JP7556880B2 - Method for producing oxide-containing ceramic sintered body and release sheet - Google Patents

Description

The present invention relates to a method for producing an oxide-containing ceramic sintered body and a release sheet.

A known method for firing ceramics is the hot press method, in which a sample (ceramic powder or ceramic compact) is fired under high temperature while being pressed. When producing ceramics using the hot press method, a spacer is generally placed between the sample and the pressing member to protect them. This spacer is often made of the same material as the other members to avoid stress concentration due to differences in thermal expansion coefficients with other members. For example, in an inert atmosphere, all members are generally made of graphite, and in an oxidizing atmosphere, all members are generally made of alumina or silicon carbide. However, this method has problems with the sample and spacer reacting with each other and sticking together or cracking because the sample and spacer come into direct contact with each other. For this reason, a method has been proposed in which a release agent is placed between the sample and the spacer (for example, Patent Documents 1 to 3).

Japanese Unexamined Patent Publication No. 10-194847 Patent No. 5002087 JP 2008-031020 A

In inert or vacuum atmospheres, graphite sheets are commonly used as release materials. However, when graphite sheets are used as release materials in hot press sintering at high temperatures, the sample and the release material may react, affecting the properties of the sample. In particular, when a carbon sheet is used as a release material to sinter an oxide ceramic sample, the carbon may react with the sample, causing the sample to evaporate, melt, or become carbide. In addition, the reaction between the release material and the sample may progress, causing the release material to be lost, and the sample may come into direct contact with the spacer, resulting in adhesion.

The present invention has been made to solve these problems, and its main objective is to suppress the reaction between the oxide-containing ceramic compact and the release agent during hot press sintering of the oxide-containing ceramic sintered body.

The method for producing an oxide-containing ceramic sintered body of the present invention comprises the steps of:
(a) preparing an oxide-containing ceramic molded body before being fired into an oxide-containing ceramic sintered body;
(b) sandwiching the oxide-containing ceramic compact between a pair of release sheets and placing it in a hot press sintering furnace, and hot press sintering the oxide-containing ceramic compact while pressing it with a pair of punches through the pair of release sheets to obtain the oxide-containing ceramic sintered compact;
A method for producing an oxide-containing ceramic sintered body, comprising:
The release sheet is formed from a carbide or nitride of at least one element selected from the group consisting of elements of Groups 4, 5, and 6 of the periodic table.

In this method for producing an oxide-containing ceramic sintered body, the release sheet is formed of a carbide or nitride of at least one element selected from the group consisting of elements of groups 4, 5, and 6 of the periodic table, so that the release sheet has low reactivity with the oxide-containing ceramic compact and the reaction with the oxide-containing ceramic compact is suppressed. Therefore, the effect on the properties of the obtained sintered body can be suppressed.

In the method for producing an oxide-containing ceramic sintered body of the present invention, the release sheet is preferably formed of at least one compound selected from the group consisting of WC, TiC, TaC, and NbC. This makes it possible to sufficiently suppress the reaction between the release sheet and the oxide-containing ceramic compact, thereby sufficiently suppressing the effect on the properties of the resulting sintered body.

In the method for producing an oxide-containing ceramic sintered body of the present invention, the thickness of the release sheet is preferably 0.1 mm or more and 5 mm or less. If the thickness of the release sheet is too thin, the oxide-containing ceramic molded body may diffuse through the gaps in the release sheet, reach the punch, and react with the punch. In contrast, if the thickness is 0.1 mm or more, the reaction between the oxide-containing ceramic molded body and the punch can be suppressed. If the thickness of the release sheet is too thick, the proportion of the release sheet in the hot press sintering furnace increases, and the productivity of the oxide-containing ceramic sintered body decreases. In contrast, if the thickness of the release sheet is 5 mm or less, the decrease in productivity of the oxide-containing ceramic sintered body can be suppressed.

In the method for producing an oxide-containing ceramic sintered body of the present invention, in the step (b), a spacer may be interposed between the release sheet and the punch. In this way, the oxide-containing ceramic compact and the punch can be protected.

In the method for producing an oxide-containing ceramic sintered body of the present invention, the release sheet is preferably one obtained by forming a slurry containing a release sheet raw material powder, a binder, and a dispersion medium into a sheet and then degreasing it. In this way, a release sheet with a large area can be obtained at low cost, and therefore an oxide-containing ceramic sintered body with a large area can be produced at low cost.

In the method for producing an oxide-containing ceramic sintered body of the present invention, the particle size of the release sheet raw material powder is preferably 0.1 μm or more and 10 μm or less. If the particle size of the release sheet raw material powder is too small, the powder may not be uniformly dispersed in the slurry, resulting in a non-uniform release sheet. In contrast, if the particle size of the release sheet raw material powder is 0.1 μm or more, the release sheet raw material powder is uniformly dispersed in the slurry, resulting in a homogeneous sheet. On the other hand, if the particle size of the release sheet raw material powder is too large, the components of the oxide-containing ceramic compact may diffuse into the gaps in the release sheet. In contrast, if the particle size of the release sheet raw material powder is 10 μm or less, a release sheet having density is obtained, and the diffusion of sample components into the gaps in the release sheet can be suppressed.

The release sheet of the present invention is
A release sheet used when hot-pressing an oxide-containing ceramic sintered body,
The release sheet is formed from a carbide or nitride of at least one element selected from the group consisting of elements of groups 4, 5, and 6 of the periodic table.

This release sheet is formed from a carbide or nitride of at least one element selected from the group consisting of elements from groups 4, 5, and 6 of the periodic table, and therefore has low reactivity with oxide-containing ceramic molded bodies, making it possible to obtain a release sheet that can suppress reaction with oxide-containing ceramic molded bodies.

In the release sheet of the present invention, the release sheet is preferably formed of at least one compound selected from the group consisting of WC, TiC, TaC, and NbC. In this way, a release sheet that can sufficiently suppress reaction with the oxide-containing ceramic molded body can be obtained.

In the release sheet of the present invention, the thickness of the release sheet is preferably 0.1 mm or more and 5 mm or less. If the thickness of the release sheet is too thin, the oxide-containing ceramic molded body may diffuse through the gaps in the release sheet, reach the punch, and react with the punch. In contrast, if the thickness is 0.1 mm or more, the reaction between the oxide-containing ceramic molded body and the punch can be suppressed. If the thickness of the release sheet is too thick, the proportion of the release sheet in the hot press sintering furnace increases, and the productivity of the oxide-containing ceramic sintered body decreases. In contrast, if the thickness of the release sheet is 5 mm or less, the decrease in productivity of the oxide-containing ceramic molded body can be suppressed.

Graphite furnace 10 cross-sectional view.

The method for producing an oxide-containing ceramic sintered body of the present embodiment includes the steps of:
(a) preparing an oxide-containing ceramic molded body before being fired into an oxide-containing ceramic sintered body;
(b) sandwiching the oxide-containing ceramic compact between a pair of release sheets and placing the compact in a hot press sintering furnace, and hot press sintering the oxide-containing ceramic compact while pressing it with a pair of punches through the pair of release sheets to obtain an oxide-containing ceramic sintered compact;
It includes.

In step (a), an oxide-containing ceramic molded body is prepared before being fired into an oxide-containing ceramic sintered body. Examples of the oxide-containing ceramic sintered body include ceramic sintered bodies containing oxides such as alumina, yttria, samaria, magnesia, and zirconia. The oxide-containing ceramic sintered body may be a ceramic sintered body containing an oxide as a main component (a component that occupies 50 mass% or more (including 100 mass%) of the total), or a ceramic sintered body containing an oxide as a secondary component (a component that occupies less than 50 mass% of the total). Examples of the ceramic sintered body containing an oxide as a secondary component include ceramic sintered bodies containing an oxide as an auxiliary component (oxide ceramics, non-oxide ceramics such as AlN, Si ₃ N ₄ , SiC, etc.) and ceramic sintered bodies having an oxide coating on the surface of the raw material powder (AlN, Si ₃ N ₄ , SiC, etc.).

In the step (a), the raw powder of the oxide-containing ceramic sintered body may be filled into a mold, and then uniaxial press molding may be performed at a predetermined pressure to produce the oxide-containing ceramic molded body. Alternatively, the raw powder of the oxide-containing ceramic sintered body may be mixed with a binder and a dispersion medium to prepare a slurry, and the slurry may be molded to produce the oxide-containing ceramic molded body. Since such an oxide-containing ceramic molded body may contain carbon components, it is preferable to use it after degreasing. The degreasing temperature may be set to a temperature at which the organic matter contained in the oxide-containing ceramic molded body is removed by heat. Examples of the binder include ethyl cellulose-based or butyral-based organic compounds. Examples of the dispersion medium include alcohols such as 2-ethylhexanol, octanol, terpineol, and butyl carbitol, and aromatic compounds such as xylene, and the like, which may be used alone or in combination. In addition, plasticizers, dispersants, sintering aids, etc. may be added. Examples of the plasticizer include organic compounds such as phthalates and adipic esters, and examples of the dispersant include esters of polyhydric alcohols and fatty acids such as sorbitan trioleate. Examples of the sintering aids include, for example, when the ceramic is alumina, _AlF3 , MgO, _{MgF2 , V2O3} , _CaO , CuO, _La2O3 , and the like, which can be added alone or in combination.

Alternatively, in step (a), the oxide-containing ceramic molded body may be produced by mold casting. In this case, a ceramic slurry containing the raw powder of the oxide-containing ceramic sintered body, a solvent, a dispersant, and a gelling agent may be poured into a mold, and the gelling agent may be chemically reacted to gel the ceramic slurry, thereby producing the oxide-containing ceramic molded body. The solvent is not particularly limited as long as it dissolves the dispersant and the gelling agent, but it is preferable to use a solvent having two or more ester bonds, such as a polybasic acid ester (e.g., dimethyl glutarate, etc.) or an acid ester of a polyhydric alcohol (e.g., triacetin, etc.). The dispersant is not particularly limited as long as it uniformly disperses the raw powder of the oxide-containing ceramic sintered body in the solvent, but it is preferable to use a polycarboxylic acid copolymer, a polycarboxylate, etc. The gelling agent may include, for example, isocyanates, polyols, and catalysts. Among these, the isocyanates are not particularly limited as long as they have an isocyanate group as a functional group, and examples thereof include tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), or modified forms thereof. The polyols are not particularly limited as long as they have two or more hydroxyl groups that can react with an isocyanate group, and examples thereof include ethylene glycol (EG), polyethylene glycol (PEG), propylene glycol (PG), and polypropylene glycol (PPG). The catalyst is not particularly limited as long as it promotes the urethane reaction between the isocyanates and the polyols, and examples thereof include triethylenediamine, hexanediamine, and 6-dimethylamino-1-hexanol. Here, the gelling reaction is a reaction in which the isocyanates and the polyols undergo a urethane reaction to form a urethane resin (polyurethane). The ceramic slurry gels due to the reaction of the gelling agent, and the urethane resin functions as an organic binder.

The release sheet used in step (b) is a material that does not react with the components of the hot press sintering furnace and does not deteriorate the properties of the ceramic molded body, and is a sheet formed of a carbide or nitride of at least one element selected from the group consisting of Groups 4, 5, and 6 of the periodic table. Examples of Group 4 include Ti, Zr, and Hf, examples of Group 5 include V, Nb, and Ta, and examples of Group 6 include Cr, Mo, and W. As the release sheet, a sheet formed of at least one compound selected from the group consisting of WC, TiC, TaC, and NbC is preferable, and a sheet formed of at least one compound selected from the group consisting of TaC and NbC is more preferable. A mixture of at least two or more compounds selected from the group consisting of WC, TiC, TaC, and NbC may also be used. The release sheet may be a molded sheet obtained by molding the raw material powder of the release sheet into a sheet, a sintered sheet obtained by sintering the molded sheet, or a single crystal sheet, but a molded sheet is preferred from the viewpoint of cost. When a molded sheet or a sintered sheet is used as the release sheet, it may contain impurities such as sintering aids as long as they do not affect the reactivity with the oxide-containing ceramic, the sinterability of the oxide-containing ceramic, or the properties of the sintered body. As the release sheet, a sheet with flat front and back surfaces (flat sheet) is preferred.

When a molded sheet obtained by molding the raw powder of the release sheet into a sheet shape is used as the release sheet, examples of the molding method include uniaxial press molding, tape molding, extrusion molding, casting molding, and injection molding, among which uniaxial press molding or tape molding is preferred. The raw powder of the release sheet may be molded as it is, or may be molded using a slurry prepared with a binder and a dispersion medium. Specific examples of the binder and dispersion medium are as described above. In addition, plasticizers, dispersants, sintering aids, etc. may be added as appropriate, and specific examples of these are also as described above. For example, when uniaxial press molding is adopted, the raw powder of the release sheet may be filled into a mold, and then uniaxial press molding may be performed at a predetermined pressure to produce a release sheet. If the release sheet contains carbon components, it is preferable to degrease the release sheet to remove the carbon components before use. In order to increase the density of the release sheet, the particle size of the raw powder of the release sheet is preferably 10 μm or less, and more preferably 5 μm or less. If the release sheet has high density, it is possible to prevent the oxide-containing ceramic molded body from diffusing into the release sheet when the oxide-containing ceramic molded body is sandwiched between a pair of release sheets and hot-press fired in step (b). The particle size of the raw material powder of the release sheet is preferably 0.1 μm or more, and more preferably 0.5 μm or more, in order to improve dispersibility when the release sheet is molded using a slurry of the raw material powder.

In step (b), the oxide-containing ceramic molded body is sandwiched between a pair of release sheets and placed in a hot press firing furnace, and the ceramic molded body is hot press fired while being pressed with a pair of punches through the pair of release sheets to obtain an oxide-containing ceramic sintered body. In this case, a spacer may be interposed between the release sheet and the punch. In addition, when firing a plurality of ceramic molded bodies, a spacer may be placed so as to contact the release sheet at any position. The thickness of the release sheet is not particularly limited, but when a molded sheet is used as the release sheet, if the thickness is too thin, the oxide-containing ceramic molded body may diffuse through the gaps in the release sheet in step (b) to reach the punch and react with the punch. In addition, when a spacer is placed between the release sheet and the punch, it may react with the spacer. In order to prevent the oxide-containing ceramic molded body from diffusing through the gaps in the release sheet to reach the punch or the spacer, the thickness of the release sheet is preferably 0.1 mm or more, more preferably 0.2 mm or more. On the other hand, if the thickness of the release sheet is too thick, the ratio of the release sheet in the hot press sintering furnace increases, and the productivity of the oxide-containing ceramic sintered body decreases. In order not to decrease the productivity of the oxide-containing ceramic sintered body, the thickness of the release sheet is preferably 5 mm or less, and more preferably 2 mm or less.

A cross-sectional view of a graphite furnace 10, which is an example of a hot press sintering furnace, is shown in FIG. 1. The graphite furnace 10 includes a graphite mold 12 having a heater function and a graphite sleeve 14 arranged inside the graphite mold 12 and divided vertically into two. When the oxide-containing ceramic molded body 16 is hot press sintered in the graphite furnace 10, the oxide-containing ceramic molded body 16 is sandwiched between a pair of release sheets 18, 18, and further sandwiched between a pair of graphite spacers 20, 20, and placed inside the graphite sleeve 14, and the oxide-containing ceramic molded body 16 is heated while being pressed by a pair of graphite punches 22, 22. When the oxide-containing ceramic is alumina, the sintering atmosphere in the hot press sintering is not particularly limited, but an inert gas such as nitrogen or Ar, or a vacuum atmosphere is preferred. The pressure is preferably 50 kgf/cm ² or more, more preferably 200 kgf/cm ² or more. The firing temperature (maximum temperature) is preferably 1700 to 2050°C, more preferably 1750 to 2000°C. When the temperature is lowered from the maximum temperature, it is preferable to apply a press pressure of 50 kgf/cm2 ^{or more} until the temperature reaches a predetermined temperature (a temperature set in the range of 1000 to 1400°C (preferably 1100 to 1300°C)). In the temperature range below the predetermined temperature, it is preferable to reduce the pressure to less than 50 kgf/ ^cm2 . In this way, it is possible to prevent cracks from occurring in the sintered body. The timing for reducing the press pressure is preferably 1200°C during temperature reduction from the viewpoint of crack suppression.

In the method for producing an oxide-containing ceramic sintered body of this embodiment described above, the release sheet is formed of a carbide or nitride of at least one element selected from the group consisting of elements of groups 4, 5, and 6 of the periodic table. Therefore, the release sheet has low reactivity with the oxide-containing ceramic molded body, and reaction with the oxide-containing ceramic molded body is suppressed. Therefore, the effect on the properties of the obtained sintered body can be suppressed.

In addition, the release sheet is preferably formed of at least one compound selected from the group consisting of WC, TiC, TaC, and NbC. This sufficiently suppresses the reaction between the release sheet and the oxide-containing ceramic compact, and sufficiently suppresses the effect on the properties of the resulting sintered body.

Furthermore, the thickness of the release sheet is preferably 0.1 mm or more and 5 mm or less. If the thickness of the release sheet is too thin, the oxide-containing ceramic molded body may diffuse through the gaps in the release sheet, reach the spacer (punch if there is no spacer, same below), and react with the spacer. On the other hand, if the thickness is 0.1 mm or more, the reaction between the oxide-containing ceramic molded body and the spacer can be suppressed. If the thickness of the release sheet is too thick, the proportion of the release sheet in the hot press sintering furnace increases, and the productivity of the oxide-containing ceramic sintered body decreases. On the other hand, if the thickness of the release sheet is 5 mm or less, the decrease in productivity of the oxide-containing ceramic sintered body can be suppressed.

Furthermore, in step (b), a spacer is interposed between the release sheet and the punch, thereby protecting the oxide-containing ceramic molding and the punch.

It is preferable that the release sheet is made by forming a slurry containing the release sheet raw material powder, a binder, and a dispersion medium into a sheet and then degreasing it. In this way, a release sheet with a large area can be obtained at low cost, and therefore a large-area oxide-containing ceramic sintered body can be produced at low cost.

The particle size of the release sheet raw material powder is preferably 0.1 μm or more and 10 μm or less. If the particle size of the release sheet raw material powder is too small, the powder may not be uniformly dispersed in the slurry, resulting in the production of a non-uniform release sheet. On the other hand, if the particle size of the release sheet raw material powder is 0.1 μm or more, the release sheet raw material powder is uniformly dispersed in the slurry, resulting in the production of a homogeneous sheet. On the other hand, if the particle size of the release sheet raw material powder is too large, the sample components may diffuse into the gaps in the release sheet. On the other hand, if the particle size of the release sheet raw material powder is 10 μm or less, a release sheet having density is obtained, and the diffusion of the sample components into the gaps in the release sheet can be suppressed.

It goes without saying that the present invention is in no way limited to the above-described embodiments, and can be implemented in various forms as long as they fall within the technical scope of the present invention.

Below, specific examples of producing oxide-containing ceramic sintered bodies are described as examples. Experimental Examples 1 to 4, 6 to 9, 11 to 14, and 16 to 19 correspond to examples of the present invention, and Experimental Examples 5, 10, 15, and 20 correspond to comparative examples. Note that the present invention is not limited to the following examples.

[Experimental Example 1]
(1) Preparation of alumina compacts Commercially available alumina powder with an average particle size (D50) of 0.6 μm was used as the raw material, and a press compact with a diameter of 20 mm and a thickness of 8 mm was obtained by uniaxial press molding using a mold. The pressing pressure was 200 kgf/ ^cm2 . The average particle size (D50) of each powder was measured using a particle size distribution measuring device (MT3300II, manufactured by Nikkiso).

(2) Preparation of release sheet: Commercially available tantalum carbide (TaC) powder with an average particle size (D50) of 1.6 μm was used as raw material, and two press molded bodies with a diameter of 20 mm and a thickness of 2 mm were prepared by uniaxial press molding using a mold, and these were used as TaC release sheets (flat sheets) for hot press sintering of alumina molded bodies. The pressing pressure was 200 kgf/ ^cm2 .

(3) Hot press sintering The TaC release sheet is laminated on the upper and lower surfaces of the alumina compact made in (1) to obtain a three-layer structure (TaC release sheet/alumina compact/TaC release sheet). In the graphite furnace 10 of Fig. 1, in argon, at a sintering temperature (maximum temperature reached) of 1700 ° C for 4 hours, and under a surface pressure of 200 kgf/cm ^2, hot press sintering is performed to obtain an alumina sintered body. After sintering, the TaC release sheet and the alumina sintered body are separated, and no reaction is observed between the TaC release sheet and the alumina sintered body by visual observation.

(4) Evaluation of alumina sintered body In order to evaluate the reactivity between the alumina sintered body and the TaC release sheet, an EDS analysis was carried out on the surface of the alumina sintered body that had been in contact with the TaC release sheet using a SEM/EDS device (manufactured by JEOL, JSM-6390). As a result, Ta and C components were not detected on the surface of the alumina sintered body. In addition, in order to check the presence or absence of a reaction between the TaC release sheet and the alumina sintered body, the obtained alumina sintered body was cut so as to pass through the center of the substrate in a direction perpendicular to the plate surface. The cut sample was smoothed on the cross section by lapping using diamond abrasive grains, and was mirror-finished by chemical mechanical polishing (CMP) using colloidal silica. A cross section of the alumina sintered body was observed using a SEM/EDS device (manufactured by JEOL, JSM-6390). As a result, Ta and C components were not detected inside the alumina sintered body, indicating that the alumina and the TaC release sheet did not react during firing.

[Experimental Example 2]
Except for using commercially available niobium carbide (NbC) powder with an average particle size (D50) of 2.3 μm as the raw material for the release sheet, an alumina sintered body was produced using the same method as in Experimental Example 1, and the reactivity was evaluated. As a result, after firing, the NbC release sheet and the alumina sintered body were separated, and no visible reaction was observed between the NbC release sheet and the alumina sintered body. In addition, Nb and C components were not detected in SEM/EDS observation of the surface and cross section of the alumina sintered body, indicating that the alumina and the NbC release sheet did not react during firing.

[Experimental Example 3]
Alumina sintered bodies were produced using the same method as in Experimental Example 1, except that commercially available tungsten carbide (WC) powder with an average particle size (D50) of 2.2 μm was used as the raw material for the release sheet, and the reactivity was evaluated. As a result, after firing, the WC release sheet and the alumina sintered body were separated, and no visible reaction was observed between the WC release sheet and the alumina sintered body. In addition, W and C components were not detected in SEM/EDS observation of the surface and cross section of the alumina sintered body, indicating that the alumina and the WC release sheet did not react during firing.

[Experimental Example 4]
Except for using commercially available titanium carbide (TiC) powder with an average particle size (D50) of 2.1 μm as the raw material for the release sheet, an alumina sintered body was produced using the same method as in Experimental Example 1, and the reactivity was evaluated. As a result, after firing, the TiC release sheet and the alumina sintered body were separated, and no visible reaction was observed between the TiC release sheet and the alumina sintered body. In addition, Ti and C components were not detected in SEM/EDS observation of the surface and cross section of the alumina sintered body, indicating that the alumina and the TiC release sheet did not react during firing.

[Experimental Example 5]
An alumina sintered body was produced in the same manner as in Experimental Example 1, except that an expanded graphite sheet (Nikafilm FL-400, manufactured by Nippon Carbon Co., Ltd.), which is a commercially available graphite sheet, was used as the release sheet, and the reactivity was evaluated. As a result, after firing, the expanded graphite sheet disappeared due to a reaction with the alumina sintered body. In addition, the alumina sintered body was thinned, and the formation of a reaction product between C (carbon) and the alumina component was confirmed. SEM/EDS observation of the deposits suggested that the deposits were metallic aluminum and aluminum carbide produced by the reduction of the alumina component by C.

[Experimental Example 6]
( ₁ ) Preparation of _Y2O3 compact Commercially available _Y2O3 powder with an average particle size (D50) of 0.4 μm was used as the raw material, and a compact with a diameter of 20 mm and a thickness of 8 mm was obtained by uniaxial press molding using a _mold . The pressing pressure was 200 kgf/ ^cm2 .

(2) Preparation of Release Sheet A TaC release sheet (flat sheet) was prepared in the same manner as in Experimental Example 1.

(3) Hot press sintering The TaC release sheet made in (2) is laminated on the upper and lower surfaces of the _{Y2O3 molded} body made in (1), and the three-layer structure (TaC release sheet/ _{Y2O3 molded} body/TaC release sheet) is hot press sintered in the graphite furnace 10 of Fig. 1 under the conditions of _N2 , sintering temperature (maximum reaching temperature) 1950 ° _C for 4 hours and surface pressure 200 kgf/ ^cm2 , to obtain _Y2O3 sintered body. After sintering, TaC release sheet and _{Y2O3 sintered} body are separated, _and no reaction is observed between TaC release sheet and _Y2O3 sintered body by visual observation.

(4) Evaluation of _{Y2O3 sintered} compact In order to evaluate the reactivity between _{Y2O3 sintered} compact and TaC release sheet, SEM/EDS observation was carried out on the surface of _{Y2O3 sintered} compact and the cross section of _Y2O3 sintered _compact in the same manner as in Experimental Example 1. As a _result , Ta and C components were not detected on the surface of _{Y2O3 sintered} compact and inside of _{Y2O3 sintered} compact, indicating that _Y2O3 and TaC release sheet do not react during firing.

[Experimental Example 7]
A Y ₂ O ₃ sintered body was produced using the same method as in Experimental Example 6, except that a commercially available niobium carbide (NbC) powder with an average particle size (D50) of 2.3 μm was used as the raw material for the release sheet, and the reactivity was evaluated. As a result, after firing, the NbC release sheet and the Y ₂ O ₃ sintered body were separated, and no visible reaction was observed between the NbC release sheet and the Y ₂ O ₃ sintered body. In addition, Nb and C components were not detected from the surface of the sintered body or the inside of the Y _{2 O 3 sintered body in SEM/EDS observation of the surface and cross section of the Y 2 O 3 sintered} body, indicating that Y ₂ O ₃ and the NbC release sheet did not react during firing.

[Experimental Example 8]
A Y ₂ O ₃ sintered body was prepared using the same method as in Experimental Example 6, except that a commercially available tungsten carbide (WC) powder with an average particle size (D50) of 2.2 μm was used as the raw material for the release sheet, and the reactivity was evaluated. As a result, it was found that the Y ₂ O ₃ sintered body and the WC release sheet were adhered to each other after firing. The obtained three-layer structure (WC release sheet/Y ₂ O ₃ sintered body/WC release sheet) was cut so as to pass through the center of the substrate in a direction perpendicular to the plate surface. The cut sample was smoothed on the cross section by lapping using diamond abrasive grains, and was mirror-finished by chemical mechanical polishing (CMP) using colloidal silica. The obtained cross-sectional sample was observed around the WC release sheet/Y ₂ O ₃ sintered body interface using a SEM/EDS device (JSM-6390, manufactured by JEOL Ltd.). As a result, trace amounts of W and C components were detected in the range of about 7 _μm in the thickness direction inside _{the Y2O3} sintered body from the _Y2O3 sintered body/WC release sheet interface. These results show that _Y2O3 and the WC release sheet hardly react with each other during firing, and that the WC release sheet can be used as _a release material. However, it was shown that processing is required to separate the WC release sheet after firing, that the WC components are slightly diffused inside _{the Y2O3} , and that the diffused area needs to be removed by grinding or the like.

[Experimental Example 9]
A Y ₂ O ₃ sintered body was prepared using the same method as in Experimental Example 6, except that a commercially available titanium carbide (TiC) powder with an average particle size (D50) of 2.1 μm was used as the raw material for the release sheet, and the reactivity was evaluated. As a result, it was found that the Y ₂ O ₃ sintered body and the TiC release sheet were fixed together after firing. The obtained three-layer structure (TiC release sheet/Y ₂ O ₃ sintered body/TiC release sheet) was cut so as to pass through the center of the substrate in a direction perpendicular to the plate surface. The cut sample was smoothed on the cross section by lapping using diamond abrasive grains, and was mirror-finished by chemical mechanical polishing (CMP) using colloidal silica. The obtained cross-sectional sample was observed around the TiC release sheet/Y ₂ O ₃ sintered body interface using a SEM/EDS device (JSM-6390, manufactured by JEOL Ltd.). As a result, trace amounts of Ti and C components were detected in the range of about 9 μm in the thickness direction inside _{the Y2O3} sintered body from the _Y2O3 sintered body/TiC release sheet interface. These results show that _Y2O3 and the _TiC release sheet hardly react during firing, and that the TiC _release sheet can be used as a release material. However, it was shown that processing is required to separate the TiC release sheet after firing, that the TiC component is slightly diffused inside _{the Y2O3} , and that the diffused area needs to be removed by grinding or the like.

[Experimental Example 10]
A Y ₂ O ₃ sintered body was produced in the same manner as in Experimental Example 6, except that a commercially available graphite sheet (Nikafilm FL-400, manufactured by Nippon Carbon) was used as the release sheet, and the reactivity was evaluated. As a result, after firing, the expanded graphite sheet disappeared due to a reaction with the Y ₂ O ₃ sintered body. In addition, the Y ₂ O ₃ sintered body was thinned, and the formation of a reaction product between C and the Y ₂ O ₃ component was confirmed. As a result of SEM/EDS observation of the reaction product, it was suggested that the reaction product was metallic yttrium, yttrium carbide, and yttrium nitride generated by the reduction and reductive nitridation of the Y ₂ O ₃ component by C.

[Experimental Example 11]
(1) Preparation of _Si3N4 compact 100 parts by mass of commercially available _{Si3N4 powder} with an average particle size (D50) of 0.7 μm were added with ₃ parts by mass of commercially available _{Al2O3 powder} with an average particle size (D50) of 0.6 μm and 5 parts by mass of commercially available _{Y2O3 powder} with an average particle size (D50) of 0.4 μm as sintering aids, and then mixed in ethanol for 24 hours using a pot mill. The resulting slurry was dried, sieved through a #100 sieve, and a press compact with a diameter of 20 mm and a thickness of 8 mm was obtained by uniaxial press molding using a mold. The pressing pressure was 200 kgf/ ^cm2 .

(2) Preparation of release sheet 100 parts by mass of commercially available tantalum carbide (TaC) powder with an average particle size (D50) of 1.6 μm was mixed with 3.2 parts by mass of acrylic binder (Orikox #2434T, manufactured by Kyoeisha Chemical Co., Ltd.), 1.3 parts by mass of bis(2-ethylhexyl) phthalate (DOP, manufactured by J-Plus Co., Ltd.) as a plasticizer, 0.2 parts by mass of polyether ester acid amine (DA-234, manufactured by Kusumoto Chemical Co., Ltd.) as a dispersant, and xylene and 1-butanol as a dispersion medium. The amount of the dispersion medium was adjusted so that the slurry viscosity was 20000 cP. The slurry thus prepared was tape-molded onto a PET film by the doctor blade method so that the thickness after drying was 200 μm, to obtain a molded sheet. This molded sheet was sandwiched between alumina setters and placed in a degreasing furnace, where it was degreased in nitrogen at 500° C. for 6 hours to produce a TaC release sheet (flat sheet) to be used when hot-pressing the Si ₃ N ₄ molded body.

(3) Hot press sintering The three-layer structure (TaC release sheet/Si ₃ N ₄ compact/TaC release sheet ₎ that is laminated on the upper and lower surfaces of the Si 3 N ₄ compact made in (1) and the TaC release sheet made in (2) is hot press sintered in the graphite furnace 10 of Fig. 1 under the conditions of sintering temperature (maximum reaching temperature) 1800 ° C in nitrogen, 4 hours, and surface pressure 200 kgf / cm ^2, to obtain Si ₃ N ₄ sintered body. After sintering, TaC release sheet and Si ₃ N ₄ sintered body are separated, and no reaction is observed between TaC release sheet and Si ₃ N ₄ sintered body by visual observation.

(4) Evaluation of _Si3N4 sintered body In _order to evaluate the reactivity of _Si3N4 sintered body with TaC release sheet, the surface of _{Si3N4 sintered} body and the cross section of _{Si3N4 sintered} body are observed by SEM/ _EDS in the same manner as in Experimental Example 1. As a result, Ta and C components are not detected from the surface of _{Si3N4 sintered} body and the _inside of _{Si3N4 sintered} body _{, and it is shown that Si3N4 and auxiliary components Al2O3, Y2O3 do not react with} TaC release sheet during firing.

[Experimental Example 12]
A Si ₃ N ₄ sintered body was produced using the same method as in Experimental Example 11, except that a commercially available niobium carbide (NbC) powder with an average particle size (D50) of 2.3 μm was used as the raw material for the release sheet, and the reactivity was evaluated. As a result, after firing, the NbC release sheet and the Si ₃ N ₄ sintered body were separated, and no visible reaction was observed between the NbC release sheet and the Si ₃ N ₄ sintered body. In addition, Nb and C components were not detected in the SEM/EDS observation of the surface and cross section of the Si ₃ N ₄ sintered body, indicating that Si ₃ N ₄ and the auxiliary components Al ₂ O ₃ and Y ₂ O ₃ did not react with the NbC release sheet during firing.

[Experimental Example 13]
A Si ₃ N ₄ sintered body was prepared using the same method as in Experimental Example 11, except that a commercially available tungsten carbide (WC) powder with an average particle size (D50) of 2.2 μm was used as the raw material for the release sheet, and the reactivity was evaluated. As a result, after firing, the WC release sheet and the Si ₃ N ₄ sintered body were separated, and no visible reaction was observed between the WC release sheet and the Si ₃ N ₄ sintered body. In addition, W and C components were not detected in the SEM/EDS observation of the surface and cross section of the Si ₃ N ₄ sintered body, indicating that Si ₃ N ₄ and the auxiliary components Al ₂ O ₃ and Y ₂ O ₃ did not react with the WC release sheet during firing.

[Experimental Example 14]
A Si ₃ N ₄ sintered body was produced using the same method as in Experimental Example 11, except that a commercially available titanium carbide (TiC) powder with an average particle size (D50) of 2.1 μm was used as the raw material for the release sheet, and the reactivity was evaluated. As a result, after firing, the TiC release sheet and the Si ₃ N ₄ sintered body were separated, and no visible reaction was observed between the TiC release sheet and the Si ₃ N ₄ sintered body. In addition, Ti and C components were not detected in the SEM/EDS observation of the surface and cross section of the Si ₃ N ₄ sintered body, indicating that Si ₃ N ₄ and the auxiliary components Al ₂ O ₃ and Y ₂ O ₃ did not react with the TiC release sheet during firing.

[Experimental Example 15]
A Si ₃ N ₄ sintered body was prepared in the same manner as in Experimental Example 11, except that a commercially available graphite sheet (Nicafilm FL-400, manufactured by Nippon Carbon) was used as the release sheet, and the reactivity was evaluated. As a result, the expanded graphite sheet and the Si ₃ N ₄ sintered body were not separated after firing. A part of the expanded graphite sheet was lost due to the reaction with Al ₂ O ₃ and Y ₂ O ₃ , which are sintering aids in the Si ₃ N ₄ sintered body, and the formation of a reaction product between C and the Al ₂ O ₃ and Y ₂ O ₃ components was recognized. As a result of carrying out SEM/EDS observation of the reaction product, it was suggested that the reaction product was metallic aluminum, aluminum carbide, metallic yttrium, and yttrium carbide.

[Experimental Example 16]
(1) Preparation of SiC molded body 100 parts by mass of commercially available SiC powder with an average particle size (D50) of 0.7 μm were added with 18 parts by mass of commercially available AlN powder with an average particle size (D50) of 0.5 μm and 12 parts by mass of commercially available Y ₂ O ₃ powder with an average particle size (D50) of 0.4 μm as sintering aids, and then mixed in ethanol for 24 hours using a pot mill. The resulting slurry was dried, sieved through a #100 sieve, and a press molded body with a diameter of 20 mm and a thickness of 8 mm was obtained by uniaxial press molding using a mold. The pressing pressure was 200 kgf/cm ² .

(2) Preparation of release sheet 100 parts by mass of commercially available tantalum carbide (TaC) powder with an average particle size (D50) of 1.6 μm was mixed with 3.2 parts by mass of acrylic binder (Orikox #2434T, manufactured by Kyoeisha Chemical Co., Ltd.), 1.3 parts by mass of bis(2-ethylhexyl) phthalate (DOP, manufactured by J-Plus Co., Ltd.) as a plasticizer, 0.2 parts by mass of polyether ester acid amine (DA-234, manufactured by Kusumoto Chemical Co., Ltd.) as a dispersant, and xylene and 1-butanol as a dispersion medium. The amount of the dispersion medium was adjusted so that the slurry viscosity was 20000 cP. The slurry thus prepared was tape-molded onto a PET film by the doctor blade method so that the thickness after drying was 200 μm, to obtain a molded sheet. This molded sheet was sandwiched between alumina setters and placed in a degreasing furnace, where it was degreased in nitrogen at 500° C. for 6 hours to produce a TaC release sheet (flat sheet) to be used when hot-pressing the SiC molded body.

(3) Hot press sintering The three-layer structure (TaC release sheet/SiC compact/TaC release sheet) that is laminated on the upper and lower surfaces of the SiC compact made in (1) and the TaC release sheet made in (2) is hot press sintered in the graphite furnace 10 of Fig. 1 under the conditions of sintering temperature (maximum reaching temperature) 2000 ° C for 4 hours and surface pressure 200 kgf / cm ² in argon, and obtain SiC sintered body. After sintering, TaC release sheet and SiC sintered body are separated, and no reaction is observed between TaC release sheet and SiC sintered body by visual observation.

(4) Evaluation of SiC sintered body In order to evaluate the reactivity between SiC sintered body and TaC release sheet, SEM/EDS observation was carried out on the surface of SiC sintered body and the cross section of SiC sintered body in the same manner as in Experimental Example 1. As a result, Ta and C components were not detected on the surface of SiC sintered body and inside of SiC sintered body, and it was shown that SiC and auxiliary components AlN and _Y2O3 did not react with TaC release _sheet during firing.

[Experimental Example 17]
A SiC sintered body was produced using the same method as in Experimental Example 16, except that a commercially available niobium carbide (NbC) powder with an average particle size (D50) of 2.3 μm was used as the raw material for the release sheet, and the reactivity was evaluated. As a result, after firing, the NbC release sheet and the SiC sintered body were separated, and no visible reaction was observed between the NbC release sheet and the SiC sintered body. In addition, Nb and C components were not detected in SEM/EDS observation of the surface and cross section of the SiC sintered body, indicating that SiC and the auxiliary components AlN and Y ₂ O ₃ did not react with the NbC release sheet during firing.

[Experimental Example 18]
A SiC sintered body was produced using the same method as in Experimental Example 16, except that a commercially available tungsten carbide (WC) powder with an average particle size (D50) of 2.2 μm was used as the raw material for the release sheet, and the reactivity was evaluated. As a result, after firing, the WC release sheet and the SiC sintered body were separated, and no visible reaction was observed between the WC release sheet and the SiC sintered body. In addition, W and C components were not detected in SEM/EDS observation of the surface and cross section of the SiC sintered body, indicating that SiC and the auxiliary components AlN and Y ₂ O ₃ did not react with the WC release sheet during firing.

[Experimental Example 19]
A SiC sintered body was produced using the same method as in Experimental Example 16, except that a commercially available titanium carbide (TiC) powder with an average particle size (D50) of 2.1 μm was used as the raw material for the release sheet, and the reactivity was evaluated. As a result, after firing, the TiC release sheet and the SiC sintered body were separated, and no visible reaction was observed between the TiC release sheet and the SiC sintered body. In addition, Ti and C components were not detected in SEM/EDS observation of the surface and cross section of the SiC sintered body, indicating that SiC and the auxiliary components AlN and Y ₂ O ₃ did not react with the TiC release sheet during firing.

[Experimental Example 20]
A SiC sintered body was produced in the same manner as in Experimental Example 16, except that an expanded graphite sheet (Nikafilm FL-400, manufactured by Nippon Carbon Co., Ltd.), which is a commercially available graphite sheet, was used as the release sheet, and the reactivity was evaluated. As a result, the expanded graphite sheet and the SiC sintered body were not separated after firing. A part of the expanded graphite sheet disappeared due to a reaction with Y ₂ O ₃ , which is a sintering aid in the SiC sintered body, and the formation of a reaction product between C and the Y ₂ O ₃ component was confirmed. SEM/EDS observation of the reaction product suggested that the reaction product was metallic yttrium and yttrium carbide.

This application claims priority from Japanese Patent Application No. 2019-215374, filed on November 28, 2019, the entire contents of which are incorporated herein by reference.

The present invention can be used when hot press firing oxide-containing ceramic sintered bodies.

10 Graphite furnace, 12 graphite mold, 14 graphite sleeve, 16 ceramic molding, 18 release sheet, 20 graphite spacer, 22 graphite punch.

Claims (9)

(a) preparing an oxide-containing ceramic molded body before being fired into an oxide-containing ceramic sintered body;
(b) sandwiching the oxide-containing ceramic compact between a pair of release sheets and placing it in a hot press sintering furnace, and hot press sintering the oxide-containing ceramic compact while pressing it with a pair of punches through the pair of release sheets to obtain the oxide-containing ceramic sintered compact;
A method for producing a ceramic sintered body comprising:
The release sheet is formed of a carbide of at least one element selected from the group consisting of elements of Groups 4, 5, and 6 of the periodic table.
Method for producing oxide-containing ceramic sintered bodies. The release sheet is formed of at least one compound selected from the group consisting of WC, TiC, TaC and NbC,
A method for producing the oxide-containing ceramic sintered body according to claim 1. The thickness of the release sheet is 0.1 mm or more and 5 mm or less.
A method for producing the oxide-containing ceramic sintered body according to claim 1 or 2. In the step (b), a spacer is interposed between the release sheet and the punch.
A method for producing the oxide-containing ceramic sintered body according to any one of claims 1 to 3. The release sheet is obtained by forming a slurry containing a release sheet raw material powder, a binder, and a dispersion medium into a sheet shape and then degreasing the same.
A method for producing the oxide-containing ceramic sintered body according to any one of claims 1 to 4. The particle size of the release sheet raw material powder is 0.1 μm or more and 10 μm or less.
A method for producing the oxide-containing ceramic sintered body according to claim 5. A release sheet used when hot-pressing an oxide-containing ceramic sintered body,
The release sheet is formed of a carbide of at least one element selected from the group consisting of elements of Groups 4, 5, and 6 of the periodic table.
Release sheet. The release sheet is formed of at least one compound selected from the group consisting of WC, TiC, TaC and NbC,
The release sheet according to claim 7. The thickness of the release sheet is 0.1 mm or more and 5 mm or less.
The release sheet according to claim 7 or 8.

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