WO2024029228A1

WO2024029228A1 - Sintered zirconia object

Info

Publication number: WO2024029228A1
Application number: PCT/JP2023/023396
Authority: WO
Inventors: 清治伴; 裕太安岡
Original assignee: 共立マテリアル株式会社; 清治伴
Priority date: 2022-08-04
Filing date: 2023-06-23
Publication date: 2024-02-08
Also published as: JP7568234B2; JP2024021848A

Abstract

The present invention provides a sintered zirconia object that has a surface, at least some of which has excellent breaking toughness, and that has a reduced degree of thermal expansion. This sintered zirconia object comprises zirconia and a vanadium-group element, wherein the vanadium-group element localizes in at least some of a surface layer. In one embodiment of this sintered zirconia object, the concentration of the vanadium-group element in the surface-layer surface where the vanadium-group element localizes is at least 1.5 times as high as the concentration of the vanadium-group element in a portion that is lowest in the concentration of the vanadium-group element along the depth direction from said surface, or the portion that is lowest in the concentration of the vanadium-group element does not contain the vanadium-group element.

Description

Zirconia sintered body

The present invention relates to a zirconia sintered body. This application claims priority based on Japanese Patent Application No. 2022-124979 filed on August 4, 2022, and the entire content of that application is incorporated herein by reference. There is.

Zirconia sintered bodies with a small amount of yttria (Y ₂ O ₃ ) dissolved in solid solution (hereinafter also referred to as "partially stabilized zirconia sintered bodies") are used as dental materials (for example, dentures) due to their high strength, toughness, and aesthetics. It is widely used as a biomaterial for products such as dental prosthetics, denture mill blanks, orthodontic brackets), etc. For example, Patent Document 1 contains yttrium oxide and/or ytterbium oxide in a proportion of 3.5 mol% to 5.0 mol%, and contains niobium oxide and/or tantalum oxide in a proportion of 0.3 mol% to 1.5 mol%. A zirconia sintered body comprising: This zirconia sintered body has excellent fracture toughness, excellent translucency, and excellent hydrothermal deterioration resistance.

Additionally, Patent Documents 2 and 3 disclose techniques for distributing a desired compound in a zirconia cut object with high uniformity. Further, Patent Document 4 discloses a technique regarding a zirconia cut object with adjusted porosity.

International Publication No. 2021-229840 International Publication No. 2018-155459 Japanese Patent Application Publication No. 2021-165222 Japanese Patent Application Publication No. 2020-33338

By the way, the present inventor is considering adding a vanadium group element to the zirconia sintered body to improve fracture toughness. However, when a vanadium group element is contained in a zirconia sintered body, the coefficient of thermal expansion becomes high. That is, there is a trade-off relationship between the fracture toughness value and the coefficient of thermal expansion, and it is difficult to achieve both. When the coefficient of thermal expansion of the zirconia sintered body increases, for example, when porcelain is baked on the surface of the zirconia sintered body (for example, when used as a dental material and colored), the zirconia sintered body and the porcelain may Problems such as cracking may occur due to a difference in thermal expansion coefficients.

Therefore, the present invention was made in view of the above-mentioned circumstances, and its main purpose is to provide a zirconia sintered body that has excellent fracture toughness on at least a portion of its surface and has a suppressed coefficient of thermal expansion. It is about providing.

The zirconia sintered body disclosed herein contains zirconia and a vanadium group element, and the vanadium group element is unevenly distributed in at least a part of the surface layer. This makes it easier for stress-induced phase transformation to occur in the surface layer of the zirconia sintered body, thereby improving fracture toughness at the surface of the surface layer. Additionally, in general, when a zirconia sintered body contains a vanadium group element, the thermal expansion coefficient increases; Since the concentration of the elements is relatively low, an increase in the coefficient of thermal expansion can be suppressed. As a result, it is possible to improve the fracture toughness and suppress the coefficient of thermal expansion in at least a portion of the surface.

In a preferred embodiment of the zirconia sintered body disclosed herein, the concentration of the vanadium group element at the surface layer where the vanadium group element is unevenly distributed is the lowest concentration of the vanadium group element in the depth direction of the surface. The vanadium group element is not contained in the portion where the concentration of the vanadium group element is 1.5 times or more higher than the concentration of the vanadium group element in the portion, or where the concentration of the vanadium group element is the lowest. This achieves a higher level of improvement in fracture toughness and suppression of the coefficient of thermal expansion.

In a preferred embodiment of the zirconia sintered body disclosed herein, the tetragonal c/a axis length ratio at the surface of the surface layer where the vanadium group elements are unevenly distributed obtained from the X-ray diffraction pattern, and the depth direction of the surface layer. The difference between the c/a axis length ratio of the tetragonal crystal and the portion where the concentration of the vanadium group element is lowest is 0.001 or more. This achieves a higher level of improvement in fracture toughness and suppression of the coefficient of thermal expansion.

In one embodiment of the zirconia sintered body disclosed herein, niobium (Nb) may be included as the vanadium group element.

One embodiment of the zirconia sintered body disclosed herein may further contain yttrium oxide and/or ytterbium oxide as a stabilizer. Further, in one embodiment of the zirconia sintered body disclosed herein, when the total of the zirconia and the stabilizer is 100 mol%, the concentration of the stabilizer may be 3 mol% or more and 6 mol% or less.

In one aspect of the zirconia sintered body disclosed herein, the fracture toughness value of at least a part of the surface of the surface layer where the vanadium group element is unevenly distributed is 4.5 MPa√m or more, and the average fracture toughness value at 25°C to 500°C is The coefficient of linear expansion may be 10×10 ⁻⁶ /K or less.

FIG. 1 is a Nb mapping image (magnification: 100) of a cut surface of the zirconia sintered body of Example 1. FIG. 2 is a Nb mapping image (magnification: 100) of the cut surface of the zirconia sintered body of Reference Example 1. FIG. 3 is a graph showing the Nb ₂ O ₅ concentration distribution of the zirconia sintered body based on elemental mapping. FIG. 4 is a graph showing the Nb ₂ O ₅ concentration distribution of the zirconia sintered body based on quantitative analysis of all elements. FIG. 5 is a graph showing the c/a axis length ratio of the tetragonal crystal in the cut plane of the zirconia sintered body of Example 1. FIG. 6 is a graph showing fracture toughness values in each example. FIG. 7 is a graph showing the average coefficient of linear expansion in each example.

Hereinafter, embodiments of the technology disclosed herein will be described. Matters other than those specifically mentioned in this specification that are necessary for implementation are based on the technical content taught in this specification and the general technical common knowledge of a person skilled in the art in the relevant field. can be understood based on The contents of the technology disclosed herein can be implemented based on the contents disclosed in this specification and common general technical knowledge in the field. In addition, in this specification, when a numerical range is described as "A to B (where A and B are arbitrary numbers)", it means "above A and below B", and "beyond A" It includes the meanings of "less than B", "more than A and less than B", and "more than A and less than B".

The zirconia sintered body disclosed herein contains at least zirconia (ZrO ₂ ) and a vanadium group element. Moreover, the zirconia sintered body may further contain a stabilizer. The zirconia sintered body contains zirconia as a main component. Here, "containing zirconia as a main component" means that zirconia accounts for the largest proportion of the compounds constituting the zirconia sintered body. When the entire zirconia sintered body is 100% by mass, the proportion of zirconia is, for example, 70% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more. A high proportion of zirconia can improve the strength, toughness, etc. of the zirconia sintered body.

Examples of vanadium group elements include vanadium (V), niobium (Nb), and tantalum (Ta). The zirconia sintered body contains at least one of V, Nb, and Ta. The vanadium group element is contained in the zirconia sintered body, for example, as an oxide. Examples of oxides containing vanadium group elements include X ₂ O ₅ (X represents a vanadium group element). According to Non-Patent Document 1, vanadium group elements are dissolved in zirconia and increase the c/a axis length ratio (tetragonality) of the tetragonal crystal of the zirconia sintered body (that is, distort the crystal). This makes it easier for stress-induced phase transformation (phase transformation from tetragonal to monoclinic) to occur, thereby improving the fracture toughness value of the zirconia sintered body.

In the zirconia sintered body disclosed herein, vanadium group elements are unevenly distributed at least in a part of the surface layer of the zirconia sintered body. When the surface area of the zirconia sintered body is 100%, the vanadium group element may be unevenly distributed (exist) in the surface layer in a range of 2% or more of the surface area, for example, 5% or more, 10% or more, 20% or more, Vanadium group elements may be unevenly distributed in the surface layer in a range of 30% or more, 50% or more, 70% or more, 90% or more, or 100% (that is, the entire surface of the zirconia sintered body). As a result, stress-induced phase transformation can easily occur in the surface layer (including the surface) of the zirconia sintered body where vanadium group elements are unevenly distributed, and the fracture toughness value on the surface of the zirconia sintered body can be improved. In addition, with this configuration, the concentration of vanadium group elements is relatively low in parts other than the surface layer of the zirconia sintered body (for example, inside the surface layer of the zirconia sintered body), so that the concentration of vanadium group elements is not increased. It is possible to suppress an increase in the coefficient of thermal expansion that may occur accordingly. As a result, the surface layer of the zirconia sintered body, where vanadium group elements are unevenly distributed, exhibits excellent fracture toughness, and the increase in the coefficient of thermal expansion inside the zirconia sintered body can be suppressed, resulting in improved fracture toughness and thermal expansion. It is estimated that this will result in a reduction in the rate. Note that this mechanism is an estimate and does not limit the present technology in any way.

In the zirconia sintered body disclosed herein, the concentration of the vanadium group element at the surface layer where the vanadium group element is unevenly distributed is the concentration of the vanadium group element at the part where the concentration of the vanadium group element is the lowest in the depth direction of the surface. for example, 1.5 times or more, 2 times or more, 5 times or more, 10 times or more, 20 times or more, or 30 times or more. Note that in the portion where the concentration of the vanadium group element is the lowest, the concentration of the vanadium group element may be 0 mol % (that is, no vanadium group element is included). As a result, a zirconia sintered body having superior fracture toughness and a suppressed coefficient of thermal expansion is realized. In this specification, the "depth direction" refers to a direction from a plane in contact with the surface of the zirconia sintered body and the point of contact with the surface, perpendicular to the plane, toward the inside of the zirconia sintered body. say.

The concentration of vanadium group elements on the surface layer of the zirconia sintered body where vanadium group elements are unevenly distributed is, for example, 0.1 mol% or more in terms of X ₂ O ₅ (X represents a vanadium group element), and is preferably is 0.3 mol% or more, more preferably 0.5 mol% or more, even more preferably 0.7 mol% or more, particularly preferably 0.9 mol% or more. A high concentration of vanadium group elements tends to increase the tetragonal crystallinity of the zirconia sintered body (that is, the c/a axis length ratio of the tetragonal crystal increases). This makes it easier for phase transformation accompanied by a volume change to occur when stress is applied to the surface of the zirconia sintered body, making it possible to further increase the fracture toughness value. Further, although not particularly limited, the concentration of vanadium group elements on the surface of the zirconia sintered body is, for example, 10 mol % or less in terms of X ₂ O ₅ (X represents a vanadium group element), and 5 mol %. % or less, 3 mol % or less, or 2 mol % or less. Note that the concentration of vanadium group elements in the zirconia sintered body can be measured by scanning electron microscopy-wavelength dispersive X-ray spectroscopy (SEM-WDX).

The concentration of vanadium group elements in the part where the concentration of vanadium group elements in the depth direction from the surface of the zirconia sintered body is lowest (typically near the center inside the zirconia sintered body) is calculated as X ₂ O ₅ (X represents a vanadium group element), for example, less than 0.1 mol%, 0.05 mol% or less, 0.03 mol% or less, 0.01 mol% or less, or 0 mol% (that is, the vanadium group element (not included). The increase in the coefficient of thermal expansion can be suppressed by having a low concentration of vanadium group elements or by not including vanadium group elements inside the zirconia sintered body.

In a zirconia sintered body, the region from the surface of the surface layer where vanadium group elements are unevenly distributed to the part where the concentration of vanadium group elements is lowest in the depth direction of the surface is equally divided into two regions, a surface side region and an inner side region. At this time, the concentration of vanadium group elements in the surface side region is higher than the concentration of vanadium group elements in the inner side region. For example, the concentration of vanadium group elements in the surface side region of the zirconia sintered body may be 1.5 times or more, 2 times or more, 5 times higher than the concentration of vanadium group elements in the inner side region of the zirconia sintered body. It may be higher than 10 times, 20 times or more, or 30 times or more. Moreover, the vanadium group element does not need to be included in the inner region. As a result, a zirconia sintered body having superior fracture toughness and a suppressed coefficient of thermal expansion is realized.

Note that the "surface side region" refers to a region closer to the surface than the midpoint of the distance from the surface of the zirconia sintered body where vanadium group elements are unevenly distributed to the part where the concentration of vanadium group elements is lowest in the depth direction of the surface. It refers to the area on the near side. Furthermore, the "inner region" refers to the region farther from the surface than the midpoint of the distance from the surface of the zirconia sintered body to the part with the lowest concentration of vanadium group elements in the depth direction of the surface. means.

The tetragonal c/a axis length ratio (hereinafter also referred to as "tetragonality A") at the surface layer where vanadium group elements are unevenly distributed in the zirconia sintered body is the concentration of vanadium group elements in the depth direction of the surface. may be higher than the c/a axis length ratio of the tetragonal crystal (hereinafter also referred to as "tetragonal crystallinity B") at the lowest portion. The difference between tetragonal crystallinity A and tetragonal crystallinity B (where A>B) can be, for example, 0.001 or more, 0.00125 or more, 0.0015 or more, or 0.00175 or more. The higher the value of tetragonal crystallinity, the more likely phase transformation to monoclinic crystal occurs when stress is applied, and the fracture toughness value can be improved. On the other hand, a high value of tetragonal crystallinity can increase the coefficient of thermal expansion. Therefore, as mentioned above, the large difference between the tetragonal crystallinity A and the tetragonal crystallinity B makes it possible to improve the fracture toughness in the surface layer of the zirconia sintered body and suppress the increase in the coefficient of thermal expansion. can.
The "tetragonal c/a axis length ratio" is determined by measuring the profile of the X-ray diffraction pattern in the cross section of the zirconia sintered body using integrated powder X-ray analysis software: PDXL2 (manufactured by Rigaku Software Co., Ltd.). be able to. In one example of a specific analysis method, first, the software automatically determines the peak position from the explanatory profile. Next, the lattice constant (d value) of the (004) plane corresponding to the c-axis where the diffraction angle (2θ) is around 73°, and the (400) plane corresponding to the a-axis where the 2θ is around 74.5°. The c/a axis length ratio is calculated from the d value. In this way, the c/a axis length ratio of the tetragonal crystal can be obtained.

The value of tetragonal crystallinity A is not particularly limited, but may be 1.0165 or more, 1.0170 or more, 1.0175 or more, or 1.018 or more. The higher the tetragonal crystallinity, the more likely phase transformation to monoclinic crystal occurs when stress is applied, and the fracture toughness value can be improved. Further, although not particularly limited, the value of tetragonal crystallinity A may be, for example, 1.02 or less, 1.019 or less, or 1.0185 or less.

The value of tetragonal crystallinity B is not particularly limited, but may be, for example, 1.012 or more, 1.013 or more, or 1.014 or more. Further, the tetragonal crystallinity B is not particularly limited, but may be, for example, less than 1.017 or 1.0168 or less. When the tetragonal crystallinity B is within the above range, an increase in the coefficient of thermal expansion can be suppressed.

Examples of the stabilizer that can be included in the zirconia sintered body include yttrium oxide ( _Y2O3 ), _ytterbium oxide ( _Yb2O3 ), cerium oxide ( _Ce2O3 ₎ , and erbium oxide ( _Er2O3 ₎ _. ), oxides containing alkaline earth metal elements such as calcium oxide (CaO) and magnesium oxide (MgO), and oxides containing other transition metal elements. Among these, yttrium oxide and ytterbium oxide are preferably used. By containing yttrium oxide and/or ytterbium oxide, the proportion of tetragonal crystals in the zirconia sintered body can be increased, and the fracture toughness value and strength can be improved. In addition, one type of stabilizer may be contained alone, or two or more types may be contained. Furthermore, all of the stabilizers may be solid-dissolved in the zirconia, or a non-solid-dissolved stabilizer that is not solid-dissolved in the zirconia may be included.

The concentration of the stabilizer is not particularly limited, but when the total of zirconia and the stabilizer is 100 mol%, for example, it is 1.5 mol% or more, 2 mol% or more, 2.5 mol%. or more, or 3 mol% or more. Further, the concentration of the stabilizer may be, for example, 6 mol% or less, 5 mol% or less, 4.5 mol% or less, 4.2 mol% or less, or 3.5 mol% or less. Note that when yttrium oxide and/or ytterbium oxide is included as a stabilizer, the above concentration range of the stabilizer is particularly preferably employed.

The zirconia sintered body may further contain aluminum oxide (alumina: Al ₂ O ₃ ). Aluminum oxide can lower the firing temperature for producing zirconia sintered bodies. Further, in a zirconia sintered body containing alumina, abnormal grain growth is suppressed, so that the strength and translucency of the zirconia sintered body can be improved. Furthermore, since the low temperature deterioration resistance can be improved, the strength and translucency of the zirconia sintered body can be maintained for a long period of time. On the other hand, since alumina remains as an impurity inside the sintered body and acts as a light scattering factor, the alumina content should not be too high. Therefore, when the entire zirconia sintered body is taken as 100% by mass, the content of alumina is preferably 0.30% by mass or less, 0.15% by mass or less, 0.1% by mass or less, or 0. It can be up to .05% by weight.

Furthermore, the zirconia sintered body may contain a conventionally known coloring agent to the extent that the effects of the technology disclosed herein are not significantly impaired. Examples of the colorant include transition metal elements, lanthanoid rare earth elements, and the like. Examples of such elements include iron, nickel, cobalt, manganese, praseodymium, neodymium, europium, gadolinium, and erbium. The amount of the colorant may be, for example, 5% by mass or less, 1% by mass or less, and 0.5% by mass or less based on the entire zirconia sintered body.

Furthermore, the zirconia sintered body may contain elements that may be unavoidably mixed. Examples include hafnium, silicon, titanium, and the like. The total content of these elements is preferably 2.5% by mass or less, more preferably 2% by mass or less, for example 1.8% by mass or less in terms of oxide, based on the entire zirconia sintered body. It would be good if it were.

The shape of the zirconia sintered body is not particularly limited, but includes, for example, a columnar shape such as a disc, a cylinder, or a prismatic shape; a polyhedral shape such as a rectangular parallelepiped, a cube, or a polygon; a spherical shape; a rugby ball. It may have a shape or an irregular shape. The zirconia sintered body may be in the shape of a dental material, for example, a denture such as a denture for front teeth or a denture for back teeth, a denture mill blank, an orthodontic bracket, a dental prosthesis, a bridge, a crown, etc. .

The shortest distance from the surface of the surface layer where vanadium group elements are unevenly distributed in the zirconia sintered body to the part of the surface where the concentration of vanadium group elements is lowest in the depth direction is not particularly limited, but is 1.5 mm. It is preferably 2 mm or more, 2.5 mm or more, or 3 mm or more. Thereby, it is possible to improve the fracture toughness in the surface layer portion of the zirconia sintered body and to suppress an increase in the coefficient of thermal expansion.

The fracture toughness value of at least a part of the surface of the surface layer where vanadium group elements are unevenly distributed in the zirconia sintered body is, for example, 4.5 MPa√m or more, 6 MPa√m or more, 9 MPa√m or more, 10 MPa√m or more, It may be 11 MPa√m or more, or 12 MPa√m or more. The "fracture toughness value" in this specification refers to a value measured in accordance with the IF method specified in JIS R 1607:2015.

In this specification, the thermal expansion coefficient of the zirconia sintered body is evaluated using the average linear expansion coefficient at 25° C. to 500° C. measured according to JIS R 1618 as an index. The average linear expansion coefficient of the zirconia sintered body at 25° C. to 500° C. is, for example, 10×10 ⁻⁶ /K or less, and 9.9×10 ⁻⁶ /K or less, or 9.8×10 ⁻⁶ /K or less.

Roughly speaking, the zirconia sintered body disclosed herein may include a forming process, a calcination process, a vanadium group element imparting process, a drying process, and a firing process. Note that the manufacturing process including these steps is an example of manufacturing the zirconia sintered body disclosed herein, and does not limit the manufacturing method of the zirconia sintered body disclosed herein. Further, these steps may be omitted as necessary, and other steps may be included in an appropriate order.

In the forming process, first, raw material powder for the zirconia sintered body disclosed herein is prepared. As the raw material powder, at least zirconia powder is prepared. The zirconia powder may be appropriately changed depending on the composition of the zirconia sintered body to be produced, and may be, for example, a partially stabilized zirconia powder containing a stabilizer in a proportion that can be included in the above-mentioned zirconia sintered body. Further, the aluminum oxide powder may be mixed with the zirconia powder in a proportion that can be contained in the above-mentioned zirconia sintered body. The raw material powder may be used in its powder form, or may be prepared into granules by spray drying or the like.

Next, the prepared raw material powder is molded to obtain a molded body. The molding method is not particularly limited, and for example, pressure molding, injection molding, extrusion molding, casting molding, etc. can be adopted. As the pressure forming, for example, cold isostatic pressing (CIP), hot isostatic pressing (HIP), etc. are preferably adopted. According to CIP or HIP, a high-density molded body can be manufactured, so that the fracture toughness value can be further improved.

In the calcination step, the compact is pre-sintered by heating to obtain a pre-sintered body. Such heating may remove components such as moisture and impurities that may be contained in the molded article. In addition, pre-sintering can reduce voids that may exist in the molded object (object to be processed), so it is possible to suitably prevent cracks that may occur during sintering due to high-temperature and high-speed heating. Preliminary sintering can be carried out at a heating temperature of, for example, 800°C to 1200°C, preferably 900°C to 1100°C. Since the heating time may vary depending on the shape, size, composition, etc. of the molded article, it may be adjusted as appropriate, and may be, for example, from 0.5 hours to 5 hours. The molded body can be heated by a known method, and for example, a heating device such as a muffle furnace, an electric furnace, or a microwave firing furnace can be used.

In the vanadium group element application step, a vanadium group element-containing material containing a vanadium group element is applied to the temporary sintered body. The vanadium group element-containing material may be, for example, a solution, a sol, etc., and a sol is particularly preferred. Examples of the solution include a chloride solution of a vanadium group element, a metal alkoxide solution, and the like. When the vanadium group element-containing material is a sol, particles containing the vanadium group element are preferably dispersed in a dispersion medium. Examples of the particles include oxides containing vanadium group elements. Specific examples of such oxides include V ₂ O ₅ , Nb ₂ O ₅ , Ta ₂ O ₅ and the like. The dispersion medium is not particularly limited, and may be, for example, water, an organic solvent, or the like. In the sol, the proportion of particles containing vanadium group elements in the entire sol (sol concentration) is not particularly limited, but is, for example, about 1% by mass to 10% by mass, preferably about 5% by mass to 10% by mass. If the sol concentration (ratio of particles) is too low, vanadium group elements will not be sufficiently placed on the surface of the temporary sintered body, resulting in insufficient improvement in fracture toughness when producing a zirconia sintered body. It may happen.

Examples of methods for applying the vanadium group element material to the temporary sintered body include impregnating a part or the whole of the temporary sintered body with the vanadium group element-containing material, and applying the vanadium group element-containing material to the surface of the temporary sintered body. For example, applying

When impregnating the temporary sintered body with a vanadium group element-containing material, the impregnation time may be changed as appropriate depending on the shape and size of the temporary sintered body, for example, about 0.1 hour to 48 hours, preferably. It can be about 4 hours to 24 hours.

The drying step is a step in which the temporary sintered body after the vanadium group element imparting step is dried to remove liquid components (for example, dispersion medium) contained in the vanadium group element-containing material. The drying method is not particularly limited, and can be appropriately selected from natural drying, blast drying, hot air drying, drying by heating using a heating furnace, vacuum drying, suction drying, freeze drying, and the like. As an example of drying by heating, drying can be carried out under conditions of 80° C. to 150° C. for about 0.5 hours to 20 hours. Note that the drying step is not an essential step and can be omitted as appropriate.

In the firing process, a zirconia sintered body is obtained by firing the temporary sintered body. The firing method can be performed by a known method, for example, by using a heating device such as a muffle furnace, an electric furnace, or a microwave firing furnace. The firing temperature is not particularly limited, but may be, for example, 1300°C to 1600°C, or 1400°C to 1500°C. The holding time after reaching the firing temperature may be, for example, 1 hour to 5 hours, or 1.5 hours to 3 hours.

The zirconia sintered body disclosed herein can be used in various applications where zirconia sintered bodies have been conventionally used, and can be suitably used for structural members, dental materials, etc., for example. Examples of dental materials include dentures such as dentures for front teeth and dentures for back teeth, denture mill blanks, orthodontic brackets, dental prostheses, bridges, and crowns.

As mentioned above, specific aspects of the technology disclosed herein include those described in the following sections.
Item 1: A zirconia sintered body containing zirconia and a vanadium group element, the vanadium group element being unevenly distributed in at least a part of the surface layer.
Item 2: The concentration of the vanadium group element at the surface of the surface layer where the vanadium group element is unevenly distributed is 1. Item 2. The zirconia sintered body according to Item 1, wherein the vanadium group element is not contained in the portion where the concentration of the vanadium group element is 5 times or more higher or the lowest concentration of the vanadium group element.
Item 3: The c/a axis length ratio of the tetragonal crystal at the surface of the surface layer where the vanadium group element is unevenly distributed, obtained from the X-ray diffraction pattern, and the part where the concentration of the vanadium group element in the depth direction of the surface layer is the lowest. Item 3. The zirconia sintered body according to item 1 or 2, wherein the difference from the c/a axis length ratio of the tetragonal crystal is 0.001 or more.
Item 4: The zirconia sintered body according to any one of Items 1 to 3, containing niobium (Nb) as the vanadium group element.
Item 5: The zirconia sintered body according to any one of Items 1 to 4, further comprising yttrium oxide and/or ytterbium oxide as a stabilizer.
Item 6: The zirconia sintered body according to item 5, wherein the concentration of the stabilizer is 3 mol% or more and 6 mol% or less when the total of the zirconia and the stabilizer is 100 mol%.
Item 7: The fracture toughness value of at least a part of the surface of the surface layer where the vanadium group element is unevenly distributed is 4.5 MPa√m or more, and the average linear expansion coefficient at 25° C. to 500° C. is 10×10 ⁻⁶ /K. The zirconia sintered body according to any one of Items 1 to 6 below.

Examples related to the technology disclosed herein will be described below, but these examples are not intended to limit the technology disclosed herein.

<Test 1>
In Test 1, the distribution of Nb and the c/a axis length ratio (tetragonal crystallinity) in the zirconia sintered body were analyzed.

(Example 1)
Zirconia powder (manufactured by Kyoritsu Materials Co., Ltd.) containing 3 mol % of yttrium oxide (Y ₂ O ₃ ) was prepared. After filling 15 g of this powder into a mold with a bottom surface measuring 50 mm long and 15 mm wide, preforming was performed at a pressure of 20 MPa to produce a preformed body. After taking out the preform from the mold, the preform was subjected to CIP molding at a pressure of 196 MPa to produce a molded product. The molded body was a rectangular parallelepiped with a length of 50 mm, a width of 14 mm, and a height of 6.8 mm. This molded body was calcined at 1000° C. for 30 minutes to obtain a calcined body. The calcined body was impregnated with Nb ₂ O ₅ sol (manufactured by Taki Chemical Co., Ltd., product number: Nb-G6000, sol concentration: 6% by mass) for 24 hours, and then dried at 120° C. for 16 hours. . After drying, sintering was performed at 1450° C. for 2 hours to obtain the zirconia sintered body of Example 1. The sintered body was a rectangular parallelepiped with a length of 40 mm, a width of 11.5 mm, and a height of 5.6 mm.

(Reference example 1)
A raw material powder was prepared by mixing Nb ₂ O ₅ powder to zirconia powder (manufactured by Kyoritsu Materials Co., Ltd.) containing 3 mol % of yttrium oxide (Y ₂ O ₃ ) in an amount of 1 mol % of the entire powder. After filling 15 g of the raw material powder into a mold with a bottom surface measuring 50 mm long and 15 mm wide, preforming was performed by applying a pressure of 20 MPa to produce a preformed body. After taking out the preform from the mold, the preform was subjected to CIP molding at a pressure of 196 MPa to produce a molded product. The molded body was a rectangular parallelepiped with a length of 50 mm, a width of 14 mm, and a height of 6.8 mm. This molded body was calcined at 1000° C. for 30 minutes to obtain a calcined body. This calcined body was fired at 1450° C. for 2 hours to obtain a zirconia sintered body of Reference Example 1. The sintered body was a rectangular parallelepiped with a length of 40 mm, a width of 11.5 mm, and a height of 5.6 mm.

(Analysis of Nb concentration distribution)
The zirconia sintered body was cut perpendicularly to the long side direction (40 mm side direction) to prepare a test piece having a cut surface (11.5 mm x 5.6 mm) at the midpoint of the long side. After mirror-finishing the cut surface, the cut surface was analyzed using a scanning electron microscope-wavelength dispersive X-ray spectroscopy (SEM-WDX). For SEM-WDX, JXA-iHP200F Hyper Probe manufactured by JEOL Ltd. was used as an electron probe microanalyzer (EPMA). Two methods were used to measure the Nb concentration distribution: a method using the results of the Nb characteristic X-ray intensity of the elemental mapping image, and a method using the results of quantitative analysis of all elements.

Elemental mapping was performed using a detector: Nb WDS detector PET, accelerating voltage: 15.0 kV, irradiation current: 5.0 × 10 ^-8 A, collection time: 10 ms, pixel size: 0.025 μm (at magnification: 10000), It was carried out under the condition of 2.5 μm (at magnification: 100). Elemental mapping was performed along the short side direction of the cut surface, passing through the center of the cut surface. A mapping image (magnification: 100) of Nb in Example 1 is shown in FIG. Further, a mapping image (magnification: 100) of Nb of Reference Example 1 is shown in FIG. In the Nb mapping image, relatively bright areas (relatively close to white) indicate high Nb concentration, and relatively dark areas (relatively close to black) indicate low Nb concentration. The Nb ₂ O ₅ concentration of the zirconia sintered body of Example 1 was determined by setting the value obtained by subtracting the background from the average value of the characteristic X-ray intensity of Nb of Reference Example 1 as 1 mol % of Nb ₂ O ₅ . Specifically, a number line is drawn with the origin (0 mm) at the center of the cut plane in the short side direction (vertical direction in FIG. 1) of the cut plane, and the upward direction of the mapping image is the positive direction, and the downward direction is The Nb ₂ O ₅ concentration was determined at positions of 0 mm, ±0.5 mm, ±1.5 mm, ±2.5 mm, and ±2.7 mm, with the value being the negative direction. The results are shown in Figure 3.

Quantitative analysis of all elements was carried out under the following conditions: detector: Nb WDS detector PET, accelerating voltage: 15.0 kV, irradiation current: 5.0 × 10 ^-8 A, collection time: 500 ms. Quantitative analysis of all elements was performed from the midpoint of one long side (11.5 mm side) of the cut surface toward the center of the cut surface (in the depth direction). The Nb concentration measured on the cut surface of the test piece of Reference Example 1 was converted into Nb ₂ O ₅ concentration, and the average concentration was set to 1 mol%. Then, the Nb concentration at the cut surface of the test piece of Example 1 was converted into Nb ₂ O ₅ concentration and standardized using the results of Reference Example 1. The results are shown in Figure 4. In the graph shown in FIG. 4, the horizontal axis indicates the distance (depth) from the surface in the short side direction of the cut surface, and the vertical axis indicates the Nb ₂ O ₅ concentration.

(Measurement of c/a axis length ratio)
Using an X-ray diffraction device (device name: Ultima IV, manufactured by Rigaku Co., Ltd.), an X-ray diffraction pattern profile on the cut surface of the test piece of Example 1 was obtained. The c/a axis length ratio of the tetragonal crystal was measured from the profile of the X-ray diffraction pattern using integrated powder X-ray analysis software: PDXL2 (manufactured by Rigaku Software Co., Ltd.). The results are shown in Figure 5. The horizontal axis of the graph in FIG. 5 indicates the distance from the surface in the short side direction of the cut plane, and the vertical axis indicates the c/a axis length ratio of the tetragonal crystal. Note that the measurement conditions for X-ray diffraction (XRD) are as follows.
・X-ray detector: D/tex Ultra (attached device)
・Scan speed: 0.4°/min
・Sampling width: 0.02°
・Divergence slit: 1.0mm
・Divergent vertical slit: 10mm
・Scattering slit: 8mm
・Light receiving slit: Open ・Voltage: 40kV
・Current: 40mA
・Measurement area: 72~76°

(Evaluation of test 1)
As shown in FIGS. 1, 3, and 4, in Example 1, almost no Nb was detected inside the zirconia sintered body, and it was found that Nb was unevenly distributed in the surface layer. Moreover, as shown in FIG. 5, it can be seen that the c/a axis length ratio of the tetragonal crystal is large on the surface where Nb is unevenly distributed. On the other hand, as shown in FIGS. 2 to 4, it can be seen that in Reference Example 1, Nb is almost evenly distributed in the zirconia sintered body.

<Test 2>
In Test 2, fracture toughness and average coefficient of linear expansion were evaluated.

(Example 2)
Zirconia powder (manufactured by Kyoritsu Materials Co., Ltd.) containing 3 mol% _of _Y2O3 was prepared. Approximately 1.5 g of this powder was filled into a mold with a diameter of 7 mm, and then preformed at a pressure of 0.78 MPa to produce a preformed body. After taking out the preform from the mold, the preform was subjected to CIP molding at a pressure of 196 MPa to produce a molded product. This molded body was calcined at 1000° C. for 30 minutes to obtain a calcined body. The calcined body was impregnated with Nb ₂ O ₅ sol (manufactured by Taki Chemical Co., Ltd., product number: Nb-G6000, sol concentration: 6% by mass) for 4.5 hours, and then dried at 120°C for 16 hours. went. After drying, sintering was performed at 1450° C. for 2 hours to obtain a zirconia sintered body of Example 2. The sintered body had a cylindrical shape with a diameter of 5.5 mm and a height of 10 mm.

(Example 3)
A zirconia sintered body of Example 3 was obtained in the same manner except that the Y ₂ O ₃ concentration of Example 2 was changed from 3 mol % to 4.2 mol %.

(Reference example 2)
A raw material powder was prepared by mixing Nb ₂ O ₅ powder to zirconia powder (manufactured by Kyoritsu Materials Co., Ltd.) containing 3 mol % of yttrium oxide (Y ₂ O ₃ ) in an amount of 1 mol % of the entire powder. Approximately 1.5 g of this powder was filled into a mold with a diameter of 7 mm, and then preformed at a pressure of 0.78 MPa to produce a preformed body. After taking out the preform from the mold, the preform was subjected to CIP molding at a pressure of 196 MPa to produce a molded product. This molded body was calcined at 1000° C. for 30 minutes to obtain a calcined body. This calcined body was fired at 1450° C. for 2 hours to obtain a zirconia sintered body of Reference Example 2. The sintered body had a cylindrical shape with a diameter of 5.5 mm and a height of 10 mm.

(Reference example 3)
A zirconia sintered body of Reference Example 3 was obtained in the same manner as in the method for producing the zirconia sintered body of Reference Example 2, except that the Y ₂ O ₃ concentration was changed from 3 mol % to 4.2 mol %.

(Comparative example 1)
A zirconia sintered body of Comparative Example 1 was obtained in the same manner as in the method for manufacturing the zirconia sintered body of Reference Example 2 except that Nb ₂ O ₅ powder was not mixed.

(Comparative example 2)
A zirconia sintered body of Comparative Example 2 was obtained in the same manner as in the method for manufacturing the zirconia sintered body of Reference Example 3 except that Nb ₂ O ₅ powder was not mixed.

(Measurement of fracture toughness value)
The surface of the zirconia sintered body was mirror-polished to a depth of about 0.05 mm, and the fracture toughness value on this surface was measured. The measurement was performed according to the IF method of JIS R 1607:2015. The indentation load of the Vickers indenter was 10 kgf (approximately 98 N), and the indentation time of the Vickers indenter was 30 seconds. The results are shown in FIG.

(Measurement of average linear expansion coefficient)
The average linear expansion coefficient at 25° C. to 500° C. was measured using a thermomechanical analyzer (manufactured by NETZSCH, product name: TMA4000SA). The measurement was performed according to JIS R 1618. Note that the load: 20 g, the temperature increase rate: 5 K/min, and the measurement atmosphere: air. The results are shown in FIG.

(Evaluation of Test 2)
As shown in FIG. 6, the zirconia sintered bodies of Examples 2 and ₃ and Reference Examples 2 and 3 containing Nb ₂ O 5 have a higher fracture toughness value than Comparative Examples 1 and 2 that do not contain Nb ₂ O ₅ . has become higher. On the other hand, as shown in FIG. 7, in Reference Examples 2 and 3, the average coefficient of linear expansion was larger than that in Comparative Examples 1 and 2, whereas in Examples 2 and 3, the increase in the average coefficient of linear expansion was suppressed. It had been. Therefore, by unevenly distributing Nb on the surface layer of the zirconia sintered body, a fracture toughness equivalent to that of a zirconia sintered body in which Nb is distributed almost uniformly is achieved, and it is also equivalent to a zirconia sintered body that does not contain Nb. It can be seen that a coefficient of thermal expansion of is achieved.

Although specific examples of the technology disclosed herein have 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 illustrated above.

Claims

Contains zirconia and vanadium group elements,
The vanadium group element is unevenly distributed in at least a part of the surface layer,
Zirconia sintered body.
The concentration of the vanadium group element at the surface of the surface layer where the vanadium group element is unevenly distributed is 1.5 times or more than the concentration of the vanadium group element at the lowest concentration of the vanadium group element in the depth direction of the surface. The zirconia sintered body according to claim 1, wherein the vanadium group element is not contained in a portion where the concentration of the vanadium group element is high or the lowest.
The c/a axis length ratio of the tetragonal crystal at the surface of the surface layer where the vanadium group element is unevenly distributed obtained from the X-ray diffraction pattern, and the tetragonal crystal c/a axis length ratio of the tetragonal crystal at the part where the concentration of the vanadium group element in the depth direction of the surface is lowest. The zirconia sintered body according to claim 1, wherein the difference from the c/a axis length ratio is 0.001 or more.
The zirconia sintered body according to any one of claims 1 to 3, containing niobium (Nb) as the vanadium group element.
The zirconia sintered body according to any one of claims 1 to 3, further comprising yttrium oxide and/or ytterbium oxide as a stabilizer.
The zirconia sintered body according to claim 5, wherein the concentration of the stabilizer is 3 mol% or more and 6 mol% or less when the total of the zirconia and the stabilizer is 100 mol%.
A fracture toughness value of at least a part of the surface of the surface layer where the vanadium group element is unevenly distributed is 4.5 MPa√m or more,
The average linear expansion coefficient at 25°C to 500°C is 10 × 10 -6 /K or less,
The zirconia sintered body according to any one of claims 1 to 3.