Preparation method of boron carbide powder

Abstract

The invention belongs to the field of inorganic materials, and particularly relates to a preparation method of boron carbide powder, boron carbide is prepared by adopting a sol-gel method, according to the method, raw materials are mixed at a molecular level, a B-O-C bond formed by reaction enables carbon and boron to be dispersed more uniformly, the effective contact area is increased, and the reaction condition is mild and easy to control. The hydroxy acid is prepared in a suspension polymerization mode in the process of preparing the boron carbide powder, the hydroxy acid is added into a reaction system, the hydroxy acid, PVA and boric acid can react to form boric acid ester, the microstructure of a boric acid ester precursor can be regulated by adding the hydroxy acid, and the boron carbide powder which is complete in crystal form and better in purity can be prepared conveniently. In the preparation process of the hydroxy acid, a pore-forming agent is adopted to perform pore-forming operation on a polymeric material, so that a pore structure with relatively uniform pore size distribution can be formed on the surface of a polymer, and boron carbide powder with more uniform particle size and particle size distribution can be formed in the subsequent cracking and carbonization process.

Description

Technical Field

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

[0002] Boron carbide (B4C) is a ceramic material with unique properties, which is widely used in the fields of nuclear industry, military industry, electronics and wear-resistant materials. Boron carbide has important application value in bulletproof armor, cutting tools, wear-resistant parts and nuclear reactor control rods due to its high hardness, high melting point, low density, good chemical corrosion resistance and neutron absorption ability. However, the preparation method of boron carbide powder has a direct impact on its performance and application effect.

[0003] At present, the preparation methods of boron carbide powder mainly include high-temperature solid phase method, chemical vapor phase method, solution precipitation method and self-propagating high-temperature synthesis method. However, these methods have many problems in practical applications. For example: the high-temperature solid phase method is to mix a boron source (such as boron oxide or boric acid) with a carbon source (such as graphite or activated carbon) and react under high temperature conditions to obtain boron carbide powder. This method is simple to operate, but the reaction temperature usually needs to exceed 2000°C, the energy consumption is high, and the particle size of the obtained powder is large, which is difficult to meet the needs of nano- or micron-level powders. In addition, this method is easy to introduce impurities, affecting the purity of boron carbide. The chemical vapor phase method generates boron carbide powder by reacting gaseous boron and carbon compounds at high temperature. This method can prepare high-purity, fine-particle boron carbide, but its equipment is complex, the reaction conditions are harsh, and the production cost is high, making it difficult to achieve large-scale industrial application. The solution precipitation method mixes the boron source and the carbon source in a solution to form a precursor, which is then treated at high temperature to obtain boron carbide powder. This method can effectively control the particle size and morphology of the particles, but there are problems such as low reaction efficiency, complex process steps and high equipment requirements. Self-propagating high-temperature synthesis uses the heat released by the reaction itself to drive the reaction and is an energy-saving preparation method. However, this method is difficult to accurately control the morphology and particle size of the product, and the product is prone to agglomeration, resulting in a decrease in its performance.

[0004] The existing technology faces many challenges in the preparation process of boron carbide powder, including harsh preparation conditions, complex process, high energy consumption, and difficulty in controlling the particle size and purity of the powder. Therefore, developing a method for preparing boron carbide powder with simple process, mild reaction conditions, low energy consumption, and high purity and uniform particle size has become a technical problem that needs to be solved in the field of boron carbide materials. Summary of the invention

[0005] In order to solve the technical problems existing in the above-mentioned background technology, the present invention provides a method for preparing boron carbide powder, using hydroxy acid as a modifier and adopting a solid phase precursor method to prepare boron carbide powder, which can obtain high-purity and well-crystalline boron carbide powder at a relatively low calcination temperature.

[0006] An object of the present invention is to provide a method for preparing boron carbide powder, which is characterized by comprising the following steps:

[0007] S1: Preparation of precursor: polyvinyl alcohol and boric acid are weighed according to a molar ratio of polyvinyl alcohol:boric acid of 1:3, and then hydroxy acid is added, mixed and crushed, and calcined to obtain a precursor.

[0008] S2: Cracking of precursor: After the reaction of the precursor is completed, keep the atmosphere and heating rate of the box furnace constant, increase the temperature to 650-700°C, maintain for 2-4 hours, then stop heating, and wait for the temperature in the furnace to cool naturally to room temperature to obtain the cracking product.

[0009] S3: Preparation of boron carbide: Grind the cracking product prepared in step S2 and transfer it to a high-temperature tube furnace. After excluding the air, introduce argon at a flow rate of 0.2L / h. At the same time, increase the temperature to 1200-1500°C at a heating rate of 10°C / min and maintain it for 2-4 hours. After the reaction is completed, cool it to room temperature in the furnace to obtain B4C powder.

[0010] Furthermore, the hydroxy acid in step S1 is prepared by the following method:

[0011] The suspension polymerization method is adopted, GMA and TAIC are used as polymerization monomers, n-heptane is used as a porogen, and azobisisoheptanonitrile is used as an initiator. The corresponding polymer is obtained by free radical polymerization, and then the polymer is subjected to ring-opening treatment with CO2 to obtain the hydroxy acid.

[0012] Further, the mass ratio of GMA and TAIC is 1:1-3, the mass ratio of n-heptane is 2-3 times the total weight of the polymerization monomers, the mass ratio of azobisisoheptanenitrile is 0.1%-0.3% of the total weight of the polymerization monomers, and the oil-water ratio of the suspension polymerization is 1:3;

[0013] Furthermore, the specific process steps of CO2 ring opening are: hydrolyzing the polymer obtained by suspension polymerization with NaOH solution, controlling the reaction temperature at 50-70°C, reacting for 3-5h under stirring, and separating and purifying to obtain the polymer.

[0014] Furthermore, in step S1, the molar ratio of the hydroxy acid to the polyvinyl alcohol is 1:6-8.

[0015] Furthermore, the process conditions for crushing in step S1 are: crushing the mixture to 1-5 um.

[0016] Furthermore, the calcination process conditions in step S1 are as follows: the crushed mixture is placed in a box-type atmosphere furnace, and the temperature in the furnace is raised to 200° C. at a heating rate of 10° C. / min in an air atmosphere, and maintained for 1-2 hours. Subsequently, the system temperature is raised to 250° C. at the same heating rate, and the reaction is carried out for 4-6 hours.

[0017] Furthermore, in step S2, the heating rate of the box furnace is 10°C / min.

[0018] Furthermore, the specific conditions for grinding in step S3 are: grinding the pyrolysis product to 1-5 um.

[0019] Beneficial effects:

[0020] The present invention adopts a sol-gel method to prepare boron carbide. This method allows raw materials to be mixed at the molecular level. The BOC bonds formed by the reaction make the carbon and boron dispersion more uniform, the effective contact area is increased, and the reaction conditions are mild and easy to control.

[0021] In the process of preparing boron carbide powder, the present invention adopts a suspension polymerization method to prepare hydroxy acid, which is added to the reaction system. The hydroxy acid, PVA and boric acid can react to form boric esters. The addition of hydroxy acid can regulate the microstructure of the boric ester precursor, which is convenient for preparing boron carbide powder with better crystal integrity and purity.

[0022] The hydroxy acid of the present invention uses a porogen to perform pore-forming operation on the polymer material during the preparation process, which can form a pore structure with relatively uniform pore size distribution on the polymer surface, and is helpful to form boron carbide powder with more uniform particle size and particle size distribution during the subsequent cracking and carbonization process. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a scanning electron microscope image of the boron carbide prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0024] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. The present invention can be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided so that this disclosure will be thorough and complete, and the concept of the present invention will be fully conveyed to those skilled in the art, and the present invention will only be limited by the claims.

[0025] It should be noted that the hydroxy acids described in the following examples and comparative examples are all prepared by the following method:

[0026] The preparation is carried out by suspension polymerization, and the oil phase and the water phase are respectively configured according to the mass ratio of oil phase: water phase of 1:3, and the composition of the oil phase is: the mass ratio of GMA and TAIC is 1:2; the mass ratio of n-heptane is 2 times the total weight of the polymerized monomers, and the initiator azobisisoheptanonitrile is 0.2% of the total mass of the polymerized monomers; the water phase contains a polyvinyl alcohol solution with a mass fraction of 5%. The stirring speed of the suspension polymerization is 260 rpm, the reaction temperature is 78°C, and the reaction time is 8h. After the reaction is completed, the Soxhlet extraction method is used to remove the excess porogen and the unreacted polymer, and then the polymer obtained by the suspension polymerization is hydrolyzed with a NaOH solution with a concentration of 5%, the reaction temperature is controlled at 50-70°C, and the reaction is stirred for 3-5h, and the hydroxy acid of the present invention is obtained by separation and purification.

[0027] Example 1

[0028] Weigh polyvinyl alcohol and boric acid according to the molar ratio of polyvinyl alcohol: boric acid of 1:3, then add hydroxy acid, the molar ratio of hydroxy acid to polyvinyl alcohol is 1:6, mix and crush to a particle size of 1-5um, put the crushed mixture into a box-type atmosphere furnace, and raise the temperature in the furnace to 200℃ at a heating rate of 10℃ / min in an air atmosphere, and keep it for 1h. Then raise the temperature of the system to 250℃ at the same heating rate, react for 4h, and obtain the precursor. When the precursor reaction is completed, maintain the atmosphere conditions of the box-type furnace, raise the temperature to 650℃ at a heating rate of 10℃ / min, keep it for 2 hours, then stop heating, and wait for the temperature in the furnace to cool naturally to room temperature to obtain the pyrolysis product. The cracking product prepared in step S2 was ground to a particle size of 1-5 um and then transferred to a high-temperature tube furnace. After the air was removed, argon was introduced at a flow rate of 0.2 L / h. At the same time, the temperature was increased to 1200°C at a heating rate of 10°C / min and maintained for 2 hours. After the reaction was completed, the mixture was cooled to room temperature in the furnace to obtain B4C powder.

[0029] Example 2

[0030] Weigh polyvinyl alcohol and boric acid according to the molar ratio of polyvinyl alcohol: boric acid of 1:3, then add hydroxy acid, the molar ratio of hydroxy acid to polyvinyl alcohol is 1:7, mix and crush to a particle size of 1-5um, put the crushed mixture into a box-type atmosphere furnace, and raise the temperature in the furnace to 200℃ at a heating rate of 10℃ / min in an air atmosphere, and keep it for 2h. Then raise the system temperature to 250℃ at the same heating rate, react for 5h, and obtain the precursor. When the precursor reaction is completed, maintain the atmosphere conditions of the box-type furnace, raise the temperature to 680℃ at a heating rate of 10℃ / min, keep it for 3 hours, then stop heating, and wait for the temperature in the furnace to cool naturally to room temperature to obtain the pyrolysis product. The cracking product prepared in step S2 was ground to a particle size of 1-5 um and then transferred to a high-temperature tube furnace. After the air was removed, argon was introduced at a flow rate of 0.2 L / h. At the same time, the temperature was increased to 1300°C at a heating rate of 10°C / min and maintained for 4 hours. After the reaction was completed, the mixture was cooled to room temperature in the furnace to obtain B4C powder.

[0031] Example 3

[0032] Weigh polyvinyl alcohol and boric acid according to the molar ratio of polyvinyl alcohol: boric acid of 1:3, then add hydroxy acid, the molar ratio of hydroxy acid to polyvinyl alcohol is 1:8, mix and crush to a particle size of 1-5um, put the crushed mixture into a box-type atmosphere furnace, and raise the temperature in the furnace to 200℃ at a heating rate of 10℃ / min in an air atmosphere, and keep it for 2h. Then raise the system temperature to 250℃ at the same heating rate, react for 6h, and obtain the precursor. When the precursor reaction is completed, maintain the atmosphere conditions of the box-type furnace, raise the temperature to 700℃ at a heating rate of 10℃ / min, keep it for 4 hours, then stop heating, and wait for the temperature in the furnace to cool naturally to room temperature to obtain the cracking product. The cracking product prepared in step S2 was ground to a particle size of 1-5 um and then transferred to a high-temperature tube furnace. After the air was removed, argon was introduced at a flow rate of 0.2 L / h. At the same time, the temperature was increased to 1500°C at a heating rate of 10°C / min and maintained for 4 hours. After the reaction was completed, the mixture was cooled to room temperature in the furnace to obtain B4C powder.

[0033] Example 4

[0034] Weigh polyvinyl alcohol and boric acid according to the molar ratio of polyvinyl alcohol: boric acid of 1:3, then add hydroxy acid, the molar ratio of hydroxy acid to polyvinyl alcohol is 1:6, mix and crush to a particle size of 1-5um, put the crushed mixture into a box-type atmosphere furnace, and raise the temperature in the furnace to 200℃ at a heating rate of 10℃ / min in an air atmosphere, and keep it for 2h. Then raise the temperature of the system to 250℃ at the same heating rate, react for 4h, and obtain the precursor. When the precursor reaction is completed, maintain the atmosphere conditions of the box-type furnace, raise the temperature to 660℃ at a heating rate of 10℃ / min, keep it for 4 hours, then stop heating, and wait for the temperature in the furnace to cool naturally to room temperature to obtain the cracking product. The cracking product prepared in step S2 was ground to a particle size of 1-5 um and then transferred to a high-temperature tube furnace. After the air was removed, argon was introduced at a flow rate of 0.2 L / h. At the same time, the temperature was raised to 1480°C at a heating rate of 10°C / min and maintained for 4 hours. After the reaction was completed, the mixture was cooled to room temperature in the furnace to obtain B4C powder.

[0035] Field emission scanning electron microscopy analysis (SEM) A field emission scanning electron microscope (SEM) produced by Hitachi, Japan, model: SU8010, with an accelerating voltage of 10Kv, was used to detect the samples after gold spraying, and the microstructure and crystal morphology of the samples prepared with different hydroxy acid addition amounts were observed on the surface.

[0036] Particle size analysis (LPSA) Laser particle size analyzer produced by Malvern Instruments Ltd., UK, model: Mastersizer-3000, scattering angle of 90.0°, particle size range of 10 nanometers to 3000 microns.

[0037] The particle size of the boron carbide powder prepared in Example 2 of the present invention is shown in the following table:

[0038] project D10 D50 D90 Particle size / um 14.36 25.13 44.63

[0039] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A method for preparing boron carbide powder, characterized in that: The following steps are included: S1: Preparation of precursor: polyvinyl alcohol and boric acid are weighed according to a molar ratio of polyvinyl alcohol:boric acid of 1:3, and then hydroxy acid is added, mixed and crushed, and calcined to obtain a precursor; S2: Cracking of precursor: After the reaction of the precursor is completed, the atmosphere conditions and heating rate of the box furnace are kept constant, the temperature is raised to 650-700°C, maintained for 2-4 hours, and then the heating is stopped. The temperature in the furnace is cooled naturally to room temperature to obtain the cracking product; S3: Preparation of boron carbide: Grind the cracking product prepared in step S2 and transfer it to a high-temperature tube furnace. After excluding the air, introduce argon at a flow rate of 0.2L / h. At the same time, increase the temperature to 1200-1500°C at a heating rate of 10°C / min and maintain it for 2-4 hours. After the reaction is completed, cool it to room temperature in the furnace to obtain B4C powder.

2. The method for preparing boron carbide powder according to claim 1, characterized in that: In step S1, the hydroxy acid is prepared by the following method: suspension polymerization is used, GMA and TAIC are used as polymerization monomers, n-heptane is used as a porogen, and azobisisoheptanonitrile is used as an initiator, and free radical polymerization is used to obtain the corresponding polymer, and then the polymer is subjected to ring-opening treatment with CO2 to obtain the hydroxy acid.

3. The method for preparing boron carbide powder according to claim 2, characterized in that: The mass ratio of GMA to TAIC is 1:1-3, the mass ratio of n-heptane is 2-3 times the total weight of the polymerization monomers, and the oil-water ratio of the suspension polymerization is 1:

3.

4. The method for preparing boron carbide powder according to claim 2, characterized in that: The specific process steps of CO2 ring opening are: hydrolyzing the polymer obtained by suspension polymerization with NaOH solution, controlling the reaction temperature at 50-70°C, reacting for 3-5 hours under stirring, and separating and purifying to obtain the polymer.

5. The method for preparing boron carbide powder according to claim 1, characterized in that: In step S1, the molar ratio of the hydroxy acid to the polyvinyl alcohol is 1:6-8.

6. The method for preparing boron carbide powder according to claim 1, characterized in that: The process conditions for crushing in step S1 are: crushing the mixture to 1-5 um.

7. The method for preparing boron carbide powder according to claim 1, characterized in that: The process conditions for calcination in step S1 are as follows: the crushed mixture is placed in a box-type atmosphere furnace, and the temperature in the furnace is increased to 200°C at a heating rate of 10°C / min in an air atmosphere, maintained for 1-2 hours, and then the system temperature is increased to 250°C at the same heating rate, and reacted for 4-6 hours.

8. The method for preparing boron carbide powder according to claim 1, characterized in that: The heating rate of the box furnace in step S2 is 10°C / min.

9. The method for preparing boron carbide powder according to claim 1, characterized in that: The specific conditions for grinding in step S3 are: grinding the pyrolysis product to 1-5 um.

10. The method for preparing boron carbide powder according to claim 2, characterized in that: The content of azobisisoheptylnitrile is 0.1%-0.3% of the total mass of the polymerization monomers.

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