Method for preparing boron carbide powder and boron carbide bulletproof ceramic prepared therefrom

Abstract

The present invention belongs to the field of special ceramics, and specifically relates to a method for preparing a boron carbide powder. The method comprises the steps of: S1, pre-dispersion, involving: weighing two raw boron carbide powders in different particle size ranges, spraying a first dispersion solution onto the raw boron carbide powders and then dispersing same; S2, a sanding treatment, involving: transferring a slurry obtained from the pre-dispersion treatment to a high-speed sand mill, adding two boron carbide grinding balls of different sizes, and performing sanding at a speed of 18-20 m / s for 6-10 h, with the mass ratio of the boron carbide grinding balls to the raw boron carbide powders being 3-5:1; S3, mixing and slurrying, involving: placing the sanded slurry into a high-speed dispersion machine, performing spraying with a second dispersion solution, adding a sintering aid, and then adding an aqueous solution of a water-soluble phenol-formaldehyde resin and an aqueous solution of sodium carboxymethyl cellulose to obtain a mixed slurry; and S4, spray granulation. In the present invention, two raw boron carbide powders in different particle size ranges are used to directly prepare the boron carbide powder used for producing a pressed blank; the process steps are short, the production cost is relatively low, and the method is suitable for large-scale production and application.

Description

A method for preparing boron carbide powder and boron carbide bulletproof ceramics Technical Field

[0001] The invention belongs to the field of special ceramics, and in particular relates to a method for preparing boron carbide powder. Background Art

[0002] Boron carbide features low density, high strength, high-temperature stability, and excellent chemical stability. High-purity, fine-particle boron carbide powder can be used to produce specialty boron carbide ceramic products through hot pressing, plasma discharge sintering, or pressureless sintering. Pressureless sintering is challenging for materials with high covalency, such as boron carbide, and requires appropriate powder design to achieve a high-density sintered body. Smaller powder sizes increase the specific surface area and the driving force for sintering. Furthermore, finer powders generate more structural defects during the preparation process, resulting in higher sintering activity and promoting sintering and densification. Therefore, an effective method for achieving densification through pressureless sintering is powder nano-crystallization. Nano-crystallization of boron carbide powder is a crucial foundation for the densification of boron carbide ceramics through pressureless sintering.

[0003] In the prior art, when preparing special boron carbide ceramic products, a submicron-grade boron carbide raw material powder with a specific particle size range is first obtained through mechanical methods. The powder is then configured and pressed into a green compact, which is then sintered using a specific sintering process. For example, the invention application "CN102432014 A Method for Preparing Submicron-Grade Boron Carbide Powder" discloses that when preparing submicron boron carbide powder, the boron carbide raw material powder, a dispersant, water, and dielectric balls are directly placed in a sand mill and sand-milled for 3-60 hours. The dielectric balls are then filtered out to obtain a boron carbide slurry. This method requires a very long grinding time to obtain a submicron-grade powder, and there is a phenomenon of powder agglomeration, resulting in incomplete grinding. The invention application "CN113480314A A Process for Preparing Boron Carbide Ceramics by Pressureless Sintering" first ball-mills the boron carbide raw material powder to obtain a submicron powder. Then, a water solvent, a dispersant, a sintering aid, etc. are added and ground again to obtain a slurry. The slurry is then spray-dried to obtain a granulated powder, which is then pressed into shape and then pressurelessly sintered. This process has the following shortcomings: on the one hand, it takes a long time to sand-grind the boron carbide raw material powder to obtain submicron-level powder, which requires high energy consumption and a long time; on the other hand, the particle size of the boron carbide powder is concentrated in the submicron level of 0.5-1.0μm, and there is limited room for improvement in the performance of the sintered product.

[0004] Since the purity of industrial raw materials used in the production of boron carbide cannot be strictly controlled, various impurities will be introduced during the production process. These impurities will affect the grinding and crushing efficiency of boron carbide particles and also affect the performance of subsequent pressureless sintered products.

[0005] Therefore, it is now necessary to develop a new, efficient, low-cost, and short process method that can directly use commercially available micron-sized boron carbide raw materials to prepare high-performance boron carbide powder, so as to obtain special boron carbide ceramic products with good compactness, low density, good toughness, and high ballistic performance.

[0006] Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for preparing boron carbide powder with low cost and high efficiency, which can obtain special boron carbide ceramic products with good compactness, low density, good toughness and high ballistic performance.

[0008] The specific scheme of the present invention is as follows:

[0009] A method for preparing boron carbide powder comprises the following steps:

[0010] S1. Pre-dispersion: Boron carbide raw material powders of two particle size ranges are placed in a high-speed disperser, the disperser is started, and a first dispersion solution is sprayed onto the surface of the boron carbide raw material powder through multiple atomizing nozzles provided on the barrel of the high-speed disperser. After all the first dispersion solution is sprayed, the powder is dispersed for another 0.5-1 hour, and the disperser is turned off;

[0011] S2, sand milling: transfer the pre-dispersed slurry of S1 to a high-speed sand mill, add two sizes of boron carbide grinding balls, and the mass ratio of boron carbide grinding balls to boron carbide raw material powder is 3-5:1. After nitrogen is filled, the linear speed is 18-20m / s, the grinding time is 6-10h, and the boron carbide grinding balls are filtered out;

[0012] S3, mixing and slurrying: placing the sand-milled slurry of S2 in a high-speed disperser, spraying a second dispersion solution onto the surface of the slurry through multiple atomizing nozzles provided on the barrel of the high-speed disperser, and adding a sintering aid in an amount of 2-3% of the total mass of the boron carbide raw material powder in multiple times. After all the second dispersion solution is sprayed, the mixture is dispersed for 10-30 minutes; then, a water-soluble phenolic resin aqueous solution is added through multiple atomizing nozzles, and sodium carboxymethyl cellulose is added in multiple times. The mixture is dispersed for 2-3 hours to obtain a mixed slurry;

[0013] S4, spray granulation: adjusting the solid content of the mixed slurry prepared in S3 to 30-45%, the vacuum degree of vacuum spray drying to 0.04-0.05 MPa, and the outlet temperature of vacuum spray drying to 95-100° C. to obtain boron carbide powder for granulation.

[0014] Furthermore, the first dispersing solution is a tetramethylammonium hydroxide aqueous solution, the mass ratio of the tetramethylammonium hydroxide aqueous solution to the boron carbide raw material powder is 1-1.2:1, and the total mass of the tetramethylammonium hydroxide is 1-2% of the total mass of the boron carbide raw material powder.

[0015] Furthermore, the two sizes of boron carbide grinding balls are boron carbide grinding balls with diameters of 6-8 mm and 1-2 mm in a mass ratio of 1:1.

[0016] Furthermore, the sintering aid is a mixture of titanium carbide, zirconium carbide, and lanthanum carbide with an average particle size of 0.5-1 μm, and the mass ratio of titanium carbide: zirconium carbide: lanthanum carbide is 2:1:1.

[0017] Furthermore, the mass of the water-soluble phenolic resin is 5-10% of the total mass of the boron carbide raw material powder, and the mass of the sodium carboxymethyl cellulose is 2-3% of the total mass of the boron carbide raw material powder.

[0018] Furthermore, the sodium carboxymethyl cellulose is dispersed using hot water at 80-99°C.

[0019] Furthermore, the second dispersing solution is a polyethylene glycol aqueous solution, and the mass of the polyethylene glycol is 1-2% of the total mass of the boron carbide raw material powder.

[0020] Furthermore, the S1 pre-dispersion step also includes S0, a pre-treatment step, and the pre-treatment step specifically includes:

[0021] First, boron carbide raw material powders of two particle size ranges are placed in a container, NaF powder is added, and stirred evenly; then, an appropriate amount of dilute hydrochloric acid solution with a concentration of 0.01-0.02 mol / L is added, and stirring is continued at 20-65°C for 1-5 hours, followed by centrifugation, and the solid obtained by centrifugation is collected;

[0022] The separated solid is first washed with deionized water for 1-3 times, then washed with isopropyl alcohol solution for 1-3 times, and dried to obtain pretreated boron carbide raw material powders in two particle size ranges.

[0023] Furthermore, the two particle size ranges of boron carbide raw material powders are boron carbide with an average particle size of 10-20 μm and an average particle size of 40-50 μm in a mass ratio of 1:1.

[0024] Furthermore, the mass of the NaF powder is 0.05-0.1% of the total mass of the boron carbide raw material powder.

[0025] The present invention also provides a boron carbide bulletproof ceramic, which is prepared by using the boron carbide powder prepared by the above method, and then undergoing a compacting and pressureless sintering process.

[0026] The beneficial effects of the present invention include at least the following:

[0027] 1. Since industrial boron carbide raw material powder is produced using the electric arc furnace carbothermal reduction method, its particle size typically ranges from 10-50μm and contains impurities such as iron, iron oxide, aluminum, aluminum oxide, and silicon oxide. Before producing boron carbide bulletproof ceramic products, the boron carbide particles must be ground to submicron levels to achieve densified, high-performance boron carbide ceramic products through pressureless sintering. During the sand milling process, the presence of these impurities can interfere with the contact between the boron carbide particles and the dispersant, affecting the dispersion and, consequently, the crushing of the boron carbide particles. The impact of the grinding media and the boron carbide particles during sand milling generates transient high temperatures, which can soften the metal or metal oxide and cause them to adhere to the boron carbide particles, making them more difficult to effectively crush. Furthermore, high levels of iron and boron oxide impurities can hinder the refinement of the submicron boron carbide particles during pressureless sintering, thereby reducing the density and toughness of the ceramic product.

[0028] Preliminary experiments revealed that various impurities account for approximately 0.1-0.2% of the boron carbide raw material powder. By adding sodium fluoride and hydrochloric acid, the iron, iron oxide, aluminum, aluminum oxide, and boron oxide in the boron carbide raw material powder react with hydrochloric acid or hydrofluoric acid to dissolve them. This pretreatment effectively removes impurities such as iron, iron oxide, aluminum, aluminum oxide, and silicon oxide, significantly improving the dispersibility of the boron carbide particles and the subsequent sand milling process. After impurity removal, the boron carbide raw material powder is washed with an isopropyl alcohol solution to remove soluble substances such as sodium ions and to modify the surface of the boron carbide raw material powder, preventing powder agglomeration.

[0029] 2. When using the sand milling technology in the prior art, it was found that the boron carbide raw material powder had agglomeration. After experimental analysis, the reason is that when water and dispersant are directly added to the micron-sized boron carbide raw material powder at one time, even if a long high-speed dispersion is used, the small agglomerates in the boron carbide raw material powder will still remain unbroken. When all the water solvent and dispersant are added at one time, because the amount of dispersant is much smaller than the amount of boron carbide raw material powder, some boron carbide particles will quickly absorb the water solvent and dispersant, while other boron carbide particles will have difficulty contacting the dispersant, resulting in uneven contact between the boron carbide particles and the water solvent and dispersant, causing some boron carbide particles to remain dry particles during subsequent grinding. The dry particles are then crushed by the grinding medium to form small particles. Because they are not coated with the water solvent and dispersant, the crushed small particles are easily agglomerated again due to the influence of intermolecular forces. Therefore, using the sand milling technology in the prior art requires a large amount of grinding medium and a long grinding process to obtain submicron-level boron carbide particles, which is time-consuming, labor-intensive, and consumes a lot of energy.

[0030] In the present invention, the dispersant and deionized water are fully mixed in advance to form a first dispersed solution, and then uniformly sprayed onto the boron carbide particles while stirring in a high-speed disperser, thereby improving the uniformity of the contact between the boron carbide particles and the tiny droplets, and allowing all the boron carbide particles to be uniformly exposed to the dispersant and the aqueous solvent as much as possible. Because water can act as a solvent to form a suspension effect on the boron carbide raw material powder, it prevents the boron carbide particles from agglomerating together, breaks the agglomeration force between the boron carbide particles, and a reversible reaction occurs between the unsaturated bonds on the surface of the boron carbide particles and the water molecules, which helps the formation and expansion of cracks in the boron carbide particles to be easily ground, thereby promoting the grinding process. The first dispersed solution is evenly sprayed through the nozzle, ensuring that the vast majority of the boron carbide particles are coated with the aqueous solvent and dispersant, reducing the amount of grinding media used, significantly reducing the time for mixing and dispersion, and significantly reducing the dry agglomeration of the boron carbide particles and the phenomenon of reagglomeration of small particles broken during the grinding process, thereby greatly improving the grinding efficiency and grinding quality. The addition of alkaline tetramethylammonium hydroxide improves the dispersibility of boron carbide particles and provides an alkaline environment for sand milling, ensuring the stability of boron carbide crushing. Nitrogen is added to reduce the oxygen content in the sand milling environment to prevent oxygen from reacting with boron carbide or other impurities during the transient high temperature environment of sand milling.

[0031] 3. The present invention uses boron carbide grinding balls, made of the same material as the boron carbide particles, as the grinding medium, avoiding the contamination of the raw material by using stainless steel balls. Compared to using a single sanding medium, using two sizes of media for sanding improves sanding efficiency, allowing for the production of finer, uniformly distributed submicron boron carbide particles in a shorter timeframe. During sanding, the larger sanding media initially crush the powder, while the smaller sanding media simultaneously subject it to high-frequency extrusion and collision. The combination of the two sizes of sanding media efficiently converts gravitational potential energy into sanded powder, significantly reducing sanding time and improving both sanding efficiency and crushing effectiveness. The present invention utilizes boron carbide raw material powders of two particle size ranges, which are pre-dispersed and then directly sand-milled to produce mixed boron carbide particles with particle sizes ranging from 100 nanometers to 1 micron. The different particle sizes of boron carbide particles are combined, allowing the smaller particles to fill the gaps between the larger particles. This increases the overall density of the pressed green compact, reduces porosity, and thus enhances the compactness of the sintered product. In the present invention, a tetramethylammonium hydroxide aqueous solution is used as the first dispersing solution for the boron carbide raw material powder. Since tetramethylammonium hydroxide is a non-ionic wetting and dispersing agent, it is non-ionized and non-charged in water, and can effectively reduce the surface tension of the boron carbide powder and improve the wettability, thereby reducing the adsorption between the boron carbide particles and reducing the agglomeration phenomenon. The dispersion efficiency is high, and a suitable environment is provided for sand milling and crushing.

[0032] 4. The present invention employs an aqueous polyethylene glycol solution as the second dispersing solution, which can surface-modify the nano- and submicron-sized boron carbide particles obtained after sand milling. This chemical bond forms on the surface of the boron carbide particles, providing a certain degree of surface activity and establishing a cross-linked structure between the boron carbide particles and the phenolic resin. This helps improve the dispersibility and stability of the nano- and submicron-sized boron carbide particles and reduces aggregation. The aqueous polyethylene glycol solution and water-soluble phenolic resin are uniformly dissolved in water in advance and then evenly sprayed onto the surface of the slurry through a nozzle, significantly improving the mixing uniformity with the slurry.

[0033] 5. The present invention adds sintering aids of titanium carbide, zirconium carbide and lanthanum carbide with an average particle size of 0.5-1 μm, which can effectively pin the grain boundaries, inhibit the growth of boron carbide grains, play a role in grain refinement and strengthening, and improve the fracture toughness of boron carbide products; at the same time, it reduces the grain boundary energy, increases the surface energy, and forms neck connections between adjacent boron carbide particles during high-temperature sintering, thereby promoting densification and grain refinement, reducing the ceramic sintering temperature, and improving the sintering density. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG1 is a schematic diagram of the preparation process of boron carbide powder in Example 1 of the present invention;

[0035] FIG2 is a schematic diagram of the particle size distribution of boron carbide sampled and tested after sand milling in Example 1 of the present invention and Comparative Example 5, wherein the horizontal axis is the particle size range of the boron carbide particles and the vertical axis is the percentage;

[0036] FIG3 is a schematic diagram of the particle size distribution of boron carbide sampled and tested after sand milling in Comparative Examples 1 and 2 of the present invention, wherein the horizontal axis is the particle size range of the boron carbide particles and the vertical axis is the percentage. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0038] Example 1

[0039] The method for preparing boron carbide powder in this embodiment includes the following steps:

[0040] S0. Pretreatment of boron carbide raw material powder:

[0041] First, 60 kg of boron carbide raw material powder with two particle size ranges of 10-20 μm and 40-50 μm in a mass ratio of 1:1 was placed in a stirring container, 0.06 kg of NaF powder was added, and stirred evenly; then, while stirring, a total of 150 L of a 0.02 mol / L dilute hydrochloric acid solution was added in multiple portions, and stirring was continued at room temperature of 20-35°C for 5 hours. Then, centrifugation was performed, and the solid obtained by centrifugation was collected;

[0042] The separated solid was washed three times with deionized water, then washed twice with isopropyl alcohol solution, and dried to obtain pretreated boron carbide raw material powders of two particle size ranges;

[0043] S1, pre-dispersion: take 50kg of the pretreated boron carbide raw material powders of two particle size ranges and place them in a high-speed disperser, start the disperser, 200-300r / m, and spray the first dispersed solution of tetramethylammonium hydroxide aqueous solution onto the surface of the boron carbide raw material powder through multiple atomizing nozzles provided on the barrel of the high-speed disperser, the atomizing nozzle aperture is less than 0.3mm, the atomized particles are ≤30μm, and the nozzle flow rate is ≤0.1L / min. The tetramethylammonium hydroxide aqueous solution: the mass ratio of the boron carbide raw material powder is 1:1, and the total mass of the tetramethylammonium hydroxide is 0.5kg. The tetramethylammonium hydroxide aqueous solution is prepared with deionized water. After all the first dispersed solutions are sprayed, they are dispersed at 300-400r / m for 1h, and the disperser is turned off;

[0044] S2, sand milling: transfer the pre-dispersed slurry of S1 to a high-speed sand mill, add two sizes of boron carbide grinding balls, the two sizes of boron carbide grinding balls are boron carbide grinding balls with a diameter of 6-8 mm and 1-2 mm in a mass ratio of 1:1, and the mass ratio of boron carbide grinding balls to boron carbide raw material powder is 3:1. After nitrogen is injected, the linear speed is 18-19 m / s, the grinding time is 10 hours, and the boron carbide grinding balls are filtered out;

[0045] S3, mixed slurry: the slurry after sand milling in S2 is placed in a high-speed disperser at 200-300r / m for dispersion, and the second dispersion solution is sprayed onto the surface of the slurry through multiple atomizing nozzles provided on the barrel of the high-speed disperser. The second dispersion solution is a polyethylene glycol aqueous solution, and the mass of polyethylene glycol is 1% of the total mass of the boron carbide raw material powder, that is, 0.5kg; at the same time, 1kg of sintering aid with a mass of 2% of the total mass of the boron carbide raw material powder is added in multiple times. The sintering aid is a mixture of titanium carbide, zirconium carbide, and lanthanum carbide with an average particle size of 0.5-1μm, titanium carbide: carbon The mass ratio of zirconium carbide to lanthanum carbide is 2:1:1. After all the second dispersion solution is sprayed, it is dispersed at 300-400 rpm for 30 minutes. Then, a water-soluble phenolic resin aqueous solution is added through multiple atomizing nozzles, wherein the mass of the water-soluble phenolic resin is 5% of the total mass of the boron carbide raw material powder, that is, 2.5 kg. At the same time, a sodium carboxymethyl cellulose aqueous solution, which is dissolved in 90°C hot water and stored below 35°C, is added in multiple portions, wherein the mass of the sodium carboxymethyl cellulose is 2% of the total mass of the boron carbide raw material powder, that is, 1 kg. The mixture is dispersed at 500-600 rpm for 3 hours to obtain a mixed slurry.

[0046] S4, spray granulation: adjusting the solid content of the mixed slurry prepared in S3 to 35%, the vacuum degree of the vacuum spray drying to 0.04-0.05 MPa, and the outlet temperature of the vacuum spray drying to 95-98° C. to obtain boron carbide powder for granulation.

[0047] The boron carbide powder prepared in this embodiment is used to prepare a special boron carbide bullet-proof ceramic. The subsequent steps refer to the relevant content described in the invention application with publication number CN113587728B, specifically including: placing the boron carbide powder for granulation in a mold, using hydraulic and isostatic pressing to form the boron carbide powder into a green body with a relative density of ≥60%; placing the green body in a sintering boat and performing pressureless sintering to prepare the special boron carbide bullet-proof ceramic.

[0048] Example 2

[0049] The method for preparing boron carbide powder in this embodiment includes the following steps:

[0050] S0. Pretreatment of boron carbide raw material powder:

[0051] First, 60 kg of boron carbide raw material powder with two particle size ranges of 10-20 μm and 40-50 μm in a mass ratio of 1:1 was placed in a container, 0.03 kg of NaF powder was added, and stirred evenly; then, 300 L of 0.01 mol / L dilute hydrochloric acid solution was added in multiple portions while stirring, and the mixture was stirred at 30-50°C for 3 hours. The mixture was then centrifuged and the solid obtained by centrifugation was collected;

[0052] The separated solid was washed twice with deionized water, then washed three times with isopropyl alcohol solution, and dried to obtain pretreated boron carbide raw material powders of two particle size ranges;

[0053] S1, pre-dispersion: take 50kg of the pretreated boron carbide raw material powders of two particle size ranges and place them in a high-speed disperser, start the disperser at 200-300r / m, and spray the first dispersion solution of tetramethylammonium hydroxide aqueous solution onto the surface of the boron carbide raw material powder through multiple atomizing nozzles provided on the barrel of the high-speed disperser (nozzle aperture 0.3mm or less, atomized particles ≤30μm, nozzle flow ≤0.1L / min), wherein the mass ratio of tetramethylammonium hydroxide aqueous solution to boron carbide raw material powder is 1.2:1, and the total mass of tetramethylammonium hydroxide is 1kg. After all the first dispersion solutions are sprayed, disperse them at 300-400r / m for 1h, and turn off the disperser;

[0054] S2, sand milling: transfer the pre-dispersed slurry of S1 to a high-speed sand mill, add two sizes of boron carbide grinding balls, the two sizes of boron carbide grinding balls are boron carbide grinding balls with a diameter of 6-8 mm and 1-2 mm in a mass ratio of 1:1, and the mass ratio of boron carbide grinding balls to boron carbide raw material powder is 5:1. After filling with nitrogen, the linear speed is 19-20 m / s, the grinding time is 6 hours, and the boron carbide grinding balls are filtered out;

[0055] S3, mixed slurry: the slurry after sand milling in S2 is placed in a high-speed disperser at 200-300r / m for dispersion, and the second dispersion solution is sprayed onto the surface of the slurry through multiple atomizing nozzles provided on the barrel of the high-speed disperser. The second dispersion solution is a polyethylene glycol aqueous solution, and the mass of polyethylene glycol is 2% of the total mass of the boron carbide raw material powder, that is, 1kg; at the same time, 1.5kg of sintering aid with a mass of 3% of the total mass of the boron carbide raw material powder is added in multiple times. The sintering aid is a mixture of titanium carbide, zirconium carbide, and lanthanum carbide with an average particle size of 0.5-1μm, titanium carbide: zirconium carbide : The mass ratio of lanthanum carbide is 2:1:1. After all the second dispersion solution is sprayed, it is dispersed at 300-400 r / m for 20 minutes; then a water-soluble phenolic resin aqueous solution is added through multiple atomizing nozzles, wherein the mass of the water-soluble phenolic resin is 10% of the total mass of the boron carbide raw material powder, that is, 5 kg; at the same time, a sodium carboxymethyl cellulose aqueous solution, which is dispersed and dissolved in 95°C hot water and placed below 25°C, is added in multiple times, the mass of the sodium carboxymethyl cellulose is 3% of the total mass of the boron carbide raw material powder, that is, 1.5 kg, and dispersed at 500-600 r / m for 2.5 hours to obtain a mixed slurry;

[0056] S4, spray granulation: adjusting the solid content of the mixed slurry prepared in S3 to 45%, the vacuum degree of vacuum spray drying to 0.04-0.05 MPa, and the outlet temperature of vacuum spray drying to 98-100° C. to obtain boron carbide powder for granulation.

[0057] The boron carbide powder prepared in this example is used to prepare boron carbide special bullet-proof ceramics, and the preparation method is the same as that in Example 1.

[0058] Example 3

[0059] The method for preparing boron carbide powder in this embodiment includes the following steps:

[0060] S0. Pretreatment of boron carbide raw material powder:

[0061] First, 60 kg of boron carbide raw material powder with two particle size ranges of 10-20 μm and 40-50 μm in a mass ratio of 1:1 was placed in a container, 0.04 kg of NaF powder was added, and stirred evenly; then, while stirring, 200 L of a 0.02 mol / L dilute hydrochloric acid solution was added in multiple portions, totaling 200 L, and stirring was continued at 50-65°C for 1 hour. The mixture was then centrifuged and the solid obtained by centrifugation was collected;

[0062] The separated solid was washed three times with isopropyl alcohol solution and dried to obtain pretreated boron carbide raw material powders of two particle size ranges;

[0063] S1, pre-dispersion: take 50kg of the pretreated boron carbide raw material powders of two particle size ranges and place them in a high-speed disperser, start the disperser, 200-300r / m, and spray the first dispersion solution of tetramethylammonium hydroxide aqueous solution onto the surface of the boron carbide raw material powder through multiple atomizing nozzles provided on the barrel of the high-speed disperser (nozzle aperture 0.3mm or less, atomized particles ≤30μm, nozzle flow ≤0.1L / min), wherein the mass ratio of tetramethylammonium hydroxide aqueous solution to boron carbide raw material powder is 1.1:1, and the total mass of tetramethylammonium hydroxide is 0.75kg. After all the first dispersion solutions are sprayed, disperse them at 300-400r / m for 0.5h, and turn off the disperser;

[0064] S2, sand milling: transfer the pre-dispersed slurry of S1 to a high-speed sand mill, add boron carbide grinding balls of two sizes with diameters of 6-8 mm and 1-2 mm in a mass ratio of 1:1, and the mass ratio of boron carbide grinding balls to boron carbide raw material powder is 3:1. After nitrogen is filled, the linear speed is 19-20 m / s, the grinding time is 8 hours, and the boron carbide grinding balls are filtered out;

[0065] S3, mixed slurry: the slurry after sand milling in S2 is placed in a high-speed disperser at 200-300r / m for dispersion, and the second dispersion solution is sprayed onto the surface of the slurry through multiple atomizing nozzles provided on the barrel of the high-speed disperser. The second dispersion solution is a polyethylene glycol aqueous solution, and the mass of polyethylene glycol is 1% of the total mass of the boron carbide raw material powder, that is, 0.5kg; at the same time, 1kg of sintering aid with a mass of 2% of the total mass of the boron carbide raw material powder is added in multiple times. The sintering aid is a mixture of titanium carbide, zirconium carbide, and lanthanum carbide with an average particle size of 0.5-1μm, titanium carbide: carbon The mass ratio of zirconium carbide to lanthanum carbide is 2:1:1. After all the second dispersion solution is sprayed, it is dispersed at 300-400 rpm for 15 minutes. Then, a water-soluble phenolic resin aqueous solution is added through multiple atomizing nozzles, wherein the mass of the water-soluble phenolic resin is 10% of the total mass of the boron carbide raw material powder, that is, 5 kg. At the same time, a sodium carboxymethyl cellulose aqueous solution, which is dissolved in 95°C hot water and stored below 25°C, is added in multiple times, wherein the mass of the sodium carboxymethyl cellulose is 2% of the total mass of the boron carbide raw material powder, that is, 1 kg. The mixture is dispersed at 500-600 rpm for 3 hours to obtain a mixed slurry.

[0066] S4, spray granulation: adjusting the solid content of the mixed slurry prepared in S3 to 35-38%, the vacuum degree of vacuum spray drying to 0.04-0.05 MPa, and the outlet temperature of vacuum spray drying to 95-100° C. to obtain boron carbide powder for granulation.

[0067] The boron carbide powder prepared in this example is used to prepare boron carbide special bullet-proof ceramics, and the preparation method is the same as that in Example 1.

[0068] Example 4

[0069] As shown in FIG1 , the method for preparing boron carbide powder in this embodiment includes the following steps:

[0070] S1, pre-dispersion: take 50kg of boron carbide raw material powder with two particle size ranges of average particle size of 10-15μm and average particle size of 40-50μm in a mass ratio of 1:1 and place it in a high-speed disperser, start the disperser, 200-300r / m, and spray the first dispersion solution of tetramethylammonium hydroxide aqueous solution onto the surface of the boron carbide raw material powder through multiple atomizing nozzles provided on the barrel of the high-speed disperser (nozzle aperture 0.2mm, atomized particles ≤30μm, nozzle flow ≤0.1L / min), wherein the mass ratio of tetramethylammonium hydroxide aqueous solution to boron carbide raw material powder is 1:1, and the total mass of tetramethylammonium hydroxide is 0.85kg. After all the first dispersion solutions are sprayed, disperse them at 300-400r / m for 1h, and turn off the disperser;

[0071] S2, sand milling: transfer the pre-dispersed slurry of S1 to a high-speed sand mill, add boron carbide grinding balls of two sizes with diameters of 6-8 mm and 1-2 mm in a mass ratio of 1:1, and the mass ratio of boron carbide grinding balls to boron carbide raw material powder is 4:1. After nitrogen is filled, the linear speed is 19-20 m / s, the grinding time is 9 hours, and the boron carbide grinding balls are filtered out;

[0072] S3, mixed slurry: the slurry after sand milling in S2 is placed in a high-speed disperser at 200-300r / m for dispersion, and the second dispersion solution is sprayed onto the surface of the slurry through multiple atomizing nozzles provided on the barrel of the high-speed disperser. The second dispersion solution is a polyethylene glycol aqueous solution, and the mass of polyethylene glycol is 1.5% of the total mass of the boron carbide raw material powder, that is, 0.75kg; at the same time, 1.25kg of sintering aids with a mass of 2.5% of the total mass of the boron carbide raw material powder are added in multiple times. The sintering aids are titanium carbide, zirconium carbide, and lanthanum carbide with an average particle size of 0.5-1μm. A mixture of titanium carbide: zirconium carbide: lanthanum carbide in a mass ratio of 2:1:1, after all the second dispersed solution is sprayed, it is dispersed at 300-400 r / m for 25 minutes; then, a water-soluble phenolic resin aqueous solution is added through multiple atomizing nozzles, wherein the mass of the water-soluble phenolic resin is 8% of the total mass of the boron carbide raw material powder, that is, 4 kg; at the same time, a sodium carboxymethyl cellulose aqueous solution, which is dissolved in 85-95°C hot water and allowed to cool to room temperature, is added in multiple times, the mass of the sodium carboxymethyl cellulose is 1.5 kg, and it is dispersed at 500-600 r / m for 2.5 hours to obtain a mixed slurry;

[0073] S4, spray granulation: adjusting the solid content of the mixed slurry prepared in S3 to 40-45%, the vacuum degree of vacuum spray drying to 0.04-0.05 MPa, and the outlet temperature of vacuum spray drying to 99-100° C. to obtain boron carbide powder for granulation.

[0074] The boron carbide powder prepared in this example is used to prepare boron carbide special bullet-proof ceramics, and the preparation method is the same as that in Example 1.

[0075] The following are comparative examples of the present invention.

[0076] Comparative Example 1

[0077] The preparation method of the boron carbide powder in this comparative example is the same as that in Example 1 except steps S1 and S3:

[0078] S1. Place the pretreated boron carbide raw material powders of two particle size ranges in a high-speed disperser, add equal weight of deionized water to the boron carbide raw material powder at one time, start the disperser at 300-400 rpm and disperse for 1-1.5 hours, then turn off the disperser.

[0079] S3, mixed slurry: the slurry after sand grinding in S2 is placed in a high-speed disperser, and a sintering aid with a mass of 1 kg is added at one time. The sintering aid is a mixture of titanium carbide, zirconium carbide and lanthanum carbide with an average particle size of 0.5-1 μm, and the mass ratio of titanium carbide: zirconium carbide: lanthanum carbide is 2:1:1. Then, a water-soluble phenolic resin aqueous solution is added at one time, wherein the mass of the water-soluble phenolic resin is 2.5 kg; at the same time, a sodium carboxymethyl cellulose aqueous solution is added at one time, which is dispersed and dissolved in 90°C hot water and placed below 35°C, and the mass of the sodium carboxymethyl cellulose is 1 kg. Disperse at 500-600 r / m for 3-3.5 hours to obtain a mixed slurry.

[0080] In this comparative example, deionized water was added once during the pretreatment process, and tetramethylammonium hydroxide was not added; other substances were added once during the mixing and pulping process, and polyethylene glycol was not added.

[0081] Comparative Example 2

[0082] The preparation method of the boron carbide powder in this comparative example is the same as that in Example 1 except steps S1 and S3:

[0083] S1. Pre-dispersion: 50 kg of pretreated boron carbide raw material powders of two particle size ranges were placed in a high-speed disperser, and a first dispersing solution of tetramethylammonium hydroxide aqueous solution was added at one time, wherein the mass ratio of tetramethylammonium hydroxide aqueous solution to boron carbide raw material powder was 1:1, and the total mass of tetramethylammonium hydroxide was 0.5 kg. The disperser was started and dispersed at 200-300 rpm for 15 minutes, then at 300-400 rpm for 1 hour, and then the disperser was turned off.

[0084] S3, mixed slurry: the slurry after sand milling in S2 is placed in a high-speed disperser, and a second dispersing solution is added at one time, which is a polyethylene glycol aqueous solution with a mass of 0.5 kg. A sintering aid with a mass of 1 kg is added at one time. The sintering aid is a mixture of titanium carbide, zirconium carbide and lanthanum carbide with an average particle size of 0.5-1 μm, and the mass ratio of titanium carbide: zirconium carbide: lanthanum carbide is 2:1:1. A water-soluble phenolic resin aqueous solution is added at one time, wherein the mass of the water-soluble phenolic resin is 2.5 kg. At the same time, a sodium carboxymethyl cellulose aqueous solution with a mass of 1 kg is added at one time, which is dispersed and dissolved in 90°C hot water and placed below 35°C. The mixture is dispersed at 500-600 r / m for 3-3.5 hours to obtain a mixed slurry.

[0085] In this comparative example, tetramethylammonium hydroxide aqueous solution was added once during the pretreatment process, and polyethylene glycol aqueous solution, sintering aid, sodium carboxymethyl cellulose aqueous solution and water-soluble phenolic resin aqueous solution were added once during the mixed pulping process.

[0086] Referring to the statistical graph of the particle size distribution of boron carbide after sand milling of Comparative Examples 1 and 2 in FIG3 , in Comparative Example 1, the proportion of boron carbide with a particle size of less than 1 μm is 0.21, and the proportion of particles between 1-10 μm is 0.79; in Comparative Example 2, the proportion of boron carbide with a particle size of less than 1 μm is 0.36, and the proportion of particles between 1-10 μm is 0.64. In Comparative Example 1, deionized water is added to the boron carbide raw material powder in a single step in the S1 pre-dispersion step, and tetramethylammonium hydroxide is not added. Although the particle size of the boron carbide particles after sand milling is between 1-10 μm, the proportion of boron carbide particles below 1 μm is relatively small. In Comparative Example 2, an aqueous solution of tetramethylammonium hydroxide is added to the boron carbide raw material powder during the S1 pre-dispersion step. Compared with Comparative Example 1, the boron carbide particle size distribution after sand milling is significantly improved, but the proportion of boron carbide above 1 μm is still relatively large. The reason is that the one-time addition of deionized water or tetramethylammonium hydroxide aqueous solution fails to evenly disperse all the boron carbide particles, resulting in powder agglomeration. In addition, the micron-sized boron carbide is broken and then reagglomerated during the sand milling process.

[0087] Comparative Example 3

[0088] The preparation method of boron carbide powder in this comparative example is the same as that in Example 1 except for the sintering aid added in step S3:

[0089] Step S3, mixing and slurrying: adding 1 kg of sintering aid in multiple times, the sintering aid is titanium carbide micropowder with an average particle size of 0.5-1 μm. In this comparative example, the sintering aid is titanium carbide, and zirconium carbide and lanthanum carbide are not added.

[0090] Comparative Example 4

[0091] The preparation method of the boron carbide powder in this comparative example is the same as that in Example 1 except for step S0 pretreatment and step S2 sanding treatment:

[0092] S0. Pretreatment of boron carbide raw material powder:

[0093] First, 60 kg of boron carbide raw material powder with an average particle size of 10-20 μm is placed in a container, and NaF powder is added, with the mass of the NaF powder being 0.3% of the total mass of the boron carbide raw material powder, i.e., 0.18 kg, and stirred evenly. Then, an appropriate amount of 0.02 mol / L dilute hydrochloric acid solution is added in multiple times, totaling 150 L, and the mixture is continuously stirred at 50-65° C. for 1 hour. The mixture is then centrifuged and the solid obtained by centrifugation is collected. The separated solid is first washed once with deionized water, then washed twice with an isopropyl alcohol solution, and dried to obtain pretreated boron carbide raw material powders with two particle size ranges.

[0094] S2. Sand milling: Transfer the pre-dispersed slurry of S1 to a high-speed sand mill, add boron carbide grinding balls with a diameter of 1-2 mm, the mass ratio of boron carbide grinding balls to boron carbide raw material powder is 3:1, the grinding linear speed is 18-19 m / s, the grinding time is 10 h, and the boron carbide grinding balls are filtered out.

[0095] In this comparative example, boron carbide powder with a particle size range of 10-20 μm was used as the raw material. During sand milling, only boron carbide grinding balls with a diameter of 1-2 mm were used for the grinding process. Testing after sand milling revealed that all particles had a particle size distribution concentrated between 0.5 and 3 μm, with a particle size D50 of 0.8-1.0 μm. Approximately 32% of the boron carbide particles were smaller than 1 μm.

[0096] Comparative Example 5

[0097] The preparation method of the boron carbide powder in this comparative example is the same as that in Example 1 except for the sanding treatment in step S2:

[0098] S2. Sand milling: Transfer the pre-dispersed slurry of S1 to a high-speed sand mill, add boron carbide grinding balls with a diameter of 6-8 mm, the mass ratio of boron carbide grinding balls to boron carbide raw material powder is 3:1, the grinding linear speed is 18-19 m / s, the grinding time is 10 h, and the boron carbide grinding balls are filtered out.

[0099] In this comparative example, only boron carbide grinding balls with a diameter of 6-8 mm were used for sand milling.

[0100] In Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 5, the boron carbide raw material powder was sand-milled, the boron carbide grinding balls were filtered out, and then 1 kg of the dried powder was taken out and the boron carbide particle size distribution range was detected by sieving.

[0101] Referring to the statistical graph of the particle size distribution of boron carbide after sanding for Example 1 and Comparative Example 5 in FIG2 , it can be seen that in Comparative Example 5, only boron carbide grinding balls with a diameter of 6-8 mm were used for sanding. Approximately 0.38% of the boron carbide particles had a particle size distribution below 1 μm, approximately 0.52% had a particle size between 1-5 μm, and approximately 0.1% had a particle size between 5-10 μm, indicating that most boron carbide particles remained in the micron range after crushing. In Example 1, however, 0.56% of the boron carbide particles had a particle size below 1 μm, indicating that the vast majority of boron carbide particles were in the nanometer range, and approximately 0.38% of the boron carbide particles had a particle size between 1-4 μm. Therefore, in Example 1, two sizes of grinding media are used, and its grinding efficiency is better than that in Comparative Example 5. The obtained boron carbide particle size is finer, and the proportion of nano-scale boron carbide is larger. Subsequent tests on the prepared ceramic products show that the ratio of micron-scale boron carbide to nano-scale boron carbide is about 4:6, which is more conducive to the density and grain refinement of pressureless sintering.

[0102] The boron carbide powders prepared in Examples 1-4 and Comparative Examples 1-5 were used to prepare boron carbide special bullet-proof ceramic sheets using the steps in Example 1. The actual density and hardness were tested, and the relative density was calculated. The results are shown in Table 1.

[0103] Comparative Example 6

[0104] The preparation method of the boron carbide powder in this comparative example is the same as that in Example 1 except step S3:

[0105] S3. Mixing and slurrying: adding 1 kg of sintering aid in multiple times. The sintering aid is titanium carbide and zirconium carbide particle powder with an average particle size of 0.5-1 μm. The mass ratio of titanium carbide to zirconium carbide is 1:1.

[0106] Compared with Example 1, no lanthanum carbide was added in this comparative example.

[0107] Table 1 Performance test results of boron carbide ceramic sheets prepared in various embodiments and comparative examples

[0108] According to the test results of Examples 1 to 4 in Table 1 above, the actual density of the boron carbide ceramic sheet prepared by the method of the present invention is greater than or equal to 2.72 g / cm 3 The relative density can reach more than 98.5%, and the Vickers hardness HV1.0 is between 3100 and 3200. The boron carbide ceramic sheet prepared by the present invention has high density, good compactness, and high hardness, and is suitable for use as a reinforced bulletproof insert and bulletproof armor.

[0109] In Example 4, the boron carbide raw material powder was not pretreated for impurity removal, and its relative density was 98.5%, which was slightly lower than the relative density of the boron carbide ceramic sheets of Examples 1-3, but higher than the relative density of the boron carbide ceramic sheets of Comparative Examples 1-6. This shows that by using the pretreatment, sanding and mixing steps of the present invention, the boron carbide raw material powder that has not been treated for impurities can be directly treated to obtain a ceramic product with good density, and that the pretreatment, sanding and mixing steps of the present invention on the boron carbide raw material powder that has been treated for impurities can achieve a more excellent improvement in density.

[0110] Comparing the test data of Example 1 and Comparative Example 3, in Comparative Example 3, the sintering aid is titanium carbide, and zirconium carbide and lanthanum carbide are not added. The relative density of the boron carbide ceramic product obtained by sintering is 97.9%, indicating that the addition of zirconium carbide and lanthanum carbide as sintering aids can significantly improve the relative density and Vickers hardness of the pressureless sintered boron carbide ceramic.

[0111] Comparing the test data of Example 1 and Comparative Example 4, in Comparative Example 4, boron carbide raw material powder with a particle size range of 10-20 μm was used as the raw material, and only boron carbide grinding balls with a diameter of 1-2 mm were used for sand milling during sand milling. After sand milling, it was found that the particle size distribution of all particles was concentrated between 0.5-3 μm, and boron carbide particles below 1 μm accounted for about 32%. Therefore, in Comparative Example 4, a boron carbide grinding ball was used to sand mill the boron carbide raw material powder with a particle size range of 10-20 μm. Under the same sand milling time as in Example 1, the proportion of boron carbide particles below 1 μm obtained did not reach 50%. Subsequent experimental verification found that the solution of Comparative Example 4 needed to extend the sand milling time to 16-20 hours and increase the ratio of boron carbide grinding balls to raw material powder to 8:1 in order to obtain a better sand milling effect, which significantly increased the energy consumption, duration and cost of the sand milling process.

[0112] From the comparison of the test results of the boron carbide ceramic sheets of the embodiment and the comparative example in Table 1, it can be seen that the present invention adopts two boron carbide raw material powders with different particle size ranges to directly pre-disperse, sand grind, and mix and slurry to obtain boron carbide powder for green body granulation, optimizes the production process, and is suitable for large-scale industrial production; by optimizing the pre-dispersion treatment, the phenomenon of powder agglomeration is significantly reduced, and the use of two sand grinding media is combined to significantly improve the sand grinding efficiency. Compared with the original 10-24h sand grinding time, the sand grinding time is reduced by half, which greatly saves the processing time; providing an optimized mixing and slurrying process, significantly improving the mixing efficiency of the powder, and significantly improving the density of the sintered product, so that a density greater than or equal to 2.72g / cm can be obtained. 3 , boron carbide ceramic products with excellent anti-ballistic properties and Vickers hardness HV1.0 greater than 3100.

[0113] The above is only an embodiment and does not limit the present invention in any way. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, use the technical content disclosed above to make many possible changes, modifications or modifications to the technical solution of the present invention into equivalent embodiments with equivalent changes. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention should fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing boron carbide powder, characterized in that, It includes the following steps: S1. Predispersion: Take boron carbide raw material powders with two particle size ranges and place them in a high-speed disperser. Start the disperser, and spray the first dispersion solution onto the surface of the boron carbide raw material powders through multiple atomizing nozzles arranged on the barrel of the high-speed disperser. After all the first dispersion solution is sprayed, disperse for another 0.5 - 1 h, and then turn off the disperser; S2. Sand grinding treatment: Transfer the slurry after the predispersion treatment in S1 to a high-speed sand mill, add boron carbide grinding balls of two sizes. The mass ratio of the boron carbide grinding balls to the boron carbide raw material powders is 3 - 5:

1. After filling with nitrogen, the linear velocity is 18 - 20 m / s, the grinding time is 6 - 10 h, and then filter to remove the boron carbide grinding balls; S3. Mixing and pulping: Place the slurry after the sand grinding treatment in S2 in a high-speed disperser, and spray the second dispersion solution onto the surface of the slurry through multiple atomizing nozzles arranged on the barrel of the high-speed disperser. At the same time, add a sintering aid with a mass of 2 - 3% of the total mass of the boron carbide raw material powders in multiple batches. After all the second dispersion solution is sprayed, disperse for another 10 - 30 min; then add an aqueous solution of water-soluble phenolic resin through multiple atomizing nozzles, and add an aqueous solution of sodium carboxymethyl cellulose in multiple batches while performing dispersion treatment to obtain a mixed slurry; the sintering aid is a mixture of titanium carbide, zirconium carbide, and lanthanum carbide with an average particle size of 0.5 - 1 μm, and the mass ratio of titanium carbide:zirconium carbide:lanthanum carbide is 2:1:1; S4. Spray granulation: Adjust the solid content of the mixed slurry prepared in S3 to 30 - 45%, the vacuum degree of vacuum spray drying is 0.04 - 0.05 MPa, and the outlet temperature of vacuum spray drying is 95 - 100 °C to obtain boron carbide powder for granulation.

2. The preparation method of boron carbide powder according to claim 1, characterized in that, The first dispersion solution is an aqueous solution of tetramethylammonium hydroxide. The mass ratio of the aqueous solution of tetramethylammonium hydroxide to the boron carbide raw material powders is 1 - 1.2:1, and the total mass of the tetramethylammonium hydroxide is 1 - 2% of the total mass of the boron carbide raw material powders.

3. The preparation method of boron carbide powder according to claim 2, characterized in that, The two sizes of boron carbide grinding balls are boron carbide grinding balls with diameters of 6 - 8 mm and 1 - 2 mm and a mass ratio of 1:

1.

4. The preparation method of boron carbide powder according to claim 3, characterized in that, The mass of the water-soluble phenolic resin is 5 - 10% of the total mass of the boron carbide raw material powders, and the mass of the sodium carboxymethyl cellulose is 2 - 3% of the total mass of the boron carbide raw material powders.

5. The preparation method of boron carbide powder according to claim 4, characterized in that, The second dispersion solution is an aqueous solution of polyethylene glycol, and the mass of the polyethylene glycol is 1 - 2% of the total mass of the boron carbide raw material powders.

6. The preparation method of boron carbide powder according to any one of claims 1-5, characterized in that, Before the S1 predispersion step, there is also an S0 pretreatment step, and the pretreatment step specifically includes: First, place the boron carbide raw material powders with two particle size ranges in a container, add NaF powder, and stir evenly; then add an appropriate amount of dilute hydrochloric acid solution with a concentration of 0.01 - 0.02 mol / L, continuously stir at 20 - 65 °C for 1 - 5 h, and then perform centrifugal separation to collect the solid obtained by centrifugal separation; Then add isopropanol solution to wash 1 - 3 times, and dry to obtain the pretreated boron carbide raw material powders with two particle size ranges.

7. The preparation method of boron carbide powder according to claim 6, characterized in that, The two particle size ranges of boron carbide raw material powders are boron carbide with an average particle size of 10 - 20 μm and an average particle size of 40 - 50 μm and a mass ratio of 1:

1.

8. The preparation method of boron carbide powder according to claim 7, characterized in that, The mass of the NaF powder is 0.05 - 0.1% of the total mass of the boron carbide raw material powder to be pretreated in S0.

9. A boron carbide bulletproof ceramic, characterized in that, The boron carbide powder is prepared by subjecting the boron carbide powder prepared by the preparation method of the boron carbide powder according to any one of claims 1 - 8 to a compacting treatment and a pressureless sintering process.

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