Method for manufacturing radiation-shielding core-shell composite, and radiation-shielding core-shell composite manufactured using same

Abstract

The present invention relates to a method for manufacturing a radiation-shielding core-shell composite, and a radiation-shielding core-shell composite. According to one aspect of the present invention, the method for manufacturing a radiation-shielding core-shell composite is provided, the method comprising the steps of: (a) dissolving a metal and an organic ligand in an organic solvent so as to form a mixed solution; (b) adding, to the mixed solution, a powder that contains a reinforcing agent for neutron absorption, and then heating same; (c) adding a reaction accelerator to the mixed solution so as to form, on the surface of the powder, metal-organic framework (MOF) particles in which the metal and an organic ligand are coordinated; and (d) separating out the powder having the MOF particles formed thereon, and then heat-treating same at a temperature of 600-900°C for one to three hours so as to obtain a core-shell composite in which a shell layer comprising a metal oxide or a metal carbide is formed on the surface of the powder.

Description

Method for manufacturing a core-shell composite for radiation shielding and a core-shell composite for radiation shielding manufactured thereby

[0001] The present invention relates to a method for manufacturing a core-shell composite for radiation shielding and a core-shell composite for radiation shielding manufactured thereby, and more particularly, to a method for manufacturing a core-shell composite for radiation shielding using a metal-organic framework and a core-shell composite for radiation shielding manufactured thereby.

[0002] This invention was conducted with the support of the National Research Foundation of Korea (NRF) funded by the government (Ministry of Science and ICT) (RS-2022-NR068258, RS-2023-00281508).

[0003] Radiation refers to alpha, beta, proton, neutron, gamma, and X-ray radiation that ionize matter when passing through them. Neutrons, in particular, can directly affect atoms and molecules, damaging cells and tissues. They can also damage DNA and cause cancer. Therefore, radiation shielding materials that can block neutrons, which are harmful to the human body and the environment, are essential in fields where radiation is applied.

[0004] Conventional neutron shielding materials are known to use compounds containing a high content of light atomic numbers, such as hydrogen (H), oxygen (O), and carbon (C), with similar masses, and substances with large neutron absorption cross sections, such as paraffin, carbon, boron, lithium, and gadolinium, mixed into a polymer or metal substrate. However, when neutron absorbing materials are mixed into a polymer or metal substrate, the thermal conductivity of the substrate may decrease, and internal stress and deformation may occur when the temperature changes due to differences in the coefficient of thermal expansion between the neutron absorbing material and the substrate. Some neutron absorbing materials may react with the substrate, causing chemical instability. Furthermore, if the neutron absorbing material is not evenly distributed within the substrate, the shielding effect may become uneven, and the overall neutron absorption efficiency may decrease. Increasing the thickness of the shielding material may be necessary to increase the concentration of the neutron absorbing material, but this is not desirable because it may increase the weight of the shielding material and deteriorate its mechanical properties.

[0005] The present invention is intended to solve such conventional problems, and aims to provide a core-shell composite for radiation shielding and a method for manufacturing the same, which improves the thermal, mechanical, and chemical stability of a neutron absorbing material and has high radiation shielding performance.

[0006] However, these tasks are exemplary and the scope of the present invention is not limited thereby.

[0007] According to one aspect of the present invention, a method for manufacturing a core-shell composite for radiation shielding is provided.

[0008] The method for producing the core-shell composite for radiation shielding comprises the steps of: (a) preparing a mixed solution by dissolving a metal and an organic ligand in an organic solvent; (b) adding a powder containing a neutron absorption enhancer to the mixed solution and heating the same; (c) adding a reaction accelerator to the mixed solution to form metal-organic framework (MOF) particles in which the metal and the organic ligand are coordinately bonded on the surface of the powder; and (d) separating the powder on which the MOF particles are formed and heat-treating the same at a temperature of 600 to 900°C for 1 to 3 hours to obtain a core-shell composite in which a shell layer containing a metal oxide or metal carbide is formed on the surface of the powder.

[0009] In one embodiment, the metal of step (a) may be characterized as being a neutron absorbing metal including at least one selected from the group consisting of gadolinium (Gd), samarium (Sm), cadmium (Cd), lithium (Li), and dysprosium (Dy).

[0010] According to one embodiment, the organic ligand of step (a) may be characterized by including at least one selected from the group consisting of isophthalic acid, 2-methylimidazole, imidazole, salicylic acid, benzenetricarboxylic acid, and terephthalic acid (1,4-benzenedicarboxylic acid).

[0011] In one embodiment, the neutron absorption enhancer of step (b) may be characterized by being a boron-based material including at least one selected from the group consisting of cubic boron nitride (cBN), boron carbide (B4C), and boron nitride nanotubes (BNNT).

[0012] In one embodiment, the neutron absorption enhancer of step (b) may be characterized by being a carbon-based material including at least one selected from the group consisting of diamond, graphene, carbon nanotubes (CNTs), and nano carbon fibers.

[0013] In one embodiment, the step (a) may be a mixture of a metal and an organic ligand in a molar ratio of 1:1.

[0014] In one embodiment, the reaction accelerator of step (c) may be characterized by including tetrahydrofuran.

[0015] In one embodiment, the heat treatment of step (d) may be performed under atmospheric or vacuum conditions.

[0016] In one embodiment, the step (d) may be a step in which the metal in the MOF particle is oxidized or carbonized to form a metal oxide or metal carbide.

[0017] In one embodiment, the step (d) may be a step in which the metal oxide layer or metal carbide layer is coated to a thickness of 1 nm or more and less than 1 μm.

[0018] According to another aspect of the present invention, a core-shell composite for radiation shielding is provided.

[0019] The core-shell composite for radiation shielding comprises a core part including a powder containing a neutron absorption enhancer; and a shell layer surrounding the surface of the core part and including a metal oxide or carbide; wherein the shell layer has a thickness of 1 nm or more and less than 1 μm.

[0020] In one embodiment, the metal may be characterized as being a neutron absorbing metal comprising at least one selected from the group consisting of gadolinium (Gd), samarium (Sm), cadmium (Cd), lithium (Li), and dysprosium (Dy).

[0021] In one embodiment, the neutron absorption enhancer may be characterized as being a boron-based material including at least one selected from the group consisting of cubic boron nitride (cBN), boron carbide (B4C), and boron nitride nanotubes (BNNT).

[0022] In one embodiment, the neutron absorption enhancer may be characterized as being a carbon-based material including at least one selected from the group consisting of diamond, graphene, carbon nanotubes (CNTs), and nano carbon fibers.

[0023] According to another aspect of the present invention, a radiation shielding material is provided in which the core-shell composite for radiation shielding is provided in a packed structure.

[0024] In one embodiment, the core-shell composite for radiation shielding may be provided in a form dispersed within a matrix including at least one selected from the group consisting of aluminum, magnesium, and alloys thereof.

[0025] According to an embodiment of the present invention as described above, a core part including a powder containing a neutron absorption enhancer is coated with a shell layer including a metal oxide or metal carbide derived from a metal-organic framework to form a composite, thereby improving radiation shielding performance and providing a method for manufacturing a core-shell composite for radiation shielding with excellent stability, and a core-shell composite for radiation shielding manufactured thereby can be provided.

[0026] Of course, the scope of the present invention is not limited by these effects.

[0027] Figure 1 is a flowchart of a method for manufacturing a core-shell composite for radiation shielding according to an embodiment of the present invention.

[0028] FIG. 2 is a diagram schematically illustrating a method for manufacturing a core-shell composite for radiation shielding according to an embodiment of the present invention.

[0029] FIG. 3 is a graph showing neutron absorption performance according to changes in the thickness of the shell layer of a core-shell composite for radiation shielding according to one embodiment of the present invention.

[0030] FIGS. 4A to 4C and FIG. 5 are drawings showing SEM photographs and EDS analysis results of a core-shell composite for radiation shielding implemented according to one embodiment of the present invention.

[0031] FIG. 6 is an SEM photograph of a core-shell composite for radiation shielding according to one embodiment of the present invention.

[0032] FIG. 7 is a drawing showing the results of EDS analysis of a core-shell composite for radiation shielding implemented according to one embodiment of the present invention.

[0033] FIG. 8 is a drawing showing the results of XRD analysis of a core-shell composite for radiation shielding implemented according to one embodiment of the present invention.

[0034] FIGS. 9 and 10 are SEM photographs of a core-shell composite for radiation shielding according to one embodiment of the present invention.

[0035] FIG. 11a and FIG. 11b are drawings showing SEM photographs and EDS analysis results of a core-shell composite for radiation shielding according to one embodiment of the present invention.

[0036] Hereinafter, various embodiments of the present invention will be described in detail with reference to the attached drawings. These embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art. The following embodiments may be modified in various different forms, and the scope of the present invention is not limited to the following embodiments. Rather, these embodiments are provided to more faithfully and completely explain the present disclosure and to fully convey the spirit of the present invention to those skilled in the art. In addition, the thickness and size of each layer in the drawings are exaggerated for convenience and clarity of explanation.

[0037] The term "core-shell" used in the present invention means a core and a shell structure surrounding the core, and may also be described as "core@shell" in this specification.

[0038] Hereinafter, a method for manufacturing a core-shell composite for radiation shielding according to an embodiment of the present invention and a core-shell composite for radiation shielding manufactured thereby will be described.

[0039] First, a method for manufacturing a core-shell composite for radiation shielding will be described with reference to FIGS. 1 and 2. FIG. 1 is a flowchart illustrating a method for manufacturing a core-shell composite for radiation shielding according to an embodiment of the present invention, and FIG. 2 is a drawing sequentially illustrating a method for manufacturing a core-shell composite for radiation shielding according to an embodiment of the present invention.

[0040] Referring to FIG. 1, the core-shell composite for radiation shielding is manufactured by sequentially performing the following steps: a step of preparing a mixed solution by dissolving a metal and an organic ligand in an organic solvent (S10), a step of adding a powder containing a neutron absorption enhancer to the mixed solution and then heating it (S20), a step of adding a reaction accelerator to the mixed solution to form metal-organic framework (MOF) particles in which the metal and the organic ligand are coordinately bonded on the surface of the powder (S30), and a step of obtaining a core-shell composite in which a shell layer containing a metal oxide or metal carbide is formed on the surface of the powder after separating the powder on which the MOF particles are formed and then heat-treating the powder (S40).

[0041] The above step (S10) is a step of preparing a mixed solution by dissolving a metal and organic ligand, which are raw materials for MOF synthesis, in an organic solvent.

[0042] The above metal can be dissolved in an organic solvent and exist as a divalent, trivalent or tetravalent cation, and any of alkali metals, rare earth metals, and transition metals can be used. In an embodiment of the present invention, since the metal is converted into a metal oxide or metal carbide through a heat treatment step after forming MOF particles to form a shell layer, it is preferable to use a material with excellent neutron absorption ability. For example, at least one selected from the group consisting of gadolinium (Gd), samarium (Sm), cadmium (Cd), lithium (Li) and dysprosium (Dy) can be used.

[0043] The neutron absorption cross section is an indicator of neutron absorption capacity, and is a value that represents the probability that a neutron will be absorbed by an atomic nucleus. The absorption cross section is mainly given for thermal neutrons. The metals gadolinium (Gd), samarium (Sm), cadmium (Cd), lithium (Li), and dysprosium (Dy) mentioned above are all materials with excellent neutron absorption capacity, and among them, gadolinium (Gd) has the best neutron absorption capacity with a neutron absorption cross section of about 44,000 barn. In addition, samarium (Sm) is also a material with excellent neutron absorption capacity with a neutron absorption cross section of about 6,500 barn.

[0044] Depending on the metal to be used, an appropriate metal salt is prepared. For example, gadolinium nitrate (Gd(NO3)3), samarium nitrate (Sm(NO3)3), cadmium acetate (Cd(CH3COO)2), lithium chloride (LiCl), dysprosium nitrate (Dy(NO3)3), etc. can be used. These metal salts can be dissolved in organic solvents and form coordination bonds with organic ligands to participate in the MOF structure.

[0045] The organic ligand may be various organic ligands used in MOF synthesis, and for example, at least one selected from the group consisting of isophthalic acid, 2-methylimidazole, imidazole, salicylic acid, benzenetricarboxylic acid, and terephthalic acid (1,4-benzenedicarboxylic acid) may be used.

[0046] The above metal and organic ligand are mixed in an appropriate ratio. Preferably, the metal and organic ligand can be mixed in a 1:1 molar ratio. When the content ratio of the metal and organic ligand in the mixed solution is 1:1 molar ratio, the ligands and the metal ions can be coordinated to form MOF particles of an appropriate size and shape.

[0047] Organic solvents that have high solubility include N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dichloromethane (DCM), acetonitrile, acetone, diethylformamide, ethanol, methanol, and water. Since the solvent affects the properties of the MOF, it is desirable to select it according to the characteristics of the desired MOF.

[0048] The above step (S20) is a step of loading a powder containing a neutron absorption enhancer having a function of enhancing neutron absorption into the mixed solution prepared in step (S10), and stirring and heating the mixture.

[0049] The above neutron absorption enhancer is a material constituting the core portion in the core-shell composite according to an embodiment of the present invention, and a boron-based material or a carbon-based material may be used.

[0050] The above boron-based material has a large microscopic absorption cross-section and a wide energy distribution, making it suitable for shielding neutrons. For example, one or more boron-based materials selected from the group consisting of cubic boron nitride (cBN), boron carbide (B4C), and boron nitride nanotubes (BNNT) can be used. Boron carbide (B4C) has a high boron content, is chemically and thermally stable, and has excellent mechanical properties. Boron nitride nanotubes (BNNT) are materials in which the carbon of graphene, a planar material, is replaced with boron and nitrogen. They have thermal conductivity and mechanical properties similar to carbon nanotubes, and are thermally and chemically stable at high temperatures of 800°C or higher, and are materials with excellent thermal neutron absorption capacity. These compounds can provide high neutron absorption efficiency as radiation shielding materials.

[0051] Examples of the carbon-based materials include diamond, graphene, carbon nanotubes (CNTs), or nano carbon fibers. For example, spent nuclear fuel in nuclear power plants continuously emits heat and thermal neutrons during radioactive decay, and radiation shielding materials with heat dissipation properties and thermal neutron absorption capabilities are required to safely manage this. Since the carbon-based materials have excellent thermal conductivity, they can efficiently remove heat when used as radiation shielding materials. For example, diamond has a thermal conductivity of approximately 2200 W / m·K, and graphene, with its two-dimensional bonding structure consisting of a single atomic layer, exhibits a very high thermal conductivity of 5000 W / m·K. In addition, the thermal conductivity of single-walled carbon nanotubes (SWCNTs) among carbon nanotubes can reach approximately 3500 W / m·K, and although the thermal conductivity of nano carbon fibers is lower, their pores and large surface area can provide excellent neutron capture capabilities.

[0052] Meanwhile, when the boron-based material or carbon-based material is dispersed in a metal or polymer matrix to enhance the radiation shielding effect, problems such as agglomeration and clumping between particles, which may cause variations in neutron absorption capacity, and the carbon-based material reacting with the metal and becoming chemically unstable may occur. The present invention is intended to overcome the above problems, and according to one embodiment, when an oxide or carbide of a metal such as gadolinium is thinly coated on the surface of a boron-based powder, uniform dispersion within the matrix is ​​possible, thereby enhancing neutron absorption capacity and reducing the interface, thereby improving thermal conductivity. In addition, according to another embodiment, when an oxide or carbide of a metal such as gadolinium is thinly coated on the surface of a carbon-based powder, heat dissipation and neutron absorption performance can be simultaneously enhanced, and the reaction of the carbon-based material with the metal matrix can be suppressed, which may be advantageous for controlling the microstructure of the composite material. Here, the neutron absorption performance may include both the performance of slowing fast neutrons and absorbing thermal neutrons. As illustrated in Fig. 2(a), a powder containing a neutron absorption enhancer is charged into a reactor containing a mixed solution of metal and organic ligand, and then stirring is performed. At this time, heating may be performed simultaneously with stirring so that the reactants are uniformly mixed. For example, heating may be performed until the temperature reaches 140°C while stirring at 100 to 300 rpm.

[0053] The above step (S30) is a step of adding a reaction accelerator to the mixed solution resulting from the step (S20) to form a metal-organic framework (MOF) particle in which the metal and organic ligand are coordinately bonded on the powder surface.

[0054] In one embodiment, the reaction promoter may be at least one selected from the group consisting of an organic acid, an inorganic acid, a base, water, and an organic solvent. As the organic solvent, for example, tetrahydrofuran (THF) may be used, but is not limited thereto, and a known material may be used. The reaction promoter may promote mixing of reactants and induce a MOF synthesis reaction at a high temperature. By adding the reaction promoter to the mixed solution, as illustrated in FIG. 2(b), MOF particles are coated on the surface of the neutron absorption enhancer (11).

[0055] In an embodiment of the present invention, by using the MOF synthesis process, MOF particles can be uniformly coated on the surface of the neutron absorption enhancer (11), and the composition and thickness of the coating layer can be easily controlled by appropriately selecting the type and amount of metal and organic ligand that are materials of the MOF.

[0056] The above step (S40) is a step of obtaining a core-shell composite in which a shell layer including a metal oxide or metal carbide is formed on the surface of the powder by heat-treating the powder in which the MOF particles are formed at a temperature of 600 to 900°C for 1 to 3 hours after separating the powder.

[0057] The temperature during the above heat treatment is preferably 600 to 900°C, which corresponds to the temperature at which the organic matter of the MOF is converted into a metal oxide or metal carbide. When the powder having MOF particles formed on the surface is heat-treated, a metal oxide or metal carbide can be formed on the surface of the powder. Since the material constituting the MOF contains not only metal but also carbon and oxygen, carbonization and oxidation through heat treatment are possible even at relatively low temperatures. For example, when reacting samarium metal and carbon to produce samarium carbide, a temperature of 1500°C or higher is usually required, whereas when forming samarium carbide from MOF according to an embodiment of the present invention, the reaction can occur even at 600 to 900°C.

[0058] If the heat treatment temperature is lower than 600°C, sufficient oxidation or carbonization is not achieved, making it difficult to expect the above-mentioned advantages. If the carbonization temperature is higher than 900°C, the neutron absorption efficiency may decrease, which is not desirable.

[0059] As an example, the heat treatment may be performed in the order of temperature increase, temperature maintenance, and cooling, and the heat treatment process may be divided into primary and secondary stages, etc., as needed.

[0060] Heat treatment time can also affect the rate of oxidation or carbonization. In one embodiment, the heat treatment time is preferably 1 to 3 hours. A heat treatment time of less than 1 hour may not sufficiently carbonize, and a heat treatment time of more than 3 hours may reduce neutron absorption efficiency, making it undesirable.

[0061] In one embodiment, the heat treatment in step (S40) may be performed under atmospheric or vacuum conditions. Under atmospheric conditions, oxidation of the metal may occur, forming a metal oxide, while under vacuum conditions, carbonization of the metal may occur, forming a metal carbide. Specifically, the vacuum condition may be performed under an inert gas atmosphere, such as nitrogen or argon. The inert gas atmosphere prevents oxidation of the MOF and allows the carbonization reaction to occur more uniformly.

[0062] The above metal oxides and metal carbides may vary depending on the type of metal constituting the MOF. For example, the metal oxides may include gadolinium oxide (Gd2O3), samarium oxide (Sm2O3), etc., and the metal carbides may include gadolinium carbide (Gd2C3, GdC2), samarium carbide (Sm2C3), etc.

[0063] As illustrated in Fig. 2(c), as the MOF is converted into a metal oxide or metal carbide, a core-shell composite (10) is formed, which includes a neutron absorption enhancer (11) and a shell layer (12) surrounding its surface. This can improve the structural stability of the neutron absorption enhancer (11). This allows the core-shell composite (10) to be used more stably.

[0064] Here, it is preferable that the shell layer (12) be coated to a thickness of 1 nm or more and less than 1 μm. If the thickness is thicker than 1 μm, the neutron absorption efficiency may decrease rapidly, and if the thickness is thinner than 1 nm, the thermal and structural stability of the core-shell composite (10) may deteriorate.

[0065] FIG. 3 is a graph showing the neutron absorption performance according to the thickness change of the shell layer of a core-shell composite for radiation shielding according to an embodiment of the present invention. In FIG. 3, the y-axis represents the macroscopic cross section, which is the product of the number density of atomic nuclei reacting with neutrons and the reaction cross section. The lower the macroscopic cross section, the lower the neutron absorption efficiency. As shown in FIG. 3, the macroscopic cross section is high from when the shell layer is 1 nm thick until it reaches about 100 nm, and when it becomes thicker than 1 μm (= 1000 nm), the neutron absorption efficiency rapidly decreases. Therefore, the thickness of the shell layer is preferably 1 nm or more and less than 1 μm.

[0066] When directly coating the surface of a neutron-absorbing enhancer with metal oxides or carbides, it can be difficult to achieve a uniform coating of the desired thickness. Furthermore, while metal oxides and carbides are generally stable at high temperatures, neutron-absorbing enhancers can operate at a different temperature range. Therefore, if high temperatures are required during the coating process, the properties of the neutron-absorbing enhancer may change. Furthermore, differences in the coefficients of thermal expansion between the neutron-absorbing enhancer and the metal oxide / carbide can cause cracking or delamination during the coating process. This can reduce the durability of the coating.

[0067] In contrast, when MOF is first coated on the surface of a neutron absorption enhancer according to an embodiment of the present invention and then a metal oxide or metal carbide is converted from the MOF, a stable and uniform coating can be implemented at a relatively low temperature, and a shell layer can be formed firmly without interfering with the function of the neutron absorption enhancer.

[0068] According to another aspect of the present invention, a core-shell composite for radiation shielding is provided.

[0069] The core-shell composite for radiation shielding comprises: a core portion including a powder containing a neutron absorption enhancer; and a shell layer surrounding the surface of the core portion and including a metal oxide or carbide. At this time, the thickness of the shell layer is characterized by being 1 nm or more and less than 1 μm.

[0070] The above neutron absorption enhancer is a material constituting the core portion in the core-shell composite according to an embodiment of the present invention, and a boron-based material or a carbon-based material may be used. For example, at least one boron-based material selected from the group consisting of cubic boron nitride (cBN), boron carbide (B4C), and boron nitride nanotubes (BNNT) may be used. As the carbon-based material, diamond, graphene, carbon nanotubes (CNTs), or nano carbon fibers may be used.

[0071] The metal oxide or carbide constituting the above shell layer may include one or more metals selected from the group consisting of gadolinium (Gd), samarium (Sm), cadmium (Cd), lithium (Li), and dysprosium (Dy). For example, the metal oxide may include gadolinium oxide (Gd2O3), samarium oxide (Sm2O3), etc., and the metal carbide may include gadolinium carbide (Gd2C3, GdC2), samarium carbide (Sm2C3), etc.

[0072] According to another aspect of the present invention, a radiation shielding material is provided in which the core-shell composite for radiation shielding is provided in a packed structure.

[0073] In one embodiment, the core-shell composite for radiation shielding may be used alone, without being dispersed in a metal or polymer matrix. In another embodiment, the core-shell composite for radiation shielding may be provided in a dispersed form in a metal or polymer matrix, so as to prevent the radiation shielding material from being damaged by corrosion. For example, the core-shell composite for radiation shielding may be provided in a dispersed form in a matrix comprising at least one selected from the group consisting of aluminum, magnesium, and alloys thereof.

[0074] The radiation shielding material according to an embodiment of the present invention can be applied to all materials, articles, or devices requiring radiation shielding, and can be used by being attached to, for example, fiber textiles, plastics, glass, etc.

[0075] Hereinafter, preferred examples are presented to aid in understanding the present invention. However, the following examples are provided only to facilitate a better understanding of the present invention, and the scope of the present invention is not limited by the examples.

[0076] 1. Manufacturing Example 1: Synthesis of cBN@Gd2O3

[0077] Gadolinium(III) nitrate hexahydrate (GdN3O9·6H2O) and dimethylformamide (DMF) were mixed in a 1:1 ratio and dissolved in 300 ml of isophthalic acid. cBN powder was added to the prepared solution and heated to 140°C at 200 rpm. After that, 150 ml of tetrahydrofuran was added and the mixture was reacted for 40 minutes. The resulting solid was separated by filtration, washed with DMF, and dried at room temperature. After that, it was heat-treated at 600°C for 1 hour under air conditions.

[0078] 2. Manufacturing Example 2: Synthesis of cBN@Gd2C3 and cBN@GdC2

[0079] In the above Manufacturing Example 1, the reaction was performed in the same manner as in the above Manufacturing Example 1, except that the heat treatment was performed in a vacuum and argon atmosphere.

[0080] 3. Manufacturing Example 3: Synthesis of B4C@Gd2O3

[0081] Gadolinium(III) nitrate hexahydrate (GdN3O9·6H2O) and dimethylformamide (DMF) were mixed in a 1:1 ratio and dissolved in 300 ml of isophthalic acid. B4C powder was added to the prepared solution and heated to 140°C at 200 rpm. After that, 150 ml of tetrahydrofuran was added and the mixture was reacted for 40 minutes. The resulting solid was separated by filtration, washed with DMF, and dried at room temperature. After that, it was heat-treated at 600°C for 1 hour under air conditions.

[0082] 4. Manufacturing Example 4: Synthesis of B4C@Gd2C3 and B4C@GdC2

[0083] In the above Manufacturing Example 3, the reaction was performed in the same manner as in the above Manufacturing Example 3, except that the heat treatment was performed in a vacuum and argon atmosphere.

[0084] 5. Manufacturing Example 5: Synthesis of Diamond@Gd2O3

[0085] Gadolinium(III) nitrate hexahydrate (GdN3O9·6H2O) and dimethylformamide (DMF) were mixed in a 1:1 ratio and dissolved in 300 ml of isophthalic acid. Diamond powder was added to the prepared solution and heated to 140°C at 200 rpm. After that, 150 ml of tetrahydrofuran was added and the mixture was reacted for 40 minutes. The resulting solid was separated by filtration, washed with DMF, and dried at room temperature. After that, it was heat-treated at 600°C for 1 hour under air conditions.

[0086] 6. Manufacturing Example 6: Synthesis of BNNT@Gd2O3

[0087] Gadolinium(III) nitrate hexahydrate (GdN3O9·6H2O) and dimethylformamide (DMF) were mixed in a 1:1 ratio and dissolved in 300 ml of isophthalic acid. BNNT powder was added to the prepared solution and heated to 140°C at 200 rpm. Afterwards, 150 ml of tetrahydrofuran was added and the mixture was reacted for 40 minutes. The resulting solid was separated by filtration, washed with DMF, and dried at room temperature. Afterwards, it was heat-treated at 600°C for 1 hour under air conditions.

[0088] <Experimental Example>

[0089] The surface characteristics of the core-shell composite synthesized according to the above manufacturing example were observed and the physical properties were measured.

[0090] FIGS. 4a to 4c and FIG. 5 are drawings showing SEM photographs and EDS analysis results of core-shell composites for radiation shielding implemented according to Manufacturing Examples 1 and 2, respectively.

[0091] Fig. 4a is cBN, Fig. 4b is cBN-MOF, and Fig. 4c is cBN@Gd2O3. In Fig. 5, (a) cBN, (b) cBN-MOF, and (c) cBN@Gd carbide.

[0092] By observing FIGS. 4a to 4c and FIG. 5, it was confirmed that Gd oxide and carbide were uniformly formed on the surface of the cBN powder.

[0093] Figure 6 is an SEM photograph of a core-shell composite for radiation shielding according to the above-mentioned manufacturing example 3. Observing Figures 6 (a) to (c), it was confirmed that Gd oxide was uniformly formed on the surface of the B4C powder with a thickness of ~100 nm.

[0094] Figure 7 is a diagram showing (a) a SEM photograph and (b) an EDS analysis result of a core-shell composite for radiation shielding implemented according to the above manufacturing example 3. The elemental analysis result confirmed that Gd oxide was formed on the surface of the B4C powder.

[0095] Fig. 8 is a diagram showing the results of XRD analysis of a core-shell composite for radiation shielding implemented according to the above Manufacturing Example 3. As a result of observing XRD peaks before and after coating in Fig. 8, it was confirmed that a peak was formed around 28° after coating, and the main peak of cubic-Gd2O3 was confirmed.

[0096] Figures 9 and 10 are SEM photographs of core-shell composites for radiation shielding according to Manufacturing Examples 4 and 5, respectively. From Figures 9 (a) to (c), it was confirmed that Gd carbide was uniformly formed on the surface of the B4C powder. From Figures 10 (a) to (b), it was confirmed that Gd oxide was uniformly formed on the surface of the diamond powder.

[0097] Fig. 11a is a SEM photograph of a core-shell composite for radiation shielding according to Manufacturing Example 6, and Fig. 11b is a drawing showing the results of EDS analysis of the core-shell composite for radiation shielding according to Manufacturing Example 6. From this, it was confirmed that Gd oxide was uniformly formed with a thickness of ~10 nm on the surface of the BNNT powder, and the result of elemental analysis confirmed that Gd oxide was formed on the surface of the BNNT powder.

[0098] Hereinafter, the results of an experiment on the neutron absorption capacity of an Al-B4C@Gd2O3 radiation shielding material in which B4C@Gd2O3 synthesized according to the above Manufacturing Example 3 is dispersed in an aluminum (Al) matrix are described.

[0099] As a comparative example, an Al-B4C radiation shielding material is provided in which uncoated B4C powder is dispersed in an aluminum matrix. In this case, the B4C@Gd2O3 particles and the B4C powder are dispersed in the same 15% volume ratio within the aluminum matrix.

[0100] Specimen radiation shielding material absorption cross-sectional area coefficient (cm) -1 ) Comparative Example Al-B4C12.7 Example (Manufacturing Example 3) B4C@Gd2O317.057

[0101] As shown in Table 1, the neutron absorption capacity analysis results show that the absorption cross-section coefficient of Al-B4C, a comparative example of the present invention, is 12.7 cm -1 In contrast, the neutron absorption cross-section coefficient of B4C@Gd2O3, which is an embodiment of the present invention, is 17.057 cm -1 It was confirmed that the absorption cross-section coefficient was 4.357 cm by introducing a trace amount (0.355 vol.%) of Gd2O3 coating layer on the surface of B4C powder. -1 It can be seen that the absorption cross-sectional area coefficient is improved by more than 34% compared to the comparative example, Al-B4C.

[0102] That is, it can be confirmed that the neutron absorption capacity is superior in the embodiment of the present invention that provides a composite having a core-shell structure compared to the comparative example of the present invention that does not introduce a core-shell structure.

[0103] In addition, in the embodiment of the present invention, compared to the comparative example, the contact interface with the base is reduced, so that the thermal conductivity of the radiation shielding material can be improved, and there is an effect of uniformly dispersing the core-shell composite in the base.

[0104] While the present invention has been described with reference to the embodiments illustrated in the drawings, these are merely exemplary, and those skilled in the art will appreciate that various modifications and equivalent alternative embodiments are possible. Therefore, the true scope of technical protection of the present invention should be determined by the technical spirit of the appended claims.

Claims

1. (a) A step of preparing a mixed solution by dissolving a metal and an organic ligand in an organic solvent; (b) a step of adding a powder containing a neutron absorption enhancer to the above mixed solution and then heating it; (c) a step of adding a reaction accelerator to the mixed solution to form a metal-organic framework (MOF) particle in which the metal and organic ligand are coordinately bonded on the powder surface; and (d) a step of obtaining a core-shell composite in which a shell layer including a metal oxide or metal carbide is formed on the surface of the powder by heat-treating the powder in which the MOF particles are formed at a temperature of 600 to 900°C for 1 to 3 hours after separation; Method for manufacturing core-shell composite for radiation shielding.

2. In paragraph 1, The metal of step (a) above, It is characterized by being a neutron absorbing metal comprising at least one selected from the group consisting of gadolinium (Gd), samarium (Sm), cadmium (Cd), lithium (Li), and dysprosium (Dy). Method for manufacturing core-shell composite for radiation shielding.

3. In paragraph 1, The organic ligand of step (a) above is Characterized in that it comprises at least one selected from the group consisting of isophthalic acid, 2-methylimidazole, imidazole, salicylic acid, benzenetricarboxylic acid, and terephthalic acid (1,4-benzenedicarboxylic acid). Method for manufacturing core-shell composite for radiation shielding.

4. In paragraph 1, The neutron absorption enhancer of step (b) above is A boron-based material characterized by including at least one selected from the group consisting of cubic boron nitride (cBN), boron carbide (B4C), and boron nitride nanotubes (BNNT). Method for manufacturing core-shell composite for radiation shielding.

5. In paragraph 1, The neutron absorption enhancer of step (b) above is A carbon-based material characterized by comprising at least one selected from the group consisting of diamond, graphene, carbon nanotubes (CNTs) and nano carbon fibers. Method for manufacturing core-shell composite for radiation shielding.

6. In paragraph 1, Step (a) above, A mixture of metal and organic ligand in a 1:1 molar ratio, Method for manufacturing core-shell composite for radiation shielding.

7. In paragraph 1, The reaction accelerator of step (c) above is, Containing tetrahydrofuran, Method for manufacturing core-shell composite for radiation shielding.

8. In paragraph 1, The heat treatment in step (d) above is performed under atmospheric or vacuum conditions. Method for manufacturing core-shell composite for radiation shielding.

9. In paragraph 1, Step (d) above, A step in which the metal in the MOF particle is oxidized or carbonized to form a metal oxide or metal carbide. Method for manufacturing core-shell composite for radiation shielding.

10. In paragraph 1, Step (d) above, The step in which the above shell layer is formed with a thickness of 1 nm or more and less than 1 μm, Method for manufacturing core-shell composite for radiation shielding.

11. A core portion comprising a powder containing a neutron absorption enhancer; and A shell layer surrounding the surface of the core portion and including a metal oxide or carbide; The thickness of the above shell layer is 1 nm or more and less than 1 μm, Core-shell composites for radiation shielding.

12. In paragraph 11, The above metal is, It is characterized by being a neutron absorbing metal comprising at least one selected from the group consisting of gadolinium (Gd), samarium (Sm), cadmium (Cd), lithium (Li), and dysprosium (Dy). Core-shell composites for radiation shielding.

13. In paragraph 11, The above neutron absorption enhancer is, A boron-based material characterized by including at least one selected from the group consisting of cubic boron nitride (cBN), boron carbide (B4C), and boron nitride nanotubes (BNNT). Core-shell composites for radiation shielding.

14. In paragraph 11, The above neutron absorption enhancer is, A carbon-based material characterized by comprising at least one selected from the group consisting of diamond, graphene, carbon nanotubes (CNTs) and nano carbon fibers. Core-shell composites for radiation shielding.

15. A core-shell composite for radiation shielding according to any one of claims 11 to 14 is provided in a packed structure. Radiation shielding material.

16. In paragraph 15, The core-shell composite for radiation shielding is characterized in that it is provided in a form dispersed in a matrix including at least one selected from the group consisting of aluminum, magnesium and alloys thereof. Radiation shielding material.

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