Method for producing a refractory sintered body and method for supplying boron into a nuclear fusion reactor

Abstract

Provided are a manufacturing method capable of molding a difficult-to-sinter powder of an inorganic substance that is difficult to mold and sintering a difficult-to-sinter material without applying pressure, and a method for supplying boron into a fusion reactor. 【Solution means】The method for manufacturing a difficult-to-sinter body includes a molding step of filling a raw material of a difficult-to-sinter powder of an inorganic substance that is difficult to mold into a heat-resistant container made of metal, and heating the difficult-to-sinter powder together with the container at a temperature lower than the lower melting point among the melting points of the difficult-to-sinter powder under normal pressure in a vacuum or an inert atmosphere to obtain a difficult-to-sinter body. A fixed amount of the difficult-to-sinter body manufactured by the method for manufacturing a difficult-to-sinter body is supplied into a fusion reactor.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a refractory sintered body and a method for supplying boron into a nuclear fusion reactor.

Background Art

[0002] Currently, high melting point, high strength, and lightweight engineering ceramic materials such as boron, boron nitride, boron carbide, zirconia, and yttria have attracted attention as lightweight and highly durable materials in fields such as aerospace and the automotive industry. The need for an inexpensive manufacturing technology for engineering ceramic materials having such characteristics is increasing.

[0003] The molding methods can be classified into wet molding and dry molding. Wet molding is typified by casting molding in which an organic binder, a dispersant, a sintering aid, and water are mixed with raw material powder to form a slurry, which is then poured into a molding die for molding, and extrusion molding or injection molding in which the slurry is extruded for molding. This method cannot be used for materials that react with the liquid to be mixed, and is mainly used for molding ceramics. On the other hand, dry molding is typified by press molding in which raw material powder is put into a die and pressed, and can be applied to all materials. However, if the fluidity of the powder is poor like that of a refractory sintered material, the shape cannot be maintained even when pressed, so an organic binder as an adhesive is mixed and press molding is performed. When an organic binder is used, a debinder for removing the organic binder during heating is required. However, since the organic binder cannot burn in a vacuum or an inert gas, it is necessary to add water vapor for decomposition, but it cannot be applied to raw materials that react with water.

[0004] In addition, the sintering of refractory materials is difficult, and pressure sintering, which applies pressure and heats, is used, or a method of mixing a sintering aid and sintering by heating under normal pressure or in a vacuum is used. However, the method of sintering while applying high pressure can only sinter flat plate shapes and cannot be applied to complex shapes. The method of adding a sintering aid is a method of generating a liquid phase in the voids of the main raw material by mixing a low melting point material and sintering with the viscous stress of the liquid phase. Therefore, mixing a low melting point material reduces the heat resistance temperature and mechanical strength (see Patent Document 1 and Patent Document 2).

[0005] Furthermore, carbon furnaces are mainly used for high-temperature furnaces, but this causes a problem that the raw material powder is carbonized.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to solve the above problems and provide a manufacturing method capable of molding refractory powder that is difficult to mold and sintering refractory materials without applying pressure. Another object of the present invention is to provide a method for supplying boron produced by the above method into a nuclear fusion reactor.

Means for Solving the Problems

[0008] In order to solve the above problems, the manufacturing method of a refractory body of the present invention includes a molding step of filling a heat-resistant container with a raw material of refractory powder, which is an inorganic substance, and molding it, and after the molding step, heating and firing the raw material filled in the container to obtain a refractory body maintained in a shape along the inner surface shape of the container.

[0009] Further, it is preferable that the container is formed of a deployable metal foil. "Deployable" means that, from the shape of the container, it includes the meaning that it can be extended or torn by an external force.

[0010] The shape of this container may be not only a simple shape but also a complex shape, as long as it is a shape into which the hard-to-sinter powder can be filled. When the hard-to-sinter powder is covered with a metal container and fired in a carbon furnace, carbonization of the hard-to-sinter powder at high temperatures is prevented.

[0011] Further, in the heating step, it is preferable to heat the container and the hard-to-sinter powder together at a temperature lower than the lower melting point of the melting points of the container and the hard-to-sinter powder under normal pressure in a vacuum or an inert atmosphere to obtain a hard-to-sinter body.

[0012] Further, the hard-to-sinter powder contains any one of boron, silicon carbide, yttria, boron nitride, zirconia, boron carbide, tungsten carbide, titanium nitride, titanium carbide, molybdenum, tungsten, and alumina.

[0013] Further, the hard-to-sinter powder may be boron. Further, the hard-to-sinter powder may be silicon carbide. Further, the hard-to-sinter powder may be yttria.

[0014] The hard-to-sinter powder may be boron nitride. The hard-to-sinter powder may be zirconia. The hard-to-sinter powder may be boron carbide.

[0015] The hard-to-sinter powder may be tungsten carbide. The hard-to-sinter powder may be titanium nitride. The hard-to-sinter powder may be titanium carbide.

[0016] The refractory powder may be molybdenum. The refractory powder may be tungsten. The refractory powder may be alumina.

[0017] The refractory compact may be formed into a pellet shape by being molded by the container. As a method for supplying boron into a fusion reactor, it is proposed to supply a certain amount of the refractory compact made of boron as a raw material produced by the method for producing the refractory compact into the fusion reactor.

Advantages of the Invention

[0018] According to the present invention, a refractory powder can be molded, and a refractory compact can be produced without applying pressure.

Brief Description of the Drawings

[0019]

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Figure 13

Mode for Carrying Out the Invention

[0020] <1. Refractory Powder> The refractory powder is an inorganic substance containing ceramic powder, metal powder, or semi-metal powder. Examples of the ceramic powder include powders of silicon carbide, yttria, boron nitride, zirconia, boron carbide, tungsten carbide, titanium nitride, titanium carbide, and alumina. These refractory powders are typical examples where molding is difficult without adding an organic binder.

[0021] Examples of the metal powder include powders of molybdenum and tungsten. Examples of the semi-metal powder include powder of boron. The purity of the main component of these refractory powders is preferably 95% or more. Further, it is still better if the purity of the main component of the refractory powder is 99% or more, but it is not limited.

[0022] The particle size of the powder is preferably from several nm to several μm, and particularly preferably from submicron to about several μm, but it is not limited. <2. Sintering Conditions> <2.1. Sintering Temperature> When the melting point of the refractory powder exceeds the melting point of tantalum (3020 °C), the upper limit of the heating temperature for sintering the refractory sintered body under vacuum or normal pressure in the heating process is less than the melting point of tantalum.

[0023] Also, when the melting point of the refractory powder is below the melting point of tantalum (3020 °C), the upper limit of the heating temperature for forming the refractory sintered body under normal pressure is less than the melting point of the refractory powder. Also, after forming the refractory powder by filling it into a heat-resistant container, the sintering temperature under normal pressure is set to be higher than the sintering temperature when sintering under high pressure.

[0024] Generally, in refractory sintered bodies (for example, materials such as zirconia), the higher the sintering temperature, the higher the density. Therefore, the influence of the sintering temperature on the density is significant. This is because heating promotes the diffusion and bonding of atoms, reducing the porosity and increasing the density of the entire material.

[0025] The melting point of silicon carbide is 2700°C, which is below the melting point of tantalum (3020°C). The sintering temperature of silicon carbide is preferably 1100 - 2680°C. The melting point of yttria is 2425°C, which is below the melting point of tantalum (3020°C). The sintering temperature of yttria is preferably 1400 - 2400°C.

[0026] The melting point of boron nitride is 2700°C, which is below the melting point of tantalum (3020°C). The sintering temperature of boron nitride is preferably 1200 - 2680°C. The melting point of zirconia is 2715°C, which is below the melting point of tantalum (3020°C). The sintering temperature of zirconia is preferably 1100 - 2700°C.

[0027] The melting point of boron carbide is 2427°C, which is below the melting point of tantalum (3020°C). The sintering temperature of boron carbide is preferably 1400 - 2400°C. The melting point of tungsten carbide is 2870°C, which is below the melting point of tantalum (3020°C). The sintering temperature of tungsten carbide is preferably 1400 - 2850°C.

[0028] The melting point of titanium nitride is 2700°C, which is below the melting point of tantalum (3020°C). The sintering temperature of titanium nitride is preferably 1400 - 2680°C. The melting point of titanium carbide is 3160°C, which exceeds the melting point of tantalum (3020°C). The sintering temperature of titanium carbide is preferably 1000 - 3000°C.

[0029] The melting point of molybdenum is 2600 °C, which is below the melting point of tantalum (3020 °C). The sintering temperature of molybdenum is preferably 1400 - 2580 °C. The melting point of tungsten is 3422 °C, which exceeds the melting point of tantalum (3020 °C). The sintering temperature of tungsten is preferably 1400 - 3000 °C, which is below the melting point of tantalum (3020 °C).

[0030] The melting point of boron is 2300 °C, which is below the melting point of tantalum (3020 °C). The sintering temperature of boron is preferably 1400 - 2280 °C. The melting point of alumina is 2072 °C, which is below the melting point of tantalum (3020 °C). The sintering temperature of alumina is preferably 1100 - 2050 °C.

[0031] Note that as a representative example, the heating furnace is a carbon furnace, but it is not limited to a carbon furnace. When using a carbon furnace, the refractory powder is covered with a metal container, so that the refractory powder can be prevented from being carbonized by the carbon furnace at high temperatures.

[0032] <2.2. Holding Time> The holding time may be determined according to the type of refractory powder, the thickness of the refractory body, etc., and is not limited, but 1 hour or more and 10 hours or less is preferable.

[0033] <2.3. Firing Atmosphere> Atmospheric pressure sintering is generally carried out in air or an inert gas. The manufacturing method of the present invention is pressureless sintering carried out in an inert atmosphere with an inert gas such as argon, or in a vacuum.

[0034] In addition, for sintering, there are generally liquid phase sintering in which an additive is used to generate a liquid phase at a high temperature to promote densification, and solid phase sintering in which densification is achieved by mass transfer between solid phases without passing through a liquid phase. <3. Container> The heat-resistant container is formed of a metal plate, for example, a tantalum plate, or a metal foil, for example, a tantalum foil. The shape of the container is not limited, but after the container body is filled with the refractory powder, the container body may be sealed with a lid box in a form where the refractory powder is sealed. In this case, the container includes the container body and the lid box. Alternatively, instead of the lid box, the open side of the container used when filling may be crushed to seal. In this way, the refractory powder filled in the container is covered by the container (including the lid) by the lid box or by crushing. This process corresponds to the molding process.

[0035] The shape of the container may be not only a simple shape but also a complex shape as long as it can be filled with the refractory powder. Note that the heat-resistant container refers to one that can withstand the heating temperature in the heating process.

[0036] For example, the shape of the container can include, but is not limited to, a cylindrical shape and a square box shape. Figs. 1(a) and 1(b) are examples of a cylindrical container. Fig. 1(a) shows a cylindrical container 10 formed by winding a tantalum foil around a cylinder. Since the tantalum foil has flexibility, as shown in Fig. 1(a), the lower end 10a is crushed and closed. In this state, after filling the refractory powder into the container 10 from the open upper end 10b, as shown in Fig. 1(b), the upper end 10b is crushed and thus closed.

[0037] Fig. 2(a) is an example of a square box-shaped container 20. The square box-shaped container 20 (in this case, the container body) is formed into a bottomed box shape, for example, by press-forming a tantalum plate.

[0038] In the state shown in Fig. 2(a), after the refractory powder is filled into the container 20 (container body) from the open upper end, as shown in Fig. 2(b), a lid box 22 formed into a covered square box shape by press-forming is also placed on it.

[0039] <Example> <Examples 1 to 7> Examples 1 to 7 will be described below.

[0040] In Examples 1 and 2, the 6-mm-diameter container 10 in Fig. 1(a) was filled with boron powder and compacted along the longitudinal direction of the container 10. Then, after the upper end 10b of the container 10 was crushed, firing was performed in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were a temperature increase of 30°C per minute and holding at the sintering temperature of 2000°C for 1 hour. The heating here corresponds to the heating process. The refractory compacts of Examples 1 and 2 yielded 0.16 g.

[0041] In Example 3, the 6-mm-diameter container 10 in Fig. 1(a) was filled with boron powder and compacted along the longitudinal direction of the container 10. Then, after the upper end 10b of the container 10 was crushed, firing was performed in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were a temperature increase of 30°C per minute and holding at the sintering temperature of 2000°C for 5 hours. The heating here corresponds to the heating process. The refractory compact of Example 3 yielded 0.27 g.

[0042] In Example 4, the 6-mm-diameter container 10 in Fig. 1(a) was filled with boron powder and compacted along the longitudinal direction of the container 10. Then, after the upper end 10b of the container 10 was crushed, firing was performed in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were a temperature increase of 30°C per minute and holding at the sintering temperature of 2000°C for 10 hours. The heating here corresponds to the heating process. The refractory compact of Example 4 yielded 0.49 g.

[0043] In Example 5, the 6-mm-diameter container 10 in Fig. 1(a) was filled with boron powder and compacted along the longitudinal direction of the container 10. Then, after the upper end 10b of the container 10 was crushed, firing was performed in a carbon furnace under vacuum at a sintering temperature of 1800°C. The heating conditions were a temperature increase of 30°C per minute and holding at the sintering temperature of 1800°C for 1 hour. The heating here corresponds to the heating process. The refractory compact of Example 5 yielded 0.78 g.

[0044] In Example 6, the 6-mm-diameter container 10 in Fig. 1(a) was filled with boron powder and compacted along the longitudinal direction of the container 10. Then, after the upper end 10b of the container 10 was crushed, firing was performed in a carbon furnace under vacuum at a sintering temperature of 1600°C. The heating conditions were such that the temperature was raised at 30°C per minute and held at the sintering temperature of 1600°C for 1 hour. The heating here corresponds to the heating process. The refractory sintered body of Example 6 obtained was 1.02 g.

[0045] In Example 7, the 6-mm-diameter container 10 in Fig. 1(a) was filled with boron powder and compacted along the longitudinal direction of the container 10. Then, after the upper end 10b of the container 10 was crushed, firing was performed in a carbon furnace under vacuum at a sintering temperature of 1400°C. The heating conditions were such that the temperature was raised at 30°C per minute and held at the sintering temperature of 1400°C for 1 hour. The heating here corresponds to the heating process. The refractory sintered body of Example 7 obtained was 0.42 g.

[0046] Note that the container 10 used in Examples 1 to 7 was formed to have a diameter of 6 mm by winding tantalum foil with a thickness of 50 μm around a 6-mm-diameter rod. The filling amount of boron powder into the container 10 depends on the length of the container in the example.

[0047] As the refractory powder of boron, a commercially available product (manufactured by Nilaco Corporation, product number: B-054101, purity: 98%) was used.

[0048]

Table 1

[0049] <Refractory sintered bodies of Example 1 and Example 2> Figs. 3(a) and 3(b) are photographs of the refractory sintered bodies of Example 1 and Example 2. In Example 1 and Example 2, it was confirmed that sintering shrinkage progressed from the shape filled in the container 10 by firing and was formed into a columnar shape along the inner surface shape of the container and this shape was maintained.

[0050] <Hard-to-sinter compacts of Example 3 and Example 4> Figures 3(c) and 3(d) are photographs of the hard-to-sinter compacts of Example 3 and Example 4. In Example 3 and Example 4, it was confirmed that sintering shrinkage progressed from the shape filled in the container 10 by firing and was formed into a columnar shape along the inner surface shape of the container and maintained this shape. Also, since the holding time of Example 4 is longer than that of Example 3, it was confirmed that sintering shrinkage was more advanced.

[0051] <Hard-to-sinter compact of Example 5> Figure 3(e) is a photograph of the hard-to-sinter compact of Example 5. In Example 5, it was confirmed that sintering shrinkage progressed from the shape filled in the container 10 by firing and was sintered into the same columnar shape as the shape of the tantalum container along the inner surface shape of the container and maintained this shape. As shown in Figure 3(e), the lower end of the hard-to-sinter compact spreads out in a flaring shape as it goes downward. This is because the lower end of the container 10 is crushed, and the lower end side of the container 10 has a shape where the thickness gradually becomes thinner, and it was confirmed that the shape of the hard-to-sinter compact was also formed into the shape of the tantalum container.

[0052] <Hard-to-sinter compact of Example 6> Figure 3(f) is a photograph of the hard-to-sinter compact of Example 6. In Example 6, it was confirmed that sintering shrinkage progressed from the shape filled in the container 10 by firing and was formed into the same columnar shape as the shape of the tantalum container along the inner surface shape of the container and maintained this shape. As shown in Figure 3(f), although two hard-to-sinter compacts are shown, they are separated into two when taken out of the container 10. It has a slightly embrittled tendency compared to the hard-to-sinter compact of Example 5. However, when the hard-to-sinter compact of Example 6 is premised on use in pellet (columnar) form, it is at a level where there is no problem in use in pellet (columnar) form.

[0053] <Hard-to-sinter compact of Example 7> Figure 3(g) is a photograph of the refractory sintered compact of Example 7. In Example 7, it was confirmed that sintering shrinkage progressed from the shape filled in the container 10 by firing and was formed into a columnar shape same as that of the tantalum container having a shape along the inner surface shape of the container and maintained this shape. As shown in Figure 3(g), although three refractory sintered compacts are shown, they are separated into three when taken out from the container 10. It has a slightly more brittle tendency than the refractory sintered compact of Example 6. However, when the refractory sintered compact of Example 7 is assumed to be used in a pellet (columnar) shape, it is at a level where there is no problem in using it in a pellet (columnar) shape.

[0054] <Examples of Use of the Refractory Sintered Compacts of Examples 1 to 7> Examples of using the columnar (pellet-shaped) boron of Examples 1 to 7 in nuclear fusion power generation will be described.

[0055] Regarding nuclear fusion power generation, nuclear fusion power generation using deuterium and tritium is being studied as the first-generation nuclear fusion power plant because of the ease of the reaction. However, a large number of neutrons are generated in the reaction, the activation of the nuclear fusion reactor materials cannot be avoided, and tritium itself as the fuel is also a radioactive substance.

[0056] In addition to the above, there are also reactions between deuterium and deuterium and reactions between deuterium and helium in other nuclear fusion reactions, but still a large number of neutrons are generated. Therefore, what is expected is the nuclear fusion reaction between protons and boron that generates almost no neutrons.

[0057] As a method for supplying fuel to a nuclear fusion power plant for this nuclear fusion reaction between protons and boron, injecting boron powder into the plasma has also been studied, but it is difficult to supply a certain amount of boron to the targeted site. For this reason, if pellet-shaped boron is injected, supply of a certain amount of boron powder to the targeted site can be expected.

[0058] <Examples 8 to 12> Examples 8 to 12 will be described. In Example 8, the 6-mm-diameter container 10 in Fig. 1(a) was filled with tungsten carbide and compacted along the longitudinal direction of the container 10. Subsequently, after the upper end 10b of the container 10 was crushed, firing was performed in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were heating up at 30°C per minute and holding at the sintering temperature of 2000°C for 1 hour. The heating here corresponds to the heating process. As the refractory sintered body of Example 8, 4.21 g was obtained.

[0059] For tungsten carbide, a commercially available product (manufactured by Nirako Co., product number: W-467201, purity: 99.5%) was used. In Example 9, the 6-mm-diameter container 10 in Fig. 1(a) was filled with titanium nitride and compacted along the longitudinal direction of the container 10. Subsequently, after the upper end 10b of the container 10 was crushed, firing was performed in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were heating up at 30°C per minute and holding at the sintering temperature of 2000°C for 1 hour. The heating here corresponds to the heating process. As the refractory sintered body of Example 9, 1.69 g was obtained.

[0060] For titanium nitride, a commercially available product (manufactured by Nirako Co., product name: TI-457301, purity: 99%) was used. In Example 10, the 6-mm-diameter container 10 in Fig. 1(a) was filled with titanium carbide and compacted along the longitudinal direction of the container 10. Subsequently, after the upper end 10b of the container 10 was crushed, firing was performed in a carbon furnace under vacuum at a sintering temperature of 2000°C. The heating conditions were heating up at 30°C per minute and holding at the sintering temperature of 2000°C for 1 hour. The heating here corresponds to the heating process. As the refractory sintered body of Example 10, 1.26 g was obtained.

[0061] For titanium carbide, a commercially available product (manufactured by Nirako Co., product number: TI-457201, purity: 98%) was used. In Example 11, a container 10 with a diameter of 6 mm in Fig. 1(a) was filled with molybdenum and pressed along the longitudinal direction of the container 10. Then, after the upper end 10b of the container 10 was crushed, firing was performed at a sintering temperature of 2000 °C under vacuum in a carbon furnace. The heating conditions were heating up at 30 °C per minute and holding at the sintering temperature of 2000 °C for 1 hour. The heating here corresponds to the heating process. As the refractory sintered body of Example 11, 1.78 g was obtained.

[0062] As molybdenum, a commercially available product (manufactured by High Purity Chemical Laboratory, product number: MOE05PB, purity: 99.9% or more) was used. In Example 12, a container 10 with a diameter of 6 mm in Fig. 1(a) was filled with tungsten and pressed along the longitudinal direction of the container 10. Then, after the upper end 10b of the container 10 was crushed, firing was performed at a sintering temperature of 2000 °C under vacuum in a carbon furnace. The heating conditions were heating up at 30 °C per minute and holding at the sintering temperature of 2000 °C for 1 hour. The heating here corresponds to the heating process. As the refractory sintered body of Example 12, 3.44 g was obtained.

[0063] As tungsten, a commercially available product (manufactured by Nilaco Corporation, product number: W-464101, purity: 99.95%) was used.

[0064]

Table 2

[0065] <Refractory sintered bodies of Examples 8 to 12> In Examples 8 to 12, either one end in the vertical direction of the refractory sintered body spreads out in a flaring shape more than the other end. This is because one end side of the container 10 is crushed and the thickness of the container 10 gradually becomes thinner, so the shape of the refractory sintered body is also formed accordingly.

[0066] <Refractory sintered bodies of Examples 8 and 9> Figures 4 and 5 are photographs of the refractory sintered body of tungsten carbide of Example 8 and a photograph of the refractory sintered body of titanium nitride of Example 9. In both Example 8 and Example 9, it was confirmed that sintering shrinkage progressed from the shape filled in the container 10 by sintering and the shape was the same as that of the tantalum container having a shape along the inner surface shape of the container, and the shape was maintained in a cylindrical shape.

[0067] <Refractory Sintered Bodies of Example 10, Example 11, and Example 12> Figures 6, 7, and 8 are a photograph of the refractory sintered body of titanium carbide of Example 10, a photograph of the refractory sintered body of molybdenum of Example 11, and a photograph of the refractory sintered body of tungsten of Example 12.

[0068] In Example 10, Example 11, and Example 12, it was confirmed that sintering shrinkage progressed from the shape filled in the container 10 by sintering and the shape was the same as that of the tantalum container having a shape along the inner surface shape of the container, and the shape was maintained in a cylindrical shape.

[0069] <Examples 13 to 18> Examples 13 to 18 will be described. In Example 13, the container 10 having a diameter of 10 mm in Fig. 1(a) was filled with silicon carbide and its upper end 10b was crushed, and then sintering was performed at a sintering temperature of 2000 °C under vacuum in a carbon furnace. The heating conditions were that the temperature was raised at 30 °C per minute and held at the sintering temperature of 2000 °C for 1 hour. The heating here corresponds to the heating process. As the refractory sintered body of Example 13, 1.06 g was obtained.

[0070] As the silicon carbide, a commercially available product (manufactured by High Purity Chemical Laboratory, product number: SII01PB, purity: 99%) was used. In Example 14, the container 10 having a diameter of 6 mm in Fig. 1(a) was filled with yttria and its upper end 10b was crushed, and then sintering was performed at a sintering temperature of 2000 °C under vacuum in a carbon furnace. The heating conditions were that the temperature was raised at 30 °C per minute and held at the sintering temperature of 2000 °C for 1 hour. The heating here corresponds to the heating process. As the refractory sintered body of Example 14, 1.13 g was obtained.

[0071] Italy used a commercially available product (manufactured by Shin-Etsu Chemical Co., Ltd., purity: 99.9%). In Example 15, the 6-mm-diameter container 10 in Fig. 1(a) was filled with boron nitride and its upper end 10b was crushed, and then sintering was performed at a sintering temperature of 2000 °C under vacuum in a carbon furnace. The heating conditions were heating up at 30 °C per minute and holding at the sintering temperature of 2000 °C for 1 hour. The heating here corresponds to the heating process. As the refractory sintered body of Example 15, 0.18 g was obtained.

[0072] For boron nitride, a commercially available product (manufactured by Mizushima Alloy Iron Co., Ltd., GRADE, HP-2, JB) was used. In Example 16, the 6-mm-diameter container 10 in Fig. 1(a) was filled with zirconia and its upper end 10b was crushed, and then sintering was performed at a sintering temperature of 2000 °C under vacuum in a carbon furnace. The heating conditions were heating up at 30 °C per minute and holding at the sintering temperature of 2000 °C for 1 hour. The heating here corresponds to the heating process. As the refractory sintered body of Example 16, 1.12 g was obtained.

[0073] For zirconia, a commercially available product (manufactured by Kyoritsu Ceramics Raw Materials Co., Ltd., product number: KZ-0Y, purity: 99.9%) was used. In Example 17, the 6-mm-diameter container 10 in Fig. 1(a) was filled with boron carbide and its upper end 10b was crushed, and then sintering was performed at a sintering temperature of 2000 °C under vacuum in a carbon furnace. The heating conditions were heating up at 30 °C per minute and holding at the sintering temperature of 2000 °C for 1 hour. The heating here corresponds to the heating process. As the refractory sintered body of Example 17, 0.84 g was obtained.

[0074] For boron carbide, a commercially available product (manufactured by ESK Ceramics) was used. In Example 18, the 6-mm-diameter container 10 shown in Fig. 1(a) was filled with alumina, and after its upper end 10b was crushed, sintering was carried out in a carbon furnace under vacuum at a sintering temperature of 1800°C. The heating conditions were such that the temperature was raised at 30°C per minute and held at the sintering temperature of 1800°C for 1 hour. The heating here corresponds to the heating step. As the refractory sintered body of Example 18, 0.67 g was obtained. As the alumina, a commercially available product (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity: 99.99%) was used.

[0075]

Table 3

[0076] <Refractory sintered bodies of Example 13 and Example 14> Fig. 9 is a photograph of the refractory sintered body of silicon carbide of Example 13. Fig. 10 is a photograph of the refractory sintered body of yttria of Example 14.

[0077] It was confirmed that the refractory sintered bodies of Example 13 and Example 14 were formed in a columnar shape that maintained the shape along the inner surface shape of the container as the sintering shrinkage progressed from the shape filled in the container 10 by firing.

[0078] <Refractory sintered bodies of Example 15, Example 16, Example 17, and Example 18> Fig. 11 is a photograph of the refractory sintered body of boron nitride of Example 15. Fig. 12 is a photograph of the refractory sintered body of zirconia of Example 16. Fig. 13 is a photograph of the refractory sintered body of boron carbide of Example 17. The photograph of the refractory sintered body of Example 18 was omitted.

[0079] The refractory compacts of Example 15, Example 16, Example 17, and Example 18 were confirmed to be formed in a columnar shape and maintain this shape, where the sintering shrinkage progressed from the shape filled in the container 10 by firing to a shape along the inner surface shape of the container. Note that the refractory compact of boron carbide in Example 17 was divided into three pieces when taken out from the container 10. Each of the divided refractory compacts itself maintained a hard sintered state.

[0080] Note that the refractory compacts of the examples were columnar (pellet-shaped), but by changing the shape of the container, it is also possible to make them into other shapes. The refractory compacts formed in the shapes listed in the above examples or other shapes can be applied to the following fields.

[0081] ·Refractory compacts of tungsten carbide and titanium carbide can be used as cemented carbide materials. ·Refractory compacts of titanium nitride can be used, for example, as anticorrosive coatings, medical implants, and surgical tools.

[0082] ·Refractory compacts of molybdenum can be used as tools or electronic substrates. ·Refractory compacts of tungsten can be used as armor materials and shielding materials. ·Refractory compacts of silicon carbide can be used in the semiconductor and aerospace fields.

[0083] ·Refractory compacts of yttria can be used in lasers and high-temperature superconductivity. ·Refractory compacts of boron nitride can be used as release agents and lubricants. ·Refractory compacts of zirconia can be used as piezoelectric elements and biomaterials.

[0084] ·Refractory compacts of boron carbide can be used as shielding materials and for bulletproof applications.

Explanation of Signs

[0085] 10…Container 20…Container

Claims

1. A method for producing a difficult-to-sinter body, comprising: a molding step of filling a heat-resistant container with a difficult-to-sinter powder raw material, which is an inorganic material, and molding the powder; and a heating step of, after the molding step, heating the raw material filled in the container without adding a sintering aid and without applying pressure, and sintering the raw material without combustion synthesis, thereby obtaining a difficult-to-sinter body that maintains a shape that matches the inner shape of the container.

2. The method for producing a difficult-to-sinter body according to claim 1 , wherein the container is formed of a freely expandable metal foil.

3. The method for producing a difficult-to-sinter body according to claim 2, wherein the heating step is performed in a vacuum or in an inert atmosphere under normal pressure at a temperature lower than the melting point of the container and the difficult-to-sinter powder to obtain a difficult-to-sinter body.

4. The method for producing a difficult-to-sinter body according to claim 3, wherein the sinter-resistant powder contains any one of boron, silicon carbide, yttria, boron nitride, zirconia, boron carbide, tungsten carbide, titanium nitride, titanium carbide, molybdenum, tungsten, and alumina.

5. The method for producing a difficult-to-sinter body according to claim 4, wherein the difficult-to-sinter powder is boron.

6. The method for producing a difficult-to-sinter body according to claim 4, wherein the difficult-to-sinter powder is silicon carbide.

7. The method for producing a difficult-to-sinter body according to claim 4, wherein the difficult-to-sinter powder is yttria.

8. The method for producing a difficult-to-sinter body according to claim 4, wherein the difficult-to-sinter powder is boron nitride.

9. The method for producing a difficult-to-sinter body according to claim 4, wherein the difficult-to-sinter powder is zirconia.

10. The method for producing a difficult-to-sinter body according to claim 4, wherein the difficult-to-sinter powder is boron carbide.

11. The method for producing a difficult-to-sinter body according to claim 4, wherein the difficult-to-sinter powder is tungsten carbide.

12. The method for producing a difficult-to-sinter body according to claim 4, wherein the difficult-to-sinter powder is titanium nitride.

13. The method for producing a difficult-to-sinter body according to claim 4, wherein the difficult-to-sinter powder is titanium carbide.

14. The method for producing a difficult-to-sinter body according to claim 4, wherein the difficult-to-sinter powder is molybdenum.

15. The method for producing a difficult-to-sinter body according to claim 4, wherein the difficult-to-sinter powder is tungsten.

16. The method for producing a difficult-to-sinter body according to claim 4, wherein the difficult-to-sinter powder is alumina.

17. The method for producing a difficult-to-sinter body according to claim 5 , wherein the difficult-to-sinter body is formed into a pellet shape by the container.

18. The difficult-to-sinter body produced by the method for producing a difficult-to-sinter body according to claim 17, A method for supplying boron to a fusion reactor by supplying a constant amount of boron to the fusion reactor.

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