Neutron shielding aluminum-based boron carbide composite material and preparation method thereof

Abstract

The present invention discloses a neutron shielding aluminum-based boron carbide composite material and a preparation method thereof; the aluminum-based boron carbide composite material comprises boron carbide particles, graphitized nanocarbon, and an aluminum matrix; the present invention shields neutrons by boron carbide particles, and absorbs or gathers helium bubbles by graphitized nanocarbon, thereby avoiding the generation of a large number of dispersed or gathered helium bubbles in the aluminum matrix after neutron absorption, thereby improving the comprehensive properties of the material such as neutron shielding, radiation damage resistance, and mechanics. The preparation method adopts a powder metallurgy technical process, which is suitable for near-net-shape preparation of aluminum-based composite materials with high volume content of boron carbide particles, and is also suitable for forming and processing large-scale component products such as wide and medium-thick plates of aluminum-based composite materials with medium and low volume content, and can be used in neutron shielding application scenarios such as ground spent fuel storage and transportation, spacecraft and nuclear-powered aircraft.

Description

Technical Field

[0001] The invention belongs to the technical field of neutron absorbing materials and aluminum-based composite materials, and provides an aluminum-based boron carbide composite material for shielding neutrons and a preparation method thereof. Background Art

[0002] Boron carbide (B4C) has low density, high specific strength and specific modulus, good thermal shock resistance, and excellent neutron absorption. Therefore, the aluminum-based boron carbide composite material obtained by combining medium-high volume fraction B4C with Al is a good lightweight structural functional integrated composite material, especially in neutron absorption.

[0003] The reason why B4C has good thermal neutron absorption ability is mainly due to the isotope 10 B has an ultra-high neutron absorption cross section (3837Barn), and has the characteristics of wide neutron capture energy spectrum, no radioactive isotope production after decay, low secondary radiation energy, and high temperature resistance. 10 B captures a neutron and the following reaction occurs:

[0004] 10 B+n=Li+He+2.78Mv

[0005] However, when B4C is used in reactor control elements or nuclear shielding materials, the He released after capturing neutrons will exist in the bulk material in the form of helium bubbles, which are easy to aggregate and grow, causing swelling of the material, affecting the neutron shielding effect and mechanical properties of the device, and affecting its service life.

[0006] Patent document CN 106947888 A discloses a high-energy ray shielding composite material and a preparation method thereof; the high-energy ray shielding composite material and the preparation method thereof use micron-grade powder, which is easy to purchase and inexpensive; hot isostatic forming and sintering are carried out simultaneously, the process is simple, the material is uniform, the material density is high, and the relative density reaches more than 99.8%. However, although the high-energy ray shielding composite material has the dual effect of shielding x-rays, gamma rays and neutrons, it cannot control 10 The aggregation or growth behavior of He bubbles produced after B captures neutrons seriously threatens the reliability and service life of shielding composite materials. Summary of the invention

[0007] In view of the above problems, the present invention provides an aluminum-based boron carbide composite material for shielding neutrons and a preparation method thereof.

[0008] The technical solution of the present invention is as follows:

[0009] A neutron shielding aluminum-based boron carbide composite material, the aluminum-based boron carbide composite material comprises, by volume fraction:

[0010] Boron carbide particles 5-50%

[0011] Graphitized nanocarbon 0.05~5%

[0012] The balance is aluminum-based powder.

[0013] Preferably, the aluminum-based boron carbide composite material comprises, by volume fraction:

[0014] Boron carbide particles 25-35%

[0015] Graphitized nanocarbon 0.5~2%

[0016] The balance is aluminum-based powder.

[0017] The preparation method of the neutron shielding aluminum-based boron carbide composite material comprises the following steps:

[0018] 1) uniformly dispersing and compounding graphitized nano-carbon and aluminum-based powder to prepare graphitized nano-carbon / aluminum composite powder;

[0019] 2) uniformly dispersing and compounding the graphitized nano-carbon / aluminum composite powder and the boron carbide particles to prepare a boron carbide-graphitized nano-carbon / aluminum mixed powder;

[0020] 3) The boron carbide-graphitized nano-carbon / aluminum mixed powder is pressed, sintered, and deformed to obtain the aluminum-based boron carbide composite material.

[0021] The graphitized nanocarbon includes at least one of graphitized carbon nanotubes, graphene nanosheets, graphitized carbon nanofibers, graphitized buckyballs, graphitized carbon capsules, and graphitized hollow microspheres, and has a characteristic size of 1 to 500 nm, preferably 10 to 50 nm.

[0022] The particle size of the boron carbide particles ranges from 1 to 500 μm, and preferably ranges from 10 to 40 μm.

[0023] Neutron absorption essentially relies on the B10 isotope in the B element. The higher the B content, the better the absorption effect. However, for aluminum-based composite materials, a high B4C content will easily cause B4C particles to aggregate and make it difficult to sinter together to form a dense bulk material.

[0024] The aluminum matrix includes one or more of pure aluminum, 1 series aluminum alloy, 2 series aluminum alloy, 5 series aluminum alloy, 6 series aluminum alloy, and 7 series aluminum alloy. The preferred aluminum matrix is ​​5 series or 6 series aluminum alloy.

[0025] In step 1), the graphitized nano-carbon and the aluminum-based powder are uniformly dispersed and compounded by high-speed mechanical fusion, variable speed ball milling, mechanical ball milling, slurry-assisted compounding or in-situ growth of nano-carbon;

[0026] In step 2), the graphitized nano-carbon / aluminum composite powder and the boron carbide particles are uniformly dispersed and compounded by mechanical mixing, mechanical ball milling, high-speed stirring mixing or air flow mixing.

[0027] The boron carbide-graphitized nano-carbon / aluminum mixed powder compact is produced by die pressing, cold isostatic pressing or powder encapsulation.

[0028] In step 3), the sintering is performed by vacuum sintering, atmosphere protection sintering, hot pressing sintering or hot isostatic pressing sintering; the sintering temperature ranges from 500 to 650° C. and the holding time is 0.1 to 10 hours.

[0029] In step 3), the deformation processing adopts extrusion, rolling, forging, ring forging or spinning method.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) In the present invention, boron carbide particles are used to shield neutrons, and further absorb or collect helium bubbles through graphitized nanocarbon. The graphitized nanocarbon has a more stable morphology, rich pore structure or carbon layer interface, and is used to absorb or collect the generated helium bubbles, avoiding the generation of a large number of dispersed or collected helium bubbles in the aluminum matrix after neutron absorption, thereby improving the material's neutron shielding, radiation damage resistance, and mechanical comprehensive properties. In addition to ensuring the neutron absorption and shielding effect, the present invention can also control or delay the damage caused by neutron irradiation. The He bubbles generated after absorbing neutrons are smaller and more dispersed, and it is difficult to grow large bubbles, ensuring that the material performance deteriorates more slowly.

[0032] (2) The present invention has further discovered that only graphitized nanocarbon of nanometer size can be dispersed more diffusely and evenly in the metal matrix. At a low content, only when the size is small enough can the nanocarbon be evenly dispersed at any position of the metal matrix, thereby absorbing or controlling the He bubbles that are the inevitable product after boron carbide absorbs neutrons. If the size is slightly larger and the quantity is insufficient, the He ion size is very small and can diffuse, aggregate and grow in the metal, which will cause the metal matrix to produce a large number of large bubbles and damage (lose the mechanical strength of the metal itself).

[0033] (3) The composite of carbon nanomaterials improves the mechanical properties of materials and is conducive to lightweight design of materials.

[0034] (4) The preparation method adopts powder metallurgy technology, which is suitable for the near-net-shape preparation of aluminum-based composite materials with high volume content (35-55 vol.%) of boron carbide particles, and is also suitable for the forming processing of large-scale component products such as wide and thick plates of aluminum-based composite materials with medium and low volume content (15-35 vol.%). It can be used in neutron shielding application scenarios such as ground spent fuel storage and transportation, spacecraft and nuclear-powered aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0036] Figure 1 This is a schematic diagram of the structure of the aluminum-based boron carbide composite material for shielding neutrons according to the present invention. DETAILED DESCRIPTION

[0037] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0038] Figure 1 Shown is a schematic structural diagram of a neutron shielding aluminum-based boron carbide composite material of the present invention.

[0039] Example 1

[0040] This embodiment provides a neutron shielding aluminum-based boron carbide composite material, which is composed of 31.7 Vol.% boron carbide particles, 1.5 Vol.% graphitized carbon nanotubes and a pure aluminum matrix. The boron carbide particles have a specification of w10; the graphitized carbon nanotubes have an average diameter of 20nm (diameter range 10-30nm), and an average length of 5μm (length range 2-10μm); the matrix is ​​a 30μm pure aluminum powder with a purity of 99.9%.

[0041] The method for preparing the neutron shielding aluminum-based boron carbide composite material comprises the following steps:

[0042] Step 1) ball-milling 10 g of graphitized carbon nanotubes and 690 g of aluminum powder at 100 rpm for 4 hours to prepare a graphitized carbon nanotube / aluminum composite powder;

[0043] Step 2) adding 300 g of boron carbide particles to the graphitized carbon nanotube / aluminum composite powder, first blending at a low speed of 100 rpm for 3 hours, and then ball milling at a high speed of 200 rpm for 2 hours to prepare a boron carbide-graphitized carbon nanotube / aluminum mixed powder;

[0044] Step 3) 1 kg of the boron carbide-graphitized carbon nanotube / aluminum mixed powder was pressed into an ingot with a diameter of 80 mm under a pressure of 180 tons, sintered at 580° C. for 3 hours for densification, and extruded into a 50 mm×10 mm plate to obtain a dense boron carbide-graphitized carbon nanotube / aluminum composite material.

[0045] Comparative Example 1

[0046] The difference between this comparative example and Example 1 is that no graphitized carbon nanotubes are added, and the aluminum-based boron carbide composite material of this comparative example is a composite material composed of 31.7 Vol. % boron carbide particles and a pure aluminum matrix.

[0047] Comparative Example 2

[0048] The difference between this comparative example and Example 1 is that the graphitized carbon nanotubes are replaced by ordinary carbon nanotubes, and the aluminum-based boron carbide composite material of this comparative example is a composite material composed of boron carbide particles, ordinary carbon nanotubes and a pure aluminum matrix. The boron carbide particle specification is w10; the ordinary carbon nanotubes have an average diameter of 20nm (diameter range 10-30nm), and an average length of 5μm (length range 2-10μm).

[0049] Comparative Example 3

[0050] The difference between this comparative example and Example 1 is that the specifications of the graphitized carbon nanotubes are different. The aluminum-based boron carbide composite material of this comparative example is a composite material composed of boron carbide particles, graphitized carbon nanotubes and a pure aluminum matrix. The specifications of the boron carbide particles are w10; the average diameter of the graphitized carbon nanotubes is 5nm (diameter range 2-10nm), and the average length is 3μm (length range 1-5μm).

[0051] Comparative Example 4

[0052] The difference between this comparative example and Example 1 is that the specifications of the graphitized carbon nanotubes are different. The aluminum-based boron carbide composite material of this comparative example is a composite material composed of boron carbide particles, graphitized carbon nanotubes and a pure aluminum matrix. The specifications of the boron carbide particles are w10; the average diameter of the graphitized carbon nanotubes is 50nm (diameter range 40-60nm), and the average length is 15μm (length range 10-20μm).

[0053] Performance Testing

[0054] The size and number (density) of He bubbles after irradiation were characterized and analyzed by field emission transmission electron microscopy (TEM), model FEI Talos F200X G2, with an accelerating voltage of 200KV.

[0055] Table 1

[0056]

[0057] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A neutron shielding aluminum-based boron carbide composite material, characterized in that: The aluminum-based boron carbide composite material is composed of the following substances in volume fractions: Boron carbide particles 20-35% Graphitized nanocarbon 0.5~2% The balance is aluminum-based powder; The graphitized nanocarbon is a graphitized carbon nanotube; the average diameter of the graphitized carbon nanotube is 20nm, and the diameter range is 10-30nm; the average length is 5μm, and the length range is 2-10μm.

2. A method for preparing the neutron shielding aluminum-based boron carbide composite material according to claim 1, characterized in that: The preparation method comprises the following steps: 1) uniformly dispersing and compounding graphitized nano-carbon and aluminum-based powder to prepare graphitized nano-carbon / aluminum composite powder; 2) uniformly dispersing and compounding the graphitized nano-carbon / aluminum composite powder and the boron carbide particles to prepare a boron carbide-graphitized nano-carbon / aluminum mixed powder; 3) The boron carbide-graphitized nano-carbon / aluminum mixed powder is pressed, sintered, and deformed to obtain the aluminum-based boron carbide composite material.

3. The preparation method according to claim 2, characterized in that: The particle size of the boron carbide particles ranges from 10 to 40 μm.

4. The preparation method according to claim 2, characterized in that: The aluminum matrix includes one or more of pure aluminum, 1 series aluminum alloy, 2 series aluminum alloy, 5 series aluminum alloy, 6 series aluminum alloy, and 7 series aluminum alloy.

5. The preparation method according to claim 2, characterized in that: In step 1), the graphitized nano-carbon and the aluminum-based powder are uniformly dispersed and compounded by high-speed mechanical fusion, variable speed ball milling, mechanical ball milling, slurry-assisted compounding or in-situ growth of nano-carbon; In step 2), the graphitized nano-carbon / aluminum composite powder and the boron carbide particles are uniformly dispersed and compounded by mechanical mixing, mechanical ball milling, high-speed stirring mixing or air flow mixing.

6. The preparation method according to claim 2, characterized in that: The boron carbide-graphitized nano-carbon / aluminum mixed powder compact is produced by molding, cold isostatic pressing of powder or encapsulation.

7. The preparation method according to claim 2, characterized in that: In step 3), the sintering is performed by vacuum sintering, atmosphere protection sintering, hot pressing sintering or hot isostatic pressing sintering; the sintering temperature ranges from 500 to 650° C. and the holding time is 0.1 to 10 hours.

8. The preparation method according to claim 2, characterized in that: In step 3), the deformation process adopts extrusion, rolling, forging, ring forging or spinning method.

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