WO2015093549A1

WO2015093549A1 - White zirconia sintered body, production method therefor, and application therefor

Info

Publication number: WO2015093549A1
Application number: PCT/JP2014/083469
Authority: WO
Inventors: 勲山下; 絋平今井; 山内　正一; 津久間　孝次
Original assignee: 東ソー株式会社
Priority date: 2013-12-19
Filing date: 2014-12-17
Publication date: 2015-06-25
Also published as: TW201524936A; JP2015231934A; JP6464713B2

Abstract

Provided is a white zirconia sintered body that does not transmit light even as a thin member, has a stable color tone, and has excellent design characteristics. The white zirconia sintered body is characterized by: including a zirconia sintered body and a silica having 1-20 wt% cristobalite crystal structure; having a relative density of at least 97%; and having a total light transmittance (1 mm thickness) for D65 light rays of no more than 2%.

Description

White zirconia sintered body, method for producing the same, and use thereof

The present invention relates to a white zirconia sintered body whose color tone does not change depending on the thickness of a base material and a method for producing the same.

Because of its high strength and toughness, zirconia sintered bodies are widely used in industrial products such as grinding media and bearings. Furthermore, in recent years, various colored zirconia sintered bodies have been developed. The colored zirconia sintered body is widely used for decorative purposes and jewelry.
A pure zirconia sintered body is a sintered body having a translucent milky white color tone. Generally, in order to color a zirconia sintered body having such a color tone, an inorganic compound having high thermal stability is used as a pigment. For example, as a method of coloring a zirconia sintered body to black or blue, a transition metal oxide (Patent Document 1) or a rare earth oxide (Patent Document 2) is added as a pigment, and coloring by light absorption derived from the pigment is used. A method for coloring a zirconia sintered body has been reported.

On the other hand, a white zirconia sintered body to which alumina has been added (Patent Document 3) has been reported as a zirconia sintered body having optical transparency and a high-grade white color. Further, a zirconia sintered body to which 2 to 25 wt% of silica containing cristobalite is added is disclosed (Patent Document 4).

Incidentally, glass materials such as tempered glass and crystallized glass are used for exterior members (hereinafter also simply referred to as “exterior members”) for portable electronic devices and the like. However, these glass materials are difficult to color. Therefore, the use of a zirconia sintered body that can be easily colored with a pigment as an exterior member as an alternative to a glass material has been studied.

The member used for the exterior member is preferably as light as possible. Therefore, when the zirconia sintered body is used as an exterior member, it is necessary to reduce the thickness. A zirconia sintered body exhibiting a dark color tone, such as a zirconia sintered body using a black pigment or the like, is colored using light absorption. Therefore, even if the sintered body is thin, the color tone is stable. On the other hand, in the white zirconia sintered body, light is transmitted through the sintered body by reducing the thickness of the sintered body. As a result, there is a problem that the color of the base member is transparent, the color of the zirconia sintered body and the color of the base member overlap, and the color tone changes from the base material zirconia sintered body, Furthermore, there is a problem that the color tone of the base material is different from the color tone of the exterior member in which the base material and the base are combined.

At present, quartz glass used as an exterior member has been studied to reduce the transmittance by introducing pores into the glass. For example, a method has been reported in which bubbles are generated in quartz glass by a foaming agent, thereby reducing the transmittance of quartz glass (Patent Document 5). However, due to the generated bubbles, there is a problem that the strength of the quartz glass is lowered and further, water is contained in the open pores generated in the quartz glass. Therefore, the transmittance reduction method using a foaming agent cannot be applied to quartz glass used as an exterior member application requiring high strength.

The present invention relates to a white zirconia sintered body that is suitable for exterior members such as portable electronic devices and has a high design and high density and does not transmit light.

Japanese Laid-Open Patent Publication No. 2006-342036 Japanese Unexamined Patent Publication No. 06-92638 Japanese Unexamined Patent Publication No. 2000-75053 Japanese Laid-Open Patent Publication No. 11-278928 Japanese Unexamined Patent Publication No. 10-152332

A conventional white zirconia sintered body has optical transparency. For this reason, when the sintered body is thin, the color change such as the transparency of the base and the color tone after the change have been problems. When a conventional zirconia sintered body is used for an exterior member of an electronic device or the like that tends to be downsized, in order to stabilize the color tone of the exterior member, the zirconia sintered body should be thickened until the base is not transparent. Was necessary.
An object of the present invention is to provide a white zirconia sintered body that does not transmit light as a thin member, has a stable color tone, and is excellent in design. Furthermore, it aims at providing the manufacturing method of the said zirconia sintered compact, and its use.

Investigators examined the light transmission relationship with the inclusions of white zirconia sintered bodies. As a result, the light transmittance of the white zirconia sintered body can be controlled by light scattering by the inclusions. Furthermore, the zirconia sintered body containing silica is non-uniform in the structure of the silica particles in the sintered body. It was found that a white zirconia sintered body that does not transmit light can be obtained by increasing the property.

That is, the gist of the present invention is as follows.
[1] A zirconia sintered body and silica having a cristobalite crystal structure of 1 to 20 wt%, a relative density of 97% or more, and a total light transmittance (1 mm thickness) of D65 light of 2% A white zirconia sintered body characterized by the following.
[2] The white zirconia sintered body according to the above [1], wherein the total light transmittance (1 mm thickness) of D65 light is 0.5% or less.
[3] The color tone (L *, a *, b *) of the sintered body exhibits white in the range of L * = 90 to 96, a * = − 1 to +1, b * = − 1 to +2, The white zirconia sintered body according to [1] or [2].

[4] The white zirconia sintered body according to any one of [1] to [3], wherein the zirconia sintered body is made of zirconia including yttria.
[5] The white zirconia sintered body according to any one of [1] to [4], wherein the yttria concentration is 2 to 4 mol% with respect to zirconia.
[6] The white zirconia sintered body according to any one of [1] to [5], wherein the silica content is 5 to 30 wt%.
[7] The white zirconia sintered body according to any one of [1] to [6], wherein the average crystal grain size of silica in the sintered body is 0.1 to 1 μm.

[8] A mixing step of mixing zirconia powder and silica powder having an average particle size of 1 μm or less to obtain a mixed powder, a forming step of forming the mixed powder to obtain a formed body, and a sintering step of sintering the formed body The method for producing a white zirconia sintered body according to any one of the above [1] to [7].
[9] The method for producing a white zirconia sintered body according to the above [8], wherein in the sintering step, sintering is performed at 1400 ° C. or higher under no pressure.
[10] After the sintering step is performed under pressureless sintering at 1400 ° C. or higher to obtain a primary sintered body, the primary sintered body is subjected to a pressure of 50 MPa or more using a non-reducing container, The method for producing a white zirconia sintered body according to [8] or [9] above, wherein hot isostatic pressing is performed at a temperature of 1400 to 1600 ° C.

[11] A member comprising the white zirconia sintered body according to any one of [1] to [7].
[12] The member according to [11], which is used for an exterior of an electronic device, a decorative article, or a dental material.

The white zirconia sintered body of the present invention does not transmit light even as a thin member, has a stable color tone, has excellent design properties, and has high strength, such as a thin member such as a portable exterior member, a decorative article, and a dental It is excellent as a material.

The XRD pattern of the white zirconia sintered compact of Example 3 and Example 9. FIG. The XRD pattern of the white zirconia sintered compact of Examples 14, 16, and 18. 3 is an SEM image of the white zirconia sintered body of Example 1. FIG. 20 is an SEM image of a white zirconia sintered body of Example 18. FIG. 2 is an SEM image of a thermally etched product of the white zirconia sintered body of Example 1. FIG. 4 is a TEM image of the white zirconia sintered body of Example 1. FIG.

The zirconia sintered body of the present invention contains silica, 1 to 20 wt (wt)% of the silica has a cristobalite crystal structure, and the relative density of the sintered body is 97% or more. The total light transmittance (1 mm thickness) is 2% or less. Therefore, the color tone of the zirconia sintered body of the present invention does not change regardless of the thickness of the sintered body.

The refractive index n of zirconia is 2.2, while the refractive index n of silica is 1.4.
When the white zirconia sintered body of the present invention contains silica and zirconia having a large difference in refractive index, the white zirconia sintered body has strong light scattering, and light transmission of zirconia is suppressed. Thereby, the white zirconia sintered body of the present invention becomes a zirconia sintered body having no color tone change (hereinafter, also simply referred to as “color tone change”) due to a change in the thickness of the sintered body.

The white zirconia sintered body of the present invention contains silica containing 1 to 20 wt% of cristobalite crystal structure (hereinafter also simply referred to as “cristobalite”). Thereby, the zirconia sintered body of the present invention has not only a change in color tone but also a sufficient mechanical strength as an exterior member.
That is, the silica contained in the white zirconia sintered body of the present invention comprises at least one of amorphous or crystalline silica and cristobalite. At least one of amorphous or crystalline silica is silica other than cristobalite.
Examples of the silica other than cristobalite include at least one silica selected from the group consisting of tridymite, quartz, stishovite, cosite, and amorphous, and at least one of quartz and amorphous. Any silica or especially quartz may be used.

The silica contained in the white zirconia sintered body of the present invention preferably contains cristobalite and quartz from the viewpoint of high thermal stability and easy structure having nonuniformity due to phase transition.
Silica having cristobalite (hereinafter also referred to as “cristobalite-type silica”) undergoes a volume change at about 200 ° C. due to an α (low temperature phase) -β (high temperature phase) phase transition. Due to this volume change, microcracks or the like are generated in the silica particles contained in the white zirconia sintered body. Such non-uniformities such as microcracks are introduced into the silica particles in the sintered body, and the light scattering effect by the silica particles can be improved.

The white zirconia sintered body of the present invention is not a zirconia sintered body containing silica containing cristobalite only on the surface of the sintered body, but contains at least silica containing cristobalite inside the sintered body. Therefore, the white zirconia sintered body of the present invention can confirm silica containing cristobalite not only on the surface of the sintered body but also on the polished surface of the sintered body and the cross section of the sintered body.

The content of silica in the white zirconia sintered body of the present invention is 5 to 30 wt%, more preferably 5 to 20 wt%, more preferably 5 to 15 wt% from the viewpoint of combining light transmission and strength. preferable. Here, the content of silica in the present invention is the weight ratio of silica to the total weight of the white zirconia sintered body of the present invention. In the present invention, the silica content can be determined by composition analysis.
The cristobalite contained in the silica in the white zirconia sintered body of the present invention is 1 to 20 wt%, preferably 1 to 15 wt%. When the content of cristobalite is less than 1 wt%, the effect of light scattering is reduced, and the color tone change is increased. When the content of cristobalite is 1.5 wt% or more, and further 1.9 wt% or more, the color tone change is further suppressed.

On the other hand, if the content of cristobalite exceeds 20 wt%, the volume expansion due to the phase transition of silica becomes too large, and defects such as cracks occur in the sintered body itself. A sintered body containing such defects is easily broken. When the content of cristobalite is 15 wt% or less, and further 13.5 wt% or less, the sintered body is more difficult to break. Since the color tone does not change depending on the thickness of the sintered body, that is, it has a stable color tone and the sintered body is difficult to break, the content of cristobalite is 1 to 15 wt%, and further 1 to 13 0.5 wt%, preferably 1 to 11 wt%, more preferably 1.5 to 15 wt%, and even more preferably 1.5 to 13.5 wt%, and 1.9 to 13.3 wt%, It is preferably 1.9 to 10.6 wt%, and more preferably 1.9 to 9.2 wt%.

In the present invention, the content of cristobalite can be determined by powder X-ray diffraction (hereinafter referred to as “XRD”) measurement. That is, it can be determined from the cristobalite phase fraction obtained from the following equation from the XRD peak area of zirconia and the XRD peak area of cristobalite in the XRD pattern of the white zirconia sintered body of the present invention.
Cristobalite content (wt%)
= Cristobalite phase fraction (wt%)
= I _{s (101)} / (I _{s (101)} + I _{c (111)} + _{IT (111)} )
In the above formula, Is ₍₁₀₁₎ is the XRD peak area of the (101) plane of cristobalite, I _{c (111)} is the XRD peak area of the cubic (111) plane of zirconia, and IT ₍₁₁₁₎ is the zirconia This is the XRD peak area of the tetragonal (111) plane. Usually, Is ₍₁₀₁₎ and Ic ₍₁₁₁₎ are confirmed as a single XRD peak of 2θ = 30.2 ± 2 ° in an XRD measurement using a CuKα ray (λ = 1.5405Å) as a source. can do.

In addition, by using the XRD peak area of any one of tridymite, quartz, stishovite, and cosite instead of _{Is (101)} in the above formula, the content of silica having these crystal structures is obtained. Can do. The XRD peak of each crystal structure can be confirmed as the following 2θ XRD peak in XRD measurement using a CuKα ray (λ = 1.5405Å) as a radiation source.
Cristobalite: 2θ = 21.9 ± 2 °
Tridymite: 2θ = 20.5 ± 2 °
Quartz: 2θ = 26.6 ± 2 °
Stishovite: 2θ = 30.2 ± 2 °
Cosite: 2θ = 28.7 ± 2 °
When the silica is amorphous, the content of amorphous silica can be obtained from the above formula by using the diffraction intensity of the broad peak having the highest diffraction intensity instead of Is ₍₁₀₁₎ .

The white zirconia sintered body of the present invention contains silica particles containing at least either crystalline or amorphous silica and cristobalite. From the viewpoint of increasing light scattering, the average crystal grain size of the silica particles contained in the white zirconia sintered body of the present invention is preferably 0.1 to 1 μm, more preferably 0.3 to 0.7 μm. preferable. By setting the average crystal grain size of the silica particles within this range, the number of silica particles (hereinafter also referred to as “silica phase”) in the white zirconia sintered body can be increased. Increasing the number of silica particles enables more sufficient light scattering. Moreover, light can be efficiently scattered by setting the average crystal grain size of silica particles, which serve as a light scattering source, to approximately the same as the wavelength of light, that is, 0.1 μm to 1 μm. Thereby, the color tone of the white zirconia sintered body of the present invention exhibits a clearer white.

The shape of the silica particles contained in the white zirconia sintered body of the present invention is not particularly limited, and may be an indefinite shape. It becomes easier to scatter light because the particle shape is indefinite. Further, the silica particles preferably have different shapes. That is, the shape of the silica particles contained in the white zirconia sintered body of the present invention is preferably at least two of a spherical shape, a polyhedral shape, and an indefinite shape. As the shape of the silica particles becomes non-uniform, the light transmission of the white zirconia sintered body of the present invention is more easily suppressed.

In the white zirconia sintered body of the present invention, the zirconia sintered body is preferably made of zirconia containing yttria, that is, the zirconia in the white zirconia sintered body is preferably yttria-containing zirconia. By including yttria as a stabilizer, the white zirconia sintered body of the present invention has sufficiently high strength as an exterior member.
The zirconia in the white zirconia sintered body of the present invention may contain a stabilizer other than yttria. Examples of the stabilizer other than yttria include at least one selected from the group of calcia, magnesia, and ceria. Among these, from the viewpoint of strength and industrial, the zirconia sintered body in the white zirconia sintered body of the present invention is preferably an yttria-containing zirconia sintered body, that is, the zirconia is yttria-containing zirconia.

The yttria concentration (also referred to as yttria content) of zirconia contained in the white zirconia sintered body of the present invention is 2 to 4 mol% with respect to zirconia, that is, the yttria concentration of zirconia in the white zirconia sintered body is It is preferably 2 to 4 mol%. Thereby, the white zirconia sintered body of the present invention has excellent strength. The yttria concentration is preferably 2.5 to 3.5 mol%, more preferably 2.8 to 3.2 mol%, and more preferably 3 mol%.

The white zirconia sintered body of the present invention has a relative density of 97% or more. When the relative density is 97% or more, the white zirconia sintered body of the present invention has sufficient strength as an exterior member. On the other hand, if the relative density is less than 97%, the strength of the sintered body tends to be insufficient. Therefore, the relative density of the white zirconia sintered body of the present invention is preferably 98% or more, more preferably 99% or more. Thereby, for example, the three-point bending strength of the white zirconia sintered body of the present invention is 500 MPa or more, preferably 900 MPa or more, and more preferably 1200 MPa or more.

The white zirconia sintered body of the present invention has the high relative density as described above, but does not have the light transmittance of the conventional zirconia sintered body and zirconia sintered body. Therefore, the white zirconia sintered body of the present invention has a total light transmittance (hereinafter referred to as “total light transmittance of D65 light (1 mm thickness)” when the thickness of the sintered body is 1 mm and D65 is used as a light source. , “Total light transmittance (1 mm thickness)” or simply “total light transmittance”) is 2% or less. If the total light transmittance is 2% or less, the change in color tone is small. As the total light transmittance decreases, the color tone does not change depending on the thickness of the sintered body, that is, the color tone becomes stable. In order to obtain a more stable color tone, the total light transmittance is preferably 1.5% or less, more preferably 1% or less, still more preferably 0.5% or less, and even more preferably 0.1% or less. If the total light transmittance is 0% or more, further more than 0%, or even 0.005% or more, the color tone hardly changes. Therefore, the white zirconia sintered body of the present invention has a total light transmittance of 0% or more and 2% or less, more than 0% and 2% or less, further 0.005% or more and 2% or less, and further 0.000. 005% to 1.5%, further 0.005% to 1%, further 0.005% to 0.5%, and further 0.005% to 0.1% are preferable. .

The color tone (L *, a * and b *) of the white zirconia sintered body of the present invention is preferably L * = 90 to 96, a * = − 1 to +1 and b * = − 1 to +2. Here, L * is a lightness index, and a * and b * are chromaticness indices. When L *, a *, and b * are in a color tone satisfying this range, the white zirconia sintered body of the present invention exhibits a bright white color. L * = 90 to 96, a * = − 0.4 to 0, and b * = 0.3 to 1.5, and further L * = 91.21 in order to exhibit a white color without more transparency. It is preferable that ˜95.53, a * = − 0.37 to −0.16 and b * = 0.29 to 1.42.

The method for producing a zirconia sintered body of the present invention includes a mixing step of mixing a zirconia powder and a silica powder having an average particle size of 1 μm or less to obtain a mixed powder, a forming step of forming the mixed powder to obtain a formed body, and the A molding step of sintering the molded body.

The zirconia powder used in the production method of the present invention is not particularly limited as long as it contains a predetermined amount of yttria. The amount of yttria contained in the zirconia powder is 2.5 to 3.5 mol%, more preferably 2.8 to 3.2 mol%, and more preferably 3 mol%.
From an industrial viewpoint, the zirconia powder is preferably a yttria solid solution zirconia powder containing the above amount of yttria. An example of such zirconia powder is TZ-3YS (manufactured by Tosoh Corporation).

As the silica powder used in the production method of the present invention, any silica powder can be used as long as the average particle diameter is 1 μm or less. The silica powder is preferably at least one silica powder selected from the group of cristobalite, tridymite, quartz, stishovite, cosite, and amorphous, and more preferably at least one selected from the group of cristobalite, quartz, and amorphous. Silica powder is preferred, and amorphous silica is more preferred. An example of silica powder that can be used industrially is 1-FX (manufactured by Tatsumori).
Moreover, even if it is a large silica powder whose average particle diameter exceeds 1 micrometer, the silica powder which grind | pulverized this by arbitrary grinding | pulverization methods, such as a ball mill, a bead mill, and a jet mill, and made the average particle diameter 1 micrometer or less can also be utilized. In the present invention, the average particle diameter of the silica powder is a value measured as a median value (D50) in volume distribution measurement.

In the mixing step, zirconia powder and silica powder are mixed to obtain a mixed powder. In addition, powder of components other than zirconia and silica can also be mixed with mixed powder. Examples of other components include zircon.
When these powders are mixed, the method is not particularly limited as long as both are uniformly dispersed. Since mixing can be performed more uniformly, the mixing method is, for example, at least one of a wet ball mill and a wet stirring mill, but in any case, wet mixing is preferable.

In the molding process, a compact is obtained from the mixed powder. If a molded body having an arbitrary shape is obtained, a general method can be used as the molding method. Examples of the molding method include any one selected from the group of press molding, injection molding, sheet molding, extrusion molding, and cast molding. An example of a simple molding method is press molding.

In the firing step, the molded body is fired to obtain the white zirconia sintered body of the present invention. In the firing step, a molded body obtained by molding the above-mentioned mixed powder of zirconia powder and silica powder is preferably fired at 1400 ° C. or higher, and more preferably sintered at 1400-1600 ° C. By sintering at 1400 ° C. or higher, cristobalite type silica is precipitated in the silica particles. As a result, the white zirconia sintered body is a sintered body that exhibits a stable white color with suppressed light transmission and no change in color tone depending on the thickness of the sintered body.

The firing step is preferably performed at 1400 ° C. or higher under no pressure. As the silica powder, even when using silica powder containing various polymorphic phases such as at least two or more selected from the group of amorphous, cristobalite, tridymite, stishovite, cosite, and quartz, By sintering at 1400 ° C. or higher, more preferably 1450 ° C. or higher, more preferably 1500 ° C. or higher, the cristobalite phase can be precipitated on the silica in the obtained white zirconia sintered body.

The firing atmosphere in the firing step may be any of an oxidizing atmosphere, a reducing atmosphere, and an inert atmosphere. As the oxidizing atmosphere, baking can be performed in an air atmosphere, which is convenient and preferable.
Sintering under no pressure includes sintering at 1400 ° C. or higher in the air for 1 to 10 hours. Note that “under no pressure” is a pressure that does not result in a pressurized state, more preferably atmospheric pressure. More preferable non-pressurized firing includes firing in the air at atmospheric pressure.

As a preferable firing step, a sintered body is sintered under no pressure, and then subjected to a hot isostatic pressing (hereinafter referred to as “HIP”) treatment.
In a preferred firing step, a sintered body (hereinafter also referred to as “primary sintered body”) obtained by sintering without pressure (hereinafter also referred to as “primary sintered body”) is subjected to HIP treatment and HIP. Get a treatment. By HIP treatment, silica is treated at high temperature and high pressure. Thereby, the further nonuniformity is introduce | transduced into a silica phase and the light transmittance of the white zirconia sintered compact of this invention can further be reduced.

If the primary sintering temperature is 1400 ° C. or higher, the HIP treatment temperature (hereinafter also referred to as “HIP temperature”) may be 1400 ° C. or lower, for example, 1250 ° C. or higher, further 1300 ° C. or higher. preferable. The HIP temperature may be 1400 ° C. or higher, and the HIP temperature is preferably 1400 to 1600 ° C., more preferably 1450 to 1550 ° C. from the viewpoint of introducing non-uniformity and strength.

The HIP treatment pressure (hereinafter also referred to as “HIP pressure”) is preferably 50 MPa or more, and more preferably 100 to 200 MPa. By setting the HIP pressure to 50 MPa or more, cracks and the like are more likely to occur in the silica particles, so that non-uniformity in the silica phase is more easily introduced.

The HIP processing time (hereinafter also referred to as “HIP time”) is preferably at least one hour. If the HIP process is at least 1 hour, non-uniformity can be introduced even during the HIP process. Since the HIP treatment does not need to be more than necessary, the HIP time is preferably 10 hours or less, more preferably 5 hours or less.

The pressure medium for HIP treatment (hereinafter simply referred to as “pressure medium”) may be a non-oxidizing atmosphere. The pressure medium may be an inert gas, and can be exemplified by at least one of nitrogen gas and argon gas. The pressure medium is preferably argon gas.

The container used in the HIP treatment is preferably an alumina container or other non-reducing container. Thereby, the reduction | restoration of the sintered compact which is a to-be-processed sample in HIP processing is suppressed. In HIP processing, generally, a sample to be processed is accommodated in a carbon container. When a reducing container such as a carbon container is used, the sample to be treated is likely to be colored by the reduction with carbon. Furthermore, silica may react with carbon and volatilize. These problems can be avoided by using a semi-sealed non-reducing container. Further, by using a semi-sealed non-reducing container, re-firing (tempering) treatment after the HIP treatment becomes unnecessary. Here, the semi-sealed non-reducing container refers to a state where a container made of a non-reducing material such as alumina is not sealed. As a more specific semi-sealed reducing container, a crucible-shaped container made of a non-reducing material is sealed, and the container is covered with a non-reducing material.

As a more preferable firing step, after sintering at 1400 ° C. or higher under no pressure to obtain a primary sintered body, a sintering method in which the primary sintered body is subjected to HIP treatment using a non-reducing container, pressure is applied. (HIP pressure) is preferably 50 MPa or more, more preferably 50 to 150 MPa, and temperature (HIP temperature) is preferably 1400 to 1600 ° C., more preferably 1450 to 1500 ° C. it can. Thereby, a white zirconia sintered body having a particularly low total light transmittance and a high strength can be obtained.

The white zirconia sintered body of the present invention does not have light transmittance. Therefore, even if the sintered body is thin, it is possible to provide a stable color tone without being affected by the color tone of the member used as the base of the sintered body. Thereby, the white zirconia sintered compact of this invention can be used conveniently as exterior members, such as a portable electronic device. Furthermore, the white zirconia sintered body of the present invention can be suitably used as a decorative product such as a watch or a jewelry, and a dental material.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The present invention is not limited to the examples.

(Quantitative determination of cristobalite phase fraction)
The content of cristobalite in the silica of the sintered body sample was quantified by determining the cristobalite phase fraction by XRD measurement. Using the XRD peak areas of zirconia cubic (I _{c (111)} ) and tetragonal (IT ( ₁₁₁₎ ), and cristobalite (I _{s (101} )), the cristobalite phase fraction was determined from the following equation. . In addition, XRD measurement was performed about the mirror polishing surface after carrying out mirror polishing of the sintered compact sample.
Cristobalite content (wt%)
= Cristobalite phase fraction (wt%)
= I _{s (101)} / (I _{s (101)} + I _{c (111)} + _{IT (111)} ) × 100

(Relative density)
The density (measured density) of the zirconia sintered body was determined by measuring the weight in water by the Archimedes method. Zirconia (manufactured by Tosoh Corporation, TZ-3YS), silica, and the true density of alumina, as respectively ^{6.0956g / cm 3, 2.3g / cm} 3, and 3.99 g / cm ^3, the measured density to the true density The relative density was calculated as a value. In addition, the theoretical density of cristobalite type | mold silica was used for the true density of said silica.

(Total light transmittance)
After processing the zirconia sintered body of an Example or a comparative example to sample thickness 1mm, what carried out double-sided mirror surface polishing to surface roughness Ra = 0.02 micrometer or less was used as a measurement sample. The surface roughness Ra is a value obtained by extracting a reference length from the roughness curve in the direction of the average line, and summing and averaging the absolute values of deviations from the average line of the extracted portion to the measurement curve. Arithmetic mean height.
Using a haze meter (device name: NDH5000, manufactured by Nippon Denshoku Co., Ltd.), the total light transmittance of the measurement sample was measured by a method according to JIS K7105 “Testing method for optical properties of plastic”. The light source was D65 light.

(Scanning electron microscope)
In order to examine the average crystal grain size of silica in the zirconia sintered body sample, observation was performed with a scanning electron microscope (hereinafter referred to as “SEM”). The measurement sample was subjected to surface grinding, and then mirror polished using diamond abrasive grains (average particle diameters: 9 μm, 6 μm, and 1 μm). Gold was deposited on the measurement sample after mirror polishing, and this was observed. A sample obtained by thermally etching the zirconia sintered body sample was also subjected to SEM observation in the same manner, and the average crystal grain size of the zirconia crystal particles was obtained. For SEM, an apparatus manufactured by JEOL Ltd. (JEM-2000FX) was used.

(Transmission electron microscope)
In order to investigate the non-uniformity of silica in the zirconia sintered body, observation with a transmission electron microscope (hereinafter referred to as “TEM”) was performed. The sample was thinned by FIB (Focused Ion Beam), and then measured by argon ion milling and carbon deposition. The TEM used was a device manufactured by JEOL (JEM-2000FX). The measurement conditions were TEM observation with an acceleration voltage of 200 kV.

(Measurement of brightness and hue)
A sintered body that was processed to a thickness of 1 mm and mirror-polished to a surface roughness Ra = 0.02 μm or less was used as a measurement sample.
Using a precision spectrophotometric colorimeter (device name: TC-1500SX, manufactured by Tokyo Denshoku Co., Ltd.) according to the method according to Section 5.3 and Section 5.4 of JIS K7105 “Optical Properties Test for Plastics” The brightness and hue were measured.
In the measurement, the D65 light beam is applied to a measurement sample with a black plate on the back surface, the light transmitted through the measurement sample is reflected by the black plate, the light transmitted through the measurement sample is measured again, and the lightness index L *, chromaty The Knes index a * and b * were determined. In addition, D65 light ray was used for the measurement and the viewing angle was set to 2 degrees.

(Bending strength)
The bending strength was measured by a three-point bending test based on JIS R1601 “Fine ceramic bending strength test method”. Ten samples were measured for one sample, and the average value of the three three-point bending strengths was taken as the bending strength of the measuring sample.

(Hydrothermal degradation test)
Pure water and a measurement sample (zirconia sintered body) were placed in a stainless steel pressure-resistant container, and this was maintained at 140 ° C. After 10 hours, 18 hours, 36 hours, and 72 hours of holding time, the measurement sample is taken out from the container, XRD measurement is performed, and the monoclinic volume fraction of the measurement sample (hereinafter also referred to as “monoclinic rate”). ) Was quantified. The monoclinic rate was calculated using the formula (1).
X = (Im (111) + Im (11-1)) / (Im (111) + Im (11-1) + It (111) + Ic (111)) (1)
Here, X is a monoclinic crystal ratio, and Im, It, and Ic are monoclinic, tetragonal, and cubic powder X-ray diffraction peaks of zirconia, respectively. Further, the parentheses in Im, It and Ic in the formula (1) indicate the reflection index.

Examples 1 to 3
(Preparation of raw material powder)
A mixed powder of zirconia powder and silica powder was prepared as a raw material powder. First, 10 wt% silica powder was added to 3 mol% yttria stabilized zirconia powder. As the 3 mol% yttria-stabilized zirconia powder, one produced by a hydrolysis method (trade name: TZ-3YS, manufactured by Tosoh Corporation, average particle size 0.3 μm, surface area 7 m ² / g) was used. The silica powder includes high-purity silica powder synthesized by a melting method (amorphous silica, trade name: 1-FX, manufactured by Tatsumori Co., Ltd., average particle size 0.38 μm, surface area 30 m ² / g, purity 99% or more. )It was used.
These powders were mixed in a ball mill for 72 hours using 10 mm diameter balls made of zirconia in an ethanol solvent, and dried to obtain raw material powders.

(Preparation of primary sintered body)
The raw material powder is molded at a pressure of 50 MPa by a die press and then further CIP-molded at a pressure of 200 MPa using a cold isostatic press (hereinafter referred to as “CIP”) apparatus, and a cylindrical shape having a diameter of 20 mm and a thickness of 2 mm. A molded body was obtained.
The obtained cylindrical molded body was accommodated in an alumina container and fired (primary sintering) to obtain a zirconia sintered body (primary sintered body).
The sintering conditions for the primary sintering were, in air, a temperature increase rate of 100 ° C./hour, and a sintering temperature of 1400 ° C. (Examples 1 and 2) and 1500 ° C. (Example 3). The sintering time was 2 hours.

(Preparation of HIP processing body)
A zirconia sintered body (primary sintered body) obtained by sintering in air was subjected to HIP treatment to obtain a HIP-treated body. The obtained processed body was the white zirconia sintered body of this example.
The HIP treatment conditions were a temperature of 1450 ° C. (Example 3) and 1500 ° C. (Examples 1 and 2). The HIP pressure was 150 MPa, and the holding time for the HIP treatment was 1 hour. Note that argon gas having a purity of 99.9% was used as the pressure medium, and the sample was processed using a semi-sealed container made of alumina.

The obtained HIP-treated body (white zirconia sintered body of this example) was white. The relative density of each white zirconia sintered body was 99% or more.
Table 1 shows the total light transmittance of the obtained white zirconia sintered body. The total light transmittance of any white zirconia sintered body was 0.5% or less. In these examples, white zirconia sintered bodies having extremely low transmittance were obtained. Table 1 also shows the color tone when a black plate is used as the back plate.
It turned out that the white zirconia sintered compact of an Example shows high brightness L * (90 or more), even if the back is black. This confirmed that the white zirconia sintered body of the example did not transmit the base color.

Example 4
A HIP-treated body was obtained by the same method as in Example 1 except that the amount of silica added was 20 wt%. The obtained processed body was the white zirconia sintered body of this example. The atmospheric sintering temperature was 1400 ° C., and the HIP temperature in the HIP treatment was 1500 ° C.
Table 1 shows the total light transmittance of the obtained white zirconia sintered body. The relative density of the white zirconia sintered body was 99% or more, and the total light transmittance was 0.01%. In this example, a white zirconia sintered body with extremely low transmittance was obtained. Table 1 also shows the color tone when a black plate is used as the back plate. It was found that the obtained white zirconia sintered body showed high brightness L * (90 or more) even when the back was black.

Examples 5 to 7
5 wt% silica was added, the atmospheric sintering temperature was 1400 ° C. (Example 5) and 1500 ° C. (Examples 6 and 7), and the HIP temperature was 1400 ° C. (Example 5) and 1500 ° C. ( A white zirconia sintered body was produced under the same conditions as in Example 1 except that Examples 6 and 7) were used. The results are shown in Table 1. In any of the examples, a white zirconia sintered body having a relative density of 99% or more, a total light transmittance of 2% or less, and a lightness L * of 90 or more was obtained.

Examples 8 to 13
A white zirconia sintered body to which 10 wt% silica was added was prepared in the same manner as in Example 1. That is, the atmospheric sintering temperature was set to 1500 ° C. (Examples 8 and 9) or 1400 ° C. (Examples 10 to 13), and the HIP temperature was set to 1300 ° C. (Examples 8 and 10 to 12) or 1400 ° C. A HIP-treated body was obtained in the same manner as in Example 1 except that Example 9 and 13) were used. The obtained processed body was the white zirconia sintered body of these examples. The obtained results are summarized in Table 1. In these examples, a white zirconia sintered body having a relative density of 99% or more, a total light transmittance of 2% or less, and a lightness L * of 90 or more was obtained.

Examples 14 to 18
A 10 wt% silica-added zirconia powder was produced in the same manner as in Example 1. The powder was molded to obtain a molded body. The obtained molded body was sintered at a temperature of 1400 ° C. (Examples 14 and 15), 1450 ° C. (Example 16), or 1500 ° C. (Examples 17 and 19). Sintering was performed in the atmosphere, the holding temperature was 2 hours, and the heating rate was 100 ° C./h. The obtained sintered body was used as the white zirconia sintered body of these examples. The results are shown in Table 1. In each example, a white zirconia sintered body having a relative density of 99% or more, a total light transmittance of 2% or less, and a lightness L * of 90 or more was obtained.

Example 19
A 20 wt% silica-added zirconia powder was produced in the same manner as in Example 1. The powder was molded to obtain a molded body. The obtained molded body was sintered at 1500 ° C. in the atmosphere. The holding temperature for sintering was 2 hours, and the heating rate was 100 ° C./h. The obtained sintered body was used as the white zirconia sintered body of this example. The results are shown in Table 1. As shown in Table 1, the relative density of the white zirconia sintered body of the present invention was 99% or more, the total light transmittance was 2% or less, and the lightness L * was 90 or more.

Example 20 (Identification of Crystal Phase)
XRD measurement was performed on the white zirconia sintered bodies of Example 3, Example 9, Example 14, Example 16, and Example 18. The results are shown in FIGS. XRD peaks attributed to tetragonal zirconia and cristobalite were observed in all the sintered bodies. In any of the sintered bodies, no XRD peak due to monoclinic zirconia was confirmed.
In addition, in the XRD pattern of the white zirconia sintered bodies of Examples 3 and 9 subjected to the HIP treatment, a weak peak was confirmed in the vicinity of 2θ = 27 °. This is considered to be caused by silica other than cristobalite type silica such as quartz, that is, polymorphism of silica.

Example 21 (Observation of Silica Crystal Particles)
In order to investigate the dispersibility of silica, SEM observation was performed on the white zirconia sintered body obtained in Example 1 and Example 18. In any of the sintered bodies, the average crystal grain size of the silica crystal particles contained in the white zirconia sintered body was 1 μm or less. Moreover, the SEM photograph of Example 1 and 18 is shown in FIG.3 and FIG.4, respectively. 3 and 4, the white portion is zirconia crystal particles and the black portion is silica particles. Thus, it was confirmed that the shape of the silica particles in the white zirconia sintered body of Example 1 and FIG. 18 was mainly an indeterminate shape and was a polyhedral or indeterminate crystal particle.

Example 22 (Measurement of average crystal grain size of crystal grains)
In order to investigate the average crystal grain size of the zirconia crystal particles of the white zirconia sintered body, the white zirconia sintered body obtained in Example 1 was subjected to thermal etching at 1400 ° C. for 1 hour, and after the thermal etching, The SEM observation of the joint was performed. An SEM observation diagram is shown in FIG. The average crystal grain size of the zirconia crystal particles of the white zirconia sintered body determined by the planimetric method was 0.5 μm.

Example 23 (observation of silica dispersibility)
In order to investigate the non-uniformity of the silica, the white zirconia sintered body obtained in Example 1 was observed with a TEM. The obtained TEM observation figure is shown in FIG. In the silica particles in the white zirconia sintered body subjected to the HIP treatment, contrast shades derived from the heterogeneous interface were observed. As a result of electron diffraction, a peak attributed to α-quartz was observed in addition to α-cristobalite in the silica particles. This confirmed that the silica particles contained cristobalite and quartz.

Examples 24-26
A HIP-treated body was obtained in the same manner as in Example 1 except that the amount of silica added was 5 wt% (Example 24), 10 wt% (Example 25), and 20 wt% (Example 26). The obtained processed body was the white zirconia sintered body of this example. The atmospheric sintering temperature was 1400 ° C., and the HIP temperature was 1500 ° C.
A three-point bending test was performed on the obtained white zirconia sintered body. The results are shown in Table 2.

Example 27
A white zirconia sintered body was produced in the same manner as in Example 1. The atmospheric sintering temperature was 1400 ° C., and the HIP sintering temperature was 1500 ° C. The obtained white zirconia sintered body was subjected to double-side grinding and then double-side polished to obtain a zirconia plate having a thickness of about 1 mm. The density of the obtained zirconia plate was 5.230 g / cm ³ and the relative density was 99.4%.

Each surface of the obtained zirconia plate and glass fiber reinforced plastic (trade name: epoxy / glass cloth laminate molded product SL-EC, manufactured by Nitto Shinko Co., Ltd.) was washed with acetone. Next, an epoxy-based thermosetting resin (trade name: XN1245SR, manufactured by Nagase ChemteX Corporation) is uniformly applied to the adhesive surface, and the load is uniformly applied to the upper and lower surfaces of the composite plate. And a composite plate was obtained by bonding under conditions of 30 minutes.

The obtained composite plate was cut to a size of 32 mm × 25 mm. The composite plate having a thickness of about 0.8 mm was finally obtained by grinding and polishing the zirconia plate side of the cut composite plate. Grinding and polishing were carried out under conditions that produce as little residual stress as possible. There was no peeling of the adhesive or chipping of the zirconia plate due to processing, and the composite plate had high workability. For the calculation of the apparent density, 2.0 g / cm ³ was used as the reinforced plastic density.

The thickness of the produced composite plate was 0.750 mm. The thickness of each layer of the composite plate was 0.221 mm for the zirconia plate, 18 μm for the adhesive layer, and 0.511 mm for fiber reinforced plastics. The thickness of the zirconia plate / fiber reinforced plastics was 0.43. The composite plate had an apparent density of 2.9 g / cm ³ and a Vickers hardness of 1200. As for the color tone of the composite plate, L *, a *, and b * were 92.0, −0.33, and 0.04, and the lightness L * was 90 or more.

A steel ball drop test was performed in 5 cm increments. The test result was 25 cm, and it was found that the composite plate did not crack even when a hard sphere was dropped from 25 cm and exhibited high impact resistance.
Further, a steel ball drop test was performed in which a healthy portion of the tested test piece was aimed at and dropped once from a steel ball drop height of 30 cm. There was no crack and the impact resistance was higher than that evaluated in 5 cm increments. It is considered that a high value was exhibited because there was no interface peeling of the adhesive layer due to repeated impact tests.

Comparative Example 1
Using only zirconia powder (TZ-3YS, manufactured by Tosoh Corporation) as a raw material powder not containing silica, a molded body was obtained in the same manner as in Example 1. The obtained molded body was sintered in the atmosphere at an atmospheric sintering temperature of 1500 ° C. for 2 hours to obtain a primary sintered body. The obtained primary sintered body was subjected to HIP treatment at an HIP sintering temperature of 1500 ° C., an HIP treatment time of 1 hour, and an HIP treatment pressure of 150 MPa to produce a sintered body of this comparative example. The results are shown in Table 3. The obtained sintered body showed translucency, and the lightness L * was less than 90.

Comparative Example 2
Using only zirconia powder (TZ-3YS, manufactured by Tosoh Corporation) as a raw material powder not containing silica, a molded body was obtained in the same manner as in Example 1. The obtained molded body was sintered in the atmosphere at an atmospheric sintering temperature of 1500 ° C. for 2 hours to obtain a sintered body. The results are shown in Table 3. The obtained sintered body showed translucency, and the lightness L * was less than 90.

Comparative Example 3
Zirconia (TZ-3YS, manufactured by Tosoh Corporation) to which 5 wt% of amorphous silica was added was sintered at 1350 ° C. for 2 hours to obtain a sintered body. As a result of XRD measurement, no peaks due to cristobalite and other silica polymorphs were observed. The results are shown in Table 3. The silica particles of the sintered body were composed only of amorphous silica and did not contain cristobalite type silica. The sintered body had a total light transmittance of over 2% and a lightness L * of less than 90.

Comparative Example 4
A zirconia sintered body was produced in the same manner as in Example 1 except that 50 wt% silica was added. The atmospheric sintering temperature was 1400 ° C., and the HIP temperature was 1500 ° C. The relative density of the obtained sintered body was 99.5%. The sintered body was a sintered body having cracks in zirconia crystal particles in addition to the microcracks in the silica particles. As a result of XRD measurement, the cristobalite phase fraction was 32 wt%.

Reference example 1
Using the sintered bodies of Example 24, Example 25, Example 26, and Comparative Example 1, a hydrothermal deterioration test was performed. The results are shown in Table 4. It was found that in the sintered body of the example containing silica, the appearance of monoclinic crystals was suppressed as compared with the sintered body without addition of silica that was sintered at the same sintering temperature. Thereby, it has confirmed that the white zirconia sintered compact of this invention was hard to hydrothermally deteriorate.

The white zirconia sintered body of the present invention does not transmit light as a thin member, has a stable color tone, is excellent in design, and has high strength. Therefore, it is suitable for exterior members of electronic devices and the like that tend to be miniaturized, and can also be used as ornaments such as watches and jewelry, and also as dental materials.
It should be noted that the specification, claims, drawings and Japanese Patent Application No. 2013-262188 filed on December 19, 2013 and Japanese Patent Application No. 2014-10000972 filed on May 14, 2014 The entire contents of the abstract are hereby incorporated by reference as the disclosure of the specification of the present invention.

*. XRD peak due to cristobalite +. XRD peak due to zirconia

Claims

It contains a zirconia sintered body and silica having a cristobalite crystal structure of 1 to 20 wt%, has a relative density of 97% or more, and has a total light transmittance (1 mm thickness) of D65 light of 2% or less. A white zirconia sintered body characterized by that.
2. The white zirconia sintered body according to claim 1, wherein the total light transmittance (1 mm thickness) of D65 light is 0.5% or less.
The color tone (L *, a *, b *) of the sintered body exhibits a white color in a range of L * = 90 to 96, a * = − 1 to +1, b * = − 1 to +2. Item 3. A white zirconia sintered body according to item 1 or 2.
The white zirconia sintered body according to any one of claims 1 to 3, wherein the zirconia sintered body is made of zirconia containing yttria.
The white zirconia sintered body according to any one of claims 1 to 4, wherein the yttria concentration is 2 to 4 mol% with respect to zirconia.
The white zirconia sintered body according to any one of claims 1 to 5, wherein the content of silica is 5 to 30 wt%.
The white zirconia sintered body according to any one of claims 1 to 6, wherein an average crystal grain size of silica particles in the sintered body is 0.1 to 1 µm.
It has a mixing step of mixing a zirconia powder and a silica powder having an average particle size of 1 μm or less to obtain a mixed powder, a forming step of forming the mixed powder to obtain a formed body, and a sintering step of sintering the formed body. The manufacturing method of the white zirconia sintered compact as described in any one of Claims 1 thru | or 7 characterized by the above-mentioned.
The method for producing a white zirconia sintered body according to claim 8, wherein in the sintering step, sintering is performed at 1400 ° C or higher under no pressure.
In the sintering step, after sintering at 1400 ° C. or higher under no pressure to obtain a primary sintered body, the primary sintered body is subjected to a pressure of 50 MPa or more and a temperature of 1400 to 1600 in a non-oxidizing atmosphere. The method for producing a white zirconia sintered body according to claim 8 or 9, wherein hot isostatic pressing is performed at a temperature of 10 ° C.
A member comprising the white zirconia sintered body according to any one of claims 1 to 7.
The member according to claim 11, wherein the member is used for an exterior of an electronic device, a decoration, or a dental material.