A method for preparing boron carbide powder

Abstract

The present invention provides a method for preparing boron carbide powder, which belongs to the field of ceramic powder technology and aims to solve the problems in nuclear reactor protection, such as high application cost of boron carbide ceramics and difficulty in meeting the density requirements of traditional powders; and difficulty in powder molding and uneven loading in ceramic preparation. In the preparation method provided by the present invention, nuclear-grade boron carbide powder is used as raw material to prepare a mixed slurry; the mixed slurry is spray-granulated to obtain a spherical boron carbide material, which is then sieved to obtain a first boron carbide material with a particle size of 3 to 20 μm and a second boron carbide material with a particle size of 30 to 80 μm; the remaining boron carbide material is cold isostatically pressed and crushed to obtain a third boron carbide material with a particle size of 0.1 to 0.8 mm; the three materials are processed and mixed according to a ratio to obtain boron carbide powder. Boron carbide powder has high bulk density and tap density, and the tap density can reach 1.70 g / cm 3 The above mentioned density reaches the level of bulk boron carbide ceramics, which can realize uniform filling of complex-shaped containers, has low preparation cost and is suitable for industrial production.

Description

Technical Field

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

[0002] Boron carbide, second only to diamond and cubic boron nitride in hardness, exhibits high hardness, wear resistance, and compressive strength. Its excellent mechanical properties and low density make it a popular material for body armor and vehicle armor in military ceramics. In the field of functional ceramics, boron carbide's high thermal neutron capture cross section, the safety of its capture products, and its diverse isotopic properties make it a popular neutron absorber / shielder in the nuclear field.

[0003] Ordinary boron carbide powder has low bulk density and tap density. The bulk density is about 0.5g / cm 3 , tap density is 1.0g / cm 3 . Its low bulk density and tap density make it difficult for it to meet the requirements of nuclear reactor external protection as a neutron absorption / shielding material. However, due to the physical properties of high hardness and brittleness, the boron carbide bulk ceramics that meet the density requirements are difficult to process into complex shapes and have high costs. In addition, low bulk density / tap density boron carbide powder is difficult to load into the mold during the hot pressing process of ceramic products, and it is difficult to achieve uniform loading. When boron carbide powder is used in nuclear reactors, it is difficult to directly load the reactor mold. Summary of the Invention

[0004] In response to the above-mentioned problems existing in the prior art, the present invention provides a method for preparing boron carbide powder to solve the problems in the existing methods, such as the difficulty in loading the mold and achieving uniform loading during the hot pressing preparation of ceramic products with low bulk density / tapped density boron carbide powder; and the difficulty in directly loading the reactor mold when used in nuclear reactors.

[0005] The specific content of the invention is as follows:

[0006] In a first aspect, the present invention provides a method for preparing boron carbide powder, the method comprising the following steps:

[0007] S1: Nuclear-grade boron carbide powder is used as raw material, phenolic resin is used as a 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%;

[0008] 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;

[0009] 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;

[0010] 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, and then mixing the first boron carbide material: the second boron carbide material: the third boron carbide material in a mass ratio of 0-0.1:0.1-0.4:0.5-0.9 to obtain boron carbide powder.

[0011] Optionally, in step S1, based on 100 wt% of the mixed slurry, the amount of phenolic resin added is 5 wt% to 20 wt%, and the balance is deionized water.

[0012] Optionally, in step S1, the wet ball milling ball-to-material ratio is 3:1, and the ball milling time is 4 to 16 hours.

[0013] Optionally, in 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.

[0014] Optionally, in step S3, the molding pressure of the cold isostatic pressing is 80 MPa to 120 MPa.

[0015] Optionally, in step S4, the sintering is performed under an argon atmosphere, the sintering temperature is 2100° C. to 2320° C., and the sintering time is 5 to 8 hours;

[0016] 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 .

[0017] Optionally, in 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:

[0018] Ball milling the first boron carbide material so that the median diameter of the first boron carbide material is 6 to 12 μm;

[0019] Ball milling the second boron carbide material so that the median diameter of the second boron carbide material is 50-60 μm;

[0020] 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.

[0021] Optionally, 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.

[0022] In a second aspect, the present invention provides a boron carbide powder prepared by the preparation method described in the first aspect, wherein the boron carbide powder has a bulk density greater than 1.1 g / cm 3 , tap density greater than 1.70g / cm 3 .

[0023] In a second aspect, the present invention provides an application of boron carbide powder produced by the preparation method described in the first aspect. 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:

[0024] The present invention provides a method for preparing boron carbide powder. The boron carbide powder prepared by this process has high bulk density and tap density, and the tap density can reach 1.70g / cm 3 The above mentioned density reaches the level of bulk boron carbide ceramics, which can realize uniform filling of complex-shaped containers, has low preparation cost and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 A flow chart of a method for preparing boron carbide powder provided in an embodiment of the present invention is shown;

[0027] Figure 2 A schematic diagram showing the principle of proportioning and mixing of boron carbide powder provided in an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means a limitation on the present invention and its application or use. Based on the embodiments of the present invention, any product that is identical or similar to the present invention and is obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts falls within the scope of protection of the present invention. In addition, all other embodiments obtained by ordinary technicians in this field without carrying out creative work fall within the scope of protection of the present invention.

[0029] Where specific experimental steps or conditions are not specified in the examples, the conventional experimental steps or conditions described in the prior art in the art may be used. Reagents and other instruments used, for which the manufacturer is not specified, are commercially available conventional reagent products. Furthermore, the accompanying drawings are merely schematic illustrations of embodiments of the present invention and are not necessarily drawn to scale. Identical reference numerals in the figures denote identical or similar parts, and their repeated descriptions will be omitted. Some block diagrams shown in the accompanying drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0030] Technologies, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such technologies, methods, and equipment should be considered part of the description of the present invention.

[0031] In the description of the present invention, it should be understood that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0032] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Before describing in detail the method for preparing boron carbide powder provided by the present invention, it is necessary to describe the related technologies as follows:

[0034] Boron carbide, second only to diamond and cubic boron nitride in hardness, exhibits high hardness, wear resistance, and compressive strength. Its excellent mechanical properties and low density make it a popular material for body armor and vehicle armor in military ceramics. In the field of functional ceramics, boron carbide's high thermal neutron capture cross section, the safety of its capture products, and its diverse isotopic properties make it a popular neutron absorber / shielder in the nuclear field.

[0035] Ordinary boron carbide powder has low bulk density and tap density. The bulk density is about 0.5g / cm 3 , tap density is 1.0g / cm 3 The low bulk density and tap density make it difficult for boron carbide powder to meet the requirements of nuclear reactor protection as a neutron absorption / shielding material. However, due to the high hardness and brittleness of boron carbide bulk ceramics that meet the density requirements, complex shapes are difficult to process and have high costs. In addition, low bulk density / tap density boron carbide powder is difficult to mold and achieve uniform loading during the hot pressing process of ceramic products.

[0036] In order to enable those skilled in the art to more clearly understand the present invention, the preparation method of the boron carbide powder of the present invention is now described in detail through the following examples.

[0037] In a first aspect, the present invention provides a method for preparing boron carbide powder. Figure 1 The flowchart of the method for preparing boron carbide powder provided by the embodiment of the present invention is shown as follows: Figure 1 As shown, the preparation method comprises the following steps:

[0038] S1: Nuclear-grade boron carbide powder is used as raw material, phenolic resin is used as a 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%;

[0039] 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;

[0040] 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;

[0041] 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, and then mixing the first boron carbide material: the second boron carbide material: the third boron carbide material in a mass ratio of 0-0.1:0.1-0.4:0.5-0.9 to obtain boron carbide powder.

[0042] By adopting this technical solution, nuclear-grade boron carbide usually contains a higher proportion of boron-10 isotope to enhance its neutron shielding effect in nuclear reactors.

[0043] As a sintering aid, phenolic resin decomposes at high temperatures, releasing gases (such as water vapor and carbon dioxide). These gases help open up the gaps between particles and promote particle rearrangement. The residual carbon after decomposition can fill the gaps between particles, increasing the contact area between particles and thus improving the density of the final product. Phenolic resin softens and flows at relatively low temperatures, which helps form a preliminary interconnected network during the initial sintering stages and reduces the difficulty of subsequent densification. It also reduces the presence of oxides on the particle surface, thereby lowering the sintering activation energy and enabling good sintering results at lower temperatures. The decomposition products of phenolic resin act as reducing agents, helping to remove certain metal oxide impurities and purifying the internal environment of the sintered body, thereby promoting the formation of a purer and more uniform microstructure.

[0044] Phenolic resin acts as a binder, increasing the viscosity of the slurry while maintaining adequate fluidity for easy operation during the spray granulation process. After drying, the phenolic resin forms a preliminary mechanical bond between the powder particles, significantly improving the strength of the green body (unsintered body) and preventing breakage during subsequent processing and handling. The decomposition behavior of phenolic resin during sintering can be controlled by adjusting the added dosage, thereby influencing the dimensional accuracy and shrinkage of the final product.

[0045] The solid content of the mixed slurry is controlled at 40wt%~60wt%, ensuring that the slurry has good fluidity and appropriate viscosity, which is convenient for spray granulation.

[0046] Spray granulation technology converts the mixed slurry into spherical particles, improving the powder's fluidity and compaction density. Spray granulation atomizes the liquid material (mixed slurry) into fine droplets, which are then rapidly dried in hot air to form dry granules. This produces granules with a narrow particle size distribution and regular shape, helping to improve the product's fluidity, compressibility, and solubility.

[0047] The first boron carbide material and the second boron carbide material of different particle sizes are screened out by screening, and the materials of the remaining particle sizes are formed into a third boron carbide material by cold isostatic pressing and crushing. The three materials are then sintered at high temperature to improve the material strength. During the sintering process, some materials may stick together. After the high-temperature sintering, the three materials are reprocessed and crushed and / or ball-milled to obtain materials with corresponding particle size ranges again. The reprocessed materials have a more uniform particle size distribution.

[0048] Figure 2 The schematic diagram of the principle of mixing the boron carbide powder provided in the embodiment of the present invention is shown as follows: Figure 2As shown, three types of boron carbide materials with matching particle sizes are mixed according to a ratio to obtain boron carbide powder. This method helps to improve the contact between particles and reduce porosity, thereby increasing the density and mechanical strength of the final product.

[0049] In some embodiments, in step S1, based on 100 wt% of the mixed slurry, the amount of the phenolic resin added is 5 wt% to 20 wt%, and the balance is deionized water.

[0050] By adopting this technical solution, an appropriate amount of phenolic resin (5wt%~20wt%) helps to improve the adhesion of the slurry and the degree of densification during the sintering process.

[0051] In some embodiments, in step S1, the wet ball milling ball-to-material ratio is 3:1, and the ball milling time is 4 to 16 hours.

[0052] The adoption of this technical solution ensures that the components in the slurry are fully dispersed and evenly mixed.

[0053] In some embodiments, in step S2, spray granulation is used to obtain a spherical boron carbide material, the spray granulation air inlet temperature is 200°C~250°C, the air outlet temperature is 120~140°C, and the particle size of the spherical boron carbide material obtained by spray granulation is 3μm-100μm.

[0054] With this technical solution, the selection of the air inlet temperature and the air outlet temperature ensures the morphology and fluidity (Hall velocity) of the particles, helps to form highly fluid spherical particles, and makes the final product have excellent processing properties.

[0055] In some embodiments, in 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; and the Hall flow rate of the first boron carbide material is 50-60 g / min.

[0056] This technical solution simplifies the preparation of quasi-spherical boron carbide materials, improving the powder's fluidity and compaction density. Because the first and second boron carbide materials have different particle size ranges and therefore different flow rates, they can be initially separated based on the difference in flow rates. This reduces the workload and energy consumption of subsequent screening.

[0057] In some embodiments, in step S3, the cold isostatic pressing pressure is 80 MPa to 120 MPa.

[0058] The adoption of this technical solution ensures close contact between the third boron carbide material particles, reduces the porosity, and improves the density of the material.

[0059] In some embodiments, in step S4, the high-temperature sintering is performed in an argon atmosphere, the sintering temperature is 2200° C. to 2320° C., and the sintering time is 5 to 8 hours;

[0060] 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 .

[0061] By 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.

[0062] In some embodiments, in 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:

[0063] Ball milling the first boron carbide material so that the median diameter of the first boron carbide material is 6 to 12 μm;

[0064] Ball milling the second boron carbide material so that the median diameter of the second boron carbide material is 50-60 μm;

[0065] 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.

[0066] By adopting this technical solution, the first boron carbide material, the second boron carbide material and the third boron carbide material after sintering are subjected to at least one of ball milling and crushing, respectively. While ensuring that the three materials have a high density, the particle size distribution of the three materials is further made more uniform, which is beneficial to the subsequent mixing ratio. Small particle size materials are more easily filled in the gaps of large particle size materials.

[0067] In some embodiments, 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.

[0068] By adopting this technical solution, the bulk density of the powder can be optimized, and the loose density and tap density can be increased.

[0069] In addition, the present invention also provides a boron carbide powder prepared by the preparation method, wherein the boron carbide powder has a bulk density greater than 1.1 g / cm 3 , tap density greater than 1.70g / cm 3 .

[0070] By adopting this technical solution, the boron carbide powder has higher bulk density and tap density, high hardness, high wear resistance and high compressive strength.

[0071] 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.

[0072] By adopting this technical solution, the high bulk density and tap density of boron carbide powder can meet the requirements of nuclear reactor external protection and is easy to process. In addition, the present invention also provides a boron carbide powder prepared by the preparation method, wherein the bulk density of the boron carbide powder is greater than 1.1g / cm 3 , tap density greater than 1.70g / cm 3 .

[0073] By adopting this technical solution, the boron carbide powder has higher bulk density and tap density, high hardness, high wear resistance and high compressive strength.

[0074] 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.

[0075] By adopting this technical solution, the higher bulk density and tap density of boron carbide powder can meet the requirements of nuclear reactor external protection and is easy to process.

[0076] Example 1

[0077] A certain amount of nuclear-grade boron carbide powder was weighed as raw material, and 8wt% phenolic resin was added as a binder and sintering aid. The mixture was then mixed with deionized water to form a 55wt% solids slurry. The mixture was wet-ball milled for 8 hours at a ball-to-batch ratio of 3:1. The slurry was dried and spheroidized using spray granulation with an inlet air temperature of 220°C and an outlet air temperature of 130°C. The resulting quasi-spherical boron carbide material was sieved to obtain a first boron carbide material with a particle size of 3-20μm, a second boron carbide material with a particle size of 30-80μm, and a remaining boron carbide material. The Hall flow rate of the second boron carbide material was 65g / min, while that of the first boron carbide material was 54g / min. The remaining boron carbide material was placed in a cold isostatic pressing mold and isostatically pressed at 120MPa for 5 minutes to produce a green block. This green block was then crushed to produce a third boron carbide material with a particle size of 0.1-0.8mm. The three precursor materials (first boron carbide material, second boron carbide material, and third boron carbide material) were placed in a graphite crucible and heated to 2200°C under an argon atmosphere. The sintering time was 6 hours and the materials were naturally cooled to room temperature. The density of the three particle size powders / fragments was tested using mercury intrusion porosimetry, and the true density of the third boron carbide material was 2.30 g / cm3 The true density of the second boron carbide material is 2.24g / cm 3 The first boron carbide material has a true density of 2.21 g / cm 3 . The second boron carbide material was ball-milled in a ball mill for 3 hours to obtain a second boron carbide material with D50=55μm; the first boron carbide material was ball-milled in a ball mill for 6 hours to obtain a first boron carbide material with D50=8μm; the third boron carbide material was ball-milled in a ball mill for 6 hours to obtain a third boron carbide material with a particle size range of 0.43~0.72mm. The three materials were mixed in a mass ratio of 0.7:0.25:0.05 of the third boron carbide material: the second boron carbide material: the first boron carbide material, and mixed in a high-speed mixer to obtain a boron carbide powder with uniform particle size distribution. The bulk density and tap density of the boron carbide powder were tested using an intelligent powder property analyzer. The bulk density of the boron carbide powder was 1.16g / cm 3 , the tap density is 1.74g / cm 3 .

[0078] Example 2

[0079] A certain amount of nuclear-grade boron carbide powder was weighed as raw material, and 8wt% phenolic resin was added as a binder and sintering aid. The mixture was then mixed with deionized water to form a 55wt% solids slurry. The mixture was wet-ball milled for 8 hours at a ball-to-batch ratio of 3:1. The slurry was dried and spheroidized using spray granulation with an inlet air temperature of 220°C and an outlet air temperature of 130°C. The resulting quasi-spherical boron carbide material was sieved to obtain a first boron carbide material with a particle size of 3-20μm, a second boron carbide material with a particle size of 30-80μm, and a remaining boron carbide material. The Hall flow rate of the second boron carbide material was 65g / min, while that of the first boron carbide material was 54g / min. The remaining boron carbide material was placed in a cold isostatic pressing mold and isostatically pressed at 120MPa for 5 minutes to produce a green block. This green block was then crushed to produce a third boron carbide material with a particle size of 0.1-0.8mm. The three precursor materials (first boron carbide material, second boron carbide material, and third boron carbide material) were placed in a graphite crucible and heated to 2200°C under an argon atmosphere. The sintering time was 6 hours and the materials were naturally cooled to room temperature. The density of the three particle size powders / fragments was tested using mercury intrusion porosimetry, and the true density of the third boron carbide material was 2.30 g / cm 3 The true density of the second boron carbide material is 2.24g / cm 3 The first boron carbide material has a true density of 2.21 g / cm 3. The second boron carbide material was ball-milled in a ball mill for 3 hours to obtain a second boron carbide material with D50=55μm; the first boron carbide material was ball-milled in a ball mill for 6 hours to obtain a first boron carbide material with D50=8μm; the third boron carbide material was ball-milled in a ball mill for 6 hours to obtain a third boron carbide material with a particle size range of 0.43~0.72mm. The three powders were mixed in a mass ratio of 0.78:0.2:0.02 of the third boron carbide material: the second boron carbide material: the first boron carbide material, and mixed in a high-speed mixer to obtain boron carbide powder with uniform particle size distribution. The bulk density and tap density of the boron carbide powder were tested using an intelligent powder property analyzer. The bulk density of the boron carbide powder was 1.18g / cm 3 , the tap density is 1.71g / cm 3 .

[0080] Example 3

[0081] A certain amount of nuclear-grade boron carbide powder was weighed as raw material, and 8wt% phenolic resin was added as a binder and sintering aid. The mixture was then mixed with deionized water to form a 55wt% solids slurry. The mixture was wet-ball milled for 8 hours at a ball-to-batch ratio of 3:1. The slurry was dried and spheroidized using spray granulation with an inlet air temperature of 220°C and an outlet air temperature of 130°C. The resulting quasi-spherical boron carbide material was sieved to obtain a first boron carbide material with a particle size of 3-20μm, a second boron carbide material with a particle size of 30-80μm, and a remaining boron carbide material. The Hall flow rate of the second boron carbide material was 65g / min, while that of the first boron carbide material was 54g / min. The remaining boron carbide material was placed in a cold isostatic pressing mold and isostatically pressed at 120MPa for 5 minutes to produce a green block. This green block was then crushed to produce a third boron carbide material with a particle size of 0.1-0.8mm. The three precursor materials (first boron carbide material, second boron carbide material, and third boron carbide material) were placed in a graphite crucible and heated to 2200°C under an argon atmosphere. The sintering time was 6 hours and the materials were naturally cooled to room temperature. The density of the three particle size powders / fragments was tested using mercury intrusion porosimetry, and the true density of the third boron carbide material was 2.30 g / cm 3 The true density of the second boron carbide material is 2.24g / cm 3 The first boron carbide material has a true density of 2.21 g / cm 3. The second boron carbide material was ball-milled in a ball mill for 3 hours to obtain a second boron carbide material with D50=55μm; the first boron carbide material was ball-milled in a ball mill for 6 hours to obtain a first boron carbide material with D50=8μm; the third boron carbide material was ball-milled in a ball mill for 6 hours to obtain a third boron carbide material with a particle size range of 0.43~0.72mm. The three powders were mixed in a mass ratio of 0.62:0.3:0.08 of the third boron carbide material: the second boron carbide material: the first boron carbide material, and mixed in a high-speed mixer to obtain boron carbide powder with uniform particle size distribution. The bulk density and tap density of the boron carbide powder were tested using an intelligent powder property analyzer. The bulk density of the boron carbide powder was 1.15g / cm 3 , the tap density is 1.76g / cm 3 .

[0082] Comparative Example

[0083] A certain amount of nuclear-grade boron carbide powder was weighed as raw material, and 8wt% phenolic resin was added as a binder and sintering aid. The mixture was prepared into a 55wt% solids slurry in deionized water and wet ball milled for 8 hours at a ball-to-batch ratio of 3:1. The slurry was dried and spheroidized using spray granulation with an inlet air temperature of 220°C and an outlet air temperature of 130°C. The resulting spherical boron carbide powder was placed in a cold isostatic pressing mold and isostatically pressed at 120 MPa for 5 minutes to produce a green block. This green block was then crushed into boron carbide fragments with a particle size of 0.1-0.8 mm. The resulting boron carbide fragments were placed in a graphite crucible, heated to 2200°C under argon, sintered for 6 hours, and naturally cooled to room temperature. The boron carbide fragments were then ball milled in a ball mill for 6 hours to obtain boron carbide powder. The bulk density and tap density of boron carbide powder were tested using an intelligent powder property analyzer. The bulk density of the boron carbide powder was 0.86 g / cm 3 , the tap density is 1.23g / cm 3 .

[0084] The relevant data of the above Examples 1-3 and Comparative Examples are summarized in Table 1 below:

[0085] Table 1. Experimental and test data related to Examples 1-3 and Comparative Examples

[0086]

[0087] As can be seen from the data in the table above, when other processing methods are the same, the use of three powders with mutually compatible particle sizes for mixing can greatly improve the bulk density and tap density compared to powders with a single particle size. Figure 2As shown in the figure, this is mainly because, after the powders with matching particle sizes are mixed, the small-sized powder can fill the gaps in the large-sized powder, thereby reducing the proportion of powder gaps and increasing the bulk density of the powder. Especially after the powders are more densely packed by vibration or tapping, the relative positions between the three-sized powder particles are optimized, reducing the gaps between the particles, so that more small-sized powder can be filled into the gaps in the large-sized powder. By optimizing the ratio of the three powders, boron carbide powders with different bulk densities and tapped densities can be obtained, and the tapped density can reach 1.70g / cm 3 The above mentioned density reaches the level of bulk boron carbide ceramics, enabling uniform loading of complex-shaped containers. The low production cost makes it suitable for industrial production. For example, it can be used as a neutron absorption / shielding material in nuclear reactors.

[0088] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations 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 any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.

[0089] For simplicity of description, the method embodiments are described as a series of actions. However, those skilled in the art should be aware that the present invention is not limited by the order of the actions described, as certain steps can be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also be aware that the embodiments described in this specification are preferred embodiments, and the actions and components involved are not necessarily required for the present invention.

[0090] The above is a detailed introduction to the method for preparing boron carbide powder provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods 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 ideas. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting 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 as raw material, phenolic resin as a 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%; based on the mass of the mixed slurry as 100wt%, the amount of the phenolic resin added is 5wt% to 20wt%, and the balance is deionized water; 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, and then mixing the first boron carbide material: the second boron carbide material: the third boron carbide material in a mass ratio 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, wherein: In the step S1, the wet ball milling ratio is 3:1, and the ball milling time is 4 to 16 hours.

3. The method for preparing boron carbide powder according to claim 1, wherein: In 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.

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

5. The method for preparing boron carbide powder according to claim 1, wherein: 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 .

6. The method for preparing boron carbide powder according to claim 1, wherein: 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 milling the first boron carbide material so that the median diameter of the first boron carbide material is 6 to 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.

7. The method for preparing boron carbide powder according to claim 1, wherein: 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.

8. A boron carbide powder prepared by the preparation method according to any one of claims 1 to 7, 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 .

9. An application of boron carbide powder prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The boron carbide powder can be used as a neutron absorption / shielding material in a nuclear reactor.

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