Preparation method of B4C / Al composite material for neutron / gamma ray coordinated protection

Abstract

The invention discloses a method for preparing a B4C / Al composite material for neutron / gamma ray coordinated protection, which comprises the following steps: adding mixed powders of Er2O3 and B4C in different mass ratios to PVA and RO water for ball milling and mixing, preparing a green body at a pressure of 373MPa by using a press, introducing Ar as a protective gas in a tubular furnace, obtaining a preform after high-temperature sintering, and finally coating pure Al particles and sintering at 1200°C in a tubular furnace to obtain a B4C / Al composite material. The novel B4C / Al composite material prepared by the invention has both neutron and gamma ray protection performance, can improve the utilization rate of the material, and is more widely used in the field of nuclear protection.

Description

Technical Field

[0001] The invention belongs to the field of nuclear protection materials, and in particular relates to a method for preparing a B4C / Al composite material for neutron / gamma ray coordinated protection. Background Art

[0002] Nuclear energy has the most development prospects among the current new energy sources. However, with the use of nuclear fuel, a large amount of spent fuel with strong radioactivity, high toxicity and strong heat release will be produced, which will cause serious radiation pollution to the surrounding environment and humans, and the spent fuel needs to be reprocessed. During the reprocessing process of spent fuel, spontaneous fission will lead to a high neutron flux, so materials with good neutron protection performance are needed. With the rapid development of the nuclear power industry, the development of materials with better neutron protection performance is particularly important. Among many nuclear protection materials, B4C / Al composite material is an ideal choice. When B4C decays after absorbing neutrons, no radioactive isotopes are produced and the secondary radiation energy is low. However, due to the poor fracture toughness and plastic deformation ability of B4C, it cannot be used alone, and the addition of Al can greatly improve these defects. The neutron protection performance of B4C / Al composite material is positively correlated with the content of B4C. At present, only the infiltration method can prepare B4C / Al composite material with 55vol% B4C, which meets the requirement of high boron content. Among them, the advantage of pressureless infiltration compared with pressurized infiltration is that it can prepare composite materials with large size and complex shape.

[0003] In addition, among the enriched solid nuclides at the tail end of spent fuel reprocessing, heavy elements such as plutonium, uranium, americium, neptunium, and curium will produce a large amount of gamma rays in addition to neutrons during the fission process. Gamma rays are electromagnetic waves with a wavelength much shorter than ultraviolet rays. High-quality elements or nuclides are usually used to shield gamma rays. Heavy elements such as Pb, Er, and W have excellent gamma ray protection effects. There are a series of gamma ray shielding products containing Pb in China, but the toxicity and high density of Pb limit its further application. Summary of the invention

[0004] In view of the above problems, the present invention provides a method for preparing a B4C / Al composite material with neutron / gamma ray synergistic protection, and prepares a B4C / Al composite material with excellent neutron / gamma ray synergistic protection performance.

[0005] The method for preparing a B4C / Al composite material for neutron / gamma ray coordinated protection of the present invention comprises the following steps:

[0006] Step 1: Raw material preparation: B4C powder with a purity of ≥99.9%, Er2O3 powder, pure Al particles, and polyvinyl alcohol.

[0007] Step 2: Ball milling: Pour the mixed powders of Er2O3 and B4C in different mass ratios into a grinding jar filled with agate grinding balls, add PVA and RO water in sequence, and then put them into a planetary ball mill for ball milling. Pour the suspension into a metal plate, dry it in a drying oven, grind it, sieve it, and put it into a glass jar for standby use.

[0008] Step 3: Green body pressing: Add the mixed powder into a customized alloy mold and use a press to prepare the green body, maintaining the pressure at 373 MPa for 2-5 minutes.

[0009] Step 4: Preform sintering: Place the crucible with the green body in the center of the tube furnace, evacuate the air in the tube and introduce protective atmosphere Ar, sinter at high temperature and keep warm for a period of time, and cool with the furnace after sintering is completed.

[0010] Step 5: Pressureless infiltration: First, put the preform covered with Al particles into a corundum crucible, then place the crucible in the center of a tubular furnace, evacuate the air in the tube and introduce a protective atmosphere of Ar, sinter at high temperature and keep warm for a period of time, and cool with the furnace after sintering is completed.

[0011] Furthermore, in step 1, the median particle size of B4C is 3.5 μm, the particle size of Er2O3 is 1 μm, and the particle size of pure Al particles is 1 mm.

[0012] Furthermore, in step 2, the amount of Er2O3 added is 1-8wt.%, and the amount of PVA added is 2-8wt.%, calculated in weight percentage.

[0013] Furthermore, in step 2, the rotation speed of the ball mill can be 180-280 rpm, and the time can be 4-10 hours.

[0014] Furthermore, in step 2, the drying temperature is 80° C. and the baking time is 10 h.

[0015] Furthermore, the gas flow rate of Ar in step 4 and step 5 is 80 sccm.

[0016] Furthermore, in step 4, the sintering temperature is 1500° C. and the insulation time is 120 min.

[0017] Furthermore, in step 5, the sintering temperature is 1200° C., the holding time is 30 min, and the temperature is reduced to 300° C. and then cooled in the furnace.

[0018] The invention discloses a method for preparing a B4C / Al composite material for neutron / gamma ray coordinated protection. The prepared B4C / Al composite material for neutron / gamma ray coordinated protection is used in the transportation and storage of spent fuel.

[0019] The beneficial technical effects of the present invention are:

[0020] 1. The Er2O3-doped B4C / Al composite material prepared by the present invention has the characteristics of simple preparation process and low cost.

[0021] 2. The Er2O3-doped B4C / Al composite material prepared by the present invention increases the proportion of B4C in the composite material and can greatly improve the neutron protection performance of the material.

[0022] 3. The present invention prepares Er2O3-doped B4C / Al composite materials, which also have the characteristics of gamma-ray protection, so that the composite materials have the function of neutron / gamma-ray synergistic protection and are more widely used in the field of nuclear protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the principle of preform sintering and pressureless infiltration of the present invention.

[0024] Figure 2 This is the sintering temperature rise and fall curve of the preform of the present invention.

[0025] Figure 3 This is the temperature rise and fall curve of the pressureless infiltration of the present invention.

[0026] Figure 4 This is a backscattered electron morphology image of the composite material prepared in the present invention.

[0027] Figure 5 This is a Vickers hardness diagram of the composite material prepared in the present invention.

[0028] Figure 6 This is a high temperature compression rheological stress curve of the composite material prepared in the present invention. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Embodiment 1:

[0031] Step 1: Raw material preparation: B4C powder with a purity of ≥99.9%, Er2O3 powder, pure Al particles, and polyvinyl alcohol (PVA1799).

[0032] Step 2: Ball milling mixture: Weigh a certain mass of Er2O3 powder and B4C powder and pour them into a grinding jar filled with agate grinding balls, add appropriate amount of PVA and RO water in turn (mass ratio Er2O3: B4C: PVA = 1: 95: 4), then put them into a planetary ball mill for ball milling, pour the suspension into a metal plate, dry it in a drying oven at 80°C for 10 hours, then grind it, sieve it to obtain a uniformly mixed B4C mixed powder, and put it into a 100mL glass jar for standby use.

[0033] Step 3: Green body pressing: Use an electronic balance to weigh a certain mass of mixed powder and add it into a 45mm×15mm alloy mold. Use a press to prepare a green body and keep the pressure at 373MPa for 3min. After taking out, put the rectangular green body into a corundum crucible filled with carbon paper.

[0034] Step 4: Preform sintering: Principle as follows Figure 1 As shown, the corundum crucible containing the green body is placed in the center of the tubular sintering furnace, sintered at 1500℃ for 2h and then cooled in the furnace. The sintering atmosphere is Ar to prevent oxidation of the preform, and the gas flow rate is about 80sccm. Figure 2 shown.

[0035] Step 5: Pressureless infiltration: Place the preform covered with Al particles in a corundum crucible, first use a mechanical pump to remove the air in the furnace, then introduce Ar from the other side, with a gas flow rate of about 80sccm, adjust the inlet and outlet valves to ensure argon flow, and introduce Ar until sintering is completed and the temperature is cooled to room temperature. The heating and cooling curve is as follows: Figure 3 The crucible is taken out, and a wire cutting is performed at the position of the preform to obtain a new type of neutron / γ-ray synergistic protection B4C / Al composite material.

[0036] Embodiment 2-4

[0037] The preparation method is the same as that in Example 1, except that the doping amount of Er2O3 is changed; the specific parameters are shown in Table 1.

[0038] Table 1 Addition amount of main components in Examples 2-4

[0039]

[0040] The backscattered electron images of the different Er2O3-doped B4C / Al composite materials prepared in Examples 1-4 are shown in the attached figure. Figure 4 As shown, (a), (b), (c), and (d) are doped with Er2O3 in amounts of 1wt.%, 2wt.%, 5wt.%, and 8wt.%, respectively. According to the principle of backscattered electron imaging, the marking of the areas where the phases Er2O3, B4C, and Al are located is shown in the figure. The figure shows that Er2O3 is successfully mixed into the composite material and is evenly distributed, which can effectively improve the neutron / gamma ray synergistic protection performance of the composite material. Figure 5 The Vickers hardness of B4C / Al composites doped with different Er2O3 is shown in the figure: 276.90HV, 311.51HV, 309.90HV and 363.04HV, respectively, indicating that the hardness of the composite material increases with the Er2O3 doping amount. Figure 6It is shown that the peak flow stresses of the four composite materials are 202.84MPa, 170.55MPa, 204.68MPa and 176.22MPa, and the fracture strains are 27.66%, 17.77%, 20.56% and 19.67%, respectively, indicating that the composite materials have good high-temperature plastic deformation ability.

[0041] The method of the present invention is used to prepare a new B4C / Al composite material with excellent neutron / gamma-ray synergistic protection performance. During the transportation and storage of spent fuel, since the new B4C / Al composite material in the invention has a high boron content and excellent neutron protection performance, the prepared spent fuel loading container will be thinner, which can reduce the use of materials and improve the utilization rate of the composite material. At the same time, in the tail end concentrated solid nuclides of spent fuel post-processing, heavy elements such as plutonium, uranium, americium, neptunium, and curium will also produce a large amount of gamma rays during the fission process, and high-quality elements or nuclides are usually selected for gamma ray shielding. Heavy elements such as Pb, Er, and W have excellent gamma ray protection effects. There are a series of gamma ray shielding products containing Pb in China, but the toxicity and high density of Pb limit its further application. The present invention comprehensively considers and successfully adds a certain amount of Er2O3 to the B4C / Al composite material. The new B4C / Al composite material of the present invention can also be used in the spent fuel post-processing process for gamma ray protection. The novel B4C / Al composite material prepared by the present invention not only has excellent neutron protection performance and improves the utilization rate of materials, but also has a gamma ray protection effect, and is more widely used in the field of nuclear protection.

Claims

1. A method for preparing a B4C / Al composite material for neutron / gamma ray coordinated protection, characterized in that: The following steps are involved: Step 1: Raw material preparation: B4C powder with a purity of ≥99.9%, Er2O3 powder, pure Al particles, and polyvinyl alcohol; Step 2: Ball milling: Pour the mixed powders of Er2O3 and B4C in different mass ratios into a grinding jar filled with agate grinding balls, add polyvinyl alcohol and RO water in sequence, and then put them into a planetary ball mill for ball milling. Pour the suspension into a metal plate, dry it in a drying oven, grind it, sieve it, and put it into a glass jar for standby use. In step 2, the amount of Er2O3 added is 1-8 wt%, and the amount of polyvinyl alcohol added is 2-8 wt% by weight; Step 3: Green body pressing: Add the mixed powder into a customized alloy mold and use a press to prepare the green body, holding the pressure at 373 MPa for 2-5 min; Step 4: Preform sintering: Place the crucible containing the green body in the center of the tube furnace, evacuate the air in the tube and introduce the protective atmosphere Ar, sinter at high temperature, the sintering temperature is 1500℃, and keep the temperature for 120 min. After sintering is completed, cool it with the furnace; Step 5: Pressureless infiltration: First place the preform covered with pure Al particles in a corundum crucible, then place the crucible in the center of the tubular furnace, evacuate the air in the tube and introduce protective atmosphere Ar, set the sintering temperature to 1200°C, keep warm for 30 minutes, cool to 300°C and then cool with the furnace.

2. The method for preparing a B4C / Al composite material for neutron / gamma ray coordinated protection according to claim 1, characterized in that: In the step 1, the median particle size of the B4C powder is 3.5 µm, the particle size of the Er2O3 powder is 1 µm, and the particle size of the pure Al particles is 1 mm.

3. The method for preparing a B4C / Al composite material for neutron / gamma ray coordinated protection according to claim 1, characterized in that: In step 2, the rotation speed of the ball mill is 180-280 rpm, and the time is 4-10 h.

4. The method for preparing a B4C / Al composite material for neutron / gamma ray coordinated protection according to claim 1, characterized in that: In step 2, the drying temperature is 80° C. and the drying time is 10 h.

5. The method for preparing a B4C / Al composite material for neutron / gamma ray coordinated protection according to claim 1, characterized in that: The gas flow rate of Ar in step 4 and step 5 is 80 sccm.

6. A method for preparing a B4C / Al composite material for neutron / gamma ray coordinated protection according to any one of claims 1 to 5, characterized in that: The prepared B4C / Al composite material with neutron / gamma ray synergistic protection is used in the transportation and storage of spent fuel.

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