Lightweight high-temperature-resistant high-performance n / gamma composite shielding material for space nuclear reactor

Abstract

A kind of light-weight high-temperature-resistant high-performance n / γ composite shielding material for space nuclear reactor, the composition of composite shielding material is: Gd-MOF mass fraction is 5wt%-40wt%, Pb-MOF mass fraction is 10wt%-40wt%, PI is matrix, high H content of PI is used to slow down fast neutron into thermal neutron, and the synergistic effect of high thermal neutron absorption cross section of Gd and high efficient γ shielding of Pb, combined with the chemical coordination characteristics of outer electron of Gd and Pb, metal-organic framework MOF porous structure is prepared, in-situ chemical synthesis is used to realize the interpenetration and winding of PI molecular chain in Gd-MOF and Pb-MOF porous structure, to improve the mechanical properties of composite material, and high efficient n / γ composite shielding function is obtained, the shielding material composition is good in uniformity, with high efficient n / γ composite shielding function and good comprehensive mechanical properties, resistant to high and low temperature and anti-radiation aging, can be used for long time in-260℃~+350℃ environment, can be applied to the demand of light-weight high-temperature-resistant high-performance n / γ composite shielding material for space nuclear reactor and micro-advanced nuclear energy system.

Description

Technical Field

[0001] This invention relates to a lightweight, high-temperature resistant, high-performance n / γ composite shielding material for space nuclear reactors, belonging to the field of lightweight polymer-based neutron (n) and gamma (γ) composite shielding. It can be used for high-performance n / γ composite shielding of space nuclear reactors operating in deep space with high day-night temperature differences and for lightweight launch payloads. Background Technology

[0002] As humanity's exploration and utilization of space deepens, high-power satellites, deep space exploration, space stations, and future extraterrestrial bases all require high-power, long-life space energy sources. Currently, spacecraft energy supply mainly relies on solar energy, chemical energy, and nuclear energy (radioisotope batteries). Solar cells are currently the most widely used spacecraft power source, characterized by high efficiency, safety, reliability, and long lifespan. However, solar cells are limited by sunlight conditions and cannot operate in sunlight-free environments such as deep space, resulting in lower power output. Chemical batteries have a simple structure and mature technology, but are difficult to operate for long periods. Radioisotope batteries also have low power output, making it difficult to meet the high-power electricity demands of spacecraft. In contrast, space nuclear reactors (referred to as "space reactors") generate heat through continuous chain fission reactions and couple it to a thermoelectric conversion system to supply electricity. They feature high energy density, high output power, long operating life, and strong environmental adaptability, making them the preferred power source for future high-power, long-life space missions and deep space exploration missions.

[0003] Due to the limited space in spacecraft and satellites, space reactor power supplies must be small and lightweight to reduce the load during launch. Currently, most space reactor power supplies use miniaturized nuclear reactors cooled by liquid metal with higher thermal efficiency. These reactors have a more compact and efficient system layout. However, the high energy and dose of n and gamma radiation from these reactors necessitate shielding materials that comprehensively address n and gamma ray protection, the large temperature difference between day and night in space (-200℃ to +180℃), and factors such as material volume, weight, and structural stability. Therefore, traditional n and gamma shielding materials are no longer sufficient to meet these application requirements.

[0004] This study leverages the synergistic effect of high-performance engineering resin polyimide (PI) with its high hydrogen (H) content to moderate fast neutrons into thermal neutrons, the high thermal neutron absorption cross section of Gd for thermal neutron absorption, and the comprehensive and efficient shielding of secondary gamma rays generated by the interaction of Pb with n and Gd against gamma rays generated within the nuclear reactor. Combining the chemical coordination characteristics of Gd and Pb, porous functional fillers with metal-organic frameworks (MOFs) such as Gd-MOF and Pb-MOF are prepared. An in-situ chemical synthesis method is used to achieve the interpenetration and entanglement of PI molecular chains within the porous structures of Gd-MOF and Pb-MOF, simultaneously improving the comprehensive mechanical properties of the composite material while achieving efficient n / γ composite shielding. Furthermore, the composite material exhibits resistance to high and low temperatures, radiation aging, and lightweight properties, making it suitable for the needs of my country's space nuclear reactors and micro-scale advanced nuclear energy systems for lightweight, high-temperature resistant, and high-performance n / γ composite shielding materials. Summary of the Invention

[0005] The technical problem this invention aims to solve is to provide a lightweight, high-temperature resistant, high-performance n / γ composite shielding material for space nuclear reactors, addressing the need for novel lightweight, high-temperature resistant, and efficient n / γ composite shielding in the special service environment of space nuclear reactors. This invention designs nanoporous Gd-MOF as an n absorber and Pb-MOF as a γ shielding filler, using polyimide (PI) with excellent mechanical properties and high H content as the matrix. The high-performance n / γ composite shielding material is prepared using an in-situ chemical synthesis method and an optimized chemical synthesis process. The composite shielding material of this invention features lightweight, resistance to high and low temperatures, resistance to radiation aging, efficient n / γ composite shielding function, and excellent comprehensive mechanical properties.

[0006] The technical solution of the present invention is as follows: a lightweight, high-temperature resistant, high-performance n / γ composite shielding material for space nuclear reactors, wherein the composite shielding material uses a gadolinium-based metal-organic framework as a neutron absorber and a lead-based metal-organic framework as a γ-ray shielding material as functional fillers, and uses polyimide as a matrix, and is synthesized by in-situ chemical synthesis.

[0007] Based on the total mass of the composite shielding material, the composition of the composite shielding material is as follows: a gadolinium-based metal-organic framework with a mass fraction of 5wt%-40wt%, a lead-based metal-organic framework with a mass fraction of 10wt%-40wt%, and the balance being polyimide. For example, based on the total mass of the composite shielding material, the composition of the composite shielding material is as follows: a gadolinium-based metal-organic framework with a mass fraction of 5wt%, 5.1wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, 10wt%, 10.5wt%, 11wt%, 11.5wt%, 12wt%, 14wt%, 16wt%, 18wt%, 20wt%, 22wt%, 24wt%, 26wt%. The weights are 10 wt%, 10.5 wt%, 11 wt%, 11.5 wt%, 12 wt%, 14 wt%, 16 wt%, 18 wt%, 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt%, 30 wt%, 32 wt%, 34 wt%, 36 wt%, 38 wt%, or 40 wt%, with the balance being polyimide.

[0008] The preparation of the lightweight, high-temperature resistant, high-performance n / γ composite shielding material for space nuclear reactors, as described above, includes the following steps:

[0009] (1) Preparation of nanoporous Gd-MOF functional materials for n-absorbents. Utilizing the high thermal neutron absorption cross-section of rare earth element Gd and combining the chemical coordination characteristics of Gd's outer electrons, nanoporous Gd-MOF metal-organic framework n-absorbent functional materials were prepared by negative pressure filtration and high-temperature removal of crystal water.

[0010] (2) Preparation of nanoporous Pb-MOF γ-ray shielding functional material. Based on the principle of interaction between γ-rays and matter, Pb with a high Z atomic number is selected as the γ-ray shielding functional filler. Based on the chemical coordination characteristics of the outer electrons of Pb, nanoporous Pb-MOF metal-organic framework γ-ray shielding functional material is prepared by chemical coordination synthesis method.

[0011] (3) High-efficiency n / γ composite shielding composition design. According to the different shielding efficiencies required for n and γ, the composition of the composite material is: Gd-MOF mass fraction of 5wt%-40wt%, Pb-MOF mass fraction of 10wt%-40wt%, PI as matrix, and the mass fraction ratio of Gd-MOF and Pb-MOF can be adjusted according to the specific n and γ ray shielding requirements.

[0012] (4) High-performance preparation of n / γ composite shielding materials. Based on the specific requirements for n and γ ray shielding, a suitable mass fraction ratio of Gd-MOF and Pb-MOF was selected through neutron transport theory simulation and calculation. An in-situ chemical synthesis method was employed, with the assistance of a dispersant, magnetic force, and ultrasonic stirring, to achieve the interpenetration and entanglement of PI molecular chains in the porous structures of Gd-MOF and Pb-MOF, and to obtain uniform dispersion of Gd-MOF and Pb-MOF in the PI matrix, thereby improving the comprehensive mechanical properties of the composite material. Finally, imidization was carried out using a stepped heating method to obtain a high-performance n / γ composite shielding material.

[0013] The preferred synthesis process for Gd-MOF preparation in step (1) is as follows: GdCl3·6H2O hexahydrate and pyromellitic dianhydride (PMDA) are dissolved in N,N-dimethylformamide (DMF) at a molar ratio of GdCl3·6H2O:PMDA:DMF = (5-20):(3-15):(60-200). Triethylamine is added dropwise while stirring on a magnetic stirrer. After a flocculent suspension is formed, the solution is transferred to a hydrothermal reactor and heated in a muffle furnace at 90-180℃ for 8-16 hours. After cooling to room temperature, the supernatant is removed using a vacuum filter to obtain a white precipitate. The precipitate is washed sequentially with DMF, ethanol, and diethyl ether, and finally dried and dehydrated in a vacuum drying oven to obtain Gd4(1,2,4,5-BTEC)3(H2O). 12 • 20H2O, high temperature heating to remove water of crystallization to obtain Gd-MOF powder.

[0014] The preferred synthesis process for Pb-MOF preparation in step (2) is as follows: Pb(NO3)2, terephthalic acid (PTA), N,N-dimethylacetamide (DMA) and water (H2O) are added to a reaction vessel in a molar ratio of Pb(NO3)2:PTA:DMA:H2O = (0.1~2.5):(0.1~2.5):(50~400):(140~600) and ultrasonically stirred at room temperature for 10-50 minutes; the reaction vessel is sealed and placed in an oven and kept at 80-190℃ for 6-24 hours; after cooling to room temperature, colorless transparent crystals are obtained, which are then washed with DMA, filtered, and dried to obtain Pb-MOF material.

[0015] The preferred in-situ chemical synthesis process in step (4) is as follows: First, Gd-MOF and Pb-MOF powders are dissolved in anhydrous N,N-dimethylformamide (DMA) solvent, then 4,4′-diaminodiphenyl ether (ODA) is added, and N2 is passed through and stirred under ice-water bath conditions at 0-6℃. Then, pyromellitic dianhydride (PMDA) organic ligand is added uniformly multiple times under magnetic stirring and ultrasonic assistance, and stirred for 2-6 hours to generate polyamic acid (PAA); wherein, by mass ratio (wt%), Gd-MOF:Pb-MOF:DMA:ODA:PMDA=(5~40): (10~40):(20~150):(10~42.5):(10~42.5); After pouring the polymer solution into the mold, place it in an oven / muffle furnace and keep it at 60-90℃ for 1-3h to allow the solvent to evaporate completely. Then, use a step heating method to adjust the oven / muffle furnace to 95-130℃, 140-170℃, 180-210℃ and 220-250℃ respectively and keep them for 1-2h respectively. Finally, adjust the temperature to 280-350℃ and keep it for 1-2h for imidization treatment. Finally, cool to room temperature to obtain (Gd,Pb)-MOF / PI composite polymer material.

[0016] The principle of this invention is:

[0017] like Figure 1 As shown, this invention is based on the principle of interaction between n and gamma rays and matter. It uses Gd, an element with a high neutron absorption cross section, as the n-absorbing functional material, and Pb, an element with a high atomic number (Z), as the gamma-ray shielding functional material. Based on the chemical coordination characteristics of the outer electrons of Gd and Pb, n and gamma-absorbing functional fillers with nanoporous structures, Gd-MOF and Pb-MOF, are prepared respectively. High hydrogen (H) content polyimide (PI) polymer is used as the matrix. The synergistic effect of the three elements on the slowing down and absorption of n and gamma rays is utilized to improve the n / γ composite shielding performance of the composite material. Through in-situ chemical synthesis, the PI molecular chains are intercalated and entangled in the porous structures of Gd-MOF and Pb-MOF during the molecular chain polymerization process. Chemical dispersants combined with magnetic stirring and ultrasonic stirring are used to regulate the uniform dispersion of Gd-MOF and Pb-MOF in the PI matrix, thereby improving the comprehensive mechanical properties of the composite material. Ultimately, this achieves a combination of comprehensive mechanical properties and highly efficient n and gamma composite shielding function.

[0018] Advantages of this invention:

[0019] (1) The composite shielding material of the present invention has a more efficient n / γ composite shielding performance. Based on the shielding principle of "first slowing down and then absorbing" of neutrons and the interaction mechanism between γ-rays and matter, the present invention uses PI with high H content as a matrix to slow down fast neutrons into thermal neutrons, and preferably uses Gd element with high thermal neutron absorption cross section as n absorber to absorb the slowed thermal neutrons. It also uses Pb element with high Z content to comprehensively shield the secondary γ-rays generated by the interaction between n and Gd and the γ-rays generated in the nuclear reactor as functional materials to prepare a highly efficient n / γ composite shielding material integrating slowing down and absorption. The present invention fully utilizes and explores the synergistic effect of the fast neutron slowing effect of H element in PI polymer matrix, the high thermal neutron absorption cross section of Gd element and the efficient γ-ray shielding function of high Z element Pb, which greatly improves the n and γ-ray composite shielding efficiency of the material. In addition, the mass fraction ratio of Gd-MOF and Pb-MOF can be adjusted according to the specific n and γ-ray shielding requirements under different usage conditions to realize the on-demand design of the composite shielding function of the material.

[0020] (2) The n / γ composite shielding material of the present invention has high and low temperature resistance and radiation aging resistance. According to the service environment and application requirements of space nuclear reactor shielding materials, polyimide (PI) polymer is used as the matrix, which has comprehensive properties such as high and low temperature resistance (-269℃~+400℃), high strength, radiation aging resistance, corrosion resistance, small coefficient of thermal expansion, and self-extinguishing. After in-situ chemical composite with Gd-MOF and Pb-MOF, the high and low temperature resistance and radiation aging resistance of the composite material can be further improved, and it can be used for a long time in space environments such as space and deep space with high day and night temperature difference and complex cosmic radiation.

[0021] (3) The n / γ composite shielding material prepared by this invention has superior comprehensive mechanical properties. This invention utilizes a chemical dispersant combined with magnetic stirring and ultrasonic stirring to uniformly disperse the n absorber Gd-MOF and γ shielding Pb-MOF functional filler into the PI matrix. An in-situ chemical synthesis method is adopted, which enables the PI molecular chains to interpenetrate and entangle in the porous structure of Gd-MOF and Pb-MOF during the polymerization process. This fundamentally improves the interface structure and interaction mode between the functional filler and the polymer matrix, further enhancing the comprehensive mechanical properties of the composite material. It has superior comprehensive mechanical properties compared to polymer composite materials prepared by traditional inorganic-organic addition methods. Attached Figure Description

[0022] Figure 1 A schematic diagram illustrating the principle of this invention;

[0023] Figure 2 A schematic diagram of the preparation process of the n / γ composite shielding material of the present invention. Detailed Implementation

[0024] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0025] The preparation process of this invention is as follows: Figure 2 As shown in the example below:

[0026] Example 1: The design and preparation steps of the (40Gd,10Pb)-MOF / PI n / γ composite shielding material are as follows:

[0027] (1) Preparation of nanoporous Gd-MOF as an n-absorbent functional material. The synthesis process of Gd-MOF is as follows: 20 mmol of gadolinium chloride hexahydrate Gd(Cl)3·6H2O and 15 mmol of pyromellitic dianhydride (PMDA) are dissolved in 200 ml of N,N-dimethylformamide (DMF). Triethylamine is added dropwise while stirring on a magnetic stirrer. After a flocculent suspension is formed, the solution is transferred to a hydrothermal reactor and heated at 90 °C for 16 h in a muffle furnace. After cooling to room temperature, the supernatant is removed by a vacuum filter to obtain a white precipitate. The precipitate is washed with DMF, ethanol and diethyl ether in sequence. Finally, the water of crystallization is removed at high temperature in a vacuum drying oven to obtain Gd-MOF powder.

[0028] (2) Preparation of nanoporous Pb-MOF as a γ-shielding functional material. The synthesis process of Pb-MOF is as follows: 0.1 mmol of Pb(NO3)2 and 0.1 mmol of terephthalic acid (PTA) are dissolved in a glass container in 50 mmol of N,N-dimethylacetamide (DMA) and 140 mmol of water (H2O) and stirred at room temperature for 30 minutes; then the container is sealed and placed in an oven and kept at 190℃ for 6 hours; slowly cooled to room temperature to obtain colorless transparent crystals; finally, Pb-MOF is obtained by washing with DMA, filtering and drying.

[0029] (3) High-efficiency n / γ composite shielding composition design. Based on the requirements of n and γ shielding efficiency, the composition of the composite material is designed as follows: 40wt% Gd-MOF, 10wt% Pb-MOF, and the balance is PI matrix.

[0030] (4) High-performance preparation of n / γ composite shielding materials. The in-situ chemical synthesis process of (40Gd,10Pb)-MOF / PI is as follows: 0.712g of Gd-MOF and 0.235g of Pb-MOF are dissolved in 20mL of anhydrous N,N-dimethylformamide (DMA) in a container, then 1.602g of 4',4-diaminodiphenyl ether (ODA) is added, and the mixture is stirred under N2 in an ice bath at 1-4℃. Then, 1.766g of pyromellitic dianhydride (PMDA) is slowly added. Polyamic acid (PAA) was generated by stirring for 6 hours. Then, the stirred polymerization solution was poured into a mold or glass container and placed in an oven and heated at 90°C for 1 hour to evaporate all the solvent. Finally, it was placed in an intelligent muffle furnace and heated at 100°C, 150°C, 200°C, 250°C and 350°C for 1 hour each to complete thermal imidization. After natural cooling to room temperature, (40Gd,10Pb)-MOF / PI composite material was obtained.

[0031] (5) The n / γ composite shielding material prepared through the above steps and processes was subjected to tensile property testing using an Instron 3369 universal testing machine at room temperature (25℃) according to ISO 527-2-2012 (or equivalent GB / T 1040.2-2006). The tensile strength of the material was ≥170 MPa at a load loading rate of 2 mm / min. 241 Am-Be neutron source and 137 Cs / 60 The Co isotope gamma source was tested for n / γ composite shielding. The thermal neutron shielding efficiency reached over 98% and the gamma-ray shielding rate reached over 90% with a thickness of 5mm. It can be used for a long time in the range of -260℃ to +350℃ and has good anti-aging properties.

[0032] Example 2: The design and preparation steps of the (5Gd,40Pb)-MOF / PI n / γ composite shielding material are as follows:

[0033] (1) Preparation of nanoporous Gd-MOF as an absorbent material. The synthesis process of Gd-MOF is as follows: 5 mmol of gadolinium chloride hexahydrate Gd(Cl)3·6H2O and 3 mmol of pyromellitic dianhydride (PMDA) are dissolved in 60 ml of N,N-dimethylformamide (DMF). Triethylamine is added dropwise while stirring on a magnetic stirrer. After a flocculent suspension is formed, the solution is transferred to a hydrothermal reactor and heated at 150 °C for 8 h in a muffle furnace. After cooling to room temperature, the supernatant is removed by a vacuum filter to obtain a white precipitate. The precipitate is washed with DMF, ethanol and diethyl ether in sequence. Finally, the water of crystallization is removed at high temperature in a vacuum drying oven to obtain Gd-MOF powder.

[0034] (2) Preparation of nanoporous Pb-MOF as a γ-shielding functional material. The synthesis process of Pb-MOF is as follows: 0.25 mmol of Pb(NO3)2 and 0.25 mmol of terephthalic acid (PTA) are dissolved in a container in 400 mmol of N,N-dimethylacetamide (DMA) and 600 mmol of H2O, and stirred at room temperature for 50 minutes; the container is sealed and placed in an oven and kept at 100℃ for 24 hours; the container is slowly cooled to room temperature to obtain colorless transparent crystals, which are then washed with DMA, filtered, and dried to obtain Pb-MOF.

[0035] (3) High-efficiency n / γ composite shielding composition design. Based on the requirements of n and γ shielding efficiency, the composition of the composite material is designed as follows: the mass fraction of Gd-MOF is 5wt%, the mass fraction of Pb-MOF is 40wt%, and the balance is PI matrix.

[0036] (4) High-performance preparation of n / γ composite shielding materials. The in-situ chemical synthesis process of (5Gd,40Pb)-MOF / PI is as follows: 0.089g of Gd-MOF and 0.938g of Pb-MOF are dissolved in 20mL of anhydrous N,N-dimethylformamide (DMA) in a container, then 1.762g of 4',4-diaminodiphenyl ether (ODA) is added, and the mixture is stirred under N2 in an ice bath at 1-6℃. Then, 1.943g of pyromellitic dianhydride (PMDA) is slowly added. The mixture was stirred for 3 hours to generate polyamic acid (PAA). Then, the stirred polymerization solution was poured into a mold or glass container and placed in an oven and heated at 60°C for 3 hours to evaporate all the solvent. Finally, it was placed in an intelligent muffle furnace and heated at 95°C, 140°C, 180°C, 220°C and 280°C for 2 hours in sequence to complete thermal imidization. After natural cooling to room temperature, (5Gd,40Pb)-MOF / PI composite material was obtained.

[0037] (5) The n / γ composite shielding material prepared by the above steps and processes was subjected to tensile property testing using an Instron 3369 universal testing machine at room temperature (25℃) according to ISO 527-2-2012 (or equivalent GB / T 1040.2-2006). The tensile strength of the composite material was ≥180 MPa when the load loading rate was 2 mm / min. 241 Am-Be neutron source and 137 Cs / 60 The Co isotope gamma source was tested for n / γ composite shielding. The thermal neutron shielding efficiency reached over 85% and the gamma-ray shielding rate reached over 99% with a thickness of 5mm. It can be used for a long time in the range of -260℃ to +350℃ and has good anti-aging properties.

[0038] In summary, this invention provides a lightweight, high-temperature resistant, high-performance n / γ composite shielding material for space nuclear reactors. This material offers advantages such as excellent n / γ composite shielding effect, superior comprehensive mechanical properties, resistance to radiation aging, resistance to high and low temperatures, and lightweight design. Through optimized structural design of the functional filler, the interfacial structure and interaction mode between the n / γ absorbing functional filler and the polymer matrix are improved. This solves the problems of poor temperature resistance, easy aging, and insufficient comprehensive mechanical properties of existing polymer-based n / γ shielding materials when the amount of functional filler added is high. It exhibits superior comprehensive mechanical properties compared to polymer composite materials prepared by traditional inorganic-organic additive methods. Furthermore, this invention allows for adjustment of the mass fraction ratio of Gd-MOF and Pb-MOF according to specific n and γ ray shielding requirements to achieve better n and γ shielding effects. It is suitable for high-performance n / γ composite shielding materials used in my country's space nuclear reactors, which operate under high day-night temperature differences and require lightweight launch payloads. In addition, Gd-MOF and Pb-MOF can be composited into other high-temperature resistant, high-H-content polymer matrices (such as EP, AFG-90H resins, etc.) to expand their application to radiation shielding materials for other micro-miniature advanced nuclear energy systems and nuclear devices that require lightweight, high-temperature resistance, and efficient n / γ shielding.

[0039] The parts of this invention not described in detail are well-known to those skilled in the art. The embodiments described above are merely preferred embodiments of the invention, and do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Various modifications and improvements to the technical solutions of this invention made by those skilled in the art without departing from the spirit of the invention should fall within the protection scope defined by the claims of this invention.

Claims

1. A lightweight high-temperature-resistant high-performance n / γ composite shielding material for space nuclear reactors, characterized in that: The composite shielding material adopts gadolinium-containing metal organic framework as a neutron absorber and lead-containing metal organic framework as a gamma ray shielding material as functional fillers, and polyimide as a matrix, and is composed of n / gamma composite shielding material by in-situ chemical synthesis; The synthesis process of the gadolinium-containing metal organic framework is as follows: GdCl3·6H2O and pyromellitic dianhydride are dissolved in a solvent N,N-dimethylformamide, and molar ratio GdCl3·6H2O: pyromellitic dianhydride: N,N-dimethylformamide = (5-20):(3-15):(60-200) is added to a magnetic stirrer, and triethylamine is added dropwise while stirring, and after the formation of flocculent suspension, the solution is transferred to a hydrothermal reactor, heated at 90-180 DEG C for 8-16 hours in a muffle furnace, cooled to room temperature, and the supernatant is removed by using a suction filter to obtain a white precipitate, which is washed with N,N-dimethylformamide, ethanol and diethyl ether in sequence, and finally placed in a vacuum drying oven for high-temperature heating to remove crystal water to obtain a gadolinium-containing metal organic framework powder; The synthesis process of the lead-containing metal organic framework is as follows: Pb(NO3)2 and terephthalic acid are dissolved in a solvent N,N-dimethylacetamide and water, and molar ratio Pb(NO3)2: terephthalic acid: N,N-dimethylacetamide: water = (0.1-2.5):(0.1-2.5):(50-400):(140-600) is added to a reaction container and ultrasonically stirred at room temperature for 10-50 minutes; the reaction container is sealed and placed in an oven, and kept at a temperature of 80-190 DEG C for 6-24 hours; cooled to room temperature to obtain colorless transparent crystals, which are washed with N,N-dimethylacetamide, filtered and dried to obtain a lead-containing metal organic framework material.

2. The composite shielding material of claim 1, wherein: The composition of the composite shielding material is that the mass fraction of the gadolinium-containing metal organic framework is 5wt%-40wt%, the mass fraction of the lead-containing metal organic framework is 10wt%-40wt%, and the balance is polyimide.

3. The composite shielding material of claim 1, wherein: The in-situ chemical synthesis method of the gadolinium-containing metal organic framework, the lead-containing metal organic framework and the polyimide comprises the following steps: dissolving the gadolinium-containing metal organic framework and the lead-containing metal organic framework powders in anhydrous N, N-dimethylformamide solvent, then adding 4, 4'-diamino diphenyl ether, stirring under N2 in an ice water bath at 0-6 ℃, adding the organic ligand of pyromellitic dianhydride (PMDA) multiple times uniformly under magnetic and ultrasonic stirring, and stirring for 2-6 h to generate polyimide acid; wherein, the mass ratio of the gadolinium-containing metal organic framework : the lead-containing metal organic framework : N, N-dimethylformamide : 4, 4'-diamino diphenyl ether : pyromellitic dianhydride is (5-40) : (10-40) : (20-150) : (10-42.5) : (10-42.5); keeping the polymer solution at 60-90 ℃ for 1-3 h to make the solvent volatilize completely, then using the stepwise heating method to sequentially rise to 95-130 ℃, 140-170 ℃, 180-210 ℃ and 220-250 ℃ and respectively keep for 1-2 h, then adjusting the temperature to 280-350 ℃ and keeping for 1-2 h for imidization treatment, and finally cooling to room temperature to obtain the composite shielding material.

Images