Method for producing zirconia calcined body and its use

Abstract

To provide a zirconia calcined body for high-speed firing that exhibits superior translucency when fired at a high speed than when fired at a low speed. [Solution] The method for producing a zirconia calcined body disclosed herein includes a producing step of producing a zirconia sol slurry containing zirconia powder, a rare earth dispersion step of dispersing rare earth particles having an average particle size of 300 nm or less in the zirconia sol slurry, a recovery step of recovering mixed particles containing zirconia particles and rare earth particles from the zirconia sol slurry, and a heating step of producing a partially stabilized zirconia powder by heating the mixed particles. According to the production method configured as above, a zirconia calcined body in which zirconia and rare earth oxides are uniformly dispersed can be produced. This zirconia calcined body exhibits an unprecedented effect of exhibiting better translucency when fired at a high speed than when fired at a low speed.

Description

[Technical field]

[0001] The technology disclosed herein relates to a method for producing a zirconia calcined body, and a method for producing a zirconia calcined body and a zirconia sintered body. [Background technology]

[0002] Zirconia sintered bodies are widely used as biomaterials such as dental materials (e.g., dentures, dental prostheses, denture mill blanks, orthodontic brackets). It is known that when a small amount of rare earth oxide (yttria (Y2O3), ytterbia (Yb2O3), etc.) is dissolved as a stabilizing component in this zirconia sintered body (hereinafter also simply referred to as "sintered body"), the strength, toughness, aesthetics, etc. are greatly improved. This zirconia sintered body is manufactured by firing a zirconia calcined body (hereinafter also simply referred to as "calcined body") containing zirconia and rare earth oxide. An example of a manufacturing procedure for this zirconia calcined body is disclosed in Patent Document 1. The manufacturing method described in Patent Document 1 includes, for example, a mixing step of mixing zirconia sol with rare earth oxide, a drying step of drying the zirconia sol, and a heating step of heating zirconia and rare earth oxide at a low temperature lower than the sintering temperature.

[0003] In recent years, rapid firing of the calcined body in the production of a zirconia sintered body has been considered. Specifically, in the conventional production of a zirconia sintered body, a long-term firing process (low-speed firing) was performed in which a predetermined firing temperature was maintained for several hours (about 1 to 4 hours). In contrast, if rapid firing with a shortened holding time of 30 minutes or less could be realized, the production efficiency of the zirconia sintered body could be significantly improved. An example of this rapid firing is disclosed in Patent Document 2. In the production method described in Patent Document 2, the holding time of the firing process is set to less than 20 minutes. According to Patent Document 2, it is said that a zirconia sintered body having the translucency required for a dental prosthetic material can be produced in a short time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2023-171832 A [Patent Document 2] JP 2024-7519 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, it is known that when the firing process in the production of a zirconia sintered body is changed from low-speed firing to high-speed firing, the translucency of the produced sintered body decreases. This trade-off between firing time and translucency has not yet been overcome, and is a problem that requires improvement. For example, in the examples of Patent Document 2, high-speed firing with various firing patterns is performed on multiple types of zirconia calcined bodies. However, the examples of Patent Document 2 show excellent translucency among sintered bodies produced by high-speed firing, and do not realize translucency that greatly exceeds that of sintered bodies produced by low-speed firing (reference examples in Patent Document 2).

[0006] The technology disclosed herein has been made in order to overcome the above-mentioned trade-off, and is directed to a technology related to a zirconia calcined body for rapid sintering that exhibits superior translucency during rapid sintering compared to slow sintering. [Means for solving the problem]

[0007] The present inventor conducted a study to realize a zirconia calcined body for high-speed sintering that solves the above problems, and came to the following findings. First, it has been known that when low-speed sintering is performed, bubbles in the sintered body are removed by heating for a long time, improving the light transmittance. However, in high-speed sintering, it is difficult to sufficiently remove bubbles in the sintered body because the heating time is short. Therefore, the present inventor thought that it is necessary to control the refractive index associated with the segregation of rare earth oxides in order to improve the light transmittance in high-speed sintering. Specifically, inside the zirconia sintered body after sintering, there is a difference in the solid solution state of the rare earth oxide. Then, in the region where the solid solution state of the rare earth oxide is locally different, the refractive index of the transmitted light changes. In other words, if there are many regions where the solid solution state is locally different, it becomes a light scattering factor that reduces the light transmittance of the sintered body. Based on such findings, the present inventor concluded that in high-speed sintering, where it is difficult to remove bubbles, it is better to improve the light transmittance by uniformly dispersing the rare earth oxide throughout the sintered body.

[0008] Here, high-speed firing, which has a short retention time, has the characteristic that the crystal structure is unlikely to change before and after firing because the calcined body is sintered in a short time. The inventors of the present invention paid attention to this point and thought that if a zirconia calcined body in which fine rare earth oxides are dispersed is used as a raw material, the translucency of the zirconia sintered body after production can be improved. As a result of various experiments, they discovered that when the degree of dispersion of rare earth oxides in the entire zirconia calcined body exceeds a predetermined value, a previously unseen effect is exhibited in which high-speed firing exhibits better translucency than low-speed firing. The technology disclosed herein relates to this zirconia calcined body for high-speed firing.

[0009] First, the method for producing a zirconia calcined body disclosed herein includes a producing step of producing a zirconia sol slurry containing zirconia powder, a rare earth dispersing step of dispersing rare earth particles having an average particle diameter of 300 nm or less in the zirconia sol slurry, a recovering step of recovering mixed particles containing zirconia and a rare earth compound from the zirconia sol slurry, a heating step of producing a partially stabilized zirconia powder by heating the mixed particles, and a forming and heating step of forming the partially stabilized zirconia powder into a desired shape and then heating it.

[0010] In the rare earth dispersion step of the manufacturing method disclosed herein, rare earth particles having an average particle size of 300 nm or less are dispersed in a zirconia sol slurry. By heating the mixed particles containing these fine rare earth particles, a partially stabilized zirconia powder in which zirconia and rare earth oxide are suitably interdiffused can be obtained. By molding this partially stabilized zirconia powder into a desired shape and then heating it, a zirconia calcined body for rapid sintering can be produced.

[0011] As another aspect of the technology disclosed herein, a zirconia calcined body is provided. The zirconia calcined body disclosed herein is a zirconia calcined body containing zirconia and a rare earth oxide. This calcined body has a tetragonal matrix with a c / a axial length ratio of 1.008 or more. The calcined body disclosed herein is characterized in that the difference (XY) between the content X (mol%) of rare earth oxide in the zirconia calcined body based on XRF analysis and the amount Y (mol%) of rare earth oxide in the matrix based on XRD analysis is 1 mol% or less.

[0012] The zirconia calcined body having the above-mentioned structure is characterized in that the rare earth oxide is uniformly dispersed and the second phase in which the coarse rare earth oxide is unevenly distributed is small. Specifically, the "content X of rare earth oxide in the zirconia calcined body based on XRF analysis" in the above-mentioned structure indicates the total amount of rare earth oxide present in the entire zirconia calcined body. Meanwhile, the "amount Y of rare earth oxide in solid solution in the parent phase based on XRD analysis" indicates the amount of rare earth oxide dispersed on the parent phase side. That is, when the difference XY between these values ​​is small, the second phase in which the rare earth oxide is unevenly distributed is small, and the dispersion of the rare earth oxide in the entire calcined body is improved. Here, the zirconia calcined body having the above-mentioned structure is characterized in that the difference XY is 1 mol% or less. Since the zirconia calcined body has zirconia and rare earth oxide uniformly dispersed in advance, it can be used as a zirconia calcined body for high-speed firing that exhibits better translucency during high-speed firing than during low-speed firing.

[0013] In addition, a method for producing a zirconia sintered body is provided as another aspect of the technology disclosed herein. The method for producing a zirconia sintered body disclosed herein includes a calcined body preparation step of housing the zirconia calcined body having the above-mentioned configuration inside a sintering furnace, a heating step of heating the inside of the sintering furnace to a predetermined sintering temperature, a holding step of holding the temperature at the sintering temperature for a predetermined holding time, and a cooling step of cooling the inside of the sintering furnace to a predetermined cooling temperature. In this method for producing a zirconia sintered body, the holding time is 30 minutes or less.

[0014] In the method for producing a zirconia sintered body having the above-mentioned configuration, a zirconia calcined body having a difference XY of 1 mol% or less is subjected to high-speed sintering with a retention time of 30 minutes or less. This makes it possible to produce a zirconia sintered body while maintaining a state in which zirconia and rare earth oxides are uniformly dispersed. As a result, a zirconia sintered body exhibiting excellent translucency can be produced in a short time. [Brief description of the drawings]

[0015] [Figure 1]1 is a flowchart outlining a method for producing a zirconia calcined body according to a first embodiment. [Diagram 2] 1 is a flowchart outlining a method for producing a zirconia sintered body according to a first embodiment. [Diagram 3] 5 is a flowchart showing an outline of a method for producing a zirconia calcined body according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, some embodiments of the technology disclosed herein will be described. Matters other than those specifically mentioned in this specification and necessary for carrying out this technology can be understood based on the technical content taught by this specification and the general technical common sense of a person skilled in the art in the relevant field. The contents of the technology disclosed herein can be carried out based on the contents disclosed in this specification and the technical common sense of a person skilled in the art in the relevant field. In this specification, when a numerical range is described as "A to B (where A and B are arbitrary numerical values)", it means "A or more and B or less", and also includes the meanings of "more than A and less than B", "more than A and B or less", and "more than A and less than B".

[0017] <First embodiment> 1. Manufacturing method of zirconia calcined body First, a first embodiment of the method for producing a zirconia calcined body disclosed herein will be described. FIG. 1 is a flow chart showing an outline of the method for producing a zirconia calcined body according to the first embodiment. As shown in FIG. 1, the method for producing a zirconia calcined body disclosed herein includes a generating step S10, a rare earth dispersion step S20, a recovery step S30, a heating step S40, and a molding and heating step S60. In the first embodiment, the rare earth dispersion step S20 includes a rare earth addition step S22 and a precipitation step S24. In addition, the manufacturing method according to this embodiment includes a particle size adjustment step S50 between the heating step S40 and the molding and heating step S60. Each step will be described below.

[0018] (1) Generation process S10 In the generating step S10, a zirconia sol slurry containing zirconia powder is generated. The term "zirconia powder" here refers to a powder material containing zirconia (ZrO2) as a main component. Incidentally, "containing zirconia as a main component" means that no components other than zirconia are intentionally contained. Therefore, powder materials containing unavoidable impurities derived from raw materials, manufacturing processes, etc. are included in the zirconia powder in the technology disclosed herein. Incidentally, examples of impurities in the zirconia powder include metal materials such as hafnium, calcium, silicon, aluminum, and titanium, and compounds of these metals (typically oxides). Another example of impurities includes metallic zirconium. Incidentally, when the total amount of substances of the constituent components of the zirconia powder is 100 mol%, the amount of substance of zirconia is preferably 95 mol% or more (particularly preferably 98 mol% or more). Such zirconia powder with few impurities can be particularly suitably used in the manufacturing method according to this embodiment.

[0019] The average particle size of the zirconia powder is preferably 10 nm or more, more preferably 20 nm or more, even more preferably 30 nm or more, and particularly preferably 40 nm or more. The grain boundaries of the zirconia particles can become the crystal interfaces of the zirconia sintered body after firing. Therefore, as the average particle size of the zirconia powder increases, the number of interfaces between the parent phase and the second phase in the zirconia sintered body after firing decreases, and the translucency is likely to be improved. On the other hand, the upper limit of the average particle size of the zirconia powder is preferably 150 nm or less, more preferably 125 nm or less, and particularly preferably 100 nm or less. By reducing the average particle size of the zirconia powder, a zirconia calcined body that is easy to sinter even in high-speed firing can be produced. In this specification, the "average particle size" refers to the particle size (D) corresponding to 50% cumulatively from the fine particle side in the volume-based particle size distribution measured by a particle size distribution analyzer (manufactured by Horiba, Ltd., model: LA-960). 50 ) refers to

[0020] The content of the zirconia powder in the zirconia sol slurry is not particularly limited, and may be 1 wt% or more, 3 wt% or more, or 5 wt% or more. On the other hand, the upper limit of the content of the zirconia powder is preferably 40 wt% or less, more preferably 30 wt% or less, and particularly preferably 20 wt% or less. As the content of the zirconia powder decreases, the dispersibility in the slurry is more likely to improve. Here, the "content of the zirconia powder" is a mass ratio when the total mass of the zirconia sol slurry is 100 wt%.

[0021] The method for producing the zirconia sol slurry is not particularly limited, and a conventionally known production method can be appropriately adopted. Examples of the production method include a hydrothermal synthesis method and a hydrolysis method. In the hydrothermal synthesis method, a coprecipitate obtained by mixing a zirconium salt with an alkali or the like is heated at 100 to 200°C (particularly preferably about 120°C) in the presence of a liquid medium. By carrying out the hydrolysis reaction at such a temperature, homogeneous nucleation is promoted, and there is an advantage that the sol size distribution becomes sharp. In addition, in the hydrolysis method, the zirconium salt is hydrolyzed by heating the zirconium salt in the presence of a liquid medium. According to these methods, a zirconia sol slurry in which zirconia powder is suitably dispersed in the liquid medium can be easily produced. In addition, a liquid that does not dissolve zirconia and can dissolve the rare earth raw material described later is used as the liquid medium of the zirconia sol slurry. As such a liquid medium, water and the like can be mentioned.

[0022] (2) Rare earth dispersion process S20 In the rare earth dispersion step S20, rare earth particles having an average particle size of 300 nm or less are dispersed in the zirconia sol slurry. By dispersing such fine rare earth particles in the slurry, a partially stabilized zirconia powder in which zirconia and rare earth oxide are suitably diffused can be obtained. The average particle size of the rare earth particles is preferably 250 nm or less, more preferably 225 nm or less, and particularly preferably 200 nm or less. As the average particle size of the rare earth particles becomes smaller, the distribution of the rare earth oxide in the partially stabilized zirconia powder can be made more uniform. On the other hand, if the rare earth particles become too small, there is a risk that the rare earth particles will aggregate in the slurry. From this viewpoint, the average particle size of the rare earth particles is preferably 1 nm or more, more preferably 5 nm or more, and particularly preferably 10 nm or more.

[0023] The means for dispersing rare earth particles in the zirconia sol slurry is not particularly limited, and various means can be selected as necessary. For example, the rare earth dispersion step S20 in the first embodiment includes a rare earth addition step S22 and a precipitation step S24. Through these steps, a slurry in which rare earth particles of 300 nm or less are dispersed can be easily obtained. The following is a detailed explanation.

[0024] (2-a) Rare earth addition step S22 In the rare earth addition step S22, the rare earth raw material is dissolved in the zirconia sol slurry. This allows the rare earth element to be uniformly present in the zirconia sol slurry. In this specification, the "rare earth raw material" is a compound containing a rare earth element. In addition, in consideration of the performance (strength, toughness, aesthetics, etc.) of the zirconia sintered body after firing, yttrium (Y) and ytterbium (Yb) are suitable as rare earth elements, and yttrium is particularly suitable. In addition, the rare earth raw material is required to be a material that is soluble in the zirconia sol slurry. For this reason, the rare earth raw material is preferably a halide such as chloride, bromide, or iodide, hydroxide, sulfide, sulfate, or nitrate of the above rare earth element. In consideration of the performance after firing and solubility in the slurry, etc., in a comprehensive manner, the rare earth raw material is particularly preferably yttrium chloride.

[0025] In the rare earth addition step S22, it is preferable to adjust the amount of rare earth raw material dissolved so that the abundance ratio of the rare earth element to the Zr element satisfies a predetermined range. For example, when the total amount of the Zr element and the rare earth element in the slurry is 100 mol%, the amount of the rare earth element is preferably 3 mol% or more, more preferably 3.2 mol% or more, even more preferably 3.4 mol% or more, and particularly preferably 3.5 mol% or more. This makes it possible to obtain a partially stabilized zirconia powder containing sufficient rare earth oxide. On the other hand, the upper limit of the amount of the rare earth element is preferably 6 mol% or less, more preferably 5.8 mol% or less, and particularly preferably 5.6 mol% or less. This makes it possible to prevent rare earth oxide that has not been introduced into zirconia from being mixed into the partially stabilized zirconia powder as an impurity.

[0026] In the first embodiment, the pH of the zirconia sol slurry before the addition of the rare earth raw material is adjusted to 4 or less. This can suppress the aggregation of zirconia particles in the slurry. In addition, by making the zirconia sol slurry acidic, the rare earth raw material can be appropriately dissolved. The pH of the slurry before the addition of the rare earth raw material is preferably 2 or less, more preferably 1 or less, further preferably 0.7 or less, and particularly preferably 0.5 or less. As the pH of the slurry decreases, the dispersibility of the zirconia particles tends to be further improved. In addition, the lower limit of the pH of the slurry is not particularly limited, and may be 0.1 or more, 0.2 or more, or 0.3 or more. The means for adjusting the pH of the slurry is not particularly limited. For example, the pH of the slurry may be lowered by adding a pH adjuster such as hydrochloric acid. In addition, if the pH of the slurry is 4 or less when generated by hydrothermal synthesis or hydrolysis, the pH adjustment may not be performed.

[0027] (2-b) Precipitation step S24 In the precipitation step S24, the pH of the zirconia sol slurry is increased to 6 to 9. This allows rare earth compounds to be precipitated in the slurry. Specifically, rare earth elements are dissolved in the zirconia sol slurry supplied to the precipitation step S24. By precipitating rare earth compounds from this slurry, fine rare earth particles of 300 nm or less can be homogeneously present in the slurry. Although this does not limit the technology disclosed herein, the rare earth particles precipitated in this step are oxides, hydroxides, etc. of rare earth elements. After precipitation, the rare earth particles are uniformly dispersed in the gaps between the zirconia particles in the slurry.

[0028] In this step, it is advisable to add an alkali to the zirconia sol slurry. This makes it possible to easily increase the pH of the slurry. Examples of the alkali that can be used include ammonia, sodium hydroxide, and potassium hydroxide. Among these, ammonia is particularly preferred because it can prevent metal elements (such as Na) from becoming impurities in the partially stabilized zirconia powder after production.

[0029] In addition, in this step, it is preferable to add the alkali while stirring the zirconia sol slurry. This allows the rare earth compound to precipitate in a state in which the zirconia particles are uniformly dispersed in the slurry, thereby further improving the degree of dispersion of zirconia and the rare earth compound. The specific stirring means is not particularly limited, and any conventionally known stirring device can be used without particular limitation. Examples of this stirring means include a ball mill, a mixer, a disperser, and a kneader.

[0030] (3) Recovery process S30 In the recovery step S30, mixed particles containing zirconia and a rare earth compound are recovered from the zirconia sol slurry. As described above, in the manufacturing method according to this embodiment, fine rare earth compounds are uniformly dispersed in the slurry before recovery. This allows mixed particles in which zirconia and a rare earth compound are uniformly dispersed to be recovered. The specific method for recovering the mixed particles is not particularly limited, and any conventionally known method for separating a powder material from a liquid can be used without particular limitation. For example, the mixed particles can be recovered by appropriately combining means such as filtration, centrifugation, and drying.

[0031] (4)Heating process S40 In the heating step S40, the mixed particles obtained in the recovery step S30 are heated to produce a partially stabilized zirconia powder. Specifically, if the rare earth compound in the mixed particles is a compound other than an oxide, the rare earth compound is oxidized to a rare earth oxide in the early stage of the heating step S40. Then, in the heating step S40, the mixed particles in which zirconia and rare earth oxide are uniformly dispersed are heated. In the mixed particles, the zirconia and rare earth oxide are close to each other, so that the zirconia and rare earth oxide are favorably interdiffused. This makes it possible to obtain a partially stabilized zirconia powder in which zirconia and rare earth oxide are uniformly dispersed. By using this partially stabilized zirconia powder, it is possible to obtain a zirconia calcined body in which the rare earth oxide is uniformly dispersed.

[0032] The heating conditions in this step are not particularly limited, and conventionally known heating conditions employed in the manufacture of zirconia calcined bodies can be employed without particular limitation. For example, the heating temperature in the heating step S40 is set to a temperature (e.g., 900°C to 1200°C) at which mutual diffusion between zirconia and rare earth oxide occurs and at which zirconia is not sintered. This allows the partially stabilized zirconia powder to be appropriately manufactured. The heating atmosphere in the heating step S50 is not particularly limited, and can be an air atmosphere, an oxidizing atmosphere, a reducing atmosphere, or the like. The time for the heating step S40 may be, for example, 1.5 hours to 5 hours, or 2 hours to 4 hours. In the heating step S40, conventionally known heating furnaces (e.g., muffle furnaces, electric furnaces, microwave furnaces, etc.) can be used without particular limitation.

[0033] (5) Particle size adjustment process S50 In addition, in the method for producing the calcined body according to this embodiment, a particle size adjustment step S50 for adjusting the particle size of the partially stabilized zirconia powder is carried out between the heating step S40 and the molding and heating step S60. Note that the particle size adjustment step S50 can employ any conventionally known particle size adjustment technique without any particular restrictions. For example, the partially stabilized zirconia powder after heating may be pulverized and then sieved with a mesh or the like. This allows the partially stabilized zirconia powder of the desired particle size to be obtained.

[0034] In this step, by controlling the average particle size of the partially stabilized zirconia powder to a specific range, a higher quality zirconia calcined body can be obtained. Specifically, the average particle size of the partially stabilized zirconia powder after particle size adjustment is preferably 300 nm or less, more preferably 250 nm or less, and particularly preferably 200 nm or less. By refining the partially stabilized zirconia powder in this step, it becomes easier to prepare a dense zirconia calcined body in the forming and heating step S60. On the other hand, if the average particle size of the partially stabilized zirconia powder is made too small, the crystallinity of the zirconia calcined body after the forming and heating step S60 (after calcination) may deteriorate, and the c / a axial length ratio may decrease. From this viewpoint, the average particle size of the partially stabilized zirconia powder after particle size adjustment is preferably 50 nm or more, more preferably 100 nm or more, and particularly preferably 150 nm or more.

[0035] (6) Molding heating process S60 Next, in the forming and heating step S60, the partially stabilized zirconia powder is formed into a desired shape and then heated (calcined) to produce a zirconia calcined body. Specifically, in the forming and heating step S60, the partially stabilized zirconia powder after the particle size adjustment step S50 is first mixed with a binder. Then, this mixture is formed into a desired shape. By heating (calcining) this molded body, the binder is burned off and a part of the partially stabilized zirconia powder is melted and fixed. This allows the manufacture of a zirconia calcined body. In addition, in the forming and heating step S60, a conventionally known molding method for zirconia sintered bodies can be adopted without any particular restrictions. For this reason, in this specification, detailed conditions (type of binder, amount of binder added, molding means, heating conditions, etc.) will not be described. In addition, the shape of the molded body produced in this step is not particularly limited, and examples thereof include a plate-like, disk-like, rectangular parallelepiped, cubic, columnar, etc.

[0036] In addition, the zirconia sintered body after firing described later may contain alumina. This can suppress grain growth during firing, thereby improving the strength of the sintered body after firing. The raw material of this alumina is preferably added together with the binder in the forming and heating step S60. Examples of the alumina source include alumina powder, alumina sol, hydrated alumina, aluminum hydroxide, aluminum chloride, aluminum nitrate, and aluminum sulfate. These alumina sources become alumina in the firing process described later and are dispersed in the sintered body. The amount of the alumina source added is preferably adjusted so that the Al element is 0.01 mol% or more (preferably 0.02 mol% or more, particularly preferably 0.04 mol% or more) relative to the total substance amount (100 mol%) of the components of the calcined body. This can favorably improve the strength of the sintered body. On the other hand, alumina is a light scattering factor, and may reduce the translucency of the sintered body. For this reason, the amount of the alumina source added should be adjusted so that the Al element is 0.2 mol% or less (preferably 0.15 mol% or less, particularly preferably 0.1 mol% or less) relative to the total amount of substance (100 mol%) of the constituent components of the calcined body. In addition, the zirconia sintered body after firing may contain a trace amount (for example, 0.1 mol% or less) of an additive component for the purpose of coloring or the like. Examples of such a trace amount of additive component include iron, nickel, cobalt, manganese, niobium, praseodymium, neodymium, europium, erbium, and the like. These trace amounts of additive components are also preferably added together with the binder in the forming and heating step S60.

[0037] 2. Zirconia calcined body The method for producing a zirconia calcined body according to the first embodiment has been described above. According to this production method, a zirconia calcined body in which zirconia and rare earth oxides are uniformly dispersed can be produced. This zirconia calcined body exhibits an unprecedented effect of exhibiting superior translucency during high-speed firing compared to low-speed firing. The calcined body after production will be described below.

[0038] The zirconia calcined body according to this embodiment is a molded body containing zirconia and rare earth oxides. Zirconia and rare earth oxides have already been described, so a duplicated description will be omitted. In this specification, the "zirconia calcined body" is a calcined body mainly composed of zirconia and rare earth oxides. Here, "mainly composed of zirconia and rare earth oxides" means that the composite material amount of zirconia and rare earth oxides is 90 mol% or more (more preferably 91 mol% or more, even more preferably 92 mol% or more, and particularly preferably 93 mol% or more) relative to the total material amount (100 mol%) of the components of the calcined body. The material amounts of the components of this calcined body are measured by XRF analysis, which will be described later.

[0039] The amount of zirconia relative to the total amount of components of the calcined body (100 mol%) is preferably 85 mol% or more, more preferably 86 mol% or more, even more preferably 87 mol% or more, and particularly preferably 88 mol% or more. As the content of zirconia in the calcined body increases, the strength, toughness, hydrothermal deterioration resistance, etc. of the zirconia sintered body after firing tend to improve. On the other hand, from the viewpoint of ensuring the amount of other additives (rare earth oxides, etc.), the amount of zirconia is preferably 96 mol% or less, more preferably 95 mol% or less, even more preferably 94 mol% or less, and particularly preferably 93 mol% or less.

[0040] Here, the zirconia calcined body has a tetragonal crystal with a c / a axial length ratio of 1.008 or more as a parent phase. This c / a axial length ratio can be measured by X-ray diffraction measurement (XRD: X-ray diffraction) targeting the surface of the zirconia calcined body. Specifically, the surface of the zirconia calcined body is roughly polished using a 9 μm diamond grinding wheel, and then mirror-polished using 1 μm abrasive grains to expose the measurement cross section. Next, an X-ray diffraction pattern in the measurement cross section is obtained using a commercially available X-ray diffraction analyzer (Malvern PaNalytical, model: X'Pert Pro Alpha-1). Then, the X-ray diffraction pattern is subjected to Rietveld analysis using crystal analysis software (RIETAN-FP). This tetragonal crystal with a c / a axial length ratio of 1.008 or more becomes the parent phase of stabilized zirconia (typically yttria-stabilized zirconia).

[0041] The conditions for obtaining the X-ray diffraction pattern are as follows: X-ray source: CuKαI ray Tube voltage: 45kV Tube current: 40mA Measurement range: 10°≦2θ≦90° Scan speed: 1.5° / min Step width: 0.0131°

[0042] In this specification, the term "parent phase" refers to a crystal phase that exceeds 50% of the crystal phases constituting the zirconia calcined body. In other words, the zirconia calcined body according to this embodiment has a tetragonal abundance ratio of 1.008 or more in a c / a axial length ratio exceeding 50%. In this specification, a crystal phase other than the parent phase (i.e., a crystal phase with a total abundance ratio of less than 50%) is referred to as a "second phase". The number of crystal phases that become the second phase may be one or more. In other words, the zirconia calcined body according to this embodiment includes a calcined body having three or more crystal phases. The abundance ratio of the parent phase in the zirconia calcined body according to this embodiment is preferably 72% or more, more preferably 74% or more, even more preferably 75% or more, and particularly preferably 76% or more. As the abundance ratio of the parent phase increases, the number of boundaries between the parent phase and the second phase decreases, and therefore the permeability of the zirconia sintered body after firing tends to improve. The upper limit of the ratio of the parent phase is not particularly limited and may be 100%. That is, the zirconia calcined body according to this embodiment also includes a single-phase calcined body consisting of only tetragonal crystals with a c / a axial length ratio of 1.008 or more. The composition ratio of the crystal phase can be measured by the analysis of the X-ray diffraction pattern described above.

[0043] Here, the zirconia calcined body according to this embodiment is characterized in that the difference (XY) between the content X (mol%) of rare earth oxide in the zirconia calcined body based on XRF analysis and the amount Y (mol%) of rare earth oxide in the matrix based on XRD analysis is 1 mol% or less. As described above, the "content X of rare earth oxide in the zirconia calcined body based on XRF analysis" indicates the total amount of rare earth oxide present in the entire zirconia calcined body. On the other hand, the "amount Y of rare earth oxide in the matrix based on XRD analysis" indicates the amount of rare earth oxide dispersed in the matrix side. In other words, when the difference XY between these numerical values ​​is small, the second phase in which rare earth oxide is unevenly distributed is reduced, and it can be said that the dispersion of rare earth oxide in the entire calcined body is improved. And the zirconia calcined body according to this embodiment is characterized in that the difference XY is 1 mol% or less. Since this zirconia calcined body has zirconia and rare earth oxide uniformly dispersed therein in advance, it can be used as a zirconia calcined body for high-speed firing that exhibits better translucency during high-speed firing than during low-speed firing.

[0044] The difference XY is preferably 1 mol% or less, more preferably 0.9 mol% or less, even more preferably 0.8 mol% or less, and particularly preferably 0.7 mol% or less. This makes it possible to obtain a zirconia calcined body more suitable for high-speed firing. On the other hand, the lower limit of the difference XY is not particularly limited, and may be 0.1 mol% or more.

[0045] The rare earth oxide content X in the zirconia calcined body is preferably 3 mol% or more, more preferably 3.2 mol% or more, even more preferably 3.4 mol% or more, and particularly preferably 3.5 mol% or more. As the rare earth oxide content X in the entire calcined body increases, the translucency of the zirconia sintered body after firing tends to improve. On the other hand, a calcined body having a small rare earth oxide content X has improved mechanical properties (strength, toughness, etc.). From this viewpoint, the rare earth oxide content X is preferably 6 mol% or less, more preferably 5.5 mol% or less, and particularly preferably 5 mol% or less. In this specification, the "rare earth oxide content X" is obtained by measuring the content of rare earth elements using an X-ray fluorescence analyzer (XRF: X-ray Fluorescence) and converting the content of the rare earth elements into the amount of oxide.

[0046] On the other hand, the amount Y of rare earth oxide in the matrix is ​​preferably 3.2 mol% or more, more preferably 3.3 mol% or more, even more preferably 3.4 mol% or more, and particularly preferably 3.5 mol% or more. As the amount Y of rare earth oxide in the matrix increases, the generation of a second phase in which rare earth oxide is unevenly distributed can be suppressed. The upper limit of the amount Y of rare earth oxide in the matrix is ​​not particularly limited, and may be approximately the same as the content X of rare earth oxide in the entire calcined body (X=Y). The specific upper limit of the amount Y of rare earth oxide in the matrix can be 5 mol% or less (typically 4.9 mol% or less, for example 4.8 mol% or less). The "amount Y of rare earth oxide in the matrix based on XRD analysis" in this specification can be measured according to the following procedure. First, as described above, the c / a axial length ratio of the matrix can be measured by analyzing the X-ray diffraction pattern. By substituting the c / a axial length ratio of the parent phase into a predetermined calculation formula, the "amount Y of rare earth oxide in the parent phase" can be calculated. The calculation formula is selected from conventionally known formulas depending on the type of rare earth oxide. For example, when the rare earth oxide is yttria (Y2O3), the amount Y of rare earth oxide (yttria) in the parent phase can be calculated by using the following formula (1). In this specification, the "amount Y of rare earth oxide in the parent phase" is not limited to the amount calculated based on the following formula (1). For example, when the rare earth oxide is ytterbia (Yb2O3), the "amount Y of rare earth oxide in the parent phase" can be calculated based on other conventionally known calculation formulas.

number

[0047] In addition, the zirconia calcined body according to this embodiment preferably has the difference XY of 1 mol % or less over 50% or more (preferably 75% or more) of the surface of the zirconia calcined body. 2 ) is the measurement target, any measurement location (diameter: 1 cm, area: approximately 0.75 cm 2) was scanned and measured. Then, it is preferable to change the measurement location and perform measurements at two to three locations, and the difference XY at each measurement location should be 1 mol% or less. The zirconia calcined body according to this embodiment is manufactured by calcining mixed particles in which fine rare earth compounds are uniformly dispersed. Therefore, it is easy to confirm that the uneven distribution of rare earth elements is suppressed in this zirconia calcined body at any of the multiple measurement locations. That is, according to the technology disclosed herein, a crystal structure in which the difference XY is 1 mol% or less can be confirmed in most of the zirconia calcined body. When this zirconia calcined body is rapidly sintered, a zirconia sintered body exhibiting excellent translucency as a whole can be obtained.

[0048] 3. Manufacturing method of zirconia sintered body The zirconia calcined body according to this embodiment has been described above. Next, a method for producing a zirconia sintered body using this zirconia calcined body will be described. FIG. 2 is a flow chart for explaining the method for producing a zirconia sintered body according to this embodiment. As shown in FIG. 2, the method for producing a zirconia sintered body includes a calcined body preparation step S110, a heating step S120, a holding step S130, and a cooling step S140. Each step will be described below.

[0049] (1) Calcined body preparation process S110 In this step, the zirconia calcined body is placed inside a firing furnace. In this embodiment, as described above, a zirconia calcined body in which rare earth oxides are uniformly dispersed (in other words, the above XY is 1 mol % or less) is used. The means for preparing the zirconia calcined body is not particularly limited. For example, the manufacturing method described in "1. Manufacturing method of zirconia calcined body" above may be carried out, or a manufactured zirconia calcined body may be purchased. In this step, the prepared zirconia calcined body is placed inside a heating furnace. As the heating furnace here, a conventionally known heating furnace (e.g., a muffle furnace, an electric furnace, a microwave firing furnace, etc.) may be used without any particular limitation.

[0050] (2) Heating process S120 In this step, the inside of the firing furnace is heated to a predetermined firing temperature. The firing temperature here is set within a range of, for example, 1400°C to 1700°C (preferably 1550°C to 1650°C). This allows the calcined body containing zirconia and rare earth oxide to be sufficiently sintered. The temperature-raising step S120 may be divided into a plurality of steps. For example, the temperature-raising step S120 in this embodiment includes a first temperature-raising step S122 and a second temperature-raising step S124, as shown in FIG. 2.

[0051] (2-a) First heating step S122 In the first heating step S122, the temperature is raised to a first temperature of 1000°C to 1100°C at a heating rate of 150°C / min or more. This first temperature is set to a temperature lower than the temperature at which densification of zirconia occurs. In the first heating step S122, the temperature is raised to the first temperature at a heating rate faster than that of the second heating step S124 described later. Even if the low-temperature region below the densification temperature is heated at a high speed, there is little adverse effect on the sintering (densification) of zirconia. This makes it possible to further shorten the firing time while sufficiently securing the density of the zirconia sintered body after production. The heating rate in the first heating step S122 is preferably 160°C / min or more, more preferably 170°C / min or more, even more preferably 180°C / min or more, and particularly preferably 190°C / min or more. This makes it possible to shorten the time of the first heating step S122, which contributes to improving production efficiency. In addition, when the calcined body according to this embodiment is used, the translucency of the sintered body after firing tends to be improved by increasing the heating rate and shortening the first heating step S122. On the other hand, the upper limit of the heating rate in the first heating step S122 is preferably 250°C / min or less, more preferably 240°C / min or less, even more preferably 230°C / min or less, and particularly preferably 220°C / min or less. When the heating rate in the first heating step S122 is slowed down, the temperature unevenness between the inside and the surface of the calcined body is reduced, and the strength is easily improved by homogenizing the composition.

[0052] (2-b) Second heating step S124 Next, in the second heating step S124, the temperature is raised to a second temperature of 1500°C to 1700°C at a heating rate of 30°C / min to less than 150°C / min. This second temperature is higher than the temperature at which zirconia is densified. That is, in the second heating step S124, the temperature is raised to the second temperature at a relatively slow heating rate. This allows the density of the zirconia sintered body after production to be sufficiently ensured. The heating rate in the second heating step S124 is preferably 35°C / min or more, more preferably 40°C / min or more, even more preferably 45°C / min or more, and particularly preferably 50°C / min or more. As in the first heating step S122, in this embodiment, the translucency of the sintered body after firing tends to be improved by increasing the heating rate and shortening the firing time. On the other hand, the upper limit of the heating rate in the second heating step S124 is preferably 130° C. / min or less, more preferably 120° C. / min or less, further preferably 110° C. / min or less, and particularly preferably 100° C. / min or less, which allows the zirconia to be more suitably densified.

[0053] (3) Holding process S130 In the holding step S130, the firing temperature is maintained and the holding time is determined in advance. As a result, the stabilized zirconia in the calcined body is sintered, and the zirconia sintered body is produced. As described above, when the zirconia calcined body according to the present embodiment is used, even if the holding time in this step is shortened to 30 minutes or less, a zirconia sintered body having excellent translucency can be produced. The holding time in the holding step S130 may be 20 minutes or less, 15 minutes or less, or 10 minutes or less. More preferably, the holding time is preferably 7.5 minutes or less, more preferably 5 minutes or less, even more preferably 2.5 minutes or less, and particularly preferably 1 minute or less. This allows the production time of the sintered body to be further shortened. The lower limit of the holding time is not particularly limited, and may be 0.5 minutes or more. The holding time may be 0 minutes. Specifically, the method for producing a zirconia sintered body disclosed herein also includes an embodiment in which the cooling step S140 is started without carrying out the holding step S130 after the second heating step S126 is completed. Even when such an embodiment is adopted, a zirconia sintered body having excellent translucency and in which rare earth oxides are uniformly dispersed can be produced.

[0054] (5) Cooling process S140 In the cooling step S140, the inside of the firing furnace is cooled to a predetermined cooling temperature. This allows the zirconia sintered body after firing to be collected. The cooling rate in the cooling step S140 is preferably 50°C / min or more, more preferably 75°C / min or more, and particularly preferably 100°C / min or more. As in the first heating step S122 and the second heating step S124, the translucency of the sintered body after firing tends to be improved by improving the cooling rate and shortening the total firing time. In addition, the improvement of the cooling rate can also contribute to improving production efficiency. On the other hand, the upper limit of the cooling rate in the cooling step S140 is preferably 450°C / min or less, more preferably 425°C / min or less, and particularly preferably 400°C / min or less. This allows the generation of cracks due to rapid cooling to be suppressed.

[0055] The produced zirconia sintered body exhibits excellent translucency, with a total light transmittance of 44.5% or more (preferably 45% or more, more preferably 45.5% or more, and particularly preferably 46% or more), despite having been subjected to high-speed sintering. Therefore, the zirconia calcined body according to this embodiment allows a sintered body having excellent translucency to be produced with high production efficiency.

[0056] As described above, in this embodiment, a raw material (zirconia calcined body) in which zirconia and rare earth oxides are homogenized in advance is used. For this reason, it is preferable to shorten the total firing time (total time from the first heating step S120 to the holding step S140) so that the crystal structure does not change significantly during the firing process. This makes it possible to manufacture a zirconia sintered body with better translucency. Specifically, the total firing time in this embodiment is preferably 120 minutes or less, more preferably 60 minutes or less, and particularly preferably 30 minutes or less. On the other hand, as long as the calcined body can be sufficiently sintered, the lower limit of the total firing time is not particularly limited. For example, the total firing time may be 10 minutes or more, 12 minutes or more, or 14 minutes or more.

[0057] <Other embodiments> The first embodiment of the technology disclosed herein has been described above. Note that the above embodiment shows one aspect to which the technology disclosed herein is applied, and does not limit the technology disclosed herein. In other words, in the technology disclosed herein, as long as the objective of realizing a zirconia calcined body for rapid firing that exhibits superior translucency during rapid firing compared to slow firing can be achieved, various configurations can be appropriately modified from the above-mentioned first embodiment.

[0058] 1. Second embodiment In the first embodiment, the rare earth adding step S22 and the precipitating step S24 are performed in the rare earth dispersing step S20. In other words, in the first embodiment, the rare earth element dissolved in the slurry is precipitated to realize a slurry in which rare earth particles having an average particle size of 300 nm or less are dispersed. However, the rare earth dispersing step S20 is not limited to the procedure described in the first embodiment as long as it can disperse fine rare earth particles in the slurry. For example, FIG. 3 is a flowchart showing an outline of a method for producing a zirconia calcined body according to the second embodiment. As shown in FIG. 3, the rare earth dispersing step S20 in the second embodiment includes an adding step S26 and a stirring step S28. Each step will be described below. Note that the steps other than the rare earth dispersing step S20 are the same as those in the first embodiment, so that repeated explanations will be omitted.

[0059] (1) Addition step S26 In the addition step S26, rare earth particles having an average particle size of 300 nm or less are added to the zirconia sol slurry. Specifically, in the first embodiment, rare earth particles are precipitated to generate fine rare earth particles in the zirconia sol slurry. In contrast, in the addition step S26 of the second embodiment, rare earth particles controlled to an average particle size of 300 nm or less are directly added to the zirconia sol slurry. Even when such a configuration is adopted, it has been confirmed by experiments that a zirconia calcined body for rapid sintering can be manufactured. Note that, as the rare earth particles here, oxides, hydroxides, etc. of rare earth elements can be used. Among these, oxides of rare earth elements are preferable because they enable stable manufacture.

[0060] (2) Mixing process S28 In the stirring step S28, the zirconia sol slurry is stirred to disperse the rare earth particles. This allows the fine rare earth particles to be uniformly present in the zirconia sol slurry, so that a zirconia calcined body for rapid sintering can be reliably produced. Then, by carrying out the above-mentioned recovery step S30 and heating step S40 after this stirring step S28, a zirconia calcined body in which zirconia and rare earth oxides are uniformly dispersed can be produced.

[0061] In the manufacturing method according to the present embodiment, it is preferable to carry out dispersion of rare earth particles in a state in which the pH of the zirconia sol slurry is acidic. This can suppress aggregation of each particle (zirconia particle, rare earth particle) in the slurry, so that the dispersibility of zirconia and rare earth oxide in the zirconia calcined body after production can be further improved. The pH of the slurry in this step is preferably 4 or less, more preferably 2 or less, even more preferably 1 or less, and particularly preferably 0.5 or less. As the pH of the slurry decreases, the dispersibility of each particle tends to improve. The lower limit of the pH of the slurry is not particularly limited, and may be 0.1 or more, 0.2 or more, or 0.3 or more. The means for adjusting the pH of the slurry is not particularly limited. For example, the pH of the slurry may be lowered by adding a pH adjuster such as hydrochloric acid. In addition, if the pH of the slurry is 4 or less when produced by hydrothermal synthesis or hydrolysis, the pH adjustment may not be performed.

[0062] In addition, other stirring conditions in the stirring step S28 are appropriately changed according to various conditions such as the viscosity of the zirconia sol slurry, the amount of rare earth particles added, and the average particle diameter, and therefore do not limit the technology disclosed herein. However, examples of stirring means include a ball mill, a mixer, a disperser, and a kneader. The rotation speed in stirring is preferably 100 rpm or more, more preferably 200 rpm or more, even more preferably 300 rpm or more, and particularly preferably 400 rpm or more. The upper limit of the rotation speed is not particularly limited, and may be 1000 rpm or less. The stirring time is preferably 10 minutes or more, more preferably 20 minutes or more, even more preferably 30 minutes or more, and particularly preferably 40 minutes or more. The upper limit of the stirring time is also not particularly limited, and may be 180 minutes or less. By considering these conditions, fine rare earth particles can be more uniformly dispersed in the zirconia sol slurry.

[0063] [Test example] Test examples relating to the technology disclosed herein are described below. However, the following test examples are not intended to limit the technology disclosed herein to the contents described below.

[0064] <First test> In this test, 13 types of zirconia calcined bodies with different manufacturing conditions were prepared (samples 1 to 13). Then, XRF analysis and XRD analysis were performed on each sample to measure the difference (XY) between the rare earth oxide content X in the zirconia calcined body and the solid solution amount Y of the rare earth oxide in the matrix.

[0065] 1. Sample Preparation (Sample 1) In sample 1, a zirconia calcined body was produced through the procedure of dissolving and precipitating the rare earth raw material. Specifically, first, a zirconium oxychloride solution was subjected to hydrothermal synthesis to obtain a zirconia sol slurry. The pH of the slurry after synthesis was measured to be pH=1.5, so in this sample, the rare earth raw material was dissolved without adjusting the pH. In this sample, yttrium chloride was used as the rare earth raw material. The amount of yttrium chloride added was set so that yttria was 4.27 mol% relative to the total substance amount (100 mol%) of zirconia and yttria. Next, ammonia was added to the zirconia sol slurry to increase the pH of the slurry to 7. As a result, yttrium compounds (yttria, etc.) were precipitated from the slurry. The average particle size of the yttrium compounds after this precipitation was measured by TEM observation and found to be 70 nm. Next, the slurry was dried at 180°C for 5 hours to recover mixed particles containing zirconia and yttria. The mixed particles were then heated at 1120°C for 4 hours to obtain a partially stabilized zirconia powder. The zirconia powder was pulverized in a ball mill using zirconia balls (diameter: 1 mm). The pulverized powder was then screened using a mesh sieve to obtain a zirconia powder with an average particle size of 150 nm to 200 nm. The zirconia powder was molded into a disk shape with a diameter of 2 cm, and then heated (calcined) at 1100°C for 2 hours to obtain a calcined zirconia body.

[0066] (Sample 2~3) For Samples 2 and 3, except for the difference in the amount of yttria added, the zirconia calcined bodies were prepared in the same manner as for Sample 1. The amount of yttria added and the average particle size for each sample are shown in Table 1.

[0067] (Samples 4-12) In Samples 4 to 12, rare earth particles adjusted to a predetermined average particle size were added to the slurry without going through the procedure of dissolving and precipitating the rare earth raw material. Specifically, in Samples 4 to 12, the pH of the slurry generated in the same procedure as Sample 1 was adjusted to 2, and then the powder rare earth raw material (yttrium oxide particles) was added. Note that the amount of yttria added and the average particle size were made different for Samples 4 to 12. The amount of yttria added and the average particle size for each sample are shown in Table 1. Then, a zirconia calcined body was obtained through the same recovery process and calcination process as Sample 1.

[0068] 2.Evaluation Test In this test, the content X of rare earth oxide in the calcined zirconia body and the amount Y of rare earth oxide in solid solution in the matrix were measured according to the above-mentioned measurement procedure. Then, based on the measurement results, the difference XY between the content X of rare earth oxide in the calcined zirconia body and the amount Y of rare earth oxide in solid solution in the matrix was measured. The results are shown in Table 1.

[0069] In this test, XRD analysis was performed at three different measurement points for one sample (calcined body). The c / a axis length ratio was measured at each measurement point based on Rietveld analysis, and the region with the highest crystal ratio was determined to be the parent phase. The calculation results are also shown in Table 1.

[0070] [Table 1]

[0071] As shown in Table 1, in Samples 1 to 4, 6 to 9, and 11, the difference (XY) between the content X of rare earth oxide in the zirconia calcined body and the amount Y of rare earth oxide dissolved in the matrix was 1 mol% or less. As described above, it is understood that yttria is uniformly dispersed in such calcined bodies. In other words, it was found that by dispersing yttria particles with an average particle size of 300 nm or less in the slurry, a zirconia calcined body in which segregation of yttria is suitably suppressed can be obtained.

[0072] <Second test> Next, in the second test, zirconia sintered bodies were manufactured using the calcined bodies obtained in the first test. In this test, 22 types of zirconia sintered bodies (Test Examples 1 to 22) were manufactured by combining nine types of calcined bodies (Samples 1 to 5, 8 to 10, and 12) with seven types of firing treatments (sintering patterns 1 to 6) with different conditions. Then, the total light transmittance of the sintered bodies after the manufacture was measured to evaluate the translucency.

[0073] 1. Firing conditions As mentioned above, six different firing patterns were set in this test. Detailed temperature profiles for each firing pattern are shown in Table 2.

[0074] [Table 2]

[0075] 2. Sample Selection As described above, in this test, 22 types of test examples were carried out by combining 9 types of calcined bodies (samples 1 to 5, 8 to 10, and 12) with 7 types of firing treatments (firing patterns 1 to 6). Specific combinations of calcined bodies and firing treatments are shown in Table 3.

[0076] 3.Evaluation Test (1) Baking time The total time required from the start of firing to the completion of cooling was calculated for each of Test Examples 1 to 22. The calculation results are shown in Table 3.

[0077] (2) Measurement of total light transmittance In this test, the total light transmittance was measured to evaluate the translucency of the zirconia sintered body after firing. In measuring the total light transmittance, the zirconia sintered body after firing (Test Examples 1 to 22) was first processed into a disk-shaped test piece having a thickness of 1 mm. Next, both sides of the test piece were mirror-polished using diamond slurry (average particle size 0.5 μm) as an abrasive. Then, the total light transmittance of the D65 light source in the thickness direction was measured. For the measurement, a haze meter NDH4000 manufactured by Nippon Denshoku Industries Co., Ltd. was used. The results are shown in Table 3.

[0078] [Table 3]

[0079] First, as shown in Test Examples 13 and 14, in Sample 5 in which XY exceeds 1 mol%, Test Example 13 in which low-speed firing (Pattern 3) was performed had better translucency after firing than Test Example 14 in which high-speed firing (Pattern 1) was performed. This is in line with conventional knowledge, and is believed to be due to the fact that bubbles in the sintered body were removed by the long-term low-speed firing. On the other hand, in the other samples, high-speed firing exhibited better translucency than low-speed firing (see Test Examples 1 to 12, 15 to 18). From this, it is presumed that in samples in which XY exceeds 1 mol%, the translucency is improved by a mechanism different from the removal of bubbles. And in these samples, rare earth oxides are uniformly distributed throughout the calcined body. From this, it is presumed that in samples in which XY exceeds 1 mol%, the crystal structure of the sintered body after firing is homogeneous, and therefore the translucency is improved.

[0080] Although the technology disclosed herein has been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples exemplified above. In other words, the technology disclosed herein includes the forms described in items 1 to 9 below.

[0081] <Item 1> A generating step of generating a zirconia sol slurry containing zirconia powder; a rare earth dispersion step of dispersing rare earth particles having an average particle size of 300 nm or less in the zirconia sol slurry; a recovery step of recovering mixed particles containing zirconia particles and rare earth particles from the zirconia sol slurry; a heating step of producing a partially stabilized zirconia powder by heating the mixed particles; a forming and heating step of forming the partially stabilized zirconia powder into a desired shape and then heating the formed shape; A method for producing a zirconia calcined body, comprising:

[0082] <Item 2> The rare earth dispersion step includes: a rare earth addition step of dissolving a rare earth raw material in the zirconia sol slurry having a pH of 4 or less; a precipitation step of precipitating a rare earth compound by increasing the pH of the zirconia sol slurry to 6 to 9; 2. A method for producing a zirconia calcined body according to item 1, comprising:

[0083] <Item 3> 3. The method for producing a calcined zirconia body according to item 2, wherein in the precipitation step, ammonia is added to the zirconia sol slurry to increase the pH of the slurry.

[0084] <Item 4> The rare earth dispersion step includes: An addition step of adding rare earth particles having an average particle size of 300 nm or less to the zirconia sol slurry; a stirring step of stirring the zirconia sol slurry to disperse the rare earth particles; 2. A method for producing a zirconia calcined body according to item 1, comprising:

[0085] <Item 5> 5. The method for producing a calcined zirconia body according to any one of items 1 to 4, further comprising a particle size adjusting step of adjusting a particle size of the partially stabilized zirconia powder between the heating step and the forming and heating step.

[0086] <Item 6> 6. The method for producing a calcined zirconia body according to any one of items 1 to 5, wherein the rare earth particles are yttria.

[0087] <Item 7> A zirconia calcined body containing zirconia and a rare earth oxide, The parent phase is a tetragonal crystal with a c / a axial length ratio of 1.008 or more. A zirconia calcined body, characterized in that a difference (XY) between a content X (mol%) of the rare earth oxide in the zirconia calcined body based on an XRF analysis and a solid solution amount Y (mol%) of the rare earth oxide in the parent phase based on an XRD analysis is 1 mol% or less.

[0088] <Item 8> 8. The zirconia calcined body according to item 7, wherein the rare earth oxide is yttria.

[0089] <Item 9> Item 9. The zirconia calcined body according to item 7 or 8, wherein the content X of the rare earth oxide is 3 mol % or more and 6 mol % or less.

[0090] <Item 10> 10. The zirconia calcined body according to any one of items 7 to 9, wherein the amount Y of the rare earth element in solid solution in the matrix is ​​3.2 mol % or more and 5 mol % or less.

[0091] <Item 11> 11. The zirconia calcined body according to any one of items 7 to 10, wherein the parent phase is present in an amount of 75% or more and 100% or less based on the entirety of the zirconia calcined body.

[0092] <Item 12> A calcined body preparation step of placing the zirconia calcined body according to any one of items 7 to 11 in a firing furnace; a temperature increasing step of increasing the temperature inside the firing furnace to a predetermined firing temperature; A holding step of holding the firing temperature for a predetermined holding time; a cooling step of cooling the inside of the firing furnace to a predetermined cooling temperature; Equipped with The method for producing a zirconia sintered body, wherein the holding time is 30 minutes or less.

Claims

1. A generating step of generating a zirconia sol slurry containing zirconia powder; a rare earth dispersion step of dispersing rare earth particles having an average particle size of 300 nm or less in the zirconia sol slurry; a recovery step of recovering mixed particles containing zirconia particles and rare earth particles from the zirconia sol slurry; a heating step of producing a partially stabilized zirconia powder by heating the mixed particles; a forming and heating step of forming the partially stabilized zirconia powder into a desired shape and then heating the formed shape; A method for producing a zirconia calcined body, comprising:

2. The rare earth dispersion step includes: a rare earth addition step of dissolving a rare earth raw material in the zirconia sol slurry having a pH of 4 or less; a precipitation step of precipitating a rare earth compound by increasing the pH of the zirconia sol slurry to 6 to 9; The method for producing the zirconia calcined body according to claim 1, comprising:

3. 3. The method for producing a calcined zirconia body according to claim 2, wherein in the precipitation step, ammonia is added to the zirconia sol slurry to increase the pH of the slurry.

4. The rare earth dispersion step includes: An addition step of adding rare earth particles having an average particle size of 300 nm or less to the zirconia sol slurry; a stirring step of stirring the zirconia sol slurry to disperse the rare earth particles; The method for producing the zirconia calcined body according to claim 1, comprising:

5. The method for producing a calcined zirconia body according to claim 1 , further comprising the step of: performing a particle size adjusting step of adjusting a particle size of the partially stabilized zirconia powder between the heating step and the molding and heating step.

6. The method for producing a zirconia calcined body according to any one of claims 1 to 5, wherein the rare earth particles are yttria.

7. A zirconia calcined body containing zirconia and a rare earth oxide, The matrix phase is a tetragonal crystal with a c / a axial length ratio of 1.008 or more. A zirconia calcined body, characterized in that a difference (X-Y) between a content X (mol %) of the rare earth oxide in the zirconia calcined body based on an XRF analysis and a solid solution amount Y (mol %) of the rare earth oxide in the parent phase based on an XRD analysis is 1 mol % or less.

8. The zirconia calcined body according to claim 7 , wherein the rare earth oxide is yttria.

9. The zirconia calcined body according to claim 7, wherein the content X of the rare earth oxide is 3 mol % or more and 6 mol % or less.

10. 8. The zirconia calcined body according to claim 7, wherein the amount Y of the rare earth element in solid solution in the parent phase is 3.2 mol % or more and 5 mol % or less.

11. The zirconia calcined body according to claim 7, wherein the parent phase is present in an amount of 75% or more and 100% or less of the entire zirconia calcined body.

12. A calcined body preparation step of housing the zirconia calcined body according to any one of claims 7 to 11 inside a firing furnace; a temperature increasing step of increasing the temperature inside the firing furnace to a predetermined firing temperature; a holding step of holding the firing temperature for a predetermined holding time; a cooling step of cooling the inside of the firing furnace to a predetermined cooling temperature; It is equipped with The method for producing a zirconia sintered body, wherein the holding time is 30 minutes or less.

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