Ionizing radiation resistant powder with core-shell porous structure, and preparation method and application thereof

Abstract

This invention relates to the field of radiation protection materials technology, specifically providing a core-shell porous structure for ionizing radiation protection powder, its preparation method, and its applications. The powder of this invention has a solid core of tungsten-bismuth composite oxide and a porous shell layer covering the solid core and containing functional elements for absorbing thermal neutrons. Prepared through a specific combination of materials and process parameters, it achieves broad-spectrum composite protection against X / γ-rays and neutrons. It can achieve good composite properties with various polymer substrates while maintaining mechanical properties. This provides a core solution for developing a new generation of high-performance, lightweight, and flexible protective materials suitable for complex radiation scenarios such as nuclear medicine and nuclear energy, demonstrating significant technological advancement and broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of radiation protection materials technology, specifically to a core-shell porous structure for preventing ionizing radiation, its preparation method, and its application. Background Technology

[0002] The widespread application and deepening of ionizing radiation technology in many fields such as medical diagnosis, industrial flaw detection, and scientific experiments have led to an increasing and more diversified demand for high-performance radiation protection materials. Traditional shielding products, such as those made of lead, have a long history of use, but their inherent biological toxicity, excessive weight, and lack of flexibility make them increasingly difficult to meet the comprehensive requirements of modern protection, which emphasize safety, lightness, and flexible fit.

[0003] In recent years, polymer-based composite shielding materials have become a research focus in this field due to their advantages such as lightweight, ease of processing, and adjustable shielding performance. However, the inorganic powder fillers commonly used in existing composite systems generally face key problems such as poor interfacial compatibility with the polymer matrix, weak bonding force, and a significant decrease in the mechanical properties of the composite material at high filling ratios. This greatly limits their large-scale application in practice. Therefore, developing a novel powder filler that combines high-efficiency radiation shielding capability with excellent matrix compatibility has significant theoretical value and practical application prospects for promoting performance breakthroughs and practical implementation of composite protective materials. Summary of the Invention

[0004] Therefore, it is necessary to provide an anti-ionizing radiation powder with a core-shell porous structure, its preparation method, and its applications. The anti-ionizing radiation powder of this invention has a core-shell porous structure, which, while ensuring high radiation shielding effectiveness, can also significantly improve the interfacial bonding force between the filler and the polymer material, making it suitable for preparing high-performance flexible composite shielding materials.

[0005] The present invention adopts the following technical solution: This invention provides an anti-ionizing radiation powder with a core-shell porous structure, comprising a solid core of tungsten-bismuth composite oxide and a porous shell coating the solid core. The solid core of the tungsten-bismuth composite oxide is a microsphere prepared by hydrothermal reaction and pre-sintering of a precursor solution. The precursor solution is mainly prepared by mixing a bismuth source, nitric acid, a tungsten source, and a complexing agent. The porous shell is a porous shell prepared by mixing the coating liquid and the solid microspheres of the tungsten-bismuth composite oxide with the coating liquid, stirring and evaporating the solvent, pre-drying, and multi-stage programmed sintering. The coating liquid is mainly prepared by mixing a thermally absorbing neutron functional element, a pore-forming template agent, and a dispersant.

[0006] In some embodiments, the molar ratio of bismuth to tungsten is (1~3): (1~3).

[0007] In some embodiments, the molar ratio of the sum of bismuth and tungsten elements to the functional element absorbing thermal neutrons is (1~5):1, preferably (2~3):1.

[0008] In some embodiments, the bismuth source is selected from at least one of bismuth nitrate, bismuth chloride, bismuth citrate, and bismuth acetate, more preferably bismuth nitrate.

[0009] In some embodiments, the tungsten source is selected from at least one of ammonium metatungstate, sodium tungstate, and zinc tungstate, more preferably ammonium metatungstate.

[0010] In some embodiments, the complexing agent is selected from at least one of citric acid, tartaric acid, oxalic acid, ethylenediaminetetraacetic acid, and gluconic acid, with citric acid being more preferred. Preferably, the molar ratio of bismuth-tungsten to citric acid is (3~1):(1~2), which can promote better shielding effect when the powder material is applied.

[0011] In some embodiments, the functional element for absorbing thermal neutrons is derived from rare earth elements such as gadolinium, samarium, and dysprosium sources. The gadolinium source is preferably at least one of gadolinium nitrate, gadolinium chloride, and gadolinium acetate. More preferably, gadolinium nitrate is used, as gadolinium, in conjunction with bismuth and tungsten, can promote better shielding effects when the powder material is applied.

[0012] In some embodiments, the pore-forming template agent is selected from at least one of polyethylene glycol (PEG), polymethyl methacrylate microspheres (PMMA), polystyrene (PS), and ammonium bicarbonate. Preferably, the polymethyl methacrylate microspheres (PMMA) have a particle size of 100-300 nm; more preferably, the mass ratio of gadolinium nitrate to PMMA is (1-3):1, which can promote better overall shielding effect and tensile strength properties when the powder material is applied.

[0013] In some embodiments, the dispersant is selected from at least one of polyvinylpyrrolidone, polyacrylic acid, and sodium hexametaphosphate; preferably polyvinylpyrrolidone, and the amount used is about 1% of the sum of the masses of the bismuth source, tungsten source, and gadolinium source, which can promote better shielding effect and tensile strength properties when the powder material is applied.

[0014] The ionizing radiation shielding powder with a core-shell porous structure has a density of 5.5~6.2 g / cm³, an average particle size of 1~10 μm, and a shell porosity of 30%~60%.

[0015] This invention also provides a method for preparing ionizing radiation-resistant powder with a core-shell porous structure, comprising the following steps: A precursor solution mainly composed of bismuth source, nitric acid, tungsten source and complexing agent was prepared. The precursor solution was subjected to hydrothermal reaction, the product was washed by centrifugation, dried and pre-sintered to obtain solid microspheres of tungsten-bismuth composite oxide. An ethanol-water coating solution containing a functional element for absorbing thermal neutrons, a pore-forming template agent, and a dispersant was prepared. The ethanol-water coating solution was mixed with the solid microspheres of tungsten-bismuth composite oxide, the solvent was evaporated by stirring, and after drying, multi-stage programmed sintering was performed to obtain powder with a solid core and a porous shell of tungsten-bismuth composite oxide.

[0016] In some embodiments, the precursor solution is weakly acidic, preferably with a pH of 6-7, and the hydrothermal reaction parameters are: temperature of 150-180 °C and duration of 18-24 h.

[0017] In some embodiments, the washing process involves alternating centrifugal washing with deionized water and anhydrous ethanol multiple times.

[0018] In some embodiments, the pre-sintering parameters are: heating rate of 2~4℃ / min, heating to 500~650℃ and holding for 2~3h.

[0019] In some embodiments, the parameters for stirring and evaporation are: 60~70℃ water bath, 200~300 rpm, and continuous evaporation of ethanol solvent for 4~6 hours.

[0020] In some embodiments, the parameters for the multi-stage programmed sintering are as follows: in an air atmosphere, the temperature is increased to 350-450°C at a rate of 1-3°C / min, then increased to 500-600°C at a rate of 2-5°C / min and held for 2-3 hours; then the temperature is increased to 800-850°C at a rate of 3-5°C / min and held for 1-3 hours.

[0021] This invention also provides a composite membrane prepared by mixing the core-shell porous anti-ionizing radiation powder with a polymer. Preferably, the polymer is a liquid silicone rubber system, and the powder filling amount is preferably high (greater than 50%), achieving better overall shielding effect and tensile strength performance.

[0022] The present invention also provides the application of the core-shell porous structure of the anti-ionizing radiation powder or the composite film in the preparation of radiation protection products.

[0023] Compared with the prior art, the core technical advantages and beneficial effects of this invention are as follows: This invention addresses the core problems of existing radiation-shielding composite materials, such as weak interfacial bonding between the shielding filler and the polymer matrix, susceptibility to embrittlement and fracture under high filler content, and the limited functionality of traditional materials in dealing with mixed radiation fields. It provides a core-shell porous structure for ionizing radiation protection, along with its preparation method and applications. Through a three-step synergistic process of "hydrothermal synthesis - template coating - multi-stage calcination," a heterogeneous gradient structure of "high atomic number dense core - multifunctional porous shell" is precisely constructed within the powder, cleverly synergizing multiple protection mechanisms and resolving the pain point of poor material interfacial compatibility. The mechanism lies in the high electron density of the dense tungsten-bismuth composite oxide core, providing efficient shielding against X / γ rays; the rare earth elements such as gadolinium (Gd) introduced into the outer shell have a large thermal neutron absorption cross-section, which, combined with the porous structure, extends and increases the collision path and probability of neutrons, giving the material significant neutron absorption capability. This partitioned functional design of "core shielding + outer shell absorption" achieves broad-spectrum composite protection against "X / γ rays and neutrons." Meanwhile, the porous structure of the anti-ionizing radiation powder shell layer can provide abundant and strong mechanical anchoring points for the polymer matrix, forming a stable "mechanical interlocking" interface structure, which fundamentally ensures the mechanical reliability and stability of the composite material under high filling volume.

[0024] Through extensive experimental research, this invention has also discovered that by using specific combinations of materials and process parameters, the powder with a core-shell porous structure prepared can achieve an X-ray shielding efficiency of over 60%, a γ-ray shielding efficiency of over 40%, and a neutron shielding efficiency of over 90% when applied to composite membrane materials, with a tensile strength of not less than 6.8 MPa, resulting in superior overall performance.

[0025] The core-shell porous structure powder of this invention serves as an innovative multifunctional filler, capable of achieving excellent composites with various polymer substrates. This allows the final material to simultaneously integrate highly efficient broadband radiation shielding performance, excellent neutron absorption potential, significantly enhanced mechanical strength, and good processing flexibility within a single system. This design overcomes multiple technical bottlenecks, including the narrow shielding spectrum of traditional materials, the high toxicity of lead-based materials, and the poor mechanical properties of highly filled composite materials.

[0026] The core-shell porous structure powder of the present invention has the advantages of being green and environmentally friendly, having adjustable structural properties, and having controllable preparation process. It provides a core solution for developing a new generation of high-performance, lightweight, and flexible protective materials suitable for complex radiation scenarios such as nuclear medicine and nuclear energy, and has significant technological advancements and broad application prospects. Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope image of the solid microspheres of tungsten-bismuth composite oxide prepared in Example 1.

[0028] Figure 2 This is a scanning electron microscope image of the core-shell precursor powder prepared in Example 1.

[0029] Figure 3 This is a photograph of the powder with a core-shell porous structure prepared in Example 1.

[0030] Figure 4 This is a schematic diagram of the microstructure of the powder with a core-shell porous structure prepared in Example 1.

[0031] Figure 5 This is a scanning electron microscope image of the powder with a core-shell porous structure prepared in Example 1. Detailed Implementation

[0032] Traditional shielding materials have long faced fundamental contradictions when dealing with complex radiation environments: lead-based materials pose toxicity and environmental risks, and cannot meet the requirements for lightweight and flexibility; while commonly used fillers in lead-free composite materials have weak interfacial bonding with the polymer matrix, and high filler content can easily lead to material embrittlement, while also failing to meet the broad-spectrum protection requirements for X / γ rays and neutrons. Therefore, developing a novel lead-free filler that combines efficient broad-spectrum shielding, strong interfacial bonding, and good process adaptability has become a core breakthrough for promoting the development of next-generation high-performance radiation protection materials.

[0033] The technical concept of this invention lies in addressing the core bottleneck of existing composite shielding materials, which struggle to synergistically achieve broad-spectrum protection, high mechanical reliability under high filling conditions, and good processability. It provides a core-shell porous structure for ionizing radiation protection powder, composite film, and their preparation methods and applications. By precisely designing a heterogeneous structure and elemental partitioning of a "high atomic number dense core-rare earth porous functional shell," the integration of X / γ-ray shielding and neutron absorption functions is achieved at the microscopic level. Furthermore, the porous nature of the outer shell forms a strong mechanically interlocking interface with the polymer matrix. This fundamentally solves the challenge of synergistic effects between shielding effectiveness, broad-spectrum protection, and the mechanical properties of composite materials, providing an innovative material basis and reliable technical approach for developing lightweight, flexible, high-strength protective products suitable for complex radiation scenarios.

[0034] The present invention will be further described in detail below with reference to specific embodiments, so that those skilled in the art can more clearly understand the present invention. The following embodiments are only used to illustrate the present invention, and are not intended to limit the scope of the present invention. Based on the specific embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention. In the embodiments of the present invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art; in the embodiments of the present invention, unless specifically specified, the technical means used are conventional means well known to those skilled in the art.

[0035] Example 1 This embodiment provides a method for preparing powder and thin film materials with a core-shell porous structure, including the following steps: S1. Preparation of precursor solution: 121.28 g of bismuth nitrate (Bi(NO3)3・5H2O) (0.25 mol) was dissolved in 2.5 L of 0.6 mol / L dilute nitric acid solution to obtain a clear bismuth nitrate solution (bismuth element concentration 0.1 mol / L). Then, 30.79 g of ammonium metatungstate (NH4)6H2W... 12 O 40 ·xH2O (0.0104 mol) and 72.05 g citric acid (0.375 mol) were dissolved in 250 mL of deionized water. After complete dissolution, an ammonium metatungstate complexing agent solution (tungsten element concentration of 0.5 mol / L) was obtained.

[0036] Add the ammonium metatungstate complexing agent solution to the above bismuth nitrate solution and stir at 300 rpm for 30 min; add 25% ammonia water dropwise to the above mixed solution until the pH of the mixed solution is 6.5, to obtain a homogeneous and stable precursor solution.

[0037] S2. Preparation of solid microspheres of tungsten-bismuth composite oxide by hydrothermal reaction and pre-sintering densification reaction: The precursor solution obtained in step S1 was placed in a high-pressure reactor for hydrothermal reaction at 180 °C for 24 h. After the reaction, all the product was transferred to centrifuge tubes and washed alternately with deionized water and anhydrous ethanol at 4000 rpm for 15 min each time, for a total of 3 washes. The washed product was then transferred to a petri dish and dried in a vacuum drying oven at 70 °C for 10 h. Subsequently, the dried powder product was placed in an alumina crucible and placed in a box-type muffle furnace. The temperature was increased to 600 °C at 3 °C / min and held at this temperature for 3 h. The product was then cooled with the furnace to obtain solid microspheres of tungsten-bismuth composite oxide.

[0038] S3. Constructing the core-shell structure: 54.17 g gadolinium nitrate (Gd(NO3)3・5H2O) (0.125 mol), 27.085 g polymethyl methacrylate microspheres (PMMA) (particle size 300 nm, purchased from Zhongke Jinyan (Beijing) Technology Co., Ltd.), and 2.063 g polyvinylpyrrolidone (PVP) were added to 1 L of ethanol-water mixed solvent (volume ratio 1:1) to obtain the coating solution.

[0039] Subsequently, the solid microspheres of tungsten-bismuth composite oxide obtained in step S2 were added to the coating solution, and the coating solution was placed in a 70°C water bath and continuously evaporated for 6 h under mechanical stirring at 300 rpm. Finally, the solid microspheres of tungsten-bismuth composite oxide coated with gadolinium were dried in an oven at 70°C for 10 h to obtain core-shell precursor powder.

[0040] S4. Multi-stage programmed sintering and shaping to prepare powders with core-shell porous structures: The core-shell precursor powder obtained from S3 was placed in a tube furnace for multi-stage programmed sintering: under an air atmosphere, the temperature was first increased to 450 ℃ at a rate of 2 ℃ / min, then increased to 600 ℃ at a rate of 5 ℃ / min, and held at this temperature for 2 h; then the temperature was increased to 840 ℃ at a rate of 5 ℃ / min, and held at this temperature for 1 h, and then naturally cooled to finally obtain powder with a core-shell porous structure.

[0041] S5. Preparation of composite thin films: 260 g of the core-shell porous powder obtained in step S4 was mixed with 140 g of liquid silicone rubber (purchased from Shandong Beigebao New Material Co., Ltd., physicochemical parameters: the silicone rubber is an A / B two-component liquid silicone rubber with a mass ratio of A to B of 1:1). The mixture was mixed in a planetary mixer at 600 rpm under vacuum for 45 min. The mixed material was then coated onto a glass plate with a wet film thickness of 1.2 mm. The film was then cured in a 100°C oven for 30 min. After cooling, the film was peeled off to obtain a 1 mm thick composite film.

[0042] The microstructure of the powder product prepared in this embodiment was tested, and the results are shown in the figures below. Figures 1 to 5 .

[0043] like Figure 1 As shown, the prepared tungsten-bismuth composite oxide solid microspheres exhibit a regular spherical solid structure with high sphericity, uniform size, and a relatively smooth surface without obvious pores or defects, which fully demonstrates the good effect of hydrothermal reaction and pre-sintering treatment.

[0044] Depend on Figure 2 The microscopic morphology of the core-shell precursor powder after coating shows that the powder particles still maintain a complete spherical structure, but the surface is rougher. This indicates that the solid core surface has been uniformly coated with a dense composite shell layer without large pores, which verifies that the stirring evaporation coating process can achieve uniform deposition of the shell layer.

[0045] Depend on Figure 3 The appearance of the powder shows that it is light yellow in color, with no obvious impurities, and has a fine texture and is relatively loose overall.

[0046] Depend on Figure 4 The microscopic diagrams visually represent the powder structure modules.

[0047] Depend on Figure 5 The scanning electron microscope images further characterize that the powder particles still maintain a complete spherical shape, the shell region has a regular and uniform pore distribution, the boundary between the core and the shell is clear and distinct, the shell thickness is uniform and there is no shedding or damage, proving that the programmed sintering process not only ensures the stability of the porous structure, but also maintains the integrity of the core and shell as a whole.

[0048] Tests showed that the density of the ionizing radiation shielding powder with a core-shell porous structure in this embodiment is 5.5~6.2 g / cm³.

[0049] The composite film prepared in this embodiment is flat and smooth sheet-like, light milky white in color, with no obvious particle agglomeration marks or crack defects on the surface, regular edges and good formability, and also has significant flexibility. This indicates that the powder with core-shell porous structure prepared has excellent interfacial bonding with the silicone rubber matrix.

[0050] Example 2 Referring to the preparation method steps of Example 1, this example investigates the effect of different molar ratios of bismuth and tungsten on the performance of the prepared composite thin film material. The test contents include: (1) Ionizing radiation protection performance test: The prepared flexible radiation-resistant composite film material was cut into 15cm×15cm samples with a thickness of 1mm. Ionizing radiation protection tests were conducted according to the methods published in YY / T 0292.1-2020 "Medical diagnostic X-ray radiation protection equipment - Part 1: Determination of material attenuation performance" and ASTM E262-17 "Standard method for measuring thermal neutron reactivity by radioactive counting technique", and the shielding rate was calculated. Among them, the incident energy of X-rays was 60keV, 80keV, 100keV, and 120keV, the incident energy of γ-rays was 662keV (Cs-137), and the incident energy of neutron rays was 0.025 eV.

[0051] (2) Tensile property test: The tensile strength of the obtained flexible radiation-resistant composite film material was tested according to the method published in GB / T 528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber".

[0052] The statistical results are shown in the table below: Statistical table of the effects of different molar ratios of bismuth and tungsten on the properties of the prepared composite thin film materials As can be seen from the table above: Under the condition that other conditions remain unchanged, when the molar ratio of bismuth to tungsten is (1~3):(3~1), the X-ray shielding efficiency is greater than 60%, the gamma-ray shielding efficiency is greater than 40%, and the overall neutron shielding efficiency is maintained in the range of 92%~94%. However, when tungsten is not present, the gamma-ray shielding efficiency of the composite film material will be significantly reduced. Furthermore, it can be deduced that: As the proportion of Bi increases, the shielding effect of the material against low-energy X-rays strengthens; while as the proportion of W increases, the shielding ability against medium-energy X-rays becomes more prominent. This is because Bi has a K absorption edge of approximately 90 keV and a high oxide density, resulting in a high energy matching degree with low-energy X-rays ≤120 keV. It can efficiently capture these photons through the photoelectric effect and convert them into photoelectrons, thus exhibiting extremely strong shielding efficiency against low-energy X-rays. However, Bi's Compton scattering cross section for 662 keV medium-energy γ-rays is lower than that of W, so its shielding effect in this frequency band is relatively weaker.

[0053] W oxide also has a high density, and it mainly relies on Compton scattering to target medium-energy gamma rays ≥662keV. At the same time, W has a high electron density, which can effectively scatter high-energy photons to reduce their penetration ability. However, W has a weaker photoelectric effect cross section in the low-energy X-ray region than Bi, so its shielding efficiency against low-energy rays is not as good as Bi.

[0054] As for neutron shielding, it is mainly the responsibility of gadolinium (Gd) in the shell, and is independent of the ratio of W and Bi in the core. Since the molar ratio of Gd in the shell remains fixed in the core-shell structure, and the porous structure can extend the collision path of neutrons, the neutron shielding efficiency of the material is always relatively stable with minimal fluctuation.

[0055] Example 3 Referring to the preparation method steps of Example 1 (maintaining a bismuth-tungsten molar ratio of 2:1) and the performance testing method steps of Example 2, this example investigates the effect of different molar ratios of the sum of bismuth and tungsten with gadolinium on the performance of the prepared composite thin film material.

[0056] The statistical results are shown in the table below: As can be seen from the table above: Under otherwise constant conditions, when the molar ratio of bismuth to tungsten to gadolinium is (2~3):1, the X-ray shielding efficiency is greater than 60%, the gamma-ray shielding efficiency is greater than 40%, and the neutron shielding efficiency remains greater than 90%. When gadolinium is absent, the neutron shielding efficiency will decrease sharply.

[0057] Furthermore, it can be deduced that: X-ray / gamma-ray shielding is primarily achieved by Bi and W in the core, while neutron shielding is handled by the Gd-rich shell combined with a porous structure. The shielding efficiency increases with increasing (Bi+W) content and decreases with decreasing content. This is because the K-absorption edges of Bi and W are complementary, enabling efficient capture of low-to-medium energy X-rays (60-120 keV) through the photoelectric effect, while Gd contributes little to this energy range. Simultaneously, the high electron density of W enhances Compton scattering of 662 keV high-energy gamma rays, with Bi playing a supporting role, and the shell having no significant impact on gamma-ray absorption. Neutron shielding efficiency increases with increasing Gd content, while the Bi and W in the core do not substantially contribute to neutron absorption.

[0058] Therefore, adjusting the (Bi+W):Gd molar ratio is the key to balancing the shielding effectiveness of the two types. Only by choosing an appropriate ratio can Bi and W be concentrated in the core to enhance X / γ ray protection, while Gd can improve the neutron shielding effect in the shell through the porous structure.

[0059] Example 4 Referring to the preparation method steps of Example 1 (maintaining a bismuth-tungsten molar ratio of 2:1) and the performance testing method steps of Example 2, this example investigates the effect of different bismuth-tungsten-citric acid molar ratios on the performance of the prepared composite thin film material.

[0060] The statistical results are shown in the table below: As can be seen from the table above: Under otherwise constant conditions, when the molar ratio of bismuth-tungsten to citric acid is (3~1):(1~3), the X-ray shielding efficiency is greater than 60%, the gamma-ray shielding efficiency is greater than 39%, and the neutron shielding efficiency remains in the range of 92%~94%. The absence of citric acid leads to a lack of citric acid complexation, resulting in a slight decrease in shielding performance.

[0061] Further deduction can be made: The carboxyl group of citric acid can simultaneously complex Bi³⁺ and W. 6The complexation process forms a stable complex, which prevents premature precipitation of metal ions and ensures the uniformity and stability of the precursor solution. Simultaneously, the complexation directly determines the microstructure of the solid core of the tungsten-bismuth composite oxide synthesized subsequently via hydrothermal synthesis: when the complexation is sufficient, the core has high sphericity and a dense interior, with uniform distribution of Bi and W elements, maximizing the probability of interaction with X / γ rays and thus ensuring high shielding efficiency. Insufficient complexation leads to premature precipitation of some metal ions, resulting in irregular core morphology, internal porosity, and uneven aggregation of Bi and W elements, making it easier for rays to penetrate through pores or structural defects, thus reducing shielding efficiency. Excessive complexation leaves a small amount of carbon impurities in the pre-sintering stage due to excess citric acid, or causes slight roughness on the core surface and a density slightly lower than the optimal ratio, resulting in decreased shielding efficiency.

[0062] Furthermore, citric acid only affects the preparation process of the core and does not change the Gd content and porosity of the shell, so it has no significant impact on neutron shielding effectiveness.

[0063] Example 5 Referring to the preparation method steps of Example 1 and the performance testing method steps of Example 2, this example investigates the effect of different pH values ​​of the precursor solution in step S1 on the performance of the prepared composite thin film material.

[0064] The statistical results are shown in the table below: As can be seen from the table above: Under otherwise unchanged conditions, both excessively high and excessively low pH values ​​of the precursor solution will reduce radiation shielding efficiency and also have a certain impact on tensile strength.

[0065] Furthermore, it can be deduced that: In the precursor solution, citric acid reacts with Bi³⁺ and W through its carboxyl group. 6 The citrate ion forms a stable complex, thus preventing premature precipitation of metal ions. Within a weakly acidic to near-neutral pH range of 6-7, the citrate ion exhibits the strongest coordination ability, efficiently complexing two metal ions simultaneously to form a homogeneous and stable mixed system. Simultaneously, its adsorption and crystal growth rate reach equilibrium, which is most conducive to the formation of solid microspheres of tungsten-bismuth composite oxide with high sphericity, uniform size, and dense internal structure. If the pH deviates from this range, the complexation effect will significantly weaken. When the pH is too low (<6, excessively acidic), it will inhibit the ionization of citrate, reducing its complexation efficiency with metal ions, and partially affecting Bi³⁺ and W⁻. 6Bi³⁺ will prematurely form amorphous precipitates, leading to stratification and heterogeneity of the precursor solution. If the pH is too high (>7, alkaline), Bi³⁺ easily hydrolyzes to form bismuth hydroxide precipitate, which cannot participate in the complexation reaction, ultimately resulting in uneven distribution of metal elements in the precursor. Simultaneously, improper pH leads to poor sphericity, rough surfaces, and internal porosity in the tungsten-bismuth composite oxide microspheres generated by the hydrothermal reaction. Uneven aggregation of Bi and W elements and the irregular, porous core surface cannot provide a uniform deposition substrate for the shell, resulting in incomplete shell coating, uneven thickness, and even shell detachment. Ultimately, the synergistic effect of "core shielding + shell neutron absorption" in the powder is weakened, and the "mechanical interlocking" between the porous shell and the polymer matrix is ​​also weakened due to structural defects, leading to a decrease in the mechanical properties of the composite material. Only by strictly controlling the pH within the weakly acidic to near-neutral range of 6-7 can the complexation reaction be ensured, the core be dense and regular, and the shell coating be uniform, ultimately achieving broad-spectrum radiation protection and high mechanical compatibility of the powder.

[0066] Example 6 Referring to the preparation method steps of Example 1 and the performance testing method steps of Example 2, this example investigates the effect of different mass ratios of pore-forming template agent polymethyl methacrylate microspheres (PMMA) and gadolinium source on the performance of the prepared composite film material.

[0067] The statistical results are shown in the table below: As can be seen from the table above: Under otherwise constant conditions, when the mass ratio of gadolinium nitrate to PMMA is (1~3):1, the X-ray shielding efficiency is greater than 60%, the gamma-ray shielding efficiency is greater than 40%, the neutron shielding efficiency is greater than 90%, and the tensile strength is above 6.8. When PMMA is not present, the interfacial bonding force between the powder and the silicone rubber matrix is ​​drastically weakened, and the tensile strength is only 4.93 MPa.

[0068] Furthermore, it can be deduced that: The amount of PMMA used will affect various properties of the material by changing the shell porosity: for X-ray shielding, the more PMMA used, the higher the shell porosity, and the easier it is for the rays to pass through the pores and avoid the Bi and W in the core, thus slightly reducing the shielding efficiency; conversely, reducing the amount of PMMA used will lengthen the ray path and improve the X-ray shielding efficiency.

[0069] The principle for gamma-ray shielding is similar. Since its shielding effect mainly depends on the W element in the core, the efficiency will slightly decrease with the increase of PMMA dosage. Regarding neutron shielding, the more PMMA used, the higher the shell porosity, which disperses the gadolinium and reduces the gadolinium concentration per unit volume. This decreases the probability of neutron absorption and collision with gadolinium, resulting in lower shielding efficiency. Conversely, less PMMA results in a more concentrated gadolinium element and higher neutron shielding efficiency.

[0070] The change in tensile strength is related to the adaptability of porosity. When the porosity is in a moderate range, the matrix and shell can form a stable interlocking structure, and the tensile strength reaches its maximum. Too much or too little PMMA will weaken the interfacial bonding force between the two, thereby reducing the tensile strength.

[0071] Example 7 Referring to the preparation method steps of Example 1 and the performance testing method steps of Example 2, this example investigates the effect of different proportions of the dispersant polyvinylpyrrolidone (PVP) to the total mass of bismuth source, tungsten source and gadolinium source (hereinafter referred to as PVP content ratio) on the performance of the prepared composite film material.

[0072] The statistical results are shown in the table below: As can be seen from the table above: Under otherwise identical conditions, when the PVP content is around 1%, the X-ray shielding efficiency is greater than 60%, the gamma-ray shielding efficiency is greater than 40%, the neutron shielding efficiency is greater than 90%, and the tensile strength is greater than 8 MPa. When PVP is absent, the powder undergoes severe agglomeration, and the shielding efficiency decreases. When the PVP content is too high, the organic components remaining after sintering disrupt the powder density and elemental distribution, resulting in a significant reduction in shielding efficiency.

[0073] Furthermore, it can be deduced that: As a powder dispersant, PVP mainly inhibits the agglomeration of Bi / W core and Gd shell powders, as well as the agglomeration between powders, through steric hindrance. Its dosage directly affects the dispersion uniformity of the powder, and thus relates to various properties of the material.

[0074] For X-ray and gamma-ray shielding, within a suitable range of PVP dosage, as the dosage increases, the powder dispersibility gradually improves, the "blank area" without shielding elements in the matrix decreases, the probability of interaction between rays and high Z elements is maximized, and the shielding efficiency will increase accordingly. However, when the PVP dosage exceeds this range, the PVP sintering residue will reduce the powder density, the interaction intensity between rays and high Z elements will weaken, and the shielding efficiency will decrease.

[0075] The variation pattern of neutron shielding is consistent with this. The better the powder dispersion, the more uniform the distribution of Gd in the matrix, and the higher the probability of collision and capture of neutrons and Gd. Therefore, the neutron shielding efficiency will increase as the amount of PVP increases within a suitable range. Too much or too little PVP will reduce the shielding efficiency.

[0076] The change in tensile strength is also related to the amount of PVP used. When the amount is appropriate, the uniformly dispersed powder bonds more tightly with the matrix interface, the stress transfer is more uniform, and the tensile strength gradually increases. If the amount is excessive, the PVP sintering residue will weaken the interfacial bonding force between the powder and the matrix, and the tensile strength will decrease accordingly. Therefore, only by controlling the amount of PVP within an appropriate range can the powder dispersibility be optimized, while balancing shielding efficiency and tensile strength, so that all performance aspects are at a better level.

[0077] Example 8 Referring to the preparation method steps of Example 1 and the performance testing method steps of Example 2, this example investigates the influence of different process steps on the performance of the prepared composite thin film material. The experimental groups are as follows: Non-multi-stage programmed temperature rise sintering: Compared with Example 1, programmed sintering is not used in step S4. The core-shell precursor powder obtained in step S3 is directly placed in a tube furnace and heated to 820°C at a rate of 5°C / min for 4 hours to obtain the powder. Steps without constructing a core-shell porous structure: Compared with Example 1, in step S1, equal amounts of gadolinium nitrate, polymethyl methacrylate microspheres (PMMA), 2.063g of polyvinylpyrrolidone (PVP), ammonium metatungstate, and citric acid were directly mixed, added to a bismuth nitrate solution, and ammonia water was added dropwise to prepare a precursor solution. Hydrothermal synthesis and densification were carried out, and multi-stage programmed sintering was performed to obtain powder.

[0078] The statistical results are shown in the table below: As can be seen from the table above: Under otherwise identical conditions, when using non-multi-stage programmed sintering, the gamma-ray shielding efficiency is below 40%, the neutron shielding efficiency decreases, and the tensile strength also decreases. This indicates that the rapid decomposition of residual organic matter causes damage to the core-shell structure and powder agglomeration, resulting in a decrease in the density of Bi / W in the core and a worsening of the uniformity of Gd distribution in the shell. This not only reduces the shielding efficiency of X / γ rays and neutrons but also weakens the interfacial bonding force between the powder and the matrix, leading to a decrease in tensile strength. Under otherwise identical conditions, when the step of constructing a core-shell porous structure is omitted, the gamma-ray shielding efficiency is below 40%, and the neutron shielding efficiency and tensile strength decrease significantly. This indicates that for powders without a core-shell structure, the dispersed distribution of Bi / W reduces the concentration of high-Z elements per unit volume, thus weakening the X / γ-ray shielding efficiency. Simultaneously, the dispersed distribution of Gd and the lack of porous pathways also reduce the neutron shielding effect. Furthermore, the lack of interfacial interlocking due to the absence of a core-shell porous structure in solid particles further reduces the tensile strength of the material.

[0079] Example 9 Referring to the preparation method steps of Example 1 and the performance testing method steps of Example 2, this example investigates the effect of replacing gadolinium nitrate with samarium nitrate (Sm(NO3)3・5H2O) and dysprosium nitrate (Dy(NO3)3・5H2O) in equal amounts on the performance of the prepared composite thin film material.

[0080] The statistical results are shown in the table below: As can be seen from the table above: Under otherwise identical conditions, when samarium nitrate or dysprosium nitrate is used to replace gadolinium nitrate, the neutron shielding efficiency decreases significantly, while the X-ray shielding efficiency, gamma-ray shielding efficiency, and mechanical properties such as tensile strength remain essentially unchanged.

[0081] In other words, when Gd is replaced with Sm or Dy, the prepared powder still has a certain neutron shielding effect. This shows that the process has good element compatibility and the shell can be compatible with a variety of elements with high thermal neutron absorption cross sections. However, since the thermal neutron absorption cross sections of these elements are much lower than those of Gd, the neutron shielding efficiency is relatively lower.

[0082] Example 10 Referring to the preparation method steps of Example 1 and the performance testing method steps of Example 2, this example investigates the effect of different filling amounts of powder in silicone rubber (referring to the percentage of powder in the total mass of powder and silicone rubber) on the performance of the prepared composite film material.

[0083] The statistical results are shown in the table below: As can be seen from the table above: Under otherwise identical conditions, the X / γ ray shielding efficiency decreases significantly when the powder filling content is below 50%. When the filling content is above 65%, it leads to reduced tensile strength, poor material flowability, and increased susceptibility to molding defects.

[0084] Furthermore, it can be deduced that: As the powder filling amount increases, the concentrations of Bi / W and Gd per unit volume gradually increase, thus the shielding efficiency against X / γ rays and neutrons continues to rise. At the same time, the powder and matrix interface are tightly bonded, stress transfer is uniform, and tensile strength gradually increases, reaching its optimal value at a filling amount of 30%. However, when the powder content continues to increase, local agglomeration begins, which weakens the interfacial bonding force and introduces a large number of interfacial defects, leading to a decrease in tensile strength. At high filling amounts, although the material exhibits excellent ionizing radiation shielding performance, its tensile strength is poor and cannot meet practical requirements.

[0085] Changes in powder loading directly affect the shielding and mechanical properties of the material. As the loading gradually increases to 30%, the concentrations of Bi / W and Gd per unit volume increase, thus continuously improving the shielding efficiency against X / γ rays and neutrons. Simultaneously, within this range, the powder is uniformly dispersed, tightly bonded to the matrix interface, and stress transfer is smooth, leading to a gradual increase in tensile strength, which reaches its optimal level at 30% loading. When the loading continues to increase, localized agglomeration of the powder is prone to occur. This not only weakens the interfacial bonding between the powder and the matrix but also generates numerous interfacial defects, causing a decrease in tensile strength. Under high loading conditions, although the material exhibits excellent shielding performance against ionizing radiation, its tensile strength deteriorates significantly, making it difficult to meet the mechanical requirements of practical applications.

[0086] The above experimental example first used bismuth nitrate and ammonium metatungstate as raw materials, and introduced sodium citrate as a complexing agent and morphology modifier. The reaction was carried out in a precisely controlled weakly acidic hydrothermal environment. After washing, drying and pre-sintering, solid microspheres of tungsten-bismuth composite oxide with high sphericity and dense interior were obtained. Next, gadolinium nitrate was used as a gadolinium source and dissolved together with selected pore-forming template agent and dispersant in an ethanol-water mixed solvent to form a coating solution. Under continuous stirring and heating conditions, the shell precursor was uniformly and completely deposited on the surface of the solid core using the principle of evaporation-induced self-assembly, to obtain core-shell precursor powder. Then, the precursor powder was precisely programmed to calcine. The template agent was decomposed at a lower temperature to construct a porous structure, and the shell was crystallized and densified at a higher temperature. Finally, a powder material with a "dense core-porous functional shell" heterostructure, which has both high efficiency in X / γ-ray shielding and potential neutron absorption capabilities, and excellent interfacial bonding with the polymer matrix was successfully obtained.

[0087] Bismuth nitrate, ammonium metatungstate, and gadolinium nitrate (preferred) were selected as raw materials to construct a "bismuth-tungsten-gadolinium" composite oxide system. This combination design is based on the complementary advantages and functional partitioning of each component in terms of physical properties and shielding mechanism, aiming to synergistically achieve the integration of wide-spectrum shielding and core-shell structure. Among them, bismuth (Bi) has a high atomic number (83), its oxide density is large, and its photoelectric effect cross section for low-energy X / γ rays is extremely large, resulting in excellent shielding effectiveness. Its K absorption edge is about 90 keV, making it an ideal basic component for constructing a highly efficient lead-free shielding core. Tungsten (W) also has a high atomic number (74) and high density, and its Compton scattering effect for medium-energy rays is significant. Its K absorption edge is about 69 keV. It forms an effective connection and complementarity with bismuth in the decay energy spectrum, jointly ensuring the excellent shielding performance of the core in a wide energy range. Gadolinium (Gd), as a rare earth element, has a very large thermal neutron absorption cross section. Introducing it into the outer shell can endow the material with the ability to absorb neutrons in mixed radiation fields. At the same time, its oxide has good stability, which helps to strengthen the shell structure. The three components are spatially distributed through a heterogeneous configuration of "dense core-porous shell," which not only achieves the functional integration of X / γ-ray shielding and neutron absorption, but also fundamentally improves the interfacial bonding problem with the polymer matrix due to the porous nature of the outer shell. All selected raw materials are environmentally friendly and stable compounds with good process compatibility, aligning with the development trend of green, high-performance protective materials.

[0088] Beyond the above examples, the inventors' team summarized and discovered during extensive experimental research that: This invention essentially utilizes an innovative three-step process of "hydrothermal synthesis - template coating - programmed calcination" to successfully construct a heterogeneous gradient structure of "high Z-density tungsten bismuth core - rare earth porous gadolinium shell", achieving functional integration of X / γ-ray shielding and neutron absorption.

[0089] The powder of this invention has a core-shell heterogeneous porous structure, comprising a dense high-Z core and a functionalized porous shell layer arranged sequentially from the inside out. The dense high-Z core is a tungsten-bismuth composite oxide, and the functionalized porous shell layer is a gadolinium-containing oxide. Preferably, the above-mentioned radiation-shielding powder with a core-shell porous structure has a density of 5.5~6.2 g / cm³, an average particle size of 1~10 μm, and a shell porosity of 30~60%.

[0090] The porous structure of the outer shell not only enhances the neutron moderation and absorption pathways, but also provides a robust mechanical interlocking interface for the polymer matrix, thus maintaining excellent mechanical properties and flexibility even with high filler content (60%~65%).

[0091] The ionizing radiation shielding powder material system of the present invention with a core-shell porous structure fundamentally solves the technical problems of high toxicity, poor flexibility, narrow protection spectrum of traditional shielding materials, as well as weak interface and easy brittleness of high-filled composite materials. It is suitable for lightweight and flexible protective equipment and structural components in complex radiation scenarios such as nuclear medicine, nuclear energy facilities, and aerospace.

[0092] This invention essentially provides a method for preparing an anti-ionizing radiation powder with a core-shell porous structure, comprising the following steps: S1. Preparation of solid core precursor solution: First, dissolve the bismuth source in dilute nitric acid solution to obtain a clear bismuth salt dilute nitric acid solution; then dissolve the tungsten source and complexing agent in water to obtain a tungsten source complexing agent solution; add the tungsten source complexing agent solution to the bismuth salt dilute nitric acid solution, stir continuously until homogeneous, and adjust the pH to weakly acidic to obtain a homogeneous and stable precursor solution. S2. Hydrothermal synthesis and densification: The precursor solution obtained in step S1 is placed in a high-pressure reactor for hydrothermal reaction. After the reaction is completed, the product is centrifuged, washed and dried, and then pre-sintered to obtain solid microspheres of tungsten-bismuth composite oxide. S3. Construction of core-shell structure: Gadolinium source (thermal neutron-absorbing functional element), pore-forming template agent and dispersant are stirred and dissolved in a mixed solvent in proportion to form an alcohol-water coating solution; under continuous stirring and heating conditions, tungsten-bismuth composite oxide solid microspheres obtained in step S2 are added, stirred and evaporated for coating, and then dried to obtain core-shell precursor powder; S4. Multi-stage programmed sintering and shaping: The core-shell precursor powder obtained in S3 is placed in a tube furnace for multi-stage programmed sintering, first at low temperature and then at high temperature, and finally an anti-ionizing radiation powder with a core-shell porous structure can be obtained.

[0093] In step S1, the bismuth source can be one of bismuth nitrate, bismuth chloride, bismuth citrate, and bismuth acetate, preferably bismuth nitrate; the tungsten source can be one of ammonium metatungstate, sodium tungstate, and zinc tungstate, preferably ammonium metatungstate; the complexing agent can be one of citric acid, tartaric acid, oxalic acid, ethylenediaminetetraacetic acid, and gluconic acid, preferably citric acid; the total molar ratio of the complexing agent to the metal ions in the bismuth and tungsten sources is preferably (3~1):(1~3); the molar ratio of bismuth element in the bismuth source to tungsten element in the tungsten source is (1~3):(1~3), preferably (1.8~2.2):1; the concentration of dilute nitric acid is 0.6~0.8 mol / L, and its dosage is 8~12 mL per millimole of bismuth ions; the tungsten source and complexing agent are dissolved in water, and the concentration of tungsten element in the mixed solution is 0.05~0.5 mol / L, preferably 0.2~0.5 mol / L. mol / L; The pH adjustment procedure is as follows: adjust the pH of the mixed solution to 6~7 dropwise with 25% ammonia water; the stirring speed is 200~400 rpm, and the time is 30~45 min.

[0094] Preferably, bismuth nitrate and ammonium metatungstate are selected as raw materials, and citric acid is selected as a complexing agent. This is because bismuth nitrate has excellent solubility in dilute nitric acid and can provide stable Bi2O3. 3+ Source; Ammonium metatungstate, as a water-soluble polytungstate, can gradually release WO4. 2- This facilitates reaction control; citric acid is an excellent bifunctional complexing agent, and its carboxyl group can effectively complex Bi. 3+ and W 6+ To prevent premature precipitation and the formation of a uniform precursor, the Bi:W molar ratio is controlled at (1.8~2.2):1, which enables broader spectral coverage from low-energy X-rays to medium-energy gamma rays, achieving a more efficient composite radiation shielding effect. The use of dilute nitric acid at specific concentrations and amounts aims to provide a sufficient acidic environment to dissolve the bismuth salt and inhibit Bi... 3+ During hydrolysis, the dosage is optimized to avoid excessive dilution. Then, the pH of the mixed solution is precisely controlled within the range of 6.5 to 7 using ammonia. This weakly acidic to near-neutral environment is the most suitable pH range for crystal nucleation and growth. At this pH, the adsorption of citrate ions and the crystal growth rate reach equilibrium, which is most conducive to the formation of microspheres with good sphericity, uniform size, and high density.

[0095] In step S2, the hydrothermal reaction temperature is 150-180℃ and the time is 18-24h. The centrifugal washing process is as follows: all the product is transferred to centrifuge tubes and washed alternately with deionized water and anhydrous ethanol (2000-4000 rpm, 10-15 min / time) 3 times each. The drying process is as follows: the washed product is transferred to a petri dish and placed in a vacuum drying oven at 40-70℃ for 8-12h. The pre-sintering process is as follows: the dried powder product is placed in an alumina crucible, placed in a box-type muffle furnace, heated to 500-650℃ at 2-4℃ / min, and held at this temperature for 2-3h. Then, it is cooled with the furnace. The preferred heating rate is 2-3℃ / min, the preferred temperature is 550-650℃, and the preferred holding time is 3h.

[0096] The hydrothermal reaction provides sufficient driving force, and the optimal temperature range is 160-180°C. This is because at this temperature, the dielectric constant of water decreases and the ion product increases, significantly enhancing the solubility of reactants and the reaction rate, thus providing ample energy for nucleation and crystallization. Furthermore, a holding time of 20-24 hours provides sufficient time for the "dissolution-recrystallization" process, ensuring the complete transformation of the amorphous precursor into the crystalline phase. This facilitates the dissolution of small particles and the growth of larger particles through the Ostwald Ripening mechanism, thereby eliminating internal porosity and ensuring sufficient crystallization and densification. Pre-sintering thoroughly decomposes and removes residual organic matter from the hydrothermal products. Simultaneously, solid-state diffusion further eliminates lattice defects and micropores at grain boundaries, making the particles more compact. It also promotes moderate grain growth, increases crystallinity, and enhances material density and stability, resulting in highly crystalline, high-purity, and internally dense spherical solid nuclei.

[0097] In step S3, the preferred thermal neutron-absorbing functional element is gadolinium, which can be one of gadolinium nitrate, gadolinium chloride, and gadolinium acetate, preferably gadolinium nitrate; the pore-forming template agent can be one of polyethylene glycol (PEG), polymethyl methacrylate microspheres (PMMA), polystyrene (PS), and ammonium bicarbonate, preferably polymethyl methacrylate microspheres (PMMA), with a particle size preferably of 100-300 nm and a mass ratio of PMMA to gadolinium source preferably of 1:(1-3); the dispersant is one of polyvinylpyrrolidone (PVP), polyacrylic acid, and sodium hexametaphosphate, preferably polyvinylpyrrolidone (PVP); the mixed solvent is composed of ethanol and water in a volume ratio of 1:1, and the gadolinium ion concentration is 0.05-0.15 mol / L; the continuous stirring and heating process is as follows: the coating solution is placed in a water bath at 60-70℃ and continuously evaporated for 4-6 minutes under mechanical stirring at 200-300 rpm. The drying process is as follows: the solid microspheres of tungsten-bismuth composite oxide coated with gadolinium are dried in an oven at 60-80℃ for 10-12 h.

[0098] Gadolinium nitrate is readily soluble in an ethanol-water mixture, forming a uniform ionic precursor. It decomposes completely during subsequent calcination, leaving no harmful residues, making it an ideal raw material for preparing gadolinium oxide shells. The preferred pore-forming template agent is polymethyl methacrylate (PMMA) microspheres, which completely decompose into gas at 300–450°C, leaving clean, regular spherical pores in the shell without ash residue. PVP is preferably used as a polymeric dispersant, effectively preventing the solid core and PMMA microspheres from settling and agglomerating in the coating solution through the steric hindrance effect of its long chains, ensuring uniform coating. Simultaneously, PVP has a certain viscosity, which helps to "bond" and fix the gadolinium source precursor and PMMA microspheres to the core surface during solvent evaporation, forming a complete coating layer.

[0099] In step S3, the molar ratio of the sum of bismuth and tungsten elements in the core to the functional element for absorbing thermal neutrons in the shell of the core-shell precursor powder is (1~5):1, preferably (1~3):1; the porous shell contains at least one functional element for absorbing thermal neutrons, which may be one or more of samarium (Sm), gadolinium (Gd), europium (Eu), dysprosium (Dy), and boron (B), preferably gadolinium.

[0100] By limiting the molar ratio of bismuth, tungsten, and gadolinium within a certain range, the mass ratio of the core to the shell can be controlled, thereby achieving an optimized ratio of "main body shielding for X / γ rays" and "neutron-absorbing porous interface layer." Furthermore, the preparation process of this invention has good element compatibility, and the shell layer can be adapted to one or more elements with high thermal neutron absorption cross-sections, such as samarium (Sm), gadolinium (Gd), europium (Eu), dysprosium (Dy), and boron (B).

[0101] In step S4, the low-temperature sintering process is as follows: under an air atmosphere, the temperature is increased to 350-450℃ at a rate of 1-3℃ / min; the medium-temperature sintering process is as follows: the temperature is increased to 500-600℃ at a rate of 2-5℃ / min, and held at this temperature for 2-3 hours; the high-temperature sintering process is as follows: the temperature is increased to 800-850℃ at a rate of 3-5℃ / min, and held at this temperature for 1-3 hours, followed by natural cooling.

[0102] The core advantage and principle of the optimized multi-stage programmed sintering lies in the precise "staged temperature control" strategy, which synergistically achieves the stable formation of porous structures and the full crystallization of the shell material. The low-temperature stage employs a slow-to-medium heating rate followed by holding, which thoroughly decomposes the pore-forming agent and organic precursors, preventing rapid gas release that could lead to structural damage and thus stabilizing the formation of a porous framework. Subsequently, the high-temperature stage involves rapid heating followed by a short holding period, which promotes the full crystallization of the shell oxide to enhance strength. Simultaneously, strictly limiting the duration of the high temperature effectively inhibits pore closure caused by surface diffusion, ultimately achieving the design goal of a "porous shell."

[0103] This invention also provides an application of a core-shell porous structure ionizing radiation shielding powder, which is filled into a polymer substrate to prepare a flexible radiation-resistant composite film material. The polymer substrate can be one of silicone rubber, polyethylene, polymethyl methacrylate, or epoxy resin, preferably liquid silicone rubber.

[0104] The filling amount of ionizing radiation-resistant powder with a core-shell porous structure in the flexible radiation-resistant composite film material is 50-70%, preferably 60-65%, at which point the overall performance is better.

[0105] The ionizing radiation shielding powder with a core-shell porous structure of this invention can be widely used as a core functional filler in various radiation protection scenarios, such as nuclear waste packaging materials and radiation shielding plates in the nuclear industry, protective coatings for radiotherapy equipment and medical radiation protection clothing in medical scenarios, and radiation shielding layers for spacecraft cabins in the aerospace field. It can provide efficient and flexible material solutions for ionizing radiation protection in different scenarios.

[0106] It should be noted that the above embodiments are only for further elaboration and explanation of the technical solution of the present invention, and are not intended to further limit the technical solution of the present invention. The method of the present invention is only a preferred embodiment and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A radiation-shielding powder with a core-shell porous structure, characterized in that, It has a solid core of tungsten-bismuth composite oxide and a porous shell covering the solid core; The solid core of the tungsten-bismuth composite oxide is a microsphere prepared by hydrothermal reaction and pre-sintering of a precursor solution. The precursor solution is mainly prepared by mixing bismuth source, nitric acid, tungsten source and complexing agent. The porous shell is prepared by mixing the coating liquid with the solid microspheres of tungsten-bismuth composite oxide, stirring and evaporating the solvent, pre-drying and multi-stage programmed sintering. The coating liquid is mainly prepared by mixing thermal neutron-absorbing functional elements, pore-forming template agents and dispersants.

2. The ionizing radiation shielding powder with a core-shell porous structure according to claim 1, characterized in that, The bismuth source is selected from at least one of bismuth nitrate, bismuth chloride, bismuth citrate, and bismuth acetate; and / or The tungsten source is selected from at least one of ammonium metatungstate, sodium tungstate, and zinc tungstate; and / or The complexing agent is selected from at least one of citric acid, tartaric acid, oxalic acid, ethylenediaminetetraacetic acid, and gluconic acid.

3. The ionizing radiation shielding powder with a core-shell porous structure according to claim 1, characterized in that, The neutron-absorbing functional element is derived from a gadolinium source, a samarium source, or a dysprosium source, wherein the gadolinium source is selected from at least one of gadolinium nitrate, gadolinium chloride, and gadolinium acetate; and / or The pore-forming template agent is selected from at least one of polyethylene glycol, polymethyl methacrylate microspheres, polystyrene, and ammonium bicarbonate; and / or The dispersant is selected from at least one of polyvinylpyrrolidone, polyacrylic acid, and sodium hexametaphosphate.

4. The ionizing radiation shielding powder with a core-shell porous structure according to any one of claims 1 to 3, characterized in that, The molar ratio of bismuth to tungsten is (1~3): (1~3), and the molar ratio of the sum of bismuth and tungsten to the functional element that absorbs thermal neutrons is (1~5):

1.

5. The ionizing radiation shielding powder with a core-shell porous structure according to claim 4, characterized in that, The molar ratio of the sum of bismuth and tungsten elements to the functional elements for absorbing thermal neutrons is (2~3):

1.

6. A method for preparing an anti-ionizing radiation powder with a core-shell porous structure as described in any one of claims 1 to 5, characterized in that, Includes the following steps: A precursor solution mainly composed of bismuth source, nitric acid, tungsten source and complexing agent was prepared. The precursor solution was subjected to hydrothermal reaction, the product was washed by centrifugation, dried and pre-sintered to obtain solid microspheres of tungsten-bismuth composite oxide. An ethanol-water coating solution containing a functional element for absorbing thermal neutrons, a pore-forming template agent, and a dispersant was prepared. The ethanol-water coating solution was mixed with the solid microspheres of tungsten-bismuth composite oxide, the solvent was evaporated by stirring, and after drying, multi-stage programmed sintering was performed to obtain powder with a solid core and a porous shell of tungsten-bismuth composite oxide.

7. The method for preparing the ionizing radiation shielding powder with a core-shell porous structure according to claim 6, characterized in that, The precursor solution has a pH of 6-7, and the hydrothermal reaction parameters are: temperature 150-180 °C, duration 18-24 h; and / or The pre-sintering parameters are: heating rate 2~4℃ / min, heating to 500~650℃ and holding for 2~3h.

8. The method for preparing the anti-ionizing radiation powder with a core-shell porous structure according to claim 6, characterized in that, The parameters for the multi-stage programmed sintering are as follows: under an air atmosphere, the temperature is increased to 350-450℃ at a rate of 1-3℃ / min, then increased to 500-600℃ at a rate of 2-5℃ / min and held for 2-3 hours; then the temperature is increased to 800-850℃ at a rate of 3-5℃ / min and held for 1-3 hours.

9. A composite membrane, characterized in that, It is prepared by mixing the ionizing radiation-resistant powder with a core-shell porous structure as described in any one of claims 1 to 5 with a polymer.

10. The application of the ionizing radiation shielding powder with a core-shell porous structure as described in any one of claims 1 to 5 or the composite film as described in claim 9 in the preparation of radiation protection products.

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