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CN-122000098-A - High-heat-conductivity hafnate-based neutron absorption material, and preparation method and application thereof

CN122000098ACN 122000098 ACN122000098 ACN 122000098ACN-122000098-A

Abstract

The invention discloses a high-heat-conductivity hafnate-based neutron absorbing material, a preparation method and application thereof, wherein the neutron absorbing material has a compact microscopic complex phase structure and comprises a hafnate base phase, a modified whisker reinforced phase and a heat conducting network, the hafnate base phase is taken as a neutron absorbing main body and consists of a compound with a chemical formula of A 2 Hf 2 O 7 , wherein A is a rare earth element, the hafnate base phase has a defective fluorite structure or pyrochlore structure, the modified whisker reinforced phase is dispersed in the hafnate base phase and consists of composite whiskers with a core-shell structure, the composite whiskers take silicon carbide whiskers as cores and a compact hafnium silicate layer as shells, and the heat conducting network is formed by mutually contacting or overlapping at least part of modified whiskers at the grain boundary of the hafnate base phase.

Inventors

  • RAN GUANG
  • ZHU SHENGYOU
  • Chen Duyue

Assignees

  • 厦门大学

Dates

Publication Date
20260508
Application Date
20260209

Claims (10)

  1. 1. The high-heat-conductivity hafnate-based neutron absorbing material is characterized by having a compact microscopic complex phase structure, and comprising a hafnate-based phase, a modified whisker reinforced phase and a heat conducting network; The hafnate matrix phase is taken as a neutron absorption main body and consists of a compound with a chemical formula of A 2 Hf 2 O 7 , wherein A is a rare earth element, and the hafnate matrix phase has a defective fluorite structure or pyrochlore structure; The modified whisker reinforced phase is dispersed in the hafnate matrix phase and consists of composite whiskers with a core-shell structure, wherein the composite whiskers take silicon carbide whiskers as cores and compact hafnium silicate layers as shells; And the modified whisker reinforced phase is dispersed at the grain boundary of the hafnium acid salt base phase, and at least part of modified whiskers are mutually contacted or overlapped to form a continuous network structure.
  2. 2. The high thermal conductivity hafnate-based neutron absorbing material of claim 1, wherein the rare earth element in the hafnate matrix phase is one or more of dysprosium, yttrium, gadolinium, samarium or erbium.
  3. 3. The high thermal conductivity hafnate-based neutron absorbing material of claim 2, wherein 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 hafnate is (Dy x Er 1-x ) 2 Hf 2 O 7 ; wherein, the value range of x is 0.3-0.7.
  4. 4. The high-heat-conductivity hafnate-based neutron absorbing material of claim 1, wherein the modified whisker reinforced phase accounts for 5-25% of the high-heat-conductivity hafnate-based neutron absorbing material, the shell thickness of the hafnium silicate layer is 10 nm-200 nm, the hafnium silicate layer is densely coated on the surface of the silicon carbide whisker and forms chemical metallurgical bonding with the hafnate matrix phase, and the length-diameter ratio of the silicon carbide whisker is larger than 20 and the diameter is 0.1-2.0 mu m.
  5. 5. A method of preparing a high thermal conductivity hafnate-based neutron absorbing material according to any one of claims 1 to 4, comprising the steps of: s1, carrying out surface activation pretreatment on silicon carbide whiskers; The specific process of step S1 is as follows: S11, acid washing and impurity removal, namely immersing the silicon carbide whisker into dilute hydrofluoric acid solution for ultrasonic cleaning, removing surface impurities, washing with deionized water to be neutral, and drying; s12, oxidation activation, namely placing the dried silicon carbide whisker into a muffle furnace, and performing heat treatment for 1.5 hours at 400 ℃ in an air atmosphere, and introducing hydroxyl active sites on the surface of the silicon carbide whisker for enhancing the subsequent sol adsorption; S2, preparing a hafnium silicate precursor by adopting a step-by-step hydrolysis method; S3, coating a layer of hafnium silicate precursor on the surface of the pretreated silicon carbide whisker by adopting a sol-gel method, and performing precursor conversion heat treatment to obtain a modified whisker; S4, performing high-energy ball milling and mixing on rare earth oxide, hafnium oxide raw material powder and sintering auxiliary agents which form a hafnate matrix to obtain matrix precursor mixed powder, mixing the matrix precursor mixed powder and modified whiskers in a solvent, performing deagglomeration and mixing of whiskers by using ultrasonic dispersion and wet flexible ball milling, and drying to obtain composite powder; s5, loading the composite powder into a die, and performing densification sintering on the composite powder at the temperature of 1500-1800 ℃ by adopting a spark plasma sintering or hot-pressing sintering process, wherein the pressure is 30-MPa-60 MPa, oxide raw materials react in situ to generate a hafnium acid salt base phase in the sintering process, and a precursor layer on the surface of the modified whisker is converted into a dense HfSiO 4 interface layer, so that the dense high-heat-conductivity hafnium acid salt base neutron absorbing material is obtained.
  6. 6. The method for preparing a high thermal conductivity hafnate-based neutron absorbing material according to claim 5, wherein the specific process of step S2 is as follows: S21, pre-hydrolyzing a silicon source, namely weighing ethyl orthosilicate, dissolving the ethyl orthosilicate in absolute ethyl alcohol, adding deionized water, dropwise adding hydrochloric acid to adjust the pH value to 2-3, magnetically stirring the mixture at room temperature for 1.5 hours, and pre-hydrolyzing the ethyl orthosilicate to obtain silica sol; s22, preparing a hafnium source solution, namely weighing hafnium oxychloride and dissolving the hafnium oxychloride in deionized water to obtain the hafnium source solution; s23, mixing the sol, namely dripping a hafnium source solution into the prehydrolyzed silica sol, controlling the mole ratio of hafnium to silicon to be 1:1, and continuously stirring for 30 minutes to obtain a uniform and transparent hafnium silicate precursor.
  7. 7. The method for preparing a high thermal conductivity hafnate-based neutron absorbing material according to claim 5, wherein the specific process of step S3 is as follows: s31, dispersing, namely adding the silicon carbide whisker pretreated in the step S1 into the hafnium silicate precursor prepared in the step S2, and performing ultrasonic dispersion to enable the silicon carbide whisker to be dispersed and suspended singly without agglomeration to obtain a suspension; s32, gelation, namely dropwise adding dilute ammonia water into the suspension in a magnetic stirring state, and adjusting the pH value of the suspension to 7.5 to enable hydroxides of hafnium and silicon to start coprecipitation and polycondensation reaction on the surface of silicon carbide whiskers to form a gel layer; s33, aging and drying, namely stopping stirring after the gel layer is formed, standing and aging for 12 hours to strengthen a gel network, then filtering and separating solid, alternately washing 3 times by using absolute ethyl alcohol and deionized water, and drying in a 90 ℃ oven for 12 hours to obtain coated powder; And S34, precursor conversion heat treatment, namely placing the dried coating powder into a tube furnace, heating to 900 ℃ under the protection of argon, and preserving heat for 2 hours to convert a gel layer on the surface of the silicon carbide whisker into an amorphous or microcrystalline HfO 2 -SiO 2 mixed oxide precursor layer to obtain the modified whisker.
  8. 8. The method for preparing a high thermal conductivity hafnate-based neutron absorbing material according to claim 5, wherein in the step S4, the sintering aid is a composite aid of niobium oxide and yttrium oxide, and the total addition amount of the composite aid is 0.5-wt% to 2.0-wt% of the mass of the matrix precursor mixed powder.
  9. 9. The method of claim 5, wherein in step S5, the densification sintering is performed by unidirectional hot-press sintering or directional spark plasma sintering, so that the preferred orientation direction of the modified whisker is consistent with the dominant heat direction of the material, and an anisotropic continuous heat conduction network structure is constructed.
  10. 10. Use of the high thermal conductivity hafnate-based neutron absorber material of any one of claims 1 to 4 in a nuclear reactor control rod, neutron shielding material or extremely hot environmental structure.

Description

High-heat-conductivity hafnate-based neutron absorption material, and preparation method and application thereof Technical Field The invention belongs to the technical field of nuclear energy structure and function integrated materials, and particularly relates to a high-heat-conductivity hafnate-based neutron absorption material, a preparation method and application thereof, which are particularly suitable for nuclear reactor control rods, neutron shielding members and extreme heat environment structural members. Background The rare earth hafnate (RE 2Hf2O7) ceramic material is considered to be a new generation long-life nuclear reactor control rod and neutron shielding material for replacing the traditional boron carbide (B 4 C) and silver indium cadmium (Ag-In-Cd) alloy due to the characteristics of excellent neutron absorption cross section, high melting point, good chemical stability, no helium release under irradiation and the like. Hafnates are considered to be very potential nuclear reactor control rods or shielding materials due to their excellent neutron absorption properties. However, the existing hafnate-based ceramic materials still face a double bottleneck of thermophysical properties and chemical compatibility that is difficult to overcome when going to engineering applications: 1) Rare earth hafnates typically have a complex defective fluorite or pyrochlore crystal structure, strong lattice non-harmonic vibrations, severe phonon scattering, resulting in very low intrinsic thermal conductivity (typically < 2W/(m·k)). Under the high-energy neutron irradiation environment of the reactor, a large amount of heat is generated in the material due to neutron capture reaction, so that the central temperature of the core block is rapidly increased, huge thermal gradient and thermal stress are generated, cracking and even pulverization of the core block are extremely easy to induce, and the safe operation of the reactor is seriously threatened; 2) In order to solve the heat conduction problem, the conventional thinking is to add a second phase material (such as silicon carbide SiC, diamond or graphite) with high heat conduction into the matrix, but the simple compounding method has the problem of high-temperature interface reaction in a hafnate system. In the high-temperature sintering process (usually more than 1500 ℃), high-heat-conductivity reinforcing phases such as silicon carbide (SiC) and the like are extremely easy to generate serious interfacial chemical reaction with an oxide matrix (hafnate or rare earth oxide) to generate silicate glass phases or gas products (such as CO) with low melting points, so that the high-heat-conductivity phases are consumed, the compactness of the material is damaged, and the mechanical property of the material is also greatly reduced; 3) Thermal expansion mismatch problems hafnate ceramics typically have a relatively high Coefficient of Thermal Expansion (CTE) (about 10x 10 -6/K) while the CTE of the commonly used high thermal conductivity enhancement phase (e.g., siC) is relatively low, and this mismatch in coefficient of thermal expansion can create microcracks at the phase interface during severe temperature cycling of reactor shutdown, further blocking heat flow transmission and reducing material strength. Therefore, development of a novel hafnate-based composite material system is needed, not only can effectively inhibit harmful interface reaction in the high-temperature sintering process, but also can realize remarkable improvement of heat conductivity with lower addition amount, thereby realizing synergistic optimization of nuclear performance, thermophysical performance and mechanical performance. Disclosure of Invention In order to solve the problems, the invention provides a high-heat-conductivity hafnate-based neutron absorbing material, a preparation method and application thereof, wherein the method comprises the steps of constructing a continuous heat conduction network, optimizing thermal expansion matching property and blocking high-temperature interface reaction, the thermal conductivity, mechanical property and chemical stability of the material are obviously improved, and the material can be widely applied to nuclear reactor control rods, neutron shielding materials or extreme thermal environment structural members, and the requirement of severe working conditions is met. In order to achieve the above purpose, the present invention adopts the following technical scheme: The preparation method of the high-heat-conductivity hafnate-based neutron absorbing material comprises the steps of compact microscopic multiphase structure, including a hafnate matrix phase, a modified whisker reinforced phase and a heat conducting network; The hafnate matrix phase is taken as a neutron absorption main body and consists of a compound with a chemical formula of A 2Hf2O7, wherein A is a rare earth element, and the hafnate matrix phase has a defective fluorite st