JP7606793B1 - Composite having radiation shielding function and method for manufacturing the composite having radiation shielding function - Google Patents

Abstract

The present invention relates to a composite material having a novel structure that contains a high content of powder having radiation shielding properties.
[Solution] A composite having a radiation-shielding function and a manufacturing method thereof, the composite being formed by impregnating and filling all of the voids of a preform made of a mixture containing one or more types of radiation-shielding powder 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, the radiation-shielding powder containing the radiation-shielding powder in a total content range of 3 to 85%, and a liquid silica-based binder, and solidifying the mixture to form a composite, or by impregnating 25% or more of the voids of the preform with a liquid organic/inorganic sealing agent, and solidifying the mixture to form a composite, and the liquid silica-based binder having properties that allow the preform to be formed at a temperature at which the radiation-shielding powder is not decomposed.
[Selection diagram] None

Description

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 (Gd ₂ O ₃ ) powder, boron carbide (B ₄ C) powder, boron oxide (B ₂ O ₃ ) powder, boron (B) powder, barium sulfate (BaSO ₄ ) powder, strontium oxide (SrO) powder, tungsten (W) powder, tungsten oxide (W ₂ O ₃ ) powder, tungsten carbide (WC) powder, molybdenum (Mo) powder, molybdenum oxide (MoO ₃ ) powder, iron (Fe) powder, iron oxide (Fe ₂ O _{3 )} powder, and the like. The present invention relates to a composite material obtained by impregnating voids of a porous preform containing at least one selected from the group consisting of aluminum metal, aluminum alloy, zinc, tin and lead, and a ferrite powder mainly composed of iron oxide (hereinafter, these are collectively referred to as a radiation-shielding powder group), with 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, 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 more and 900° C. or less, and then solidifying the molten metal, or a composite material having a radiation-shielding function obtained by impregnating a liquid organic/inorganic sealing agent, heat-treating the agent, and solidifying the composite material (hereinafter, these are simply referred to as a composite material), and a method for producing the same. In particular, the present invention relates to a technology that enables the realization of a composite material obtained by compounding the radiation-shielding powders listed above in a state in which decomposition of the radiation-shielding powders is suppressed.

In the medical field, radiation shielding materials are used in consideration of X-rays and radiation generated by medical devices and equipment. In the nuclear industry, materials that block radiation such as X-rays, gamma rays, and neutron rays are used in containers and equipment for handling and storing unused nuclear fuel. Radiation shielding materials are required to 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, but in recent years, there has been a demand for radiation shielding materials that are lightweight, have high heat dissipation properties, and have a high radiation shielding effect, especially for structural members that require radiation shielding effects.

Conventional radiation shielding materials generally use metallic lead or metallic tungsten. However, these materials have a large specific gravity, and structural materials made of materials with a large specific gravity are quite heavy, so the range of use is limited. As described below, in order to produce a lightweight structure with a radiation shielding effect, a material has been proposed in which B ₄ C powder or BaSO ₄ powder, which has a radiation shielding effect and a small specific gravity, is combined with a resin or a metal. However, there is a problem in that the content of these powders with a radiation shielding effect in the structure is low, limiting the range of application.

Patent Document 1 proposes a method for producing an aluminum radiation shield containing B ₄ C as described below. Specifically, the radiation shield is proposed by producing a compact of a mixed powder consisting of boron carbide (B ₄ C) powder and aluminum powder, sintering the compact at a low sintering temperature of 10 to 50°C by vacuum sintering, HIP, or hot pressing, blending the B ₄ C with the aluminum, and then heating, melting, and casting the compact. In this method, the content of B ₄ C in the radiation shield is limited to a range of 0.5 to 5 mass %, and if the content exceeds this, the viscosity of the molten metal increases, making casting difficult. Therefore, it has been difficult to produce a radiation shield having a greater radiation shielding effect and a B ₄ C content of more than 5v %.

Patent Document 2 discloses a method of adding an inorganic binder to a mixture of boron carbide (B ₄ C) particles and aluminum borate whiskers, forming the mixture, sintering the formed product under high-temperature conditions at 1250° C. for 4 hours in an argon atmosphere to produce a preform, and impregnating the preform with molten aluminum alloy at high pressure to produce a radiation shielding composite. In this method, boron carbide and ceramic whiskers are mixed and sintered at a high temperature of 1100 to 1400° C. to produce a preform that can withstand high-pressure impregnation with aluminum, and the preform is impregnated with molten aluminum alloy to produce a composite. This method has the problem that the preform must be produced at high temperature, which makes it expensive, and furthermore, the boron carbide content can only be 1 to 15 wt %, making it impossible to increase the boron carbide content in the radiation shielding composite.

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 (B ₄ C), and metal powder containing aluminum, and heating the solid piece to an infiltration temperature at which the solid piece melts and infiltrating for 1 minute to 24 hours. According to the study by the present inventors, this method requires a long reaction time because the aluminum alloy is naturally infiltrated (infiltrated) into the preform, and unstable Al ₄ C ₃ is formed in the air and the preform is not completely infiltrated in some cases, making it impossible to obtain a dense and stable radiation shielding composite.

Patent Document 4 proposes a method of manufacturing a composite by heating a mixture of boron carbide powder and aluminum alloy powder, or a mixed powder compact thereof, to a predetermined temperature and holding the mixture at a semi-molten state, and forging or rolling the mixture under such conditions. According to the inventors' investigations, this method was unable to manufacture composites with a large area or thick walls, as the molding is performed at high temperatures. In addition, this technology involves forced forging in a semi-molten state, which causes problems such as unevenness of the radiation shielding powder and aluminum alloy, and the inability to manufacture products with a wall thickness of 10 mm or more.

Patent Document 5 also proposes a container material in which boron fibers are combined with an aluminum alloy base containing boron. However, the boron fiber content is still low, and boron fibers are expensive, so the range of use is limited.

JP 2002-20828 A JP 2003-121590 A Patent No. 4426293 Japanese Patent Application Laid-Open No. 60-096746 Japanese Patent Application Publication No. 10-319183

As mentioned above, the radiation shielding materials of the prior art are heavy when metallic lead or metallic tungsten is used as the radiation shielding powder, or when powders such as boron carbide (B ₄ C) or barium sulfate (BaSO ₄ ) are used, the content of the powder having a radiation shielding effect is low in any composite, and a high content could not be realized. In addition, as a prior art, a material in which a radiation shielding powder is mixed with gypsum, rubber, or resin has been proposed. However, in the case of a material using rubber as a matrix, it is difficult to use it for a long time at 200°C or higher because it is an organic matter. In addition, in the case of a material using gypsum as a matrix, there is a problem that a dehydration reaction of gypsum occurs when it is used for a long time at a temperature of 100°C or higher, and it is not possible to use it for a long time at a high temperature.

In view of the above-mentioned state of the prior art, the present inventors considered that if a method could be developed to 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, iron oxide, etc., from low to high, and to prepare materials that can be used at high temperatures, the range of radiation shielding applications as structural members (structures) and parts of radiation-related machines would be significantly expanded. In addition, even if radiation shielding powders such as tungsten powder and molybdenum powder, which have a specific gravity of 10 or more, are combined with other materials at a content level that allows stable radiation shielding effect to be exerted, and a lightweight material is obtained as a composite, the range of use would be significantly expanded, as it can be used depending on the application.

The present inventors recognized that, in light of the current state of the art, a composite material having the following characteristics is desired as a highly practical radiation shielding material. That is, the present inventors recognized that a composite material having high strength and a high content of radiation shielding powder, particularly a content of 3v% or more, preferably 60v% or more, and more preferably up to 85v%, a thickness of 5mm or more, preferably 10mm or more, a high radiation shielding effect, lightweight, and usable for large structures, building wall materials, machine protective structures, and further a composite material 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 said low melting point metal and other metals (hereinafter, these may be referred to as "aluminum, etc."), all of which have high thermal conductivity, is desired. It is to be noted that low melting point metals other than zinc, tin, and lead can also be used as long as they do not impair the object of the present invention. In this specification, volume % is also written as "v%" and mass % is also written as "w%".

Therefore, the object of the present invention is to develop a composite of a new configuration with a high radiation shielding effect, containing a high content of powder with radiation shielding function (radiation shielding powder). 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, for example, from a low content of 3v% to 85v%, to a high content, and which has the strength required for structures such as parts and members that make up 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.

The above object can be achieved by the present invention, which provides a composite having a radiation shielding function as described below.
[1] A composite having a radiation-shielding function, comprising a powder having a radiation-shielding effect, the powder being composited in a total amount of 3 volume % or more and 85 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 in 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, and then solidified to form a composite, or at least 25 volume % or more of the voids in 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, wherein the non-powdered silica-based binder has a property capable of forming a porous molded body (preform), which is the molded and fired product, at a temperature at which the radiation-shielding powder is not decomposed.

Preferred forms of the above-mentioned complex having a radiation shielding function are as follows.
[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, a liquid silicone resin, a silicone resin solution obtained by dissolving a silicone resin in an organic solvent, and a silica alkoxide made of silica and an organic substance and cured by heating 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.

[3] The liquid organic/inorganic pore-shielding agent is present in the voids of the porous molded body (preform) as a solidified organic/inorganic pore-shielding agent and/or a heat-treated organic/inorganic pore-shielding agent, and the solidified organic/inorganic pore-shielding agent and/or the heat-treated organic/inorganic pore-shielding agent occupy 25% by volume or more of the 100% by volume of the voids of the porous molded body (preform) before impregnation, and when the entire preform after impregnation is taken as 100% by volume, the solidified organic/inorganic pore-shielding agent and/or the heat-treated organic/inorganic pore-shielding agent occupy 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.
A liquid methyl silicate compound which is methyl silicate Si(OCH ₃ ) ₄ or a dimer or tetramer oligomer obtained by partially hydrolyzing the methyl silicate, and which is adjusted so that the non-volatile component is 30 mass % or more;
A liquid ethylsilicate compound which is ethylsilicate Si(OC ₂ H ₅ ) ₄ or a dimer or tetramer oligomer obtained by partially hydrolyzing the ethylsilicate, and which is adjusted so that the non-volatile component is 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;
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 which are alkoxysilane derivatives and react with moisture in the air to undergo a condensation reaction to generate silicone-oxygen organic compounds (Si—O—R).

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 said low-melting-point metal and another metal; and a powder having a radiation-shielding effect in a total amount of 3 vol% or more and 85 vol% or less, the method comprising the steps of:
a step of 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, to form a mixture, 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 of a 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 to 900°C, into the porous molded body (preform) obtained in the step, holding the molten metal at a high pressure of 20 MPa to 200 MPa 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 volume % or more and 85 volume % or less, the powder being composited, the method comprising the steps of:
a step of 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, to form a mixture, and then firing the obtained molded body at a temperature of 300° C. or more and 900° C. or less to prepare a porous molded body (preform);
and a compounding step of: 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 at a pressure of 10 atmospheres or less by pressurizing the liquid organic/inorganic sealing agent after vacuum impregnation, and then heating the liquid organic/inorganic sealing agent 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), thereby compounding the radiation-shielding powder with a component derived from the liquid organic/inorganic sealing agent.

A preferred embodiment of the method for producing the composite having a radiation-shielding function described above in [5] or [6] 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(OCH ₃ ) ₄ or a dimer or tetramer oligomer obtained by partially hydrolyzing the methyl silicate, and which is adjusted so that the non-volatile component is 30 mass % or more;
A liquid ethylsilicate compound which is ethylsilicate Si(OC ₂ H ₅ ) ₄ or a dimer or tetramer oligomer obtained by partially hydrolyzing the ethylsilicate, and which is adjusted so that the non-volatile component is 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;
The method for producing the composite having a radiation-shielding function according to the above item [6], wherein the alkoxysilane derivative is at least one selected from the group consisting of liquid alkoxysilane compounds which react with moisture in the air to undergo a condensation reaction to produce a silicone-oxygen-organic compound (Si—O—R).

[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, a liquid silicone resin, a silicone resin solution obtained by dissolving a silicone resin in an organic solvent, and a silica alkoxide made of silica and an organic substance and heated and cured at a temperature of 900°C or less, and the mixture is obtained by adding 0.5 to 10 parts by mass, in terms of _SiO2 , of the liquid silica-based binder to 100 parts by mass of the radiation-shielding powder.

[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 such a manner that, when the total of the aluminum metal powder, aluminum alloy powder, or ceramic powder, and the radiation-shielding powder is taken as 100 mass%, 0.5 to 10 mass% of the non-powdered silica-based binder is added in terms of _SiO2 to produce a porous molded body (preform).

Conventionally, structures containing radiation shielding powders have generally been manufactured as composites by mixing the radiation shielding powder with aluminum, rubber, or resin. In contrast, according to the present invention, a composite having a radiation shielding function, which is similar in configuration to the above, is made by using a molded body (preform) containing radiation shielding powder whose filling rate is controlled from low to high, and in which all of the voids in the molded body (preform) are impregnated with molten aluminum or the like and solidified to form a composite, or a composite having a radiation shielding function, which is impregnated with a liquid organic/inorganic sealing agent in at least 25% by volume or more of the voids in the molded body (preform) and solidified to form a composite, is stably provided. In addition, by applying each manufacturing method of the present invention according to the intended use of the composite and skillfully utilizing the above two types of configuration, it is possible to stably obtain various composites having high practical value and suitable for desired characteristics, for example, in which the filling rate of the radiation shielding powder is controlled from low to high, and which have excellent radiation shielding function with strength suited to the purpose. The features of the technology of the present invention are as follows.

A first feature of the present invention is that one or more types of radiation-shielding powders appropriately selected from a group of radiation-shielding powders having different functionality and characteristics, including gadolinium oxide (Gd ₂ O ₃ ) powder, boron carbide (B ₄ C) powder, boron oxide (B ₂ O ₃ ) powder, boron (B) powder, barium sulfate (BaSO ₄ ) _powder , strontium oxide (SrO) powder, tungsten (W) powder, tungsten oxide (W 2 O ₃ ) powder, tungsten carbide (WC) powder, molybdenum (Mo) powder, molybdenum oxide (MoO ₃ ) powder, iron (Fe) powder, iron oxide (Fe ₂ O ₃ ) powder, and ferrite powder mainly composed of iron oxide, can be used according to the purpose of use, etc. In other words, according to the present invention, it is possible to provide a variety of radiation-shielding composites composed of a single radiation-shielding powder or various combinations of radiation-shielding powders.

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, according to the present invention, it is possible to provide composites of various configurations with different radiation shielding functions, as listed below. That is, it is possible to provide not only composites obtained by impregnating each powder of the specific radiation shielding powder group specified in the present invention with a molten metal or liquid organic/inorganic sealing agent such as aluminum and solidifying it, but also composites obtained by impregnating two types of radiation shielding powders, boron carbide and tungsten, and boron carbide and barium sulfate, or three types of radiation shielding powders, boron carbide and tungsten, and barium sulfate as necessary, with a molten metal or liquid organic/inorganic sealing agent such as aluminum and solidifying it. Thus, 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.

The second feature of the present invention is that it is possible to provide a composite having a 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 of the various radiation shielding powders listed above, and by adding aluminum powder or aluminum alloy powder as necessary. According to the present invention, it is possible to manufacture a structure made of a composite having a radiation shielding function that achieves a filling rate (volume fraction) of the radiation shielding powder of 50v% or more, which is particularly required for a high shielding effect.

The third feature of the present invention is that the composite having a radiation shielding function 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 consisting 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, a composite having a high content of radiation shielding powder with an aluminum matrix can be provided, in which all of the voids in the porous molded body (preform) are impregnated and filled with at least one 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 the low-melting point metal and other metals, and solidified to form a composite. In addition, by impregnating at least 25% by volume of the voids in the porous molded body (preform) with a liquid organic/inorganic sealing agent and then heating the mixture to a temperature of 200°C or higher and 900°C or lower, the liquid organic/inorganic sealing agent is solidified and composited to provide a composite having a different configuration with a high content of radiation shielding powder.

Furthermore, in the case of any of the composites having the above-mentioned 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 in the composite is not decomposed, thereby obtaining the following effects. That is, by being configured in this way, the composite having the radiation-shielding function of the present invention has high strength in which the radiation-shielding powder specified in the present invention is bound by aluminum or an organic/inorganic sealing agent, and in addition, the radiation-shielding powder used is not decomposed and can be used at high temperatures of 300°C or more. Hereinafter, in the specification of the present invention, "molten aluminum" or "molten aluminum" is described as a representative example of molten aluminum metal. That is, in the specification of the present invention, the terms "molten aluminum" or "molten aluminum" are described to include not only molten aluminum metal, but also 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 and other metals (for example, 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 inventors' investigations, if 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, so this is not preferable.

The fourth feature of the present invention is that, according to the study by the present inventors, when aluminum metal or aluminum alloy melted at high temperature is used as a molten metal for compounding with a radiation-shielding powder, the following problem occurs, but this problem has been solved. According to the present invention, even radiation-shielding powders such as boron carbide, which reacts with aluminum to produce Al ₄ C ₃ , which shows a decomposition reaction with moisture in the air, barium sulfate, which reacts with molten aluminum at high temperatures to produce Al ₂ O ₃ , BaO and SO ₂ , and strontium sulfate, tungsten, iron powder, and aluminum borate, which undergo oxidative degradation, thermal decomposition, and generation of unstable substances at temperatures above 900°C, can be used as raw materials, and a composite can be produced that can be stably used even at temperatures of 300°C or higher. Therefore, since it is possible to use a wide variety of radiation-shielding powders as specified in the present invention, the present invention can significantly expand the application range of the composite.

FIG. 1 is a schematic diagram showing a state in which molten aluminum 1 is cast into a preform 2 in the first manufacturing method.
1 is a schematic diagram showing placing a heated preform 2 in a mold of a press 10 and pouring molten aluminum 1 into the mold. 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 therewith. FIG. 1 is a schematic diagram showing how, after cooling, the lower punch 4 is pushed up to remove the composite 3 in a state in which the impregnated molten aluminum has solidified. FIG. 13 is a schematic diagram for illustrating 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.

The following describes preferred embodiments of the present invention, but the present invention is not limited to these embodiments.

The radiation-shielding composite of the present invention is a composite having a radiation-shielding function, which contains a total of 3 volume % or more and 85 volume % or less of powders having a radiation-shielding effect, the powders being obtained by compounding the powders, and the radiation-shielding powders having the radiation-shielding effect are selected from the group consisting of gadolinium oxide (Gd ₂ O ₃ ) powder, boron carbide (B ₄ C) powder, boron oxide (B ₂ O ₃ ) powder, boron (B) powder, barium sulfate (BaSO ₄ ) powder, strontium oxide (SrO) powder, tungsten (W) powder, tungsten oxide (W ₂ O ₃ ) powder, tungsten carbide (WC) powder, molybdenum (Mo) powder, molybdenum oxide (MoO ₃ ) powder, iron (Fe) powder, iron oxide (Fe ₂ O _{3 )} powder, and the like. a porous molded body (preform) which is a molded and fired product made of a mixture containing one or more types of radiation-shielding powders selected from the group consisting of ferrite powders mainly composed of iron oxide and silica-based binders that are not powdery, and which is impregnated and filled with molten aluminum in all of the voids thereof, and then solidified to form a composite, or a porous molded body (preform) which is impregnated with a liquid organic/inorganic sealing agent in at least 25 volume % or more of the voids thereof, and then solidified to form a composite, and which is characterized in that the non-powdered silica-based binder is capable of forming the porous molded body (preform) (hereinafter, also simply referred to as a preform) which is the molded and fired product, at a temperature at which the radiation-shielding powder is not decomposed.

The composite having the radiation shielding function of the present invention having the above-mentioned configuration can be produced by the manufacturing method of the present invention comprising, for example, the first or second means described below, which can provide a stable composite while suppressing decomposition of the radiation shielding powder, and therefore a high-quality composite that meets the intended use and provides the various effects of the present invention described above can be easily and stably prepared.

The radiation-shielding composite of the present invention, in which all of the voids in the preform having the specific configuration described above are impregnated and filled with "molten aluminum" and solidified to form a composite, can be easily and stably prepared by the first manufacturing method of the present invention described below. As described above, "molten aluminum" and "molten aluminum" refer to at least one molten 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.

The first manufacturing method of the present invention is a method for preparing a composite having a radiation shielding function, which contains an aluminum matrix and a powder having a radiation shielding effect in a total amount within the range of 3 volume % or more and 85 volume % or less, and the powder is 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. The method is characterized by comprising the steps of: molding a mixture obtained by adding a non-powdered silica-based binder to a certain powder and mixing the mixture; and firing the obtained molded body at a temperature of 300° C. or more and 900° C. or less to produce a porous molded body (preform); and casting molten aluminum into the preform obtained in the step at a temperature of 300° C. or more and 900° C. or less, and holding the preform at a high pressure of 20 MPa or more and 200 MPa or less for 3 to 15 minutes, for example, for about 3 to ₅ minutes, in order to impregnate the preform with the molten aluminum. Thereafter, the composite in a state in which the molten aluminum is impregnated is immediately taken out and cooled, thereby suppressing decomposition of the radiation shielding powder in the composite and generation of unstable substances such as _Al4C3 .

In the first manufacturing 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 when the total of the aluminum powder, aluminum alloy powder, or ceramic powder and the radiation-shielding powder is taken as 100 mass%. By configuring in this way, it is possible to more easily 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 volume% to 85 volume%. This will be described later.

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 manufacturing method of the present invention described below.

The second manufacturing method of the present invention is a method for manufacturing a composite having a radiation shielding function, which prepares a composite containing a total of 3 volume % or more and 85 volume % or less of powders having a radiation shielding effect, the powders being compounded together, and the composite is formed by adding a non-powdered silica-based binder to 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 mainly composed of iron oxide, and mixing the powders to form a mixture. The method is characterized by comprising a step of baking the molded body at a temperature of 300°C or higher and 900°C or lower to produce a porous molded body (preform), and a step of vacuum-impregnating the voids of the preform obtained in the step of producing the 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 a step of impregnating the voids of the preform obtained in the step of producing the preform with a pressure of 10 atmospheres or less by pressurizing the liquid organic/inorganic sealing agent, and then heating the liquid organic/inorganic sealing agent to a temperature of 300°C or higher and 900°C or lower, so that 25% by volume or more of the solidified liquid organic/inorganic sealing agent and/or the heat-treated liquid organic/inorganic sealing agent remain relative to 100% by volume of the voids of the preform, thereby compositing the radiation-shielding powder with a component derived from the liquid organic/inorganic sealing agent.

<Process for producing porous molded body (preform)>
The details of the first and second manufacturing methods of the composite having a radiation shielding function of the present invention will be described below. 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.

[Radiation shielding powder raw material, etc.]
In the present invention, as the radiation shielding powder used as the raw material for producing the preform, one or more selected from the group consisting of gadolinium oxide (Gd ₂ O ₃ ) powder, boron carbide (B ₄ C) powder, boron oxide (B ₂ O ₃ ) powder, boron powder, barium sulfate (BaSO ₄ ) powder, strontium oxide (SrO) powder, tungsten (W) powder, tungsten oxide (W ₂ O ₃ ) powder, tungsten carbide (WC) powder, molybdenum (Mo) powder, molybdenum oxide (MoO ₃ ) powder, iron (Fe) powder, iron oxide (Fe ₂ O ₃ ) powder, and ferrite powder mainly composed of iron oxide are used. In the prior art, 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 the weight of the structure (composite) would increase and there is a need to consider the impact on the environment. 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.

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 filling rate of the radiation-shielding powder in the composite. In this way, it becomes possible to freely control the filling rate (volume rate) of the radiation-shielding powder constituting the composite of the present invention to a wide range. In this case, in the manufacturing process of the porous molded body (preform) constituting the manufacturing method of the present invention, aluminum powder, aluminum alloy powder, or ceramic powder is further added as necessary 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 in terms of SiO ₂ is added to the total volume of these powders, 100 v %, to manufacture the preform. The manufacturing method is the same as the manufacturing method of the composite of the present invention, except that aluminum powder, aluminum alloy powder, or ceramic powder is used as necessary. For this reason, in the following explanation, a method of manufacturing a preform including the above-mentioned optional configuration will be explained.

The average particle size of the radiation shielding powder used in the manufacturing 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 necessary is preferably 0.3 μm or more and 500 μm or less. The reason for setting the average particle size to 0.3 μm or more is that materials with an average particle size smaller than that tend to aggregate with each other and become so-called lumps in an aggregated state, and when two or more types of powder are used, it is not preferable because it may be difficult to uniformly mix them. In addition, there is a tendency that it becomes difficult to uniformly mix the silica-based binder added to the above-mentioned powder (powder). In addition, when a powder with an average particle size of less than 0.3 μm is used, the powder filling rate in the preform obtained by molding by press molding, CIP molding, casting molding, etc. tends to be low, so there is a risk that it will not be possible to produce a preform with a high volume fraction (Vf) of the radiation shielding powder that characterizes the present invention. On the other hand, when a large powder exceeding 500 μm is used, the powder packing is 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. In addition, according to the inventors' investigations, 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 used as necessary is low, and it becomes impossible to produce a strong preform, which is also undesirable in this respect.

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

Although it varies depending on the type and particle size of the radiation shielding powder, according to the study by the inventors, the volume fraction (Vf) of the preform usually obtained in the preform manufacturing process constituting the manufacturing method of the present invention is generally around 50v%. According to the study by the inventors, when increasing the volume fraction Vf of the radiation shielding powder in the preform, it is preferable to mix particles with a large average particle size and particles with a small average particle size so that the small particles are mixed between the large particles. In addition, in the present invention, when two or more types of radiation shielding powder are mixed, it may be a mixture of the same type of radiation shielding powder with different average particle sizes, or a mixture of different types of radiation shielding powder. If it is desired to produce a preform with the required Vf in the present invention, a test mix may be performed in advance and the mixture of particles used to produce the preform may be determined by calculating from the bulk density of the preform. According to the inventors' research, by using the manufacturing method of the present invention, it is possible to produce preforms with a Vf of up to 85v% by appropriately mixing the 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 technology up to now.

In the use of a composite having a radiation shielding function, various situations are conceivable. For example, the higher the volume fraction (Vf) of the radiation shielding powder in the 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 lowered 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 necessary, the content of the radiation shielding powder in the preform produced can be appropriately controlled to 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 process. 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 or aluminum alloy or specific low melting point metal or specific low melting point alloy impregnated in a later process (referred to as "molten aluminum" in the specification of the present invention) will be the amount of aluminum in the composite, so the amount of aluminum in the structure having a radiation shielding function 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 structure having a radiation shielding function.

As described above, for example, by adopting a combination of large and small particles of a specific radiation-shielding powder, or by appropriately using means such as the addition of aluminum powder or the like as necessary, the manufacturing method of the present invention can easily produce a composite of radiation-shielding powder and molten aluminum, in which the blending amount of the radiation-shielding powder is controlled over a wide range of Vf (filling rate) from 3v% to 85v%. According to the inventors' studies, a composite with a radiation-shielding powder content of less than 3v% is not practical because the radiation shielding effect is too low. Furthermore, according to the inventors' studies, with conventional technology, it is difficult to achieve a Vf of 85v% or more, even if particle blending and various molding methods are used.

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

Next, a mixture of the radiation shielding powder defined in the present invention and aluminum powder or the like, which is used as necessary, 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 produce a porous molded body (preform). The following describes these components.

(Non-powdered silica-based binder)
The non-powdered silica-based binder constituting the present invention is suitably at least one liquid silica-based binder (hereinafter also referred to as "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 made of silica and an organic substance and cured by heating at a temperature of 900° C. or less. The liquid silica-based binder is added in a required amount according to the amount of the radiation-shielding powder, etc., used.

The amount of the liquid silica-based binder used in the present invention is, for example, about 0.5 to 10 parts by mass, calculated as _SiO2 , per 100 parts by mass of the mixture powder of the radiation-shielding powder containing aluminum powder or the like as necessary. According to the study by the present inventors, an amount of less than 0.5 parts by mass is not preferable because the strength exhibited as a binder is small. On the other hand, even if the amount exceeds 10 parts by mass, the binder function is exhibited, but the relative content of the radiation-shielding powder is low, so there is no need to add more than this.

The liquid silica-based binders such as ethyl silicate described above are compounds of silica (Si) and organic matter, which are thermally decomposed to become ultrafine powder _SiO2 . Water glass becomes ultrafine powder _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 mμ (nm) or less are dispersed as colloids in water or an organic solvent. The reason for using these silica-based binders is to strengthen the preform to be used in the next process.

By using ethyl silicate or silicone resin, which contains silica that is thermally decomposed at low temperatures to change to _SiO2 , or colloidal silica of ultrafine _SiO2 dispersed in water glass or a solvent, which also produces _SiO2 at low temperatures, the binder and the radiation shielding powder can be mixed uniformly. According to the study by the present inventors, these silica-based binders are ultrafine powders, and in the process of the manufacturing method of the present invention, the silica-based binders go from a state where they are uniformly mixed in the preform at the molecular level to an amorphous (non-crystalline) state, and then ultrafine _{SiO2 powder} is produced while remaining uniform, so that a strong preform can be produced.

In the next step, the mixed powder, which is the raw material of the preform prepared above, is molded and fired to produce a preform. What is important in the present invention is to prevent decomposition of the radiation shielding powder in the process of manufacturing the composite of the present invention so that the function targeted by the present invention is not impaired. For this reason, in the manufacturing method of the present invention, the firing temperature when molding and firing to produce a preform must be a low temperature of 900°C or less. In contrast, all of the liquid silica-based binders used in the present invention can fully exert their binder effect even at 900°C or less. Here, when using a silica-based binder in the manufacturing process of ordinary ceramics, silica powder of submicrons to several μm is generally used. And in the conventional technology, when using silica powder as a binder, it is necessary to produce a preform by firing at a temperature of 1100°C or more in order to exert the strength of the obtained preform. However, the above-mentioned conventional technology cannot be applied to the technology of the composite of the present invention. In the manufacturing method of the present invention, when forming and firing to produce a preform, and when impregnating the produced preform with molten aluminum, it is necessary to prevent decomposition of the radiation shielding powder, so the temperature must be low, at 900°C or less. This will be described later.

In the manufacturing 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 case is preferably a Henschel mixer that stirs at high speed with high shear force, or a mixer equipped with a birdcage-shaped rotor made of thin wires. When adding the liquid silica-based binder, an appropriate amount of organic binder such as PVA or PVB may be added as necessary within a range that does not impair the object of the present invention.

Next, the 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 using a general method such as press molding, tapping molding, or CIP molding.

In the manufacturing method of the present invention, the molded body obtained as described above is heated and sintered at a temperature of 300°C to 900°C to harden it and produce a preform. According to the inventors' investigations, 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 of 300°C or higher, the added liquid silica-based binder is effective and a strong preform can be produced. In addition, for the following reasons, in the manufacturing method of the present invention, it is necessary to produce the preform by sintering at a temperature of 900°C or lower.

For example, when boron carbide (B ₄ C) is used as the radiation shielding powder, it may decompose into BO and CO ₂ at high temperatures in air, so it is necessary to sinter it at a temperature of 900°C or less. In addition, when boron carbide (B ₄ C) is used as the material for forming the preform, if aluminum powder or the like is added as necessary, Al ₄ C ₃ generated from boron carbide and aluminum may undergo the following decomposition reaction at high temperatures. The Al ₄ C ₃ generated by the following decomposition reaction is unstable and reacts with moisture in the air to decompose into Al(OH) ₃ and CH _3. However, it is not preferable for Al ₄ C ₃ to remain in the composite.
B ₄ C + Al → Al ₄ C ₃ +B

In addition, when barium sulfate is used as the radiation shielding powder, _BaSO4 decomposes into BaO and _SO2 at high temperatures, so in this case too, it is not preferable to sinter at high temperatures. In addition, since the following decomposition reaction may occur, it is not preferable to sinter at high temperatures above 900°C.
Al+BaSO ₄ →BaO+Al ₂ O ₃ +SO (gas)

When tungsten (W) is used as the radiation shielding powder, tungsten becomes _WO3 at high temperatures in air, which is undesirable since it reduces the effect of adding a silica-based binder. According to the study by the present inventors, in order to suppress the above-mentioned series of reactions, 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 a stable preform of radiation shielding powder.

<Process for preparing the composite>
Next, in the first manufacturing 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 at high pressure, and then solidified to produce a composite having a radiation shielding function. In the second manufacturing 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 the liquid is impregnated under pressure after vacuum impregnation, and then the sealing agent is heated to a temperature of 300° C. or higher and 900° C. or lower to solidify and compound, thereby producing a composite having a radiation shielding function. Hereinafter, the steps for producing the composite in the first manufacturing method of the present invention and the second manufacturing method of the present invention will be described respectively.

[First manufacturing method]
In the first manufacturing method of the present invention, a composite having a radiation shielding function is prepared, which contains aluminum as a matrix and a powder having a radiation shielding effect in a range of 3 volume % or more and 85 volume % or less in total. Specifically, a preform prepared as described above is used, and a molten metal 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 the low melting point metal and other metals (in the present specification, a molten metal including these molten metals is also called "molten aluminum" representing aluminum metal and aluminum alloy) is cast into the preform at a temperature of 300°C to 900°C, and the molten aluminum is impregnated into the entire voids of the preform at a high pressure of 20 MPa to 200 MPa for 3 to 15 minutes, for example, about 3 to 5 minutes, and then immediately removed within 15 minutes after the start of impregnation with the molten aluminum and cooled to obtain a composite. More specifically, the composite is formed by the following procedure.

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

First, the preform previously prepared is preheated at a temperature of 300°C or more and 900°C or less in order to be impregnated with the molten aluminum. If the preheating temperature of the preform is less than 300°C, the impregnated molten aluminum is cooled and solidified quickly in the process of casting and impregnating the molten aluminum described below, which is not preferable because it is difficult to impregnate the entire void of the preform. According to the study by the present inventors, if the preheating temperature of the preform is 300°C or more, the molten aluminum is impregnated into the entire void of the preform. However, if the preheating temperature exceeds 900°C, for example, boron carbide, which is a radiation shielding powder, and aluminum used for impregnation with the molten aluminum react to generate Al ₄ C ₃ , or BaSO ₄ may decompose, which is not preferable.

Next, the process of impregnating the preform preheated as described above 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.

(1) As shown in Fig. 1A, a preform 2 preheated at 300°C to 900°C is placed on the lower punch 4 of a press die 10 that has been preheated to about 200°C to 300°C with 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, molten aluminum at a temperature of 700°C to 900°C is preferably used.
1B, an upper punch 5 of a press 10 is placed 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 minutes to 15 minutes in order to impregnate the voids of the preform 2 with the molten aluminum 1.
1C , immediately after the preform 2 is impregnated (specifically, within about 15 minutes after the start of the impregnation with the molten aluminum), the lower punch 4 is pushed up from its lower part, 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.

Below, points to be noted in the process of impregnating the molten aluminum 1 into the preform 2, which is a series of porous molded bodies, as described above, will be explained. First, when aluminum metal or aluminum alloy is used, a casting temperature of less than 600°C is not preferable because the molten aluminum hardens in a short time and does not impregnate the entire voids of 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 (B ₄ C) in the radiation shielding powder decomposes to produce Al ₄ C ₃ , or when barium sulfate (BaSO ₄ ) is used as the radiation shielding powder, BaSO ₄ may thermally decompose.

In the first manufacturing method of the present invention, the pressure for impregnation of the molten aluminum is 20 MPa or more and 200 MPa or less. A pressure of less than 20 MPa is not preferable because the pressure is too low and the molten aluminum may not impregnate the entire voids in the preform. Since sufficient impregnation is achieved 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' investigations, good impregnation can be achieved even at a pressure of about 100 MPa, for example.

The composite obtained by high pressure infiltration is held for 3 minutes, preferably for about 5 minutes, and then removed from the mold within at least 15 minutes from the start of the infiltration of the molten aluminum. If the composite obtained by high pressure infiltration of the molten aluminum into the voids of the preform is held in the mold for a long time exceeding 15 minutes, for example, boron carbide and aluminum may react to produce Al ₄ C ₃ or BaSO ₄ may decompose, resulting in a composite that violates the provisions of the present invention and must be avoided.

In the above explanation, a method of high-pressure impregnation of molten aluminum into a porous molded body (preform) using a high-pressure press as shown in Figure 1 was exemplified. However, the present invention is not limited to this, and any configuration that allows molten aluminum to be cast and filled into the preform at 20 MPa or more may be used, for example, a die-casting machine or squeeze-casting machine may 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, a composite having a stable and dense radiation shielding function and containing a radiation shielding powder with a Vf of 3% to 85v% can be produced.

[Second manufacturing method]
In the second manufacturing method of the present invention, a composite having a radiation-shielding function is prepared, which contains a powder having a radiation-shielding effect in a total range of 3 volume % or more and 85 volume % or less, and 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 volume % or more relative to 100 volume % of the voids in the preform obtained as described above.

(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, three types of liquid compounds having a low viscosity of 50 mPa·s or less and containing 30 mass % or more of non-volatile components, for example, as listed below.
(1) Type 1: Liquid ethyl silicate [Si(OC ₂ H ₅ ) ₄ ] having an alcohol Si bond or liquid oligomers obtained by partial hydrolysis of the ethyl silicate to form dimers or tetramers, as well as liquid alkoxides such as methyl silicate [Si(OCH ₃ ) ₄ ] and liquid oligomers obtained by partial hydrolysis thereof, which are adjusted so that the non-volatile components are 30 mass% or more.

(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 mass% or more. R in the general formula is an organic group such as a methyl group, an ethyl group, a vinyl group, a phenyl group, an acetyl group, etc. Specifically, for example, liquid compounds such as silicone oil or a silicone adhesive dissolved in an organic solvent can be used.

(3) Third type: A liquid alkoxysilane compound which is an alkoxysilane derivative and reacts with moisture in the air to undergo a condensation reaction to generate a silicone oxygen organic compound (Si-O-R) as shown in the following reaction formula. For example, a compound such as a one-part room temperature curing sealant described in Japanese Patent No. 3816354 can be used. For example, a commercially available product such as Permeate (registered trademark, manufactured by D&D Co., Ltd.) can be used.

(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 originating from a liquid organic/inorganic sealing agent is present in the voids of a preform produced as described above using a radiation shielding powder as a raw material, in a volume of 25% or more relative to 100% by volume. As a specific procedure, a liquid organic/inorganic sealing agent containing 30% or more by mass of non-volatile components and having a viscosity of 50 mPa·s or less is vacuum-impregnated into the voids of a porous molded body (preform), or is impregnated at a pressure of 10 atmospheres or less by applying pressure 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 material of the liquid organic/inorganic sealing agent remain in 25% (1/4) or more of the entire voids when the entire voids of the preform are taken as 100% by volume, thereby complexing the radiation shielding powder and the component originating from the liquid organic/inorganic sealing agent. That is, the ratio of the entire voids in the preform is about 15v% to 40v%, so that the components derived from the organic/inorganic sealant remain in the voids at 1/4 or more of the voids, that is, 4v% to 10v% or more. In other words, the obtained composite has a high ratio of 60v% to 85v% of the fired 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 is voids. In addition, the amount of liquid silica-based binder mixed with the radiation-shielding powder is preferably about 0.5 to 10 parts by mass of the liquid silica-based binder in terms of _SiO2 added to 100 parts by mass of the radiation-shielding powder in the present invention, so that a composite having a high ratio of the radiation-shielding powder can be obtained. These points are the same for the composite obtained by the first manufacturing method.

The liquid organic/inorganic sealant used in the second manufacturing method of the present invention has a low viscosity of 50 mPa·s or less so that it can be easily impregnated into the preform. If the viscosity exceeds 50 mPa·s, the organic/inorganic sealant is unlikely to impregnate the fine parts of the preform, and a strong composite may not be obtained. In addition, it is essential that the liquid organic/inorganic sealant contains 30 wt% or more of non-volatile matter relative to 100 wt% of the sealant. In the second manufacturing method of the present invention, the organic/inorganic sealant is impregnated into the voids so that it is present at least 25 v% relative to the entire voids of the preform (100 v%), and then heated to 200°C to 900°C to composite the radiation shielding powder and the organic/inorganic sealant. That is, by heating at the above-mentioned temperatures, the liquid organic/inorganic sealant impregnated in the voids of the preform becomes a solidified liquid organic/inorganic sealant or a heat-treated liquid organic/inorganic sealant, both of which are solids, and remains in the voids of the preform.

The preform used in the manufacturing method of the present invention, which is prepared as a composite as described above, is a porous body in which voids are present in about 15 to 40 v % of the entire preform (100 v %). 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 are present in a proportion of 25 v % or more of the entire voids of the preform (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 are fixed in some (25 v % or more) or all of the voids of the preform.

According to the study by the present inventors, when 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 25v% relative to the entire voids of the preform (100v%), it is not possible to obtain a composite having a strong and practical radiation shielding function. In addition, a preferred configuration of the composite obtained by the second manufacturing method of the present invention is 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 about 5v% or more relative to the entire preform (100v%). For example, when the proportion of voids in the preform is 20v%, 25% (1/4) of that, that is, 5v% relative to 100v% of the preform, is the organic inorganic sealing agent. In the above example, the fired product of the mixture containing the radiation-shielding powder constituting the preform occupies 80v%. As described 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 to 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 79.5v%, resulting in a strong composite.

In the second manufacturing method of the present invention, the silica-based binder required for producing the preform and the liquid organic/inorganic sealant to be impregnated into the obtained preform may be the same compound. However, the liquid organic/inorganic sealant used for impregnating the voids in the preform must be impregnated into the preform so that the sealant impregnated into the voids in the preform must ultimately remain in a solidified state, and therefore must 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 common.

As described above, in the second manufacturing method of the present invention, the preform impregnated with the liquid organic/inorganic sealing agent is heated at a temperature of 200° C. or more and 900° C. or less. The reason why the heating temperature is set to 200° C. or more in this case is as follows. By setting the heating temperature to 200° C. or more, the liquid alkoxysilane compound that generates siloxane bonds, ethyl silicate oligomers, or silicone oxygen organic compounds (Si—O—R) in the compound used as the liquid organic/inorganic sealing agent is thermally decomposed, and the compound functions as a silica-based binder or a Si—OR-based organic/inorganic binder, thereby strengthening the preform. In addition, the reason why the heating temperature is set to 900° C. or less is to prevent the powder having a radiation shielding effect, including B ₄ C and BaSO ₄ , constituting the preform, from being decomposed or oxidized.

The procedure of the second manufacturing method of the present invention will be described with reference to FIG. 2. 30 in FIG. 2 is 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 in the reduced pressure vessel 30 before the organic and inorganic sealing agent 31 is impregnated into the gaps. The opening and closing tool 33 of the reduced pressure vessel 30 is closed, and the reduced pressure vessel 30 is depressurized from a pressure reduction port 36 provided in the reduced pressure vessel 30 using a vacuum pump (not shown). When the reduced pressure vessel 30 is reduced to approximately zero atmospheric pressure, the organic and inorganic sealing agent 31 is gradually introduced from the organic and inorganic sealing agent introduction container 35 into the interior container 34. At this time, the amount of organic and inorganic sealing agent 31 introduced is predicted in advance so that the organic and inorganic sealing agent 31 is completely impregnated into the preform 32 and the entire preform 32 is immersed.

After the organic/inorganic sealing agent 31 is added as described above, the vacuum is maintained for about 5 to 10 minutes, and the organic/inorganic sealing agent 31 is vacuum-impregnated into the voids in the preform 32. After the impregnation is complete, the pressure vessel 30 is gradually opened to the atmosphere, and air is introduced into the reduced pressure vessel 30. After the reduced pressure vessel 30 is filled with atmospheric air, air that has been decompressed to about 10 atmospheres using compressed air from a compressor or the like (not shown) is gradually introduced from the pressure port 37, and after pressurizing to about 4 atmospheres, the pressure is kept for about 5 to 10 minutes, and the organic/inorganic sealing agent 31 is impregnated into the preform 32.

The compressed air in the reduced pressure vessel 30 is then gradually released until atmospheric pressure is reached, at which point the preform with the solidified liquid organic/inorganic sealant and/or the heat-treated liquid organic/inorganic sealant fixed in the voids is removed, gradually dried, and heated to 300-400°C to obtain a composite with radiation shielding properties.

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 fired product made of 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, % means volume % unless otherwise specified. Due to the special circumstances that require handling radiation to measure the shielding effect, the radiation shielding rate of the composites of Examples 1 to 3 was requested to be measured by an external measurement institution. The radiation shielding rate measured by the external institution was higher than that of conventional materials.

<Example of a method for impregnating a preform with molten aluminum>
[Example 1]
450g of _B4C powder #800 (manufactured by Dojin Sangyo Co., Ltd.) with an average particle size of 16μm was mixed for 30 minutes in a V-type mixer. 5g of ethyl silicate was added to the mixed powder as a liquid binder, and all of them were placed in a Henschel mixer that applies shear force to the powder and stirred at high speed for 15 minutes to mix uniformly. The obtained mixed powder was placed in a 100mm x 100mm mold, a lid was placed on it, and press molding was performed at a pressure of 160kgf/ ^cm2 . This molded body was placed in a sintering furnace, heated to 400°C at a heating rate of 50°C/hour, then held at 400°C for 3 hours to sinter, and then naturally cooled. The obtained sintered body (preform) had a shape of 100mm x 100mm x 35mm and weighed 449g. Calculated from the true specific gravity of boron carbide ( _B4C ) of 2.51, this preform had a bulk specific gravity of 1.31, a filling rate (Vf) of boron carbide of 52%, and voids of 48%. This preform was heated at a heating rate of 100°C/hour and held at 500°C to wait in the heated state for the next aluminum impregnation by high-pressure pressing.

A die with an inner diameter of 300φ installed in a high-pressure press was heated to approximately 250°C with a burner. Then, the preform that had been waiting in a heated state was placed in the die of the press, and molten aluminum melted at 800°C was poured into the die, and high-pressure casting was performed as described below. As shown in Figures 1A and 1B, after molten aluminum 1 melted at 800°C was poured into the die containing the preform 2, the upper punch 5 of the press 10 was immediately lowered and a load was applied to the upper punch 5 so that the pressure of the molten aluminum 1 was 70 MPa. As mentioned above, since the inner diameter of the die is 300φ, the load of the press 10 corresponds to approximately 500 t.

After the load was applied and maintained for 5 minutes, the upper punch 5 was removed, and the lower punch 4 was immediately pushed up to lift the impregnated body (composite) 3 to the top of the press (see Figure 1C), and the composite 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.

The specific gravity of the composite taken out was measured to be 2.61. This value was almost the same as the calculated value when the voids in the preform were completely impregnated with aluminum, so it was concluded that the above-mentioned taken out product was a dense composite of _B4C and aluminum. The content (volume filling rate) of light boron carbide with a specific gravity of 2.52 was a high content of 52v%, so a light composite with a specific gravity of 2.61 could be produced. In addition, when a part of the obtained composite was cut out and the surface was subjected to X-ray diffraction measurement, _the generation of _Al4C3 caused by the decomposition of _B4C could not be confirmed.

The material obtained above, with a volume filling rate (Vf) of 52v% and a thickness of 35 mm, was subjected to measurement of the radiation shielding effect by an external measurement agency. As a result, the shielding effect against neutrons of the _isotope Cf252 of californium (Cf) was 61%, which was a high value. Furthermore, a bending test was performed on the composite of this example based on JIS-R1061, and the strength was 183 MPa, which was high. These facts show that the composite obtained in this example is a useful material that effectively combines the properties of the _B4C powder, which is lightweight and has excellent _radiation shielding effect and is used as a raw material, and is composited in its original state without decomposition.

[Example 2]
230 g of _B4C powder #180 (manufactured by Dojin Sangyo Co., Ltd.) having an average particle size of 70 μm and 260 g of _B4C powder #800 having 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 mixed for 15 minutes in a Henschel mixer as in Example 1.

The obtained mixed raw material was press molded and sintered in the same manner as in Example 1 to produce a preform having a shape of 100 mm x 100 mm x 26 mm, a bulk density of 1.66, a _B4C filling rate Vf of 66%, and a porosity of 34 v%. The obtained preform was placed in a mold of a high-pressure press in the same manner as in Example 1 and high-pressure impregnated with molten aluminum. Thereafter, it was naturally cooled in the same manner as in Example 1, and the solidified aluminum around the composite was removed.

The specific gravity of this composite was 2.57, which was almost the same as the calculated value when aluminum was impregnated into the voids of the preform, and it was a dense composite made of B ₄ C and aluminum. In addition, X-ray diffraction was performed on the surface of the composite in the same manner as in Example 1. As a result, as in Example 1, the generation of Al ₄ C ₃ and the like could not be observed. As described above, by combining B ₄ C powders with different average particle sizes and using them as raw materials, a composite with a B ₄ C powder filling rate of 66v% higher than that in Example 1 could be produced. In addition, a light composite with a specific gravity of 2.57 could be produced despite the high B ₄ C filling rate.

The material obtained above, with a volume filling rate (Vf) of 66v% and a thickness of 26 mm, was subjected to measurement of the radiation shielding effect by an external measurement agency. As a result, the shielding effect against neutrons of the _isotope Cf252 of californium (Cf) was 31%, which was a high value. In addition, a bending test was performed on the composite of this example based on JIS-R1061, and the strength was 193 MPa, which was high. These facts show that the composite obtained in this example is a useful material that effectively combines the properties of the _B4C powder, which is lightweight and has excellent _radiation shielding effect and is used as a raw material, and is composited in its original state without decomposition.

[Example 3]
820 g of A-200 (trade name, manufactured by Takehara Chemical Industry Co., Ltd.), which is a barium sulfate (BaSO ₄ ) 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 in which a soluble silicone resin KR-200 (manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in ethanol to prepare a silicone-based resin solution with a concentration of 20 wt % by mass. Then, 50 g of the prepared silicone-based resin solution was added to the mixed BaSO ₄ powder, and high-speed stirring was performed using a Henschel mixer in the same manner as in Example 1.

The preform produced by the same method and procedure as in Example 1 had a shape of 100 mm x 100 mm x 28 mm, a bulk specific gravity of 2.92, and a filling rate of BaSO ₄ of 65 v%. Next, in the same manner as in Example 1, the preform was impregnated with molten aluminum at high pressure and processed to extract a composite. The specific gravity of the composite was 3.86, which was almost the same as the calculated value (theoretical value), and it was confirmed that it was a dense composite made of BaSO ₄ and aluminum.

The material obtained above with a volume filling rate (Vf ₎ of 65v% and a thickness of 28mm was subjected to measurement of the radiation shielding effect by an external measurement agency. As a result, the projection rate of cesium (Cs) gamma rays Cs137 was 35%, and the shielding rate of X-rays 150Kv was 99.5%, which were high values. In addition, a bending test was performed on the composite of this example based on JIS-R1061, and the strength was 193Mpa, which was high. These facts show that the composite obtained in this example is a useful material that effectively combines the properties of _BaSO4 powder, which is _lightweight and has excellent radiation shielding effect, and is used as a raw material and is combined in its original state without decomposition.

[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 to this, and the mixture was stirred at high speed with a Henschel mixer in the same manner as in Example 1.

The preform produced by the same method and procedure as in Example 1 had a size of 100 mm x 100 mm x 33 mm, a bulk density of 1.30, and a total filling rate of _B4C powder and aluminum powder (Al powder) of 50 v%. Next, the preform was high-pressure impregnated with molten aluminum in the same manner as in Example 1, and processed to extract a composite. The specific gravity of the composite in this example was 2.65, which was almost the same as the calculated value when all the voids in the preform were impregnated with molten aluminum.

Since the volume ratio of the B ₄ C powder and the Al powder in the two types of raw material powder is approximately 1:1, about 50v% of the preform is aluminum powder. Therefore, the amount of aluminum in the obtained composite is 75v% in total including the aluminum impregnated in the preform, so the composite is composed of 75v% aluminum powder and the remaining 25v% B ₄ C powder. From the above, it was confirmed that it is possible to control the concentration of the radiation shielding powder by mixing an appropriate amount of aluminum powder into the raw material of the preform. Moreover, in the above case, by using B ₄ C powder as the raw material of the preform, a light composite with a specific gravity of 2.65 could be manufactured. In addition, a bending test was performed on the composite of this embodiment based on JIS-R1061, and the result was a high strength of 182 MPa.

[Example 5]
The raw material for the preform was prepared by adding 280 g of _BaSO4 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, which was the same as that used in Example 3. The raw material was stirred at high speed with a Henschel mixer in the same manner as in Example 1.

Thereafter, a preform produced by the same method and procedure as in Example 1 had a shape of 100 mm × 100 mm × 38 mm, a bulk density of 1.77, and a total filling rate (Vf) of the BaSO ₄ powder and the Al powder of 55v%.

Next, the preform obtained above was infiltrated with molten aluminum at high pressure in the same manner as in Example 1, and processed to extract a composite. The specific gravity of the prepared composite was 2.99, which was almost the same as the calculated value for the dense body. In the composite of this example, 70v% of the preform was aluminum powder, so that the total of the aluminum in the composite including the impregnated aluminum was 84v%, and the remaining 16v% was BaSO ₄ powder. Thus, the composite of this example, like the composite of Example 4, is an example in which it is possible to control the concentration of barium sulfate powder, which is a radiation shielding powder in the composite, by mixing aluminum powder into the raw material of the preform. In addition, a bending test was performed on the composite of this example based on JIS-R1061, and the result was a high strength of 212 MPa.

[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.), which is _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 to this, and high-speed stirring was performed using a Henschel mixer in the same manner as in Example 1.

Thereafter, a preform was produced by the same method and procedure as in Example 1, and had a size of 100 mm x 100 mm x 38 mm, a bulk density of 2.00, and a total filling rate (Vf) of the _B4C and _BaSO4 powders of 57v%.

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 the same as the calculated value when the preform was 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 manufactured by the manufacturing method of the present invention. In addition, a bending test was performed on the composite of this example based on JIS-R1061, and the result was a high strength of 199 MPa.

[Example 7]
380g of B ₄ C powder #800 (manufactured by Dojin Sangyo Co., Ltd.) with an average particle size of 16 μm and 1270g of tungsten metal powder W-4 (manufactured by Nippon Shinkinzoku Co., Ltd.) with an average particle size of 3 μm were used and uniformly mixed in the same manner as in Example 1. At that time, water glass No. 4 (manufactured by Fuji Chemical Co., Ltd.) was diluted with water and used as a binder, and an amount equivalent to 16 g of SiO ₂ was added and stirred at high speed with a Henschel mixer in the same manner as in Example 1. Then, a preform was produced by the same method and procedure as in Example 1. The preform had a shape of 100 mm x 100 mm x 32 mm, its bulk specific gravity was 5.18, and the total filling rate (Vf) of B ₄ C and tungsten W was 68%.

Next, the composite was high-pressure impregnated with molten aluminum in the same manner as in Example 1, processed, and extracted. The specific gravity of the composite was 6.04, which was almost the same as the calculated value when the preform was impregnated with molten aluminum. The obtained 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.

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

[Example 8]
Using the same _B4C powder #800 (manufactured by Dojin Sangyo Co., Ltd.) with an average particle size of 16 μm as in Example 1, an ethyl silicate binder was added, mixed, molded, and fired in the same manner to prepare a preform with dimensions of 100 mm x 100 mm x 35 mm, the same bulk density of 1.31, a boron carbide filling rate (Vf) of 52%, and a void of 48 v%. The preform was heated and left on standby at a temperature of 400° C.

The preform was placed in a mold with an inner diameter of 300 mm heated to 250°C in the same manner as in Example 1, and a low melting point alloy (zinc alloy: ZDC2, specific gravity 6.8) melted at 500°C was cast, and high pressure impregnated at 70 MPa (500 t as press load). After holding for 10 minutes, the composite was immediately cooled, cooled to room temperature, and removed. The specific gravity of the composite was 4.18, and it was a composite material impregnated with almost 100% low melting point zinc alloy. There was no decomposition reaction due to the generation of _B4C . Furthermore, a bending test was performed on the composite of this example based on JIS-R1061, and the strength was high at 223 MPa.

[Comparative Examples 1 and 2]
The same B ₄ C powder as used in Example 1 was used and mixed, and 2 g of fine silica powder (manufactured by Yamamori Tsuchimoto Seisakusho Co., Ltd.) having 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 in the same manner as in Example 1, press-molded, and the molded bodies were fired at different temperatures of 400° C. and 800° C., respectively, and cooled. The obtained molded bodies did not have the strength of a preform in either firing temperature, could not be handled, and could not be subjected to high-pressure impregnation with molten aluminum.

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

[Comparative Example 5]
A B ₄ C preform was prepared in the same manner as in Example 1, and the obtained preform was placed in a mold and cast at 900°C using molten aluminum in the same manner as in Example 1. In this comparative example, the temperature was then held at 900°C for 20 minutes, and a composite was prepared in the same manner as in Example 1. When the surface of the composite was processed, the surface was blackened, so a part of it was cut out and examined by X-ray diffraction. As a result, in addition to the main raw material B ₄ C, small peaks of Al ₄ C ₃ were observed at 2θ = 31.8°, 35.8°, 40.1°, and 55°. From this, it was confirmed that in the case of the composite of this comparative example, if the composite is kept at a high temperature in the press mold for a long time, the raw material B ₄ C of the preform will be partially decomposed, and the composite will not be in a good condition.

[Comparative Example 6]
890 g of A-200 (trade name, manufactured by Takehara Chemical Industry Co., Ltd.), a _BaSO4 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 dissolved in ethanol, similar to that used in Example 3, was added, and high-speed stirring was performed with a Henschel mixer in the same manner as in Example 1.

The preform produced by the same method and procedure as in Example 1 had a shape of 100 mm x 100 mm x 33 mm, and the filling rate of BaSO ₄ was 60 v%. Next, it was set in a mold in the same manner as in Example 1, impregnated with molten aluminum at 950 ° C., processed, and the composite was taken out. When the surface was processed and observed visually, there were many pores. The reason for this is thought to be that BaSO ₄ was decomposed into BaO and SO ₂ when heated at high temperatures.

Table 1 shows the preparation conditions for the preforms in Examples 1 to 8 and Comparative Examples 1 to 6, as well as the properties and evaluation of each of the composites obtained in Examples 1 to 8 and Comparative Examples 5 and 6. In Table 1, "Yes" or "No" for decomposition indicates whether decomposition was observed in the radiation shielding powder that constitutes each composite.

<Example of a method for impregnating a preform with an organic/inorganic sealant>
Next, the method of producing a radiation shielding composite by impregnating a special liquid organic inorganic sealing agent into the voids of a porous molded body (preform) according to the second production method of the present invention will be described with reference to examples and comparative examples. The reason for carrying out bending tests on the composites in the following examples is as follows. When the voids of the 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 having a configuration in which the voids of the 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 impregnating with molten aluminum described above, and some voids may remain. According to the study by the present inventors, even in such a configuration, as long as the liquid organic inorganic sealing agent occupies 25% by volume or more of the voids of the preform before being impregnated with the liquid organic inorganic sealing agent, the composite obtained will have 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 pore-sealing agent and/or the heat-treated organic/inorganic pore-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.

[Example 9]
A preform weighing 262 g and having dimensions of 100 mm x 100 mm x 20 mm was produced using 270 g of B ₄ C powder #800 (manufactured by Dojin Sangyo Co., Ltd.) with an average particle size of 16 μm and the same material composition as in Example 1 described above, and was mixed, molded, fired, and cooled in the same manner. The obtained preform had a bulk density of 1.31 calculated from the true specific gravity of boron carbide (B ₄ C) of 2.51, a filling rate (Vf) of boron carbide of 52 v%, and a void of 48 v%.

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

A vacuum was drawn through the vacuum port 36 by a vacuum pump (not shown) to the entire reduced pressure vessel 30, and this was maintained for 10 minutes. After that, the vacuum was released to return the inside of the reduced pressure vessel 30 to normal pressure, and then 7 atmospheres of air from a compressor (not shown) was reduced to 4 atmospheres by a pressure reducing device (not shown) and slowly introduced into the reduced pressure vessel 30 to pressurize the entire reduced pressure vessel to 4 atmospheres, and this was maintained for 5 minutes to pressure-impregnate the permeate into the preform 32.

After that, the reduced pressure vessel 30 was returned to atmospheric pressure, and the preform 32 was taken out of the indoor vessel 34 and left to stand overnight. The temperature was then raised at 50°C/hour, and heat-treated at 400°C for 3 hours to produce a composite having a radiation shielding function. The specific gravity of this material (composite) was measured, and the composite was found to be 52v% _B4C , 30v% organic/inorganic sealing agent (62.5v% of the voids in the preform), and 18v% voids. The specific gravity of the obtained material (composite) is summarized in Table 2.

The material (composite) obtained above, with a volume filling rate (Vf) of 52v% and a thickness of 20 mm, was subjected to measurement of the radiation shielding effect by an external measurement agency. The shielding rate of the _neutron beam Cf252, an isotope of Cf, was measured, and the shielding rate was 30%, which was a high value. There is no example of a shielding material that has such a neutron shielding rate with a thickness of _{20 mm} . This result shows that the composite obtained in this example is a useful material that effectively combines the properties of the B ₄ C powder, which is lightweight and has excellent radiation shielding effect and is used as a raw material, without decomposition, and is composited as it is. Meanwhile, a test piece for measuring bending strength of 3 mm x 4 mm x 40 mm was prepared from the composite obtained above, and a bending test was performed based on JIS-R1061. As a result, a strength of 25 MPa was obtained. This value is about 5 to 10 times that of gypsum board and concrete plate, which were measured using the same method, confirming that the material is fully suitable for use as exterior wall material and radiation storage containers.

[Example 10]
Using 230 g of _B4C powder #180 (manufactured by Dojin Sangyo Co., Ltd.) having an average particle size of 70 μm and 100 g of _B4C powder #800 having an average particle size of 16 μm, a molded body of 100 mm x 100 mm x 20 mm was prepared in the same manner as in Example 2. This molded body was fired at 400° C. in the same manner as in Example 1 to obtain a preform with a weight of 235 g and a bulk density of 1.66. The obtained preform had a volume filling rate (Vf) of _B4C of about 66 v% and a void of 32 v%. The obtained preform was vacuum-impregnated with permeate in the same manner as in Example 8 and heat-treated at 400° C. to obtain a radiation shielding material with 66 v% _B4C , 19 v% permeate (organic inorganic sealing agent) (59.4 v% of the voids in the preform), and 15% voids.

The material (composite) of the _B4C powder obtained above, with a volume filling rate (Vf) of 66v% and a thickness of 20 mm, was subjected to measurement of the radiation shielding effect by an external measurement agency. The shielding rate of the neutron radiation of the isotope Cf252 of Californium (Cf) was measured, and the shielding rate was 34%, which was a high value. In addition, a bending test piece was prepared in the same manner as in Example 8, and the bending strength was measured, which showed a high value of 41 MPa.

[Example 11]
In the same formulation as in Example 3, 240 g of A-200 (trade name, manufactured by Takehara Chemical Industry Co., Ltd.), which is a barium sulfate (BaSO ₄ ) 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 in which a soluble silicone resin KR-200 (manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in ethanol to prepare a silicone-based resin solution with a concentration of 20 wt % by mass. Then, 15 g of the prepared silicone-based resin solution was added to the mixed BaSO ₄ powder, and mixed powder was obtained by high-speed stirring with a Henschel mixer in the same manner as in Example 1.

The mixed powder obtained above was placed in a 60 mmφ mold, press molded under a pressure of 160 kg/ ^cm2 , and heated at 400°C in the same manner as in Example 1 to produce a preform in the shape of a disk of 60 mmφ x 27.8 mm thickness and weighing 235 g. The bulk density of the obtained preform was 2.95, with 65v% _BaSO4 and 35v% voids.

Next, a composite was obtained as follows, using a liquid organic inorganic sealing agent on the preform obtained above. As a liquid organic inorganic sealing agent, ethyl silicate oligomer manufactured by Colcoat Co., Ltd., containing 40 wt% in terms of _SiO2 , was placed in a container, and the preform obtained above was immersed in it, and the preform was impregnated with ethyl silicate by vacuum and pressure of 4 atmospheres. Then, the impregnated body impregnated with the liquid organic inorganic sealing agent was taken out of the container, left in air for 48 hours, and heat-treated at 400°C for 3 hours to obtain a composite having a radiation shielding function, in which _BaSO4 was 65v%, the non-volatile content of _SiO2 generated from ethyl silicate was 10v% (28.6v% of the voids in the preform), and the remainder was 23v%.

The material (composite) of _BaSO4 powder obtained above with a volume filling rate (Vf) of 65v% and a thickness of 27.8 mm was measured for its radiation shielding effect by an external measurement agency. As a result, the projection rate of cesium (Cs) gamma rays Cs137 was 36%, and the shielding rate of X-rays 150Kv was 99.7%, which were high values. In addition, a bending test piece was prepared in the same manner as in Example 1, and the bending strength was measured, showing a high value of 28 MPa, confirming that the material is fully usable as a structure.

[Example 12]
54 g of B ₄ C powder with an average particle size of 16 μm and 110 g of A-200 (product name) BaSO ₄ 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×30 mm, and having a bulk density of 1.93. The obtained preform had 29 v% B ₄ C, 29 v% BaSO ₄ , and 42 v% voids.

Using a reduced pressure vessel 30 as shown in Fig. 2 and liquid ethyl silicate as an 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 having a radiation shielding function. 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.

The material (composite) containing the _B4C powder, _BaSO4 powder, and liquid organic-inorganic sealing agent obtained above was measured for its radiation shielding effect by an external measurement agency. As a result, the projection rate of cesium (Cs) gamma rays Cs137 was 25%, and the shielding rate of X-rays 150Kv was 98%, which were high values. In addition, a bending test piece was prepared in the same manner as in the other examples, and the bending strength was measured, showing a high value of 32Mpa, confirming that the material is sufficiently usable industrially as a structure.

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.

[Comparative Examples 7 to 10]
Test pieces were prepared using the preforms used in preparing the composites of Examples 9 to 12 having the configurations shown in Table 2, which were not impregnated with the liquid organic/inorganic sealing agent and were not composited, and the bending strength was measured in the same manner as in the examples. The measurement results obtained are summarized in Table 3. For comparison, the bending strength multipliers for each of the composites of Examples 9 to 12 are shown in parentheses. As shown in Table 3, it was confirmed that the bending strength of the composites of the examples in which the organic/inorganic sealing agent was composited to the preform could be significantly improved compared to the materials of the comparative examples.

[Comparative Example 11]
A preform having a bulk density of 1.31, a filling rate (Vf) of B ₄ C of 52v%, and a void of 48v% was used as prepared in Example 9, and the composite of Comparative Example 11 was obtained by compounding with an organic inorganic sealant as described below. Permeate HS-200 having a non-volatile content of 85w%, a viscosity of 15.5mPa·s, a specific gravity of 1.15, and a siloxane bond, similar to that used in Example 9, was used as a liquid organic inorganic sealant, and this was diluted with ethanol to adjust the non-volatile content to 20w%. Then, after impregnating the liquid organic inorganic sealant in the same manner as in Example 9, a composite material was obtained by heat treatment. From the results of weight measurement, the material was 52v% B ₄ C, 8v% organic inorganic sealant (16.0v% of the voids in the preform), and 36v% 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 believed to be that the amount of the organic-inorganic composite agent occupying the voids of the preform was low.

[Comparative Example 12]
A preform having a bulk density of 2.95, a filling rate (Vf) of BaSO ₄ of 65v%, and a void of 35v% was used as prepared in Example 11, and the composite of Comparative Example 12 was obtained by compounding with an organic inorganic sealant as follows. As a liquid organic inorganic sealant, the liquid ethyl silicate oligomer solution used in Example 11 was diluted with water to adjust the non-volatile content of SiO ₂ to a 10w% solution. Then, the preform was impregnated with the liquid organic inorganic sealant in the same manner as in Example 11, and then the material was heat-treated to obtain a composite material. From the results of the weight measurement, the material was 65v% BaSO ₄ , 4v% non-volatile content of SiO ₂ generated from ethyl silicate (11v% of the voids in the preform), and 31v% of the voids remained. The bending strength of this material was measured in the same manner as in the Examples, and was found to be low at 9 MPa.

[Comparative Example 13]
A preform having a bulk density of 1.31, a filling rate (Vf) of B ₄ C of 52v%, and a void of 48v%, similar to that prepared in Example 9, was used, and the composite with an organic/inorganic sealant was obtained as follows to obtain a composite of Comparative Example 13. As a liquid organic/inorganic sealant, a silicone resin KR220l (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) solution having a viscosity of 150 mPa.m dissolved in ethanol with a non-volatile content of 40w% was used. The silicone resin solution was impregnated into a preform by the same operation as that performed in Example 9, and a composite material was obtained by heat treatment. The obtained material had a Vf of 52v% for B ₄ C, a non-volatile content of 3v% of SiO ₂ generated from the silicone resin (6.2v% of the voids in the preform), and a void of 45v%. When the bending strength of this material was measured by the same method as in the example, the bending strength was 6 MPa, which was low. The reason for this is believed to be that the silicone resin solution, which has a high viscosity, did not sufficiently impregnate the preform, and the amount of the organic/inorganic sealing agent impregnated was low.

Reference Signs List 1: Molten aluminum 2: Preform 3: Composite impregnated with molten aluminum 4: Lower punch 5: Upper punch 10: Press die 30: Reduced pressure vessel 31: Organic/inorganic sealing agent 32: Preform
33: Opening and closing tool for reduced pressure vessel 34: Indoor vessel 35: Organic/inorganic sealing agent supply vessel 36: Reduced pressure port 37: Pressurized port 38: Pressure gauge

Claims (9)

A composite having a radiation-shielding function, comprising a powder having a radiation-shielding effect, the powder being composited together in a total amount within a range of 3 volume % or more and 85 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 in 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, and then solidified to form a composite, or at least 25 volume % or more of the voids in the porous molded body (preform) are impregnated with a liquid organic/inorganic sealing agent, which is then solidified to form a composite, and
The composite having a radiation -shielding function is characterized in that the non-powdered silica-based binder is at least one selected from the group consisting of a liquid silicone resin, a silicone resin solution obtained by dissolving a silicone resin in an organic solvent, and a silica alkoxide made of silica and an organic substance and cured by heating at a temperature of 900°C or less, and has a property of being able to form a porous molded body (preform) that is the molded and fired product at a temperature at which the radiation-shielding powder is not decomposed. 2. The composite having a radiation-shielding function according to claim 1, wherein 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. The composite having a radiation shielding function according to claim 1, wherein the liquid organic/inorganic pore-blocking agent is present in the voids of the porous molded body (preform) as a solidified organic/inorganic pore-blocking agent and/or a heat-treated organic/inorganic pore-blocking agent, and the solidified organic/inorganic pore-blocking agent and/or the heat-treated organic/inorganic pore-blocking agent occupies 25% by volume or more of the 100% by volume of the voids of the porous molded body (preform) before impregnation, and the solidified organic/inorganic pore-blocking agent and/or the heat-treated organic/inorganic pore-blocking agent occupies 5% by volume or more of the entire preform after impregnation, taking it as 100% by volume. 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(OCH ₃ ) ₄ or a dimer or tetramer oligomer obtained by partially hydrolyzing the methyl silicate, and which is adjusted so that the non-volatile component is 30 mass % or more;
A liquid ethylsilicate compound which is ethylsilicate Si(OC ₂ H ₅ ) ₄ or a dimer or tetramer oligomer obtained by partially hydrolyzing the ethylsilicate, and which is adjusted so that the non-volatile component is 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 composite having a radiation-shielding function according to claim 1 or 3, which is at least any one selected from the group consisting of liquid alkoxysilane compounds which 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). A method for producing a composite having a radiation-shielding function, 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 said 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 volume % or more and 85 volume % or less, comprising:
a step of adding a non-powdered silica-based binder to one or more of the 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 mainly composed of iron oxide, and then molding the mixture, and firing the obtained molded body at a temperature of 300° C. or higher and 900° C. or lower to produce a porous molded body (preform); the non-powdered silica-based binder used in the step is at least one liquid silica-based binder selected from the group consisting of a liquid silicone resin, a silicone resin solution obtained by dissolving a silicone resin in an organic solvent, and a silica alkoxide made of silica and an organic substance and heated and cured at a temperature of 900° C. or lower ; and
a step of casting a molten metal of at least one of a 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 to 900°C, into the porous molded body (preform) obtained in the step, holding the molten metal at a high pressure of 20 MPa to 200 MPa 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. 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 volume % or more and 85 volume % or less, the powder being composited, the method comprising the steps of:
a step of 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, to form a mixture, and then firing the obtained molded body at a temperature of 300° C. or more and 900° C. or less to prepare a porous molded body (preform);
and a compounding step of: 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 at a pressure of 10 atmospheres or less by pressurizing the liquid organic/inorganic sealing agent after vacuum impregnation, and then heating the liquid organic/inorganic sealing agent 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), thereby compounding the radiation-shielding powder with a component derived from the liquid organic/inorganic sealing agent. 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(OCH ₃ ) ₄ or a dimer or tetramer oligomer obtained by partially hydrolyzing the methyl silicate, and which is adjusted so that the non-volatile component is 30 mass % or more;
A liquid ethylsilicate compound which is ethylsilicate Si(OC ₂ H ₅ ) ₄ or a dimer or tetramer oligomer obtained by partially hydrolyzing the ethylsilicate, and which is adjusted so that the non-volatile component is 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 any one selected from the group consisting of liquid alkoxysilane compounds which react with moisture in the air to undergo a condensation reaction to produce a silicone-oxygen-organic compound (Si-O-R). 7. The method for producing a composite having a radiation-shielding function according to claim 5 or 6, wherein 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. The method for producing a composite having a radiation-shielding function according to claim 5, further comprising adding an aluminum powder, an aluminum alloy powder, or a ceramic powder to the radiation-shielding powder in an amount of 0.5 to 10 mass% in terms of _SiO2 when the total of the aluminum metal powder, the aluminum alloy powder, or the ceramic powder and the radiation-shielding powder is taken as 100 mass%, to produce a porous molded body (preform).

Images