Powder and method for producing the same

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 zirconia as a matrix, a method for producing the same, and a green compact and a sintered body using the same.

Background Art

[0002] Sintered bodies of zirconia (zirconium oxide; ZrO 2 ) are used in a wide range of applications such as grinding applications, optical applications, decorative applications, and dental applications. Since zirconia has a sense of transparency (so-called light-transmitting sense) in addition to mechanical properties, investigations have been widely made on its application to dental applications and decorative applications. Furthermore, investigations have been made on production methods and raw material powders suitable for these applications.

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] In Patent Document 1, since HIP treatment is required to impart translucency, inexpensive powders can be used, but the manufacturing cost tends to be high as a method for manufacturing a sintered body having translucency. Further, although a sintered body having high translucency can be obtained by atmospheric pressure sintering of the powder of Patent Document 2, precise control of manufacturing conditions is required to stably manufacture such a powder industrially. Further, the nanometer zirconia of Patent Document 3 has a high manufacturing cost because it uses special manufacturing equipment such as supercritical drying and is not suitable from the viewpoint of industrial manufacturing.

[0006] An object of the present disclosure is to provide at least one of a zirconia powder suitable for industrial use as a raw material powder of a sintered body having high translucency even by atmospheric pressure sintering, a method for manufacturing the same, a method for manufacturing a green compact using the same, and a method for manufacturing a sintered body using the same.

Means for Solving the Problems

[0007] In the present disclosure, an industrial zirconia powder suitable as a raw material powder of a sintered body of zirconia having translucency and a method for manufacturing the same were studied. As a result, by paying attention to the state of the powder, particularly the composition and the energy state, a powder capable of obtaining a sintered body having higher translucency even by atmospheric pressure sintering was found. At the same time, by improving a part of the manufacturing process, it was found that such a powder can be obtained without requiring special manufacturing equipment or precise control of manufacturing conditions.

[0008] That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows. [1] A 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, containing chlorine. [4] The powder according to [3] above, having a chlorine content of 100 ppm or more and 500 ppm or less. [5] The BET specific surface area is 6 m 2 / g or more and 15 m 2 / g or less, and the powder according to any one of [1] to [4] above. [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, containing an actinide element. [8] A process of setting 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 and an alkali solution to obtain a coprecipitate, and heat-treating the coprecipitate, and a method for producing a zirconia powder according to any one of [1] to [7] above, characterized by having these steps. [9] The production method according to [8] above, wherein the raw material solution contains ammonium chloride.

[10] A method for producing a green compact 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. [Advantages of the Invention]

[0009] According to the present disclosure, even in the case of atmospheric pressure sintering, a sintered body having high translucency can be obtained, and at least one of a zirconia powder suitable for industrial production, a method for producing the same, a method for producing a green compact using the same, and a method for producing a sintered body using the same can be provided. [Embodiments for Carrying Out the Invention]

[0010] Hereinafter, an example of an embodiment of the powder of the present disclosure will be shown and described.

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

[0012] This embodiment relates to a zirconia powder. The zirconia powder in this embodiment (hereinafter also referred to as "zirconia powder") is a powder having zirconia (ZrO 2 ) as a matrix (main component), and is not limited to a powder composed only of zirconia. Further, 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 having a function of stabilizing the crystal structure of zirconia, and is preferably an element that stabilizes the crystal structure of zirconia without coloring it. Specific examples of the stabilizing element include one or more selected from the group consisting of yttrium (Y), calcium (Ca), and magnesium (Mg), and more preferably yttrium.

[0014] The content of the stabilizing element is an amount that stabilizes the crystal phase in which the crystal phase of zirconia contains a tetragonal crystal phase, and is 2 mol% or more and 8 mol% or less. Preferred contents of the stabilizing element (hereinafter also referred to as "amount of stabilizing element", and when the stabilizing element is yttrium or the like, also referred to as "amount of yttrium", etc.) include more than 2 mol%, 2.5 mol% or more, or 3 mol% or more, and 7 mol% or less, 6 mol% or less, 4.5 mol% or less, or 4 mol% or less. Further, it may be more than 2 mol% and 7 mol% or less, 2.5 mol% or more and 6 mol% or less, 3 mol% or more and 4.5 mol% or less, or 3 mol% or more and 4 mol% or less.

[0015] The amount of the stabilizing element in this embodiment is the molar ratio [mol%] of the stabilizing element in terms of oxide to the total of the stabilizing element and zirconia in terms of oxide. Further, in the powder containing titanium, the amount of the stabilizing element is TiO 2It may be determined from the molar ratio [mol%] of the stabilized element in terms of oxide to the total of the converted titanium, the stabilized element in terms of oxide, and zirconia. The conversion of the stabilized element in terms of oxide in the present embodiment is such that yttrium is Y 2 O 3 , calcium is CaO, and magnesium is MgO.

[0016] The powder of the present embodiment contains titanium (Ti) of 50 ppm or less (50 mass ppm or less). It is known that titanium of 2000 ppm (0.2 mass%) or more is added to zirconia to promote grain growth of crystal grains in the sintered body. On the other hand, the powder of the present embodiment contains titanium (that is, the content of titanium is more than 0 ppm (more than 0 mass ppm)), and contains an amount that does not substantially promote grain growth of crystal grains in the sintered body. By containing such a trace amount of titanium and having the activation energy described later, sintering in heat treatment in a relatively high temperature range is likely to be promoted even during the sintering process. Thereby, it is considered that a sintered body having high translucency can be obtained even by normal atmospheric pressure sintering. It is more preferable that the titanium contained in the powder of the present embodiment is titanium derived from the raw material, whereby the activation energy of the powder of the present embodiment is easily obtained. The powder of the present embodiment contains titanium above the measurement limit (for example, more than 0 ppm, further more than 5 ppm, and still further 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, and examples include more than 0 mass ppm and 50 mass ppm or less, more than 5 mass ppm and 40 mass ppm or less, or more than 10 mass ppm and 30 mass ppm or less.

[0017] The content of titanium in the present embodiment (hereinafter, also referred to as "titanium amount") is the mass ratio [ppm] of titanium in terms of TiO 2 conversion to the total of the converted titanium, the stabilized element in terms of oxide, and zirconia. When the powder of the present embodiment contains alumina or the like, the titanium amount is calculated based on the metal element in terms of oxide, titanium in terms of TiO 2 conversion to the total of the converted titanium, the stabilized element in terms of oxide, and zirconia. 2 conversion to the total of the converted titanium, the stabilized element in terms of oxide, and zirconia.2 It may be the mass ratio of titanium [ppm] after conversion.

[0018] In the measurement of the titanium amount, these may be measured by ICP mass spectrometry using a general ICP mass spectrometer (for example, device name: NexION300S, manufactured by Perkin Elmer).

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

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

[0021] In the measurement of the stabilizing element amount and the alumina amount, 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), respectively.

[0022] The powder of this embodiment contains hafnia (HfO, an inevitable impurity of zirconia2 ) may be included. The hafnia content varies depending on the zirconia raw ore and its treatment method. Also, in this embodiment, when calculating a value based on a composition such as density, hafnia may be regarded as zirconia and this may be used to determine it.

[0023] The powder of this embodiment may be composed of zirconia containing a stabilizing element, titanium, and, if necessary, alumina, but may contain an actinide element if the amount is sufficiently small. The actinide elements that can 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 further, thorium may be mentioned. Actinide elements are derived from raw ores such as zircon sand, and it is considered that their remaining in the powder can affect the activation energy of the powder.

[0024] When containing an actinide element, its content (hereinafter, also referred to as "actinide amount", and when the actinide is thorium or the like, also referred to as "thorium amount" or the like respectively) is above the measurement 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 can be exemplified as being 700 mass ppb or less or 500 mass ppb or less, and examples include 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 actinide amount in this embodiment is the mass ratio [ppb] of the actinide (element) to the mass of the powder.

[0026] In the measurement of the actinide amount, 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). As the chlorine content of the powder of this embodiment, it can be exemplified as 0 mass ppm or more, more than 0 mass ppm or 100 mass ppm or more, and also 500 mass ppm or less, 300 mass ppm or less or 250 mass ppm or less. Also, examples include 0 mass ppm or more and 500 mass ppm or less, or more than 0 mass ppm and 300 mass ppm or less.

[0028] The amount of chlorine in this embodiment is the mass ratio [ppm] of chlorine to the powder mass, determined from X-ray fluorescence 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 Y 2 O 3 [mol] / (Y 2 O 3 +ZrO 2 ), the amount of titanium [ppm] is TiO 2 [g] / (Y 2 O 3 +ZrO 2 +TiO 2 +ThO 2 +Al 2 O 3 ), and the amount of alumina [ppm] is Al 2 O 3 [g] / (Y 2 O 3 +ZrO 2 +TiO 2 +ThO 2 +Al 2 O 3 ), respectively.

[0030] Also, in the powder, the amount of actinoid is determined from the mass of actinoid (element) / mass of powder [ppb], and similarly, chlorine, which is a non-metallic element, is determined from the mass of chlorine (Cl) / mass of powder [ppm]. The mass of the powder in the calculation of the amount of actinoid and the amount of chlorine is the Ig.Loss mass, which is the mass of the powder after being treated in an air atmosphere 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 or more and 300 kJ / mol or less, contains a stabilizing element and trace amounts of titanium, preferably titanium derived from the raw material, and by having such an activation energy, sintering in a high temperature range is promoted. As a result, densification is likely to be promoted prior to the growth of the 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 is preferably 300 kJ / mol or less, 290 kJ / mol or less, or 270 kJ / mol or less. Examples thereof include 225 kJ / mol or more and 300 kJ / mol or less, 240 kJ / mol or more and 290 kJ / mol or less, 260 kJ / mol or more and 290 kJ / mol or less, or 260 kJ / mol or more and 270 kJ / mol or less as the activation energy.

[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 the measurement sample when the formed powder is used as the measurement sample and heated.

[0033] The measurement conditions of the sample length are as follows. Measurement sample: A rectangular parallelepiped shaped compact with a length of 4 mm, a width of 4 mm, and a height of 5 mm Heating / cooling atmosphere: Air atmosphere Heating rate: 5 °C / min Maximum temperature reached: ~1500 °C Measurement interval of sample length: △T = 5 °C interval Cooling rate: 5 °C / min The heating and cooling of the measurement sample may be performed using a general thermodilatometer (for example, TD5020SE, manufactured by NETZSCH). For the measurement sample, 1.25 ± 0.01 g of the powder of this embodiment is weighed, uniaxially compression molded at a molding pressure of 20 MPa, and then cold isostatic pressing treatment (hereinafter also referred to as "CIP treatment") is performed at 200 MPa to obtain a rectangular parallelepiped shaped compact with a length of 4 mm, a width of 4 mm, and a height of 5 mm, which may be fired in an air atmosphere at 500 °C for 1 hour.

[0034] The measured value (L T ’) of the sample length during temperature increase includes the influence of thermal expansion. Therefore, the value of the sample length (L T ) used for calculating the activation energy is the corrected value obtained by removing the influence of thermal expansion from the measured value (L T ’). The corrected value is obtained by correcting the measured value with the coefficient of thermal expansion, and the correction by the coefficient of thermal expansion can be performed by a known method according to the thermal dilatometer used, such as a method using a standard sample.

[0035] For the change amount (△L) of the corrected sample length (L 0 ) with respect to the sample length (L T ) before temperature increase within the range of 0% or more and 4% or less, the corrected sample length (L T ) and the temperature T at the obtained temperature T are plotted on an Arrhenius plot in the form of ln[T 3 / 5 ·△(1 - L T / L 0 ), and the activation energy can be obtained from the slope of the linear approximation formula obtained from the plot.

[0036] Note that the above Arrhenius plot corresponds to the left side of the following formula, and the activation energy can be obtained by analyzing the plot with the formula on the right side. That is, since the slope of the linear approximation formula obtained from the plot corresponds to Q / RT in the following formula, Q can be obtained from this.

[0037]

Equation

[0038] In the above formula, 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 temperature increase [mm], L T is the corrected sample length [mm] at the temperature T, and △T is 5 [K].

[0039] The BET specific surface area of the powder in this embodiment is 6 m2 / g or more or 7 m 2 / g or more, and 15 m 2 / g or less, 12 m 2 / g or less or 10 m 2 / g or less, and 6 m 2 / g or more and 15 m 2 / g or less, 7 m 2 / g or more and 12 m 2 / g or less, or 7 m 2 / g or more and 10 m 2 / g or less may be sufficient.

[0040] In this embodiment, the BET specific surface area is a value measured by a quantification method according to JIS R 1626, and may be measured by a general specific surface area automatic measuring device (for example, Tristar3000, manufactured by Micromeritics) and a five-point method using nitrogen as the adsorption gas. Prior to the measurement, a degassing treatment may be performed at 550 °C for 30 minutes in an air atmosphere for pretreatment.

[0041] 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 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 may be sufficient.

[0042] The average primary particle diameter in this embodiment is the average value of the primary particle diameters (so-called TEM diameters) observed with a transmission electron microscope. From the observation images obtained using a transmission electron microscope, 300 particles are extracted, and the equivalent circle diameters of the extracted particles are obtained using image analysis software (for example, ImageJ), and it is the average value thereof.

[0043] The powder of this embodiment preferably has little aggregation, and the average secondary particle diameter is preferably 0.7 μm or less, 0.5 μm or less, or 0.45 μm or less. The average secondary particle diameter may be equal to or greater than the average primary particle diameter, for example, 0.15 μm or more, 0.2 μm or more, or 0.3 μm or more. Preferred ranges of the average secondary particle diameter include 0.15 μm or more and 0.7 μm or less, 0.2 μm or more and 0.5 μm or less, or 0.3 μm or more and 0.45 μm or less.

[0044] The average secondary particle diameter in this embodiment is the median diameter (D50) in the volume particle size distribution of the powder measured by the wet method, and can be measured using a general device (for example, MT3300EXII, manufactured by Microtrac Bell). As the measurement sample, a powder obtained by removing slow aggregation by dispersion treatment such as ultrasonic treatment after heat treatment in an air atmosphere at 400 to 600 °C may be used as 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 in the crystal phase of zirconia. Using the powder X-ray diffraction (hereinafter also referred to as "XRD") pattern of the powder, the monoclinic ratio can be obtained from 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 formula, f m is the monoclinic ratio (%), I m (111) and I m(11-1) represents the area intensity, I, of the XRD peaks corresponding to the (111) plane and the (11-1) plane of monoclinic zirconia, respectively. t (111) represents the area intensity of the XRD peak corresponding to the (111) plane of tetragonal zirconia, and also I c (111) represents the area intensity of the XRD peak corresponding to the (111) plane of cubic zirconia.

[0048] As the conditions for measuring the XRD pattern, the following conditions can be cited. X-ray source: CuKα ray (λ = 0.15418 nm) Measurement mode: continuous scan Scan speed: 4° / min Step width: 0.02° Measurement range: 2θ = 26° to 33°

[0049] In the above XRD pattern measurement, preferably, the XRD peaks corresponding to each crystal plane of zirconia are measured as peaks having peak tops at the following 2θ.

[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) plane of tetragonal zirconia and cubic zirconia are measured repeatedly, and the 2θ of the peak top is 2θ = 30 ± 0.5°.

[0051] The area intensity of the XRD peak of each crystal plane can be obtained by using the calculation program "PRO-FIT" and separating each XRD peak by the method described in H. Toraya, J. Appl. Crystallogr., 19, 440 - 447 (1986).

[0052] The powder of this embodiment can be used in at least one of the manufacturing methods of the green body and the sintered body, and can be used as a precursor of the green body and the sintered body.

[0053] The method for manufacturing a calcined body using the powder of the present embodiment is arbitrary, and any method for manufacturing a calcined body having a step of calcining a formed body (hereinafter, also referred to as "calcination step") may be used.

[0054] The formed body is a compact of the powder of the present embodiment, which can be obtained by forming the powder of the present embodiment by a known method. Examples of the forming method include at least one selected from the group consisting of uniaxial pressing, CIP treatment, slip casting, and injection molding, preferably at least one selected from the group consisting of uniaxial pressing, CIP treatment, and injection molding.

[0055] Calcination may be performed by heat-treating the formed body (compact) at a temperature lower than the sintering temperature. Examples of the calcination conditions are as follows. Calcination atmosphere: air atmosphere Calcination temperature: 800 °C or higher and less than 1200 °C

[0056] The method for manufacturing a sintered body using the powder of the present embodiment is arbitrary, and any method for manufacturing a sintered body having a step of sintering at least one of a formed body and a calcined body containing the powder of the present embodiment (hereinafter, also referred to as "sintering step") may be used.

[0057] Sintering may be performed by a known sintering method. Examples include one or more selected from the group consisting of pressure sintering, vacuum sintering, and atmospheric pressure sintering, preferably atmospheric pressure sintering and pressure sintering, and more preferably atmospheric pressure sintering. Preferred sintering conditions are as follows. Sintering method: atmospheric pressure sintering Sintering atmosphere: air atmosphere Sintering temperature: 1200 °C or higher or 1350 °C or higher, and 1600 °C or lower or 1550 °C or lower

[0058] In the present embodiment, atmospheric pressure sintering refers to a method of sintering by heating the object to be sintered (such as a formed body or a calcined body) without applying an external force during sintering.

[0059] The sintered body obtained from the powder of the present embodiment is preferably a sintered body obtained by atmospheric pressure sintering, that is, a so-called atmospheric pressure sintered body.

[0060] The sintered body obtained from the powder of the present embodiment preferably has a total light transmittance (hereinafter, also simply referred to as "total light transmittance") of 38.5% or more, more preferably 40% or more, as measured in accordance with JIS K 7361-1 with a sample thickness of 1 mm. The higher the total light transmittance, the higher the light transmittance. However, the total light transmittance can be exemplified as 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.

[0061] In the present embodiment, the total light transmittance can be measured by a method in accordance with JIS K 7361-1. As the measurement sample, a disk-shaped sintered body with a sample thickness of 1 mm and a surface roughness Ra of both surfaces ≦ 0.02 μm can be used, and as the measuring device, a haze meter equipped with a D65 light source (for example, haze meter NDH4000, manufactured by Nippon Denshoku Industries Co., Ltd.) can be used for measurement.

[0062] The green compact and the sintered body obtained from the powder of the present embodiment can be used as members including them in the applications of known zirconia sintered bodies. For example, the green compact 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 member for a grinding machine, precision mechanical parts, optical connector parts, a biomaterial such as a dental material, a decorative member, and an exterior material such as an exterior part of an electronic device.

[0063] Next, the manufacturing method of the powder of the present embodiment will be described.

[0064] The powder of the present embodiment can be obtained by a manufacturing method characterized by having 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, a step of heating the raw material solution to obtain a zirconia sol solution, a step of mixing the zirconia solution and an alkali solution to obtain a coprecipitate, and a step of heat-treating the coprecipitate.

[0065] In the method for producing the powder of the present embodiment, there is 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 method for producing the powder of the present embodiment, a zirconium sol is obtained by so-called hydrothermal synthesis. In the precipitation step, prior to the hydrothermal synthesis, by controlling the pH of the raw material solution, metal elements coexisting in trace amounts in the zirconium source can be selectively precipitated, while precipitation of metal elements derived from the starting materials contained in excess can be prevented. As a result, in the step of heating the raw material solution to obtain a zirconia sol solution, which is then performed, a zirconium sol containing a metal element such as titanium that can contribute to improving the properties of zirconia can be obtained.

[0066] The zirconium source to be used in the precipitation step may be a salt containing zirconium (zirconium salt). The zirconium salt may be a zirconium salt industrially used, preferably a zirconium salt obtained from natural ore, and more preferably a zirconium salt obtained from zircon sand. Such zirconium salts contain a sufficient amount of titanium, and in some cases, titanium and actinoid elements. Note that high-purity zirconium salts such as reagents can also be used as the zirconium source, but from the viewpoint of production cost, it is not necessary to use such overly high-purity zirconium salts.

[0067] Specific examples of the zirconium salt include one or more selected from the group consisting of zirconium nitrate, zirconium sulfate, and zirconium oxychloride, preferably zirconium oxychloride, and more preferably zirconium oxychloride obtained from zircon sand.

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

[0069] Since the primary particles of the obtained powder are less likely to aggregate, the raw material solution containing the zirconium source and the stabilizing element source preferably contains ammonium chloride.

[0070] The solvent of the raw material solution is arbitrary, and examples include at least one of water and alcohol, and further preferably 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 may be 1 mol / L or less, or 0.5 mol / L or less, and it 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 becomes the stabilizing content of the target powder. For example, it is 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 it 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.

[0072] In the precipitation step, the pH of the raw material solution is set to be 3.5 or more and 5.5 or less, preferably 4 or more and 5 or less. If the pH of the raw material solution is within this range, the method is arbitrary, but it is preferable to mix the raw material solution and the alkali solution, and examples thereof include a method of adding the alkali solution to the raw material solution and a method of adding the raw material solution to the alkali solution. As a specific method, there is a method of adding an alkali solution to the mixed solution so that the pH is 4 ± 0.5, preferably pH is 4.5 ± 0.5.

[0073] The alkali solution used in the precipitation step is preferably an alkali solution that does not contain metal cations, and examples thereof include aqueous ammonia.

[0074] The method for producing the powder of the present embodiment includes a step of heating the raw material solution to obtain a zirconia sol solution (hereinafter, also referred to as the "sol step"). Thereby, zirconia sol is generated. The heating conditions of the raw material solution may be appropriately set according to the usage amount of the raw material solution, the type and characteristics of the heating equipment, etc., and for example, the following conditions can be mentioned. Heating temperature: 120°C or more and 250°C or less 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 the present embodiment includes a step of mixing the zirconia sol solution and an alkali solution to obtain a coprecipitate (hereinafter, also referred to as the "coprecipitation step"). By the coprecipitation step, zirconia sol in which the stabilizing element is uniformly dispersed precipitates as a coprecipitate.

[0076] The alkali solution used in the coprecipitation step (hereinafter, also referred to as the "coprecipitation alkali solution") may be the same as the alkali solution used in the precipitation step (hereinafter, also referred to as the "precipitation alkali solution"), or may be different, but it is preferably aqueous ammonia.

[0077] The method for mixing the zirconia sol solution and the coprecipitation alkali solution may be any method that can produce a coprecipitate in a practical yield, and examples include the method of adding the coprecipitation alkali solution to the zirconia sol solution and the method of adding the zirconia sol solution to the coprecipitation alkali solution. Since the pH of the zirconia sol solution is likely to be lower than the pH of the raw material solution in the precipitation step, a coprecipitate is formed by adding the coprecipitation alkali solution to increase the pH. In order to more efficiently produce the coprecipitate, the mixing method is preferably the method of adding the coprecipitation alkali solution to the zirconia sol solution so that the pH of the zirconia sol solution is 5 or more and 6.5 or less, and further 5 or more and 6 or less. As a specific method, there is a method of adding the coprecipitation alkali solution to the zirconia sol solution so that the pH is 5±0.5, preferably 5.5±0.5.

[0078] In the method for producing the powder of the present embodiment, it is preferable that at least one of the zirconium source, the stabilizing element source, the precipitation alkali solution, and the coprecipitation alkali solution contains a chloride salt.

[0079] The method for producing the powder of the present embodiment includes a step of recovering the coprecipitate (hereinafter, also referred to as the "recovery step"). In the recovery step, the coprecipitate may be recovered and washed and dried. The methods of recovery, washing, and drying may be any methods applicable to the method for producing zirconia powder. For example, as a method for recovering the coprecipitate, at least one of filtration, ultrafiltration, filter press, centrifugation, and sedimentation separation, and further at least one of ultrafiltration and filter press can be exemplified. As a method for washing the coprecipitate, it can be exemplified that a sufficient amount of pure water is passed through the coprecipitate. The drying method only needs to be a condition under which the moisture physically adsorbed on the coprecipitate is removed, and it may be dried in an air atmosphere at 100°C to 200°C.

[0080] The method for producing the powder of the present embodiment includes a step of heat-treating the coprecipitate (hereinafter, also referred to as the "heat-treatment step"). The powder of the present embodiment is obtained by the heat-treatment step. As heat-treatment conditions, the following conditions can be exemplified, and they may be appropriately set according to the processing amount of the coprecipitate to be heat-treated 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 longer, or 1 hour or longer, and 24 hours or shorter, or 12 hours or shorter

[0081] The method for producing the powder of the present embodiment may have a step of pulverizing the powder after heat treatment (hereinafter, also referred to as "pulverization step"). Thereby, the average particle diameter and BET specific surface area of the powder can be adjusted. The pulverization method may be at least either wet pulverization or dry pulverization, preferably wet pulverization, and more preferably pulverization by at least either a ball mill or a vibration mill. When subjected to wet pulverization, the powder content of the slurry containing the powder (hereinafter, also referred to as "solid content concentration") can be exemplified as 40 mass% or more and 60 mass% or less.

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

[0083] The alumina source is at least either alumina powder or sol, and preferably alumina powder, more preferably α-alumina powder. The addition amount of the alumina source may be an amount equivalent to the amount of alumina in the target zirconia powder.

[0084] In order to improve the operability (handling property), in the method for producing the powder of the present embodiment, a step of granulating the powder (hereinafter, also referred to as the "granulation step") may be included. As the granulation method, a known method can be used. The granulation method may be a method of making the powder into a slurry and spray-drying it. For example, when wet grinding is performed in the grinding step, the slurry at the grinding site may be directly spray-dried, or after adjusting the powder content (solid content concentration) in the slurry as necessary. In addition, an organic binder may be used to adjust the viscosity of the slurry to be granulated. The organic binder may be appropriately selected according to the viscosity of the slurry and the spray dryer to be used so as to obtain a desired yield. For example, an acrylic binder can be mentioned. The content of the organic binder may be appropriately changed according to the viscosity of the slurry. For example, 0.1% by mass or more and 5% by mass or less based on the mass of the slurry can be mentioned.

Example

[0085] Hereinafter, the present embodiment will be specifically described by way of examples. However, the present embodiment is not limited to these examples.

[0086] (Activation energy) Weighed 1.25 ± 0.01 g of the powder, uniaxially compression-molded it at a molding pressure of 20 MPa, and then subjected it to CIP treatment at 200 MPa to obtain a rectangular parallelepiped-shaped molded body with a length of 4 mm, a width of 4 mm, and a height of 5 mm. This was fired in an air atmosphere at 500 °C for 1 hour to obtain a measurement sample.

[0087] After measuring the length (L 0 ) [μm] of the measurement sample before temperature rise measured with a micrometer, a thermomechanical analyzer (device name: TD5020SE, manufactured by NETZSCH) was used to raise and lower the temperature of the measurement sample under the following conditions. Temperature rise and fall atmosphere: Air atmosphere Temperature rise rate: 5 °C / min Maximum temperature reached: ~1500 °C Measurement interval of sample length: △T = 5 °C interval Temperature fall rate: 5 °C / min

[0088] Sample length before temperature rise (L 0 ) with respect to the corrected sample length (L T ) change amount (△L / L 0 ), for the range of 0% or more and 4% or less, the corrected sample length (L T ) and temperature T at the obtained temperature T were plotted on an Arrhenius plot in the form of ln[T 3 / 5 ·△(1 - L T / L 0 ) / △T]. Based on the above formula, the activation energy (Q [kJ / mol]) was determined from the slope of the linear approximation formula obtained from the plot. Note that the measured value of the sample length (L T ’) was corrected using the thermal expansion coefficient (9.3×10 -6 [ / ℃]) obtained from the relationship between temperature and sample length with △T = 5°C intervals during cooling.

[0089] (BET specific surface area) Using a general specific surface area automatic measurement device (device name: Tristar3000, manufactured by Micromeritics) and nitrogen as the adsorption gas, the BET specific surface area of the powder sample was measured. Prior to the measurement, the powder sample was pretreated by degassing treatment at 550°C for 30 minutes in an air atmosphere.

[0090] (Monoclinic ratio) Using a general X-ray diffractometer (device name: MiniFlex600, manufactured by Rigaku), the XRD pattern of the powder sample was obtained. The conditions for the XRD measurement are as follows. X-ray source: CuKα ray (λ = 0.15418 nm) Measurement mode: Continuous scan Scan speed: 1° / min Step width: 0.02° Measurement range: 2θ = 26° to 33°

[0091] The monoclinic ratio f m was determined from the above formula.

[0092] (Average primary particle diameter) From the TEM observation images obtained using a transmission electron microscope, 300 particles were extracted. By analyzing the extracted particles with image analysis software (software name: ImageJ), the equivalent circle diameter of each particle was determined, and the average value was taken as the average primary particle diameter.

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

[0094] (Chlorine content) Using a scanning fluorescence X-ray analyzer (equipment name: ZSX PrimusIV, manufactured by Rigaku), the chlorine content of the powder was determined by the calibration curve method.

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

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

[0097] (Bending strength) The bending strength was measured by a three-point bending test in accordance with JIS R1601. The measurement was carried out using a column-shaped sintered body sample with a span between supports of 30 mm, a width of 4 mm, and a thickness of 3 mm, and the average value of 10 measurements was taken as the bending strength.

[0098] (Deterioration test) A sintered body sample was immersed in hot water at 140 °C for 24 hours to conduct a degradation test. The sintered body sample after the degradation test was cut, and its cross-section was observed by SEM. In the SEM observation, the structure including a large number of cracks confirmed on the surface of the sintered body was regarded as a degradation layer, and the thickness of the degradation layer was measured.

[0099] <Production of powder> Example 1 Zircon sand was melted with an aqueous sodium hydroxide 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 with a zirconium oxychloride concentration of 0.3 mol / L, an ammonium chloride concentration of 0.5 mol / L and a yttrium chloride concentration of 0.0064 mol / L. While measuring the pH so that the pH of the raw material aqueous solution became 4.5 ± 0.5, the raw material aqueous solution was stirred and ammonia water (NH 4 OH) with an ammonia concentration of 0.1 mol / L was added dropwise thereto. A zirconia sol was generated by heating the raw material aqueous solution after the dropwise addition of ammonia water at 130 °C for 50 hours to obtain a zirconia sol solution. A coprecipitate was obtained by adding ammonia water with an ammonia concentration of 0.1 mol / L to the obtained zirconia sol solution. The addition of ammonia water was carried out while stirring the reaction solution and appropriately adjusting the addition rate so that the pH of the reaction solution became 5 to 6. The obtained coprecipitate was filtered, washed with water and dried to obtain a dry powder. Next, the dry powder was heat-treated at 1010 °C for 2 hours in an air atmosphere.

[0100] The powder after heat treatment was mixed with pure water to obtain a slurry with a solid content concentration of 50% by mass, and this was treated with 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 mixed with respect to the mass of the treated slurry, and the mixed slurry was spray-dried to obtain granular powder, which was used as the powder of this example.

[0101] The powder of this example had 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 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 concentration of ytterium chloride in 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 had 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 ratio was 0%.

[0104] Example 3 Powder (powder 1) obtained by heat treatment in the same manner as in Example 1 except that the calcination temperature was 1050°C, and powder (powder 2) obtained by heat treatment in the same manner as in Example 3 were mixed so that the ratio of 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 had 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 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 1100°C, and the powder after the heat treatment, 0.24% by mass of alumina powder and pure water were mixed, and the slurry with a solid content concentration of 50% by mass was treated with a ball mill.

[0107] The powder of this example had 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 ratio was 7%.

[0108] Comparative Example 1 Commercially available 3 mol% yttrium-containing zirconia powder (product name: TZ-3YSB-E, manufactured by Tosoh Corporation) was used as the powder for this comparative example.

[0109] Comparative Example 2 To commercially available 3 mol% yttrium-containing zirconia powder (product name: TZ-3YS, manufactured by Tosoh Corporation), titania (TiO 2 ) was mixed so that the titanium content became 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, a BET specific surface area of 11.2 m 2 / g, an average primary particle diameter of 115 nm, an average secondary particle diameter of 0.44 μm, and a monoclinic ratio of 6%. It was confirmed that the composition and these physical properties were not affected by the binder.

[0113] Also, the 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 performed without using an acrylic binder. The results are shown in the table below.

[0114]

Table 2

[0115] From the above table, it can be confirmed that the composition, activation energy, BET specific surface area, average primary particle diameter, average secondary particle diameter, and monoclinic ratio are not affected by the binder.

[0116] <Preparation of green body and sintered body> 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 at a molding pressure of 20 MPa by die pressing, and then hydrostatically pressed at a molding pressure of 200 MPa to obtain a molded body. This molded body was heated at a rate of 50 °C / hour and calcined at 1000 °C for 2 hours to obtain a calcined body. Then, it was heated 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 over 35%, and furthermore, the total light transmittance of the sintered bodies of Examples 9 to 11 that did not contain alumina was 39% or more. Also, from Examples 12 and 13, it can be confirmed that the presence or absence of a binder has almost no effect on the total light transmittance, flexural strength, and thickness of the deteriorated layer.

Claims

1. 1. A method for producing a 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, 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 sol solution with an alkaline solution to obtain a coprecipitate; and heat-treating the coprecipitate.

2. The method according to claim 1 , wherein the raw material solution contains ammonium chloride.

3. The method according to claim 1 or 2, wherein the zirconium source is a zirconium salt obtained from zircon sand.

4. The method according to claim 1 or 2, wherein the heating temperature of the raw material solution is 120° C. or higher and 250° C. or lower.

5. 3. The method according to claim 1, wherein the zirconia sol solution and the coprecipitating alkali solution are mixed by adding the coprecipitating alkali solution to the zirconia sol solution so that the pH of the zirconia sol solution is 5 or more and 6.5 or less.

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