JP2010024107A - Translucent ceramic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a translucent ceramic which can be obtained by low-temperature sintering and is excellent in transparency and thermal shock resistance. <P>SOLUTION: The translucent ceramic contains a first oxide, which is shown by the chemical formula: Mg<SB>(1-x)</SB>Zn<SB>x</SB>Al<SB>2</SB>O<SB>4</SB>(on condition that 0≤x≤1) and has a spinel crystal structure, and a second oxide which is shown by the chemical formula: Mg<SB>(1-y)</SB>Zn<SB>y</SB>O (on condition that 0≤y≤0.2) and has a magnesia type crystal structure. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to translucent ceramics mainly used for optical elements for liquid crystal projectors and a method for producing the same. More specifically, the present invention relates to a translucent ceramic including an oxide having a spinel crystal structure and an oxide having a magnesia crystal structure, and a method for producing the same.

  Generally, in a liquid crystal display device or the like, a liquid crystal is used by forming a protective layer on the surface for the purpose of protecting the surface from dirt and outside air. When the liquid crystal is used for a CRT or the like, a transparent plastic is used as such a protective layer, and the object is achieved. Further, since protection of a liquid crystal screen in a mobile phone or the like requires strength, glass or the like may be used as such a protective layer.

  Recently, by forming a transparent protective layer (transparent substrate) on the front and back of such a liquid crystal screen, its surface is made transparent (this structure is called a liquid crystal panel), and light is emitted from one of the liquid crystal panels. A liquid crystal projector in which transmitted light is adjusted with a contact lens or the like is commercially available. The transparent substrate for protecting the liquid crystal screen in such a liquid crystal projector not only simply protects the liquid crystal screen from dirt and outside air, but also adiabatic protection to prevent the liquid crystal screen from being heated by a nearby light source, and It is required to have a heat dissipation purpose of dissipating the temperature rise caused by the endothermic phenomenon generated in the liquid crystal screen by the light from the light source. And since this transparent substrate itself also heats up, such a transparent substrate is also required to have heat resistance.

  Therefore, it is conceivable to use glass as the transparent substrate in such applications, and it has been proposed to use single crystal sapphire in which the thermal conductivity of ordinary glass is improved by about 20 to 30 times ( Patent Document 1). Since such single crystal sapphire has high strength and is extremely hard compared to quartz glass, a merit that a transparent substrate can be made thin is also expected. Moreover, since such single crystal sapphire is very expensive, it is economically difficult to use it alone, but it is said that this problem can be solved by using it together with glass.

  As described above, the single crystal sapphire has been expected to be used because it has various properties required for a transparent substrate for a liquid crystal projector, such as heat resistance and light transmittance, and suppressing temperature rise of the liquid crystal, though it is expensive. . However, since single crystal sapphire has the property of birefringence, it requires complicated work such as aligning the crystal axis orientation when assembling a liquid crystal projector, which reduces the production efficiency and the single crystal sapphire itself is expensive. In combination with this, there was a problem of increasing the manufacturing cost.

In order to solve this problem, various substances suitable for a transparent substrate material that does not have birefringence and are inexpensive have been studied. As one of such substances, spinel ceramics, which are translucent ceramics, have been proposed. (Patent Document 2). This spinel ceramic is a cubic ceramic represented by the chemical formula MgAl ₂ O ₄ and has a high thermal conductivity and is a transparent material.

  However, such a spinel ceramic has a characteristic that the melting point is as high as 2140 ° C. and is difficult to sinter. For this reason, when this spinel ceramic was sintered at a relatively low temperature, there was a problem that pores remained and the film was not transparent. In order to solve this problem, there has been a problem of increasing the manufacturing cost such as a high sintering temperature required to increase the densification by reducing the residual pores and increasing the power consumption of the furnace.

Furthermore, typical physical properties of MgO used for translucent ceramics and the above MgAl ₂ O ₄ are as follows. Spinel (MgAl ₂ O ₄ ) is weak against thermal shock because of its low thermal conductivity, and magnesia ( MgO) has a high thermal conductivity, but has a problem that it is vulnerable to thermal shock due to its large thermal expansion coefficient.
---------------------------------
Thermal expansion coefficient Thermal conductivity Melting point (℃)
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MgAl ₂ O ₄ 7.45 × 10 ⁻⁶ / K 18 W / mK 2140
MgO 9.7 × 10 ⁻⁶ / K 60 W / mK 2800
---------------------------------
JP 2000-284700 A JP 2007-065696 A

  The present invention has been made in view of the above-described situation, and the object of the present invention is translucency that can be sintered at a low temperature and has excellent transparency and thermal shock resistance. To provide ceramics.

  The present inventor has studied various ceramics in order to solve the above-described problems. As a result, ceramics including an oxide having a spinel crystal structure and an oxide having a magnesia crystal structure maintain transparency. The inventors have found that the thermal shock resistance is excellent and have reached the present invention.

That is, the translucent ceramic of the present invention includes a first oxide having a spinel crystal structure represented by a chemical formula Mg _(1-x) Zn _x Al ₂ O ₄ (where 0 ≦ x ≦ 1), a chemical formula And a second oxide having a magnesia type crystal structure represented by Mg _(1-y) Zn _y O (where 0 ≦ y ≦ 0.2).

  Here, the translucent ceramic is preferably composed of the first oxide and the second oxide, and the ratio of the second oxide to the total amount of the first oxide and the second oxide is It is preferable that it is 20-85 mol%. The translucent ceramic is preferably a sintered body, and preferably has a thermal conductivity of 10 W / mK or more.

  On the other hand, the present invention also relates to an optical element for a color liquid crystal projector using the above-described translucent ceramics, and also relates to a color liquid crystal projector using the optical element.

  Furthermore, the present invention also relates to a manufacturing method for manufacturing the above-described translucent ceramic, and this manufacturing method includes a raw material powder containing at least one element constituting the first oxide and the second oxide. A preparatory step for preparing a green body, a molding step for obtaining a green body by molding the raw material powder, a sintering step for obtaining a green body by sintering the green body, and And a hot isostatic pressing step of completing a translucent ceramic by hydrostatic pressing. Here, the raw material powder is preferably a hydroxide powder.

  Since the translucent ceramic of the present invention is excellent in thermal shock resistance, it is considered that even when the amount of light increases, the material is less likely to be distorted and stable projection is possible. This characteristic makes it useful as a transparent substrate for a liquid crystal projector.

  Moreover, since the translucent ceramic of the present invention is optically isotropic, it can be assembled without worrying about the orientation of the crystal axis when assembling into a liquid crystal panel. Further, since the light transmittance is good, there is little heat absorption by light from the light source, so that the temperature rise of the liquid crystal can be dissipated.

Hereinafter, the present invention will be described in more detail.
<Translucent ceramics>
The translucent ceramic of the present invention includes a first oxide represented by a chemical formula Mg _(1-x) Zn _x Al ₂ O ₄ (where 0 ≦ x ≦ 1), a chemical formula Mg _(1-y) Zn _y. And a second oxide represented by O (where 0 ≦ y ≦ 0.2). Here, the first oxide is a single crystal or polycrystal and has a spinel crystal structure, and the second oxide is a single crystal or polycrystal and has a magnesium crystal structure. Have. By using a combination of oxides having such two kinds of crystal structures, it is possible to obtain a translucent ceramic having excellent thermal shock resistance.

Here, the spinel crystal structure means that the spinel (MgAl ₂ O ₄ ) has the same crystal structure as the spinel, although the chemical composition is different. The magnesia-type crystal structure means that the magnesia (MgO) has the same crystal structure as magnesia, although the chemical composition is different.

  If the translucent ceramic of the present invention contains a large amount of a composition (crystalline phase) other than the first oxide and the second oxide, the translucency is impaired. The proportion of the composition other than the second oxide in the translucent ceramic is preferably 1 mol% or less, and is preferably composed of the first oxide and the second oxide.

  The ratio of the second oxide to the total amount of the first oxide and the second oxide is preferably 20 to 85 mol%. When it exceeds 85 mol%, the ratio of the MgO solid solution component increases and the sinterability decreases. If the amount is less than 20 mol%, the effect of thermal shock resistance cannot be obtained. These ratios can be roughly estimated from the peak intensity ratio of powder X-ray analysis.

  As described above, the translucent ceramic of the present invention is excellent in transparency and thermal shock resistance, and exhibits the characteristics of being optically isotropic. Each of these excellent characteristics is advantageously shown when the translucent ceramic is a sintered body. Therefore, the translucent ceramic of the present invention is preferably a sintered body.

The translucent ceramic of the present invention preferably has a thermal conductivity of 10 W / mK or more and a thermal expansion coefficient of 9 × 10 ⁻⁶ / K or less from the viewpoint of thermal shock resistance.

  The present inventors have also found that the thermal shock resistance of the translucent ceramic of the present invention is not only improved because of a good balance between high thermal conductivity and low thermal expansion coefficient. That is, since particles having different thermal expansion coefficients coexist, there is a large strain energy at the grain boundary. Therefore, even if cracks occur in the sintered body, the energy at which the cracks propagate is the strain energy. It is thought that it is used for mitigating. This phenomenon was found by electron microscope observation of the sintered body.

  The term “translucency” as used in the present invention means substantially transparent. For example, when the thickness of the translucent ceramic of the present invention is 1 mm, light in the wavelength region of 420 to 680 nm. The case where the linear transmittance is 85% or more. As described above, the translucent ceramic of the present invention is excellent in transparency, which is considered to be brought about by sufficiently eliminating pores and residual pores in the oxide. For this reason, it is preferable that the translucent ceramics of this invention are 99% or more of relative densities (what displayed the density with respect to the theoretical value of the said oxide%).

<First oxide>
In the present invention, the first oxide is an oxide represented by the chemical formula Mg _(1-x) Zn _x Al ₂ O ₄ (where 0 ≦ x ≦ 1) and has a spinel crystal structure. is there.

As described above, spinel (MgAl ₂ O ₄ ) is expected as a transparent material such as a transparent substrate of a liquid crystal projector, but since its melting point is high, the sintering temperature is also high, and thus low sintering. It was difficult to produce a material having high transparency at temperature. Therefore, by melting Zn into this spinel, the melting point is lowered, thereby enabling sintering at a relatively low sintering temperature, and a highly transparent ceramic can be manufactured at low cost. Incidentally, the melting point of ZnAl ₂ O ₄ (x = 1 in the above chemical formula) in which Mg in the spinel is substantially replaced with Zn is 1960 ° C., which is almost 200 ° C. lower than the melting point of spinel 2140 ° C. . Thus, since the composite oxide of the present invention has a low melting point, the sintering temperature can be set low, which is very advantageous.

From such a viewpoint, x in the chemical formula of the first oxide is preferably larger than 0, more preferably 0.2 to 1, and still more preferably 0.5 to 1. When x is 0.2 or less, the melting point is relatively small and the effect of lowering the sintering temperature is small. If it exceeds 0.5, the melting point is remarkably lowered and the effect of lowering the sintering temperature is increased, which is preferable. However, when Zn in a ratio sufficient to lower the sintering temperature of the translucent ceramic is contained in the second oxide, the first oxide in which x is 0 (that is, MgAl The translucent ceramics of the present invention can also be obtained using ₂ O ₄ ).

Note that the first oxide can maintain the spinel crystal structure at any composition ratio of Mg and Zn (x in the above chemical formula), and the crystal structure of ZnAl ₂ O ₄ is also a spinel crystal structure. Such a spinel crystal structure can be confirmed by powder X-ray diffraction or the like.

<Second oxide>
The second oxide is an oxide represented by the chemical formula Mg _(1-y) Zn _y O (where 0 ≦ y ≦ 0.2) and has a magnesia-type crystal structure. Similarly to the first oxide, zinc can be dissolved in MgO to maintain a cubic crystal, and the melting point is lowered and the sinterability is improved by the solid solution of Zn. In the chemical formula of the second oxide, when y is in the range of 0 to 0.2, the solid solution of Mg and Zn can maintain the magnesia-type crystal structure, and when y exceeds 0.2, hexagonal ZnO Is not preferable because it begins to precipitate.

  Note that when the first oxide contains Zn in a ratio sufficient to lower the sintering temperature of the translucent ceramic, the second oxide (that is, MgO) in which y is 0. ) Can also be used to obtain the translucent ceramic of the present invention. Such a magnesia-type crystal structure can be confirmed by powder X-ray diffraction or the like.

<Application>
Since the translucent ceramics of the present invention have the characteristics as described above, they satisfy the physical properties required for ordinary optical lenses. And since the translucent ceramics of this invention are especially excellent in thermal shock resistance, it is useful to use as an optical element (namely, transparent substrate) for color liquid crystal projectors. Further, since the translucent ceramic of the present invention is optically isotropic, it can be assembled without worrying about the orientation of the crystal axis when assembling a liquid crystal panel, and transparency (light transmissivity) Therefore, it is useful to use as an optical element for a color liquid crystal projector because the heat absorption by the light from the light source is small and the temperature rise of the liquid crystal can be dissipated. The present invention also relates to a color liquid crystal projector using such an optical element.

<Manufacturing method>
The manufacturing method of manufacturing the translucent ceramic of the present invention includes a preparation step of preparing a raw material powder containing at least one element constituting the first oxide and the second oxide, and forming the raw material powder. A molding process for obtaining a molded body by performing a sintering process, a sintering process for obtaining a sintered body by sintering the molded body, and hot isostatic pressing of the sintered body to complete the translucent ceramics. A hot isostatic pressing step.

Here, the preparation step is not particularly limited, and any method can be adopted as long as it is a preparation method capable of obtaining such raw material powder. As the raw material powder, one type or two or more types can be used. Although the chemical composition of such raw material powder is not particularly limited, an oxide or hydroxide containing at least one element constituting the first oxide and the second oxide can be used. MgO powder, Al ₂ O ₃ powder, ZnO powder, Mg (OH) ₂ powder, Al (OH) ₃ powder, and Zn (OH) ₂ powder can be used. In particular, it is preferable to use an inexpensive hydroxide as the raw material powder because a translucent ceramic can be obtained at a lower cost. What is necessary is just to mix | blend the compounding ratio of each raw material powder in this case so that it may become the total stoichiometric composition of the 1st oxide and 2nd oxide which are finally manufactured. In addition, commercially available Mg ₄ Al ₂ (OH) ₁₂ CO ₃ .3H ₂ O (trade name: STABIACE HT-1, manufactured by Sakai Chemical Industry Co., Ltd.), Mg _3.5 Zn _0.5 Al ₂ (OH) ₁₂ CO ₃・ 3H ₂ O (trade name: STABIOCE HT-7, manufactured by Sakai Chemical Industry Co., Ltd.), Mg _4.5 Al ₂ (OH) ₁₃ CO ₃ .3.5H ₂ O (trade name: STABIACE HT-P, Sakai Chemical Industry Co., Ltd.) A composite hydroxide powder such as that manufactured by the company may be used as a raw material powder. The average particle size of such raw material powder is preferably 1 μm or less.

When using hydroxide powder as raw material powder, it is preferable to use it after heating the hydroxide at 400 ° C. or higher to convert it to oxide powder. If the compact of the hydroxide powder is sintered as it is, a large volume shrinkage occurs when the hydroxide is converted to an oxide at about 400 ° C. or higher, and the relative density is lower than that at room temperature. To begin, it becomes difficult to densify. Therefore, the hydroxide powder is once heated at 400 ° C. or more to be converted into the oxide powder, whereby a translucent ceramic is produced in the same process as when ordinary oxide powder is used as a raw material. be able to. Even if the hydroxide powder is not subjected to such treatment, after temporarily forming the hydroxide powder, it is heated at 400 ° C. or higher in an atmospheric furnace different from the sintering furnace. By loading the temporary molded body into a forging die that has been heated to about 400 ° C. in advance and hot forging at a pressure of several thousand kg / cm ² , which is a pressure much higher than the molding pressure of ordinary ceramics. It is possible to obtain a molded body having a high relative density.

  Next, the molding step is not particularly limited, and any method can be adopted as long as such a molded body can be obtained. In addition, the magnitude | size and shape of the molded object obtained are not specifically limited.

  Next, in the hot isostatic pressing (HIP) step, the pressure medium is not particularly limited, but it is preferable to use an industrially available inert gas, which is about 100 ° C. higher than the sintering temperature. It is preferable to carry out at temperature. Then, after annealing at a temperature of about 1000 ° C. and cooling to room temperature, the translucent ceramic of the present invention can be manufactured.

  By finally performing the HIP treatment in this way, pores and residual pores in the composite oxide are sufficiently eliminated, and the translucency (linear transmittance of light in the wavelength region of 420 to 680 nm) is dramatically improved. Ceramics can be obtained. Therefore, hot isostatic pressing is extremely important in the present invention. The hot isostatic pressing process of the present invention includes annealing and cooling operations as described above.

<Coating layer>
In addition, the translucent ceramics of this invention can form a coating layer in the surface as needed. Such a coating layer is particularly preferable when it is made of a material having a refractive index lower than that of the light-transmitting ceramic because the light transmittance is good (that is, the transparency is improved).

Such a coating layer may be a single layer or a plurality of layers. However, when the coating layer is a combination of two or more layers selected from metal fluorides and metal oxides, translucent ceramics are used. Adhesiveness is good and environmental stability is excellent. Examples of the metal oxide used when the coating layer is a multilayer include SiO ₂ , TiO ₂ , Al ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₅ , ZrO _2, etc. Examples of the fluoride include MgF ₂ , YF ₃ , LaF ₃ , CeF ₃ , BaF _{2 and the} like.

  Such a coating layer is preferably formed by alternately laminating about 2 to 20 layers made of metal oxide and layers made of metal fluoride. The thickness of such a coating layer is usually preferably 5 μm or less.

  Such a coating layer is preferably formed by a physical vapor deposition method (PVD method), and can be performed by a known sputtering method, ion plating method, vacuum vapor deposition method or the like. In particular, it is preferable to use ion assist and plasma assist together because the film performance is improved.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

  The translucent ceramics described in Table 1 were produced as follows. In Table 1, sample no. 1, 2, 4, and 6 are translucent ceramics of the present invention. 3, 5, 7, and 8 are the translucent ceramics of a comparative example.

(A) Preparatory process No. in Table 1 For 1-3, MgO powder, ZnO powder, and Al ₂ O ₃ powder each having an average particle size of 0.3 μm were prepared as raw material powders, and these powders were blended in the molar ratios shown in Table 1. No. About 4-8, using the hydroxide powder (Mg (OH) ₂ powder, Zn (OH) ₂ powder, Al (OH) ₃ powder) whose average particle diameter is 0.3 micrometer each as raw material powder, What was heated at 400 degreeC by the vacuum for 5 hours was mix | blended with the molar ratio described in Table 1. This molar ratio is consistent with the stoichiometric composition of the finally obtained translucent ceramic (in Table 1, “x” in the chemical formula of the first oxide and the chemical formula of the second oxide). "Y" in the middle). The raw material powder used has a purity of 99.99% or more.

(B) Molding step A molded body (diameter 20 mm, thickness 5 mm) was produced by molding the raw material powder blended above at a pressure of 250 kg / cm ² .

(C) Sintering process The molded object produced above was loaded in the sintering furnace, and the sintered compact was obtained by sintering by an atmospheric condition and atmospheric pressure.

(D) Hot isostatic pressing (HIP) step The sintered body obtained above was heated to 1850 ° C. at 800 ° C./hour up to the temperature (HIP temperature) shown in Table 1 in argon gas, and the pressure was 1000 kg / A hot isostatic pressing process was performed by holding the sample under cm ² for 1 hour. Then, it annealed at 1000 degreeC for 24 hours, and annealed at the cooling rate of 0.5 degree-C / min to room temperature. Then, translucent ceramics (thickness 1mm) were manufactured by grind | polishing the surface. In Table 1, sample no. 1 to 5 are translucent ceramics of the present invention. 6-7 are the translucent ceramics of a comparative example. Whether or not the crystal structure of the generated phase of the translucent ceramic was “spinel type” was confirmed by powder X-ray diffraction, and “spinel” was indicated for those having “spinel crystal structure”.

<Evaluation>
(1) Relative density The relative density (the theory of the first oxide and the second oxide) of each of the translucent ceramics (referred to as HIP bodies in Table 1) after the HIP treatment obtained in Example 1 above. The density with respect to the value expressed in%) was measured by the Archimedes method.

(2) Linear transmittance Each translucent ceramic obtained in Example 1 was processed to a thickness of 1 mm, mirror-polished using diamond slurry, and the linear transmittance (thickness 1 mm) was measured with a spectrophotometer. did. As a result, the linear transmittance at a wavelength of 420 nm to 680 nm was lowest at 420 nm, and thus the linear transmittance at 420 nm was measured for each translucent ceramic.

(3) Thermal conductivity A test piece having a diameter of 10 mm and a thickness of 2 mm was cut out from the translucent ceramic obtained in Example 1, and the thermal conductivity at room temperature was measured by a laser flash method.

(4) Coefficient of thermal expansion About the same specimen as the specimen used for the measurement of the above thermal conductivity, the coefficient of thermal expansion from room temperature to 500 ° C. is measured with a differential transformer type thermal expansion coefficient measuring device, and the average thermal expansion The coefficient was calculated.

(5) Thermal shock test The same test piece as the test piece used for the measurement of the thermal conductivity was heated in the atmosphere at a temperature of 1000 ° C. for 1 hour, put into water and rapidly cooled. Thereafter, the sample was annealed at 1000 ° C. for 24 hours, gradually cooled to room temperature at a rate of 0.5 ° C./minute, and the thermal conductivity of the test piece slowly cooled to room temperature was measured. This operation is repeated up to 10 times, and when the thermal conductivity is smaller than 90% of the initial value (the thermal conductivity measured in advance before the operation), the number of repetitions minus 1 (thermal shock) The number of test clearings was recorded.

Table 1 shows the evaluation test results of the above (1) to (5).
In addition, the crystal structure of the generated phase of each translucent ceramic was confirmed by powder X-ray diffraction. “Sp” indicates that the “spinel-type crystal structure” is present, “MgO” indicates that the “magnesia-type crystal structure” Those having a ZnO phase are denoted as “ZnO”. Further, the ratio of the first oxide having a spinel crystal structure and the second oxide having a magnesia crystal structure was calculated from the peak intensity ratio and shown in Table 1.

  As is apparent from Table 1, No. 1 which is a translucent ceramic of the present invention. 1, 2, 4, 6 (Examples) are Nos. It can be seen that it has higher thermal shock resistance than the light-transmitting ceramics Nos. 7 and 8 (comparative examples not including both the first oxide and the second oxide). Moreover, the translucent ceramics of this invention are No.1. It can be seen that the translucent ceramics 3 and 5 (comparative examples in which y in the chemical formula of the second oxide is outside the scope of the present invention) have a high linear transmittance. Therefore, it was confirmed that the translucent ceramic of the present invention has an excellent effect of being excellent in transparency and having high thermal shock resistance.

  Although the embodiments and examples of the present invention have been described as described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Claims (9)

A first oxide having a spinel crystal structure represented by the chemical formula Mg _(1-x) Zn _x Al ₂ O ₄ (where 0 ≦ x ≦ 1), and a chemical formula Mg _(1-y) Zn _y O (wherein , 0 ≦ y ≦ 0.2), and a second oxide having a magnesia type crystal structure.   The translucent ceramics according to claim 1, comprising the first oxide and the second oxide.   The translucent ceramics of Claim 1 or 2 whose ratio of the 2nd oxide with respect to the total amount of a said 1st oxide and a 2nd oxide is 20-85 mol%.   The translucent ceramic according to claim 1, which is a sintered body.   The translucent ceramics in any one of Claims 1-4 whose heat conductivity is 10 W / mK or more.   The optical element for color liquid crystal projectors using the translucent ceramics in any one of Claims 1-5.   A color liquid crystal projector using the optical element according to claim 6. It is a manufacturing method which manufactures the translucent ceramics in any one of Claims 1-5,
A preparation step of preparing a raw material powder containing at least one element constituting the first oxide and the second oxide;
A molding step of obtaining a molded body by molding the raw material powder;
A sintering step of obtaining a sintered body by sintering the molded body;
A hot isostatic pressing step of completing the translucent ceramic by hot isostatic pressing the sintered body;
A method for producing translucent ceramics.   The manufacturing method of the translucent ceramics of Claim 8 whose said raw material powder is hydroxide powder.