Method for manufacturing zirconia calcined bodies and their applications

Abstract

This invention provides a zirconia calcined body for high-speed firing that exhibits superior light transmission during high-speed firing compared to low-speed firing. [Solution] The method for producing a calcined zirconia body disclosed herein includes a production step of generating a zirconia sol slurry containing zirconia powder, a rare earth dispersion step of dispersing rare earth particles with an average particle diameter 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 this production method, a calcined zirconia body in which zirconia and rare earth oxides are uniformly dispersed can be produced. This calcined zirconia body exhibits an unprecedented effect in which it shows better light transmission during high-speed firing than during low-speed firing.

Description

Technical Field

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

Background Art

[0002] Zirconia sintered bodies are widely used as biomaterials such as dental materials (for example, dentures, dental prostheses, denture mill blanks, dental orthodontic brackets). When a small amount of rare earth oxides (yttria (Y2O3), ytterbia (Yb2O3), etc.) is dissolved as a stabilizing component in this zirconia sintered body (hereinafter, also simply referred to as "sintered body"), it is known that strength, toughness, aesthetic properties, etc. are greatly improved. This zirconia sintered body is produced by firing a zirconia calcined body (hereinafter, also simply referred to as "calcined body") containing zirconia and a rare earth oxide. An example of the manufacturing procedure of 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 a zirconia sol and a rare earth oxide, a drying step of drying the zirconia sol, and a heating step of heating zirconia and a rare earth oxide at a low temperature below the sintering temperature.

[0003] By the way, in recent years, firing the calcined body at high speed in the production of zirconia sintered bodies has been studied. Specifically, in the production of conventional zirconia sintered bodies, a long-time firing process (low-speed firing) of holding a predetermined firing temperature for several hours (about 1 hour to 4 hours) has been performed. On the other hand, if high-speed firing with the holding time shortened to 30 minutes or less can be realized, the production efficiency of zirconia sintered bodies can be greatly improved. An example of this high-speed firing is disclosed in Patent Document 2. In the manufacturing method described in Patent Document 2, the holding time of the firing process is set to less than 20 minutes. According to this Patent Document 2, it is said that a zirconia sintered body having translucency required as a dental prosthesis can be produced in a short time.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-171832 [Patent Document 2] Japanese Patent Publication No. 2024-7519 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, it is known that changing the firing process in the manufacture of zirconia sintered bodies from low-speed firing to high-speed firing reduces the light transmittance of the sintered body after manufacture. This trade-off between firing time and light transmittance has not yet been overcome and is a problem that needs 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 in Patent Document 2 show excellent light transmittance among sintered bodies manufactured by high-speed firing, but they do not achieve light transmittance that significantly exceeds that of sintered bodies manufactured by low-speed firing (reference examples in Patent Document 2).

[0006] The technologies disclosed herein are intended to overcome the aforementioned trade-offs and relate to technologies for high-speed firing of zirconia calcined bodies that exhibit superior light transmission during high-speed firing compared to low-speed firing. [Means for solving the problem]

[0007] The inventors of the present invention conducted studies to realize a zirconia calcined body for high-speed firing that solves the above problems, and as a result came to the following conclusions. First, it is conventionally known that when low-speed firing is performed, the transparency is improved because bubbles in the sintered body are removed by prolonged heating. However, in high-speed firing, the heating time is short, making it difficult to sufficiently remove bubbles in the sintered body. Therefore, the inventors considered that in order to improve transparency in high-speed firing, it is necessary to control the refractive index due to the segregation of rare earth oxides. Specifically, after firing, there are differences in the concentration of the solid solution state of rare earth oxides inside the zirconia sintered body. And in regions where the solid solution state of rare earth oxides differs locally, the refractive index of transmitted light changes. In other words, if there are many regions where the solid solution state differs locally, it becomes a light scattering factor that reduces the transparency of the sintered body. Based on these findings, the inventors of the present invention concluded that in high-speed firing, where bubble removal is difficult, it is better to improve transparency by uniformly dispersing rare earth oxides throughout the sintered body.

[0008] Here, high-speed firing, which involves a short holding time, has the characteristic of sintering the calcined body in a short time, resulting in minimal change to the crystal structure before and after firing. The inventors focused on this point and hypothesized that using a zirconia calcined body in which minute rare-earth oxides are dispersed as a raw material would improve the transparency of the sintered zirconia body after manufacturing. As a result of various experiments, they discovered that when the degree of dispersion of rare-earth oxides throughout the zirconia calcined body exceeds a predetermined value, it exhibits an unprecedented effect of superior transparency during high-speed firing compared to low-speed firing. The technology disclosed herein relates to this zirconia calcined body for high-speed firing.

[0009] First, the method for producing a calcined zirconia body disclosed herein includes a production step of producing a zirconia sol slurry containing zirconia powder, a rare earth dispersion step of dispersing rare earth particles having an average particle diameter of 300 nm or less in the zirconia sol slurry, a recovery step of recovering mixed particles containing zirconia and a rare earth compound from the zirconia sol slurry, a heating step of producing partially stabilized zirconia powder by heating the mixed particles, and a molding and heating step of molding 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 with an average particle size of 300 nm or less are dispersed in a zirconia sol slurry. When this mixed particle containing fine rare earth particles is heated, a partially stabilized zirconia powder can be obtained in which zirconia and rare earth oxides are suitably interdiffused. By shaping this partially stabilized zirconia powder into a desired shape and then heating it, a zirconia calcined body for high-speed firing can be produced.

[0011] Furthermore, another aspect of the technology disclosed herein is a zirconia calcined body. 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 axis length ratio of 1.008 or higher. The calcined body disclosed herein is characterized in that the difference (XY) between the rare earth oxide content X (mol%) in the zirconia calcined body based on XRF analysis and the solid solution amount Y (mol%) of the rare earth oxide in the matrix based on XRD analysis is 1 mol% or less.

[0012] The zirconia calcined body with the above configuration is characterized by uniform dispersion of rare earth oxides and a small amount of the second phase in which coarse rare earth oxides are unevenly distributed. Specifically, in the above configuration, "Rare earth oxide content X in the zirconia calcined body based on XRF analysis" refers to the total amount of rare earth oxides present throughout the zirconia calcined body. On the other hand, "Solid solution amount Y of rare earth oxides in the matrix phase based on XRD analysis" refers to the amount of rare earth oxides dispersed in the matrix phase. In other words, as the difference XY between these values ​​decreases, the amount of the second phase in which rare earth oxides are unevenly distributed decreases, and the dispersibility of rare earth oxides throughout the calcined body is improved. Here, the zirconia calcined body with the above configuration is characterized in that the above difference XY is 1 mol% or less. Because the zirconia and rare earth oxides are uniformly dispersed in this zirconia calcined body, it can be used as a zirconia calcined body for high-speed firing, exhibiting better light transmission during high-speed firing than during low-speed firing.

[0013] Furthermore, another aspect of the technology disclosed herein is a method for manufacturing a zirconia sintered body. The method for manufacturing a zirconia sintered body disclosed herein comprises a calcination preparation step of placing the calcined zirconia body having the above configuration inside a firing furnace, a heating step of raising the temperature inside the firing furnace to a predetermined firing temperature, a holding step of maintaining the firing temperature for a predetermined holding time, and a cooling step of cooling the temperature inside the firing furnace to a predetermined cooling temperature. In this method for manufacturing a zirconia sintered body, the holding time is 30 minutes or less.

[0014] In the method for manufacturing a zirconia sintered body with the above configuration, a zirconia calcined body with a difference of XY of 1 mol% or less is subjected to high-speed firing for a holding time of 30 minutes or less. This makes it possible to manufacture 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 light transmission can be manufactured in a short time. [Brief explanation of the drawing]

[0015] [Figure 1]This is a flowchart outlining the manufacturing method of the zirconia calcined body according to the first embodiment. [Figure 2] This is a flowchart outlining the manufacturing method of the zirconia sintered body according to the first embodiment. [Figure 3] This is a flowchart outlining the manufacturing method of the zirconia calcined body according to the second embodiment. [Modes for carrying out the invention]

[0016] Some embodiments of the technology disclosed herein will be described below. Matters other than those specifically mentioned herein but necessary for implementing this technology can be understood based on the technical content taught herein and the common technical knowledge of those skilled in the art. The technology disclosed herein can be implemented based on the content disclosed herein and the common technical knowledge of the art. In this specification, when a numerical range is described as "A to B (where A and B are arbitrary numbers)," it means "A or greater and B or less," and also encompasses the meanings of "greater than A and less than B," "greater than A and less than or equal to B," and "A or greater and less than B."

[0017] <First Embodiment> 1. Method for manufacturing a calcined zirconia body First, a first embodiment of the method for manufacturing a zirconia calcined body disclosed herein will be described. Figure 1 is a flowchart showing an overview of the method for manufacturing a zirconia calcined body according to the first embodiment. As shown in Figure 1, the method for manufacturing a zirconia calcined body disclosed herein comprises a production 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, a rare earth addition step S22 and a precipitation step S24 are carried out in the rare earth dispersion step S20. Furthermore, in the manufacturing method according to this embodiment, a particle size adjustment step S50 is carried out 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 generation step S10, a zirconia sol slurry containing zirconia powder is generated. Here, the "zirconia powder" refers to a powder material mainly containing zirconia (ZrO2). Note that "mainly containing zirconia" means that components other than zirconia are not intentionally included. Therefore, a powder material containing inevitable impurities derived from raw materials, manufacturing processes, etc. is included in the zirconia powder in the technology disclosed herein. Examples of impurities in the zirconia powder include metal materials such as hafnium, calcium, silicon, aluminum, titanium, and compounds of these metals (typically oxides). Another example of an impurity is metallic zirconium. When the total amount of the constituent components of the zirconia powder is 100 mol%, the amount of zirconia is preferably 95 mol% or more (particularly preferably 98 mol% or more). Such zirconia powder with few impurities can be particularly preferably used in the manufacturing method according to this embodiment.

[0019] Also, the average particle size of the zirconia powder is preferably 10 nm or more, more preferably 20 nm or more, further 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 interface between the matrix phase and the second phase in the zirconia sintered body after firing decreases, making it easier to improve the translucency. 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. When the average particle size of the zirconia powder is reduced, a zirconia green body that can be easily sintered even by high-speed firing can be manufactured. Note that in this specification, the "average particle size" refers to the particle size (D 50 ) corresponding to 50% cumulative 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).

[0020] In addition, 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 tends to improve. Here, the "content of the zirconia powder" is the mass ratio when the total mass of the zirconia sol slurry is 100 wt%.

[0021] In addition, the method for producing the zirconia sol slurry is not particularly limited, and a conventionally known production method can be appropriately adopted. Examples of such production methods include the hydrothermal synthesis method and the hydrolysis method. In the hydrothermal synthesis method, a coprecipitate obtained by mixing a zirconium salt and 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 performing the hydrolysis reaction at such a temperature, homogeneous nucleation is promoted, so there is an advantage that the sol particle size distribution becomes sharp. 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 preferably dispersed in a liquid medium can be easily produced. The liquid medium of the zirconia sol slurry is a liquid that does not dissolve zirconia and can dissolve the rare earth raw material described below. Examples of such a liquid medium include water.

[0022] (2) Rare earth dispersion step S20 In the rare earth dispersion step S20, rare earth particles with an average particle diameter 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 can be obtained in which zirconia and rare earth oxides are suitably interdiffused. The average particle diameter 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 diameter of the rare earth particles decreases, the distribution of rare earth oxides in the partially stabilized zirconia powder can be made even more uniform. On the other hand, if the rare earth particles become too small, there is a risk of aggregation of the rare earth particles in the slurry. From this viewpoint, the average particle diameter 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 are not particularly limited, and various means can be selected as needed. For example, the rare earth dispersion step S20 in the first embodiment consists of a rare earth addition step S22 and a precipitation step S24. By going through these steps, a slurry in which rare earth particles of 300 nm or less are dispersed can be easily obtained. A detailed explanation follows below.

[0024] (2-a) Rare earth addition step S22 In the rare earth element addition step S22, the rare earth raw material is dissolved in the zirconia sol slurry. This allows the rare earth elements to be uniformly present in the zirconia sol slurry. In this specification, "rare earth raw material" refers to a compound containing rare earth elements. Considering the performance (strength, toughness, aesthetics, etc.) of the zirconia sintered body after firing, yttrium (Y) and ytterbium (Yb) are preferred as rare earth elements, with yttrium being particularly preferred. Furthermore, the rare earth raw material is required to be soluble in the zirconia sol slurry. For this reason, the rare earth raw material is preferably a halide such as chlorides, bromides, or iodides of the above-mentioned rare earth elements, as well as hydroxides, sulfides, sulfates, and nitrates. Considering the performance after firing and solubility in the slurry, yttrium chloride is particularly preferred as the rare earth raw material.

[0025] Furthermore, in the rare earth element addition step S22, it is preferable to adjust the amount of dissolved rare earth raw material so that the ratio of rare earth elements to Zr elements satisfies a predetermined range. For example, if the total amount of Zr elements and rare earth elements in the slurry is 100 mol%, the amount of rare earth elements 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 partially stabilized zirconia powder containing sufficient rare earth oxides. On the other hand, the upper limit of the amount of rare earth elements 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 oxides that were not introduced into the zirconia from being mixed into the partially stabilized zirconia powder as impurities.

[0026] In the first embodiment, the pH of the zirconia sol slurry is adjusted to 4 or less before adding the rare earth raw material. This suppresses the aggregation of zirconia particles in the slurry. Furthermore, by making the zirconia sol slurry acidic, the rare earth raw material can be properly dissolved. The pH of the slurry before adding the rare earth raw material is preferably 2 or less, more preferably 1 or less, even more 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 improve further. The lower limit of the pH of the slurry is not particularly limited and may be 0.1 or higher, 0.2 or higher, or 0.3 or higher. The means of adjusting the pH of the slurry are not particularly limited. For example, the pH of the slurry may be lowered by adding a pH adjusting agent such as hydrochloric acid. Also, if the pH of the slurry was 4 or less when produced by hydrothermal synthesis or hydrolysis, pH adjustment may not be necessary.

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

[0028] In this process, it is preferable to add an alkali to the zirconia sol slurry. This makes it easy to raise the pH of the slurry. As the alkali, ammonia, sodium hydroxide, potassium hydroxide, etc., can be used. Among these, ammonia is particularly preferred because it prevents the inclusion of metal elements (such as Na) as impurities in the partially stabilized zirconia powder after manufacturing.

[0029] Furthermore, in this process, it is preferable to add alkali while stirring the zirconia sol slurry. This allows the rare earth compound to precipitate with the zirconia particles uniformly dispersed in the slurry, thereby further improving the degree of dispersion between the zirconia and the rare earth compound. The specific stirring method is not particularly limited, and conventionally known stirring devices can be used without any particular restrictions. Examples of such stirring methods include ball mills, mixers, dispersers, and kneaders.

[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 makes it possible to recover mixed particles in which zirconia and the rare earth compound are uniformly dispersed. The specific method for recovering the mixed particles is not particularly limited, and conventionally known methods for separating powder materials from liquids can be used without any particular restriction. For example, the mixed particles can be recovered by appropriately combining means such as filtration, centrifugation, and drying.

[0031] (4)Heating process S40 In heating step S40, partially stabilized zirconia powder is produced by heating the mixed particles obtained in recovery step S30. 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 at the beginning of heating step S40. Then, in heating step S40, mixed particles in which zirconia and rare earth oxide are uniformly dispersed are heated. In these mixed particles, the distance between zirconia and rare earth oxide is close, so zirconia and rare earth oxide preferentially mutually diffuse. As a result, partially stabilized zirconia powder in which zirconia and rare earth oxide are uniformly dispersed can be obtained. By using this partially stabilized zirconia powder, a calcined zirconia body in which rare earth oxide is uniformly dispersed can be obtained.

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

[0033] (5) Particle size adjustment process S50 Furthermore, in the method for manufacturing the calcined body according to this embodiment, a particle size adjustment step S50 is performed between the heating step S40 and the molding heating step S60 to adjust the particle size of the partially stabilized zirconia powder. Note that the particle size adjustment step S50 can employ any conventionally known particle size adjustment technique without particular limitations. For example, the partially stabilized zirconia powder after heating may be crushed and then sieved with a mesh or the like. This makes it possible to obtain partially stabilized zirconia powder with a desired particle size.

[0034] In this process, a higher quality zirconia calcined body can be obtained by controlling the average particle size of the partially stabilized zirconia powder to a specific range. 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 process, it becomes easier to produce a dense zirconia calcined body in the molding and heating process 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 molding and heating process S60 (after calcination) may deteriorate, and the c / a axis 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 molding and heating step S60, a calcined zirconia body is produced by molding the partially stabilized zirconia powder into a desired shape and then heating (calcining) it. Specifically, in the molding and heating step S60, first, the partially stabilized zirconia powder after the particle size adjustment step S50 and the binder are mixed. Then, this mixture is molded into a desired shape. By heating (calcining) this molded body, the binder burns away and a portion of the partially stabilized zirconia powder melts and solidifies. This allows for the production of a calcined zirconia body. The molding and heating step S60 can employ any conventionally known method for molding zirconia sintered bodies without particular limitations. For this reason, detailed conditions (type of binder, amount of binder added, molding means, heating conditions, etc.) are omitted in this specification. Furthermore, the shape of the molded body produced in this step is not particularly limited and can be, for example, plate-shaped, disc-shaped, rectangular parallelepiped-shaped, cubic-shaped, columnar-shaped, etc.

[0036] Furthermore, the zirconia sintered body after firing, as described later, may contain alumina. This suppresses grain growth during firing, thereby improving the strength of the sintered body after firing. It is preferable to add the alumina raw material together with the binder in the molding and heating process S60. Examples of alumina sources include alumina powder, alumina sol, hydrated alumina, aluminum hydroxide, aluminum chloride, aluminum nitrate, and aluminum sulfate. These alumina sources become alumina during the firing process described later and are dispersed within the sintered body. The amount of alumina source added should be adjusted so that the amount of 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 amount of constituent components of the calcined body (100 mol%). This allows for a suitable improvement in the strength of the sintered body. On the other hand, since alumina is a light scattering factor, it may reduce the light transmittance of the sintered body. Therefore, the amount of alumina source added should be adjusted so that the amount of Al element is 0.2 mol% or less (preferably 0.15 mol% or less, and particularly preferably 0.1 mol% or less) relative to the total amount of constituent components of the calcined body (100 mol%). In addition, the zirconia sintered body after firing may contain trace amounts of additives (e.g., 0.1 mol% or less) for purposes such as coloring. Examples of these trace additives include iron, nickel, cobalt, manganese, niobium, praseodymium, neodymium, europium, and erbium. It is preferable to add these trace additives together with the binder in the molding and heating process S60.

[0037] 2. Zirconia calcined body The method for manufacturing a zirconia calcined body according to the first embodiment has been described above. According to this manufacturing 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: it shows superior light transmission during high-speed calcination compared to low-speed calcination. The calcined body after production will now be described.

[0038] The zirconia calcined body according to this embodiment is a molded body containing zirconia and rare earth oxides. Since zirconia and rare earth oxides have already been described, a redundant explanation will be omitted. In this specification, "zirconia calcined body" refers to a calcined body whose main components are zirconia and rare earth oxides. Here, "main components are zirconia and rare earth oxides" means that the amount of synthesized material 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 amount of material (100 mol%) of the constituent components of the calcined body. The amount of material of the constituent components of this calcined body is measured by XRF analysis, which will be described later.

[0039] Furthermore, the amount of zirconia relative to the total amount of components (100 mol%) of the calcined body 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 proportion of zirconia in the calcined body increases, the strength, toughness, and resistance to hydrothermal degradation of the zirconia sintered body after firing tend to improve. On the other hand, from the viewpoint of ensuring sufficient amounts of other additives (such as rare earth oxides), 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 material has a tetragonal matrix with a c / a axis length ratio of 1.008 or greater. This c / a axis length ratio can be measured by X-ray diffraction (XRD) on the surface of the zirconia calcined material. Specifically, the surface of the zirconia calcined material 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, the X-ray diffraction pattern at 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 analyzed using crystal analysis software (RIETAN-FP) to perform Rietveld analysis. This allows the c / a axis length ratio of the zirconia calcined material to be derived. A tetragonal matrix with a c / a axis length ratio of 1.008 or greater becomes the matrix for stabilized zirconia (typically yttria-stabilized zirconia).

[0041] The conditions for acquiring 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, "matrix phase" refers to the crystalline phase that makes up more than 50% of the crystalline phases constituting the zirconia calcined body. In other words, in the zirconia calcined body according to this embodiment, the proportion of tetragonal crystals with a c / a axis length ratio of 1.008 or more exceeds 50%. In this specification, crystalline phases other than the matrix phase (i.e., crystalline phases with a total proportion of less than 50%) are referred to as "secondary phases." The secondary phase may consist of one or more crystalline phases. That is, the zirconia calcined body according to this embodiment includes calcined bodies having three or more crystalline phases. In the zirconia calcined body according to this embodiment, the proportion of the matrix phase is preferably 72% or more, more preferably 74% or more, even more preferably 75% or more, and particularly preferably 76% or more. As the proportion of the matrix phase increases, the number of boundaries between the matrix phase and the secondary phase decreases, and therefore the permeability of the zirconia sintered body after firing tends to improve. Furthermore, the upper limit of the matrix phase's abundance ratio is not particularly limited and may be 100%. In other words, the zirconia calcined body according to this embodiment also includes single-phase calcined bodies consisting only of tetragonal crystals with a c / a axis length ratio of 1.008 or greater. The composition ratio of the crystalline 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 rare earth oxide content X (mol%) in the zirconia calcined body based on XRF analysis and the solid solution amount Y (mol%) of rare earth oxides in the matrix phase based on XRD analysis is 1 mol% or less. As described above, "rare earth oxide content X in the zirconia calcined body based on XRF analysis" refers to the total amount of rare earth oxides present throughout the zirconia calcined body. On the other hand, "solid solution amount Y in the matrix phase based on XRD analysis" refers to the amount of rare earth oxides dispersed in the matrix phase. In other words, when the difference XY between these values ​​becomes small, the amount of the second phase in which rare earth oxides are unevenly distributed decreases, and the dispersibility of rare earth oxides throughout the calcined body is improved. The zirconia calcined body according to this embodiment is characterized in that the above difference XY is 1 mol% or less. Because this zirconia calcined body has zirconia and rare earth oxides uniformly dispersed in it beforehand, it can be used as a high-speed calcined zirconia body that exhibits better light transmission during high-speed calcination than during low-speed calcination.

[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 that is more suitable for rapid 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 content X of rare earth oxides 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 content X of rare earth oxides in the calcined body as a whole increases, the translucency of the zirconia sintered body after firing tends to improve. On the other hand, calcined bodies with a low content X of rare earth oxides exhibit improved mechanical properties (strength, toughness, etc.). From this viewpoint, the content X of rare earth oxides is preferably 6 mol% or less, more preferably 5.5 mol% or less, and particularly preferably 5 mol% or less. In this specification, "content X of rare earth oxides" is calculated by measuring the content of rare earth elements using an X-ray fluorescence analyzer (XRF) and converting the content of said rare earth elements into oxide amounts.

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

number

[0047] Furthermore, in the zirconia calcined body according to this embodiment, it is preferable that the difference XY is 1 mol% or less in 50% or more (preferably 75% or more) of the surface of the zirconia calcined body. For example, a disc-shaped zirconia calcined body with a diameter of 2 cm (surface area: approximately 3 cm²) 2 When the measurement target is ), any measurement location (diameter: 1 cm, area: approximately 0.75 cm) can be used. 2Measurements were taken by scanning the area. Then, measurements were taken at 2 to 3 different locations, and it is desirable that the difference XY at each measurement location is 1 mol% or less. The zirconia calcined body according to this embodiment is manufactured by calcining mixed particles in which minute rare earth compounds are homogeneously dispersed. Therefore, it is easy to confirm that the uneven distribution of rare earth elements is suppressed at any of the multiple measurement locations in this zirconia calcined body. In other words, according to the technology disclosed herein, a crystal structure that satisfies the above difference XY of 1 mol% or less can be confirmed in most of the zirconia calcined body. When this zirconia calcined body is rapidly fired, a zirconia sintered body exhibiting excellent transparency as a whole can be obtained.

[0048] 3. Method for manufacturing zirconia sintered bodies The zirconia calcined body according to this embodiment has been described above. Next, a method for manufacturing a zirconia sintered body using this zirconia calcined body will be described. Figure 2 is a flowchart illustrating the manufacturing method of the zirconia sintered body according to this embodiment. As shown in Figure 2, the manufacturing method of this zirconia sintered body comprises 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) Preparation process for the calcined body 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, XY is 1 mol% or less) is used. The means of preparing the zirconia calcined body are not particularly limited. For example, the manufacturing method described in "1. Method for Manufacturing 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. In this step, any conventionally known heating furnace (e.g., muffle furnace, electric furnace, microwave firing furnace, etc.) can be used without particular limitation.

[0050] (2) Heating process S120 In this process, the inside of the firing furnace is heated to a predetermined firing temperature. The firing temperature here is set to 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 oxides to be sufficiently sintered. Note that the heating step S120 may be divided into multiple stages. For example, in this embodiment, the heating step S120 comprises a first heating step S122 and a second heating step S124, as shown in Figure 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 lower than the temperature at which zirconia densification occurs. Furthermore, in the first heating step S122, the temperature is raised to the first temperature at a faster heating rate than in the second heating step S124, which will be described later. Even if the temperature is raised rapidly in this low-temperature region below the densification temperature, there is little adverse effect on the sintering (densification) of zirconia. This allows for a sufficient density of the zirconia sintered body after manufacturing, while further shortening the firing time. 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 shortens the time of the first heating step S122, contributing to improved production efficiency. In addition, when using the calcined body according to this embodiment, shortening the first heating step S122 by increasing the heating rate tends to improve the light transmittance of the sintered body after firing. 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. Slowing down the heating rate in the first heating step S122 reduces the temperature unevenness between the inside and surface of the calcined body, which tends to improve strength due to homogenization of 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 densifies. In other words, in the second heating step S124, the temperature is raised to the second temperature at a relatively slow heating rate. This ensures sufficient density of the zirconia sintered body after manufacturing. The heating rate in the second heating step S124 is preferably 35°C / min or higher, more preferably 40°C / min or higher, even more preferably 45°C / min or higher, and particularly preferably 50°C / min or higher. Similar to the first heating step S122 described above, in this embodiment, increasing the heating rate and shortening the firing time tends to improve the light transmittance of the sintered body after firing. 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, even more preferably 110°C / min or less, and particularly preferably 100°C / min or less. This allows for more favorable densification of the zirconia.

[0053] (3) Holding process S130 In the holding step S130, the firing temperature is maintained while holding for a predetermined time. This causes the stabilized zirconia in the calcined body to sinter, and a zirconia sintered body is manufactured. As described above, by using the zirconia calcined body according to this embodiment, a zirconia sintered body with excellent light transmission can be manufactured even if the holding time in this step is shortened to 30 minutes or less. 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 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 further shortens the manufacturing time of the sintered body. The lower limit of the holding time is not particularly limited and may be 0.5 minutes or more. The holding time may also be 0 minutes. Specifically, the method for manufacturing a zirconia sintered body disclosed herein also includes an embodiment in which the cooling step S140 is started without performing the holding step S130 after the second heating step S126 is completed. Even when such an embodiment is adopted, it is possible to produce a zirconia sintered body in which rare earth oxides are uniformly dispersed and exhibit excellent light transmission.

[0054] (5) Cooling process S140 In the cooling process S140, the inside of the firing furnace is cooled to a predetermined cooling temperature. This allows for the recovery of the zirconia sintered body after firing. The cooling rate in the cooling process S140 is preferably 50°C / min or higher, more preferably 75°C / min or higher, and particularly preferably 100°C / min or higher. Similar to the first heating process S122 and the second heating process S124 described above, improving the cooling rate and shortening the total firing time tends to improve the light transmittance of the sintered body after firing. Furthermore, improving the cooling rate can also contribute to improving production efficiency. On the other hand, the upper limit of the cooling rate in the cooling process S140 is preferably 450°C / min or lower, more preferably 425°C / min or lower, and particularly preferably 400°C / min or lower. This suppresses the formation of cracks due to rapid cooling.

[0055] Furthermore, the zirconia sintered body after manufacturing exhibits excellent light transmittance, with a total light transmittance of 44.5% or more (preferably 45% or more, more preferably 45.5% or more, and especially preferably 46% or more), despite being subjected to high-speed firing. Therefore, according to the calcined zirconia body of this embodiment, a sintered body with excellent light transmittance can be manufactured with high production efficiency.

[0056] Furthermore, as described above, this embodiment uses a raw material (calcined zirconia body) in which zirconia and rare earth oxides are pre-mixed uniformly. 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 produce a zirconia sintered body with better light transmittance. 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, the lower limit of the total firing time is not particularly limited as long as the calcined body can be sufficiently sintered. 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. The above-described embodiment is merely one way in which the technology disclosed herein is applied and does not limit the technology disclosed herein. That is, if the technology disclosed herein can achieve the objective of realizing a zirconia calcined body for high-speed firing that exhibits better light transmission during high-speed firing than during low-speed firing, various configurations can be appropriately modified from the first embodiment described above.

[0058] 1. Second Embodiment In the first embodiment, the rare earth dispersion step S20 includes the rare earth addition step S22 and the precipitation step S24. In other words, in the first embodiment, a slurry containing dispersed rare earth particles with an average particle diameter of 300 nm or less is achieved by precipitating the rare earth elements dissolved in the slurry. However, the rare earth dispersion step S20 is not limited to the procedure described in the first embodiment, as long as it can disperse minute rare earth particles in the slurry. For example, Figure 3 is a flowchart outlining the method for manufacturing a calcined zirconia body according to the second embodiment. As shown in Figure 3, the rare earth dispersion step S20 in the second embodiment includes an addition step S26 and a stirring step S28. Each step will be described below. Note that steps other than the rare earth dispersion step S20 are the same as in the first embodiment, so redundant explanations will be omitted.

[0059] (1) Addition step S26 In addition step S26, rare earth particles with an average particle size of 300 nm or less are added to the zirconia sol slurry. Specifically, in the first embodiment, minute rare earth particles were generated in the zirconia sol slurry by precipitation. In contrast, in addition step S26 of the second embodiment, rare earth particles with an average particle size of 300 nm or less are directly added to the zirconia sol slurry. Experiments have confirmed that even with this configuration, zirconia calcined bodies for high-speed firing can be produced. As for the rare earth particles here, oxides and hydroxides of rare earth elements can be used. Among these, oxides of rare earth elements are preferred because they enable stable production.

[0060] (2) Stirring process S28 In the stirring step S28, the zirconia sol slurry is stirred to disperse the rare earth particles. This ensures that minute rare earth particles are uniformly distributed within the zirconia sol slurry, thereby reliably producing a zirconia calcined body for high-speed firing. Following this stirring step S28, the recovery step S30 and heating step S40 described above are carried out to produce a zirconia calcined body in which zirconia and rare earth oxides are uniformly dispersed.

[0061] Furthermore, in the manufacturing method according to this embodiment, it is preferable to disperse the rare earth particles while the pH of the zirconia sol slurry is acidic. This suppresses the aggregation of each particle (zirconia particles, rare earth particles) in the slurry, thereby further improving the dispersibility of zirconia and rare earth oxides in the calcined zirconia body after manufacturing. 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 higher, 0.2 or higher, or 0.3 or higher. The means of adjusting the pH of the slurry are not particularly limited. For example, the pH of the slurry may be lowered by adding a pH adjusting agent such as hydrochloric acid. Also, if the pH of the slurry was 4 or less when produced by hydrothermal synthesis or hydrolysis, pH adjustment may not be necessary.

[0062] The other stirring conditions in stirring step S28 can be appropriately changed depending on various conditions such as the viscosity of the zirconia sol slurry, the amount of rare earth particles added, and the average particle size, and are not limited to the technology disclosed herein. However, examples of stirring means include ball mills, mixers, dispersers, and kneaders. The rotational speed during 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 rotational 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 dispersed more uniformly in the zirconia sol slurry.

[0063] [Example Test] The following describes examples of tests relating to the technology disclosed herein. However, the following examples of tests are not intended to limit the technology disclosed herein to what is described below.

[0064] <First Exam> In this study, thirteen types of zirconia calcined bodies were prepared under different manufacturing conditions (Samples 1-13). XRF and XRD analyses 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 solubility Y of the rare earth oxide in the matrix phase.

[0065] 1. Sample preparation (Sample 1) In Sample 1, a calcined zirconia body was prepared through a procedure involving the dissolution and precipitation of rare earth raw materials. Specifically, a zirconia sol slurry was first obtained by hydrothermal synthesis in a zirconium oxychloride solution. The pH of the synthesized slurry was measured to be 1.5, so the rare earth raw material was dissolved without adjusting the pH in this sample. In this sample, yttrium chloride was used as the rare earth raw material. The amount of yttrium chloride added was set so that yttria accounted for 4.27 mol% of the total amount of zirconia and yttria (100 mol%). Next, ammonia was added to the zirconia sol slurry to raise the pH of the slurry to 7. This caused yttrium compounds (such as yttria) to precipitate from the slurry. The average particle size of the precipitated yttrium compounds 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. Then, by heating this mixed particle at 1120°C for 4 hours, a partially stabilized zirconia powder was obtained. This zirconia powder was pulverized using a ball mill with zirconia balls (diameter: 1 mm). Next, the pulverized powder was separated using a mesh sieve to obtain zirconia powder with an average particle size of 150 nm to 200 nm. After shaping this zirconia powder into a disc with a diameter of 2 cm, a calcined zirconia body was obtained by heating (calcining) it at 1100°C for 2 hours.

[0066] (Samples 2-3) In Samples 2 and 3, zirconia calcined bodies were prepared using the same procedure as in Sample 1, except that the amount of yttria added was different. The amount of yttria added and the average particle size for each sample are shown in Table 1.

[0067] (Samples 4-12) In samples 4-12, 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 4-12, the pH of the slurry produced using the same procedure as in sample 1 was adjusted to 2, and then powdered rare earth raw material (yttrium oxide particles) was added. In samples 4-12, the amount of yttria added and the average particle size were varied. Table 1 shows the amount of yttria added and the average particle size for each sample. Then, calcined zirconia bodies were obtained by performing the same recovery and calcination treatments as in sample 1.

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

[0069] Furthermore, in this study, XRD analysis was performed at three different measurement locations on a single sample (calcined body). Based on Rietveld analysis, the c / a axis length ratio was measured at each measurement location, and the region with the highest crystalline proportion was identified as the matrix phase. The results of this calculation are also shown in Table 1.

[0070] [Table 1]

[0071] As shown in Table 1, in samples 1-4, 6-9, and 11, 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 phase was 1 mol% or less. As described above, such calcined bodies are understood to have uniformly dispersed yttria. 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 yttria segregation is suitably suppressed can be obtained.

[0072] <Second Exam> 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 produced by combining nine types of calcined bodies (samples 1 to 5, 8 to 10, and 12) and seven types of firing treatments with different conditions (firing patterns 1 to 6). The light transmittance of the sintered bodies after production was then measured to evaluate their light transmission properties.

[0073] 1. Firing conditions As described above, six different firing patterns were set up in this test. The 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 test examples were conducted by combining nine types of calcined bodies (samples 1-5, 8-10, and 12) and seven types of firing treatments (firing patterns 1-6). The specific combinations of calcined bodies and firing treatments are shown in Table 3.

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

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

[0078] [Table 3]

[0079] First, as shown in Test Examples 13 and 14, in Sample 5 where XY exceeds 1 mol%, the light transmittance after firing was improved in Test Example 13, which underwent slow firing (Pattern 3), compared to Test Example 14, which underwent fast firing (Pattern 1). This is consistent with conventional knowledge and is thought to be because air bubbles in the sintered body were removed by the long-term slow firing. On the other hand, in the other samples, better light transmittance was observed during fast firing than during slow firing (see Test Examples 1-12, 15-18). From this, it is presumed that in samples where XY exceeds 1 mol%, the light transmittance is improved by a mechanism other than air bubble removal. Furthermore, in these samples, rare earth oxides are uniformly distributed throughout the calcined body. From this, it is presumed that in samples where XY exceeds 1 mol%, the light transmittance is improved because the crystal structure of the sintered body after firing is homogeneous.

[0080] The technologies disclosed herein have been described in detail above, but these are merely illustrative examples and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. In other words, the technologies disclosed herein encompass the forms described in items 1 to 9 below.

[0081] <Item 1> A production process for generating a zirconia sol slurry containing zirconia powder, A rare earth dispersion step is performed in which rare earth particles with an average particle diameter of 300 nm or less are dispersed in the zirconia sol slurry. A recovery step is performed to recover mixed particles containing zirconia particles and rare earth particles from the zirconia sol slurry. A heating step for producing partially stabilized zirconia powder by heating the mixed particles, A molding and heating step is performed in which the partially stabilized zirconia powder is molded into a desired shape and then heated. A method for producing a calcined zirconia body, including the method described above.

[0082] <Item 2> The aforementioned rare earth dispersion step is, A rare earth addition step in which a rare earth raw material is dissolved in the zirconia sol slurry having a pH of 4 or less, A precipitation step is performed to precipitate rare earth compounds by raising the pH of the zirconia sol slurry to 6-9. A method for producing a calcined zirconia body as described in item 1, including the method described in item 1.

[0083] <Item 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 aforementioned rare earth dispersion step is, The addition step involves adding rare earth particles with 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, A method for producing a calcined zirconia body as described in item 1, including the method described in item 1.

[0085] <Item 5> A method for producing a calcined zirconia body according to any one of items 1 to 4, wherein a particle size adjustment step is performed between the heating step and the molding heating step to adjust the particle size of the partially stabilized zirconia powder.

[0086] <Item 6> A 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 rare earth oxides, It has a tetragonal matrix with a c / a axis length ratio of 1.008 or greater. A zirconia calcined body characterized in that the difference (XY) between the content X (mol%) of the rare earth oxide in the zirconia calcined body based on XRF analysis and the solid solution amount Y (mol%) of the rare earth oxide in the matrix phase based on XRD analysis is 1 mol% or less.

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

[0089] <Item 9> A calcined zirconia 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> A calcined zirconia body according to any one of items 7 to 9, wherein the solid solution amount Y of the rare earth element in the matrix is ​​3.2 mol% or more and 5 mol% or less.

[0091] <Item 11> A zirconia calcined body according to any one of items 7 to 10, wherein the ratio of the matrix to the total zirconia calcined body is 75% or more and 100% or less.

[0092] <Item 12> A calcination preparation step in which a zirconia calcined body described in any one of items 7 to 11 is placed inside a calcination furnace, The process includes raising the temperature inside the firing furnace to a predetermined firing temperature, A holding step in which the firing temperature is maintained and a predetermined holding time is maintained, A cooling step in which the inside of the firing furnace is cooled to a predetermined cooling temperature. It is equipped with, A method for producing a zirconia sintered body, wherein the holding time is 30 minutes or less.

Claims

1. A production process for generating a zirconia sol slurry containing zirconia powder, A rare earth dispersion step is performed in which rare earth particles with an average particle diameter of 300 nm or less are dispersed in the zirconia sol slurry. A recovery step is performed to recover mixed particles containing zirconia particles and rare earth particles from the zirconia sol slurry. A heating step for producing partially stabilized zirconia powder by heating the mixed particles, A molding and heating step is performed in which the partially stabilized zirconia powder is molded into a desired shape and then heated. A method for producing a calcined zirconia body, including the method described above.

2. The aforementioned rare earth dispersion step is, A rare earth addition step in which a rare earth raw material is dissolved in the zirconia sol slurry having a pH of 4 or less, A precipitation step is performed to precipitate rare earth compounds by raising the pH of the zirconia sol slurry to 6-9. A method for producing a calcined zirconia body according to claim 1, including the method described in claim 1.

3. A 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 aforementioned rare earth dispersion step is, The zirconia sol slurry is given an addition step of adding rare earth particles with an average particle size of 300 nm or less, A stirring step of stirring the zirconia sol slurry to disperse the rare earth particles, A method for producing a calcined zirconia body according to claim 1, including the method described in claim 1.

5. A method for producing a calcined zirconia body according to claim 1, wherein a particle size adjustment step is performed between the heating step and the molding heating step to adjust the particle size of the partially stabilized zirconia powder.

6. The method for producing a calcined zirconia 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 rare earth oxides, It has a tetragonal matrix with a c / a axis length ratio of 1.008 or greater. A zirconia calcined body characterized in that the difference (X - Y) between the content X (mol%) of the rare earth oxide in the zirconia calcined body based on XRF analysis and the solid solution amount Y (mol%) of the rare earth oxide in the matrix phase based on 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. The calcined zirconia body according to claim 7, wherein the solid solution amount Y of the rare earth element in the matrix is ​​3.2 mol% or more and 5 mol% or less.

11. The zirconia calcined body according to claim 7, wherein the ratio of the matrix phase to the total zirconia calcined body is 75% or more and 100% or less.

12. A calcination preparation step comprising housing the zirconia calcined body according to any one of claims 7 to 11 inside a calcination furnace, The process includes raising the temperature inside the firing furnace to a predetermined firing temperature, A holding step in which the firing temperature is maintained and a predetermined holding time is maintained, A cooling step in which the inside of the firing furnace is cooled to a predetermined cooling temperature. It is equipped with, A method for manufacturing a zirconia sintered body, wherein the holding time is 30 minutes or less.

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