Superfine boron carbide powder and preparation method thereof

Abstract

The invention relates to the technical field of boron carbide, in particular to superfine boron carbide powder and a preparation method thereof.The preparation method comprises the following steps that S1, lithium chloride and boric anhydride are weighed according to the mass ratio of (2-5): 1, mixed and heated, when the temperature rises to 800-900 DEG C, the lithium chloride and the boric anhydride are molten, hot water vapor is introduced for a reaction, and a reaction product is obtained; anhydrous lithium borate and hydrochloric acid are obtained; s2, adding the anhydrous lithium borate obtained in the step S1 and carbon black into a reaction kettle according to a mass ratio of (3-9): (1-3), stirring to obtain a mixture, adding a dispersing agent into the mixture, taking absolute ethyl alcohol as a liquid-phase medium, stirring for 2-4 hours, reacting, and drying to obtain gel powder; s3, in an inert atmosphere, the obtained gel powder is subjected to heat preservation for 2-5 h at the temperature of 1650-1800 DEG C, carbon thermal reduction is conducted, and boron carbide crystal blocks are obtained; s4, circularly crushing the boron carbide crystal blocks obtained in the step S3 through a crusher and a ball mill to obtain boron carbide coarse powder; and S5, carrying out ultrasonic crushing on the obtained boron carbide coarse powder, and drying to obtain the superfine boron carbide powder. The method has the advantages that the process is simple, the controllability is high, and the boron carbide powder with uniform particle size and high fineness can be prepared.

Description

Technical Field

[0001] The invention relates to the technical field of boron carbide, and in particular to an ultrafine boron carbide powder and a preparation method thereof. Background Art

[0002] Boron carbide (B 4 C) It has the characteristics of high hardness, high melting point, good chemical stability and neutron absorption ability. It has received extensive attention in the fields of aerospace, nuclear industry, etc., such as being used as a material for special ceramics. As a special ceramic material, boron carbide is required to have a small particle size to increase the driving force of ceramic sintering, thereby increasing the density of the ceramic, refining the ceramic grains, and improving the strength and toughness of the ceramic; at the same time, boron carbide is required to have high purity to prevent impurities from being enriched at the ceramic grain boundaries when the boron carbide powder is sintered into ceramics, thereby reducing the strength and toughness of the ceramics.

[0003] However, due to the ultra-hard properties of boron carbide itself, the traditional preparation process often has problems such as uneven particle size distribution and low production efficiency. Therefore, it is of great significance to develop an efficient and controllable method for preparing ultrafine boron carbide powder. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide an ultrafine boron carbide powder and a preparation method thereof. The method has simple process and strong controllability and can prepare boron carbide powder with uniform particle size and high fineness.

[0005] The present invention is achieved through the following technical solutions: On the one hand, a method for preparing ultrafine boron carbide powder is provided, and the preparation method comprises the following steps:

[0006] Step S1, weighing lithium chloride and boric anhydride in a mass ratio of 2-5:1, mixing, heating, and when the temperature rises to 800-900° C., the lithium chloride and boric anhydride melt, and passing hot water vapor to react to obtain anhydrous lithium borate and hydrochloric acid;

[0007] Step S2, adding the anhydrous lithium borate salt and carbon black obtained in step S1 into a reaction kettle in a mass ratio of 3-9:1-3, stirring to form a mixture, adding a dispersant thereto, using anhydrous ethanol as a liquid medium, stirring for 2-4 hours to react, and drying to obtain a gel powder;

[0008] Step S3, in an inert atmosphere, the obtained gel powder is kept at 1650-1800° C. for 2-5 hours for carbothermal reduction to obtain a boron carbide crystal block;

[0009] Step S4, the boron carbide crystal block obtained in step S3 is cyclically crushed by a crusher and a ball mill to obtain a coarse boron carbide powder;

[0010] Step S5, the obtained coarse boron carbide powder is ultrasonically crushed and dried to obtain ultrafine boron carbide powder.

[0011] Through the above technical scheme, the generation of impurities can be effectively reduced and the purity of boron carbide powder can be improved by accurately controlling the above reaction conditions and raw material ratios; the hydrolysis reaction of lithium chloride and boric anhydride and the carbon thermal reduction reaction are both carried out under an inert atmosphere, avoiding the influence of oxidation; through reasonable crushing and ball milling, the particle size distribution of boron carbide powder can be effectively controlled to make it more uniform and realize continuous production, thereby improving production efficiency.

[0012] Further, in step S1, the reaction equation is as follows:

[0013] 2LiCl+2B 2 O 3 +5H 2 O→Li 2 B 4 O 7 +4HCl↑+3H 2 O (Formula I).

[0014] According to the technical scheme, lithium chloride and boric anhydride are solid at room temperature, and water exists as a reactant and a solvent in the reaction; at high temperature, the mixture of lithium chloride and boric anhydride contacts with water vapor, and a hydrolysis reaction occurs, and the lithium ions (Li + ) reacts with the boron oxygen bond (BO) in boric anhydride to form a complex structure of anhydrous lithium borate salt. — ) and hydrogen ions (H + ) are combined to generate hydrogen chloride gas, which escapes in gaseous form, while anhydrous lithium borate remains in the reaction system; the hydrogen chloride gas can be captured and treated into hydrochloric acid through appropriate tail gas treatment measures, and the hydrochloric acid is used to decompose boron ore to obtain boric acid, so that the boric acid is decomposed into the above-mentioned boric anhydride through high temperature, thereby realizing continuous production, improving production efficiency and reducing pollution to the environment.

[0015] In addition, this reaction is a reversible reaction. Under high temperature and appropriate conditions, the reaction only proceeds in the direction of generating anhydrous lithium borate salt and hydrogen chloride. The anhydrous lithium borate salt generated by this reaction is one of the key raw materials for preparing boron carbide powder. The other substances in the reaction are all common compounds, which are easy to obtain and have little impact on the environment.

[0016] Furthermore, in step S1, the hydrochloric acid is used to decompose boron ore to obtain boric acid, and the boric acid is decomposed into the boric anhydride at high temperature.

[0017] Further, in step S2, the stirring speed in the reactor is 800-1600r / min, the pressure of the reactor is 80-130KPa; the dispersant is The maleic anhydride copolymer is added in an amount of 1wt%-3wt% of the mixed material.

[0018] Through the above technical scheme, a stirring speed of 800-1600r / min can ensure that anhydrous lithium borate salt and raw materials such as carbon black are fully and evenly mixed in the reactor, ensure sufficient contact between the reactants, and improve the purity and yield of the product; the above stirring speed not only increases the shear force and collision frequency between the materials, promotes the mixing and dispersion of the materials, but also the pressure in the reactor acts on the reaction system, promotes the generation of reaction products, and avoids local overheating or too rapid reaction causing side reactions.

[0019] Further, in step S3, the conditions for carbon thermal reduction are: the heating rate below 900°C is 5-10°C / min, the heating rate above 900°C is 10-20°C / min, the heating temperature is 1650-1800°C and kept warm for 2-5h; the cooling rate above 900°C is 20-40°C / min, and the temperature below 900°C is cooled with the furnace, during which the inert gas flow rate is maintained at 1-20L / min.

[0020] Through the above technical solution, the above temperature conditions are used to effectively control the growth rate of boron carbide grains, thereby obtaining a uniform and fine boron carbide powder. If the temperature rises too slowly, local overheating will cause side reactions and a decrease in product quality; if the temperature rises too quickly, the temperature gradient of the reaction system will increase, increasing the risk of side reactions. In addition, the above holding time can help eliminate impurities and defects in the reaction system and improve the purity and quality of the product.

[0021] Further, in step S3, the equation for carbothermal reduction is as follows:

[0022] Li 2 B 4 O 7 +5C→B 4 C+Li 2 O+4CO↑+CO 2 ↑(Formula II).

[0023] Further, in step S4, the rotation speed of the crusher is 600-800 r / min, and the crushing time is 20-35 h; the rotation speed of the ball mill is 1000-1500 r / min, and the ball milling time is 10-20 h; the number of cycles N≥5-8; and the median particle size of the coarse boron carbide powder is 1-15 μm.

[0024] Furthermore, in step S5, the ultrasonic crushing is performed using an ultrasonic disperser with a power of 1000KW-1200KW and a dispersion time of 80-160min.

[0025] Furthermore, in step S5, the particle size of the ultrafine boron carbide powder is ≤2 μm.

[0026] Finally, an ultrafine boron carbide powder is provided, which is prepared by the above-mentioned preparation method of the ultrafine boron carbide powder.

[0027] Beneficial Effects

[0028] The invention generates anhydrous lithium borate salt by the reaction of lithium chloride and boric anhydride, and then performs carbon thermal reduction with carbon black. The process is simple, the raw materials are easily available, and the recycling of the raw materials is realized.

[0029] The invention effectively reduces the generation of impurities and improves the purity of boron carbide powder by precisely controlling the reaction conditions and the raw material ratio; and obtains ultrafine boron carbide powder with uniform particle size and fineness by combining crushing, ball milling and ultrasonic pulverization processes, which can meet the needs of high-end applications.

[0030] The entire preparation process of the present invention has strong controllability, is easy to carry out continuous production, and significantly improves production efficiency. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. The experimental methods without specific conditions in the following examples are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise specified, all percentages, ratios, proportions or parts are by weight.

[0033] Unless otherwise specified, the reagents and raw materials used in the examples and comparative examples of the present invention can be obtained through commercial channels.

[0034] Example 1

[0035] A method for preparing ultrafine boron carbide powder, the preparation method comprising the following steps:

[0036] Step S1, preparing lithium chloride with a purity of ≥99.0% and boric anhydride with a purity of ≥98.0%; weighing 120g of lithium chloride and 40g of boric anhydride, mixing them, heating them, and when the temperature rises to 900°C, the lithium chloride and boric anhydride melt and ionize, and hot water vapor is introduced to react to obtain 48.69g of anhydrous lithium borate salt and 39.75g of hydrochloric acid;

[0037] In step S1, the reaction equation is as follows:

[0038] 2LiCl+2B 2 O 3 +5H 2 O→Li 2 B 4 O 7 +4HCl↑+3H 2 O (Formula I).

[0039] The reaction mechanism is as follows: lithium chloride (LiCl) and boric anhydride (B 2 O 3 ) are both solid at room temperature. When heated to 900°C, they melt into liquid state, and lithium chloride is completely ionized into Li + and Cl - Ion, boric anhydride (B 2 O 3 ) is partially ionized during melting to form B(O 2- ) 3 or more complex boron-oxygen ion clusters; these ions and ion clusters move freely in the melt to form preliminary coordination compounds; hot water vapor is introduced, and the water vapor molecules dissociate into H at high temperature. 2 O molecules, H 2 O molecules react with ions and ion clusters in the melt. The oxygen atoms in the water molecules form more stable boron-oxygen bonds with the boron ions, while the hydrogen ions combine with the chloride ions to form gaseous HCl. As the reaction proceeds, Li + The ions combine with the BO ion clusters to form an ionic crystal structure of anhydrous lithium borate salt. At the same time, HCl molecules continuously escape from the reaction system because their boiling point is much lower than the reaction temperature and are treated as hydrochloric acid based on tail gas.

[0040] Step S2, adding 48.69g of anhydrous lithium borate obtained in step S1 and 8.05g of carbon black (purity ≥95.0%, ash content ≤5.0%, mass ratio of 6:1) into a reactor and stirring to form a mixture, the stirring speed in the reactor is 1200r / min, and the pressure of the reactor is 130KPa; adding 1.65g of Maleic anhydride copolymer (added amount is 3wt% of the total amount of the mixture), with anhydrous ethanol (purity ≥99.5%) as the liquid medium, stirred for 4h, dried, and obtained 58.13g of gel powder;

[0041] Step S3, under an inert atmosphere, the obtained 58.13g gel powder is carbon thermally reduced at 1700°C for 3h to obtain 15.63g boron carbide crystal block; wherein the specific reaction conditions are a heating rate of 7.5°C / min below 900°C, a heating rate of 15°C / min above 900°C, a heating temperature of 1700°C for 3h; a cooling rate of 30°C / min above 900°C, and cooling with the furnace below 900°C, during which the inert gas flow rate is maintained at 20L / min.

[0042] In step S3, the equation for carbothermal reduction is as follows:

[0043] Li 2 B 4 O 7 +5C→B 4 C+Li 2 O+4CO↑+CO 2 ↑(Formula II).

[0044] Step S4, the boron carbide crystal block obtained in step S3 is cyclically crushed by a crusher and a ball mill to obtain 15.48 g of coarse boron carbide powder; wherein the speed of the crusher is 800 r / min, and the crushing time is 30 h; the speed of the ball mill is 1500 r / min, and the ball milling time is 18 h; the number of cycles N is 6; and the median particle size of the coarse boron carbide powder is 12 μm.

[0045] Step S5, the obtained coarse boron carbide powder is crushed by a 1200KW ultrasonic disperser for 140 minutes and dried to obtain 15.32g of ultrafine boron carbide powder with a median particle size of 1μm, with a yield of 99%; the obtained ultrafine boron carbide powder is black, fine and uniform, and has no obvious agglomeration phenomenon; and the purity of the obtained ultrafine boron carbide powder reaches more than 99%, meeting the requirements of high-purity products.

[0046] Example 2

[0047] A method for preparing ultrafine boron carbide powder, the preparation method comprising the following steps:

[0048] Step S1, preparing lithium chloride with a purity of ≥99.0% and boric anhydride with a purity of ≥98.0%; weighing 160g of lithium chloride and 40g of boric anhydride, mixing them, heating them until the temperature rises to 800°C, the lithium chloride and boric anhydride melt, and passing hot water vapor into the mixture for reaction, to obtain 58.66g of anhydrous lithium borate and 72.54g of hydrochloric acid;

[0049] Step S2, adding 58.66g of anhydrous lithium borate obtained in step S1 and 19.38g of carbon black (purity ≥95.0%, ash content ≤5.0%, mass ratio of 3:1) into a reactor and stirring to form a mixture, the stirring speed in the reactor is 1200r / min, and the pressure of the reactor is 130KPa; adding 0.69g of Maleic anhydride copolymer (the addition amount is 1wt% of the total amount of the mixture), with anhydrous ethanol (purity ≥99.5%) as the liquid medium, stirred for 4h, dried, and obtained 76.53g of gel powder;

[0050] Step S3, under an inert atmosphere, the obtained 76.53g gel powder is carbon thermally reduced at 1700°C for 3h to obtain 75.88g boron carbide crystal block; wherein the specific reaction conditions are a heating rate of 5°C / min below 900°C, a heating rate of 10°C / min above 900°C, a heating temperature of 1700°C for 3h; a cooling rate of 20°C / min above 900°C, and cooling with the furnace below 900°C, during which the inert gas flow rate is maintained at 15L / min.

[0051] Step S4, the boron carbide crystal block obtained in step S3 is cyclically crushed by a crusher and a ball mill to obtain 75.65g of coarse boron carbide powder; wherein the speed of the crusher is 800r / min, and the crushing time is 30h; the speed of the ball mill is 1500r / min, and the ball milling time is 18h; the number of cycles N is 8; and the median particle size of the coarse boron carbide powder is 12μm.

[0052] Step S5, the obtained 75.65g boron carbide coarse powder is crushed by a 1200KW ultrasonic disperser for 140min and dried to obtain 76.62g ultrafine boron carbide powder with a median particle size of 1.2μm, with a yield of 96%; the obtained ultrafine boron carbide powder is black, fine and uniform, and has no obvious agglomeration phenomenon; and the purity of the obtained ultrafine boron carbide powder reaches 98.5%, which meets the requirements of high-purity products.

[0053] Example 3

[0054] A method for preparing ultrafine boron carbide powder, the preparation method comprising the following steps:

[0055] Step S1, preparing lithium chloride with a purity of ≥99.0% and boric anhydride with a purity of ≥98.0%; weighing 200 g of lithium chloride and 40 g of boric anhydride, mixing them, heating them until the temperature rises to 850° C., the lithium chloride and boric anhydride melt, and passing hot water vapor into the mixture for reaction, to obtain 58.98 g of anhydrous lithium borate and 38.55 g of hydrochloric acid;

[0056] Step S2, adding 58.98g of anhydrous lithium borate obtained in step S1 and 9.63g of carbon black (purity ≥95.0%, ash content ≤5.0%, mass ratio of 6:1) into a reactor and stirring to form a mixture, the stirring speed in the reactor is 1200r / min, and the pressure of the reactor is 130KPa; adding 0.58g of Maleic anhydride copolymer (the amount of which is 1wt% of the total amount of the mixture) is stirred for 4h with anhydrous ethanol (purity ≥99.5%) as the liquid medium, and then dried to obtain 59.63g of gel powder;

[0057] Step S3, under an inert atmosphere, the obtained 59.63g gel powder is kept at 1650°C for 2h for carbon thermal reduction to obtain 59.32g of boron carbide crystal block; wherein the specific reaction conditions are a heating rate of 7.5°C / min below 900°C, a heating rate of 15°C / min above 900°C, a heating temperature of 1700°C for 3h; a cooling rate of 30°C / min above 900°C, and cooling with the furnace below 900°C, during which the inert gas flow rate is maintained at 20L / min.

[0058] Step S4, the 59.32g boron carbide crystal block obtained in step S3 is cyclically crushed by a crusher and a ball mill to obtain 48.59g boron carbide coarse powder; wherein the speed of the crusher is 800r / min, and the crushing time is 20h; the speed of the ball mill is 1500r / min, and the ball milling time is 18h; the number of cycles N is 7; and the median particle size of the coarse boron carbide powder is 12μm.

[0059] Step S5, the obtained 48.59g boron carbide coarse powder is crushed by a 1200KW ultrasonic disperser for 140min and dried to obtain 46.16g ultrafine boron carbide powder with a median particle size of 1.5μm, with a yield of 95%; the obtained ultrafine boron carbide powder is black, fine and uniform, and has no obvious agglomeration phenomenon; and the purity of the obtained ultrafine boron carbide powder reaches more than 99%, which meets the requirements of high-purity products.

[0060] Example 4

[0061] A method for preparing ultrafine boron carbide powder, the preparation method comprising the following steps:

[0062] Step S1, preparing lithium chloride with a purity of ≥99.0% and boric anhydride with a purity of ≥98.0%; weighing 80g of lithium chloride and 40g of boric anhydride, mixing them, heating them until the temperature rises to 900°C, the lithium chloride and the boric anhydride melt, and passing hot water vapor to react, to obtain 58.32g of anhydrous lithium borate salt and 38.75g of hydrochloric acid;

[0063] Step S2, adding 58.32g of anhydrous lithium borate obtained in step S1 and 6.08g of carbon black (purity ≥95.0%, ash content ≤5.0%, mass ratio 9:1) into a reactor and stirring to form a mixture, the stirring speed in the reactor is 1600r / min, and the pressure of the reactor is 80KPa; adding Maleic anhydride copolymer (the amount of which accounts for 2wt% of the total amount of the mixture) was stirred for 4h with anhydrous ethanol (purity ≥99.5%) as the liquid medium, and dried to obtain 59.68g of gel powder;

[0064] Step S3, under an inert atmosphere, the obtained 59.68g gel powder is carbon thermally reduced at 1800°C for 5h to obtain 58.66g boron carbide crystal block; wherein the specific reaction conditions are a heating rate of 7.5°C / min below 900°C, a heating rate of 15°C / min above 900°C, a heating temperature of 1700°C for 3h; a cooling rate of 30°C / min above 900°C, and cooling with the furnace below 900°C, during which the inert gas flow rate is maintained at 20L / min.

[0065] Step S4, the 58.66g boron carbide crystal block obtained in step S3 is cyclically crushed by a crusher and a ball mill to obtain 54.78g boron carbide coarse powder; wherein the speed of the crusher is 600r / min, and the crushing time is 35h; the speed of the ball mill is 1000r / min, and the ball milling time is 20h; the number of cycles N is 5; and the median particle size of the coarse boron carbide powder is 12μm.

[0066] Step S5, the obtained coarse boron carbide powder is crushed by an 800KW ultrasonic disperser for 140 minutes and dried to obtain 53.14g of ultrafine boron carbide powder with a median particle size of 1.8μm, with a yield of 97%; the obtained ultrafine boron carbide powder is black, fine and uniform, and has no obvious agglomeration phenomenon; and the purity of the obtained ultrafine boron carbide powder reaches more than 99%, meeting the requirements of high-purity products.

[0067] Example 5

[0068] A method for preparing ultrafine boron carbide powder, the preparation method comprising the following steps:

[0069] Step S1, preparing lithium chloride with a purity of ≥99.0% and boric anhydride with a purity of ≥98.0%; weighing 200 g of lithium chloride and 40 g of boric anhydride, mixing them, heating them until the temperature rises to 850° C., the lithium chloride and boric anhydride melt, and passing hot water vapor into the mixture for reaction, to obtain 58.98 g of anhydrous lithium borate and 38.55 g of hydrochloric acid;

[0070] Step S2, adding 58.98g of anhydrous lithium borate obtained in step S1 and 9.28g of carbon black (purity ≥95.0%, ash content ≤5.0%, mass ratio of 6:1) into a reactor and stirring to form a mixture, the stirring speed in the reactor is 1200r / min, and the pressure of the reactor is 130KPa; adding Maleic anhydride copolymer (the amount of which accounts for 3wt% of the total amount of the mixture) was stirred for 4h with anhydrous ethanol (purity ≥99.5%) as the liquid medium, and dried to obtain 68.99g of gel powder;

[0071] Step S3, under an inert atmosphere, the obtained 68.99g gel powder is kept at 1650°C for 3h for carbon thermal reduction to obtain 59.68g boron carbide crystal block; wherein the specific reaction conditions are a heating rate of 7.5°C / min below 900°C, a heating rate of 15°C / min above 900°C, a heating temperature of 1700°C for 3h; a cooling rate of 30°C / min above 900°C, and cooling with the furnace below 900°C, during which the inert gas flow rate is maintained at 20L / min.

[0072] Step S4, the 59.68g boron carbide crystal block obtained in step S3 is cyclically crushed by a crusher and a ball mill to obtain 59.65g boron carbide coarse powder; wherein the speed of the crusher is 800r / min, and the crushing time is 30h; the speed of the ball mill is 1500r / min, and the ball milling time is 10h; the number of cycles N is 8; and the median particle size of the coarse boron carbide powder is 12μm.

[0073] Step S5, the obtained coarse boron carbide powder is crushed by an 800KW ultrasonic disperser for 140 minutes and dried to obtain 59.05g of ultrafine boron carbide powder with a median particle size of 2μm, with a yield of 99%; the obtained ultrafine boron carbide powder is black, fine and uniform, and has no obvious agglomeration phenomenon; and the purity of the obtained ultrafine boron carbide powder reaches more than 98.8%, which meets the requirements of high-purity products.

[0074] Comparative Example 1

[0075] A method for preparing ultrafine boron carbide powder, the preparation method comprising the following steps:

[0076] Step S1, weigh 120g of boric anhydride and 20g of carbon black and mix them evenly. In an inert atmosphere, heat the resulting mixture at 1650°C for 3h for carbothermal reduction to obtain 280g of boron carbide crystal blocks.

[0077] Step S2, the 280g boron carbide crystal block obtained in step S1 is cyclically crushed by a crusher and a ball mill to obtain 268g boron carbide coarse powder; wherein the speed of the crusher is 1000r / min, and the crushing time is 30h; the speed of the ball mill is 1500r / min, and the ball milling time is 12h; the number of cycles N is 6; and the median particle size of the coarse boron carbide powder is 12μm.

[0078] Step S3, crushing the obtained 268g boron carbide coarse powder by an 800KW ultrasonic disperser for 140min, and drying to obtain 134g ultrafine boron carbide powder with a median particle size of 3μm, with a yield of 50%; the obtained ultrafine boron carbide powder has obvious agglomeration phenomenon; and the purity of the obtained ultrafine boron carbide powder is 78%.

[0079] Comparative Example 2

[0080] A method for preparing ultrafine boron carbide powder, the preparation method comprising the following steps:

[0081] Step S1, mixing sodium chloride and boric anhydride in a mass ratio of 5:1, heating, and when the temperature rises to 850° C., the sodium chloride and boric anhydride melt, and hot water vapor is introduced to react to obtain anhydrous sodium borate and hydrochloric acid;

[0082] Step S2, adding the anhydrous sodium borate obtained in step S1 and carbon black (purity ≥95.0%, ash content ≤5.0%) in a mass ratio of 6:1 into a reactor and stirring to form a mixture, the stirring speed in the reactor is 1200r / min, and the pressure of the reactor is 130KPa; using anhydrous ethanol (purity ≥99.5%) as a liquid medium, stirring for 4h to react, and drying to obtain a gel powder;

[0083] Step S3, in an inert atmosphere, the obtained gel powder is kept at 1650° C. for 2 h for carbothermal reduction to obtain a boron carbide crystal block;

[0084] Step S4, the boron carbide crystal block obtained in step S3 is cyclically crushed by a crusher and a ball mill to obtain coarse boron carbide powder; wherein the speed of the crusher is 1000 r / min, and the crushing time is 20 h; the speed of the ball mill is 1500 r / min, and the ball milling time is 18 h; the number of cycles N is 7; and the median particle size of the coarse boron carbide powder is 12 μm.

[0085] Step S5, the obtained coarse boron carbide powder is crushed by a 1200KW ultrasonic disperser for 140 minutes and dried to obtain ultrafine boron carbide powder with a median particle size of 3 μm and uneven particle size; the obtained ultrafine boron carbide powder has obvious agglomeration phenomenon.

[0086] In summary, by comparing Examples 1 to 5, it can be seen that the ratio of lithium chloride to boric anhydride not only affects the amount of reaction product generated, but also affects the efficiency of carbon thermal reduction, thereby improving the yield and purity of boron carbide; by comparing Example 3 with Example 5, it can be seen that by adjusting The amount of maleic anhydride copolymer added and the ball milling time can greatly improve the purity and dispersibility of boron carbide powder. By comparing Examples 1-3 with Example 4, it can be seen that the changes in stirring speed, reactor pressure, the amount of maleic anhydride copolymer added and the power parameters of the ultrasonic disperser directly affect the particle size and purity of the boron carbide powder. Therefore, Examples 1-5 of the present invention can effectively control the particle size of boron carbide powder by optimizing reaction conditions and parameters, and obtain ultrafine powders with a median particle size between 1 and 2 microns, and the yields of Examples 1-5 are all higher than 95%, and the purity is higher than 98.5%; among which the best example is Example 1.

[0087] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing ultrafine boron carbide powder, characterized in that: The preparation method comprises the following steps: Step S1, weighing lithium chloride and boric anhydride in a mass ratio of 2-5:1, mixing, heating, and when the temperature rises to 800-900° C., the lithium chloride and boric anhydride melt, and passing hot water vapor to react to obtain anhydrous lithium borate and hydrochloric acid; Step S2, adding the anhydrous lithium borate salt and carbon black obtained in step S1 into a reaction kettle in a mass ratio of 3-9:1-3, stirring to form a mixture, adding a dispersant thereto, using anhydrous ethanol as a liquid medium, stirring for 2-4 hours to react, and drying to obtain a gel powder; Step S3, in an inert atmosphere, the obtained gel powder is kept at 1650-1800° C. for 2-5 hours for carbothermal reduction to obtain a boron carbide crystal block; Step S4, the boron carbide crystal block obtained in step S3 is cyclically crushed by a crusher and a ball mill to obtain a coarse boron carbide powder; Step S5, the obtained coarse boron carbide powder is ultrasonically crushed and dried to obtain ultrafine boron carbide powder.

2. The method for preparing ultrafine boron carbide powder according to claim 1, characterized in that: In step S1, the reaction equation is as follows: 2LiCl+2B2O3+5H2O→Li2B4O7+4HCl↑+3H2O (Formula I).

3. The method for preparing ultrafine boron carbide powder according to claim 1, characterized in that: In step S1, the hydrochloric acid is used to decompose boron ore to obtain boric acid, and the boric acid is decomposed into the boric anhydride at high temperature.

4. The method for preparing ultrafine boron carbide powder according to claim 1, characterized in that: In step S2, the stirring speed in the reactor is 800-1600 r / min, and the pressure in the reactor is 80-130 KPa; the dispersant is 21000 maleic anhydride copolymer, the addition amount thereof accounts for 1wt%-3wt% of the mixed material.

5. The method for preparing ultrafine boron carbide powder according to claim 1, characterized in that: In step S3, the conditions for carbon thermal reduction are: the heating rate below 900°C is 5-10°C / min, the heating rate above 900°C is 10-20°C / min, the heating temperature is 1650-1800°C and kept warm for 2-5h; the cooling rate above 900°C is 20-40°C / min, and the temperature below 900°C is cooled with the furnace, during which the inert gas flow rate is maintained at 1-20L / min.

6. The method for preparing ultrafine boron carbide powder according to claim 5, characterized in that: In step S3, the equation for carbothermal reduction is as follows: Li2B4O7+5C→B4C+Li2O+4CO↑+CO2↑(Formula II).

7. The method for preparing ultrafine boron carbide powder according to claim 1, characterized in that: In step S4, the rotation speed of the crusher is 600-800 r / min, and the crushing time is 20-35 h; the rotation speed of the ball mill is 1000-1500 r / min, and the ball milling time is 10-20 h; the number of cycles N≥5-8; and the median particle size of the coarse boron carbide powder is 1-15 μm.

8. The method for preparing ultrafine boron carbide powder according to claim 1, characterized in that: In step S5, the ultrasonic crushing is performed using an ultrasonic disperser with a power of 1000KW-1200KW and a dispersion time of 80-160min.

9. The method for preparing ultrafine boron carbide powder according to claim 1, characterized in that: In step S5, the particle size of the ultrafine boron carbide powder is ≤2 μm.

10. An ultrafine boron carbide powder, which is prepared by the method for preparing the ultrafine boron carbide powder according to any one of claims 1 to 9.