Composite having radiation shielding function and method for producing composite having radiation shielding function

Abstract

To develop a composite of a new constitution containing a powder having a radiation shielding function in a high content.SOLUTION: Molten aluminum is impregnated and filled into all voids of a preform made of a mixture containing one or more kinds of radiation shielding powders selected from gadolinium oxide, boron carbide, boron oxide, boron, barium sulfate, strontium oxide, tungsten, tungsten oxide, tungsten carbide, molybdenum, molybdenum oxide, iron powder, iron oxide powder, and ferrite powder and a liquid silica-based binder, the mixture containing the radiation shielding powders in a range of 3 to 85% in total; In the composite body having the radiation shielding function and the method for manufacturing the same, a liquid organic-inorganic sealing agent is impregnated and solidified to form the composite body, and a liquid silica-based binder has characteristics capable of forming a preform at a temperature at which the radiation shielding powder is not decomposed.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a composite having a radiation-shielding function and a method for manufacturing the composite having a radiation-shielding function. More specifically, the present invention relates to specific inorganic powders or metal powders having a radiation-shielding effect, such as gadolinium oxide (Gd2O3) powder, boron carbide (B4C) powder, boron oxide (B2O3) powder, boron (B) powder, barium sulfate (BaSO4) powder, strontium oxide (SrO) powder, tungsten (W) powder, tungsten oxide (W2O3) powder, tungsten carbide (WC) powder, molybdenum (Mo) powder, molybdenum oxide (MoO3) powder, iron (Fe) powder, iron oxide (Fe2O3) powder, and ferrite powders containing iron oxide as a main component (hereinafter collectively referred to as "iron oxide"). The present invention relates to a composite obtained by impregnating pores of a porous preform containing at least one selected from the group consisting of aluminum metal, aluminum alloy, zinc, tin, and lead, and a low-melting-point alloy of the low-melting-point metal and another metal, all of which have a melting point of 200°C or higher and 900°C or lower, and then solidifying the pores of the porous preform, which contains at least one selected from the group consisting of aluminum metal, aluminum alloy, zinc, tin, and lead ... or a composite having a radiation-shielding function, which is impregnated with a liquid organic / inorganic sealing agent, followed by heat treatment and solidification (hereinafter, these will also be simply referred to as a composite), and a method for producing the same.In particular, the present invention relates to a technology that enables the realization of a composite obtained by compounding the radiation-shielding powders listed above while suppressing decomposition of the radiation-shielding powders. [Background technology]

[0002] In medical settings, radiation-shielding shielding materials are used in consideration of X-rays and other radiation generated by medical devices and equipment. In the nuclear industry, materials that shield against radiation such as X-rays, gamma rays, and neutrons are used in containers and equipment for handling and storing unused nuclear fuel. Radiation-shielding materials must have good heat dissipation properties to block radiation and prevent nuclear chain reactions. Metals such as lead (Pb) and tungsten (W) are commonly used as radiation-shielding materials. However, in recent years, there has been a growing demand for lightweight radiation-shielding materials with high heat dissipation properties and excellent radiation-shielding properties, especially for structural components that require radiation shielding.

[0003] Conventional radiation shielding materials generally use metallic lead or metallic tungsten. However, these materials have a high specific gravity, and structural materials made from these materials are quite heavy, limiting their range of use. As described below, in order to create lightweight structures with radiation shielding effects, materials have been proposed that combine B4C powder or BaSO4 powder, which have a low specific gravity and radiation shielding effects, with resin or metal. However, the content of these radiation shielding powders in the structures is low, limiting their range of application.

[0004] Patent Document 1 proposes a method for producing an aluminum radiation shielding material containing BC, as described below. Specifically, the radiation shielding material is produced by preparing a green compact of a mixed powder consisting of boron carbide (BC) powder and aluminum powder, sintering the green compact at a low sintering temperature of 10 to 50°C by vacuum sintering, HIP, or hot pressing, allowing the BC and aluminum to blend together, and then heating, melting, and casting the resulting green compact. In this method, the BC content in the radiation shielding material is limited to a range of 0.5 to 5% by mass; a higher BC content increases the viscosity of the molten metal, making casting difficult. Therefore, it has been difficult to produce a radiation shielding material with a BC content of more than 5% by mass, which provides greater radiation shielding effect.

[0005] Patent Document 2 also discloses a method for producing a radiation-shielding composite by adding an inorganic binder to a mixture of boron carbide (BC) particles and aluminum borate whiskers, molding the mixture, sintering the molded product under high-temperature conditions of 1250°C for 4 hours in an argon atmosphere to produce a preform, and then impregnating the preform with molten aluminum alloy at high pressure. This method involves mixing boron carbide with ceramic whiskers and sintering the mixture at a high temperature of 1100 to 1400°C to produce a preform that can withstand high-pressure aluminum impregnation. The preform is then impregnated with molten aluminum alloy to produce a composite. This method is costly because the preform must be produced at a high temperature. Furthermore, the boron carbide content in the radiation-shielding composite is limited to 1 to 15 wt %, making it difficult to achieve a high boron carbide content.

[0006] Patent Document 3 discloses a method of obtaining a composite by placing a solid piece of aluminum alloy that melts at 580°C to 610°C on top of a preform made from a mixture of boron-containing ceramic powder, typically boron carbide (B4C), and metal powder containing aluminum, and then heating the preform to an infiltration temperature at which the solid piece melts and infiltrating it for 1 minute to 24 hours. According to the inventors' investigations, this method requires a long reaction time because the aluminum alloy is spontaneously impregnated (infiltrated) into the preform. In addition, unstable Al4C3 is formed in the air, and impregnation into the preform may not be 100% complete, making it impossible to obtain a dense and stable radiation-shielding composite.

[0007] Furthermore, Patent Document 4 proposes a method for producing a composite by heating a mixed powder of boron carbide powder and aluminum alloy powder, or a mixed powder compact thereof, to a predetermined temperature and maintaining the temperature, and then forging or rolling the mixture under semi-molten conditions. According to the inventors' investigations, this method has been unable to produce composites with large areas or thick walls because the forming is performed at high temperatures. Furthermore, this technique involves forced forging in a semi-molten state, which causes problems such as uneven distribution of the radiation-shielding powder and the aluminum alloy, and the inability to produce products with a wall thickness of 10 mm or more.

[0008] Patent Document 5 proposes a container material in which boron fiber is composited with an aluminum alloy base containing boron. However, the boron fiber content is still low and boron fiber is expensive, so the range of use is limited. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-20828 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-121590 [Patent Document 3] Patent No. 4426293 [Patent Document 4] Japanese Patent Application Publication No. 60-096746 [Patent Document 5] Japanese Patent Application Publication No. 10-319183 Summary of the Invention [Problem to be solved by the invention]

[0010] As mentioned above, conventional radiation-shielding materials tend to be heavy when metallic lead or tungsten is used as the radiation-shielding powder. Furthermore, even when powders such as boron carbide (B4C) or barium sulfate (BaSO4) are used, the content of the radiation-shielding powder is low, and a high content has not been achieved. Furthermore, conventional materials have been proposed in which radiation-shielding powder is mixed with gypsum, rubber, or resin. However, materials using rubber as a matrix are organic, making them difficult to use for long periods of time at temperatures above 200°C. Furthermore, materials using gypsum as a matrix have the problem of undergoing a dehydration reaction of the gypsum when used for long periods of time at temperatures above 100°C, making them unsuitable for long-term use at high temperatures.

[0011] In view of the above-mentioned state of the art, the present inventors believed that if a method could be developed that could control the content of materials (raw materials) with a high content of radiation-shielding powders such as B4C powder, BaSO4 powder, or other gadolinium oxide, strontium oxide, or iron oxide from low to high, and that could prepare materials that could be used at high temperatures, the range of radiation-shielding applications for structural members (structures) and radiation-related machine parts would be greatly expanded. Furthermore, even if radiation-shielding powders such as tungsten powder or molybdenum powder, which have a high specific gravity of 10 or more, could be composited with other materials at a content that allows stable radiation-shielding effect to be achieved, and a lightweight composite material could be produced, the range of use would be greatly expanded.

[0012] In light of the current state of the art, the present inventors recognized that a highly practical composite material with radiation-shielding function having the following properties is desired. Specifically, the present inventors recognized that a high-strength composite with a high radiation-shielding powder content, particularly a content of 3 v% or more, preferably 60 v% or more, and more preferably up to 85 v%; a high wall thickness of 5 mm or more, preferably 10 mm or more; a lightweight composite usable for large structures, architectural wall materials, and machine protective structures; and a composite of a low-melting-point metal selected from the group consisting of aluminum metal, aluminum alloy, zinc, tin, and lead, or a low-melting-point alloy of such a low-melting-point metal with another metal (hereinafter, these may be referred to as "aluminum, etc."), all of which have high thermal conductivity. Note that low-melting-point metals other than zinc, tin, and lead can also be used as long as they do not impair the objectives of the present invention. In this specification, volume % is also referred to as "v%," and mass % is also referred to as "w%."

[0013] Therefore, an object of the present invention is to develop a composite with a novel configuration that contains a high content of a powder having radiation-shielding function (radiation-shielding powder) and has a high radiation-shielding effect. Another object of the present invention is to develop a variety of composites in which the radiation-shielding powder content is controlled depending on the application, from a low content of, for example, 3v% to 85v%, to a high content, and that have the strength required for structures such as parts and members that constitute buildings or machines. A further object of the present invention is to develop a new technology that can provide an excellent composite with radiation-shielding powder, which is a composite with aluminum metal powder, aluminum alloy powder, or ceramic powder that has heat resistance and high thermal conductivity and has a matrix of molten aluminum metal or aluminum alloy. [Means for solving the problem]

[0014] The above object can be achieved by the present invention, which provides the following composite having a radiation-shielding function. [1] A composite having a radiation-shielding function, which contains a powder having a radiation-shielding effect in a composite amount of 3% by volume or more and 85% by volume or less, A porous composition which is a molded and fired product made of a mixture containing one or more types of powder having a radiation shielding effect selected from the group consisting of gadolinium oxide powder, boron carbide powder, boron powder, boron oxide powder, barium sulfate powder, strontium oxide powder, tungsten powder, tungsten oxide powder, tungsten carbide powder, molybdenum powder, molybdenum oxide powder, iron powder, iron oxide powder, and ferrite powder mainly composed of iron oxide, and a silica-based binder that is not in powder form. The voids of the molded body (preform) are all impregnated and filled with at least one of a molten low-melting point metal selected from the group consisting of aluminum metal, aluminum alloy, zinc, tin and lead, which has a melting point of 200°C or more and 900°C or less, or a low-melting point alloy of said low-melting point metal with another metal, and then solidified to form a composite, or at least 25% by volume or more of the voids of the porous molded body (preform) are impregnated with a liquid organic / inorganic sealing agent, which is then solidified to form a composite, and A composite having a radiation-shielding function, characterized in that the non-powdered silica-based binder has the property of being able to form a porous molded body (preform), which is the molded and fired product, at a temperature at which the radiation-shielding powder is not decomposed.

[0015] The following are preferred forms of the above-mentioned complex having a radiation shielding function. [2] The composite having a radiation-shielding function according to the above item [1], wherein the non-powdered silica-based binder is at least one liquid silica-based binder selected from the group consisting of water glass (sodium silicate), colloidal silica, liquid silicone resin, a silicone resin solution obtained by dissolving a silicone resin in an organic solvent, and silica alkoxide, which is made of silica and an organic substance and is heat-cured at a temperature of 900°C or less, and the mixture is obtained by adding 0.5 to 10 parts by mass of the liquid silica-based binder in terms of SiO2 to 100 parts by mass of the radiation-shielding powder.

[0016] [3] The composite having a radiation-shielding function according to [1] or [2] above, wherein the liquid organic / inorganic pore-sealing agent is present in the voids of the porous molded body (preform) as a solidified product of the organic / inorganic pore-sealing agent and / or a heat-treated product of the organic / inorganic pore-sealing agent, and the solidified product of the organic / inorganic pore-sealing agent and / or the heat-treated product of the organic / inorganic pore-sealing agent occupies 25% by volume or more of the voids (100% by volume) of the porous molded body (preform) before impregnation, and when the entire preform after impregnation is taken as 100% by volume, the solidified product of the organic / inorganic pore-sealing agent and / or the heat-treated product of the organic / inorganic pore-sealing agent occupies 5% by volume or more.

[0017] [4] The liquid organic / inorganic sealing agent has a low viscosity of 50 mPa·s or less and contains 30 mass% or more of non-volatile components. a liquid methyl silicate compound which is methyl silicate Si(OCH3)4 or a dimer or tetramer oligomer obtained by partial hydrolysis of the methyl silicate, and which is adjusted so that the non-volatile component is 30 mass% or more; a liquid ethyl silicate compound which is ethyl silicate Si(OC2H5)4 or a dimer or tetramer oligomer obtained by partial hydrolysis of the ethyl silicate, and which is adjusted so that the non-volatile component is 30 mass% or more; Silicone resin or its derivatives having siloxane bonds and adjusted so that the non-volatile component is 30% by mass or more; The composite having a radiation-shielding function according to any one of the above [1] to [3], which is at least one selected from the group consisting of liquid alkoxysilane compounds that are alkoxysilane derivatives and react with moisture in the air to undergo a condensation reaction to produce silicone-oxygen organic compounds (Si-OR).

[0018] As another embodiment, the present invention provides the following method for producing a composite having a radiation-shielding function. [5] A method for producing a composite having a radiation-shielding function, comprising: a matrix of at least one of a molten low-melting-point metal selected from the group consisting of aluminum metal, an aluminum alloy, zinc, tin, and lead, or a low-melting-point alloy of the low-melting-point metal and another metal; and a powder having a radiation-shielding effect in a total amount of 3% by volume or more and 85% by volume or less, the method comprising: a step of molding a mixture obtained by adding a non-powdered silica-based binder to one or more types of powder having a radiation shielding effect selected from the group consisting of gadolinium oxide powder, boron carbide powder, boron oxide powder, boron powder, barium sulfate powder, strontium oxide powder, tungsten powder, tungsten oxide powder, tungsten carbide powder, molybdenum powder, molybdenum oxide powder, iron powder, iron oxide powder, and ferrite powder mainly composed of iron oxide, and then firing the resulting molded body at a temperature of 300°C or higher and 900°C or lower to produce a porous molded body (preform); a step of casting a molten metal of at least one low-melting-point metal selected from the group consisting of aluminum metal, aluminum alloy, zinc, tin, and lead, or a low-melting-point alloy of said low-melting-point metal with another metal, melted at a temperature of 300°C or more and 900°C or less, and having a melting point of 200°C or more and 900°C or less, into the porous molded body (preform) obtained in the step above, and holding the molten metal at a high pressure of 20 MPa or more and 200 MPa or less for 3 to 15 minutes in order to impregnate the porous molded body (preform) with the molten metal, and then removing the composite impregnated with the molten metal within 15 minutes and cooling it, thereby suppressing decomposition of the radiation-shielding powder in the composite.

[0019] [6] A method for producing a composite having a radiation-shielding function, which comprises preparing a composite containing a powder having a radiation-shielding effect in a total amount of 3% by volume or more and 85% by volume or less, the powder being composited, the method comprising: a step of molding a mixture obtained by adding a non-powdered silica-based binder to one or more types of powder having a radiation shielding effect selected from the group consisting of gadolinium oxide powder, boron carbide powder, boron oxide powder, boron powder, barium sulfate powder, strontium oxide powder, tungsten powder, tungsten oxide powder, tungsten carbide powder, molybdenum powder, molybdenum oxide powder, iron powder, iron oxide powder, and ferrite powder mainly composed of iron oxide, and then firing the resulting molded body at a temperature of 300°C or higher and 900°C or lower to produce a porous molded body (preform); and a compounding step of: vacuum-impregnating, into voids of the porous molded body (preform) obtained in the step of producing the porous molded body (preform), a liquid organic / inorganic sealing agent containing 30% by mass or more of non-volatile components and having a viscosity of 50 mPa s or less, or impregnating the voids of the porous molded body (preform) under a pressure of 10 atmospheres or less by applying pressure after vacuum impregnation, and then heating the voids to a temperature of 200°C or more and 900°C or less, so that a solidified product of the liquid organic / inorganic sealing agent and / or a heat-treated product of the liquid organic / inorganic sealing agent remains in an amount of 25% by volume or more relative to 100% by volume of the voids of the porous molded body (preform), and compounding the radiation-shielding powder with a component derived from the liquid organic / inorganic sealing agent.

[0020] A preferred embodiment of the method for producing the composite having a radiation-shielding function described in [5] or [6] above is as follows. [7] The liquid organic / inorganic sealing agent has a low viscosity of 50 mPa·s or less and contains 30 mass% or more of non-volatile components. a liquid methyl silicate compound which is methyl silicate Si(OCH3)4 or a dimer or tetramer oligomer obtained by partial hydrolysis of the methyl silicate, and which is adjusted so that the non-volatile component is 30 mass% or more; a liquid ethyl silicate compound which is ethyl silicate Si(OC2H5)4 or a dimer or tetramer oligomer obtained by partial hydrolysis of the ethyl silicate, and which is adjusted so that the non-volatile component is 30 mass% or more; Silicone resin or its derivatives having siloxane bonds and adjusted so that the non-volatile component is 30% by mass or more; The method for producing the radiation-shielding composite according to [6] above, wherein the alkoxysilane derivative is at least one selected from the group consisting of liquid alkoxysilane compounds that react with moisture in the air to undergo a condensation reaction to produce a silicone-oxygen organic compound (Si-OR).

[0021] [8] The method for producing a composite having a radiation-shielding function according to any one of the above [5] to [7], wherein the non-powdered silica-based binder is at least one liquid silica-based binder selected from the group consisting of water glass (sodium silicate), colloidal silica, liquid silicone resin, a silicone resin solution obtained by dissolving a silicone resin in an organic solvent, and silica alkoxide, which is made of silica and an organic substance and is heat-cured at a temperature of 900°C or less, and the mixture is prepared by adding 0.5 to 10 parts by mass of the liquid silica-based binder in terms of SiO2 to 100 parts by mass of the radiation-shielding powder.

[0022] [9] The method for producing a composite having a radiation-shielding function according to the above item [5] or [8], further comprising adding aluminum powder, aluminum alloy powder, or ceramic powder to the radiation-shielding powder in an amount of 0.5 to 10 mass% of the non-powdered silica-based binder in terms of SiO2 when the total of the aluminum metal powder, aluminum alloy powder, or ceramic powder and the radiation-shielding powder is taken as 100 mass%, in the step of producing the porous molded body (preform). [Effects of the Invention]

[0023] Conventionally, structures containing radiation-shielding powder have generally been produced by mixing the radiation-shielding powder with aluminum, rubber, or resin to form a composite. In contrast, the present invention stably provides a composite having a radiation-shielding function, which is similar to the conventional structure in that it uses a molded body (preform) containing radiation-shielding powder whose filling rate is controlled from low to high, and in which all voids in the molded body (preform) are impregnated with a molten metal such as aluminum and solidified to form a composite. Alternatively, a composite having a radiation-shielding function, which is in which at least 25% by volume of the voids in the molded body (preform) are impregnated with a liquid organic / inorganic sealing agent and solidified to form a composite, can be stably provided. Furthermore, by applying each production method of the present invention according to the intended use of the composite and skillfully utilizing the above-mentioned two types of configuration, various composites having desirable properties and high practical value, for example, in which the filling rate of the radiation-shielding powder is controlled from low to high and which have excellent radiation-shielding properties and exhibit strength suited to the intended purpose, can be stably produced. The technical features of the present invention are as follows.

[0024] A first feature of the present invention is that one or more types of radiation-shielding powders can be appropriately selected from a group of radiation-shielding powders having different functions and properties, including gadolinium oxide (GdO) powder, boron carbide (BC) powder, boron oxide (BO) powder, boron (B) powder, barium sulfate (BaSO) powder, strontium oxide (SrO) powder, tungsten (W) powder, tungsten oxide (WO) powder, tungsten carbide (WC) powder, molybdenum (Mo) powder, molybdenum oxide (MoO) powder, iron (Fe) powder, iron oxide (FeO) powder, and ferrite powder containing iron oxide as a main component, as specified in the present invention, depending on the intended use, etc. In other words, the present invention makes it possible to provide a variety of radiation-shielding composites that are composed of a single radiation-shielding powder or various combinations of radiation-shielding powders.

[0025] Among the radiation-shielding powders constituting the composite of the present invention, for example, boron carbide containing boron is said to have a radiation-shielding effect against neutron rays, tungsten or tungsten carbide against gamma rays and X-rays, and barium sulfate containing barium against X-rays and gamma rays. In contrast, the present invention makes it possible to provide composites with a variety of configurations with different radiation-shielding functions, as described below. That is, it is possible to provide not only composites obtained by impregnating a single powder from the specific radiation-shielding powder group specified in the present invention with a molten metal such as aluminum or a liquid organic / inorganic sealing agent and solidifying the resulting composite, but also composites obtained by impregnating two types of radiation-shielding powders, i.e., boron carbide and tungsten, or boron carbide and barium sulfate, or, as needed, three types of radiation-shielding powders, i.e., boron carbide, tungsten, and barium sulfate, with a molten metal such as aluminum or a liquid organic / inorganic sealing agent and solidifying the resulting composite. As described above, according to the present invention, by appropriately selecting the radiation-shielding powder defined in the present invention, it is possible to provide a composite that can simultaneously shield against X-rays, gamma rays, and neutron rays.

[0026] A second feature of the present invention is that it is possible to provide a composite having radiation-shielding function in which the volume fraction of the radiation-shielding powder can be freely controlled from 3v% to 85v%, for example, by adjusting the particle size and blending ratio of the various radiation-shielding powders listed above, and by adding aluminum powder or aluminum alloy powder as needed.The present invention makes it possible to manufacture a structure made of a composite having radiation-shielding function that achieves a filling fraction (volume fraction) of the radiation-shielding powder of 50v% or more, which is required for a particularly high shielding effect.

[0027] A third feature of the present invention is that the radiation-shielding composite provided by the present invention can be made into the following two different configurations. First, in either configuration, a porous molded body (preform) is used, which is a molded and fired product of a mixture containing one or more types of radiation-shielding powder selected from the group of radiation-shielding powders specified in the present invention and a non-powdered silica-based binder. Then, all of the voids of the porous molded body (preform) are impregnated and filled with a molten metal of at least one low-melting-point metal, which has a melting point of 200°C or more and 900°C or less, selected from the group consisting of aluminum metal, aluminum alloy, zinc, tin, and lead, or a low-melting-point alloy of the low-melting-point metal with another metal, and the molten metal is solidified to form a composite, thereby providing a composite having a high content of radiation-shielding powder with an aluminum matrix or the like. Furthermore, by impregnating at least 25% by volume of the pores of the porous molded body (preform) with a liquid organic / inorganic sealing agent and then heating the preform at a temperature of 200°C or higher and 900°C or lower, the liquid organic / inorganic sealing agent is solidified and composited, thereby providing a composite having a different configuration with a high content of radiation-shielding powder.

[0028] Furthermore, in the case of any of the composites having the above-described configurations, the non-powdered silica-based binder used in preparing the preform has the property of being able to form the preform at a temperature at which the radiation-shielding powder used for the composite is not decomposed, thereby achieving the following effects. That is, with such a configuration, the composite having radiation-shielding function of the present invention has high strength because the radiation-shielding powder specified in the present invention is bound by aluminum or an organic / inorganic sealing agent. Furthermore, the radiation-shielding powder used is not decomposed, and the composite can be used at high temperatures of 300°C or higher. Hereinafter, the terms "molten aluminum" and "molten aluminum" used in the present specification refer to molten aluminum metal as a representative example. That is, in the present specification, the terms "molten aluminum" and "molten aluminum" are used to refer not only to molten aluminum metal but also to molten aluminum of a low-melting-point metal selected from the group consisting of aluminum alloys, zinc, tin, and lead, or a low-melting-point alloy of the low-melting-point metal with another metal (e.g., low-melting-point alloy solders mainly composed of tin or lead, and zinc alloys). In the specification of the present invention, the term "molten aluminum" refers to a low-melting-point metal or low-melting-point alloy having a melting point of 200°C or higher. In addition, in the present invention, it is preferable to use a low-melting-point metal or low-melting-point alloy having a melting point of 300°C or higher. That is, according to the studies of the present inventors, when a low-melting-point metal or low-melting-point alloy having a melting point of less than 300°C is used, the heat resistance of the resulting composite may not be sufficient depending on the application, and this is not preferable.

[0029] A fourth feature of the present invention is that, according to the inventors' investigations, the following problem has been encountered when using aluminum metal or aluminum alloy molten at high temperatures as a molten metal for compounding with a radiation-shielding powder. The present invention solves this problem. For example, boron carbide, which decomposes with moisture in the air to form AlC upon reaction with aluminum, barium sulfate, which decomposes with molten aluminum at high temperatures to form AlO, BaO, and SO, and strontium sulfate, tungsten, iron powder, and aluminum borate, which undergo oxidative degradation, thermal decomposition, and the generation of unstable substances at temperatures above 900°C, can be used as raw materials to produce a composite that can be stably used even at temperatures above 300°C. Therefore, since a wide variety of radiation-shielding powders as specified in the present invention can be used, the present invention significantly expands the range of applications of the composite. [Brief explanation of the drawings]

[0030] FIG. 1 is a schematic diagram showing the process of casting molten aluminum 1 into a preform 2, which is carried out in the first manufacturing method. [Figure 1A] 1 is a schematic diagram showing a heated preform 2 being placed in a mold of a press 10 and molten aluminum 1 being poured therein. [Figure 1B] 1 is a schematic diagram showing how molten aluminum 1 is cast into a preform 2 using an upper punch 5 and a lower punch 4 of a high-pressure press and then impregnated. [Figure 1C] FIG. 10 is a schematic diagram showing how, after cooling, lower punch 4 is pushed up to remove composite 3 in a state where the impregnated molten aluminum has solidified. [Figure 2] FIG. 10 is a schematic diagram for explaining an outline of a reduced pressure vessel 30 used when impregnating voids in a preform 2 with a liquid organic / inorganic sealing agent 32 in the second manufacturing method. DETAILED DESCRIPTION OF THE INVENTION

[0031] Preferred embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

[0032] The radiation-shielding composite of the present invention is a composite having a radiation-shielding function, which contains a total of 3 to 85 volume % of powders having a radiation-shielding effect, the powders being a composite of gadolinium oxide (Gd2O3) powder, boron carbide (B4C) powder, boron oxide (B2O3) powder, boron (B) powder, barium sulfate (BaSO4) powder, strontium oxide (SrO) powder, tungsten (W) powder, tungsten oxide (W2O3) powder, tungsten carbide (WC) powder, molybdenum (Mo) powder, molybdenum oxide (MoO3) powder, iron (Fe) powder, iron oxide (Fe2O3) powder, and ferrite powder containing iron oxide as the main component, all of which have a radiation-shielding effect. a porous molded body (preform) which is a molded and fired product made of a mixture containing one or more types of radiation-shielding powder selected from the group and a non-powdered silica-based binder, and which has a configuration in which molten aluminum is impregnated into and filled into all voids of the porous molded body (preform), and then solidified to form a composite, or a porous molded body (preform) which is a porous molded body (preform) which has a configuration in which at least 25% by volume of the voids of the porous molded body (preform) is impregnated with a liquid organic / inorganic sealing agent, and then solidified to form a composite, and the non-powdered silica-based binder has a property that allows the porous molded body (preform) which is a molded and fired product (hereinafter simply referred to as a preform) to be formed at a temperature at which the radiation-shielding powder is not decomposed.

[0033] The radiation-shielding composite of the present invention having the above-mentioned configuration can be produced in a stable manner while suppressing decomposition of the radiation-shielding powder by the production method of the present invention comprising, for example, the first or second means described below. Therefore, a good-quality composite that meets the intended use and provides the various effects of the present invention described above can be easily and stably prepared.

[0034] The radiation-shielding composite of the present invention, which is configured by impregnating and filling all of the voids in a preform having the specific configuration described above with "molten aluminum" and then solidifying to form a composite, can be easily and stably prepared by the first production method of the present invention described below. As mentioned above, "molten aluminum" and "molten aluminum" refer to a molten metal of at least one of aluminum metal, aluminum alloy, low-melting-point metal, and low-melting-point alloy, each having a melting point of 200°C or higher, preferably 300°C or higher and 900°C or lower.

[0035] The first manufacturing method of the present invention is a method for manufacturing a composite having a radiation-shielding function, which contains an aluminum matrix and a powder having a radiation-shielding effect in a total amount of 3 volume % or more and 85 volume % or less, and in which one or more types of powder having a radiation-shielding effect selected from the group consisting of gadolinium oxide powder, boron carbide powder, boron oxide powder, boron powder, barium sulfate powder, strontium oxide powder, tungsten powder, tungsten oxide powder, tungsten carbide powder, molybdenum powder, molybdenum oxide powder, iron powder, iron oxide powder, and ferrite powder containing iron oxide as a main component are added with a non-powdered silica-based powder. The method is characterized by comprising the steps of: molding the mixture obtained by adding and mixing a binder, and then firing the resulting molded body at a temperature of 300°C or higher and 900°C or lower to produce a porous molded body (preform); and casting molten aluminum into the preform obtained in the above step at a temperature of 300°C or higher and 900°C or lower, and holding the preform at a high pressure of 20 MPa or higher and 200 MPa or lower for 3 to 15 minutes, for example, 3 to 5 minutes, in order to impregnate the preform with the molten aluminum. Thereafter, the composite in a state impregnated with the molten aluminum is immediately removed and cooled, thereby suppressing decomposition of the radiation-shielding powder in the composite and the generation of unstable substances such as Al4C3.

[0036] In the first production method of the present invention, further, in the step of preparing the preform, aluminum powder, aluminum alloy powder, or ceramic powder may be added to the radiation-shielding powder, and the preform may be prepared by adding 0.5 to 10 mass% of the non-powdered silica-based binder in terms of SiO2, where the total of the aluminum powder, aluminum alloy powder, or ceramic powder and the radiation-shielding powder is 100 mass%. This configuration makes it easier to prepare a composite having a radiation-shielding function, which contains aluminum or an aluminum alloy as a matrix and a powder having a radiation-shielding effect, the powder being appropriately controlled in a total amount within a range of 3 to 85 volume%. This point will be described later.

[0037] The radiation-shielding composite of the present invention, which is configured by impregnating at least 25% by volume of the voids in a preform having the specific configuration described above with a liquid organic / inorganic sealing agent and solidifying it to form a composite, can be easily and stably prepared by the second production method of the present invention described below.

[0038] The second manufacturing method of the present invention is a method for manufacturing a composite having a radiation-shielding function, which comprises preparing a composite containing a total of 3 to 85 volume % of powders having a radiation-shielding effect, the powders being composited together, the composite comprising one or more types of powders having a radiation-shielding effect selected from the group consisting of gadolinium oxide powder, boron carbide powder, boron oxide powder, boron powder, barium sulfate powder, strontium oxide powder, tungsten powder, tungsten oxide powder, tungsten carbide powder, molybdenum powder, molybdenum oxide powder, iron powder, iron oxide powder, and ferrite powder containing iron oxide as the main component, and adding a non-powdered silica-based binder to the powder, and then molding the mixture obtained. and a compounding step of vacuum-impregnating a liquid organic / inorganic pore-sealing agent containing 30% by mass or more of non-volatile components and having a viscosity of 50 mPa·s or less into voids of the preform obtained in the preform-producing step, or impregnating the preform under pressure of 10 atmospheres or less by vacuum impregnation, and then heating the liquid organic / inorganic pore-sealing agent to a temperature of 300°C or more and 900°C or less, so that a solidified product of the liquid organic / inorganic pore-sealing agent and / or a heat-treated product of the liquid organic / inorganic pore-sealing agent remains in an amount of 25% by volume or more relative to 100% by volume of the voids of the preform.

[0039] <Porous molded body (preform) manufacturing process> The following describes in detail the first and second manufacturing methods of the radiation-shielding composite of the present invention. As described above, the steps of manufacturing a porous molded body (preform) constituting the first and second manufacturing methods are the same. Therefore, the step of manufacturing a preform will be described first.

[0040] [Raw radiation shielding powder, etc.] In the present invention, the radiation-shielding powder used as a raw material for producing a preform is one or more selected from the group consisting of gadolinium oxide (Gd2O3) powder, boron carbide (B4C) powder, boron oxide (B2O3) powder, boron powder, barium sulfate (BaSO4) powder, strontium oxide (SrO) powder, tungsten (W) powder, tungsten oxide (W2O3) powder, tungsten carbide (WC) powder, molybdenum (Mo) powder, molybdenum oxide (MoO3) powder, iron (Fe) powder, iron oxide (Fe2O3) powder, and ferrite powder containing iron oxide as the main component. In conventional technologies, lead powder or lead oxide powder is generally used alone as the radiation-shielding powder. However, in the present invention, the use of these radiation-shielding powders is not used because they increase the weight of the structure (composite) and have environmental impacts to be considered. In addition, these materials have low melting points and are therefore unsuitable for the manufacturing method of the present invention, which is useful for effectively obtaining the composite of the present invention.

[0041] In the present invention, in addition to the radiation-shielding powders listed above, aluminum powder, aluminum alloy powder, or ceramic powder can be added to reduce the packing rate of the radiation-shielding powder in the composite. This allows the packing rate (volume rate) of the radiation-shielding powder constituting the composite of the present invention to be freely controlled over a wide range. In this case, in the step of producing a porous molded body (preform) constituting the production method of the present invention, aluminum powder, aluminum alloy powder, or ceramic powder is further added as needed to the specific radiation-shielding powder specified in the present invention, and 0.5 to 10 mass % (w%) of the non-powdered silica-based binder, calculated as SiO2, is added to the total volume of these powders (100 v%) to produce a preform. The production method is similar to the production method of the composite of the present invention, except that aluminum powder, aluminum alloy powder, or ceramic powder is used as needed. Therefore, the following explanation will focus on a method of producing a preform including the above-mentioned optional components.

[0042] The average particle size of the radiation-shielding powder used in the production method of the present invention and the aluminum powder, aluminum alloy powder, or ceramic powder (hereinafter also referred to as "aluminum powder, etc.") used as needed is preferably 0.3 μm or more and 500 μm or less. The reason for setting the average particle size at 0.3 μm or more is that materials with an average particle size smaller than 0.3 μm tend to have particles that easily aggregate and form clumps. Furthermore, when two or more types of powder are used, uniform mixing may be difficult, which is undesirable. In addition, it tends to be difficult to uniformly mix the silica-based binder added to the powder. Furthermore, when a powder with an average particle size less than 0.3 μm is used, the powder filling rate tends to be low in preforms obtained by press molding, CIP molding, slip casting, or the like. This may prevent the production of preforms with a high volume fraction (Vf) of the radiation-shielding powder, which is a characteristic of the present invention. On the other hand, when a large powder exceeding 500 μm is used, the powder packing property is also poor, and there is a risk that a preform with a high Vf cannot be produced, as in the case of using a powder with an average particle size that is too small. Furthermore, according to the studies of the present inventors, since the coarse particles described above have a small surface area, the binder effect of the silica-based binder added to the radiation-shielding powder and the aluminum powder or the like used as needed is low, and it becomes impossible to produce a strong preform, which is also undesirable in this respect.

[0043] The "average particle size" of the radiation-shielding powder and the aluminum powder used as needed in the present invention is the particle size (median diameter) at an integrated value of 50% in the particle size distribution determined by a laser diffraction / scattering method.

[0044] Although it varies depending on the type and particle size of the radiation-shielding powder, according to the studies of the present inventors, the volume fraction (Vf) of the preform typically obtained in the preform production step constituting the production method of the present invention is generally around 50v%. According to the studies of the present inventors, when increasing the volume fraction Vf of the radiation-shielding powder in the preform, it is preferable to blend particles with a large average particle size and particles with a small average particle size so that the small particles are interposed between the large particles. Furthermore, in the present invention, when two or more types of radiation-shielding powder are blended, radiation-shielding powders of the same type but different average particle sizes may be blended together, or radiation-shielding powders of different types may be blended together. In the present invention, when it is desired to produce a preform with the required Vf, the blend of particles to be used in producing the preform can be determined by previously conducting a test blend and calculating the bulk specific gravity of the preform. According to the investigations of the present inventors, by using the manufacturing method of the present invention, it is possible to produce preforms with a Vf of up to 85v% by appropriately blending particles, and as a result, it is possible to provide composites with a high content of radiation-shielding powder, which could not be produced using conventional techniques.

[0045] Various situations can be considered when using a radiation-shielding composite. For example, the higher the volume fraction (Vf) of the radiation-shielding powder in a structure having a radiation-shielding function, the greater the radiation-shielding effect. However, depending on the application, a lower Vf may be acceptable, or the Vf of the radiation-shielding powder may be reduced in consideration of production costs. In contrast, according to an embodiment of the manufacturing method of the present invention, in which aluminum powder or the like is used as needed, the content of the radiation-shielding powder in the manufactured preform can be appropriately controlled within a wider range by a very simple means of adding a required amount of aluminum powder or the like to the specific radiation-shielding powder specified in the present invention. For example, a preform with a radiation-shielding powder Vf of 50 v% will be impregnated with 50 v% molten aluminum in the next step. In contrast, for example, if a preform formed by adding aluminum powder is used, the total amount of aluminum in the preform and the molten aluminum metal, aluminum alloy, or specific low-melting-point metal or specific low-melting-point alloy impregnated in a later step (referred to in the specification of the present invention as "molten aluminum") constitutes the amount of aluminum in the composite, and the amount of aluminum in the radiation-shielding structure made from the composite can be increased. In other words, by adding aluminum powder or the like to the preform, it becomes possible to freely control the volume fraction Vf in the radiation-shielding structure.

[0046] As described above, the manufacturing method of the present invention can easily produce a composite of radiation-shielding powder and molten aluminum, in which the radiation-shielding powder Vf (filling factor) is controlled over a wide range of 3v% to 85v%, by appropriately using means such as a combination of large and small particles of a specific radiation-shielding powder or the addition of aluminum powder as needed. According to the inventors' studies, a composite with a radiation-shielding powder content of less than 3v% is impractical because its radiation-shielding effect is too low. Furthermore, according to the inventors' studies, it is difficult to achieve a Vf of 85v% or more with conventional techniques, even when particle blends and various molding methods are utilized.

[0047] [Preform manufacturing process] In the step of producing a preform, which constitutes the manufacturing method of the present invention, first, a preform forming material is prepared as follows. One or more types of powder are selected from the specific radiation-shielding powder group defined in the present invention and described above, and aluminum powder or the like, added as needed, are thoroughly stirred and mixed using a ball mill, paddle stirrer, or the like. For example, when tungsten powder (specific gravity: 19.3) and boron carbide powder (specific gravity: 2.52), which have different specific gravities, are used as radiation-shielding powders and aluminum powder (specific gravity: 2.7) is added as needed, it is preferable to use a V-type mixer or a drum can rotary mixer, in which the entire mixing container rotates, to prevent separation due to the difference in specific gravities.

[0048] Next, a mixture of the radiation-shielding powder specified in the present invention and aluminum powder or the like, which is used as needed, is mixed with a non-powdered silica-based binder to form a molded mixture, and the molded body obtained is fired at a temperature of 300° C. or higher and 900° C. or lower to prepare a porous molded body (preform). These components will be described below.

[0049] (non-powder silica binder) Suitable examples of the non-powdered silica-based binder constituting the present invention include liquid silica-based binders (hereinafter also referred to as "liquid silica-based binders") that are at least one selected from the group consisting of water glass (sodium silicate), colloidal silica, liquid silicone resin, a silicone resin solution obtained by dissolving a silicone resin in an organic solvent, and silica alkoxides made of silica and an organic substance and cured by heating at a temperature of 900° C. or less. The liquid silica-based binders are added in the required amount depending on the amount of the radiation-shielding powder, etc., used.

[0050] The amount of the liquid silica-based binder used in the present invention is suitably, for example, about 0.5 to 10 parts by mass, calculated as SiO2, per 100 parts by mass of the mixture powder of radiation-shielding powders containing aluminum powder and the like as needed. According to the studies of the present inventors, an amount less than 0.5 parts by mass is not preferred because it does not exert sufficient strength as a binder. On the other hand, even if the amount exceeds 10 parts by mass, the binder still functions, but the relative content of the radiation-shielding powder becomes low, so there is no need to add more than this amount.

[0051] Liquid silica-based binders such as the above-mentioned ethyl silicate are compounds of silica (Si) and organic substances, which undergo thermal decomposition to form ultrafine SiO2 powder. Water glass becomes ultrafine SiO2 binder when heated with sodium silicate dissolved in water. As colloidal silica, it is preferable to use one in which extremely fine silica particles of several tens of microns (nm) or less are dispersed as a colloid in water or an organic solvent. The reason for using these silica-based binders is to strengthen the preform used in the next process.

[0052] The binder and radiation-shielding powder can be uniformly mixed by using ethyl silicate or silicone resin, which contain silica that is thermally decomposed to SiO2 at low temperatures, or water glass or colloidal silica of ultrafine SiO2 dispersed in a solvent, which similarly generates SiO2 at low temperatures. According to the studies of the present inventors, these silica-based binders are ultrafine powders, and in the steps of the manufacturing method of the present invention, they are uniformly mixed in the preform at the molecular level, then pass through an amorphous (non-crystalline) state, and then generate ultrafine SiO2 powder while remaining uniform, so that a strong preform can be produced.

[0053] In the next step, the prepared mixed powder, which is the raw material for the preform, is molded and sintered to produce a preform. It is important in the present invention to prevent decomposition of the radiation-shielding powder during the manufacturing process of the composite of the present invention, so as not to impair the intended function of the present invention. Therefore, in the manufacturing method of the present invention, the sintering temperature when molding and sintering to produce a preform must be low, at 900°C or lower. In contrast, all of the liquid silica-based binders used in the present invention are sufficiently effective as binders even at temperatures below 900°C. Here, when using silica-based binders in conventional ceramic manufacturing processes, silica powders with particle sizes ranging from submicrons to several microns are generally used. In conventional techniques, when silica powder is used as a binder, the preform must be sintered at temperatures above 1100°C to ensure the strength of the resulting preform. However, the above-mentioned conventional techniques cannot be applied to the composite technology of the present invention. In the manufacturing method of the present invention, when a preform is manufactured by molding and sintering, when the manufactured preform is impregnated with molten aluminum, etc., it is necessary to prevent decomposition of the radiation-shielding powder, so the temperature must be low, 900°C or lower. This point will be described later.

[0054] In the production method of the present invention, the liquid silica-based binder as described above is added little by little to one or more types of uniformly mixed radiation-shielding powder that may contain the aluminum powder described above. The mixer used in this process is preferably a Henschel mixer that stirs at high speed with high shear force or a mixer equipped with a birdcage-shaped rotor with thin wires. When adding the liquid silica-based binder, an appropriate amount of an organic binder such as PVA or PVB may be added as needed, provided that the object of the present invention is not impaired.

[0055] Next, a mixture containing the radiation-resistant shielding powder obtained by adding the liquid silica-based binder and uniformly mixing it as described above is used to produce a molded body by a general method such as press molding, tapping molding, or CIP molding.

[0056] In the manufacturing method of the present invention, the molded body obtained as described above is heated and fired at a temperature of 300°C to 900°C to harden it and produce a preform. According to the investigations of the present inventors, at temperatures below 300°C, the silica-based binder is not effective, and a strong preform cannot be produced. On the other hand, at temperatures above 300°C, the added liquid silica-based binder is effective, and a strong preform can be produced. Furthermore, for the following reasons, in the manufacturing method of the present invention, it is necessary to produce a preform by firing at a temperature of 900°C or less.

[0057] For example, when boron carbide (B4C) is used as the radiation shielding powder, it may decompose into BO and CO2 at high temperatures in air, so it must be fired at a temperature of 900°C or less. Furthermore, when boron carbide (B4C) is used as the preform forming material and aluminum powder or the like is added as needed, Al4C3 formed from the boron carbide and aluminum may undergo the following decomposition reaction at high temperatures: The Al4C3 formed in the following decomposition reaction is unstable and reacts with moisture in the air to decompose into Al(OH)3 and CH3. However, it is undesirable for Al4C3 to remain in the composite. B4C+Al → Al4C3+B

[0058] When barium sulfate is used as the radiation shielding powder, BaSO4 decomposes into BaO and SO2 at high temperatures, so firing at high temperatures is also not recommended.Furthermore, firing at temperatures above 900°C is also not recommended because the following decomposition reaction may occur. Al + BaSO4 → BaO + Al2O3 + SO (gas)

[0059] When tungsten (W) is used as the radiation-shielding powder, tungsten becomes WO3 at high temperatures in air, which is undesirable because it reduces the effect of adding a silica-based binder. According to the study by the present inventors, in order to suppress the series of reactions described above, it is preferable to set the firing temperature of the molded body to 900°C or less. By doing so, decomposition and oxidation are suppressed, and it becomes possible to manufacture stable radiation-shielding powder preforms.

[0060] <Complex production process> Next, in the first production method of the present invention, molten aluminum is impregnated and filled into all of the voids of the porous molded body (preform) produced as described above under high pressure, and then solidified to produce a composite having radiation-shielding properties. In the second production method of the present invention, a liquid organic / inorganic sealing agent is vacuum-impregnated into some or all of the voids of the preform, or is impregnated under pressure after vacuum impregnation, and then the agent is heated to a temperature of 300°C or higher and 900°C or lower to solidify and combine, to produce a composite having radiation-shielding properties. The steps for producing the composite in the first production method of the present invention and the second production method of the present invention will be described below.

[0061] [First manufacturing method] In a first manufacturing method of the present invention, a composite having radiation-shielding properties is prepared, comprising an aluminum matrix and a total of 3 to 85 volume % of a radiation-shielding powder. Specifically, a preform prepared as described above is used. A molten metal (such as a low-melting-point metal selected from the group consisting of aluminum metal, aluminum alloy, zinc, tin, and lead, or a low-melting-point alloy of such a low-melting-point metal with another metal) is cast into the preform at a temperature of 300 to 900°C. (In this specification, the term "molten aluminum" is used to represent aluminum metal and aluminum alloys.) The preform is then held at a high pressure of 20 to 200 MPa for 3 to 15 minutes, e.g., 3 to 5 minutes, to impregnate the entire voids of the preform with the molten aluminum. The preform is then immediately removed and cooled within 15 minutes of the start of impregnation to obtain a composite. More specifically, the composite is formed using the following procedure.

[0062] The temperature of the molten aluminum to be impregnated is set to a temperature equal to or higher than the melting point of the respective metal, typically about 50°C to 150°C higher than the melting point of the respective metal. For example, in the case of aluminum metal or aluminum alloy, the temperature is set to about 700°C to 800°C. Furthermore, in the case of using a low-melting-point alloy, a temperature of about 350°C to 500°C is appropriate for solder alloys, and a temperature of about 450°C to 550°C is appropriate for zinc alloys. Regardless of the type of molten metal used, in the present invention, it is necessary to impregnate the voids in the preform produced as described above with the molten metal at 900°C or less.

[0063] First, the preform prepared in advance is preheated at a temperature of 300°C or higher and 900°C or lower to be used for impregnation with molten aluminum. Preheating the preform to a low temperature below 300°C is undesirable because the impregnated molten aluminum rapidly cools and solidifies during the casting and impregnation process described below, making it difficult to impregnate the entire voids of the preform. According to the inventors' investigations, if the preform is preheated to a temperature of 300°C or higher, the molten aluminum can be impregnated into the entire voids of the preform. However, preheating temperatures above 900°C are undesirable because, for example, the boron carbide used as a radiation-shielding powder may react with the aluminum used for impregnation with the molten aluminum to produce Al4C3 or BaSO4 may decompose.

[0064] Next, the process of impregnating the preheated preform with molten aluminum to form a composite will be described with reference to Fig. 1. Specifically, the preform produced as described above is impregnated with molten aluminum in the following order to form a composite.

[0065] (1) As shown in Fig. 1A, a preform 2 preheated to 300°C to 900°C is placed on the lower punch 4 of a press die 10 that has been preheated to approximately 200°C to 300°C using a burner or the like. Next, molten aluminum 1 melted at a temperature of 300°C to 900°C is cast into the press die 10. When using aluminum metal or an aluminum alloy, the molten aluminum is preferably heated to a temperature of 700°C to 900°C. (2) Next, as shown in Fig. 1B, an upper punch 5 of a press 10 is placed on the preform 2 and a load is applied. A load is applied to the upper punch 5 of the press 10 so that the pressure of the molten aluminum 1 becomes 20 MPa to 200 MPa, and the molten aluminum 1 is impregnated into the pores (voids) of the preform 2. At this time, the state in which the load is applied is maintained for 3 to 15 minutes in order to impregnate the voids of the preform 2 with the molten aluminum 1. (3) Next, as shown in Figure 1C, immediately after the preform 2 is impregnated (specifically, within about 15 minutes after the start of impregnation with the molten aluminum), the preform 2 is pushed up from the bottom of the lower punch 4, and the composite 3 impregnated with the molten aluminum 1 is immediately removed. Then, the composite 3 is cooled in as short a time as possible to solidify the impregnated molten aluminum 1.

[0066] Below, we will explain the points that should be taken into consideration in the process of impregnating the molten aluminum 1 into the preform 2, which is a series of porous molded bodies described above. First, when using aluminum metal or an aluminum alloy, a casting temperature of less than 600°C is not preferable because the molten aluminum hardens in a short time and does not impregnate all of the voids in the preform. On the other hand, a casting temperature of more than 900°C is not preferable because, as explained above, for example, boron carbide (B4C) in the radiation-shielding powder may decompose to produce Al4C3, or, if barium sulfate (BaSO4) is used as the radiation-shielding powder, BaSO4 may thermally decompose.

[0067] In the first manufacturing method of the present invention, the pressure for impregnation with the molten aluminum is 20 MPa or more and 200 MPa or less. A pressure less than 20 MPa is undesirable because the pressure is too low and the molten aluminum may not completely impregnate the voids in the preform. Since impregnation is sufficient at a pressure of 20 MPa or more and 200 MPa or less, there is no need to apply pressure exceeding 200 MPa. According to the inventors' studies, good impregnation can be achieved even at a pressure of, for example, about 100 MPa.

[0068] The composite obtained by high-pressure impregnation is held for 3 minutes, preferably 5 minutes, and then removed from the mold within at least 15 minutes from the start of impregnation with the molten aluminum. If the composite obtained by high-pressure impregnation of the voids in the preform with the molten aluminum is held in the mold for a period longer than 15 minutes, for example, boron carbide and aluminum may react to produce Al4C3, or BaSO4 may decompose, resulting in a composite that violates the provisions of the present invention and must be avoided.

[0069] In the above explanation, a method of high-pressure impregnation of a porous molded body (preform) with molten aluminum using a high-pressure press as shown in FIG. 1 has been exemplified. However, the present invention is not limited to this, and any machine may be used as long as it is configured to be able to cast and fill the molten aluminum into the preform at 20 MPa or more. For example, a die-casting machine, a squeeze-casting machine, or the like may also be used. Note that the cooled composite is surrounded by aluminum, which is removed by machining to extract the composite. According to the first manufacturing method of the present invention described above, it is possible to produce a stable and dense composite having radiation-shielding properties, in which the radiation-shielding powder contains 3% to 85% by volume of Vf.

[0070] [Second manufacturing method] In the second manufacturing method of the present invention, a composite having radiation-shielding function is prepared, which is formed by compounding a solidified material resulting from a liquid organic / inorganic sealing agent in a state where the solidified material is present in an amount of 25% by volume or more relative to 100% by volume of the voids in the preform obtained as described above, and which contains a powder having a radiation-shielding effect in a total amount within the range of 3% by volume or more and 85% by volume or less.

[0071] (liquid organic / inorganic sealant) In the second production method of the present invention, it is preferable to use, as the liquid organic / inorganic sealing agent that characterizes the second production method, a liquid compound having a low viscosity of 50 mPa s or less and containing 30 mass % or more of non-volatile components, such as three liquid compounds listed below. (1)Type 1 Alkoxide compounds adjusted so that the non-volatile components are 30% by mass or more, such as liquid ethyl silicate [Si(OC2H5)4] having an alcohol Si bond, or liquid oligomers formed by partial hydrolysis of the ethyl silicate to form dimers or tetramers, or similar liquid alkoxides such as methyl silicate [Si(OCH3)4] and liquid oligomers formed by partial hydrolysis thereof.

[0072] (2) Type 2 Liquid silicone or its derivatives having a siloxane bond as the main chain of the following general formula, or silicone or its derivatives adjusted so that the non-volatile components when diluted and dissolved in a solvent are 30% by mass or more. In the general formula, R is an organic group such as a methyl group, ethyl group, vinyl group, phenyl group, or acetyl group. Specifically, for example, liquid compounds such as silicone oil or silicone adhesive dissolved in an organic solvent can be used. TIFF2026019314000001.tif23170

[0073] (3) Type 3 The alkoxysilane derivative is a liquid alkoxysilane compound that reacts with moisture in the air to undergo a condensation reaction to generate a silicone-oxygen organic compound (Si-OR) as shown in the following reaction formula. For example, a compound such as the one-component room-temperature curing sealant described in Japanese Patent No. 3816354 can be used. Examples of such a compound include commercially available products such as Permeate (registered trademark, manufactured by D&D Co., Ltd.).

[0074] TIFF2026019314000002.tif105170

[0075] (Method of compounding) In the second manufacturing method of the present invention, a composite having a radiation-shielding function is obtained, in which a solidified material derived from a liquid organic / inorganic sealing agent is present in the voids of a preform prepared as described above using a radiation-shielding powder as a raw material. Specifically, the voids of a porous molded body (preform) are vacuum-impregnated with a liquid organic / inorganic sealing agent containing 30 mass% or more of a non-volatile component and having a viscosity of 50 mPa·s or less, or impregnated under a pressure of 10 atmospheres or less after vacuum impregnation, and then heated to a temperature of 300°C or more and 900°C or less, so that the solidified material of the liquid organic / inorganic sealing agent and / or the heat-treated product of the liquid organic / inorganic sealing agent remain in 25 volume% (1 / 4) or more of the entire voids of the preform, assuming that the entire voids of the preform are 100 volume%. This composite combines the radiation-shielding powder and the component derived from the liquid organic / inorganic sealing agent. That is, since the total voids in the preform account for approximately 15v% to 40v%, components derived from the organic / inorganic sealant remain in the voids at a ratio of at least ¼ of the total voids, i.e., at least 4v% to 10v%. In other words, the resulting composite is composed of a high ratio of 60v% to 85v% of the fired product of the mixture containing the radiation-shielding powder constituting the preform, 4v% to 10v% or more of the components derived from the organic / inorganic sealant, and the remainder being voids. In addition, the amount of liquid silica-based binder mixed with the radiation-shielding powder in the present invention is preferably about 0.5 to 10 parts by mass of the liquid silica-based binder in terms of SiO2 per 100 parts by mass of the radiation-shielding powder. This allows for the production of a composite with a high ratio of radiation-shielding powder. These points also apply to the composite obtained by the first production method.

[0076] The liquid organic / inorganic sealing agent used in the second manufacturing method of the present invention, as exemplified above, has a low viscosity of 50 mPa·s or less to facilitate impregnation into the preform. If the viscosity exceeds 50 mPa·s, the organic / inorganic sealing agent will be less likely to penetrate into the fine details of the preform, potentially preventing a strong composite from being obtained. It is also essential that the liquid organic / inorganic sealing agent contain 30 wt% or more of nonvolatile matter relative to 100 wt% of the sealing agent. In the second manufacturing method of the present invention, the organic / inorganic sealing agent is impregnated into the voids of the preform so that it accounts for at least 25 v% of the total voids (100 v%) of the preform, and then the preform is heated to 200°C to 900°C to combine the radiation-shielding powder and the organic / inorganic sealing agent. That is, by heating at the above-mentioned temperatures, the liquid organic / inorganic sealing agent impregnated in the voids of the preform becomes a solidified liquid organic / inorganic sealing agent or a heat-treated liquid organic / inorganic sealing agent, both of which are solid, and remains in the voids of the preform.

[0077] The preform used in the manufacturing method of the present invention, which is prepared as a composite as described above, is a porous body having voids of approximately 15 to 40 v% relative to 100 v% of the entire preform. Therefore, the composite obtained by the second manufacturing method of the present invention, in which a liquid organic / inorganic sealing agent is impregnated into the preform and then heat-treated, is a composite in which the solidified liquid organic / inorganic sealing agent and / or the heat-treated liquid organic / inorganic sealing agent account for 25 v% or more of the voids in the preform, assuming the entire voids are 100 v%. This means that the composite obtained by the second manufacturing method of the present invention is a composite in which the solidified liquid organic / inorganic sealing agent and / or the heat-treated liquid organic / inorganic sealing agent is fixed in some (25 v% or more) or all of the voids in the preform.

[0078] According to the inventors' investigations, if the amount of the solidified liquid organic / inorganic sealing agent and / or the heat-treated liquid organic / inorganic sealing agent in the composite obtained by the second manufacturing method of the present invention is less than 25% by volume relative to the total voids of the preform (100% by volume), a composite with strong and practical radiation-shielding properties cannot be obtained. Furthermore, a preferred configuration of the composite obtained by the second manufacturing method of the present invention is, in addition to the above, that the amount of the solidified liquid organic / inorganic sealing agent and / or the heat-treated liquid organic / inorganic sealing agent remaining in the voids is approximately 5% by volume or more relative to the total voids of the preform (100% by volume). For example, if the voids in the preform account for 20% by volume, 25% (1 / 4) of that, i.e., 5% by volume relative to the total voids of the preform (100% by volume), will be the organic / inorganic sealing agent. In the above example, the fired product of the mixture containing the radiation-shielding powder that constitutes the preform accounts for 80% by volume. As mentioned above, the amount of liquid silica-based binder to be mixed with the radiation-shielding powder when producing a preform is preferably about 0.5 to 10 parts by mass of liquid silica-based binder in terms of SiO2 per 100 parts by mass of the radiation-shielding powder. Therefore, the total amount of the radiation-shielding powder, silica-based binder, and organic / inorganic sealing agent constituting the composite of the above example shows a high ratio of 70 to 79.5 v%, resulting in a strong composite.

[0079] In the second manufacturing method of the present invention, the silica-based binder required to produce the preform and the liquid organic / inorganic sealant impregnated into the resulting preform may be the same compound. However, the liquid organic / inorganic sealant used to impregnate the voids in the preform must be impregnated into the preform so that the sealant impregnated into the voids in the preform ultimately remains in a solidified state. Therefore, it is necessary for the liquid organic / inorganic sealant to have a low viscosity of 50 mPa·s or less and a non-volatile content of 30 wt% or more. Therefore, any silica-based binder that meets these requirements can be used in combination.

[0080] As previously mentioned, in the second manufacturing method of the present invention, the preform impregnated with the liquid organic / inorganic sealing agent is heat-treated at a temperature of 200°C or higher and 900°C or lower. The reason for setting the heating temperature at 200°C or higher is as follows: By setting the heating temperature at 200°C or higher, the compounds used as the liquid organic / inorganic sealing agent, such as liquid alkoxysilane compounds that generate siloxane bonds, ethyl silicate oligomers, or silicone oxygen organic compounds (Si-OR), are thermally decomposed, allowing them to function as silica-based binders or Si-OR-based organic / inorganic binders, thereby strengthening the preform. Furthermore, the reason for setting the heating temperature at 900°C or lower is to prevent the decomposition or oxidation of the powders that have a radiation shielding effect, such as B4C and BaSO4, that make up the preform.

[0081] The procedure for the second manufacturing method of the present invention will be outlined with reference to FIG. 2. In FIG. 2, 30 denotes a reduced pressure vessel used in the second manufacturing method of the present invention. A preform 32 is placed in an interior container 34 installed inside the reduced pressure vessel 30, before the organic / inorganic sealing agent 31 is impregnated into the voids. The opening and closing jig 33 of the reduced pressure vessel 30 is closed, and the interior of the reduced pressure vessel 30 is depressurized using a vacuum pump (not shown) through a pressure reduction port 36 installed on the reduced pressure vessel 30. Once the pressure inside the reduced pressure vessel 30 has reached approximately zero, the organic / inorganic sealing agent 31 is gradually introduced from an organic / inorganic sealing agent introduction container 35 into the interior container 34. The amount of organic / inorganic sealing agent 31 introduced is determined in advance to be an amount sufficient to completely impregnate the preform 32 with the organic / inorganic sealing agent 31 and to completely immerse the preform 32.

[0082] After the organic / inorganic sealing agent 31 is introduced as described above, a vacuum is maintained for approximately 5 to 10 minutes, allowing the organic / inorganic sealing agent 31 to be vacuum-impregnated into the voids of the preform 32. After the impregnation is complete, the container is gradually opened to the atmosphere, and air is introduced into the reduced pressure vessel 30. After the atmosphere inside the reduced pressure vessel 30 is returned to the atmosphere, air that has been decompressed to approximately 10 atmospheres using compressed air from a compressor or the like (not shown) is gradually introduced through the pressure inlet 37, and after pressurizing to approximately 4 atmospheres, this is kept for approximately 5 to 10 minutes, allowing the organic / inorganic sealing agent 31 to be impregnated into the preform 32.

[0083] Thereafter, the compressed air in the reduced pressure vessel 30 is gradually released, and once atmospheric pressure is reached, the preform in which the solidified liquid organic / inorganic sealing agent and / or the heat-treated liquid organic / inorganic sealing agent is fixed in the voids is taken out, gradually dried, and heated to 300 to 400°C to obtain a composite having radiation shielding properties. [Example]

[0084] Next, the present invention will be described in more detail with reference to examples and comparative examples. The present invention will be specifically described using examples and comparative examples of two manufacturing methods: a method of impregnating molten aluminum into the voids of a porous molded body (preform), which is a molded and sintered product made from a mixture of radiation-shielding powder and a non-powdered silica-based binder, and a method of impregnating an organic / inorganic sealing agent. The present invention is not limited in any way by the following examples. In the text, % refers to volume % unless otherwise specified. Due to the special circumstances that require handling of radiation in measuring the shielding effect, the radiation shielding rates of the composites of Examples 1 to 3 were measured by an external measurement institution. The radiation shielding rates measured by the external institution were higher than those of conventional materials.

[0085] <Example of method for impregnating a preform with molten aluminum> [Example 1] 450 g of B4C powder #800 (manufactured by Dojin Sangyo Co., Ltd.) with an average particle size of 16 μm was mixed for 30 minutes in a V-type mixer. 5 g of ethyl silicate was added to the mixed powder as a liquid binder, and the whole was placed in a Henschel mixer, which applies shear force to the powder, and stirred at high speed for 15 minutes to mix uniformly. The resulting mixed powder was placed in a 100 mm x 100 mm mold, a lid was placed on it, and the mixture was stirred at 160 kgf / cm. 2 The molded body was placed in a sintering furnace and heated to 400°C at a heating rate of 50°C / hour. It was then held at 400°C for 3 hours for sintering, after which it was naturally cooled. The resulting sintered body (preform) measured 100mm x 100mm x 35mm and weighed 449g. Based on the true specific gravity of boron carbide (B4C), which is 2.51, this preform had a bulk specific gravity of 1.31, a boron carbide filling rate (Vf) of 52%, and a void content of 48%. The preform was heated at a heating rate of 100°C / hour and held at 500°C, and then left in a heated state for the next aluminum impregnation step using a high-pressure press.

[0086] A mold with an inner diameter of 300 mm installed in a high-pressure press was heated to approximately 250°C using a burner. The preform, which had been left in a heated state, was then placed in the mold of the press, and molten aluminum melted at 800°C was poured into the mold, followed by high-pressure casting as described below. As shown in FIGS. 1A and 1B, molten aluminum 1 melted at 800°C was poured into the mold containing preform 2. Immediately after this, upper punch 5 of press 10 was lowered and a load was applied to upper punch 5 so that the pressure of molten aluminum 1 reached 70 MPa. As mentioned above, the inner diameter of the mold was 300 mm, which corresponds to a load of approximately 500 tons on press 10.

[0087] After the load was applied and maintained for 5 minutes, the upper punch 5 was removed, and the lower punch 4 was immediately raised to lift the impregnated body (composite) 3 to the top of the press (see Figure 1C), where it was allowed to cool naturally. After it had cooled enough to be handled, the solidified aluminum surrounding the composite 3 was removed by machining, and the composite 3 was taken out.

[0088] The specific gravity of the extracted composite was measured to be 2.61. This value was almost identical to the calculated value for when the voids in the preform were completely impregnated with aluminum, and it was therefore concluded that the material extracted above was a dense composite of B4C and aluminum. The high content (volume filling rate) of light boron carbide, with a specific gravity of 2.52, at 52v%, enabled the production of a lightweight composite with a specific gravity of 2.61. Furthermore, when a portion of the obtained composite was cut out and the surface was subjected to X-ray diffraction analysis, the formation of Al4C3 due to the decomposition of B4C was not confirmed.

[0089] The radiation shielding effectiveness of the obtained BC material, with a volume filling rate (Vf) of 52% and a thickness of 35 mm, was measured by an external measurement organization. The results showed a high shielding effectiveness of 61% for neutrons from the californium (Cf) isotope Cf252. Furthermore, a bending test based on JIS-R1061 on the composite of this example revealed a high strength of 183 MPa. These results indicate that the lightweight BC powder used as the raw material, which has excellent radiation shielding effectiveness, was compounded without decomposition, making the composite of this example a useful material that effectively combines the properties of BC powder.

[0090] [Example 2] 230 g of B4C powder #180 (manufactured by Dojin Sangyo Co., Ltd.) with an average particle size of 70 μm and 260 g of B4C powder #800 with an average particle size of 16 μm, similar to that used in Example 1, were mixed for 30 minutes in a V-type mixer. 15 g of ethyl silicate was added to the mixed powder as a liquid binder, and the mixture was mixed for 15 minutes in a Henschel mixer, as in Example 1.

[0091] The resulting mixed raw material was press-molded and sintered in the same manner as in Example 1 to produce a preform measuring 100 mm × 100 mm × 26 mm, with a bulk density of 1.66, a B4C filling rate Vf of 66%, and a porosity of 34 v%. The resulting preform was placed in a mold of a high-pressure press and high-pressure impregnated with molten aluminum in the same manner as in Example 1. Thereafter, the preform was naturally cooled in the same manner as in Example 1, and the solidified aluminum around the composite was removed.

[0092] The specific gravity of this composite was 2.57, which was almost identical to the calculated value when the voids in the preform were impregnated with aluminum, indicating that it was a dense composite composed of BC and aluminum. Furthermore, X-ray diffraction was performed on the surface of the composite using the same method as in Example 1. As a result, as in Example 1, no formation of AlC or other compounds was observed. As described above, by combining BC powders with different average particle sizes as raw materials, a composite with a BC powder filling rate of 66v%, higher than in Example 1, was produced. Furthermore, despite the high BC filling rate, a lightweight composite with a specific gravity of 2.57 was produced.

[0093] The radiation shielding effectiveness of the obtained BC material, with a volume filling factor (Vf) of 66% and a thickness of 26 mm, was measured by an external measurement organization. The results showed a high shielding effectiveness of 31% for neutrons from the californium (Cf) isotope Cf252. Furthermore, a bending test based on JIS-R1061 on the composite of this example revealed a high strength of 193 MPa. These results indicate that the lightweight BC powder used as the raw material, which has excellent radiation shielding effectiveness, was compounded without decomposition, making the composite of this example a useful material that effectively combines the properties of BC powder.

[0094] [Example 3] 820 g of A-200 (trade name, manufactured by Takehara Chemical Industry Co., Ltd.), a barium sulfate (BaSO4) powder with an average particle size of 15 μm, was mixed uniformly in the same manner as in Example 1. As a liquid binder, a silicone-based resin solution was used, prepared by dissolving soluble silicone resin KR-200 (manufactured by Shin-Etsu Chemical Co., Ltd.) in ethanol to a concentration of 20 wt% by mass. 50 g of the prepared silicone-based resin solution was then added to the mixed BaSO4 powder, and the mixture was stirred at high speed using a Henschel mixer in the same manner as in Example 1.

[0095] A preform fabricated using the same method and procedure as in Example 1 had dimensions of 100 mm x 100 mm x 28 mm, a bulk specific gravity of 2.92, and a BaSO4 filling rate of 65 v%. Next, using the same method as in Example 1, the preform was high-pressure impregnated with molten aluminum and processed to extract a composite. The specific gravity of the composite was 3.86, which was nearly identical to the calculated value (theoretical value), confirming that it was a dense composite made of BaSO4 and aluminum.

[0096] The radiation shielding effectiveness of the BaSO4 material obtained above, with a volume filling rate (Vf) of 65v% and a thickness of 28mm, was measured by an external measurement organization. The results showed high values ​​of 35% projection efficiency for cesium (Cs) gamma rays (Cs137) and 99.5% shielding efficiency for 150Kv X-rays. Furthermore, a bending test based on JIS-R1061 on the composite of this example showed a high strength of 193 MPa. These results indicate that the composite obtained in this example is a useful material that effectively combines the properties of the lightweight BaSO4 powder used as the raw material, without decomposition, and effectively combines the properties of BaSO4 powder.

[0097] [Example 4] 250 g of B4C powder #800 (manufactured by Dojin Sangyo Co., Ltd.) with an average particle size of 16 μm and 270 g of WA-100 (manufactured by Yamaishi Metals Co., Ltd.), an aluminum powder with an average particle size of 18 μm, were used as raw material powders and uniformly mixed in the same manner as in Example 1. 10 g of liquid ethyl silicate (manufactured by Colcoat Co., Ltd.) was added as a binder, and the mixture was stirred at high speed using a Henschel mixer in the same manner as in Example 1.

[0098] A preform fabricated using the same method and procedure as in Example 1 had dimensions of 100 mm x 100 mm x 33 mm, a bulk specific gravity of 1.30, and a combined filling rate of 50 v% of BC powder and aluminum powder (Al powder). Next, molten aluminum was infiltrated into the preform at high pressure using the same method as in Example 1, and a composite was extracted. The specific gravity of the composite in this example was 2.65, which was nearly identical to the calculated value when all of the voids in the preform were impregnated with molten aluminum.

[0099] Since the volume ratio of the two types of raw material powders, BC powder and Al powder, was approximately 1:1, approximately 50v% of the preform was aluminum powder. Therefore, the amount of aluminum in the resulting composite, including the aluminum impregnated in the preform, was 75v%. Therefore, the composite consisted of 75v% aluminum powder and the remaining 25v% BC powder. From the above, it was confirmed that the concentration of the radiation-shielding powder can be controlled by mixing an appropriate amount of aluminum powder into the raw material of the preform. Furthermore, in the above case, by using BC powder as the raw material of the preform, a lightweight composite with a specific gravity of 2.65 could be produced. Furthermore, a bending test of the composite of this example based on JIS-R1061 showed a high strength of 182 MPa.

[0100] [Example 5] A raw material for the preform was prepared by adding 280 g of BaSO powder A-200 (trade name, manufactured by Takehara Chemical Industry Co., Ltd.) with an average particle size of 15 μm, 395 g of aluminum powder WA-100 (manufactured by Yamaishi Metals Co., Ltd.) with an average particle size of 18 μm, and 50 g of a 20 wt % solution of silicone resin KR-200 dissolved in ethanol, the same as used in Example 3. The raw material was stirred at high speed using a Henschel mixer, as in Example 1.

[0101] Thereafter, a preform was produced using the same method and procedure as in Example 1. The preform had a size of 100 mm x 100 mm x 38 mm, a bulk specific gravity of 1.77, and a total filling rate (Vf) of BaSO4 powder and Al powder of 55v%.

[0102] Next, the preform obtained above was high-pressure infiltrated with molten aluminum using the same method as in Example 1, and processed to extract a composite. The specific gravity of the prepared composite was 2.99, which was nearly identical to the calculated value for the dense body. The composite of this example was 70v% aluminum powder in the preform, so that the total aluminum content in the composite, including the impregnated aluminum, was 84v%, with the remaining 16v% being BaSO4 powder. Thus, like the composite of Example 4, this composite is an example in which the concentration of barium sulfate powder, a radiation-shielding powder, in the composite can be controlled by mixing aluminum powder into the preform raw materials. Furthermore, a bending test of the composite of this example based on JIS-R1061 revealed a high strength of 212 MPa.

[0103] [Example 6] 270 g of B4C powder #800 (manufactured by Dojin Sangyo Co., Ltd.) with an average particle size of 16 μm and 495 g of A-200 (trade name, manufactured by Takehara Chemical Industry Co., Ltd.), a BaSO4 powder with an average particle size of 15 μm, were used as raw material powders and uniformly mixed in the same manner as in Example 1. 15 g of liquid ethyl silicate (manufactured by Colcoat Co., Ltd.) was added as a binder, and the mixture was stirred at high speed using a Henschel mixer in the same manner as in Example 1.

[0104] Thereafter, a preform was produced using the same method and procedure as in Example 1. The preform had a size of 100 mm x 100 mm x 38 mm, a bulk specific gravity of 2.00, and a total filling rate (Vf) of the B4C and BaSO4 powders of 57v%.

[0105] Next, the composite was impregnated with molten aluminum and processed in the same manner as in Example 1, and then extracted. The specific gravity of the prepared composite was 3.16, which was almost identical to the calculated value for the preform impregnated with molten aluminum. The obtained composite had 28.5v% B4C, 28.5v% BaSO4, and 43v% aluminum. As shown in this example, it was confirmed that a composite containing two types of radiation-shielding powders can be produced by the manufacturing method of the present invention. Furthermore, a bending test of the composite of this example based on JIS-R1061 showed a high strength of 199 MPa.

[0106] [Example 7] 380 g of BC powder #800 (manufactured by Dojin Sangyo Co., Ltd.) with an average particle size of 16 μm and 1270 g of tungsten metal powder W-4 (manufactured by Nippon Shinkinzoku Co., Ltd.) with an average particle size of 3 μm were mixed uniformly in the same manner as in Example 1. Water glass No. 4 (manufactured by Fuji Chemical Co., Ltd.) was diluted with water as a binder, and an amount equivalent to 16 g of SiO was added. The mixture was then stirred at high speed in a Henschel mixer in the same manner as in Example 1. A preform was then fabricated using the same method and procedure as in Example 1. The preform measured 100 mm × 100 mm × 32 mm, had a bulk density of 5.18, and a total filling rate (Vf) of BC and tungsten W was 68%.

[0107] Next, the composite was high-pressure impregnated with molten aluminum using the same method as in Example 1, processed, and extracted. The specific gravity of the composite was 6.04, which was almost identical to the calculated value for the preform impregnated with molten aluminum. The resulting composite had 48.5v% B4C, 20.4v% tungsten, and 32v% aluminum. Furthermore, a bending test was performed on the composite of this example based on JIS-R1061, and the result was a high strength of 192 MPa.

[0108] As shown in this example, a composite containing two types of radiation-shielding powders was produced by the method of the present invention, as in Example 6. Furthermore, the composite in this example contains 20.4v% tungsten, and has a specific gravity of 6.04, which is significantly lighter than the specific gravity of 19.5 of pure tungsten.

[0109] [Example 8] Using the same 16μm average particle size B4C powder #800 (manufactured by Dojin Sangyo Co., Ltd.) as in Example 1, an ethyl silicate binder was added, mixed, molded, and fired in the same manner to produce a preform measuring 100mm x 100mm x 35mm, with the same bulk density of 1.31, a boron carbide filling rate (Vf) of 52%, and a void content of 48v%. The preform was heated and left to stand at a temperature of 400°C.

[0110] Using the same method as in Example 1, the preform was placed in a mold with an inner diameter of 300 mm heated to 250°C, and a low-melting-point alloy (zinc alloy: ZDC2, specific gravity 6.8) melted at 500°C was cast into it. It was then infiltrated under high pressure at 70 MPa (500 t press load). After holding for 10 minutes, the material was immediately cooled, cooled to room temperature, and the composite was removed. The specific gravity of the composite was 4.18, and it was a composite material that was nearly 100% impregnated with the low-melting-point zinc alloy. There was no decomposition reaction due to the generation of B4C. Furthermore, a bending test based on JIS-R1061 was conducted on the composite of this example, revealing a high strength of 223 MPa.

[0111] [Comparative Examples 1 and 2] The same B4C powder as used in Example 1 was used and mixed, and 2 g of fine silica powder (manufactured by Yamamori Tsuchimoto Seisakusho Co., Ltd.) with an average particle size of 1.2 μm and 3 g of water were added to 450 g of this (net volume 182 ml), and the mixture was inserted into a mold and press-molded in the same manner as in Example 1. The molded bodies were fired at different temperatures of 400°C and 800°C, respectively, and then cooled. Regardless of the firing temperature, the obtained molded bodies lacked the strength of a preform, could not be handled, and could not be subjected to high-pressure impregnation with molten aluminum.

[0112] [Comparative Examples 3 and 4] The same B4C powder as used in Example 1 was mixed, and 4 g of fine silica powder (LeoSeal QS-9, manufactured by Tokuyama Corporation) with an average particle size of 22 nm (22 mμ) and 64 g of water were added to 450 g of this mixture (net volume 182 ml). The mixed powder was then inserted into a mold and press-molded in the same manner as in Example 1. The compacts obtained by press-molding were fired at different temperatures, either 400°C or 800°C, and then cooled. Regardless of the firing temperature, the fired compacts lacked the strength of a preform, were difficult to handle, and could not be subjected to high-pressure infiltration of molten aluminum.

[0113] Comparative Example 5 A B4C preform was prepared using the same method as in Example 1. The resulting preform was placed in a mold and cast at 900°C using molten aluminum, as in Example 1. In this comparative example, the preform was then held at 900°C for 20 minutes, after which a composite was produced using the same method as in Example 1. The surface of the composite was machined and found to be blackened, so a portion was removed and examined by X-ray diffraction. In addition to the main raw material B4C, small peaks of Al4C3 were observed at 2θ = 31.8°, 35.8°, 40.1°, and 55°. This confirmed that in the case of the composite of this comparative example, if the preform was kept at high temperatures in the press mold for a long period of time, the raw material B4C for the preform would partially decompose, resulting in an unsatisfactory composite.

[0114] Comparative Example 6 890 g of A-200 (trade name, manufactured by Takehara Chemical Industry Co., Ltd.), a BaSO powder with an average particle size of 15 μm, similar to that used in Example 5, was mixed uniformly in the same manner as in Example 1. Then, 50 g of a 20 wt % solution of silicone resin KR-200 in ethanol, similar to that used in Example 3, was added, and the mixture was stirred at high speed with a Henschel mixer in the same manner as in Example 1.

[0115] A preform produced using the same method and procedure as in Example 1 had a size of 100 mm x 100 mm x 33 mm and a BaSO4 filling rate of 60 v%. Next, it was set in a mold using the same method as in Example 1, impregnated with molten aluminum at 950°C, and processed, and the composite was removed. The surface was processed and visually inspected, revealing many pores. This is thought to be due to the decomposition of BaSO4 into BaO and SO2 when heated at high temperatures.

[0116] Table 1 shows the preparation conditions of the preforms in Examples 1 to 8 and Comparative Examples 1 to 6, and the properties and evaluations of the obtained composites in Examples 1 to 8 and Comparative Examples 5 and 6. In Table 1, the "yes" and "no" of decomposition indicate whether decomposition was observed in the radiation-shielding powder constituting each composite.

[0117] TIFF2026019314000003.tif197170

[0118] <Example of a method for impregnating a preform with an organic / inorganic sealant> Next, the second manufacturing method of the present invention, in which a special liquid organic / inorganic sealing agent is impregnated into the voids of a porous molded body (preform) to produce a radiation-shielding composite, will be described with reference to examples and comparative examples. The reason for conducting bending tests on the composites in the following examples is as follows: When the voids of a preform are impregnated with a liquid organic / inorganic sealing agent, components derived from the organic / inorganic sealing agent remain in the voids of the preform. Here, in the case of a composite in which the voids of a preform are impregnated with a liquid organic / inorganic sealing agent, it is not necessary to impregnate all of the voids of the preform, as in the case of impregnation with molten aluminum described above; some voids may remain. According to the inventors' investigations, even in such a configuration, as long as the liquid organic / inorganic sealing agent occupies 25% by volume or more of the voids (100% by volume) of the preform before impregnation with the liquid organic / inorganic sealing agent, the resulting composite has sufficient strength and can be used as a building material such as a wall material or a ceiling material. In other words, if a bending test is performed on the obtained composite to confirm its strength, it can be confirmed that a sufficient amount of the solidified organic / inorganic sealing agent and / or the heat-treated organic / inorganic sealing agent remains in the voids of the preform. As shown below, the composites of the examples have sufficient strength and are of the configuration specified in the present invention.

[0119] [Example 9] A preform weighing 262 g and measuring 100 mm x 100 mm x 20 mm was produced using 270 g of BC powder #800 (manufactured by Dojin Sangyo Co., Ltd.) with a material composition similar to that of Example 1 described above and an average particle size of 16 μm, mixed, molded, fired, and cooled in the same manner. The resulting preform had a bulk density of 1.31 calculated from the true specific gravity of boron carbide (BC), 2.51, a boron carbide filling rate (Vf) of 52 v%, and voids of 48 v%.

[0120] The organic / inorganic sealing agent used was Permeate HS-200 (trade name, manufactured by D&D Corporation; hereafter simply referred to as Permeate), which has a viscosity of 15.5 mPa·s, a specific gravity of 1.15, siloxane bonds, and a non-volatile content of 85 wt%. Using a reduced-pressure vessel 30 as shown in the schematic diagram of FIG. 2, a preform 32 was impregnated with Permeate, a liquid organic / inorganic sealing agent 31, as described below. The preform 32 obtained above was placed in an interior vessel 34 placed inside the reduced-pressure vessel 30, and weights (not shown) were placed on top to prevent it from floating. Permeate was then poured into the interior vessel 34 via an organic / inorganic sealing agent supply vessel 35, so that the entire preform was immersed in the permeate.

[0121] A vacuum was drawn across the entire reduced pressure vessel 30 using a vacuum pump (not shown) via the pressure reduction port 36, and this was maintained for 10 minutes. Thereafter, the vacuum was released to return the pressure inside the reduced pressure vessel 30 to normal pressure, and then air from a compressor (not shown) at 7 atmospheres was reduced to 4 atmospheres using a pressure reducing device (not shown) and slowly introduced into the reduced pressure vessel 30, pressurizing the entire reduced pressure vessel to 4 atmospheres. This was maintained for 5 minutes, and the permeate was pressure-impregnated into the preform 32.

[0122] After that, the reduced pressure vessel 30 was returned to atmospheric pressure, and the preform 32 was removed from the indoor vessel 34 and left overnight. The temperature was then raised at a rate of 50°C / hour, and heat-treated at 400°C for 3 hours to produce a composite with radiation shielding properties. Measurement of the specific gravity of this material (composite) revealed that the composite was 52v% B4C, 30v% organic / inorganic sealing agent (62.5v% of the voids in the preform), and the voids were 18v%. The specific gravity of the resulting material (composite) is summarized in Table 2.

[0123] The radiation shielding effectiveness of the material (composite) obtained above, with a volume filling factor (Vf) of 52% and a thickness of 20 mm, was measured by an external measurement organization. The shielding efficiency for neutron radiation from the californium (Cf) isotope Cf252 was measured, revealing a high value of 30%. No other shielding material has demonstrated such a high neutron shielding efficiency at a thickness of 20 mm. This result indicates that the composite obtained in this example is a useful material that effectively combines the properties of the lightweight and excellent radiation-shielding BC powder used as the raw material without decomposition. A 3mm x 4mm x 40mm test piece for measuring bending strength was prepared from the composite and subjected to a bending test according to JIS-R1061. The resulting strength was 25 MPa. This value is approximately 5 to 10 times that of gypsum board and concrete board measured using the same method, confirming that the material is suitable for use as exterior wall material and radiation storage containers.

[0124] [Example 10] A 100 mm × 100 mm × 20 mm molded body was produced using the same method as in Example 2, using 230 g of BC powder #180 (manufactured by Dojin Sangyo Co., Ltd.) with an average particle size of 70 μm and 100 g of BC powder #800 with an average particle size of 16 μm. This molded body was fired at 400°C in the same manner as in Example 1, resulting in a preform weighing 235 g and with a bulk specific gravity of 1.66. The resulting preform had a BC volume filling factor (Vf) of approximately 66 v% and a void content of 32 v%. This preform was vacuum-impregnated with permeate and heat-treated at 400°C in the same manner as in Example 8, resulting in a radiation shielding material with 66 v% BC, 19 v% permeate (organic / inorganic sealing agent) (59.4 v% of the void content of the preform), and 15% void content.

[0125] The radiation shielding effect of the obtained B4C powder material (composite) with a volume filling rate (Vf) of 66v% and a thickness of 20 mm was measured by an external measurement organization. The shielding factor for neutron radiation from the californium (Cf) isotope Cf252 was measured and found to be 34%, a high value. Furthermore, bending test specimens were prepared in the same manner as in Example 8, and the bending strength was measured, showing a high value of 41 MPa.

[0126] [Example 11] Using the same formulation as in Example 3, 240 g of A-200 (trade name, manufactured by Takehara Chemical Industry Co., Ltd.), a barium sulfate (BaSO4) powder with an average particle size of 15 μm, was used and mixed uniformly in the same manner as in Example 1. As a binder, a silicone-based resin solution was used, prepared by dissolving soluble silicone resin KR-200 (manufactured by Shin-Etsu Chemical Co., Ltd.) in ethanol to a concentration of 20 wt% by mass. Then, 15 g of the prepared silicone-based resin solution was added to the mixed BaSO4 powder, and mixed powder was obtained by high-speed stirring in a Henschel mixer in the same manner as in Example 1.

[0127] The mixed powder obtained above was placed in a 60 mm diameter mold and subjected to a pressure of 160 kg / cm 2 This was then heated at 400°C in the same manner as in Example 1 to produce a preform in the shape of a disk with a diameter of 60 mm, a thickness of 27.8 mm, and a weight of 235 g. The obtained preform had a bulk specific gravity of 2.95, BaSO4 content of 65v%, and voids of 35v%.

[0128] Next, a liquid organic / inorganic sealing agent was used on the preform obtained above to obtain a composite as follows. Ethyl silicate oligomer (manufactured by Colcoat Co., Ltd.) containing 40 wt% SiO2 equivalent was placed in a container as a liquid organic / inorganic sealing agent, and the preform obtained above was immersed in the container. The ethyl silicate was impregnated into the preform under vacuum and pressure of 4 atmospheres. The impregnated body impregnated with the liquid organic / inorganic sealing agent was then removed from the container, left in air for 48 hours, and heat-treated at 400°C for 3 hours to obtain a composite with radiation shielding properties, containing 65 v% BaSO4, 10 v% non-volatile SiO2 generated from ethyl silicate (28.6 v% of the voids in the preform), and the remainder 23 v%.

[0129] The material (composite) obtained above, with a volume filling rate (Vf) of 65v% of BaSO4 powder and a thickness of 27.8mm, was subjected to radiation shielding measurements by an external measurement organization. The results showed high values ​​of 36% projection efficiency for cesium (Cs) gamma rays Cs137 and 99.7% shielding efficiency for 150Kv X-rays. Furthermore, bending test specimens were prepared in the same manner as in Example 1, and the bending strength was measured. The value was a high 28MPa, confirming that the material is suitable for use in structures.

[0130] [Example 12] 54 g of BC powder with an average particle size of 16 μm and 110 g of A-200 (trade name) BaSO powder with an average particle size of 15 μm were mixed with 7 g of ethyl silicate as a liquid binder in the same manner as in Example 1, and the mixture was press-molded and fired at 400°C to obtain a preform weighing 165 g, measuring 60 mmφ x 30 mm, and having a bulk specific gravity of 1.93. The resulting preform was 29 v% BC, 29 v% BaSO, and 42 v% voids.

[0131] Using a reduced pressure vessel 30 as shown in Figure 2 and liquid ethyl silicate as the organic / inorganic sealing agent 31, the preform 32 obtained above was immersed in the ethyl silicate liquid, vacuum impregnated, and then heat-treated at 400°C in the same manner as in Example 8 to obtain a composite with radiation shielding properties. The obtained composite had 29v% B4C, 29v% BaSO4, 17v% non-volatile content of SiO2 of the ethyl silicate (40.4v% of the voids in the preform), and 25v% voids.

[0132] The radiation shielding effect of the material (composite) containing the above-obtained B4C powder, BaSO4 powder, and liquid organic / inorganic sealing agent was measured by an external measurement organization. The results showed high values ​​of 25% projection efficiency for cesium (Cs) gamma rays Cs137 and 98% shielding efficiency for 150 Kv X-rays. In addition, bending test specimens were prepared in the same manner as in the other examples, and the bending strength was measured. The value was high at 32 MPa, confirming that the material is suitable for industrial use as a structural material.

[0133] Table 2 shows the embodiments of the specific powders constituting the preforms used to form the composites of Examples 9 to 12, the amounts of organic / inorganic sealing agents in the voids of the preforms and in the composites, and the radiation shielding effects. TIFF2026019314000004.tif88170

[0134] [Comparative Examples 7 to 10] Test pieces were prepared using the preforms used in preparing the composites of Examples 9 to 12, which had the configurations shown in Table 2, but which had not yet been impregnated with a liquid organic / inorganic sealing agent, and bending strength measurements were performed in the same manner as in the Examples. The measurement results obtained are summarized in Table 3. For comparison, the bending strength multiplier for each composite of Examples 9 to 12 is shown in parentheses. As shown in Table 3, it was confirmed that the bending strength of the composites of Examples 9 to 12, in which the organic / inorganic sealing agent was compounded with the preform, was significantly improved compared to the materials of the comparative examples.

[0135] TIFF2026019314000005.tif43170

[0136] [Comparative Example 11] A preform similar to that prepared in Example 9, with a bulk density of 1.31, a B4C filling rate (Vf) of 52 v%, and voids of 48 v%, was used. It was composited with an organic / inorganic sealing agent as described below to obtain the composite of Comparative Example 11. The liquid organic / inorganic sealing agent used was Permeate HS-200, the same as that used in Example 9, with a viscosity of 15.5 mPa·s, a specific gravity of 1.15, siloxane bonds, and a nonvolatile content of 85 wt%, and was diluted with ethanol to adjust the nonvolatile content to 20 wt%. The liquid organic / inorganic sealing agent was then impregnated using the same procedure as in Example 9, followed by heat treatment to obtain a composite material. Weight measurements revealed that the material was 52 v% B4C, 8 v% organic / inorganic sealing agent (16.0 v% of the preform's voids), and 36 v% voids. The bending strength of this material was measured in the same manner as in the examples, and the bending strength was 11 MPa, which was not a high strength. The reason for this is thought to be that the amount of organic-inorganic composite agent occupying the voids in the preform was low.

[0137] [Comparative Example 12] A preform similar to that prepared in Example 11, having a bulk density of 2.95, a BaSO4 filling rate (Vf) of 65v%, and a void volume of 35v%, was used. The preform was composited with an organic / inorganic sealing agent as described below to obtain a composite of Comparative Example 12. The liquid organic / inorganic sealing agent used in Example 11 was diluted with water to a solution containing 10w% SiO2 nonvolatiles. The preform was then impregnated with the liquid organic / inorganic sealing agent using the same procedure as in Example 11, and then heat-treated to obtain a composite material. Weight measurements revealed that the material contained 65v% BaSO4, 4v% SiO2 nonvolatiles (11v% of the void volume in the preform) (31v%), and the remaining void volume was 31v%. The bending strength of this material was measured using the same method as in Example 12, revealing a low bending strength of 9MPa.

[0138] [Comparative Example 13] A preform similar to that prepared in Example 9, with a bulk density of 1.31, a B4C filling rate (Vf) of 52 v%, and a void volume of 48 v%, was used. The composite of Comparative Example 13 was obtained by compounding with an organic / inorganic sealing agent as described below. A solution of silicone resin KR220l (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) with a viscosity of 150 mPa.m dissolved in ethanol with a nonvolatile content of 40 wt% was used as the liquid organic / inorganic sealing agent. The silicone resin solution was impregnated into the preform using the same procedure as in Example 9 and then heat-treated to obtain a compounded material. The resulting material had a B4C Vf of 52 v%, a nonvolatile content of SiO2 generated from the silicone resin of 3 v% (6.2 v% of the void volume in the preform), and a void volume of 45 v%. The bending strength of this material was measured using the same method as in Example 1, and the bending strength was found to be low at 6 MPa. The reason for this is thought to be that the silicone resin solution, which has a high viscosity, did not sufficiently impregnate the preform, and the amount of impregnation of the organic / inorganic sealing agent was low.

[0139] TIFF2026019314000006.tif59170 [Explanation of symbols]

[0140] 1: Molten aluminum 2: Preform 3: Composite impregnated with molten aluminum 4: Lower punch 5: Upper punch 10: Press mold 30: Reduced pressure vessel 31: Organic and inorganic sealing agents 32: Preform 33: Opening and closing jig for reduced pressure vessel 34: Indoor container 35: Organic / inorganic sealant container 36: Pressure reduction outlet 37: Pressure port 38: Pressure gauge

Claims

1. A composite having a radiation-shielding function, comprising a powder having a radiation-shielding effect, the powder being composited together, and the powder being contained in a total amount within a range of 3% by volume or more and 85% by volume or less, A porous composition is a molded and fired product made from a mixture containing one or more types of powder having a radiation shielding effect selected from the group consisting of gadolinium oxide powder, boron carbide powder, boron powder, boron oxide powder, barium sulfate powder, strontium oxide powder, tungsten powder, tungsten oxide powder, tungsten carbide powder, molybdenum powder, molybdenum oxide powder, iron powder, iron oxide powder, and ferrite powder mainly composed of iron oxide, and a silica-based binder that is not in powder form. The porous molded body (preform) has a structure in which all of its voids are impregnated and filled with at least one of a molten low-melting point metal selected from the group consisting of aluminum metal, aluminum alloy, zinc, tin, and lead, which has a melting point of 200°C or higher but 900°C or lower, or a low-melting point alloy of said low-melting point metal with another metal, and the voids are solidified to form a composite, or at least 25% by volume or more of the voids of the porous molded body (preform) are impregnated with a liquid organic / inorganic sealing agent, which is solidified to form a composite, and A composite having a radiation-shielding function, wherein the non-powdered silica-based binder has a property that allows the formed and fired product to be formed into a porous molded body (preform) at a temperature at which the radiation-shielding powder is not decomposed.

2. The non-powdered silica-based binder is at least one liquid silica-based binder selected from the group consisting of water glass (sodium silicate), colloidal silica, liquid silicone resin, silicone resin solution obtained by dissolving silicone resin in an organic solvent, and silica alkoxide made of silica and an organic substance and heat-cured at a temperature of 900°C or less, and the mixture is prepared by mixing the liquid silica-based binder with SiO2 with respect to 100 parts by mass of the radiation-shielding powder. ２ 2. The radiation-shielding composite according to claim 1, wherein 0.5 to 10 parts by mass of the compound is added in terms of the amount of the compound.

3. 2. The composite having a radiation-shielding function according to claim 1, wherein the liquid organic / inorganic pore-sealing agent is present in the pores of the porous molded body (preform) as a solidified product of the organic / inorganic pore-sealing agent and / or a heat-treated product of the organic / inorganic pore-sealing agent, and the solidified product of the organic / inorganic pore-sealing agent and / or the heat-treated product of the organic / inorganic pore-sealing agent occupies 25% by volume or more of 100% by volume of the pores of the porous molded body (preform) before impregnation, and when the entire preform after impregnation is taken as 100% by volume, the solidified product of the organic / inorganic pore-sealing agent and / or the heat-treated product of the organic / inorganic pore-sealing agent occupies 5% by volume or more.

4. The liquid organic / inorganic sealing agent has a low viscosity of 50 mPa·s or less and contains 30 mass % or more of non-volatile components. Methyl silicate Si(OCH ３ ) ４ Alternatively, a liquid methyl silicate compound obtained by partially hydrolyzing the methyl silicate to form a dimer or tetramer oligomer, and adjusting the non-volatile component content to 30 mass % or more. Ethyl silicate Si(OC ２ H ５ ) ４ Alternatively, a liquid ethyl silicate compound obtained by partially hydrolyzing the ethyl silicate to form a dimer or tetramer oligomer, and adjusting the non-volatile component content to 30 mass % or more. a silicone resin or a derivative thereof having a siloxane bond and adjusted so that the non-volatile component content is 30% by mass or more; 4. The radiation-shielding composite according to claim 1, wherein the composite is at least one selected from the group consisting of liquid alkoxysilane compounds that are alkoxysilane derivatives and react with moisture in the air to undergo a condensation reaction to produce a silicone-oxygen organic compound (Si—O—R).

5. A method for producing a composite having a radiation-shielding function, the method comprising using at least one of a molten low-melting-point metal selected from the group consisting of aluminum metal, an aluminum alloy, zinc, tin, and lead, or a low-melting-point alloy of the low-melting-point metal and another metal as a matrix, and containing a powder having a radiation-shielding effect in a total amount within a range of 3% by volume or more and 85% by volume or less, the method comprising: a step of molding a mixture obtained by adding a non-powdered silica-based binder to one or more types of powder having a radiation shielding effect selected from the group consisting of gadolinium oxide powder, boron carbide powder, boron oxide powder, boron powder, barium sulfate powder, strontium oxide powder, tungsten powder, tungsten oxide powder, tungsten carbide powder, molybdenum powder, molybdenum oxide powder, iron powder, iron oxide powder, and ferrite powder mainly composed of iron oxide, and then firing the resulting molded body at a temperature of 300°C or higher and 900°C or lower to produce a porous molded body (preform); a step of casting a molten metal of at least one low-melting-point metal selected from the group consisting of aluminum metal, aluminum alloy, zinc, tin, and lead, or a low-melting-point alloy of the low-melting-point metal and another metal, which has been melted at a temperature of 300°C or more and 900°C or less, and which has a melting point of 200°C or more and 900°C or less, into the porous molded body (preform) obtained in the step of casting, and then holding the molten metal at a high pressure of 20 MPa or more and 200 MPa or less for 3 to 15 minutes in order to impregnate the porous molded body (preform) with the molten metal, and then removing the composite impregnated with the molten metal within 15 minutes and cooling it, thereby suppressing decomposition of the radiation-shielding powder in the composite.

6. A method for producing a composite having a radiation-shielding function, comprising preparing a composite containing a powder having a radiation-shielding effect in a total amount of 3% by volume or more and 85% by volume or less, the powder being composited, the method comprising: a step of molding a mixture obtained by adding a non-powdered silica-based binder to one or more types of powder having a radiation shielding effect selected from the group consisting of gadolinium oxide powder, boron carbide powder, boron oxide powder, boron powder, barium sulfate powder, strontium oxide powder, tungsten powder, tungsten oxide powder, tungsten carbide powder, molybdenum powder, molybdenum oxide powder, iron powder, iron oxide powder, and ferrite powder mainly composed of iron oxide, and then firing the resulting molded body at a temperature of 300°C or higher and 900°C or lower to produce a porous molded body (preform); and a compounding step of: vacuum-impregnating voids of the porous molded body (preform) obtained in the step of producing the porous molded body (preform) with a liquid organic / inorganic sealing agent containing 30% by mass or more of non-volatile components and having a viscosity of 50 mPa s or less, or impregnating the voids of the porous molded body (preform) under a pressure of 10 atmospheres or less by applying pressure after vacuum impregnation, and then heating the voids to a temperature of 200°C or more and 900°C or less, so that a solidified product of the liquid organic / inorganic sealing agent and / or a heat-treated product of the liquid organic / inorganic sealing agent remains in an amount of 25% by volume or more relative to 100% by volume of the voids of the porous molded body (preform), and compounding the radiation-shielding powder with a component derived from the liquid organic / inorganic sealing agent.

7. The liquid organic / inorganic sealing agent has a low viscosity of 50 mPa·s or less and contains 30 mass % or more of non-volatile components. Methyl silicate Si(OCH ３ ) ４ Alternatively, a liquid methyl silicate compound obtained by partially hydrolyzing the methyl silicate to form a dimer or tetramer oligomer, and adjusting the non-volatile component content to 30 mass % or more. Ethyl silicate Si(OC ２ H ５ ) ４ Alternatively, a liquid ethyl silicate compound obtained by partially hydrolyzing the ethyl silicate to form a dimer or tetramer oligomer, and adjusting the non-volatile component content to 30 mass % or more. a silicone resin or a derivative thereof having a siloxane bond and adjusted so that the non-volatile component content is 30% by mass or more; 7. The method for producing a composite having a radiation-shielding function according to claim 6, wherein the alkoxysilane derivative is at least one selected from the group consisting of liquid alkoxysilane compounds that react with moisture in the air to undergo a condensation reaction to produce a silicone-oxygen organic compound (Si—O—R).

8. The non-powdered silica-based binder is at least one liquid silica-based binder selected from the group consisting of water glass (sodium silicate), colloidal silica, liquid silicone resin, silicone resin solution obtained by dissolving silicone resin in an organic solvent, and silica alkoxide made of silica and an organic substance and heat-cured at a temperature of 900°C or less, and the mixture is prepared by mixing the liquid silica-based binder with SiO2 with respect to 100 parts by mass of the radiation-shielding powder. ２ 7. The method for producing a composite having a radiation-shielding function according to claim 5, wherein 0.5 to 10 parts by mass of the compound is added in terms of the amount of the compound.

9. Furthermore, in the step of producing the porous molded body (preform), when aluminum powder, aluminum alloy powder, or ceramic powder is added to the radiation-shielding powder, and the total amount of the aluminum metal powder, aluminum alloy powder, or ceramic powder and the radiation-shielding powder is taken as 100 mass %, the non-powdered silica-based binder is SiO ２ 6. The method for producing a composite having a radiation-shielding function according to claim 5, wherein the porous molded body (preform) is produced by adding 0.5 to 10 mass % of the compound in terms of the amount of the compound.

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