chlorine. [4] The powder according to [3] above, having a chlorine content of 100 ppm or more and 500 ppm or less. [5] BET specific surface area is 6m 2 / g or more, 15m 2 The powder according to any one of [1] to [4] above, wherein the saturation coefficient is 0.015 μm or less. [6] The powder according to any one of [1] to [5] 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, which contains 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 the above [8], 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. [Effects of the Invention]

[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. DETAILED DESCRIPTION OF THE INVENTION

[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 a powder having zirconia (ZrO2) as a matrix (main component), and is not limited to a powder consisting of zirconia alone. Furthermore, the zirconia in the zirconia powder of this embodiment may be 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 yttrium is particularly preferred.

[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%. A preferred content of the stabilizing element (hereinafter also referred to as the "stabilizing element amount," or when the stabilizing element is yttrium, also referred to as the "yttrium amount") is more than 2 mol%, 2.5 mol% to 3 mol%, or 7 mol% or less, 6 mol% to 4.5 mol%, or 4 mol% or less, and more preferably 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 converted into an oxide to the total of the stabilizing element and zirconia converted into an oxide. Furthermore, the amount of the stabilizing element in a titanium-containing powder can be determined from the molar ratio [mol%] of the stabilizing element converted into an oxide to the total of titanium converted into TiO, the stabilizing element converted into an oxide, and zirconia. In this embodiment, the oxide equivalents of the stabilizing elements can be YO for yttrium, CaO for calcium, and MgO for magnesium.

[0016] The powder of this embodiment contains 50 ppm or less (50 ppm by mass 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 ppm by mass)), 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. It is believed that this allows a sintered body with high translucency to be obtained 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 titanium at or below 40 ppm or 30 ppm, such as more than 0 ppm by mass and not more than 50 ppm by mass, more than 5 ppm by mass and not more than 40 ppm by mass, or more than 10 ppm by mass and not more than 30 ppm by mass.

[0017] The titanium content in this embodiment (hereinafter also referred to as "titanium amount") is the mass ratio [ppm] of titanium converted into TiO2 to the total of titanium converted into TiO2, the stabilizing element converted into oxide, and zirconia. Note that when the powder of this embodiment contains alumina or the like, the titanium amount may be the mass ratio [ppm] of titanium converted into TiO2 to the total of metal element converted into oxide, titanium converted into TiO2, the stabilizing element converted into oxide, and zirconia.

[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] Although the powder of this embodiment does not contain alumina, atmospheric sintering can produce a sintered body with high translucency. However, the powder may contain alumina (Al2O3). The alumina content is 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. Further examples 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 resulting sintered body, the alumina content may be 0.1% by mass or more and 3% by mass or even 0.1% by mass or more and 0.5% by mass or less.

[0020] The alumina content (hereinafter also referred to as "alumina amount") in this embodiment is the mass ratio [mass %] of aluminum converted into Al2O3 to the total of aluminum converted into Al2O3, metal elements converted into oxides, stabilizing elements converted into oxides, and zirconia.

[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 may contain hafnia (HfO), an inevitable impurity of zirconia. The hafnia content varies depending on the raw zirconia ore and its processing method. In this embodiment, when calculating values based on 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. The actinide element that may be contained in the powder of this embodiment may be one or more selected from the group consisting of actinium (Ac), thorium (Th), and protactinium (Pa), and may further include thorium. The actinide element is derived from raw material ores such as zircon sand, and its 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 the "actinide amount", and when the actinide is thorium or the like, also referred to as the "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 700 mass ppb or less or 500 mass ppb or less, for example, 0 mass ppb or more and 700 mass ppb or less, 0 mass ppb or more and 500 mass ppb or less, more than 0 mass ppb and 700 mass ppb or less, or more than 0 mass ppb and 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 is, 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 further includes 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 %] can be calculated from Y2O3 [mol] / (Y2O3+ZrO2) [mol], the amount of titanium [ppm] can be calculated from TiO2 [g] / (Y2O3+ZrO2+TiO2+ThO2+Al2O3) [g], and the amount of alumina [ppm] can be calculated from Al2O3 [g] / (Y2O3+ZrO2+TiO2+ThO2+Al2O3) [g].

[0030] 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 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 likely to be promoted prior to the growth of crystal grain size. The activation energy is preferably 225 kJ / mol or more, 240 kJ / mol or more, or 260 kJ / mol or more, and 300 kJ / mol or less, 290 kJ / mol or less, or 270 kJ / mol or less. 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. Measurement sample: Rectangular prism-shaped compact measuring 4mm long x 4mm wide x 5mm long Temperature increase / decrease atmosphere: Air Heating rate: 5°C / min Maximum temperature reached: ~1500℃ Measurement interval of sample length: △T = 5℃ interval Cooling rate: 5℃ / min The temperature of the measurement sample can be increased and decreased using a general thermal dilatometer (for example, TD5020SE, manufactured by NETZSCH). The measurement sample is 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 is then fired in an air atmosphere at 500°C for 1 hour.

[0034] The measured sample length during the temperature rise (L T The value of (L ') includes the effect of thermal expansion. T ) values are measured values (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.

[0035] The corrected sample length (L T The corrected sample length (L) at the temperature T obtained for the range of change (△L) of 0% to 4% T ) and temperature T, ln[T 3 / 5 ·△(1-L T / L0) / △T], and the activation energy can be calculated from the slope of the linear approximation obtained from the plot.

[0036] 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. In other words, the slope of the linear approximation obtained from the plot corresponds to Q / RT in the equation below, so Q can be determined from this.

[0037]

number

[0038] 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], L0 is the sample length before heating [mm], L T is the corrected sample length at temperature T [mm] and △T is 5 [K].

[0039] 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 15m 2 / g or less, 12m2 / g or less or 10m 2 / g or less, and 2 / g or more 15m 2 / g or less, 7m 2 / g or more 12m 2 / g or less, or 7m 2 / g or more 10m 2 / g or less is sufficient.

[0040] 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 5-point method using a general automatic specific surface area measuring device (e.g., Tristar 3000, manufactured by Micromeritics) and nitrogen as the adsorption gas. Prior to the measurement, the sample may be pretreated by degassing in air at 550°C for 30 minutes.

[0041] The primary particle diameter of the powder of this embodiment is 80 nm or more or 100 nm or more, and can 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.

[0042] 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).

[0043] 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.

[0044] The average secondary particle size used in this embodiment is the median size (D50) in the volume particle size distribution of a powder measured by a wet method, and can be measured using a general device (e.g., MT3300EXII, manufactured by Microtrac-Bell). 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.

[0045] The monoclinic ratio 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.

[0046] 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.

[0047] f m ={I m (111)+I m (11-1)} / [I m (111) +I m (11-1)+I t (111)+I c (111)] × 100 In the above equation, f m is the monoclinic ratio (%), I m (111) and I m(11-1) are the area 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 area intensity of the XRD peak corresponding to the (111) plane of cubic zirconia.

[0048] The conditions for measuring the XRD pattern include the following. Radiation source: CuKα radiation (λ=0.15418nm) Measurement mode: Continuous scan Scan speed: 4° / min Step width: 0.02° Measurement range: 2θ=26°~33°

[0049] 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.

[0050] 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 angle of the peak top was 2θ=30±0.5°.

[0051] The area 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).

[0052] 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.

[0053] 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").

[0054] 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.

[0055] The calcination can be carried out by heat treating the compact (powder compact) at a temperature lower than the sintering temperature, and the calcination conditions include the following. Calcination atmosphere: Air Calcination temperature: 800℃ to 1200℃

[0056] Any method for manufacturing 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").

[0057] The 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 pressure sintering Sintering atmosphere: Air Sintering temperature: 1200°C or higher or 1350°C or higher, and 1600℃ or less or 1550℃ or less

[0058] In this embodiment, atmospheric sintering is a method of sintering by heating an object to be sintered (such as a compact or a calcined body) without applying an external force.

[0059] 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.

[0060] 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 the total light transmittance can be, for example, 50% or less or 46% or less. The range of the total light transmittance can be 38.5% or more and 50% or less, 40% or more and 50% or less, or 40% or more and 46% or less.

[0061] 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.).

[0062] 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.

[0063] Next, a method for producing the powder of this embodiment will be described.

[0064] 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.

[0065] 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 the "precipitation step"). In the powder production method of this embodiment, a zirconium sol is obtained by so-called hydrothermal synthesis. In the precipitation step, the pH of the raw material solution is controlled prior to hydrothermal synthesis, thereby selectively precipitating metal elements present in trace amounts in the zirconium source while preventing the precipitation of metal elements derived from the starting materials that are present in excess. This allows a zirconium sol containing metal elements, such as titanium, that can contribute to improving the properties of zirconia to be obtained in the subsequent step of heating the raw material solution to obtain a zirconia sol solution.

[0066] The zirconium source used in the precipitation step may be a salt containing zirconium (zirconium salt). The zirconium salt may be any zirconium salt used industrially, and is 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 high-purity zirconium salts from the viewpoint of production costs.

[0067] Specific examples of the zirconium salt 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.

[0068] The stabilizing element source is a compound or salt containing the stabilizing element, and may be one or more selected from the group consisting of oxides, hydroxides, oxyhydroxides, halides, sulfates, nitrates, and acetates containing the stabilizing element, or one or more selected from the group consisting of oxides, hydroxides, and chlorides containing the stabilizing element, or 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 may be referred to as an "yttrium source" or the like) is preferably at least one of yttrium oxide (yttria) and yttrium chloride.

[0069] 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.

[0070] The solvent of the raw material solution is arbitrary, and examples thereof include at least one of water and alcohol, and further includes water.

[0071] The zirconium concentration of the raw material solution is 0.05 mol / L or more or 0.1 mol / L or more, and can be 1 mol / L or less or 0.5 mol / L or less, and can 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 can be any amount that results in the desired stabilizing content of the powder, and can be, for example, 0.003 mol / L or more and 0.005 mol / L or more, and can be 0.02 mol / L or less and 0.05 mol / L or less, and can 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.

[0072] 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 include a method of adding an alkaline solution to the raw material solution, and a method of 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.

[0073] 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.

[0074] The method for producing a powder according to the present 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 determined 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℃ or higher and 250℃ or lower Heating time: 30 minutes or more and 100 hours or less Heating state: Stirring state or standing state, preferably stirring state

[0075] 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 in which the stabilizing element is uniformly dispersed being precipitated as a coprecipitate.

[0076] 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.

[0077] The zirconia sol solution and the coprecipitating alkali solution may be mixed by any method that produces a coprecipitate in a practical yield. Examples of such methods include adding the coprecipitating alkali solution to the zirconia sol solution and adding the zirconia sol solution to the coprecipitating alkali solution. Because 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 alkali solution to raise the pH. To produce the coprecipitate more efficiently, the mixing method is preferably a method in which the coprecipitating alkali solution is added to the zirconia sol solution so that the pH of the zirconia sol solution is between 5 and 6.5, and more preferably between 5 and 6. A specific example of such a method is a method in which the coprecipitating alkali solution is added to the zirconia sol solution so that the pH is 5±0.5, preferably 5.5±0.5.

[0078] 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.

[0079] 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 method 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 may involve drying in the air at 100°C to 200°C.

[0080] 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. Examples of heat-treatment conditions include the following, which may be appropriately set depending on the amount of coprecipitate to be heat-treated and the characteristics of the heat-treatment furnace. Heat treatment atmosphere: Air Heat treatment temperature: 800°C or higher or 900°C or higher, and 1100℃ or less or 1050℃ or less Heat treatment time: 30 minutes or more or 1 hour or more, and 24 hours or less or 12 hours or less

[0081] 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.

[0082] When the powder of this embodiment contains alumina, it is preferable to mix zirconia powder with an alumina source in the pulverization step.

[0083] The alumina source is at least one of alumina powder and sol, and is 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.

[0084] 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. 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 directly, or after adjusting the powder content (solid content concentration) in the slurry as needed. 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. [Example]

[0085] The present embodiment will be specifically described below with reference to examples, but the present embodiment is not limited to these examples.

[0086] (activation energy) 1.25±0.01 g of powder was weighed out, uniaxially pressed at a molding pressure of 20 MPa, and then CIP-treated at 200 MPa to form a rectangular solid measuring 4 mm in length, 4 mm in width, and 5 mm in length. This was then fired in air at 500°C for 1 hour to prepare a measurement sample.

[0087] The length (L0) [μm] of the measurement sample before heating was measured with a micrometer, and then the measurement sample was heated and cooled under the following conditions using a thermal dilatometer (device name: TD5020SE, manufactured by NETZSCH). Temperature increase / decrease atmosphere: Air Heating rate: 5°C / min Maximum temperature reached: ~1500℃ Measurement interval of sample length: △T = 5℃ interval Cooling rate: 5℃ / min

[0088] The corrected sample length (L T ) in the range of 0% to 4%. T ) and temperature T, ln[T 3 / 5 ·△(1-L T An Arrhenius plot was made in the form of [L / L0) / △T]. Based on the above formula, the activation energy (Q [kJ / mol]) was calculated from the slope of the linear approximation equation obtained from the plot. T ') is the thermal expansion coefficient (9.3 × 10 -6 [ / ℃]) was used for correction.

[0089] (BET specific surface area) The BET specific surface area of the powder samples was measured using a general automatic specific surface area measurement device (Tristar 3000, manufactured by Micromeritics) and nitrogen as the adsorption gas. Prior to the measurement, the powder samples were pretreated by degassing in air at 550°C for 30 minutes.

[0090] (monoclinic crystal ratio) An XRD pattern of the powder sample was obtained using a general X-ray diffractometer (MiniFlex600, manufactured by Rigaku Corporation). The conditions for the XRD measurement were as follows: Radiation source: CuKα radiation (λ=0.15418nm) Measurement mode: Continuous scan Scan speed: 1° / min Step width: 0.02° Measurement range: 2θ=26°~33°

[0091] Monoclinic fraction f m was calculated from the above formula.

[0092] (Average primary particle size) 300 particles were extracted from the TEM observation 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 was used as the average primary particle diameter.

[0093] (Average secondary particle size) The volume particle size distribution curve of the powder was measured using the HRA mode of a Microtrac particle size distribution analyzer (MT3300EXII, manufactured by Microtrac Bell), and the median diameter (D50) was taken as the average secondary particle size. Prior to the measurement, the powder was heat-treated in air at 550°C, then suspended in pure water and dispersed for 10 minutes using an ultrasonic homogenizer to remove slow agglomerates.

[0094] (chlorine content) The amount of chlorine in the powder was determined by a calibration curve method using a scanning X-ray fluorescence analyzer (device name: ZSX PrimusIV, manufactured by Rigaku).

[0095] (Total light transmittance) The total light transmittance was measured using a haze meter (device name: NDH4000, manufactured by Nippon Denshoku Industries Co., Ltd.) with a D65 light source by a method in accordance with JIS K 7361-1.

[0096] The measurement sample used was a disk-shaped sintered body with a thickness of 1 mm, which had been polished on both sides so that the surface roughness was Ra≦0.02 μm.

[0097] (bending strength) The bending strength was measured by a three-point bending test in accordance with JIS R 1601. The measurement was carried out using a columnar sintered body sample with a width of 4 mm and a thickness of 3 mm, with a support distance of 30 mm, and the bending strength was calculated as the average value of 10 measurements.

[0098] (Deterioration test) A degradation test was performed by immersing the sintered body sample in hot water at 140°C for 24 hours. After the degradation test, the sintered body sample was cut and the cross section was observed using an SEM. A structure containing numerous cracks confirmed on the surface of the sintered body during SEM observation was considered to be a degradation layer, and the thickness of the degradation layer was measured.

[0099] <Powder preparation> Example 1 Zircon sand was melted in a sodium hydroxide solution and then decomposed with hydrochloric acid to obtain a zirconium oxychloride solution. Ammonium chloride, yttrium chloride pure water, and the resulting zirconium oxychloride were mixed to obtain a raw aqueous solution with 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 aqueous solution was stirred, ammonia water (NH4OH) with an ammonia concentration of 0.1 mol / L was added dropwise to the raw aqueous solution, while measuring the pH so that the pH of the raw aqueous solution was 4.5±0.5. After the addition of the ammonia water, the raw aqueous solution was heated at 130°C for 50 hours to produce a zirconia sol, yielding a zirconia sol solution. Ammonia water with an ammonia concentration of 0.1 mol / L was added to the resulting zirconia sol solution to obtain a coprecipitate. The ammonia water was added while stirring the reaction solution, and the addition rate was appropriately adjusted so that the pH of the reaction solution was 5-6. The resulting coprecipitate was filtered, washed with water, and dried to obtain a dry powder, which was then heat-treated in air at 1010°C for 2 hours.

[0100] 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 the grinding medium for the ball mill. 3.5% by mass of an acrylic binder was added to the processed slurry, and the mixed slurry was spray-dried to obtain a granular powder, which was used as the powder of this example.

[0101] 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%.

[0102] 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 of the raw material aqueous solution was 0.0114 mol / L and the calcination heat treatment temperature was 1050°C.

[0103] 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%.

[0104] Example 3 A powder (powder 1) obtained by heat treatment in the same manner as in Example 1, except that the calcination temperature was 1050°C, and a powder (powder 2) obtained by heat treatment in the same manner as in Example 3 were mixed together so that the calcined powder 1:calcined powder 2 was 49:51 (mass ratio) 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.

[0105] 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%.

[0106] 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% alumina powder, and pure water were mixed together to form a slurry with a solid content of 50 mass%, which was then processed in a ball mill.

[0107] 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%.

[0108] Comparative Example 1 A 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.

[0109] Comparative Example 2 Titania (TiO2) was mixed with commercially available zirconia powder containing 3 mol% yttrium (product name: TZ-3YS, manufactured by Tosoh Corporation) so that the titanium content was 45 ppm.

[0110] The results of these examples and comparative examples are shown in the table below.

[0111] [Table 1]

[0112] 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.

[0113] 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.

[0114] [Table 2]

[0115] 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.

[0116] <Preparation of calcined and sintered bodies> Examples 9 to 13 and Comparative Examples 3 and 4 The powders obtained in Examples 1 to 4, 8, and the Comparative Example were each molded using a mold press at a molding pressure of 20 MPa, and then isostatically pressed at a molding pressure of 200 MPa to obtain a compact. The compact was heated at a rate of 50°C / hour and calcined at 1000°C for 2 hours to obtain a calcined body. The temperature was then raised at a rate of 600°C / hour and sintered at the sintering temperature shown below for 2 hours to obtain a sintered body.

[0117] [Table 3]

[0118] All of the sintered bodies of the Examples had a high total light transmittance of more than 35%, and the sintered bodies of Examples 9 to 11, which did not contain alumina, had a total light transmittance of 39% or more. Furthermore, Examples 12 and 13 confirm that the presence or absence of a binder has almost no effect on the total light transmittance, bending strength, or thickness of the deteriorated layer.

Claims

1. A calcined body of zirconia containing 2 mol % to 8 mol % of a stabilizing element, 50 ppm or less of titanium (Ti), and 700 ppb or less of an actinide element.

2. 2. The calcined zirconia body according to claim 1, wherein the actinide element is at least one selected from the group consisting of actinium (Ac), thorium (Th), and protactinium (Pa).

3. It contains 2 mol% to 8 mol% of a stabilizing element and 50 ppm or less of titanium (Ti), and has an activation energy of 225 kJ / mol to 300 kJ / mol, a chlorine content of 100 ppm to 500 ppm, and a BET specific surface area of 6 m ２ / g or more, 15m ２ 3. The method for producing a calcined zirconia body according to claim 1, further comprising the step of calcining a compact containing zirconia powder having a viscosity of 1 / g or less.

4. A method for producing a sintered body of zirconia, comprising a step of sintering the calcined body of zirconia according to claim 1.

5. 5. The method according to claim 4, wherein the zirconia sintered body has a total light transmittance of 38.5% or more when measured in accordance with JIS K 7361-1 using a sample with a thickness of 1 mm.

6. The method according to claim 4 or 5, wherein the zirconia sintered body has a bending strength of 634 MPa or more.

7. 6. The method according to claim 4, wherein the thickness of the deteriorated layer of the zirconia sintered body after immersion in hot water at 140°C for 24 hours is 17 μm or less.

8. A zirconia sintered body containing 2 mol% or more and 8 mol% or less of a stabilizing element, 50 ppm or less of titanium (Ti), and 700 ppb or less of an actinide element, the sintered body having a total light transmittance of 38.5% or more when measured in accordance with JIS K 7361-1 with a sample thickness of 1 mm, a bending strength of 634 MPa or more, and a deterioration layer thickness of 17 μm or less after immersion in hot water at 140°C for 24 hours.

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