JP5983525B2 - Method for producing translucent metal oxide sintered body - Google Patents

Description

The present invention relates to the production how the light-transmitting metal oxide sintered body having a light-transmitting property in the visible range and / or infrared range, in particular its optical applications, solid-state laser for medium, X-rays scintillator material, gamma The present invention relates to a method for producing a translucent metal oxide sintered body used for a line scintillator material, a magneto-optical device material, an arc tube, a light refractive index window material, an optical shutter, an optical recording element, a translucent ballistic material, and the like.

  In general, in order to produce a translucent metal oxide sintered body having sufficiently high translucency in the visible region and / or the infrared region, sintering such as atmospheric pressure sintering or vacuum sintering is used. It is not sufficient to obtain a dense body having a relative density of 95% by mass or more through the densification step, and the dense body is further increased to a higher relative density by a hot isostatic pressing (HIP (Hot Isostatic Press)) treatment step. Often densified. When the transparent metal oxide sintered body at a high temperature and high pressure of 1000 ° C. or higher and several tens of MPa or higher is subjected to HIP treatment, the residual bubbles in the metal oxide sintered body may be compressed and the size may be reduced. This is because a point that can be dissolved and disappeared in the inside, a point that can be volatilized and disappeared outside the sintered body, and the like, thereby achieving further higher density. However, in the HIP process, a carbon (graphite) -based material is often used as a heating source and a heat insulating material. This carbon material is vaporized and floated at a constant concentration during the HIP process, and is heated by a metal oxide. In some cases, the metal oxide sintered body is blackened by carburizing into the sintered body. In addition, the vapor carbon reacts with a small amount of oxygen released from the metal oxide sintered body to form carbon monoxide, thereby changing the atmosphere in the HIP furnace to a reducing property, and the metal oxide sintered body is reduced based on this. As a result, oxygen defects are generated, and the metal oxide sintered body may change from dark gray to black. Regardless of the progress of densification, if the translucent metal oxide sintered body itself changes to black, the translucency in the visible region and / or the infrared region is significantly lowered. Therefore, the translucent metal oxide sintered body that has undergone the HIP treatment process may be further subjected to re-oxidation treatment by annealing or the like in the subsequent process.

For example, JP-B-2-25864 (Patent Document 1) discloses that Y ₂ O _{3 is} 2 mol% or more, TiO _{2 is} 3 to 20 mol% or more, lanthanum rare earth oxide is 0.1 to 3 mol%, and the remaining ZrO. _A method for producing a light-transmitting / fluorescent-radiating zirconia sintered body, characterized in that a molded body made of ₂ is fired in an oxygen-containing atmosphere, subjected to HIP treatment, and then oxidized, is disclosed. Produces a sintered body that loses the color of the black sintered body, has a density of 99% or more of the theoretical value, and exhibits high transparency with respect to light in the visible light region to infrared light region having a wavelength of 350 to 7000 nm. It is supposed to be possible.

  Japanese Patent Publication No. 5-55465 (Patent Document 2) discloses a method for manufacturing an object containing at least 99.9% yttrium oxide (purity), which contains at least 99.9% yttrium oxide. The raw material powder is prepared, the yttrium oxide powder is compressed to form an object containing at least 99.9% yttrium oxide, and the compressed object containing at least 99.9% yttrium oxide is sintered at an elevated temperature. And adjusting the object with closed pores and heating the object at elevated temperature and pressure for a time sufficient to bring the density to substantially 100% of the theoretical density for at least 99. By densifying an object with 9% yttrium oxide pores closed and heating the object in an atmosphere containing air, it has a density of substantially 100% of the theoretical density. Disclosed is a manufacturing method characterized by the step of annealing an object to oxidize the object, thereby restoring the stoichiometric composition to the surface of the substance, whereby a final densification (at elevated temperature) is disclosed. At a step of heating for a time sufficient to bring the density to substantially 100% of the theoretical density under pressure; HIP treatment), resulting from the reduction of the material in an oxygen-free atmosphere, A dark object in the process is said to regain oxygen and become transparent.

  Furthermore, JP 2010-241678 A (Patent Document 3) is a method for producing an optical ceramic material, which includes a step of pre-sintering at a temperature between 500 and 900 ° C., between 1400 and 1900 ° C. Sintering the pre-sinterable form at a temperature of, preferably pressurizing in vacuum, preferably at a temperature between 1400 and 2000 ° C., and preferably at a pressure between 10 and 198 MPa, Disclosed is a method for producing an optoceramic material including a step of annealing a pressure-sintered molded body at a temperature between 600 and 1600 ° C. in an oxygen-containing atmosphere, and can thereby be reduced up to the previous step of annealing. It is stated that the elements are reoxidized, thereby ensuring that they do not interfere with the desired optical properties of the optoceramic material.

  However, in the annealing in a simple oxygen atmosphere as in the above prior art examples, the translucent metal oxide sintered body that has been reduced and darkened is reoxidized and the color disappears. In many cases, the pores once compressed by the HIP treatment process are expanded again by the heating annealing process, thereby impairing the translucency and causing the translucent metal oxide sintered body to become clouded.

Therefore, in Japanese Patent No. 4237707 (Patent Document 4), light having an average crystallite diameter of 0.9 to 9 μm and a measurement wavelength of 1.06 μm is annealed in a pressurized oxygen-containing atmosphere after the HIP treatment. A rare earth garnet sintered body having a loss factor of 0.002 cm ⁻¹ or less and a transmitted wavefront distortion at a measurement wavelength of 633 nm of 0.05 λcm ⁻¹ or less has been disclosed. In this patent document, annealing is performed at a temperature of not more than hot isostatic pressing in an oxygen-containing atmosphere at a pressure of 4.5 MPa or more, and the oxygen partial pressure of the oxygen-containing atmosphere in the annealing is 900 kPa or more. Further, it is disclosed that the oxygen concentration in the atmosphere is at least 1 vol% or more, and as a result, the sintered body subjected to HIP treatment is re-oxidized to become colorless and transparent, and has an optical loss coefficient at a measurement wavelength of 1.06 μm. 0.002 cm ^-1 or less, transmitted wavefront distortion at the measurement wavelength 633nm is a 0.05Ramudacm ^-1 or less of a rare earth garnet sintered body is obtained.

Japanese Patent Publication No. 25-25864 Japanese Patent Publication No. 5-55465 JP 2010-241678 A Japanese Patent No. 4237707

  However, according to the method described in Patent Document 4, the pores compressed in the HIP treatment process do not re-expand, and the sintered body is re-oxidized to become a colorless and transparent translucent metal oxide sintered body. However, some problems remain with the annealing method disclosed herein. That is, the first problem is the large amount of oxygen used. When the oxygen concentration is required to be at least 1 vol% of the atmosphere, the furnace is filled with 1 vol% or more, depending on the charged amount of the translucent metal oxide sintered body with respect to the internal volume of the pressure annealing furnace. Only a part of the oxygen to be consumed is spent reoxidizing the sintered body, and the remaining oxygen gas may remain in the furnace in a large amount. This means that the surplus oxygen that was not consumed to re-oxidize the sintered body, regardless of whether the material of the heater, heat insulating material, and support part of the pressure annealing furnace is carbon, molybdenum, or tungsten, All of this will be consumed by reacting with these annealing furnace materials. That is, there is a problem that the life of the furnace material constituting the pressure annealing furnace is shortened in an excess oxygen atmosphere where the oxygen concentration is at least 1 vol% or more of the atmosphere. In Patent Document 4, it is said that by annealing under pressure, separation of gas dissolved in the crystallite can be prevented and generation of pores can be prevented. In the case where only a pressure lower than the atmospheric pressure applied in the HIP treatment step in the preceding stage is applied, even if re-separation of the gas completely dissolved in the crystallite can be prevented, There is a possibility that pores which are not solid-dissolved in the crystal and are only compressed and reduced between crystallites will expand again in the oxygen-containing atmosphere pressure annealing step.

The present invention has been made in view of the above circumstances, and is a translucent metal that minimizes the oxygen concentration in the re-oxidation step after the HIP treatment and further completely prevents the re-expansion of the micropores compressed by the HIP treatment. and to provide a manufacturing how of the oxide sintered body.

The present invention, in order to achieve the above object, to provide a manufacturing how the light-transmitting metal oxide sintered body below.
[1] Fabricated using oxide particles of one or more metal elements selected from the group consisting of Mg, Y, Sc, lanthanide, Ti, Zr, Al, Ga, Si, Ge, Pb, and Bi. The sintered body mainly composed of the metal oxide is subjected to a first hot isostatic pressing (first HIP) treatment as a densification treatment of the sintered body at a heat treatment temperature of 1400 to 1900 ° C., and the first HIP treatment The sintered body is discolored to gray, dark gray or black, and then the metal oxide sintered body after the first HIP treatment and an oxygen supply source for releasing oxygen or air by heating are supplied to an external atmospheric gas. Is placed in a semi-sealed heat-resistant container having a vent hole capable of flowing in, and the heat-resistant container is 1050 to 1450 ° C. in an inert gas atmosphere having an oxygen concentration of less than 1 vol % and lower than the heat treatment temperature of the first HIP treatment, and Above metal The gray compound sintered body is subjected to a second hot isostatic pressing (first 2HIP) treated with heat treatment temperature for oxidation is reoxidized sintered body turned dark gray or black color translucent sintered The manufacturing method of the translucent metal oxide sintered compact which obtains a body.
[2] The sintered body is an M ₂ O ₃ type rare earth sesquioxide sintered body (M is one or more rare earth elements selected from the group consisting of Y, Sc and lanthanide elements). The method for producing a translucent metal oxide sintered body according to [1], wherein
[3] The translucency according to [1] or [2], wherein the metal oxide particles are press-molded into a predetermined shape and then sintered, and then subjected to a first HIP treatment and a second HIP treatment. A method for producing a metal oxide sintered body.
[4] The light transmitting material according to any one of [1] to [3], wherein the oxygen supply source is made of a metal oxide that releases oxygen by decreasing a metal valence when heated. For producing a conductive metal oxide sintered body.
[5] The translucent metal according to any one of [1] to [3], wherein the oxygen supply source is a ceramic powder or a porous ceramic formed body in which oxygen gas or air is adsorbed. Manufacturing method of oxide sinter.
[6] The light transmitting device according to any one of [1] to [3], wherein the oxygen supply source is a press-molded body of Tb ₄ O ₇ powder, Pr ₆ O ₁₁ powder, or CeO ₂ powder. For producing a conductive metal oxide sintered body.
[7] Production of translucent metal oxide sintered body according to any one of [1] to [6], wherein the applied pressure of the second HIP treatment is equal to or higher than the applied pressure of the first HIP treatment. Method.
[8] The method for producing a translucent metal oxide sintered body according to any one of [1] to [7], wherein the heat-resistant container is made of Pt.
[9] The input amount of the oxygen supply source is such that the total oxygen amount contained in the oxygen supply source is 100 ppm or more with respect to the inert gas amount corresponding to the applied pressure of the furnace content integral for the second HIP process. The method for producing a translucent metal oxide sintered body according to any one of [1] to [8], wherein:
[10] The translucent metal oxide sintered body according to any one of [1] to [9], wherein the oxygen concentration in the semi-sealed heat-resistant container in the second HIP treatment is 8 vol% or more Manufacturing method.

  According to the present invention, the furnace material for HIP processing does not wear more than necessary, and it prevents re-segregation of pores dissolved in the sintered body, and also does not cause re-expansion of compressed pores. The translucent metal oxide sintered body that has been reduced by the treatment process and turned from dark gray to black is returned to a completely colorless and transparent state, and the translucency in the visible region and / or infrared region is remarkably improved. A conductive metal oxide sintered body can be produced.

It is the schematic which shows the structure of the HIP apparatus which performs the 2nd HIP process in the manufacturing method of the permeable metal oxide sintered compact concerning this invention.

Below, the manufacturing method of the permeable metal oxide sintered compact concerning this invention is demonstrated.
The manufacturing method of the translucent metal oxide sintered body according to the present invention includes a first hot isostatic press (first HIP) at a heat treatment temperature of 1100 to 2000 ° C. for a sintered body containing a metal oxide as a main component. A semi-sealed heat-resistant container having a vent hole through which an external atmospheric gas can flow into the metal oxide sintered body after the first HIP treatment and an oxygen supply source that releases oxygen or air by heating. The heat-resistant container is subjected to a second HIP treatment in an inert gas atmosphere having an oxygen concentration of less than 1 vol.% And subjected to a second HIP treatment at a heat treatment temperature lower than the heat treatment temperature of the first HIP treatment and the metal oxide sintered body is oxidized. It is characterized by obtaining a sintered body having high characteristics. The details are as follows.

[Manufacturing process]
In the present invention, using predetermined metal oxide particles as raw powder (starting raw material), press-molding into a predetermined shape, degreasing, and then sintering to densify the relative density to 95% by mass or more It is preferable to produce the sintered body. Then, the 1st hot isostatic pressing process (henceforth 1st HIP process) mentioned later is given. Thereafter, a second HIP treatment for the purpose of re-oxidizing the sintered body is performed.

(Raw material powder)
As the raw material powder used in the present invention, any metal oxide particles exhibiting translucency as a sintered body can be suitably used. That is, one kind or two or more kinds of particles selected from the group of translucent metal oxides as the sintered body can be used as the raw material powder. For example, YSZ (yttria stabilized zirconia), spinel (Al ₂ O ₃ -26 mass% MgO), PLZT (lead lanthanum zirconate titanate), alumina, YAG (Y ₃ Al ₅ O ₁₂ ), LuAG (Lu ₃ Al ₅ O ₁₂ ), TGG (Tb ₃ Ga ₅ O ₁₂ ), TAG (Tb ₃ Al ₅ O ₁₂ ), various sesquioxides, BGO (Bi ₄ Ge ₃ O ₁₂ ), GAG (Gd ₃ Al ₅ O ₁₂ ), Y ₂ Zr ₂ O ₇ and other oxide particles of constituent elements constituting metal oxides that are generally confirmed or expected to have translucency, such as Mg, Y, Sc, lanthanide, Ti, Zr It is preferably an oxide particle of one or more metal elements selected from the group consisting of Al, Ga, Si, Ge, Pb, and Bi.
What weighed these metal oxide particles to an appropriate ratio can be suitably used as a raw material powder.

In the case of producing an M ₂ O ₃ type sesquioxide sintered body (M is one or more rare earth elements selected from the group consisting of Y, Sc and lanthanide elements) Oxide particles of one or more rare earth elements selected from the group consisting of Y, Sc and lanthanide elements, particularly Y, Sc, Lu, Tb, Yb, Gd, Nd, Eu, Ho, Dy, Tm , Sm, Pr, Ce, and Er selected from the group consisting of one or more rare earth element oxide particles and Zr oxide particles may be used. Note that the amount of ZrO ₂ powder added is preferably 1% by mass or less (excluding 0% by mass), and more preferably 0.5% by mass or less. If no ZrO ₂ powder is added, bubble coalescence in the sintering process is promoted and bubble growth occurs, resulting in coarse bubbles of micron size, which may impair translucency. If ZrO ₂ powder is added in an amount of more than 1% by mass, a part of the ZrO ₂ may be segregated in the M ₂ O ₃ type sesquioxide sintered body as the second phase in the sintering process and the light transmission property may be impaired. It is not preferable.

  The purity of the metal oxide particles described above is preferably 99.9% by mass or more. Further, the particle shape thereof is not particularly limited, and for example, square, spherical and plate-like powders can be suitably used. Moreover, it can use suitably even if it is the powder which carried out secondary aggregation, and it can use suitably also if it is the granular powder granulated by granulation processes, such as a spray-dry process. Furthermore, the production process of these raw material powders is not particularly limited, and raw material powders produced by coprecipitation method, pulverization method, spray pyrolysis method, sol-gel method, alkoxide hydrolysis method, and any other synthesis method are preferably used. it can. Further, the obtained raw material powder may be appropriately treated by a wet ball mill, a bead mill, a jet mill, a dry jet mill, a hammer mill or the like.

In the present invention, the accumulation from the minimum value side in the particle size distribution of the raw material powder of the metal oxide particles to be used (the particle size distribution of the secondary particles when the particles are aggregated into secondary particles) is 2.5. % Particle diameter (D2.5 value) D2.5 value is preferably 180 nm or more and 2000 nm or less. If the D2.5 value is less than 180 nm, bubbles may coalesce and grow in the sintering process, resulting in coarse bubbles of micron size, which may impair the translucency, and the D2.5 value exceeds 2000 nm. In addition, the intergranular voids generated during molding become too coarse, and the composed particles are already large enough that the surface free energy of the particles becomes small, and the sintering does not progress easily. It may be difficult to provide a ligation.
The particle size measurement method is not particularly limited. For example, it is possible to refer to a value obtained by dispersing a powder raw material in a liquid solvent and measuring by a light scattering method or a light diffraction method. It is preferable because it can be evaluated up to

  In addition to the metal oxide group constituting the translucent metal oxide, a sintering inhibitor may be appropriately added to the raw material powder used in the present invention. In particular, in order to obtain a high translucency, it is preferable to add a sintering suppression aid corresponding to each translucent metal oxide. However, the purity is preferably 99.9% by mass or more. In addition, when a sintering inhibitor is not added, it is preferable to select a raw material powder that has a primary particle size of nano-size and extremely high sintering activity. Such a selection may be made as appropriate.

  Furthermore, it is preferable to add various organic additives for the purpose of improving quality stability and yield in the manufacturing process. In the present invention, these are not particularly limited, and various dispersants, binders, lubricants, plasticizers, and the like can be suitably used.

  In addition, an optical function activator may be appropriately added to the raw material powder used in the present invention so as to meet the target optical application. For example, a laser material that can create an inversion distribution state to cause laser oscillation at a desired wavelength, a scintillator material that receives and fluoresces ionizing radiation with high sensitivity, a phosphor that absorbs LED light and fluoresces at a different wavelength, Alternatively, as a saturable absorber for providing a saturable absorption function and causing pulse laser oscillation, various oxides of Nd and Yb, Pr, Ce, Tb, Eu, Cr and other oxides are added. There is a case. In the present invention, these activators can be added as appropriate. The purity in that case is preferably 99.9% by mass or more.

(Press molding)
In the production method of the present invention, a normal press molding process can be suitably used. That is, a very general pressing process in which a mold is filled and pressurized from a certain direction, or a CIP (Cold Isostatic Press) process in which it is sealed in a deformable waterproof container and pressurized with hydrostatic pressure can be used. The applied pressure may be appropriately adjusted while confirming the relative density of the obtained molded body, and is not particularly limited. For example, if the pressure is controlled within a pressure range of about 300 MPa or less that can be handled by a commercially available CIP device, the manufacturing cost can be suppressed. It's okay. Alternatively, not only a molding process but also a hot press process, a discharge plasma sintering process, a microwave heating process, and the like that can be performed all at once at the time of molding can be suitably used.

(Degreasing)
In the production method of the present invention, a normal degreasing step can be suitably used. That is, it is possible to go through a temperature rising degreasing process by a heating furnace. Also, the type of atmospheric gas at this time is not particularly limited, and air, oxygen, hydrogen, and the like can be suitably used. The degreasing temperature is not particularly limited, but if a raw material mixed with an organic additive is used, it is preferable to raise the temperature to a temperature at which the organic component can be decomposed and eliminated.

(Sintering)
In the production method of the present invention, a general sintering process can be suitably used. That is, a heating and sintering process such as a resistance heating method or an induction heating method can be suitably used. The atmosphere at this time is not particularly limited, but an inert gas, oxygen, hydrogen, vacuum, or the like can be suitably used.

  The sintering temperature in the sintering step of the present invention is appropriately adjusted depending on the starting material selected. In general, a temperature on the low temperature side of about several tens of degrees Celsius to 100 to 200 degrees Celsius is preferably selected from the melting point of the sintered body to be manufactured using the selected starting material. At this time, it is preferable that the relative density is densified to 95% by mass or higher as high as possible. In addition, when trying to produce a metal oxide sintered body having a temperature zone in which a phase change to a phase other than a cubic crystal exists in the vicinity of the selected temperature, the temperature should be strictly controlled to be lower than that temperature. When sintered, a phase transition from a non-cubic crystal to a cubic crystal virtually does not occur, so that an advantage that optical distortion or cracks are hardly generated in the material can be obtained.

  The sintering holding time is appropriately adjusted depending on the starting material selected. In general, about several hours is sufficient in many cases, but it is preferable to secure time for densification of the relative density of the metal oxide sintered body to 95% by mass or more.

(Hot isostatic pressing (HIP))
In the production method of the present invention, a hot isostatic press (HIP) process is always provided after the sintering process. The HIP process includes a first HIP process and a second HIP process.

-First HIP process-
The first HIP process is a conventional HIP process for obtaining a translucent metal oxide sintered body. That is, the HIP apparatus used in this process may be of a general apparatus configuration, and a sintered body that has been processed up to the above-described sintering step is placed in a high-pressure vessel of the HIP apparatus, and the compressed gas medium is used to The entire sintered body is uniformly pressurized and heated to a predetermined heat treatment temperature by an electric resistance heating type heating means disposed in a high-pressure vessel to perform HIP treatment.

Further, an inert gas such as argon as the kind of the pressurized gas medium (atmospheric gas) in this case, or Ar-O ₂ can be suitably used, applied pressure is not more than 196MPa which can be treated with the commercial HIP apparatus Simple and preferred.

  What is necessary is just to set the heat processing temperature of 1st HIP process suitably with the kind and / or sintering state of the metal oxide which comprise a sintered compact, for example, 1100-2000 degreeC, Preferably it sets in the range of 1400-1900 degreeC. . At this time, as in the case of the sintering step, it is essential that the temperature be below the melting point and / or below the phase transition point of the metal oxide constituting the sintered body. It exceeds the melting point of the metal oxide composing the metal oxide sintered body or exceeds the phase transition point, making it difficult to perform proper HIP treatment. Moreover, if the heat treatment temperature is less than 1100 ° C., the effect of improving the translucency of the sintered body cannot be obtained. In addition, although there is no restriction | limiting in particular about the holding time of heat processing temperature, It is good to adjust the time suitably with the material selected as a metal oxide which comprises a sintered compact.

  Moreover, 50-300 MPa is preferable and the pressure pressurized with the pressurized gas medium in a 1st HIP process has more preferable 100-300 MPa. If the pressure is less than 50 MPa, the translucency improvement effect may not be obtained. If the pressure exceeds 300 MPa, no further improvement in translucency can be obtained even if the pressure is increased, and the load on the device may be excessive and damage the device. There is.

  In the first HIP process, the metal oxide sintered body may be stored in a heat-resistant container having a vent hole through which an external atmospheric gas can flow, and the heat-resistant container may be placed in a HIP furnace to perform the HIP process. This heat-resistant container is made of a heat-resistant material such as platinum (Pt), graphite, molybdenum (Mo), yttria (yttrium oxide), zirconia (zirconium oxide), tantalum (Ta), tungsten (W), iridium (Ir), etc. It is. Among them, Pt is one of suitable materials as a container material for supporting the sintered body because it is chemically very stable and does not react with the metal oxide sintered body even at high temperatures. There is a risk of melting at high temperatures. Therefore, in the first HIP process, the lower limit of the heat treatment temperature is 1100 ° C. but often exceeds 1500 ° C., and the heat treatment temperature is often very high. As a material for the heat resistant container, a heat resistant material other than Pt, that is, graphite, molybdenum (Mo ), Yttria (yttrium oxide), zirconia (zirconium oxide), tantalum (Ta), tungsten (W), and iridium (Ir). In many cases, the heater material and the heat insulating material used in the first HIP process are selected from Mo, graphite, and the like.

By the way, as described above with respect to the prior art, the HIP apparatus uses a carbon (graphite) -based material as a heating source and a heat insulating material, and metal oxide sintering is caused by carbon evaporated from the material during the HIP process. The translucency of the body may decrease. In addition, when graphite is selected as the material constituting the heat-resistant container, the graphite vaporizes from the heat-resistant container during the first HIP treatment, floats at a constant concentration as vapor carbon, and comes into contact with the metal oxide sintered body. In some cases, the sintered body is carburized to blacken the sintered body. Alternatively, the vapor carbon reacts with a small amount of oxygen released from the sintered body to form carbon monoxide, and the HIP atmosphere is changed to be reducible. As a result, the sintered body is reduced to produce oxygen defects, and In some cases, the body may change from dark gray to black.
The present invention provides a method for producing a translucent metal oxide sintered body by solving the above-described problems without losing the furnace material for HIP processing more than necessary by the second HIP processing described below. To do.

-Second HIP processing (re-HIP processing)-
The second HIP process is an essential part of the present invention. This processing will be described based on the HIP device example shown in FIG.
As shown in FIG. 1, the HIP apparatus 10 used in the second HIP process includes a metal oxide sintered body 1 after the first HIP process and a semi-sealed heat-resistant container 13 having a vent hole 13a through which an external atmospheric gas can flow. An oxygen supply source 14 is accommodated, the heat-resistant container 13 is placed in a HIP furnace 11 using a carbon heater as a heating means 12, and an inert gas having an oxygen concentration of less than 1 vol% is introduced into the HIP furnace 11 as a pressurized gas medium. Thus, the heating means 12 heats the entire sintered body under pressure.

Here, the oxygen supply source 14 is preferably made of a metal oxide that releases oxygen by reducing the valence of the metal at a high temperature when heated. For example, terbium oxide (Tb ₄ O ₇ ), cerium oxide ( A material made of CeO ₂ ) or praseodymium oxide (Pr ₆ O ₁₁ ) is preferable because a state change that releases oxygen occurs when the temperature is raised to the heat treatment temperature in the second HIP treatment. As a form of the oxygen supply source 14 in this case, a powder, a molded body, or a sintered body made of a metal oxide that releases oxygen by reducing a metal valence at a high temperature when heated is preferable.

Moreover, it is preferable that the oxygen supply source 14 is a ceramic powder or a porous ceramic molded body in which oxygen gas or air is adsorbed. The ceramic used here is preferably a metal oxide constituting the metal oxide sintered body 1, and particularly preferably yttrium oxide (Y ₂ O ₃ ) or aluminum oxide (Al ₂ O ₃ ). Such a metal oxide can be used even when the above-described terbium oxide, cerium oxide, or praseodymium oxide cannot be used as a contamination-causing substance of the metal oxide sintered body 1. Note that the ceramic used here does not release oxygen even when the temperature is high, such as the heat treatment temperature of the second HIP treatment, so this ceramic has a relative density of 60% by mass or less, Or it is preferable to utilize in the state made into the porous molded object. Specifically, oxygen gas or air is adsorbed on a surface having a large surface area such as porous voids or powder existing in the porous molded body, and oxygen gas or Air is released and released. The adsorption of oxygen gas or air can be performed by exposing the powder or porous molded body to a high-concentration oxygen gas atmosphere at room temperature (25 ° C.) or in the atmosphere (for example, about 50% humidity) at room temperature (25 ° C.). Just expose. Note that the powder or porous molded body may be immersed in pure water at room temperature (25 ° C.) to adsorb moisture to form the oxygen supply source 14, in which case oxygen molecules contained in the moisture are oxygen supply sources. It is thought that it becomes.

  In addition, the kind of metal oxide which comprises the oxygen supply source 14 charged simultaneously with the metal oxide sintered compact 1 can be made according to the kind of metal oxide which comprises the metal oxide sintered compact 1 to be manufactured. It is preferable to select as appropriate a combination that does not cause contamination problems.

The input amount of the oxygen supply source 14 is such that the total oxygen amount contained in the oxygen supply source 14 is 100 ppm or more with respect to the inert gas amount corresponding to the applied pressure of the HIP furnace 11 content integral for the second HIP process. Preferably there is. When the oxygen supply source 14 is composed of a metal oxide that releases oxygen by reducing the metal valence by heating, the total oxygen amount here is released when the metal valence of the total amount of the metal oxide decreases. In the case where the oxygen supply source 14 is a ceramic powder or porous ceramic molded body on which oxygen gas or air is adsorbed, the total amount of oxygen gas adsorbed or the amount of oxygen contained in the air. Note that the total oxygen amount contained in the oxygen supply source 14 in the case where the oxygen supply source 14 is a ceramic powder or a porous ceramic molded body in which moisture is adsorbed is the amount of oxygen contained in the total amount of moisture. Then, hydrogen gas may act as a reducing gas that inhibits oxidation.
As a result, most of the released oxygen stays in the heat-resistant container 13, so that the oxygen concentration in the heat-resistant container 13 becomes higher than 100 ppm (although actual concentration measurement is impossible), which will be described later. As shown in the examples, the reoxidation proceeds to the extent that the metal oxide sintered body that has been changed from dark gray to black by the first HIP treatment as the previous step can be made colorless and transparent.

  The heat-resistant container 13 is made of a heat-resistant material, and is a crucible with a lid in which the metal oxide sintered body 1 and the oxygen supply source 14 are housed, and penetrates from the inside of the container to the outside through a part of the lid or the crucible body. A vent hole 13a is provided to make the heat-resistant container 13 in a semi-sealed state. Semi-hermetic means that the size (opening area) of the vent hole 13a is so large that the atmospheric gas in the HIP furnace 11 flows into the heat-resistant vessel 13 and the internal pressure becomes the applied pressure as the second HIP process. It means that oxygen released from the oxygen supply source 14 inside the container 13 is as small as possible so as not to flow out to the outside. Specifically, for example, if the crucible body is provided with a small kerf that serves as a gas passage and a cover is placed on the crucible body, the oxygen concentration is locally increased inside the container. Is possible and preferable. In addition, as long as the oxygen supply source 14 is disposed in the vicinity of the metal oxide sintered body 1 inside the heat-resistant container 13, there is no particular limitation on the arrangement of both.

  The heat-resistant container 13 is made of a material that does not cause a problem as a container that supports the metal oxide sintered body 1 such that the heat-resistant container 13 does not melt at the heat treatment temperature of the second HIP process. When the heat treatment temperature is less than 1500 ° C., it is preferable to use Pt which is excellent in oxidation resistance and chemically very stable.

  The heat treatment temperature of the second HIP treatment is lower than the heat treatment temperature of the first HIP treatment and is a heat treatment temperature at which the metal oxide sintered body 1 is oxidized. The heat treatment temperature at which the metal oxide sintered body 1 is oxidized refers to a temperature at which oxygen or air is released from the oxygen supply source 14 and becomes so high that the metal oxide sintered body 1 is oxidized by the oxygen or air. It is. Note that if the heat treatment temperature is lower than the temperature at which the metal oxide sintered body 1 is oxidized, the translucency of the target metal oxide sintered body 1 cannot be improved by this treatment, and if the heat treatment temperature is higher than the heat treatment temperature of the first HIP treatment. Grain growth in the metal oxide sintered body 1 is promoted, and the strength of the sintered body 1 is reduced and the optical characteristics are deteriorated. Such a heat treatment temperature is preferably 1050 to 1450 ° C., for example. If the heat treatment temperature is less than 1050 ° C., oxygen supply from the oxygen supply source 14 or oxidation of the metal oxide sintered body 1 may be insufficient, and if it exceeds 1450 ° C., it is suitable as the material of the heat-resistant container 13 for this treatment. Pt may not be used.

  In the present invention, the heat treatment temperatures for the first HIP treatment and the second HIP treatment are all temperatures of the metal oxide sintered body, but it is difficult to measure the temperature of the metal oxide sintered body 1 itself in an actual HIP apparatus. For this reason, the temperature measurement result in the HIP furnace portion of the heating means (carbon heater) 12 that has substantially the same temperature as the sintered body may be regarded as the temperature of the metal oxide sintered body 1.

Since the oxygen concentration of the pressurized gas medium is less than 1 vol%, consumption due to oxidation of the constituent members of the HIP device 10 can be suppressed. As long as the inert gas has an oxygen concentration of less than 1 vol%, it may be any of argon (Ar), inert gas such as nitrogen, or Ar—O _2. Among them, Ar is the least reactive with the furnace material. Since it is active, it can be most suitably used.

  The applied pressure in the second HIP process is the pressure of the pressurized gas medium introduced into the HIP furnace 11, and is preferably equal to or higher than the applied pressure in the first HIP process. This prevents re-segregation of pores dissolved in the crystallites constituting the metal oxide sintered body, and also causes re-expansion of pores that are compressed between crystallites, for example, at the triple point of the crystallites. Can be prevented.

As described above, in the HIP apparatus 10, it is assumed that the pressure inside the heat-resistant container 13 can be applied with atmospheric gas as in the HIP furnace 11 and the gas inside the heat-resistant container 13 can be confined to some extent. Since the oxygen supply source 14 is disposed inside the metal oxide sintered body 1 together with the metal oxide sintered body 1, oxygen or air is released from the oxygen supply source 14 during the heat treatment of the second HIP process, and the oxygen concentration inside the heat-resistant container 13 increases. Thus, the metal oxide sintered body that has been changed from dark gray to black by the first HIP treatment as the previous step can be reoxidized to be colorless and transparent. At this time, since a predetermined pressure is applied to the metal oxide sintered body, re-segregation and re-expansion of pores in the sintered body are suppressed.
Furthermore, the oxygen release is limited to the inside of the heat-resistant vessel 13, and the oxygen concentration in the HIP furnace is extremely low compared to the conventional method disclosed in Patent Document 4 in which the oxygen concentration in the entire HIP furnace is 1 vol% or more. Since the amount can be suppressed to a small level, oxidation wear of the heater material, the heat insulating material, and the support material constituting the HIP furnace can be suppressed.

(Optical polishing)
In the production method of the present invention, it is preferable to optically polish both end faces on the optically utilized axis of the metal oxide sintered body that has undergone a series of steps up to the second HIP treatment. The optical surface accuracy at this time is preferably λ / 8 or less, and particularly preferably λ / 10 or less. In addition, optical measurement can be accurately performed by appropriately forming an antireflection film on the optically polished surface.

According to the above method for producing a translucent metal oxide sintered body of the present invention, the re-segregation of pores dissolved in the sintered body that becomes crystallites without damaging the furnace material of the HIP apparatus more than necessary. The sintered body reduced from the dark gray color to the black color by the first HIP treatment is returned to a completely colorless and transparent state without causing re-expansion of the compressed pores as well as preventing the visible region and / or red. A metal oxide sintered body with significantly improved translucency in the outer region can be provided.
In the production method of the present invention, the obtained sintered body may be appropriately assembled into a device so as to meet the intended optical application.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. In addition, an average particle diameter is a weight average value by a laser beam diffraction method.

[Example 1]
An example using Lu ₂ O ₃ powder as a raw material powder of a metal oxide sintered body and Tb ₄ O ₇ powder, Pr ₆ O ₁₁ powder and CeO ₂ powder as activators will be described.
Here was obtained from Shin-Etsu Chemical Co., Ltd. Lu ₂ O ₃ powder, Tb ₄ O ₇ powder, Pr ₆ O ₁₁ powder, a CeO ₂ powder. All the purity was 99.9 mass% or more. Three kinds of powder raw materials for sintered body samples prepared by mixing these raw material powders and activators in the combinations and volume mixing ratios shown in Table 1 were prepared, and ZrO ₂ powders manufactured by Daiichi Rare Element Chemical Co., Ltd. were used for each. Was added by 0.5 mass%.

Further, an organic dispersant and an organic binder were added to each of them, and then a zirconia ball mill was dispersed and mixed in ethanol. The processing time was 24 hours. Thereafter, spray drying treatment was performed to produce granule raw materials each having an average particle size of 20 μm.
Next, the three powder raw materials thus obtained were filled into a 10 mm diameter mold, temporarily formed into a 20 mm long rod shape with a uniaxial press molding machine, and then hydrostatically pressed at a pressure of 198 MPa to obtain a CIP compact. Obtained. Subsequently, the obtained CIP compact was put into a muffle furnace, and degreased by heat treatment in the atmosphere at 800 ° C. for 3 hours.
Next, the obtained degreased molded body was charged into a vacuum heating furnace, heated to 1600-1700 ° C. at a temperature increase rate of 100 ° C./h, held for 3 hours, and then cooled at a temperature decrease rate of 600 ° C./h. Thus, a sintered body sample was obtained. At this time, the sintering temperature and holding time were adjusted so that the sintered relative densities of all the samples were substantially the same 96%.
Subsequently, each sintered body is held at a heat treatment temperature of 1600 to 1700 ° C. and a pressure of 98 to 198 MPa in an HIP furnace composed of a graphite heater, a heat insulating material, and a support material using Ar gas as a pressure medium. The first HIP treatment for 3 hours was performed. The appearance of the sintered body sample obtained at this time was light gray to gray.
Finally, as shown in FIG. 1, a sintered body sample (metal oxide sintered body 1) that has been subjected to the first HIP treatment and an oxygen supply source (oxygen supply source 14) having a predetermined charge amount shown in Table 2 are put into Pt. The same HIP as the apparatus used in the first HIP process comprising the graphite heater (heating means 12), the heat insulating material and the support material, charged simultaneously in the heat-resistant container (heat-resistant container 13) and using Ar gas as the pressure medium. Set in furnace 11, heat treatment temperature 1400-1450 ° C., set applied pressure to be equal to or higher than applied pressure of first HIP process (applied pressure 203 MPa), second HIP process (re-HIP process) for holding time 0.5 hour Went. All samples were colorless and transparent. The oxygen supply source used here is one obtained by press-molding the Tb ₄ O ₇ powder, Pr ₆ O ₁₁ powder, and CeO ₂ powder. In addition, the total amount of metal oxides during the second HIP treatment decreased the metal valence, and the oxygen concentration in the HIP furnace and the oxygen concentration in the heat-resistant vessel were estimated from the oxygen gas released from these oxygen supply sources. Incidentally, the internal volume of the HIP furnace (φ400mm × 480mmL) is 60288Cm ^3, heat-resistant container volume is 61cm ^3.
For comparison, the second HIP treatment was performed under the same conditions without using an oxygen supply source.

  The sintered body samples thus obtained were ground and polished so as to have a length of 10 mm, and then optical end faces of each sample were finally optically polished with an optical surface accuracy of λ / 8, and the center wavelength was 1064 nm. The antireflection film designed so as to be coated was coated, each transmittance at a wavelength of 1064 nm was measured, and the visible region transmission loss per unit length of the sintered body was converted and obtained. These results are also shown in Table 2.

  From the above results, in a system in which terbium, praseodymium and cerium are contained in the metal oxide sintered body, a very small amount (less than 1 g) is used in a heat-resistant container using a molded body having the same composition as each activator as an oxygen supply source. It was confirmed that the transmittance was extremely high in all sintered body samples regardless of the type of starting material, and a substantially colorless and transparent metal oxide sintered body was obtained (No. 11 to 13). ). In addition, since only the molded object of the same composition as an activator was prepared, the problem of the contamination of a sintered compact sample does not arise. On the other hand, in the examples (No. 14 to 16) in which the oxygen supply source was not charged in the heat-resistant container and second HIP processing (re-HIP processing) was performed, all the gray coloring generated in the first HIP processing remained as it is, A colorless and transparent metal oxide sintered body was not obtained.

[Example 2]
Implementation to confirm whether it is possible to eliminate the gray coloring caused by the first HIP treatment by using a metal oxide that does not release oxygen at a high temperature and does not release oxygen as a material for the oxygen supply source An example will be described.
Here, to obtain the Pacific Ocean random Co. Al ₂ O ₃ powder and Shin-Etsu Chemical Co., Ltd. Y ₂ O ₃ powder. All the purity was 99.9 mass% or more. Of these, after adding 0.5% by mass of ZrO ₂ powder manufactured by Daiichi Elemental Chemical Co., Ltd. to the Y ₂ O ₃ powder as a raw material for the sintered body sample, and further adding an organic dispersant and an organic binder Then, zirconia ball mill was dispersed and mixed in ethanol. The processing time was 24 hours. Thereafter, spray drying treatment was performed to produce a granule raw material having an average particle diameter of 20 μm.
Further, for the sintered body samples for reference ((TBY) ₂ O _3), prepared Tb ₄ O ₇ powder produced by Shin-Etsu Chemical Co., used in Example 1, Y ₂ O ₃ powder and Tb ₄ After mixing the O ₇ powder at a volume mixing ratio of 1: 1, 0.5% by mass of ZrO ₂ powder manufactured by Daiichi Rare Element Chemical Co., Ltd. was added, and after further adding an organic dispersant and an organic binder, Then, a zirconia ball mill was dispersed and mixed. The processing time was 24 hours. Thereafter, spray drying treatment was performed to produce a granule raw material having an average particle diameter of 20 μm.
Next, the obtained powder raw material was filled in a mold having a diameter of 10 mm, temporarily formed into a rod shape having a length of 20 mm with a uniaxial press molding machine, and then hydrostatically pressed at a pressure of 198 MPa to obtain a CIP compact. . Subsequently, the obtained CIP compact was put into a muffle furnace, and degreased by heat treatment in the atmosphere at 800 ° C. for 3 hours.
Next, the obtained degreased molded body was charged into a vacuum heating furnace, heated to 1600-1700 ° C. at a temperature increase rate of 100 ° C./h, held for 3 hours, and then cooled at a temperature decrease rate of 600 ° C./h. As a result, a sintered body was obtained. At this time, the sintering temperature and holding time were adjusted so that the sintered relative density of the sample was approximately 96%.
Subsequently, each sintered body is further maintained at a temperature of 1600 to 1700 ° C. and a pressure of 98 to 198 MPa in an HIP furnace composed of a graphite heater, a heat insulating material and a support material, using Ar gas as a pressurizing medium. The first HIP treatment for 3 hours was performed.
Finally, as shown in FIG. 1, among the sintered samples that have been subjected to the first HIP treatment, the Y ₂ O ₃ sintered sample is divided into several lots, and the divided sintered sample (metal oxide) Sintered body 1) and an oxygen supply source (oxygen supply source 14) having different metal oxide types and amounts as shown in Table 3 were simultaneously charged into a Pt heat-resistant container (heat-resistant container 13) and pressurized. Using Ar gas as a medium, set in the same HIP furnace 11 as the apparatus used in the first HIP treatment consisting of a graphite heater (heating means 12), a heat insulating material and a support material, and a heat treatment temperature of 1400 to 1450 ° C., The applied pressure was set to be equal to or higher than the applied pressure of the first HIP process (applied pressure 203 MPa), and the second HIP process (re-HIP process) with a holding time of 0.5 hours was performed. The oxygen supply source used here is an Al ₂ O ₃ molded body and a Y ₂ O ₃ molded body separately prepared so that the relative density of the molded body is about 55% by mass, specifically, After temporary molding with a uniaxial press molding machine, hydrostatic pressing was performed at a pressure of 198 MPa, and the resulting CIP compact was placed in a muffle furnace and heat-treated at 800 ° C. for 3 hours in the atmosphere for 3 hours to remove the fat. It was. In addition, since the exact oxygen discharge | release amount of the oxygen supply source in a present Example was unknown, the 2nd HIP process effect was estimated from the change of the coloring degree of the external appearance of a sintered compact sample.
For reference, a Pt heat-resistant sample sample (TbY) ₂ O ₃ having been subjected to the first HIP treatment and 0.4 g of the same Tb ₄ O ₇ compact as in Example 1 were used as an oxygen supply source. The container was charged and the _second HIP treatment was performed under the same conditions as in the case of the Y ₂ O ₃ sintered body sample. Further, without using the Tb ₄ O ₇ moldings, otherwise subjected to the 2HIP treatment under the same conditions.

  The sintered body samples thus obtained were ground and polished so as to have a length of 10 mm, and then optical end faces of each sample were finally optically polished with an optical surface accuracy of λ / 8, and the center wavelength was 1064 nm. The antireflection film designed so as to be coated was coated, each transmittance at a wavelength of 1064 nm was measured, and the visible region transmission loss per unit length of the sintered body was converted and obtained. These results are also shown in Table 3.

From the above results, when a metal oxide that does not release oxygen due to a decrease in metal valence at high temperatures, specifically, aluminum oxide (Al ₂ O ₃ ) or yttrium oxide (Y ₂ O ₃ ) is used. However, if the amount charged into the heat-resistant container is higher by about one digit than the amount of terbium oxide (Tb ₄ O ₇ ) that releases oxygen by reducing the metal valence at high temperature, the first HIP treatment It was confirmed that the various metal oxide sintered body samples colored in gray changed to metal oxide sintered bodies which were substantially colorless and transparent and had extremely high transmittance. On the other hand, 1.2 g charge of the oxygen supply source in Al ₂ O ₃ formed body (No.24), the sintered body samples were 2.5 g (No.29) in Y ₂ O ₃ formed body, Although there was an improvement in translucency, a slight light gray color remained. Considering from the results (No. 31, 32) of the (TbY) ₂ O ₃ sintered body sample taken for reference, the HIP furnace of oxygen gas possibly released from these oxygen sources during the second HIP process This is probably because the internal concentration was lower than 100 ppm.

  Although the present invention has been described with the embodiments shown in the drawings, the present invention is not limited to the embodiments shown in the drawings, and other embodiments, additions, modifications, deletions, etc. As long as the effects of the present invention are exhibited in any aspect, the present invention is included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Metal oxide sintered body 10 HIP apparatus 11 HIP furnace 12 Heating means 13 Heat-resistant container 13a Vent hole 14 Oxygen supply source

Claims (10)

Metal produced using oxide particles of one or more metal elements selected from the group consisting of Mg, Y, Sc, lanthanide, Ti, Zr, Al, Ga, Si, Ge, Pb, Bi A sintered body containing an oxide as a main component is subjected to a first hot isostatic pressing (first HIP) treatment at a heat treatment temperature of 1400 to 1900 ° C. as a densification treatment of the sintered body . The aggregate is discolored in gray, dark gray or black, and then external atmospheric gas can flow into the metal oxide sintered body after the first HIP treatment and an oxygen supply source that is heated to release oxygen or air Put in a semi-sealed heat-resistant container having a vent hole, and the heat-resistant container is 1050 to 1450 ° C. in an inert gas atmosphere having an oxygen concentration of less than 1 vol % and lower than the heat treatment temperature of the first HIP treatment and the metal oxidation Pottery A translucent sintered body is obtained by re-oxidizing the sintered body which has been subjected to the second hot isostatic pressing (second HIP) treatment at the heat treatment temperature at which the aggregate is oxidized to change the color to gray, dark gray or black. The manufacturing method of the translucent metal oxide sintered compact obtained. The sintered body is an M ₂ O ₃ type rare earth sesquioxide sintered body (M is one or more rare earth elements selected from the group consisting of Y, Sc and lanthanide elements). The method for producing a translucent metal oxide sintered body according to claim 1. 3. The translucent metal oxide sintered product according to claim 1, wherein the metal oxide particles are sintered after being pressed into a predetermined shape and then subjected to a first HIP treatment and a second HIP treatment. Body manufacturing method.   The translucent metal oxide according to any one of claims 1 to 3, wherein the oxygen supply source is made of a metal oxide that releases oxygen when heated by being reduced in metal valence. A method for producing a sintered body.   The translucent metal oxide sintered body according to any one of claims 1 to 3, wherein the oxygen supply source is a ceramic powder or a porous ceramic formed body in which oxygen gas or air is adsorbed. Body manufacturing method. The oxygen supply source is Tb _Four O ₇ Powder, Pr ₆ O ₁₁ Powder or CeO ₂ The method for producing a translucent metal oxide sintered body according to any one of claims 1 to 3, which is a powder press-molded body.   The method for producing a translucent metal oxide sintered body according to any one of claims 1 to 6, wherein an applied pressure of the second HIP treatment is equal to or higher than an applied pressure of the first HIP treatment.   The said heat-resistant container is a product made from Pt, The manufacturing method of the translucent metal oxide sintered compact of any one of Claims 1-7 characterized by the above-mentioned.   The input amount of the oxygen supply source is an amount such that the total oxygen amount contained in the oxygen supply source is 100 ppm or more with respect to the inert gas amount corresponding to the applied pressure of the furnace content integral for the second HIP process. The manufacturing method of the translucent metal oxide sintered compact of any one of Claims 1-8. The method for producing a translucent metal oxide sintered body according to any one of claims 1 to 9, wherein the oxygen concentration in the semi-sealed heat-resistant container in the second HIP treatment is 8 vol% or more.

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