High-thermal-conductivity hafnate-based neutron absorbing material as well as preparation method and application thereof

Abstract

The invention discloses a hafnate-based neutron absorbing material with high thermal conductivity and a preparation method and application thereof, the neutron absorbing material has a compact microscopic complex phase structure, and comprises a hafnate matrix phase, a modified whisker reinforced phase and a thermal conductive network; the hafnate matrix phase is used as a neutron absorption main body and is composed of a compound with a chemical formula of A2Hf2O7; wherein A is a rare earth element; the hafnate matrix phase has a defective fluorite structure or a pyrochlore structure; the modified whisker reinforced phase is dispersed in the hafnate matrix phase and is composed of composite whiskers with core-shell structures; the composite whisker takes a silicon carbide whisker as a core and a compact hafnium silicate layer as a shell, the modified whisker reinforced phase is dispersed at the grain boundary of the hafnate matrix phase, and at least part of the modified whiskers are in mutual contact or lap joint to form a continuous network structure; the performance of the material is remarkably improved by constructing a continuous heat conduction network, optimizing thermal expansion matching performance and blocking high-temperature interface reaction.

Description

Technical Field

[0001] This invention belongs to the field of nuclear energy structure and function integrated materials technology, specifically relating to a high thermal conductivity hafnium salt-based neutron absorbing material, its preparation method and application, which is particularly suitable for nuclear reactor control rods, neutron shielding components and structural components in extreme thermal environments. Background Technology

[0002] Rare-earth hafnium carbonate (RE2Hf2O7) ceramic materials are considered a new generation of long-life nuclear reactor control rods and neutron shielding materials due to their excellent neutron absorption cross section, high melting point, good chemical stability, and no helium release under irradiation. Hafnium carbonates are considered to have great potential as nuclear reactor control rods or shielding materials due to their excellent neutron absorption properties.

[0003] However, existing hafnium-based ceramic materials still face insurmountable bottlenecks in terms of both thermophysical properties and chemical compatibility when moving towards engineering applications: 1) Rare earth hafnium esters typically possess complex defective fluorite or pyrochlore crystal structures with strong lattice anharmonic vibrations and severe phonon scattering, resulting in extremely low intrinsic thermal conductivity (typically <2 W / (m·K)). Under high-energy neutron irradiation in reactors, the neutron capture reaction within the material generates a large amount of heat, causing a sharp increase in the core temperature, resulting in a huge thermal gradient and thermal stress. This can easily induce core cracking or even pulverization, seriously threatening the safe operation of the reactor. 2) To solve the thermal conductivity problem, the conventional approach is to add a highly thermally conductive second-phase material (such as silicon carbide SiC, diamond, or graphite) to the matrix. However, this simple composite method suffers from high-temperature interfacial reaction problems in hafnium ester systems. During high-temperature sintering (typically > 1500℃), high thermal conductivity reinforcing phases such as silicon carbide (SiC) are prone to severe interfacial chemical reactions with oxide matrices (hafnium salts or rare earth oxides), generating low-melting-point silicate glass phases or gaseous products (such as CO). This not only consumes the high thermal conductivity phase and destroys the density of the material, but also leads to a sharp decline in the mechanical properties of the material. 3) Thermal expansion mismatch problem: Hafnium ceramics typically have a high coefficient of thermal expansion (CTE) (approximately 10 × 10⁻⁶). -6 The CTE of commonly used high thermal conductivity reinforcing phases (such as SiC) is relatively low. This mismatch in thermal expansion coefficients can lead to microcracks at the phase interface during the severe temperature cycles of reactor start-up and shutdown, further blocking heat flow and reducing material strength.

[0004] Therefore, there is an urgent need to develop a new type of hafnium salt-based composite material system that can effectively suppress harmful interfacial reactions during high-temperature sintering and significantly improve thermal conductivity with a low addition amount, thereby achieving synergistic optimization of nuclear performance, thermophysical performance and mechanical performance. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a high thermal conductivity hafnium salt-based neutron absorber material, its preparation method, and its applications. This method significantly improves the thermal conductivity, mechanical properties, and chemical stability of the material by constructing a continuous thermally conductive network, optimizing thermal expansion matching, and blocking high-temperature interfacial reactions. It can be widely used in nuclear reactor control rods, neutron shielding materials, or structural components in extreme thermal environments to meet the requirements of demanding operating conditions.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a high thermal conductivity hafnium-based neutron absorbing material, wherein the high thermal conductivity hafnium-based neutron absorbing material has a dense microscopic multiphase structure, including a hafnium-based bulk phase, a modified whisker-reinforcing phase, and a thermally conductive network; Hafnium salt matrix phase: serving as the neutron absorber, composed of compounds with the chemical formula A2Hf2O7; wherein A is a rare earth element; the hafnium salt matrix phase has a defective fluorite structure or pyrochlore structure; Modified whisker-reinforced phase: dispersed in the hafnium salt matrix phase, composed of core-shell composite whiskers; the composite whiskers have silicon carbide whiskers as the core and a dense hafnium silicate layer as the shell; Thermally conductive network: The modified whisker-reinforced phase is dispersed at the grain boundaries of the hafnium salt matrix phase, and at least some of the modified whiskers are in contact with each other or overlap to form a continuous network structure.

[0007] Preferably, the rare earth element in the hafnium salt matrix phase is one or more of dysprosium, yttrium, gadolinium, samarium, or erbium.

[0008] Preferably, the rare earth element is a binary composite rare earth element combination formed by dysprosium and erbium, in which case the chemical formula of the rare earth hafnium salt is (Dy x Er 1-x )2Hf2O7; where x ranges from 0.3 to 0.7.

[0009] Preferably, the volume percentage of the modified whisker reinforcement phase in the high thermal conductivity hafnium salt-based neutron absorber is 5% to 25%; the shell thickness of the hafnium silicate layer is 10 nm to 200 nm; the hafnium silicate layer densely coats the surface of the silicon carbide whisker and forms a chemical metallurgical bond with the hafnium salt matrix phase; the silicon carbide whisker has an aspect ratio greater than 20 and a diameter of 0.1 μm to 2.0 μm.

[0010] A method for preparing a hafnium salt-based neutron absorber material with high thermal conductivity includes the following steps: S1. Surface activation pretreatment is performed on silicon carbide whiskers; The specific process of step S1 is as follows: S11. Pickling and impurity removal: Immerse the silicon carbide whiskers in a dilute hydrofluoric acid solution for ultrasonic cleaning to remove surface impurities, then wash with deionized water until neutral and dry. S12, Oxidation Activation: The dried silicon carbide whiskers are placed in a muffle furnace and heat-treated at 400 °C for 1.5 hours in an air atmosphere to introduce hydroxyl active sites on the surface of the silicon carbide whiskers to enhance subsequent sol adsorption. S2. Hafnium silicate precursor was prepared by a stepwise hydrolysis method; S3. A layer of hafnium silicate precursor was coated on the surface of pretreated silicon carbide whiskers using the sol-gel method, and modified whiskers were obtained after precursor conversion heat treatment. S4. The rare earth oxides and hafnium oxide raw material powders that make up the hafnium salt matrix are mixed with sintering aids by high-energy ball milling to obtain matrix precursor mixed powder; then the matrix precursor mixed powder is mixed with modified whiskers in a solvent, and the whiskers are deagglomerated and mixed by ultrasonic dispersion and wet flexible ball milling, and the composite powder is obtained after drying. S5. The composite powder is loaded into a mold and densified by spark plasma sintering or hot pressing at a temperature of 1500 ℃ ~ 1800 ℃ and a pressure of 30 MPa ~ 60 MPa. During the sintering process, the oxide raw material undergoes an in-situ reaction to generate a hafnium salt matrix phase, and the precursor layer on the modified whisker surface is transformed into a dense HfSiO4 interface layer, thus obtaining a dense hafnium salt-based neutron absorber material with high thermal conductivity.

[0011] Preferably, the specific process of step S2 is as follows: S21. Pre-hydrolysis of silicon source: Dissolve tetraethyl orthosilicate in anhydrous ethanol, add deionized water, and add hydrochloric acid dropwise to adjust the pH value to 2-3. Stir magnetically at room temperature for 1.5 hours to pre-hydrolyze tetraethyl orthosilicate and obtain silica sol. S22. Preparation of hafnium source solution: Weigh hafnium oxychloride and dissolve it in deionized water to obtain hafnium source solution; S23. Mixed Sol: Add the hafnium source solution dropwise into the pre-hydrolyzed silica sol, control the molar ratio of hafnium to silicon to be 1:1, and continue stirring for 30 minutes to obtain a uniform and transparent hafnium silicate precursor.

[0012] Preferably, the specific process of step S3 is as follows: S31. Dispersion: The silicon carbide whiskers pretreated in step S1 are added to the hafnium silicate precursor prepared in step S2 and ultrasonically dispersed to make the silicon carbide whiskers dispersed and suspended individually without agglomeration, thus obtaining a suspension. S32. Gelation: Under magnetic stirring, dilute ammonia is added dropwise to the suspension to adjust the pH value of the suspension to 7.5, so that hafnium and silicon hydroxides begin to co-precipitate and condensate on the surface of silicon carbide whiskers to form a gel layer. S33. Aging and Drying: After the gel layer is formed, stop stirring and let it stand for 12 hours to strengthen the gel network; then filter to separate the solid, wash it three times alternately with anhydrous ethanol and deionized water, and dry it in an oven at 90 ℃ for 12 hours to obtain the coated powder. S34. Precursor conversion heat treatment: The dried coated powder is placed in a tube furnace and heated to 900℃ under argon protection. It is held for 2 hours to convert the gel layer on the surface of silicon carbide whiskers into an amorphous or microcrystalline HfO2-SiO2 mixed oxide precursor layer, thus obtaining modified whiskers.

[0013] Preferably, in step S4, the sintering aid is a composite aid of niobium oxide and yttrium oxide; the total amount of the composite aid added is 0.5 wt% to 2.0 wt% of the mass of the matrix precursor mixed powder.

[0014] Preferably, in step S5, the densification sintering adopts unidirectional hot pressing sintering or directional discharge plasma sintering process, so that the preferred orientation direction of the modified whiskers is consistent with the dominant thermal direction of the material, and an anisotropic continuous thermally conductive network structure is constructed.

[0015] Application of a high thermal conductivity hafnium salt-based neutron absorber in nuclear reactor control rods, neutron shielding materials, or structural components in extreme thermal environments.

[0016] By adopting the above technical solution, the present invention has the following beneficial effects: 1. This invention introduces highly thermally conductive silicon carbide whiskers (SiC) into a hafnium salt matrix. w By precisely controlling its aspect ratio (L / D > 20) and volume fraction (5%-25%), a continuous, interconnected thermally conductive network was successfully constructed within a ceramic matrix with poor thermal conductivity. This structural design allows heat flow to be rapidly transferred along the low thermal resistance whisker framework, overcoming the shortcomings of traditional hafnium salt materials, such as severe phonon scattering and low intrinsic thermal conductivity. Compared to pure hafnium salt ceramics, the thermal conductivity of the composite material of this invention is significantly improved, effectively solving the problem of thermal accumulation in neutron absorbers during high-power operation in the reactor core and reducing the risk of thermal stress failure.

[0017] 2. This invention addresses the problem that hafnium salts have a high coefficient of thermal expansion and significant mismatch with the thermally conductive silicon carbide phase, which easily leads to interfacial thermal stress cracking. By introducing erbium (Er), which has a smaller ionic radius, the solid solution effect effectively reduces the lattice constant and coefficient of thermal expansion of the matrix, reduces the thermal mismatch stress between the matrix and the reinforcing phase, and significantly improves the thermal shock resistance and mechanical integrity of the material.

[0018] 3. This invention addresses the problem of material performance degradation caused by interfacial reactions (generating gaseous or low-melting-point phases) between silicon carbide and oxide matrices at high temperatures. It innovatively constructs a dense hafnium silicate (HfSiO4) shell in situ on the whisker surface. The HfSiO4 shell acts as a physical barrier, effectively blocking direct contact between SiC and the matrix, inhibiting harmful chemical reactions at high temperatures, and significantly improving the chemical stability of the material under extreme thermal environments. As an intermediate transition layer, HfSiO4 is tightly bonded to the SiC core and exhibits good chemical compatibility with the hafnium salt matrix, achieving a strong chemical metallurgical bond between the reinforcing phase and the matrix, thus avoiding the decline in mechanical properties caused by weak interfacial bonding.

[0019] 4. This invention utilizes the excellent mechanical properties of modified whiskers, employing multiple toughening mechanisms such as crack deflection, whisker bridging, and whisker pull-out to dissipate the energy required for crack propagation, significantly improving the fracture toughness and flexural strength of hafnium-based ceramics. This effectively overcomes the inherent brittleness and poor thermal shock resistance of the hafnium matrix, enabling it to withstand the severe mechanical and thermal shocks generated during emergency rod drops or power fluctuations in nuclear reactors. Furthermore, compared to randomly distributed whisker-reinforced structures, the preferentially oriented modified SiC whiskers form continuously overlapping, low-thermal-resistance channels along the dominant thermal direction within the matrix, facilitating rapid heat transfer in a specific direction. Simultaneously, this orientation structure can guide crack deflection or passivation in non-dominant thermal directions, further enhancing the material's structural stability and thermal shock resistance under high heat flux and thermal cycling conditions.

[0020] 5. In the preferred embodiment of this invention, a composite rare earth element of dysprosium (Dy) and erbium (Er) is used to construct the matrix. Both Dy and Er are high-cross-section neutron-absorbing elements, and their combination maintains the material's excellent neutron-trapping ability, extending the lifespan of the control rod. The lattice distortion and entropy stabilization effect caused by the difference in ionic radii between Dy and Er further stabilizes the pyrochlore phase structure, suppresses phase transitions at high temperatures, and ensures the material's volume stability and structural integrity throughout its entire lifespan. Attached Figure Description

[0021] Figure 1 The X-ray diffraction patterns of the composite hafnium salt materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention at room temperature are shown below. Figure 2These are scanning electron microscope images of the composite hafnium salt materials prepared in Examples 1, 1, 2 and 4 of this invention. Figure 3 This is a comparison graph showing the thermal conductivity of the composite hafnium salt materials of Examples 1-3 and Comparative Examples 1-3 as a function of temperature. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to examples. It should be understood that the specific examples described herein are merely illustrative and not intended to limit the invention.

[0023] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0024] See Figures 1 to 3 . Example 1

[0025] This embodiment prepares a (Dy) 0.5 Er 0.5 The specific steps are as follows: A hafnium bicarbonate matrix of 2Hf2O7 and a whisker-reinforced composite material with a volume percentage of 15% HfSiO4@SiC modified crystals. Step 1: Surface activation pretreatment of silicon carbide whiskers. Silicon carbide whiskers (SiC) with a diameter of 0.5 μm and an aspect ratio of 30 were selected. w ): 1) Acid washing to remove impurities: Immerse the silicon carbide whiskers in a dilute hydrofluoric acid (HF) solution and ultrasonically clean for 20 minutes to remove surface impurities. Then wash with deionized water until neutral and dry. 2) Oxidation activation: The dried silicon carbide whiskers are placed in a muffle furnace and heat-treated at 400 °C for 1.5 hours in an air atmosphere. This step introduces hydroxyl (-OH) active sites on the surface of the silicon carbide whiskers to enhance subsequent sol adsorption.

[0026] Step 2: Prepare hafnium silicate (HfSiO4) precursor using a stepwise hydrolysis method. 1) Pre-hydrolysis of silicon source: Dissolve tetraethyl orthosilicate (TEOS) in anhydrous ethanol, add a small amount of deionized water, and add hydrochloric acid dropwise to adjust the pH value to 2-3. Stir magnetically at room temperature for 1.5 hours to allow the tetraethyl orthosilicate (TEOS) to undergo pre-hydrolysis to obtain silica sol (since the hydrolysis rate of silicon is slower than that of hafnium, pre-hydrolysis can balance the reaction rates of the two). 2) Hafnium source solution: Weigh hafnium oxychloride (HfOCl2·8H2O) and dissolve it in deionized water to obtain the hafnium source solution; 3) Mixing sol: Slowly drop the hafnium source solution into the pre-hydrolyzed silica sol, control the molar ratio of hafnium to silicon to be 1:1, and continue stirring for 30 minutes to obtain a uniform and transparent hafnium silicate precursor.

[0027] Step 3: A layer of hafnium silicate precursor is coated onto the surface of the pretreated silicon carbide whiskers using the sol-gel method. After heat treatment of the precursor conversion, modified whiskers are obtained. 1) Dispersion: The silicon carbide whiskers (SiC) pretreated in step 1 are dispersed. w Add it to the hafnium silicate precursor prepared in step 2 and perform high-power ultrasonic dispersion for 40 minutes to make the silicon carbide whiskers dispersed and suspended individually without agglomeration, thus obtaining a suspension. 2) Gelation: Under magnetic stirring, dilute ammonia (NH3·H2O) is slowly added dropwise to the suspension to adjust the pH of the solution to 7.5. At this time, hafnium and silicon hydroxides begin to co-precipitate and condensate on the surface of the whiskers to form a gel layer. 3) Aging and drying: After the gel layer is formed, stop stirring and let it stand for 12 hours to strengthen the gel network; then filter to separate the solid, wash it three times alternately with anhydrous ethanol and deionized water, and dry it in an oven at 90 ℃ for 12 hours to obtain the coated powder. 4) Precursor conversion heat treatment: The dried coated powder is placed in a tube furnace and heated to 900 ℃ under argon protection and held for 2 hours. At this time, the gel layer on the surface of silicon carbide whiskers is converted into an amorphous or microcrystalline HfO2-SiO2 mixed oxide precursor layer to obtain modified whiskers.

[0028] Step 4: Preparation of composite powder 1) Matrix ingredients: according to (Dy 0.5 Er 0.5 To obtain the matrix precursor mixed powder, dysprosium oxide (Dy2O3), erbium oxide (Er2O3), and hafnium oxide (HfO2) powders were weighed according to the stoichiometric ratio of 2Hf2O7. 1.0 wt% of Nb2O5-Y2O3 composite sintering aid was added, wherein the ratio of Nb2O5 to Y2O3 was 1:1. The mixture was then subjected to high-energy ball milling for 10 hours with a ball-to-material ratio of 10:1, a filling coefficient of 0.5, and a ball milling speed of 500 rpm to obtain the matrix precursor mixed powder.

[0029] 2) Mixing: The modified whiskers and matrix precursor powder were mixed in ethanol medium at a volume ratio (modified whiskers account for 15%). After ultrasonic dispersion, the mixture was wet ball-milled for 4 hours at a ball-to-material ratio of 5:1, a filling coefficient of 0.5, and a ball milling speed of 150 rpm. The powder was then dried and sieved to obtain the composite powder. Step 5: Reaction Sintering The composite powder was loaded into a graphite mold and subjected to spark plasma sintering (SPS) at a temperature of 1650°C and a pressure of 40 MPa for 10 minutes to obtain a dense hafnium salt-based neutron absorber.

[0030] Mechanism explanation: During the high-temperature sintering process at 1650℃, the matrix oxide reacts to generate (Dy) 0.5 Er 0.5 The 2Hf2O7 phase is formed; at the same time, the HfO2-SiO2 precursor layer on the whisker surface undergoes an in-situ reaction (HfO2 + SiO2 → HfSiO4), transforming into a dense hafnium silicate (HfSiO4) crystal shell. Example 2

[0031] This embodiment prepares a high thermal conductivity composite material with a single rare earth hafnium salt matrix and a modified whisker volume percentage of 20%.

[0032] Material composition: 1) Matrix phase: Dysprosium hafnium salt with the chemical formula Dy2Hf2O7; 2) Reinforcing phase: HfSiO4@SiC modified whiskers with a core-shell structure, which account for 20% of the volume percentage in the composite material.

[0033] Preparation steps: Step 1: Surface activation pretreatment of silicon carbide whiskers, selecting silicon carbide whiskers with a diameter of 0.1 μm to 2.0 μm and an aspect ratio of 25: 1) Acid washing to remove impurities: Immerse the silicon carbide whiskers in a dilute hydrofluoric acid (HF) solution and ultrasonically clean for 20 minutes to remove surface impurities. Then wash with deionized water until neutral and dry. 2) Oxidation activation: The dried silicon carbide whiskers are placed in a muffle furnace and heat-treated at 400 °C for 1.5 hours in an air atmosphere. This step introduces hydroxyl (-OH) active sites on the surface of the silicon carbide whiskers to enhance subsequent sol adsorption.

[0034] Step 2: Prepare hafnium silicate (HfSiO4) precursor using a stepwise hydrolysis method. 1) Pre-hydrolysis of silicon source: Dissolve tetraethyl orthosilicate (TEOS) in anhydrous ethanol, add a small amount of deionized water, and add hydrochloric acid dropwise to adjust the pH to 2-3. Stir magnetically at room temperature for 1.5 hours to allow the tetraethyl orthosilicate (TEOS) to undergo pre-hydrolysis to obtain silica sol (since the hydrolysis rate of silicon is slower than that of hafnium, pre-hydrolysis can balance the reaction rates of the two). 2) Hafnium source solution: Weigh hafnium oxychloride (HfOCl2·8H2O) and dissolve it in deionized water to obtain the hafnium source solution; 3) Mixing sol: Slowly drop the hafnium source solution into the pre-hydrolyzed silica sol, control the molar ratio of hafnium to silicon to be 1:1, and continue stirring for 30 minutes to obtain a uniform and transparent hafnium silicate precursor.

[0035] Step 3: A layer of hafnium silicate precursor is coated onto the surface of the pretreated silicon carbide whiskers using the sol-gel method. After heat treatment of the precursor conversion, modified whiskers are obtained. 1) Dispersion: The silicon carbide whiskers (SiC) pretreated in step 1 are dispersed. w Add it to the hafnium silicate precursor prepared in step 2 and perform high-power ultrasonic dispersion for 40 minutes to make the silicon carbide whiskers dispersed and suspended individually without agglomeration, thus obtaining a suspension. 2) Gelation: Under magnetic stirring, dilute ammonia (NH3·H2O) is slowly added dropwise to the suspension to adjust the pH of the solution to 7.5. At this time, hafnium and silicon hydroxides begin to co-precipitate and condensate on the surface of the whiskers to form a gel layer. 3) Aging and drying: After the gel layer is formed, stop stirring and let it stand for 12 hours to strengthen the gel network; then filter to separate the solid, wash it three times alternately with anhydrous ethanol and deionized water, and dry it in an oven at 90 ℃ for 12 hours to obtain the coated powder. 4) Precursor conversion heat treatment: The dried coated powder is placed in a tube furnace and heated to 900 ℃ under argon protection and held for 2 hours. At this time, the gel layer on the surface of silicon carbide whiskers is converted into an amorphous or microcrystalline HfO2-SiO2 mixed oxide precursor layer to obtain modified whiskers.

[0036] Step 4: Preparation of composite powder 1) Matrix formulation: Weigh dysprosium oxide (Dy2O3) and hafnium oxide (HfO2) powders according to the stoichiometric ratio of Dy2Hf2O7, add 1.0 wt% of Nb2O5-Y2O3 composite sintering aid, wherein the ratio of Nb2O5 to Y2O3 is 1:1, and perform high-energy ball milling for 10 hours with a ball-to-material ratio of 10:1, a filling coefficient of 0.5, and a ball milling speed of 500 rpm to obtain matrix precursor mixed powder.

[0037] 2) Mixing: The modified whiskers and matrix precursor powder were mixed in ethanol medium at a volume ratio (modified whiskers account for 20%). After ultrasonic dispersion, the mixture was wet ball-milled for 4 hours at a ball-to-material ratio of 5:1, a filling coefficient of 0.5, and a ball milling speed of 150 rpm. The powder was then dried and sieved to obtain the composite powder. Step 5: Reaction Sintering The composite powder was loaded into a graphite mold and subjected to spark plasma sintering (SPS) at a temperature of 1650°C and a pressure of 40 MPa for 10 minutes to obtain a dense hafnium salt-based neutron absorber. Example 3

[0038] In this embodiment, a composite material with a samarium hafnium salt matrix and a modified whisker volume percentage of 10% was prepared to verify the universality of the technical solution.

[0039] Material composition: 1) Matrix phase: Dysprosium hafnium salt with the chemical formula Sm2Hf2O7; 2) Reinforcing phase: HfSiO4@SiC modified whiskers with a core-shell structure, which account for 10% of the volume percentage in the composite material.

[0040] Preparation steps: Step 1: Surface activation pretreatment of silicon carbide whiskers, selecting silicon carbide whiskers with a diameter of 0.1 μm to 2.0 μm and an aspect ratio of 25: 1) Acid washing to remove impurities: Immerse the silicon carbide whiskers in a dilute hydrofluoric acid (HF) solution and ultrasonically clean for 20 minutes to remove surface impurities. Then wash with deionized water until neutral and dry. 2) Oxidation activation: The dried silicon carbide whiskers are placed in a muffle furnace and heat-treated at 400 °C for 1.5 hours in an air atmosphere. This step introduces hydroxyl (-OH) active sites on the surface of the silicon carbide whiskers to enhance subsequent sol adsorption.

[0041] Step 2: Prepare hafnium silicate (HfSiO4) precursor using a stepwise hydrolysis method. 1) Pre-hydrolysis of silicon source: Dissolve tetraethyl orthosilicate (TEOS) in anhydrous ethanol, add a small amount of deionized water, and add hydrochloric acid dropwise to adjust the pH to 2-3. Stir magnetically at room temperature for 1.5 hours to allow the tetraethyl orthosilicate (TEOS) to undergo pre-hydrolysis to obtain silica sol (since the hydrolysis rate of silicon is slower than that of hafnium, pre-hydrolysis can balance the reaction rates of the two). 2) Hafnium source solution: Weigh hafnium oxychloride (HfOCl2·8H2O) and dissolve it in deionized water to obtain the hafnium source solution; 3) Mixing sol: Slowly drop the hafnium source solution into the pre-hydrolyzed silica sol, control the molar ratio of hafnium to silicon to be 1:1, and continue stirring for 30 minutes to obtain a uniform and transparent hafnium silicate precursor.

[0042] Step 3: A layer of hafnium silicate precursor is coated onto the surface of the pretreated silicon carbide whiskers using the sol-gel method. After heat treatment of the precursor conversion, modified whiskers are obtained. 1) Dispersion: The silicon carbide whiskers (SiC) pretreated in step 1 are dispersed. w Add it to the hafnium silicate precursor prepared in step 2 and perform high-power ultrasonic dispersion for 40 minutes to make the silicon carbide whiskers dispersed and suspended individually without agglomeration, thus obtaining a suspension. 2) Gelation: Under magnetic stirring, dilute ammonia (NH3·H2O) is slowly added dropwise to the suspension to adjust the pH of the solution to 7.5. At this time, hafnium and silicon hydroxides begin to co-precipitate and condensate on the surface of the whiskers to form a gel layer. 3) Aging and drying: After the gel layer is formed, stop stirring and let it stand for 12 hours to strengthen the gel network; then filter to separate the solid, wash it three times alternately with anhydrous ethanol and deionized water, and dry it in an oven at 90 ℃ for 12 hours to obtain the coated powder. 4) Precursor conversion heat treatment: The dried coated powder is placed in a tube furnace and heated to 900 ℃ under argon protection and held for 2 hours. At this time, the gel layer on the surface of silicon carbide whiskers is converted into an amorphous or microcrystalline HfO2-SiO2 mixed oxide precursor layer to obtain modified whiskers.

[0043] Step 4: Preparation of composite powder 1) Matrix formulation: Weigh samarium oxide (Sm2O3) and hafnium oxide (HfO2) powders according to the stoichiometric ratio of Sm2Hf2O7, add 1.0 wt% of Nb2O5-Y2O3 composite sintering aid, wherein the ratio of Nb2O5 to Y2O3 is 1:1, and perform high-energy ball milling for 10 hours with a ball-to-material ratio of 10:1, a filling coefficient of 0.5, and a ball milling speed of 500 rpm to obtain matrix precursor mixed powder.

[0044] 2) Mixing: The modified whiskers and matrix precursor powder were mixed in ethanol medium at a volume ratio (modified whiskers account for 10%). After ultrasonic dispersion, the mixture was wet ball-milled for 4 hours at a ball-to-material ratio of 5:1, a filling coefficient of 0.5, and a ball milling speed of 150 rpm. The powder was then dried and sieved to obtain the composite powder. Step 5: Reaction Sintering The composite powder was loaded into a graphite mold and subjected to spark plasma sintering (SPS) at a temperature of 1650°C and a pressure of 40 MPa for 10 minutes to obtain a dense hafnium salt-based neutron absorber.

[0045] Comparative Example 1 (Blank Control) The comparative example prepares pure dual-rare-earth hafnium salt ceramics without whisker-reinforcing phases. The specific steps are as follows: Step 1: Matrix Preparation Press (Dy) 0.5 Er 0.5 To prepare 2Hf2O7, accurately weigh dysprosium oxide (Dy2O3), erbium oxide (Er2O3), and hafnium oxide (HfO2) raw material powders, and add 1.0 wt% of Nb2O5-Y2O3 composite sintering aid (where the mass ratio of Nb2O5 to Y2O3 is 1:1) to the raw materials.

[0046] Step 2: High-energy ball milling and mixing The above ingredients were placed in a ball mill jar and mixed at a ball-to-material ratio of 10:1 and a filling coefficient of 0.5 for 10 hours at a speed of 500 rpm to obtain a uniform matrix precursor mixed powder.

[0047] Step 3: Sintering and densification The dried matrix precursor mixture powder was directly loaded into a graphite mold and densified by spark plasma sintering (SPS). The sintering temperature was set at 1650℃, the sintering pressure at 40MPa, and the holding time at 10 minutes, finally yielding pure dual rare earth hafnium salt ceramic material.

[0048] Comparative Example 2 (Control without coating layer) In this comparative example, a composite material containing 15 vol% unmodified silicon carbide whiskers was prepared to verify the role of the coating layer. The specific steps are as follows: Step 1: Surface pretreatment of silicon carbide whiskers (purification and activation only, no coating) Silicon carbide whiskers (SiC) with a diameter of 0.5 μm and an aspect ratio of 30 were selected. w The following preprocessing steps are performed: Acid washing to remove impurities: Immerse silicon carbide whiskers in dilute hydrofluoric acid (HF) solution and ultrasonically clean for 20 minutes to remove surface impurities. Then wash repeatedly with deionized water until the washing solution is neutral, and then dry. Oxidation activation: The dried silicon carbide whiskers are placed in a muffle furnace and heat-treated at 400°C for 1.5 hours in air atmosphere to introduce hydroxyl (-OH) active sites on the surface of the silicon carbide whiskers, thus completing the pretreatment (without subsequent sol-gel coating and calcination treatment).

[0049] Step 2: Mixing the matrix ingredients with high-energy ball milling Press (Dy) 0.5 Er 0.5 To prepare the matrix precursor mixture, dysprosium oxide (Dy2O3), erbium oxide (Er2O3), and hafnium oxide (HfO2) powders were weighed out according to their stoichiometric ratio. 1.0 wt% of Nb2O5-Y2O3 composite sintering aid (Nb2O5 to Y2O3 mass ratio 1:1) was added. The mixture was then placed in a ball mill jar and subjected to high-energy ball milling at 500 rpm for 10 hours with a ball-to-material ratio of 10:1, a filling factor of 0.5, and a ball-to-material ratio of 0.5, to obtain the matrix precursor mixed powder.

[0050] Step 3: Preparation of composite powder The uncoated silicon carbide whiskers pretreated in step 1 were mixed with the matrix precursor powder at a volume ratio of 15:85 (uncoated silicon carbide whiskers accounted for 15 vol%) in ethanol medium. The mixture was first ultrasonically dispersed for 40 minutes with high power, and then wet ball milled for 4 hours with a ball-to-material ratio of 5:1, a filling factor of 0.5, and 150 rpm. The mixture was then dried and sieved to obtain the composite powder.

[0051] Step 4: Sintering and densification The composite powder was loaded into a graphite mold and sintered using a spark plasma sintering (SPS) process at 1650°C and 40MPa pressure for 10 minutes to obtain a composite material containing unmodified silicon carbide whiskers.

[0052] Comparative Example 3 (Reinforced Phase Morphology Comparison) This comparative example uses silicon carbide particles (SiC). p To verify the role of high aspect ratio whiskers in the construction of thermal conductive networks, a replacement for silicon carbide whiskers was used. The specific steps are as follows: Step 1: Surface coating treatment of silicon carbide particles Silicon carbide particles (SiC) with an average particle size of 0.5 μm were selected. p The HfSiO4 sol-gel coating and heat treatment were carried out according to the following procedure: Acid washing to remove impurities: Immerse silicon carbide particles in dilute hydrofluoric acid (HF) solution and ultrasonically clean for 20 minutes to remove surface impurities. Wash with deionized water until neutral and then dry. Oxidative activation: The dried silicon carbide particles are placed in a muffle furnace and heat-treated at 400°C for 1.5 hours in air atmosphere to introduce hydroxyl active sites; Preparation of hafnium silicate precursor: A stepwise hydrolysis method was adopted. First, tetraethyl orthosilicate (TEOS) was dissolved in anhydrous ethanol, a small amount of deionized water was added, and hydrochloric acid was added dropwise to adjust the pH value to 2-3. The mixture was magnetically stirred at room temperature for 1.5 hours to obtain silica sol for pre-hydrolysis. Then, hafnium oxychloride (HfOCl2·8H2O) was weighed and dissolved in deionized water to prepare a hafnium source solution. The hafnium source solution was slowly added dropwise to the silica sol, controlling the molar ratio of hafnium to silicon to be 1:1. The mixture was stirred for another 30 minutes to obtain a uniform and transparent hafnium silicate precursor. Sol-gel coating: Oxidized and activated silicon carbide particles were added to hafnium silicate precursor and dispersed by high-power ultrasonication for 40 minutes to achieve uniform suspension; dilute ammonia was slowly added dropwise under magnetic stirring to adjust the pH to 7.5, causing hafnium and silicon hydroxides to co-precipitate and condense on the particle surface to form a gel layer; after standing and aging for 12 hours, the solid was separated by filtration, washed three times alternately with anhydrous ethanol and deionized water, and dried in a 90℃ oven for 12 hours to obtain coated powder; Precursor conversion heat treatment: The coated powder is placed in a tube furnace and heated to 900℃ under argon protection and held for 2 hours to convert the gel layer on the particle surface into an amorphous or microcrystalline HfO2-SiO2 mixed oxide precursor layer, thus obtaining modified silicon carbide particles.

[0053] Step 2: Mixing the matrix ingredients with high-energy ball milling Press (Dy) 0.5 Er 0.5 To prepare the matrix precursor powder, dysprosium oxide (Dy2O3), erbium oxide (Er2O3), and hafnium oxide (HfO2) powders were weighed out according to their stoichiometric ratio. 1.0 wt% of Nb2O5-Y2O3 composite sintering aid (Nb2O5 to Y2O3 mass ratio 1:1) was added. The mixture was placed in a ball mill jar and ball-milled at 500 rpm for 10 hours with a ball-to-material ratio of 10:1, a filling factor of 0.5, to obtain the matrix precursor mixed powder.

[0054] Step 3: Preparation of composite powder Modified silicon carbide particles and matrix precursor mixed powder were mixed in ethanol medium at a volume ratio of 15:85 (modified silicon carbide particles accounted for 15 vol%). The mixture was first ultrasonically dispersed for 40 minutes, and then wet ball milled for 4 hours at a ball-to-material ratio of 5:1, a filling coefficient of 0.5, and 150 rpm. After drying and sieving, the composite powder was obtained.

[0055] Step 4: Sintering and densification The composite powder was loaded into a graphite mold and sintered using a spark plasma sintering (SPS) process at 1650°C and 40MPa pressure for 10 minutes to obtain a composite material with silicon carbide particles as the reinforcing phase.

[0056] Comparative Example 4 (Orientation Distribution Control) This comparative study prepared a composite material with randomly distributed whiskers to verify the effect of preferred orientation on thermal conductivity. The specific steps are as follows: Step 1: Surface activation pretreatment of silicon carbide whiskers Silicon carbide whiskers (SiC) with a diameter of 0.5 μm and an aspect ratio of 30 were selected. w ): Acid washing to remove impurities: Immerse silicon carbide whiskers in dilute hydrofluoric acid (HF) solution and ultrasonically clean for 20 minutes to remove surface impurities. Wash with deionized water until neutral and then dry. Oxidation activation: The dried silicon carbide whiskers are placed in a muffle furnace and heat-treated at 400°C for 1.5 hours in air atmosphere to introduce hydroxyl (-OH) active sites.

[0057] Step 2: Preparation of hafnium silicate precursor Stepwise hydrolysis method is adopted: Pre-hydrolysis of silicon source: Measure out tetraethyl orthosilicate (TEOS) and dissolve it in anhydrous ethanol. Add a small amount of deionized water and add hydrochloric acid to adjust the pH value to 2-3. Stir magnetically at room temperature for 1.5 hours to obtain silica sol. Hafnium source solution preparation: Weigh hafnium oxychloride (HfOCl2·8H2O) and dissolve it in deionized water to obtain the hafnium source solution; Mixed sol: The hafnium source solution was slowly dripped into the silica sol, the molar ratio of hafnium to silicon was controlled at 1:1, and the mixture was stirred for 30 minutes to obtain a uniform and transparent hafnium silicate precursor.

[0058] Step 3: Preparation of modified whiskers Dispersion: The silicon carbide whiskers pretreated in step 1 are added to the hafnium silicate precursor and dispersed by high-power ultrasonication for 40 minutes to make the whiskers dispersed and suspended without agglomeration, thus obtaining a suspension. Gelation: Dilute ammonia water is added dropwise to the suspension under magnetic stirring to adjust the pH value to 7.5, so that hafnium and silicon hydroxides co-precipitate and condense on the surface of the whiskers to form a gel layer; Aging and drying: Let stand for 12 hours, filter to separate the solid, wash with anhydrous ethanol and deionized water three times alternately, and dry in a 90℃ oven for 12 hours to obtain coated powder. Precursor conversion heat treatment: The coated powder is placed in a tube furnace and held at 900℃ for 2 hours under argon protection to convert the gel layer into an amorphous or microcrystalline HfO2-SiO2 mixed oxide precursor layer, thus obtaining modified whiskers.

[0059] Step 4: Preparation of composite powder Matrix ingredients: according to (Dy 0.5 Er 0.5 )2Hf2O7 stoichiometrically weigh dysprosium oxide (Dy2O3), erbium oxide (Er2O3) and hafnium oxide (HfO2) powders, add 1.0 wt% Nb2O5-Y2O3 composite sintering aid (Nb2O5 to Y2O3 mass ratio 1:1), and mix with high-energy ball milling at parameters of ball-to-material ratio 10:1, filling coefficient 0.5 and 500 rpm for 10 hours to obtain matrix precursor mixed powder; Mixing: The modified whiskers and matrix precursor powder were mixed in ethanol medium at a volume ratio of 15:85 (modified whiskers accounted for 15 vol%). After ultrasonic dispersion for 40 minutes, the mixture was wet ball-milled at 150 rpm for 4 hours with a ball-to-material ratio of 5:1 and a filling coefficient of 0.5. The mixture was then dried and sieved to obtain the composite powder.

[0060] Step 5: Shaping and Sintering Cold isostatic pressing: The composite powder is placed in a mold and pressed into shape under a pressure of 200MPa using the cold isostatic pressing (CIP) process; Pressureless sintering: The formed blank is placed in an atmospheric pressure argon atmosphere furnace for pressureless sintering at a sintering temperature of 1650℃ and held for 2 hours to finally obtain a composite material with randomly distributed whiskers.

[0061] Performance Testing and Result Analysis 1. Physical property tests were performed on the materials prepared in the above embodiments and comparative examples: (1) The fracture toughness and flexural strength of the material were tested in accordance with the relevant requirements of ISO 14704:2016 Fine ceramics (advanced ceramics, advanced industrial ceramics) - Test method for flexural strength of monolithic ceramics at room temperature.

[0062] (2) The thermal diffusivity of the material was tested in accordance with the relevant requirements of the national standard GB / T 22588-2008 "Measurement of Thermal Diffusivity or Thermal Conductivity by Flash Method". Table 1 shows the key performance test results of each embodiment and comparative example.

[0063] Table 1: Comparison of key performance characteristics of each embodiment and comparative example sample Density (%) Thermal conductivity at 25℃ (W / m·K) Thermal conductivity 800℃ (W / m·K) Bending strength (MPa) Example 1 96.5 7.68 4.52 323 Example 2 96.8 7.80 4.65 355 Example 3 96.6 7.21 4.25 301 Comparative Example 1 97.5 2.15 1.78 153 Comparative Example 2 88.5 3.54 2.98 162 Comparative Example 3 95.2 5.49 3.35 216 Comparative Example 4 95.5 6.05 3.72 309 2. Results Analysis: Depend on Figure 1 The XRD patterns show that a stable pyrochlore solid solution structure was successfully synthesized in Comparative Example 1, with no impurity phase formation. In Example 1, in addition to the main crystalline phase diffraction peaks of the matrix, characteristic peaks of silicon carbide (SiC) were also detected. Notably, no obvious impurity peaks were detected. This indicates that the HfSiO4 coating layer exhibits excellent chemical stability during high-temperature sintering, successfully blocking the diffusion reaction between SiC and the oxide matrix, and preserving the original characteristics of the reinforcing phase and the matrix. In the XRD pattern of Comparative Example 2, in addition to the peaks of the matrix and SiC, disordered secondary phase diffraction peaks were clearly observed. This is because, due to the lack of an HfSiO4 protective layer, SiC and the matrix underwent a violent interfacial chemical reaction at 1650℃, generating low-melting-point silicides or oxide impurities, which directly undermines the structural integrity of the material.

[0064] Figure 2 The SEM images show ( Figure 2In the examples (a) Comparative Example 1, (b) Comparative Example 1, (c) Comparative Example 2, and (d) Comparative Example 4), the material prepared in Example 1 has a dense structure (density 96.5%), with whiskers uniformly dispersed in the matrix and exhibiting a clear preferred orientation (perpendicular to the SPS hot pressing direction). The material prepared in Comparative Example 2 has a loose and porous structure (density only 88.5%), and the matrix surface is severely eroded, with a large number of voids and pores left by the reaction at the interface. This damaged interface cannot transfer loads, and the pores become stress concentration points, leading to a sharp decline in mechanical and thermal properties. Compared to Example 1, in the material prepared by Comparative Example 4 using cold isostatic pressing, the SiC whiskers are randomly distributed. Although the density is acceptable, it fails to form efficient thermal conduction channels with continuous overlap along a specific direction, similar to the material prepared in Example 1. Therefore, its thermal conductivity (6.05 W / m·K) is significantly lower than that of the material prepared in Example 1 (7.68 W / m·K).

[0065] Compared with Comparative Example 1, Examples 1-3 showed significant improvements in thermal conductivity and flexural strength, demonstrating the effectiveness of introducing a high thermal conductivity whisker reinforcing phase.

[0066] Compared to Comparative Example 2, Example 1 exhibits higher density and mechanical properties. In Comparative Example 2, the lack of an HfSiO4 interface layer led to severe interfacial reactions between SiC and the matrix at high temperatures, resulting in porosity and brittle phases, thus degrading performance.

[0067] Compared with Comparative Example 3, the whisker reinforcement effect in Example 1 is significantly better than that of particle reinforcement. This is because whiskers with a high aspect ratio can more effectively overlap in the matrix to form heat conduction pathways and exert toughening mechanisms such as whisker pull-out and bridging.

[0068] Compared to Comparative Example 4, Example 1, which uses SPS sintering, exhibits a significantly higher thermal conductivity than Comparative Example 4, which uses a random distribution. This indicates that the pressure field during SPS sintering induces a preferred orientation of the whiskers in the direction perpendicular to the pressure (in-plane), thereby constructing a highly efficient thermally conductive network in that direction.

[0069] The flexural strength of Example 1 (323 MPa) is significantly higher than that of the pure matrix in Comparative Example 1 (153 MPa). This is attributed to the high aspect ratio modified SiC whiskers playing a toughening role during crack propagation through crack deflection, whisker bridging, and whisker pull-out mechanisms, thus consuming fracture energy. Meanwhile, Example 1 also outperforms the particle-reinforced Comparative Example 3 (216 MPa), demonstrating the advantage of one-dimensional whisker morphology in toughening.

[0070] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A hafnium salt-based neutron absorber material with high thermal conductivity, characterized in that, The high thermal conductivity hafnium-based neutron absorber material has a dense microscopic multiphase structure, including a hafnium-based bulk phase, a modified whisker-reinforced phase, and a thermally conductive network. Hafnium salt matrix phase: serving as the neutron absorber, composed of compounds with the chemical formula A2Hf2O7; wherein A is a rare earth element; the hafnium salt matrix phase has a defective fluorite structure or pyrochlore structure; Modified whisker-reinforced phase: dispersed in the hafnium salt matrix phase, composed of core-shell composite whiskers; the composite whiskers have silicon carbide whiskers as the core and a dense hafnium silicate layer as the shell; Thermally conductive network: The modified whisker-reinforced phase is dispersed at the grain boundaries of the hafnium salt matrix phase, and at least some of the modified whiskers are in contact with each other or overlap to form a continuous network structure.

2. The hafnium salt-based neutron absorber material as described in claim 1, characterized in that: The rare earth element in the hafnium salt matrix phase is one or more of dysprosium, yttrium, gadolinium, samarium, or erbium.

3. The hafnium salt-based neutron absorber material as described in claim 2, characterized in that: The rare earth element is a binary composite rare earth element combination formed by dysprosium and erbium, and the chemical formula of the rare earth hafnium salt is (Dy x Er 1-x )2Hf2O7; where x ranges from 0.3 to 0.

7.

4. The hafnium salt-based neutron absorber material as described in claim 1, characterized in that: The modified whisker reinforcement phase has a volume percentage of 5% to 25% in the high thermal conductivity hafnium salt-based neutron absorber; the shell thickness of the hafnium silicate layer is 10 nm to 200 nm; the hafnium silicate layer densely coats the surface of the silicon carbide whisker and forms a chemical metallurgical bond with the hafnium salt matrix phase; the silicon carbide whisker has an aspect ratio greater than 20 and a diameter of 0.1 μm to 2.0 μm.

5. A method for preparing a hafnium salt-based neutron absorber material as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Surface activation pretreatment is performed on silicon carbide whiskers; The specific process of step S1 is as follows: S11. Pickling and impurity removal: Immerse the silicon carbide whiskers in a dilute hydrofluoric acid solution for ultrasonic cleaning to remove surface impurities, then wash with deionized water until neutral and dry. S12, Oxidation Activation: The dried silicon carbide whiskers are placed in a muffle furnace and heat-treated at 400 °C for 1.5 hours in an air atmosphere to introduce hydroxyl active sites on the surface of the silicon carbide whiskers to enhance subsequent sol adsorption. S2. Hafnium silicate precursor was prepared by a stepwise hydrolysis method; S3. A layer of hafnium silicate precursor was coated on the surface of pretreated silicon carbide whiskers using the sol-gel method, and modified whiskers were obtained after precursor conversion heat treatment. S4. The rare earth oxides and hafnium oxide raw material powders that make up the hafnium salt matrix are mixed with sintering aids by high-energy ball milling to obtain matrix precursor mixed powder; then the matrix precursor mixed powder is mixed with modified whiskers in a solvent, and the whiskers are deagglomerated and mixed by ultrasonic dispersion and wet flexible ball milling, and the composite powder is obtained after drying. S5. The composite powder is loaded into a mold and densified by spark plasma sintering or hot pressing at a temperature of 1500 ℃ ~ 1800 ℃ and a pressure of 30 MPa ~ 60 MPa. During the sintering process, the oxide raw material undergoes an in-situ reaction to generate a hafnium salt matrix phase, and the precursor layer on the modified whisker surface is transformed into a dense HfSiO4 interface layer, thus obtaining a dense hafnium salt-based neutron absorber material with high thermal conductivity.

6. The method for preparing a hafnium salt-based neutron absorber material as described in claim 5, characterized in that, The specific process of step S2 is as follows: S21. Pre-hydrolysis of silicon source: Dissolve tetraethyl orthosilicate in anhydrous ethanol, add deionized water, and add hydrochloric acid dropwise to adjust the pH value to 2-3. Stir magnetically at room temperature for 1.5 hours to pre-hydrolyze tetraethyl orthosilicate and obtain silica sol. S22. Preparation of hafnium source solution: Weigh hafnium oxychloride and dissolve it in deionized water to obtain hafnium source solution; S23. Mixed Sol: Add the hafnium source solution dropwise into the pre-hydrolyzed silica sol, control the molar ratio of hafnium to silicon to be 1:1, and continue stirring for 30 minutes to obtain a uniform and transparent hafnium silicate precursor.

7. The method for preparing a hafnium salt-based neutron absorber material as described in claim 5, characterized in that, The specific process of step S3 is as follows: S31. Dispersion: The silicon carbide whiskers pretreated in step S1 are added to the hafnium silicate precursor prepared in step S2 and ultrasonically dispersed to make the silicon carbide whiskers dispersed and suspended individually without agglomeration, thus obtaining a suspension. S32. Gelation: Under magnetic stirring, dilute ammonia is added dropwise to the suspension to adjust the pH value of the suspension to 7.5, so that hafnium and silicon hydroxides begin to co-precipitate and condensate on the surface of silicon carbide whiskers to form a gel layer. S33. Aging and Drying: After the gel layer is formed, stop stirring and let it stand for 12 hours to strengthen the gel network; then filter to separate the solid, wash it three times alternately with anhydrous ethanol and deionized water, and dry it in an oven at 90 ℃ for 12 hours to obtain the coated powder. S34. Precursor conversion heat treatment: The dried coated powder is placed in a tube furnace and heated to 900℃ under argon protection. It is held for 2 hours to convert the gel layer on the surface of silicon carbide whiskers into an amorphous or microcrystalline HfO2-SiO2 mixed oxide precursor layer, thus obtaining modified whiskers.

8. The method for preparing a hafnium salt-based neutron absorber material as described in claim 5, characterized in that: In step S4, the sintering aid is a composite aid of niobium oxide and yttrium oxide; the total amount of the composite aid added is 0.5 wt% to 2.0 wt% of the mass of the matrix precursor mixed powder.

9. The method for preparing a hafnium salt-based neutron absorber material as described in claim 5, characterized in that: In step S5, the densification sintering adopts unidirectional hot pressing sintering or directional discharge plasma sintering process to make the preferred orientation direction of the modified whiskers consistent with the dominant thermal direction of the material, and to construct an anisotropic continuous thermally conductive network structure.

10. The application of a high thermal conductivity hafnium-based neutron absorber as described in any one of claims 1-4 in nuclear reactor control rods, neutron shielding materials, or structures for extreme thermal environments.

Images