Preparation method of boron carbide powder

Abstract

The invention provides a preparation method of boron carbide powder, belongs to the technical field of ceramic powder, and aims to solve the problems that in nuclear reactor protection, boron carbide ceramic is high in application cost, and the density of traditional powder is difficult to meet requirements; and in the ceramic preparation process, powder is difficult to fill in a mold, and charging is not uniform. The preparation method provided by the invention comprises the following steps: preparing mixed slurry by taking nuclear-grade boron carbide powder as a raw material; carrying out spray granulation on the mixed slurry to obtain a sphere-like boron carbide material, and then screening to obtain a first boron carbide material with the particle size of 3-20 microns and a second boron carbide material with the particle size of 30-80 microns; performing cold isostatic pressing on the residual boron carbide material, and crushing to obtain a third boron carbide material with the particle size of 0.1-0.8 mm; and treating the three materials, and mixing according to a ratio to obtain the boron carbide powder. The boron carbide powder has high apparent density and tap density, the tap density can reach 1.70 g / cm < 3 > or above and reaches the density level of bulk boron carbide ceramic, uniform charging of containers in complex shapes can be achieved, the preparation cost is low, and the method is suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic powders, and particularly to a method for preparing boron carbide powders. Background Art

[0002] Boron carbide has a hardness second only to diamond and cubic boron nitride, and has high hardness, high wear resistance and high compressive strength, etc. Its excellent mechanical properties and low density make it used as bulletproof vests and vehicle armor materials in the field of military ceramics. In the field of functional ceramics, due to the high thermal neutron capture cross-section of boron element, the safety of capture products and diverse isotope characteristics, boron carbide is often used as a neutron absorption / shielding material in the field of nuclear materials.

[0003] Ordinary boron carbide powders have relatively low loose bulk density and tapped density. The loose bulk density is about 0.5 g / cm 3 , and the tapped density is 1.0 g / cm 3 . The relatively low loose bulk density and tapped density make it difficult to meet the requirements of out-of-core protection of nuclear reactors as a neutron absorption / shielding material. For boron carbide bulk ceramics that meet the density requirements, due to their high hardness and brittleness, the processing of complex shapes is difficult and costly. In addition, boron carbide powders with low loose bulk density / tapped density are difficult to mold and uniformly charge during the hot pressing preparation of ceramic products. When boron carbide powders are applied to nuclear reactors, the operation of directly filling the reactor mold is difficult. Summary of the Invention

[0004] Aiming at the above problems existing in the prior art, the present invention provides a method for preparing boron carbide powders to solve the problems that boron carbide powders with low loose bulk density / tapped density are difficult to mold and uniformly charge during the hot pressing preparation of ceramic products, and the operation of directly filling the reactor mold is difficult when applied to nuclear reactors.

[0005] The specific content of the invention is as follows: In a first aspect, the present invention provides a method for preparing boron carbide powders, and the method includes the following steps: S1: Using nuclear-grade boron carbide powders as raw materials, phenolic resin as a sintering aid and binder, mixing with an appropriate amount of deionized water, and performing wet ball milling to obtain a mixed slurry with a solid content of 40 wt% - 60 wt%; S2: Spray granulating the mixed slurry to obtain spherical boron carbide materials, screening the spherical boron carbide materials, and respectively obtaining first boron carbide materials with a particle size of 3 - 20 μm, second boron carbide materials with a particle size of 30 - 80 μm, and remaining boron carbide materials; S3: After subjecting the remaining boron carbide materials to cold isostatic pressing and forming treatment, crushing to obtain third boron carbide materials with a particle size of 0.1 - 0.8 mm; S4: After separately placing the first boron carbide material, the second boron carbide material, and the third boron carbide material in a pressureless sintering furnace for high-temperature sintering, mix them according to a mass ratio of the first boron carbide material: the second boron carbide material: the third boron carbide material of 0 - 0.1: 0.1 - 0.4: 0.5 - 0.9 to obtain boron carbide powder.

[0006] Optionally, in the step S1, based on the mass of the mixed slurry being 100 wt%, the addition amount of phenolic resin is 5 wt% - 20 wt%, and the balance is deionized water.

[0007] Optionally, in the step S1, the ball-to-material ratio of wet ball milling is 3:1, and the ball milling time is 4 - 16 h.

[0008] Optionally, in the step S2, the Hall flow rate of the spherical boron carbide material is 50 - 80 g / min, the Hall flow rate of the second boron carbide material is 60 - 70 g / min; the Hall flow rate of the first boron carbide material is 50 - 60 g / min.

[0009] Optionally, in the step S3, the forming pressure of cold isostatic pressing is 80 MPa - 120 MPa.

[0010] Optionally, in the step S4, the sintering is carried out in an argon atmosphere, the sintering temperature is 2100 °C - 2320 °C, and the sintering time is 5 - 8 h; The true densities of the first boron carbide material, the second boron carbide material, and the third boron carbide material after high-temperature sintering treatment are all not less than 2.2 g / cm 3 .

[0011] Optionally, in the step S4, before mixing the first boron carbide material, the second boron carbide material, and the third boron carbide material, the following steps are further included: Ball mill the first boron carbide material so that the median diameter of the first boron carbide material is 6 - 12 μm; Ball mill the second boron carbide material so that the median diameter of the second boron carbide material is 50 - 60 μm; First crush the third boron carbide material, and then ball mill it so that the median diameter of the third boron carbide material is 0.4 - 0.7 mm.

[0012] Optionally, in the step S4, mix them according to a mass ratio of the first boron carbide material: the second boron carbide material: the third boron carbide material of 0.02 - 0.08: 0.2 - 0.3: 0.6 - 0.8.

[0013] Second aspect, the present invention provides a boron carbide powder prepared by the preparation method described in the first aspect above. The loose bulk density of the boron carbide powder is greater than 1.1 g / cm 3 , and the tapped density is greater than 1.70 g / cm 3 .

[0014] Second aspect, the present invention provides an application of a boron carbide powder prepared by the preparation method described in the first aspect above. The boron carbide powder can be used as a neutron absorption / shielding material in nuclear reactors. Compared with the prior art, the present invention has the following advantages: A preparation method of a boron carbide powder provided by the present invention. The boron carbide powder prepared by this process has a high loose bulk density and tapped density. The tapped density can reach 1.70 g / cm 3 or more, reaching the density level of bulk boron carbide ceramics, enabling uniform filling of containers with complex shapes, having a low preparation cost, and being suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0016] Figure 1 Shows a process flow diagram of the preparation of boron carbide powder provided by an embodiment of the present invention; Figure 2 Shows a schematic diagram of the principle of proportioning and mixing of boron carbide powder provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments of the present invention, any product obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with the features of other prior arts that is the same or similar to the present invention falls within the protection scope of the present invention. And all other embodiments obtained by those of ordinary skill in the art without creative efforts also belong to the protection scope of the present invention.

[0018] In the embodiments, if the specific experimental procedures or conditions are not specified, the operations or conditions of the conventional experimental procedures described in the existing technologies in this field can be followed. For the reagents and other instruments whose manufacturers are not specified, they are all conventional reagent products that can be obtained through commercial purchases. In addition, the attached drawings are only schematic diagrams of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings represent the same or similar parts, and thus the repeated descriptions thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0019] Technologies, methods, and devices known to those of ordinary skill in the relevant fields may not be discussed in detail, but where appropriate, such technologies, methods, and devices should be regarded as part of the specification of the present invention.

[0020] In the description of the present invention, it should be understood that the use of terms such as "first" and "second" to limit the components is only for the convenience of distinguishing the corresponding components. Without further statement, the above terms have no special meaning, and thus cannot be construed as limiting the protection scope of the present invention.

[0021] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] Before elaborating on the method for preparing boron carbide powder provided by the present invention, it is necessary to make the following explanations on the related technologies: The hardness of boron carbide is second only to that of diamond and cubic boron nitride, and it has high hardness, high wear resistance, and high compressive strength, etc. Its excellent mechanical properties and low density make it used as bulletproof vests and vehicle armor materials in the field of military ceramics. In the field of functional ceramics, due to the high thermal neutron capture cross-section of boron element, the safety of capture products, and diverse isotope characteristics, boron carbide is often used as a neutron absorption / shielding material in the field of nuclear materials.

[0023] Ordinary boron carbide powder has relatively low loose bulk density and tapped density. The loose bulk density is about 0.5 g / cm 3 , and the tapped density is 1.0 g / cm 3 . The relatively low loose bulk density and tapped density make it difficult to meet the requirements for out-of-core protection of nuclear reactors as a neutron absorption / shielding material. For boron carbide bulk ceramics that meet the density requirements, due to their physical properties of high hardness and high brittleness, the processing of complex shapes is difficult and costly. In addition, boron carbide powder with low loose bulk density / tapped density is difficult to mold and achieve uniform feeding during the hot pressing preparation of ceramic products.

[0024] To enable those skilled in the art to understand the present invention more clearly, a preparation method of boron carbide powder described in the present invention will be described in detail through the following embodiments.

[0025] In the first aspect, the present invention provides a preparation method of boron carbide powder, Figure 1 which shows the process flow chart of the preparation of boron carbide powder provided by the embodiment of the present invention. As Figure 1 shown, the preparation method includes the following steps: S1: Using nuclear-grade boron carbide powder as the raw material, phenolic resin as the sintering aid and binder, mixing with an appropriate amount of deionized water, and performing wet ball milling to obtain a mixed slurry with a solid content of 40wt% - 60wt%; S2: Spray granulating the mixed slurry to obtain spherical boron carbide materials, screening the spherical boron carbide materials to obtain first boron carbide materials with a particle size of 3 - 20μm, second boron carbide materials with a particle size of 30 - 80μm, and the remaining boron carbide materials respectively; S3: After subjecting the remaining boron carbide materials to cold isostatic pressing and forming treatment, crushing to obtain third boron carbide materials with a particle size of 0.1 - 0.8mm; S4: Respectively placing the first boron carbide materials, the second boron carbide materials and the third boron carbide materials in a pressureless sintering furnace for high-temperature sintering, and then mixing them according to the mass ratio of first boron carbide materials: second boron carbide materials: third boron carbide materials of 0 - 0.1: 0.1 - 0.4: 0.5 - 0.9 to obtain boron carbide powder.

[0026] Adopting this technical solution, nuclear-grade boron carbide usually contains a relatively high proportion of boron-10 isotope to enhance its neutron shielding effect in nuclear reactors.

[0027] Phenolic resin, as a sintering aid, decomposes at high temperatures, releasing gases (such as water vapor, carbon dioxide, etc.). These gases help to open the gaps between particles and promote particle rearrangement. The residual carbon after decomposition can fill the voids between particles, increasing the contact area between particles, thereby improving the density of the final product. Phenolic resin can soften and flow at a relatively low temperature, which helps to form a preliminary connection network in the initial stage of sintering, reducing the difficulty of subsequent densification. It can also reduce the presence of oxide on the particle surface, thereby reducing the sintering activation energy, enabling the material to achieve good sintering effect at a lower temperature. The decomposition products of phenolic resin can act as reducing agents to help remove some metal oxide impurities, purify the internal environment of the sintered body, and contribute to the formation of a more pure and uniform microstructure.

[0028] Phenolic resin is used as a binder to increase the viscosity of the slurry while maintaining appropriate fluidity, facilitating the operation of the forming process (spray granulation). After drying treatment, phenolic resin can form a preliminary mechanical connection between powder particles, significantly improving the strength of the green body (unsintered body) and facilitating subsequent processing and handling without breakage. The decomposition behavior of phenolic resin during the sintering process can be regulated by adjusting its addition amount, thereby affecting the dimensional accuracy and shrinkage rate of the final product.

[0029] The solid content of the mixed slurry is controlled at 40wt% - 60wt%, ensuring that the slurry has good fluidity and appropriate viscosity, facilitating spray granulation.

[0030] The mixed slurry is converted into spherical-like particles through spray granulation technology, improving the fluidity and compaction density of the powder. Spray granulation atomizes the liquid material (mixed slurry) into fine droplets and then rapidly dries them in hot air to form dry particles. It can produce particles with a narrow particle size distribution and regular shape, which helps to improve the fluidity, compressibility, and solubility of the product.

[0031] The first boron carbide material and the second boron carbide material with different particle sizes are screened out through sieving. The material with the remaining particle size is formed into the third boron carbide material through cold isostatic pressing and crushing, and then the strength of the material is improved by high-temperature sintering of the three materials. During the sintering process, some materials may stick together. The three materials after high-temperature sintering are processed again. After crushing and / or ball milling, materials within the corresponding particle size range are obtained again, and the particle size distribution of the reprocessed materials is more uniform.

[0032] Figure 2 The schematic diagram of the principle of mixing the boron carbide powder ratio provided by the embodiment of the present invention is shown, as Figure 2 shown, the three boron carbide materials with mutually matching particle sizes are mixed according to the ratio to obtain boron carbide powder. This method helps to improve the contact between particles, reduce the porosity, and thus improve the density and mechanical strength of the final product.

[0033] In some embodiments, in the step S1, based on the mass of the mixed slurry being 100wt%, the addition amount of phenolic resin is 5wt% - 20wt%, and the balance is deionized water.

[0034] Adopting this technical solution, an appropriate amount of phenolic resin (5wt% - 20wt%) helps to improve the adhesiveness of the slurry and the densification degree during the sintering process.

[0035] In some embodiments, in the step S1, the ball-to-material ratio of wet ball milling is 3:1, and the ball milling time is 4 - 16h.

[0036] Adopting this technical solution ensures the full dispersion and uniform mixing of each component in the slurry.

[0037] In some embodiments, in the step S2, spray granulation is used to obtain spherical boron carbide materials. The inlet air temperature for spray granulation is 200°C to 250°C, the outlet air temperature is 120 - 140°C, and the particle size of the spherical boron carbide materials obtained by spray granulation is 3μm - 100μm.

[0038] Adopting this technical solution, the selection of the inlet air temperature and the outlet air temperature ensures the particle morphology and fluidity (Hall flow rate), helps to form spherical particles with high fluidity, and enables the final product to have excellent processing performance.

[0039] In some embodiments, in the step S2, the Hall flow rate of the spherical boron carbide material is 50 - 80 g / min, the Hall flow rate of the second boron carbide material is 60 - 70 g / min; the Hall flow rate of the first boron carbide material is 50 - 60 g / min.

[0040] Adopting this technical solution, the preparation of spherical boron carbide materials is simple, which improves the fluidity and compaction density of the powder. Since the first boron carbide material and the second boron carbide material have different particle size ranges, their flow rates are different, and the first boron carbide material and the second boron carbide material can be preliminarily separated according to the different flow rates. This helps to reduce the workload and energy consumption of subsequent screening.

[0041] In some embodiments, in the step S3, the forming pressure of the cold isostatic pressing is 80 MPa to 120 MPa.

[0042] Adopting this technical solution ensures the close contact between the third boron carbide material particles, reduces the porosity, and improves the density of the material.

[0043] In some embodiments, in the step S4, the high-temperature sintering is carried out in an argon atmosphere, the sintering temperature is 2200°C to 2320°C, and the sintering time is 5 - 8 h; The true density of the first boron carbide material, the second boron carbide material, and the third boron carbide material after high-temperature sintering treatment is not less than 2.2 g / cm 3 .

[0044] Adopting this technical solution, high-temperature sintering promotes the optimization of the internal structure of the material, enhances its physical and chemical properties, and increases the true density of the material.

[0045] In some embodiments, in the step S4, before mixing the first boron carbide material, the second boron carbide material, and the third boron carbide material, the following steps are further included: Ball-mill the first boron carbide material so that the median diameter of the first boron carbide material is 6 - 12 μm; Ball-mill the second boron carbide material so that the median diameter of the second boron carbide material is 50 - 60 μm; First crush and then ball-mill the third boron carbide material so that the median diameter of the third boron carbide material is 0.4 - 0.7 mm.

[0046] With this technical solution, the sintered first boron carbide material, the second boron carbide material, and the third boron carbide material are respectively subjected to at least one of ball-milling and crushing. While ensuring that the three materials have a high density, it further makes the particle size distributions of the three materials more uniform, which is beneficial for subsequent mixing ratios. The small-particle-size materials are more likely to fill the voids of the large-particle-size materials.

[0047] In some embodiments, in step S4, mix according to a mass ratio of first boron carbide material: second boron carbide material: third boron carbide material of 0.02 - 0.08: 0.2 - 0.3: 0.6 - 0.8.

[0048] With this technical solution, the packing density of the powder can be optimized, and the apparent density and tapped density can be increased.

[0049] In addition, the present invention also provides a boron carbide powder prepared by the preparation method. The apparent density of the boron carbide powder is greater than 1.1 g / cm 3 , and the tapped density is greater than 1.70 g / cm 3 .

[0050] With this technical solution, the boron carbide powder has a high apparent density and tapped density, and has high hardness, high wear resistance, and high compressive strength.

[0051] In addition, the present invention also provides an application of the boron carbide powder prepared by the preparation method. The boron carbide powder can be used as a neutron absorption / shielding material in a nuclear reactor.

[0052] With this technical solution, the high apparent density and tapped density of the boron carbide powder can meet the requirements of out-of-core protection of the nuclear reactor and are convenient for processing. In addition, the present invention also provides a boron carbide powder prepared by the preparation method. The apparent density of the boron carbide powder is greater than 1.1 g / cm 3 , and the tapped density is greater than 1.70 g / cm 3 .

[0053] With this technical solution, the boron carbide powder has a high apparent density and tapped density, and has high hardness, high wear resistance, and high compressive strength.

[0054] In addition, the present invention also provides an application of the boron carbide powder prepared by the above preparation method. The boron carbide powder can be used as a neutron absorption / shielding material in nuclear reactors.

[0055] With this technical solution, the relatively high loose bulk density and tapped density of the boron carbide powder can meet the requirements of out-of-core protection in nuclear reactors and are convenient for processing.

[0056] Example 1 Weigh a certain amount of nuclear-grade boron carbide powder as the raw material, add 8 wt% of phenolic resin as the binder and sintering aid, and prepare a slurry with a solid content of 55 wt% in deionized water. Wet ball mill for 8 h with a ball-to-material ratio of 3:1. Spray granulation is used for drying and spheroidizing the slurry. The inlet air temperature of spray granulation is 220 °C, and the outlet air temperature is 130 °C. The obtained spherical boron carbide materials are screened to obtain the first boron carbide materials with a particle size of 3 - 20 μm, the second boron carbide materials with a particle size of 30 - 80 μm, and the remaining boron carbide materials; the Hall flow rate of the obtained second boron carbide materials is 65 g / min, and the Hall flow rate of the obtained first boron carbide materials is 54 g / min. Place the remaining boron carbide materials in a cold isostatic pressing mold, isostatically press for 5 min at a pressure of 120 MPa to prepare a green block, and crush it to prepare the third boron carbide materials with a particle size of 0.1 - 0.8 mm. Place the three obtained precursor materials (the first boron carbide materials, the second boron carbide materials, and the third boron carbide materials) in a graphite crucible, heat up to 2200 °C in an argon environment, sinter for 6 h, and naturally cool to room temperature. The density of the three kinds of powder / fragments with different particle sizes is tested by the mercury intrusion method. The true density of the third boron carbide materials is 2.30 g / cm 3 , the true density of the second boron carbide materials is 2.24 g / cm 3 , the true density of the first boron carbide materials is 2.21 g / cm 3 . Ball mill the second boron carbide materials in a ball mill for 3 h to obtain the second boron carbide materials with D50 = 55 μm; ball mill the first boron carbide materials in a ball mill for 6 h to obtain the first boron carbide materials with D50 = 8 μm; ball mill the third boron carbide materials in a ball mill for 6 h to obtain the third boron carbide materials with a particle size range of 0.43 - 0.72 mm. Mix the three materials according to the mass ratio of the third boron carbide materials: the second boron carbide materials: the first boron carbide materials of 0.7:0.25:0.05, and mix them in a high-speed mixer to obtain boron carbide powder with a uniform particle size distribution. Use an intelligent powder property analyzer to test the loose bulk density and tapped density of the boron carbide powder. The loose bulk density of this boron carbide powder is 1.16 g / cm 3 , and the tapped density is 1.74 g / cm 3 .

[0057] Example 2 Weigh a certain amount of nuclear-grade boron carbide powder as the raw material, add 8 wt% of phenolic resin as the binder and sintering aid, and prepare a slurry with a solid content of 55 wt% in deionized water. Wet ball mill for 8 h with a ball-to-material ratio of 3:1. Spray granulation is used for drying and spheroidizing the slurry. The inlet air temperature of spray granulation is 220 °C, and the outlet air temperature is 130 °C. The obtained spherical boron carbide material is screened to obtain the first boron carbide material with a particle size of 3 - 20 μm, the second boron carbide material with a particle size of 30 - 80 μm, and the remaining boron carbide material; the Hall flow rate of the obtained second boron carbide material is 65 g / min, and the Hall flow rate of the obtained first boron carbide material is 54 g / min. Place the remaining boron carbide material in a cold isostatic pressing mold, isostatically press for 5 min at a pressure of 120 MPa to prepare a green block, and crush it to prepare the third boron carbide material with a particle size of 0.1 - 0.8 mm. Place the three obtained precursor materials (the first boron carbide material, the second boron carbide material, and the third boron carbide material) in a graphite crucible, heat up to 2200 °C in an argon environment, sinter for 6 h, and naturally cool to room temperature. Use the mercury intrusion method to test the density of the three kinds of powder / fragments with different particle sizes, and obtain that the true density of the third boron carbide material is 2.30 g / cm 3 , the true density of the second boron carbide material is 2.24 g / cm 3 , the true density of the first boron carbide material is 2.21 g / cm 3 . Ball mill the second boron carbide material in a ball mill for 3 h to obtain the second boron carbide material with D50 = 55 μm; ball mill the first boron carbide material in a ball mill for 6 h to obtain the first boron carbide material with D50 = 8 μm; ball mill the third boron carbide material in a ball mill for 6 h to obtain the third boron carbide material with a particle size range of 0.43 - 0.72 mm. Mix the three kinds of powders according to the mass ratio of the third boron carbide material: the second boron carbide material: the first boron carbide material of 0.78:0.2:0.02, and mix them in a high-speed mixer to obtain boron carbide powder with a uniform particle size distribution. Use an intelligent powder property analyzer to test the loose density and tapped density of the boron carbide powder. The loose density of this boron carbide powder is 1.18 g / cm 3 , and the tapped density is 1.71 g / cm 3 .

[0058] Example 3 Weigh a certain amount of nuclear-grade boron carbide powder as the raw material, add 8wt% phenolic resin as the binder and sintering aid, and prepare a slurry with a solid content of 55wt% in deionized water. Wet ball mill for 8h with a ball-to-material ratio of 3:1. Use spray granulation to dry and spheroidize the slurry. The inlet air temperature of spray granulation is 220°C, and the outlet air temperature is 130°C. Screen the obtained spherical boron carbide material to obtain the first boron carbide material with a particle size of 3 - 20μm, the second boron carbide material with a particle size of 30 - 80μm, and the remaining boron carbide material; the Hall flow rate of the obtained second boron carbide material is 65g / min, and the Hall flow rate of the obtained first boron carbide material is 54g / min. Place the remaining boron carbide material in a cold isostatic pressing mold, isostatically press for 5min at a pressure of 120MPa to prepare a green block, and crush it to prepare the third boron carbide material with a particle size of 0.1 - 0.8mm. Place the three obtained precursor materials (the first boron carbide material, the second boron carbide material, and the third boron carbide material) in a graphite crucible, heat up to 2200°C in an argon environment, sinter for 6h, and naturally cool to room temperature. Use the mercury intrusion method to test the density of the three kinds of powder / blocks with different particle sizes, and obtain that the true density of the third boron carbide material is 2.30g / cm 3 , the true density of the second boron carbide material is 2.24g / cm 3 , the true density of the first boron carbide material is 2.21g / cm 3 . Ball mill the second boron carbide material in a ball mill for 3h to obtain the second boron carbide material with D50 = 55μm; ball mill the first boron carbide material in a ball mill for 6h to obtain the first boron carbide material with D50 = 8μm; ball mill the third boron carbide material in a ball mill for 6h to obtain the third boron carbide material with a particle size range of 0.43 - 0.72mm. Mix the three kinds of powders according to the mass ratio of the third boron carbide material: the second boron carbide material: the first boron carbide material of 0.62:0.3:0.08, and mix them in a high-speed mixer to obtain boron carbide powder with a uniform particle size distribution. Use an intelligent powder property tester to test the loose density and tapped density of the boron carbide powder. The loose density of this boron carbide powder is 1.15g / cm 3 , and the tapped density is 1.76g / cm 3 .

[0059] Comparative example Weigh a certain amount of nuclear-grade boron carbide powder as the raw material, add 8wt% phenolic resin as the binder and sintering aid, and prepare a slurry with a solid content of 55wt% in deionized water. Wet ball mill for 8h with a ball-to-material ratio of 3:1. Spray granulation is used for drying and spheroidizing the slurry. The inlet air temperature of spray granulation is 220°C, and the outlet air temperature is 130°C. The obtained spherical boron carbide powder is placed in a cold isostatic pressing mold and isostatically pressed at a pressure of 120MPa for 5min to prepare a green block, which is then crushed to prepare boron carbide fragments with a particle size of 0.1 - 0.8mm. The obtained boron carbide fragments are placed in a graphite crucible, heated to 2200°C in an argon atmosphere, sintered for 6h, and naturally cooled to room temperature. The boron carbide fragments are ball milled in a ball mill for 6h to obtain boron carbide powder. The loose bulk density and tapped density of the boron carbide powder are measured using an intelligent powder property tester. The loose bulk density of this boron carbide powder is 0.86g / cm 3 , and the tapped density is 1.23g / cm 3 .

[0060] The relevant data of the above Examples 1 - 3 and the comparative example are statistically shown in Table 1 below: Table 1. Relevant experimental and test data of Examples 1 - 3 and the comparative example

[0061] As can be seen from the data in the above table, when the other processing methods are the same, using three kinds of powders with mutually matching particle sizes for proportioning can greatly improve the loose bulk density and tapped density compared with single-particle-size powders. As Figure 2 shown, this is mainly because, for powders with mutually matching particle sizes, after proportioning and mixing, the small-particle-size powders can fill the voids of the large-particle-size powders to reduce the proportion of powder voids and increase the bulk density of the powder. Especially after the powder is more closely packed by vibration or gentle tapping, the relative positions between the powder particles of the three particle sizes are optimized, reducing the voids between the particles, enabling more small-particle-size powders to fill the voids of the large-particle-size powders. By optimizing the proportion of the three powders, boron carbide powders with different loose bulk densities and tapped densities can be obtained, and the tapped density can reach 1.70g / cm 3 or more, reaching the density level of bulk boron carbide ceramics, which can achieve uniform loading of complex-shaped containers, has a low preparation cost, and is suitable for industrial production. For example, as a neutron absorption / shielding material, it is applied to nuclear reactors.

[0062] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0063] For method embodiments, for the sake of simple description, they are all expressed as a series of combinations of actions. However, those skilled in the art should know that the present invention is not limited by the described order of actions, because according to the present invention, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and components involved are not necessarily essential to the present invention.

[0064] The above has introduced in detail the method for preparing boron carbide powder provided by the present invention. Specific examples are used herein to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation on the present invention.

Claims

1. A method for preparing boron carbide powder, characterized in that: The method comprises the following steps: S1: nuclear grade boron carbide powder is used as raw material, phenolic resin is used as sintering aid and binder, mixed with an appropriate amount of deionized water, and wet ball milled to obtain a mixed slurry with a solid content of 40wt% to 60wt%; S2: spray granulating the mixed slurry to obtain a quasi-spherical boron carbide material, and sieving the quasi-spherical boron carbide material to obtain a first boron carbide material with a particle size of 3-20 μm, a second boron carbide material with a particle size of 30-80 μm, and remaining boron carbide material; S3: After cold isostatic pressing, the remaining boron carbide material is crushed to obtain a third boron carbide material with a particle size of 0.1-0.8 mm; S4: placing the first boron carbide material, the second boron carbide material and the third boron carbide material in a pressureless sintering furnace for high-temperature sintering respectively, and then mixing them in a mass ratio of the first boron carbide material: the second boron carbide material: the third boron carbide material of 0-0.1:0.1-0.4:0.5-0.9 to obtain boron carbide powder.

2. The method for preparing boron carbide powder according to claim 1, characterized in that: In the step S1, based on 100wt% of the mass of the mixed slurry, the amount of the phenolic resin added is 5wt%-20wt%, and the remainder is deionized water.

3. The method for preparing boron carbide powder according to claim 1, characterized in that: In the step S1, the wet ball milling ball-to-material ratio is 3:1, and the ball milling time is 4 to 16 hours.

4. The method for preparing boron carbide powder according to claim 1, characterized in that: In the step S2, the Hall flow rate of the quasi-spherical boron carbide material is 50-80 g / min, the Hall flow rate of the second boron carbide material is 60-70 g / min; and the Hall flow rate of the first boron carbide material is 50-60 g / min.

5. The method for preparing boron carbide powder according to claim 1, characterized in that: In the step S3, the molding pressure of the cold isostatic pressing is 80 MPa to 120 MPa.

6. The method for preparing boron carbide powder according to claim 1, characterized in that: In the step S4, the sintering is performed in an argon atmosphere, the sintering temperature is 2100° C. to 2320° C., and the sintering time is 5 to 8 hours; The true density of the first boron carbide material, the second boron carbide material and the third boron carbide material after high temperature sintering is not less than 2.2 g / cm 3 .

7. The method for preparing boron carbide powder according to claim 1, characterized in that: In the step S4, before mixing the first boron carbide material, the second boron carbide material and the third boron carbide material, the following steps are also included: Ball milling the first boron carbide material so that the median diameter of the first boron carbide material is 6-12 μm; Ball milling the second boron carbide material so that the median diameter of the second boron carbide material is 50-60 μm; The third boron carbide material is first crushed and then ball-milled, so that the median diameter of the third boron carbide material is 0.4-0.7 mm.

8. The method for preparing boron carbide powder according to claim 1, characterized in that: In step S4, the first boron carbide material: the second boron carbide material: the third boron carbide material are mixed in a mass ratio of 0.02-0.08: 0.2-0.3: 0.6-0.

8.

9. A boron carbide powder prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The boron carbide powder has a bulk density greater than 1.1 g / cm 3 , tap density greater than 1.70g / cm 3 .

10. An application of boron carbide powder prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The boron carbide powder can be used as a neutron absorption / shielding material in a nuclear reactor.

Images