JP5325518B2 - Transparent ceramic, manufacturing method thereof, and optical element using the transparent ceramic - Google Patents

Description

  The present invention relates to a transparent ceramic, a manufacturing method thereof, and an optical element using the transparent ceramic. More specifically, the present invention relates to a polycrystalline transparent zirconia-based or hafnia-based ceramic, a manufacturing method thereof, and an optical element using the transparent ceramic.

  Since zirconia and hafnia have excellent heat resistance and corrosion resistance, they are utilized as high temperature members, refractories for ladles in glass melting furnaces and steel refining, abrasives, and the like. On the other hand, it is used for decorative articles and window materials in the visible to infrared region by utilizing its excellent optical characteristics, but most of them are used in the form of single crystals.

  Single crystal materials are less scattered and have better transmission characteristics than polycrystals (hereinafter referred to as “ceramics”), and ceramics as optical materials are rarely used. In particular, for translucent hafnia, there are very few reported examples due to the difficulty of the synthesis method, and even when the reported literature is viewed, the optical characteristics are very poor. Further, many reports have been made on translucent zirconia so far, but the sample thickness of the reported zirconia ceramic is very thin, and almost no optical constant is clearly described.

In contrast, translucent ceramics (Patent Document 1, Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3) in which TiO ₂ is added to zirconia have been reported, but their optical properties are good. In particular, with regard to linear permeability, even a sample having a thickness of only 1 mm is ground glass, and the level is such that the periphery cannot be clearly seen through the sample. Recently, translucent zirconia to which TiO ₂ is not added has been reported, but the transmission characteristics when the sample thickness is reduced have been shown. However, like the TiO ₂ -added ceramic, the optical characteristics are still sufficient. is not. In addition, translucent hafnia-based ceramics is a material with a very high specific gravity and is extremely difficult to synthesize.
JP-A-1-94843 JP-A-62-91467 JP-A-1-172264 JP 2007-246384 A K. Tsukuma, I. Yamashita, T. Kusunose, “Transparent 8mol% Y2O3-ZrO2 (8Y) Ceramics”, J. Am. Ceram. Soc., 91 [6] 813-18 (2008). K. Tsukuma, “Transparent Titania-Yttria-Zirconia Ceramics”, J.Mat. Sci., Lett., 5 [11] 1143-44 (1986). FW. Vahldiek, “Translucent ZrO2 Prepared at High Pressures”, J. LessCommon Materials, 13 [5] 530-40 (1969).

  Conventional translucent zirconia and hafnia ceramics have very large light scattering, and their optical properties are inferior compared to single crystal zirconia and hafnia. And since the degree of light scattering depends on the transmission wavelength (that is, the degree of light scattering is reduced at a long wavelength), conventional translucent zirconia and hafnia ceramic have no industrial use, and more Development of zirconia and hafnia ceramics with excellent optical properties is eagerly desired.

  On the other hand, single crystal zirconia and hafnia can be generally produced by a skull melt method, an arc melting method or the like, and have a very high transmittance in the visible to infrared region. However, when a single crystal material produced by such a method is observed through a polarizing plate, a large amount of birefringence can be observed in the material, and a large number of fringes (ie, refractive index fluctuations) are observed in the transmitted wavefront of the interferometer. Since the optical characteristics are not necessarily sufficient, it is limited to jewelry-related applications, and has not reached the situation where it is used as an optical element.

  Accordingly, a main object of the present invention is to provide a transparent zirconia or hafnia-based ceramic that is superior in optical properties than conventional transparent ceramics and can provide a shaping and structure that is difficult to achieve with a single crystal.

  Polycrystals have many crystal grain boundaries, and light loss is larger than single crystals. Therefore, optical materials such as general optical materials and more demanding laser oscillation media, and prisms and lenses used in optical equipment. It is extremely difficult to apply to.

On the other hand, as a result of intensive studies by the present inventors, (1) using a starting material having a specific particle size excellent in sinterability, (2) containing fluorine element, (3) as required Adding a certain amount of TiO ₂ , (4) vacuum sintering or sintering in an oxygen-free atmosphere at an optimum temperature, (5) HIP (or HP), (6) obtained in (5) above By heat-treating the obtained sintered body in an atmosphere containing oxygen, the remaining pores that become scattering sources can be drastically reduced, clean grain boundaries can be formed, and uniform materials with little composition variation can be formed. It was found that an optical material superior to zirconia and hafnia ceramics can be provided.

That is, the present invention relates to the following transparent ceramic, a manufacturing method thereof, and an optical element using the transparent ceramic.
1. A zirconia-based or hafnia-based ceramic stabilized by at least one stabilizing material of Y ₂ O ₃ , Sc ₂ O ₃ , MgO, CaO and a lanthanide rare earth oxide,
(1) The crystal structure of the zirconia or hafnia ceramic is cubic.
(2) The average crystal particle diameter is in the range of 5 to 300 μm,
(3) containing 0.05 to 3% by weight of fluorine element in terms of CaF ₂ ;
A transparent ceramic characterized by that.
2. Containing 0.1 to 10 wt% in yet terms of TiO ₂ of the titanium element, the transparent ceramic according to the claim 1.
3. In the thickness direction of a sample having a thickness of 5 mm, 1) the linear transmittance at a light transmission baseline at a wavelength of 500 nm is 50% or more, and 2) the linear transmittance at a light transmission baseline at a wavelength of 700 nm is 60%. The transparent ceramic according to Item 1, which is the above.
4). Item 2. The transparent ceramic according to Item 1, wherein the internal loss in light having a wavelength of 1000 nm is within 15% / cm.
5. Regarding the evaluation of the optical uniformity of a sample having a thickness of 5 mm using an interferometer, the fringe in transmission wavefront measurement is within λ in an area of 90% or more of the measurement surface (λ is the wavelength of the measured He—Ne laser at 633 nm). is shown.), transparent ceramics according to the claim 1.
6). Item 2. The transparent ceramic according to Item 1, wherein the transparent ceramic is a sintered body having a minimum thickness of 10 mm or more.
7). An optical element using the transparent ceramic according to any one of Items 1 to 6.
8). A method for producing a transparent ceramic comprising:
(1) a) zirconia or hafnia, b) at least one of Y ₂ O ₃ , Sc ₂ O ₃ , MgO, CaO and a lanthanide rare earth oxide is stabilized, and c) 0.05 to 3% by weight of fluoride A first step of obtaining a molded body by molding a raw material powder containing and having an average primary particle size of 20 to 500 nm,
(2) a second step of obtaining a calcined body by calcining the molded body at 500 to 900 ° C;
(3) A third step of obtaining a fired body by firing the calcined body at 1400-1800 ° C.,
(4) A method for producing a transparent ceramic, comprising a fourth step of obtaining a pressure fired body by pressure firing of the fired body at 1400 to 2000 ° C.
9. Item 9. The method according to Item 8, wherein the raw material powder further contains 0.1 to 10% by weight of TiO ₂ .
10. Item 9. The method according to Item 8, further comprising a step of annealing the pressure-fired body at 600 to 1600 ° C in an atmosphere containing oxygen.

  The transparent ceramic according to the present invention is not as low in optical quality as the same composition ceramics reported so far, and is equivalent to or higher than single crystal zirconia and single crystal hafnia in the visible to infrared region. In addition, the transparent ceramic of the present invention has more excellent optical properties not found in single crystals. Conventional ceramics and single crystal zirconia have considerably limited applications, but the transparent ceramic of the present invention has dramatically improved optical properties, so that it is equivalent to or better than existing single crystal materials. An optical element having performance can be provided.

  Further, since the optical loss and the optical uniformity are superior to those of the existing technology, excellent performance as an optical element can be exhibited (for example, the refractive index fluctuation and the birefringence component are very small). Therefore, it is possible to provide a characteristic technique such as that optical information can be accurately transmitted through the element. For example, a functional element in a passive and active field in an ultraviolet region of about 300 nm or more to an infrared region of visible to 5 μm or less can be provided, and performance that has been considered to be impossible until now can be exhibited.

  According to the manufacturing method of the present invention, it is not necessary to perform crystal growth for a long time at a temperature higher than the melting point (about 2400 ° C.) as in the case of single crystal manufacturing, so that energy costs can be greatly reduced, manufacturing time and mass production can be realized. be able to. In addition, since a dome, a lens, a prism, and the like can be formed near-net, the processing cost after the material is manufactured can be drastically reduced, and a complex composite material having a plurality of compositions can be provided. Provides advanced optical functions (small scattering loss, uniformity of optical quality (Δn: (refractive index fluctuation) and minimal distortion), fluorescent material) that could not be realized with zirconia and hafnia ceramics and zirconia and hafnia single crystals. it can.

  In addition, since the transparent ceramic obtained by the production method of the present invention is produced by a sintering technique, it can be formed in a near net shape into a required element shape. Therefore, it is possible to form an optical element that is difficult to process. Overcoming various technical issues such as reduction of material yield and processing cost due to processing, reduction of optical distortion inside the material due to processing (deterioration of optical quality), and economic effects occur. The problem of crystal materials can be eliminated.

Transparent ceramic The transparent ceramic of the present invention (ceramic of the present invention) is a zirconia-based or hafnia-based stabilized by at least one stabilizing material of Y ₂ O ₃ , Sc ₂ O ₃ , MgO, CaO and a lanthanide rare earth oxide. Ceramic,
(1) The crystal structure of the zirconia or hafnia ceramic is cubic.
(2) The average crystal particle diameter is in the range of 5 to 300 μm,
(3) containing a fluorine element,
It is characterized by that.

The ceramic of the present invention is a zirconia (ZrO ₂ ) -based or hafnia (HfO ₂ ) -based ceramic, and is stabilized by at least one stabilizing material of Y ₂ O ₃ , Sc ₂ O ₃ , MgO, CaO, and a lanthanide rare earth oxide. It has become.

The stabilizing material uses at least one of Y ₂ O ₃ , Sc ₂ O ₃ , MgO, CaO, and a lanthanide rare earth oxide. Examples of the lanthanide rare earth oxide include oxides containing at least one of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. In the present invention, among these stabilizing materials, for example, at least one of Y ₂ O ₃ , Sc ₂ O ₃ , Yb ₂ O ₃ , Gd ₂ O ₃ , Lu ₂ O ₃ , MgO and CaO is preferably used. Can do.

The content of the stabilizing material in the ceramic of the present invention may be an amount sufficient to form stabilized zirconia (crystal structure is cubic), and should be appropriately set according to the type of the stabilizing material used. Can do. For example, when Y ₂ O ₃ is used as the stabilizing material, it may be about 8 to 30 mol% with respect to zirconia or hafnia.

The ceramic of the present invention contains elemental fluorine. By containing a fluorine element, it is possible to obtain high optical properties while obtaining high sinterability. The content of elemental fluorine may be a content as a result of adding 0.05 to 3% by weight, preferably 0.1 to 1.5% by weight, as a fluoride in the raw material in the production process. The type of the fluoride is not particularly limited as long as it has the above action, but at least one selected from fluorides of CaF ₂ , MgF ₂ , ScF ₃ , YF ₃ , ZrF ₄ and lanthanide rare earth elements is preferably used. be able to. As the lanthanide rare earth element, the same ones as described above can be adopted. In the present invention, among these, for example, CaF ₂ can be preferably used. In this respect, the content of the fluorine element in the ceramic of the present invention is preferably 0.05 to 3% by weight, particularly 0.1 to 1.5% by weight in terms of CaF ₂ .

The content of elemental fluorine in the ceramic of the present invention is, for example, JIS
A method of separating and extracting fluorine in ceramics by thermal hydrolysis separation described in R 9301-3-11: 1999 and then analyzing by ion chromatography analysis can be used.

The ceramic of the present invention preferably contains a titanium element. The titanium element is desirably dissolved in the ceramic of the present invention. By allowing the titanium element to coexist with the fluorine element, higher permeability and the like can be obtained. The content of titanium element is preferably 10% by weight or less, particularly 5% by weight in terms of titanium oxide (TiO ₂ ). The lower limit in the case of containing titanium element is not limited, but it may be usually about 0.1% by weight in terms of titanium oxide (TiO ₂ ).

  The ceramic of the present invention is a polycrystalline body. And the average crystal particle diameter of the crystal grain in the crystal structure is in the range of 5-300 micrometers normally, Preferably it is 10-150 micrometers, More preferably, it is 30-150 micrometers. When the average crystal particle size is less than 5 μm, light scattering increases due to an increase in the number of grain boundaries. When the average crystal particle diameter exceeds 300 μm, impurity components are likely to precipitate in the grain boundary part, and pores are likely to remain inside the grain boundary part or the grain boundary part, causing light scattering as well as inferior thermomechanical characteristics, etc. There are disadvantages. In the present invention, the average crystal particle diameter is the arithmetic average value of the major diameters of 100 crystal particles in a field of view arbitrarily selected by observation with a scanning electron microscope or optical microscope.

The ceramic of the present invention has a linear transmittance of 50% or more (preferably 55% or more, more preferably 60% or more) in the light transmission baseline at a wavelength of 500 nm in the thickness direction of a 5 mm thick sample. 2) The linear transmittance at the baseline of light transmission at a wavelength of 700 nm is 60% or more (preferably 65% or more, more preferably 70% or more). When the linear transmittance of 1) is less than 50% or when the linear transmittance of 2) is less than 60%, the light scattering is very large and it is difficult to use for the application of the present invention. In the present invention, “baseline” indicates a transmission spectrum of the wavelength-transmittance when the absorption by the dopant does not occur, and shows the transmission spectrum as it is when the absorption by the dopant appears. The extrapolated (virtual) transmission spectrum is shown. In the present invention, the linear transmittance is 15 mm (diameter) when the surface roughness Rms is polished to 0.5 nm or less using a spectroscopic analyzer “Spectrometer, trade name U3500” (manufactured by Hitachi, Ltd.). Is a value measured with a spectroscopic slit width of 0.2 to 5 nm and a scanning speed of 60 to 600 nm / min.

  The ceramic of the present invention preferably has an internal loss of 15% / cm or less in a light beam having a wavelength of 1000 nm. In the present invention, the internal loss is measured using a spectroscopic analyzer “Spectrometer, trade name U3500” (manufactured by Hitachi, Ltd.). Specifically, samples having the same polishing accuracy on the sample surface and different thicknesses are prepared. For example, samples having a thickness of 1 mm and 11 mm are prepared, and the difference in transmittance between the two samples (the difference in sample thickness is 1 cm. Therefore, the difference in both transmittances is the difference in transmittance per 1 cm of sample thickness. In other words, this is the internal loss described above.The sample thickness is not limited to 1 mm and 11 mm, but the transmittance of samples with different thicknesses is measured and converted to the difference in transmittance per unit thickness of the sample. By doing so, the internal loss can be obtained.

  In the ceramic of the present invention, it is preferable that the fringe in the transmission wavefront measurement is within λ in a region where the refractive index variation Δn using an interferometer is 5 mm in thickness and is 90% or more of the measurement surface. In the ceramic of the present invention, the distribution of the optical path difference per unit length of birefringence by the strain inspection apparatus is preferably within 50 nm / cm, preferably within 30 nm / cm. By having such characteristics, optical fluctuation is small, the quality of transmitted light can be improved, and it is suitable for general optical applications.

  The ceramic of the present invention is usually used as a sintered body having a predetermined shape. However, since it has a high transmittance as described above, it is particularly suitable as an optical material even for a sintered body having a minimum thickness of 10 mm or more. Can be used. The minimum thickness here means the thickness (width) of the portion where the linear distance is the smallest in the sintered body. For example, a cube or a rectangular parallelepiped having a side of 10 mm or more, a cylinder having a diameter of 10 mm or more and a height of 10 mm or more can be used.

Production method of transparent ceramic The ceramic of the present invention is desirably produced by the following method. That is, (1) a) zirconia or hafnia, b) at least one of Y ₂ O ₃ , Sc ₂ O ₃ , MgO, CaO and a lanthanide rare earth oxide contains a stabilizer and c) a fluoride, and A first step of obtaining a molded body by molding a raw material powder having an average primary particle size of 20 to 500 nm, (2) a second step of obtaining a calcined body by calcining the molded body at 500 to 900 ° C. (3) A third step of obtaining a fired body by firing the calcined body at 1400 to 1800 ° C., and (4) obtaining a pressure fired body by subjecting the fired body to pressure firing at 1400 to 2000 ° C. The ceramic of the present invention can be suitably produced by the method for producing a transparent ceramic comprising the fourth step.

First Step In the first step, a) zirconia or hafnia, b) at least one of Y ₂ O ₃ , Sc ₂ O ₃ , MgO, CaO and a lanthanide rare earth oxide is included as a stabilizer and c) a fluoride. And a molded object is obtained by shape | molding the raw material powder whose average primary particle diameter is 20-500 nm.

  As zirconia or hafnia, those prepared by known production methods or commercially available products can be used. The zirconia purity (zirconia component + hafnia component as an inevitable impurity) is desirably 99% by weight or more. When the final product is used for optics such as prisms and lenses, it is preferably 99.9% by weight or more. Similarly, the hafnia purity (hafnia component + zirconia component as an unavoidable impurity) is desirably 99% by weight or more. When the final product is used for optics such as prisms and lenses, it is preferably 99.9% by weight or more. The ceramic of the present invention may contain an oxide or a solid solution containing both of them due to hafnia or zirconia contained as an inevitable impurity.

As a stabilizing material, at least one of Y ₂ O ₃ , Sc ₂ O ₃ , MgO, CaO, and a lanthanide rare earth oxide is blended. The blending amount of the stabilizing material may be an amount sufficient to form the stabilized zirconia, and can be appropriately set according to the type of the stabilizing material used. For example, when Y ₂ O ₃ is used as the stabilizing material, it may be about 8 to 30 mol% with respect to zirconia or hafnia.

By blending the fluoride into the raw material powder, it is possible to obtain high optical characteristics as well as better sinterability. The fluoride is not particularly _{limited, CaF 2, MgF 2, ScF} 3, YF 3, it is preferable to use at least one selected from fluoride ZrF ₄ and lanthanide rare earth elements. These fluorides can be known or commercially available. The blending amount of fluoride depends on the type of fluoride used, but is usually 0.05 to 3% by weight, preferably 0.1 to 1.5% by weight.

Moreover, in this invention, titanium oxide can also be contained in raw material powder. Thereby, the permeability | transmittance etc. of the ceramic obtained can be improved more. In particular, by including rutile TiO ₂ , even higher permeability can be obtained. The content of titanium oxide can be appropriately set according to the composition of the ceramic of the present invention, but is usually 10% by weight or less, particularly preferably 5% by weight. The lower limit in the case of adding titanium oxide is not limited, but is usually about 0.1% by weight.

  The primary particle diameter of the raw material powder used in the first step is preferably 20 to 500 nm, and particularly preferably 20 to 100 nm. When the primary particle diameter is less than 20 nm, handling is difficult, for example, 1) difficult to mold, 2) the density of the green compact is low, and the shrinkage ratio during sintering is high. Moreover, when the said primary particle diameter exceeds 500 nm, the sinterability of a raw material is scarce, and it is difficult to obtain a high-density sintered compact (in other words, a transparent sintered compact).

  Moreover, when coloring this invention ceramic, a lanthanide rare earth element or those oxides can be added to a raw material powder as a coloring material. The blending amount of the colorant can be appropriately set within a range of usually 0.1 to 10% by weight.

  The mixing of these components can be carried out by using a general mixing / grinding medium such as a pot mill (preferably the grinding medium is partially stabilized zirconia balls). In addition to the raw material powder and the stabilizing material, if necessary, at least one of a sintering aid, a dispersing agent, a binder, etc. is added to the pot mill, and pure water or alcohol is used as a solvent for several to several tens of hours. What is necessary is just to mix.

  The obtained slurry may be subjected to molding as it is, or may be molded after solid-liquid separation and solid content is recovered. The molding method is not particularly limited, and for example, cast molding, extrusion molding, injection molding, or the like can be employed as shown in FIG.

  In the present invention, after removal of solvent and granulation by spray drying apparatus to form granules of several tens of μm, the produced granules are primary molded with a predetermined mold, and then secondary molded with CIP (Cold Isostatic Press). By performing this, a molded body can be suitably produced.

2nd process In a 2nd process, a calcined body is obtained by calcining the said molded object at 500-900 degreeC. The second step is carried out for the purpose of removing the added organic components (dispersant and binder). The calcining atmosphere is usually in the air or in an oxidizing atmosphere. Although the calcining time depends on the calcining temperature and the like, the calcining time is usually about 60 to 180 minutes.

Third Step In the third step, the calcined body is fired at 1400-1800 ° C. (preferably 1400-1650 ° C.) to obtain a fired body. The firing atmosphere is not particularly limited as long as the added fluorine compound is not oxidized. For example, the firing atmosphere may be any of vacuum, reducing atmosphere, inert gas atmosphere, and the like. In addition, when implementing in a vacuum, it can be set as the conditions of pressure reduction- ^10-5 Pa. The firing time is not limited, but it may be about 30 to 300 minutes. In particular, in the third step, it is preferable that the relative density of the fired body is 90% or more.

Fourth Step In the fourth step, the fired body is subjected to pressure firing at 1400 to 2000 ° C. (preferably 1700 to 1850 ° C.) to obtain a pressure fired body. The method for pressurizing and firing is not limited, and may be, for example, an HP (Hot Press) method, an HIP (Hot Isostatic Press) method, or the like. In particular, in the present invention, the HIP method can be suitably used. For example, when Ar gas is used as a pressure medium and transparent firing is performed by pressure firing at 1400 to 2000 ° C. with HIP for 1 hour or more within a pressure range of 9.8 to 198 MPa (when transition metal oxide is added) Can obtain a colored transparent ceramic).

Fifth Step In the present invention, it is desirable to further carry out the fifth step as necessary. That is, the pressure fired body obtained above is annealed at 600 to 1600 ° C. in an atmosphere containing oxygen (hereinafter also referred to as “annealing step”).

In a stage after the fourth step, for example, a ceramic not containing TiO ₂ may be light yellow to brown, and a ceramic containing TiO ₂ may be gray to black. This is due to oxygen defects of zirconia and hafnia as main hosts, reduction of TiO _{2 and} the like. Therefore, in the present invention, a sintered body having higher optical characteristics can be obtained by further repairing oxygen defects and repairing reduction of TiO ₂ by performing the fifth step. For this reason, the annealing step is performed in the range of 600 to 1600 ° C. in an atmosphere containing oxygen. When the annealing temperature is less than 600 ° C., sufficient oxidation does not occur, and the sample exhibits a gray to black color. When the annealing temperature exceeds 1600 ° C., the oxidation reaction is promoted, but the transmittance decreases or devitrification occurs. . The annealing process time may be appropriately determined according to the annealing temperature, TiO ₂ content, sample size, and the like.

In the fifth step, it is preferable not to cause a rapid oxidation reaction in the ceramic after the HIP treatment. If an abrupt oxidation reaction occurs, optical distortion may occur in the ceramic after the annealing process, and if severe, cracks may be generated or pulverized. The control of the oxidation reaction can be carried out as appropriate depending on the heating rate, oxygen partial pressure, etc., but it is particularly important to control the heating rate. In this case, the temperature raising rate is usually in the range of 5 to 100 ° C./hr, particularly preferably in the range of 5 to 60 ° C./hr. When repairing TiO ₂ reduction or the like, it is preferable to set the temperature range from 500 ° C. or higher to 5 to 10 ° C./hr.

  The transparent ceramic thus obtained can be machined to form a predetermined optical element. For example, if a near net molding technique as shown in FIG. 2 is used, an optical element having a complicated structure or aspect can be manufactured at a low cost.

  Hereinafter, preferred embodiments of the ceramic of the present invention will be described in detail with reference to the drawings. However, the zirconia or hafnia ceramic according to the present embodiment is illustrated, and the present invention is not limited to these embodiments. In addition, in each figure, the same code | symbol is attached | subjected about a common part and the overlapping description is abbreviate | omitted.

<Embodiment 1>
FIG. 1 shows a flow sheet for the production of uncolored and colored transparent zirconia and hafnia ceramics. It is essential to use a starting material having a purity of 99% by weight or more and a primary particle size of 20 to 500 nm. This material contains sintering aids CaF, MgF ₂ and lanthanide rare earth fluoride for densification and transparency. Pot mill mixing is performed by adding a compound (if necessary, adding 0.1 to 5.0% by weight of TiO ₂ as a sintering aid), a dispersing agent and a binder. The stabilizer uses at least one of CaO, MgO, Y ₂ O ₃ , Sc ₂ O ₃ and lanthanide rare earth oxides, but the amount of stabilizer added so that the crystal structure of the sintered body is cubic. May be adjusted as appropriate. In addition, when used as a coloring or scintillator, a necessary amount of a rare earth oxide (a coloring element or a light emitting element is selected from rare earth elements) as a stabilizer may be added. Add a solvent (pure water or alcohol) and balls (partially stabilized zirconia or partially stabilized hafnia is preferably used as a grinding medium) to these raw materials and auxiliary raw materials, and mix and pulverize them for several hours to several tens of hours. Is made. The produced slurry is spray-dried by spray drying to produce granules of several tens μm level. The molding method is not limited to press molding, and casting, extrusion, injection molding and the like can be applied as shown in FIG. In the case of the press molding method, the obtained granule is put into a mold and subjected to primary molding, and this green compact is vacuum packed and then put into a CIP apparatus to perform secondary molding. The produced green compact is calcined at 500 to 900 ° C. for the purpose of removing organic components such as a binder, and the green compact after calcining is in a temperature range of 1400 to 1800 ° C. (vacuum, H ₂ or He gas). Sintered in an atmosphere or an atmosphere containing no oxygen) to produce a sintered body with a relative density of 90% or more, preferably 95% or more. In this state, since it is usually not yet transparent, it is necessary to perform HIP treatment at 1400 to 2000 ° C. (pressure medium Ar, pressure range 9.8 to 196 MPa) for 1 hour or more. If the material shape is a simple shape such as a flat plate instead of HIP, HP may be used, but the temperature range is the same and the pressure range may be 9.8 to 49 MPa. The sample after the HIP treatment is a transparent body, but the HIP conditions affect the optical properties of zirconia and hafnia ceramics, so it is necessary to set conditions according to the purpose. Ceramics added with HIP conditions (especially those treated for a long time at a high temperature) or TiO ₂ have undergone strong reduction, and the material itself has turned from pale yellow to black. In such a case, the color change due to the reduction can be recovered by heat treatment in an oxygen-containing atmosphere at a temperature of 600 to 1600 ° C. The obtained transparent zirconia or hafnia ceramic can be machined to form a predetermined optical element. Further, if a near net molding technique as shown in FIGS. 2A to 2C is used, an optical element having a complicated structure or aspect can be processed at low cost.

<Embodiment 2>
2A to 2C show a method for manufacturing a lens, a prism, and a dome-shaped optical element as an example. The prepared slurry is poured into a slip casting mold or injected into an injection molding mold to form a green compact having a lens, prism, or dome shape. The subsequent manufacturing process depends on the method shown in FIG. 1, but in the case of a single crystal or glass material, especially in the case of a dome or lens, the disk workpiece is taken out by boring and cutting to a required size diameter. Since it is necessary to process a flat surface into a curved surface, a reduction in material yield due to processing and a high cost are required. Ceramic technology such as the present invention only leaves surface polishing as the final process. For this reason, it is a matter of course that there are economic values such as productivity and cost, but it is also possible to suppress damage to the inside of the material (strain generation) due to processing.

<Embodiment 3>
3 (a) and 3 (b) show the appearance of the produced transparent zirconia and hafnia ceramic (diameter 23 mm × thickness 6 mm, diameter 10 mm × thickness 9 mm, double-sided optically polished product), optical distortion (birefringence by a polarizer), respectively. ) Shows the result of measuring the observation state. The produced ceramic has transparency comparable to that of a single crystal. In the observation with a polarizer, the state of occurrence of birefringence is a level that is slightly or hardly confirmed as shown in FIG. FIG. 3D shows the optical path difference distribution per unit length with respect to the birefringence of the produced zirconia ceramics. Excluding the peripheral part, the range is 20 nm / cm. In the measurement of the transmitted wavefront, the sample thickness is 5 mm, the flatness of both surfaces is λ / 10 (lambda is 633 nm at the measured He-Ne laser wavelength), and the parallelism of both surfaces is precisely polished within 10 sec. Was made. The transmitted wavefront of the produced zirconia ceramic was measured with an interferometer (manufactured by ZYGO). As a result, the fringe is within λ / 4, and the optically non-uniform portion is limited only to the outer peripheral portion. From this, it can be seen that the zirconia and hafnia ceramics produced in the present invention have very good optical characteristics as an optical element.

<Embodiment 4>
FIG. 4 shows a transmission spectrum at a wavelength of 350 to 800 nm of a zirconia ceramic (double-sided optical polishing) having a thickness of 6 mm. The linear transmittances at wavelengths of 500 and 700 nm reach 70% and 74%, respectively, indicating that the optical loss is very small. This ceramic contains 10 mol% of Y ₂ O ₃ as a stabilizer and 0.5 wt% of elemental fluorine as CaF ₂ . Since the theoretical transmittance of zirconia having a refractive index n = 2.2 is about 75%, the optical loss at wavelengths of 500 nm and 700 nm can be estimated as 8.3 and 1.7% / cm. This shows that there are zirconia ceramics with unprecedented performance. Furthermore, the transmittance at a measurement wavelength of 1000 nm has reached 74.7%, and the optical loss is only 0.7% / cm, indicating characteristics not reported so far.

<Embodiment 5>
FIG. 5 shows the transmittance in the short wavelength region of a sample with a sample thickness of 10 mm (tablet sample subjected to double-side optical polishing). Sample A is a raw material-free TiO ₂ additive with 0.5 wt% CaF ₂ added, and Sample B is 0.5 wt% CaF ₂ added and TiO ₂ added with 5 wt%. Conditions are the same within the scope of the present invention. As a comparative example (sample C), zirconia ceramics having a composition of the prior art category in which only TiO ₂ was added without adding fluoride was prepared under the same conditions as those of samples A and B. Prior art sample C, which does not utilize fluoride, not only has an absorption edge near 400 nm, but also has a very low transmittance over the entire measurement wavelength. On the other hand, the TiO ₂ -added type sample B of the present invention exhibits absorption at around 400 nm in the same manner, but exhibits extremely high transmittance. Sample A to which TiO ₂ is not added has a characteristic that although the transmittance is slightly inferior to that of sample B, the absorption edge is extended to 320 to 350 nm. It can be seen that the samples A and B of the present invention far surpass the prior art.

<Embodiment 6>
FIG. 6 shows fluorescence observed when ultraviolet light having a wavelength of 245 nm is irradiated on a hafnia ceramic to which 1% by weight of Sm ₂ O ₃ is added in the same manner as 1% by weight of Eu ₂ O ₃ . The ceramic contains 0.3% by weight of fluorine element as CaF _2. Although not shown, similar fluorescence could be observed when X-rays or γ-rays were irradiated. The specific gravity of the present invention the zirconia based ceramic varies depending on the kind and amount of stabilizer, 6 g / cm ³ or so, is led to the present invention hafnia ceramic becomes specific gravity of about 9~10g / cm ^3. Although detailed measurement has not been carried out, the specific gravity is heavy and the function of emitting strong fluorescence is very promising as a radiation detection (scintillator) material.

  In addition, a type that does not contain a fluorescent element is considered promising as a window related to nuclear power (a window that can shut out radiation) by taking advantage of its high specific gravity and transparency in the visible range.

<Embodiment 7>
FIG. 7 shows 1 wt% Nd ₂ O ₃ (purple), 1 wt% Tb ₄ O ₇ (orange), 1 wt% Er ₂ O ₃ (pink), 0.5 wt% Pr _6. The appearance of a colored ceramic to which O ₁₁ (orange to green) is added is shown. The ceramic contains 0.8% by weight of fluorine element as CaF _2. Each sample is transparent and has a light absorption function corresponding to the coloring.

<Eighth embodiment>
FIG. 8 is a cut stone obtained by producing a transparent zirconia ceramic containing Nd ₂ O ₃ and Er ₂ O ₃ and containing no colorant and processing it as a jewelery, as in FIG. This ceramic contains 0.25% by weight of fluorine elements as YF ₃ and CaF ₂ , respectively. This product is not inferior to natural zircon or artificially synthesized single crystal cubic zirconia, and it is difficult to achieve with the single crystal synthesis technology (changing the shade of the color step by step) and different colored ceramics. Can be manufactured arbitrarily, and it is possible to design jewelry that has never been seen before.

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

<Examples 1-112 and Comparative Examples 1-14>
In accordance with the method shown in FIG. 1, zirconia ceramics and hafnia ceramics were respectively produced using the raw materials and conditions shown in Tables 1 to 14 (Examples) and Tables 15 to 16 (Comparative Examples).

A predetermined amount of fluoride is added to each raw material powder, and further, a dispersant and a binder are added (in some embodiments, TiO ₂ powder (rutile type) is added), and then these are mixed in a pot mill to obtain a mixture. It was. Next, the mixture was spray-dried to obtain granules having a particle size of several tens of μm. Using the granule, after performing mold molding as primary molding, a molded body was obtained by performing CIP as secondary molding. The obtained molded body was calcined at 500 to 900 ° C. in the air, and then fired (main firing) at 1400 to 1800 ° C. in a predetermined atmosphere. Further, the obtained fired body was further subjected to HIP treatment to obtain a ceramic of the present invention (size: width 20 mm × length 20 mm × thickness 10 mm). The physical properties of the obtained ceramic are shown in each table.

Tables 1 and 2 mainly vary the primary particle size of zirconia and hafnia raw materials, Tables 3 and 4 vary the type of stabilizer, and Tables 5 and 6 indicate the types of fluoride. Table 7 and Table 8 are based on the premise of fluoride addition, and TiO ₂ amount is varied. Tables 9 and 10 are calcined (including atmosphere) and main firing conditions (including atmosphere). Tables 11 and 12 are those in which the temperature, time, pressure medium, and pressure conditions in HIP are changed, and Tables 13 and 14 are colored (or luminescence) by adding a lanthanide rare earth oxide. All of which are produced under the composition and manufacturing conditions of this patent.

On the other hand, in the samples described in Table 15 and Table 16, the primary particle size of the raw material is not specified, the fluoride is not added, the fluoride is added excessively, and the fluoride is in the specified amount. Those in which the TiO ₂ is excessive, the calcination temperature is high and the main calcination temperature is low, and the amount of the stabilizer is insufficient so that a tetragonal phase other than cubic crystals is detected in part of the ceramic. Show. It is clear that the optical properties of the produced zirconia and hafnia ceramics are inferior to those of the present invention. Comparative Example 15 shows the optical measurement results of commercially available single crystal zirconia.

  “Crystal structure after sintering” shown in Tables 1 to 16 is a diffraction pattern of only cubic crystals in the detection of the mineral phase of ceramics produced by a general X-ray powder diffraction method, or It shows whether other phases could be checked.

Since Examples 43 to 98 all contain TiO _2, the temperature range from room temperature to 500 ° C. in the atmosphere after HIP treatment is increased at 50 ° C./hr, and then up to 1200 ° C. for these examples. The temperature was raised slowly at 7 ° C./hr, and then annealed at 1200 ° C. for 5 hours. In all the samples of Examples 43 to 98, they were samples that exhibited gray to black and hardly passed visible light, but were colorless and transparent after annealing (light yellow for samples with a TiO ₂ content of 3% by weight or more). Or it changed to colored transparency. Of course, since the oxidation reaction hardly occurs below 600 ° C., the sample still exhibits gray to black, and when it is annealed at a temperature exceeding 1600 ° C., a significant oxidation reaction occurs and gray to black decolorization occurs. A large number of bubbles were generated inside, resulting in an extreme decrease in optical properties, and in some cases, devitrification was confirmed in all samples. On the other hand, since Examples 1-42 are TiO ₂ free samples, the main purpose is to remove oxygen defects accompanying reduction of the base material (zirconia, hafnia) by HIP treatment. For example, in Examples 1, 15, 8, and 22, an annealing process was further performed after the HIP process. In the annealing process, the temperature is raised from room temperature to 500 ° C. at 50 ° C./hr in the air, and then the temperature is raised to 1100 ° C. at a rate of temperature rise of 10 ° C./hr, and annealing is performed at 1100 ° C. for 5 hours. did. The transmittance of the sample before carrying out the annealing process is Example 1 (35% (wavelength 500 nm), 46% (wavelength 700 nm)) and Example 15 (49% (wavelength 500 nm), 62% (wavelength 700 nm)), respectively. example 8 (33% (wavelength 500 nm), 40% (wavelength 700 nm)), example 22 since was (36% (wavelength 500 nm), 47% (wavelength 700 nm)), as TiO ₂ added samples Although there is no effect, it can be seen that the optical characteristics can be further improved in the annealing step after the HIP treatment.

  In addition, in the transmittance | permeability measurement shown to Tables 1-16, the sample thickness was 5 mm and both surfaces were optically polished and it used for the measurement. Internal loss (according to the above rules) is prepared for samples with thicknesses of 1 mm and 11 mm with substantially the same surface accuracy, and the difference in transmittance between both samples (the difference in sample thickness is 1 cm. The internal loss was determined from the difference (transmittance difference per 1 cm of sample thickness). Furthermore, the uniformity of the refractive index inside the material was similarly adjusted to a sample thickness of 5 mm and optically polished on both sides. Optical uniformity can be evaluated by measuring a fringe when the wavefront of the transmitted light is observed with this interferometer.

Table 17 shows the results of using TiO ₂ having anatase structure, although the samples were prepared under the same conditions as the samples shown in Examples 73, 76, 80, 81, 88, 90, and 92 (Example 99). ~ 105). Although these also have excellent characteristics, it can be seen that it is more desirable to use TiO ₂ having a rutile structure in terms of transmittance, internal loss, refractive index uniformity, and the like.

Table 18 shows almost the same conditions as in Table 11, but Examples 106, 107, and 110 use HP for pressure sintering, and Examples 108, 109, 111, and 112 show the firing atmosphere of main sintering. In this example, He or H ₂ other than vacuum was used. In either case, a zirconia sintered body having optical properties equivalent to those in Table 11 could be produced.

<Comparative Example 15>
Optical measurement was carried out using a commercially available cubic zirconia single crystal produced by the skull melt method. A sample having a length of 10 mm, a width of 10 mm, and a thickness of 5 mm was prepared, and both surfaces (10 mm × 10 mm surface) were optically polished. The linear transmittances at wavelengths of 500 and 700 nm were 64% and 73%, respectively, and the internal loss at 1000 nm was 1.5%, which was the same level as the product of the present invention. Not reached. In addition, since the refractive index fluctuation (fringing) in transmission wavefront observation was λ / 4, it was confirmed that the ceramic of the present invention was superior in optical quality depending on the conditions.

The zirconia-based or hafnia-based ceramic (colorless and transparent) according to the present invention is a special lens in the optical field (> n = about 2.1) using a zirconia-specific or hafnia-specific high refractive index (> n = about 2.1). High refractive index (short focus) lenses, prisms, visible to infrared transmitting materials, color filter materials, jewelry (jewelry with cubic zirconia alternatives and ceramic-specific free designs), and the weight of their specific gravity Thus, it can be applied as a scintillator for detecting radiation or as a reactor window because of its high radiation shut-out property.
Further, if the lanthanide rare earth metal element is added to the ceramic of the present invention and colored, it becomes transparent zirconia and hafnia ceramic having various colors, and can be used for various applications.

It is process drawing which shows the manufacture example of a polycrystalline transparent zirconia or a hafnia medium (transparent sintered body). It is a manufacturing-process figure in the case of producing a dome (FIG. 2 (a)), a lens (FIG.2 (b)), or a prism (FIG.2 (c)). Overview of manufactured zirconia (after polishing) (FIG. 3A), overview of manufactured hafnia ceramic (after polishing) (FIG. 3B), observation of birefringence state by strain gauge (FIG. 3C) And the state (FIG.3 (d)) of optical path difference distribution is shown. The transmission spectrum of zirconia ceramics in the visible to infrared region is shown. The sample thickness is 6 mm, and both surfaces of the sample are optically polished. The theoretical transmittance calculated from the refractive index is 75%, which is a transmission characteristic close to the theoretical transmittance. (1) Sample A: 0.5 wt% CaF ₂ added without addition of TiO ₂ , (2) Sample B: 5 wt% TiO ₂ added and 0.5 wt% CaF ₂ added, (3) Sample C: 5 the transmission spectrum of the zirconia ceramic CaF ₂ no addition in wt% TiO ₂ added. Shows the light emitting state when irradiated with UV at 245nm The eu ₂ O ₃ and _Sm 2 _{O 3} in the hafnia ceramics was added each 1% by weight. An overview of a colored ceramic added with Nd (purple), Ce (orange), Er (pink), and Pr (dark green) is shown. An overview of jewelry manufactured by cutting transparent zirconia ceramics with Nd (1 wt%), Er (0.1 wt%) added, and no colorant added is shown.

Claims (10)

A zirconia-based or hafnia-based ceramic stabilized by at least one stabilizing material of Y ₂ O ₃ , Sc ₂ O ₃ , MgO, CaO and a lanthanide rare earth oxide,
(1) The crystal structure of the zirconia or hafnia ceramic is cubic.
(2) The average crystal particle diameter is in the range of 5 to 300 μm,
(3) containing 0.05 to 3% by weight of fluorine element in terms of CaF ₂ ;
A transparent ceramic characterized by that. The transparent ceramic according to claim 1, further comprising 0.1 to 10% by weight of titanium element in terms of TiO ₂ . In the thickness direction of a sample having a thickness of 5 mm, 1) the linear transmittance at a light transmission baseline at a wavelength of 500 nm is 50% or more, and 2) the linear transmittance at a light transmission baseline at a wavelength of 700 nm is 60%. The transparent ceramic according to claim 1, which is as described above. The transparent ceramic of Claim 1 whose internal loss in the light ray with a wavelength of 1000 nm is 15% / cm or less. Regarding the evaluation of the optical uniformity of a sample having a thickness of 5 mm using an interferometer, the fringe in transmission wavefront measurement is within λ in an area of 90% or more of the measurement surface (λ is the wavelength of the measured He—Ne laser at 633 nm). is shown.), transparent ceramics according to claim 1. The transparent ceramic according to claim 1, which is a sintered body having a minimum thickness of 10 mm or more. The optical element using the transparent ceramic in any one of Claims 1-6. A method for producing a transparent ceramic comprising:
(1) a) zirconia or hafnia, b) at least one of Y ₂ O ₃ , Sc ₂ O ₃ , MgO, CaO and a lanthanide rare earth oxide is stabilized, and c) 0.05 to 3% by weight of fluoride A first step of obtaining a molded body by molding a raw material powder containing and having an average primary particle size of 20 to 500 nm,
(2) a second step of obtaining a calcined body by calcining the molded body at 500 to 900 ° C;
(3) A third step of obtaining a fired body by firing the calcined body at 1400-1800 ° C.,
(4) A method for producing a transparent ceramic, comprising a fourth step of obtaining a pressure fired body by pressure firing of the fired body at 1400 to 2000 ° C. The manufacturing method according to claim 8, wherein the raw material powder further contains 0.1 to 10 wt% of TiO ₂ . The manufacturing method of Claim 8 which further includes the process of annealing the said pressurization sintered body at 600-1600 degreeC by the atmosphere containing oxygen.