A preparation system for controlling the environment for growing boron carbide crystals

Abstract

The present invention proposes a preparation system for controlling the environment for boron carbide crystal growth. The precursor is transported to a reaction furnace at a reaction temperature through rapid carbon thermal reduction, and then transported to a high-temperature arc furnace of a crystal growth reaction unit at the reaction temperature. The gas phase boron oxide and solid carbon react at a temperature above 1600°C. After entering the hot zone, the precursor is controlled to have an extremely high heating rate (10 3 ‑l0 5 K / s) to reach the reaction temperature, the boron oxide rapidly sublimates and reacts with the closely mixed carbon source to form boron carbide crystals. Carbon monoxide and excess boron oxide gas leave the high-temperature arc furnace from the exhaust pipe. The present invention can achieve the preparation of high-purity, small-size, high-density twin-containing boron carbide powder at a lower temperature and time, which has obvious advantages over the traditional carbon thermal reduction method. In addition, the boron carbide crystals prepared by the present invention can also achieve near-theoretical density at a lower temperature and a shorter residence time, making the production process more efficient.

Description

Technical Field

[0001] The invention belongs to the technical field of synthesis and preparation of boron carbide, and relates to a preparation system for controlling the boron carbide crystal growth environment. The prepared synthesized boron carbide crystal particles have smaller particle size, lower free carbon and higher crystal density. Background Art

[0002] Boron carbide (B4C) is a gray-black micro-powder ceramic material with high melting point (2350℃), high hardness (9.3), high modulus, and low density (2.52g / cm 3 ), good wear resistance, strong acid and alkali resistance, and has good neutron absorption ability, low expansion coefficient, and thermoelectric properties. Boron carbide is one of the three hardest materials known, second only to diamond and cubic boron nitride. The crystal structure of boron carbide is rhombohedral, consisting of 12 boron atoms and one carbon atom to form a regular icosahedral unit. Boron carbide can be obtained by reducing boron trioxide with carbon in an electric furnace, and is widely used in refractory materials, engineering ceramics, nuclear industry, aerospace and other fields, such as manufacturing tank armor, bulletproof vests, control rods, nozzles, etc.

[0003] Although boron carbide has many advantages, it also has disadvantages such as high brittleness and low toughness. In order to improve the mechanical properties of boron carbide and improve its engineering application value, a variety of methods are used in the prior art to prepare boron carbide crystal growth. Boron carbide crystal growth refers to the formation of single crystals or polycrystals with larger size and higher integrity by controlling the growth direction and rate of boron carbide under certain conditions. At present, the commonly used boron carbide crystal growth methods include compound crystal growth method, solvent thermal method, hot pressing method, etc. The principles of these methods are to utilize the non-equilibrium phase diagram or phase change characteristics of boron carbide to promote the growth of boron carbide from solid phase or liquid phase to a single direction under appropriate temperature, pressure, time and other conditions. Among the above methods, the compound crystal growth method uses a compound of a boron source and a carbon source as a raw material, decomposes and grows crystals at high temperature, has the advantages of easy raw material availability and simple control, but the growth temperature is high and the yield is low. The solvent thermal method uses an organic solvent as a reaction medium, can be grown at a lower temperature, is simple to operate, and is easier to control the temperature field, but is easy to introduce impurities and difficult to clean the product. The hot pressing method uses high temperature and high pressure to suppress the influence of impurities on growth and obtain longer single crystals, but the equipment is complex, the operation is difficult, and the production cost is high.

[0004] Among the existing methods for preparing boron carbide crystals, carbon thermal reduction is also a relatively common method. The carbon thermal reduction method is a method for preparing boron carbide crystals by using carbon black as a reducing agent, mixing boric acid or boron oxide with carbon powder, and then subjecting the mixture to a carbon thermal reduction reaction at high temperature. Its working principle is that B2O3 and C react at high temperature to generate B4C crystals and CO gas, that is: 2B2O3+7C→B4C+6CO. The main steps of preparing boron carbide crystals by carbon thermal reduction include: mixing B2O3 and carbon powder in a certain stoichiometric ratio; loading the mixture into a graphite crucible and placing it in a high-temperature furnace; heating the furnace to 2000-2500°C in an inert atmosphere; maintaining the temperature for several hours to complete the reaction; cooling and removing the product. High-quality B4C crystals can be obtained by controlling the atmosphere, temperature and raw material ratio during the preparation process.

[0005] Compared with other existing methods for preparing boron carbide crystals, the carbon thermal reduction method has the advantages of simple reaction, simple equipment structure, small footprint, fast construction speed, simple process operation, and the purity, particle size and phase composition of boron carbide powder can be controlled by adjusting parameters such as reaction temperature, time and atmosphere. However, when using the carbon thermal reduction method to prepare boron carbide crystals, some problems and difficulties are also faced, such as the prepared boron carbide powder has a large size, a wide particle size distribution, a high content of metal impurities, and often has unreacted free carbon. In addition, boron carbide is difficult to sinter, and other substances need to be added as sintering aids to reduce the sintering temperature, among which carbon is one of the most commonly used sintering aids, but it will cause the mechanical properties of boron carbide to decrease. Hot pressing can prepare high-density boron carbide, but it requires very high temperatures. Electric spark sintering is an alternative densification method that can achieve high density at a lower temperature and has restrictions on grain growth, but requires special equipment and technology. Summary of the invention

[0006] (I) Purpose of the invention

[0007] In view of the above defects and shortcomings of the prior art, in order to solve the problems existing in the existing preparation of boron carbide crystals by carbothermal reduction, such as large boron carbide powder size, wide particle size distribution, high metal impurity content, unreacted free carbon, high preparation temperature, and long residence time, the present invention proposes a preparation system for controlling the boron carbide crystal growth environment, which transports the precursor to the reaction furnace at the reaction temperature through rapid carbothermal reduction, and transports the precursor powder to the high-temperature arc furnace of the crystal growth reaction unit at the reaction temperature, and the gas phase boron oxide and solid carbon react at above 1600°C. After entering the hot zone, the precursor is controlled to have an extremely high heating rate (10 3 -l0 5K / s) to reach the reaction temperature, the boron oxide rapidly sublimates and reacts with the closely mixed carbon source to form a boron carbon compound. Carbon monoxide and excess boron oxide gas leave the high-temperature arc furnace from the exhaust pipe. The present invention can achieve the preparation of high-purity, small-size, high-density twin-containing boron carbide powder at a lower temperature and time, which has obvious advantages over the traditional carbon thermal reduction method. In addition, the boron carbide crystals prepared by the present invention can also achieve near-theoretical density at a lower temperature and a shorter residence time, making the production process more efficient.

[0008] (II) Technical solution

[0009] To achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] A preparation system for controlling the boron carbide crystal growth environment, comprising at least a raw material preparation unit, a raw material mixing unit, a precursor drying unit, a precursor calcining unit, a precursor crushing unit, a precursor conveying unit, and a crystal growth reaction unit, characterized in that:

[0011] --The raw material preparation unit comprises at least a boron source and a carbon source, wherein the boron source is high-purity boric acid or boron oxide, and the carbon source is highly active carbon black or graphite;

[0012] --The raw material mixing unit comprises at least a first container and a second container which are arranged adjacent to each other, wherein the boron source is dispersed in deionized water in a stirring manner in the inner cavity of the first container to form a boron slurry; the carbon source is dispersed in deionized water in a stirring manner in the inner cavity of the second container and a surfactant is added to form a carbon slurry; the carbon slurry is poured into the first container and fully stirred and mixed with the boron slurry, and the mixture is heated during the stirring process so that the water in the mixture is fully evaporated to form a carbon-boron paste;

[0013] The precursor drying unit comprises at least one low-temperature oven, which is connected to the first container via a material transport pipeline I. The carbon-boron paste formed in the first container is transported to the low-temperature oven via the material transport pipeline I and is fully dried and heated under the temperature environment to form a dry precursor;

[0014] --The precursor calcining unit comprises at least one medium-temperature calcining box, the inner cavity of which is an inert gas atmosphere. After the dry precursor formed in the low-temperature oven is transported to the medium-temperature calcining box, it is fully calcined in a medium-temperature environment and under the action of a constant inert gas flow to remove various organic substances and excess carbon and oxygen remaining in the dry precursor, and finally forms a calcined block;

[0015] --The precursor crushing unit includes at least one grinding and crushing device. The calcined blocks in the medium-temperature calcining box are cooled to room temperature and then transported to the grinding and crushing device through a transfer device to be crushed into precursor powders with a particle size of 100 microns;

[0016] --The precursor delivery unit comprises at least a screw feeder, a sealed hopper and a cold tube feeder, wherein:

[0017] The screw feeder is arranged in a horizontal state as a whole and includes a feeding end and a discharging end.

[0018] The sealed hopper is used to store precursor powder that meets the particle size requirements. The sealed hopper is a closed sealed structure as a whole, and its bottom is connected to the feeding end of the screw feeder through a gate valve.

[0019] The cold pipe feeder is arranged in a vertical state as a whole, and is a hollow tubular component as a whole. The top of the cold pipe feeder is connected to an inert gas source through a pipeline. A feed port connected to the discharge end of the screw feeder is provided on the side wall near the top, and a cooling medium sleeve is provided on the outer side of the side wall. The cooling medium sleeve is connected to a low-temperature cooling medium source through a connecting pipeline to form a cooling medium circulation loop. The bottom open end of the cold pipe feeder forms its discharge port;

[0020] --The crystal growth reaction unit comprises a vertical high-temperature electric arc furnace which is in an overall closed state, wherein:

[0021] The inner cavity side wall of the high temperature electric arc furnace is provided with two arc-shaped plate-shaped graphite electrodes arranged opposite to each other.

[0022] A disc-shaped support base is provided at the bottom of the inner cavity center of the high-temperature electric arc furnace, and at least one cylindrical high-temperature insulation container which is arranged concentrically with the support base and has an open top is fixedly provided on the top surface of the support base, and at least one heat-resistant crucible which is arranged concentrically with the support base and has an open top is fixedly provided in the high-temperature insulation container, and a radial gap is provided between the heat-resistant crucible and the high-temperature insulation container, and the bottom of the high-temperature insulation container is provided with an air vent which is connected to the inner cavity of the disc-shaped support base, and the bottom of the disc-shaped support base is provided with an exhaust port which is connected to the inner cavity thereof, and the exhaust port is connected to the outside through an exhaust pipeline,

[0023] The cold tube feeder passes through the top of the high-temperature arc furnace and extends into the top opening of the heat-resistant crucible. The precursor powder in the cold tube feeder falls into the heat-resistant crucible under the action of gravity and reacts in a high-temperature environment to generate boron carbide crystals. The boron carbide crystal powder generated by the reaction accumulates in the heat-resistant crucible. The gaseous byproducts including carbon monoxide and excess boron oxide gas and the inert gas generated by the reaction leave the system through the gap between the heat-resistant crucible and the high-temperature isolation container, the vent holes at the bottom of the high-temperature isolation container, the exhaust port at the bottom of the disc-shaped support base, and the exhaust pipeline in sequence.

[0024] Preferably, in the raw material preparation unit, the raw material component mass ratio between the boron source and the carbon source after metering and weighing should be maintained in the range of 10:7 to 10:8.5 to ensure the completeness of the subsequent reaction between the two and the purity of the product.

[0025] Preferably, in the raw material mixing unit, the first container and the second container are both open containers with an open top and a closed bottom, wherein:

[0026] At least one heating device is provided on the outer wall of the first container and at least one stirring device is provided in the inner cavity thereof, and the boron source is dispersed in deionized water by stirring with the aid of the first stirring device at a temperature of about 80° C. in the inner cavity of the first container to form a boron slurry;

[0027] At least one lifting and tilting device is provided at the bottom of the second container and at least one second stirring device is provided in the inner cavity thereof, and the carbon source is dispersed in deionized water in the inner cavity of the second container by stirring with the aid of the second stirring device and a surfactant is added to form a carbon slurry;

[0028] After the carbon source is formed into carbon slurry, the carbon slurry in the second container is slowly poured into the first container at a small inclination angle under the action of the lifting and tilting device and is fully stirred and mixed with the boron slurry under the action of the first stirring device. During the stirring process, the heating device is in a started state, and the heating time should at least ensure that the water in the mixture is fully evaporated to form a carbon-boron paste.

[0029] Furthermore, in the raw material mixing unit, the surfactant added when forming the carbon slurry is a polyethylene glycol ether non-ionic surfactant, a polyoxyethylene ether surfactant, a fatty alcohol polyethylene glycol ether surfactant, a sodium dodecyl sulfate salt ionic surfactant or a hexadecyl trimethyl ammonium salt ionic surfactant.

[0030] Preferably, in the raw material mixing unit, the boron source and the carbon source are stirred in the inner cavities of the first and second containers for about 30 minutes, so that the boron source and the carbon source are fully dispersed in the deionized water; and the heating degree of the heating device does not exceed 100°C.

[0031] Preferably, in the precursor drying unit, the drying heating temperature of the oven is between 120° C. and 140° C., and the drying time is not less than 12 hours.

[0032] Preferably, in the precursor calcination unit, the medium-temperature calcination box is a closed box and forms an airflow circulation loop with an inert gas source through a gas pipeline, so that the inner cavity of the medium-temperature calcination box is an inert gas atmosphere, and the medium-temperature calcination box is connected to the low-temperature oven through a material conveying pipeline II. After the dry precursor formed in the low-temperature oven is transported to the medium-temperature calcination box through the material conveying pipeline II, it is fully calcined in a medium-temperature environment and under the action of a constant inert gas flow to remove various organic substances including surfactants and excess carbon and oxygen remaining in the dry precursor, and finally forms a calcined block.

[0033] Furthermore, in the precursor calcination unit, the medium-temperature calcination box is a tubular electric furnace, the inert gas is argon, and the dry precursor is calcined under a constant argon flow in the tubular electric furnace. The calcination temperature does not exceed 600° C. and the calcination time does not exceed 10 minutes to remove various organic substances including surfactants and excess carbon and oxygen remaining in the dry precursor, while not significantly affecting the crystal structure and chemical composition of subsequent boron carbide products.

[0034] Preferably, in the precursor pulverizing unit, the grinding and pulverizing device is a quartz mortar or a ceramic mortar, and force needs to be applied slowly during the grinding process to prevent the generation of large amounts of heat. The particle size of the precursor powder after grinding should be maintained at 125 to 425 μm.

[0035] Preferably, in the precursor conveying unit, the cold tube feeder is cooled by its cooling medium sleeve, and the temperature in the hollow tubular cavity is controlled at 400-500°C, and after the temperature in the inner cavity of the high-temperature arc furnace reaches at least 1600°C, the gate valve at the bottom of the sealed hopper is opened, and the precursor powder is conveyed to the cold tube feeder by the action of the screw feeder, and passed into the inner cavity of the high-temperature arc furnace under the entrainment of inert gas.

[0036] Furthermore, before the temperature in the inner cavity of the high-temperature electric arc furnace stabilizes at above 1600°C, the precursor powder is kept in the sealed hopper. After the furnace temperature stabilizes at above 1600°C, the gate valve at the bottom of the sealed hopper is opened, and the precursor powder is transported to the cold pipe feeder under the action of the screw feeder to maintain a relatively low temperature, and is passed into the high-temperature electric arc furnace under the entrainment of inert gas.

[0037] Furthermore, after the furnace temperature of the high-temperature electric arc furnace stably reaches above 1600°C, the gate valve at the bottom of the sealed hopper is opened, and the precursor powder is transported to the cold pipe feeder at a feeding rate of 1.5 to 3 g / min under the action of the screw feeder, and is passed into the high-temperature electric arc furnace under the entrainment of inert gas.

[0038] Furthermore, the two graphite electrodes in the high-temperature electric arc furnace are electrically connected to a high-power power supply through a wire, so that a high-power electric arc is generated between the two graphite electrodes, and the position of the cold pipe feeder extending into the high-temperature electric arc furnace should ensure that the precursor powder discharged from its discharge port is in the hot zone of the high-temperature plasma flow between the high-power electric arcs, and the inert gas entrained by the precursor powder is used to prevent the precursor powder from oxidizing and facilitate heat transfer, so that the precursor powder finally enters the hot zone at a speed of 10 3 -10 5 K / s heating rate to achieve reaction temperatures above 1600 °C.

[0039] Furthermore, the ventilation rate of the inert gas in the cold tube feeder is 400-600 ml / min. The inert gas in the passage, on the one hand, carries the precursor powder into the hot zone in the high-temperature arc furnace and matches the heating rate of the hot zone to achieve sufficient conversion of the precursor powder into boron carbide crystals; on the other hand, it prevents oxidation of the precursor powder and facilitates heat transfer, and prevents the accumulation of gas by-products produced by the reaction in the hot zone from affecting the reaction.

[0040] Preferably, in the crystal growth reaction unit, the high-temperature isolation container is made of graphite, ceramic or silicon-carbon high-temperature refractory materials.

[0041] The second object of the present invention is to provide a method for controlling the boron carbide crystal growth environment. The preparation system for controlling the boron carbide crystal growth environment of the present invention is characterized in that the preparation method comprises at least the following steps:

[0042] SS1. Raw material preparation

[0043] Providing high-purity boric acid or boron oxide as a boron source, providing highly active carbon black or graphite as a carbon source, the raw material component mass ratio between the boron source and the carbon source after metering and weighing should be maintained in the range of 10:7 to 10:8.5 to ensure the completeness of the subsequent reaction between the two and the purity of the product;

[0044] SS2. Raw material mixing

[0045] First, the boron source is dispersed in deionized water in a first container in a stirring manner to form a boron slurry; and the carbon source is dispersed in deionized water in a second container in a stirring manner and a surfactant is added to form a carbon slurry;

[0046] Secondly, pouring the carbon slurry into the first container and fully stirring and mixing with the boron slurry, and heating during the stirring process so that the water in the mixture is fully evaporated to form a carbon-boron paste;

[0047] SS3. Precursor drying

[0048] The carbon-boron paste formed in the first container is transported to a low-temperature oven via a material transport pipeline I and fully dried and heated under the temperature environment to form a dry precursor;

[0049] SS4. Precursor calcination

[0050] After the dried precursor prepared in step SS3 is transported to a medium-temperature calcination box in an inert gas atmosphere, it is fully calcined in a medium-temperature environment and under the action of a constant inert gas flow to remove various organic substances and excess carbon and oxygen remaining in the dried precursor, and finally formed into a calcined block;

[0051] SS5. Precursor crushing

[0052] The calcined blocks in the medium-temperature calcination box of step SS4 are cooled to room temperature and then transported to the grinding and crushing device through a transfer device to be crushed into precursor powders with a particle size of 100 microns;

[0053] SS6. Precursor delivery and high temperature crystal growth

[0054] First, the precursor powder is kept in the sealed hopper, and the high temperature arc furnace is started and preheated until the temperature in the inner cavity thereof is stabilized at above 1600° C.;

[0055] Secondly, when the furnace temperature of the high-temperature electric arc furnace is stabilized at above 1600°C, the gate valve at the bottom of the sealed hopper is opened, and the precursor powder is conveyed to the cold pipe feeder at a feeding rate of 1.5 to 3 g / min to maintain a relatively low temperature under the action of a screw feeder while the inner cavity temperature of the cold pipe feeder is controlled at 400 to 500°C, and is then introduced into the high-temperature electric arc furnace under the entrainment of an inert gas at a ventilation rate of 400 to 600 ml / min;

[0056] Then, after the precursor powder completes the boron carbide reaction under high temperature conditions, an inert gas is continuously introduced into the furnace body and the precursor powder is stopped from being transported to the high-temperature electric arc furnace, and the high-temperature electric arc furnace is continuously cooled in an inert gas atmosphere to reduce its furnace temperature;

[0057] Finally, after the temperature of the high-temperature electric arc furnace is lowered to room temperature, the boron carbide crystal powder in the heat-resistant crucible is collected by cyclone separation and filtration, and impurities and gases therein are removed.

[0058] Preferably, in the above step SS2, the boron source is dispersed in deionized water by stirring with the help of the first stirring device under a temperature environment of about 80°C in the inner cavity of the first container and forms a boron slurry; the stirring time of the boron source and the carbon source in the inner cavities of the first and second containers is about 30 minutes, so that the boron source and the carbon source are fully dispersed in the deionized water; the heating degree of the heating device does not exceed 100°C.

[0059] Preferably, in the above step SS2, after the carbon source is formed into carbon slurry, the carbon slurry in the second container is slowly poured into the first container at a smaller inclination angle under the action of the lifting and tilting device and is fully stirred and mixed with the boron slurry under the action of the first stirring device, and the heating device is in a started state during the stirring process, and the heating time should at least ensure that the water in the mixture is fully evaporated to form a carbon-boron paste.

[0060] Preferably, in the above step SS3, the carbon-boron paste is dried and heated in a low-temperature oven at a temperature between 120° C. and 140° C., and the drying time is not less than 12 hours.

[0061] Preferably, in the above step SS4, after the dried precursor is transported to the medium-temperature calcining box via the material transport pipeline II, it is fully calcined in a medium-temperature environment and under the action of a constant inert gas flow to remove various organic substances including surfactants and excess carbon and oxygen remaining in the dried precursor, and finally forms a calcined block.

[0062] Preferably, in the above step SS4, the dried precursor is calcined under a constant argon flow in the medium temperature calcination box, the calcination temperature does not exceed 600° C., and the calcination time does not exceed 10 min, so as to remove various organic substances including surfactants and excess carbon and oxygen remaining in the dried precursor, while not significantly affecting the crystal structure and chemical composition of subsequent boron carbide products.

[0063] Preferably, in the above step SS5, the grinding process needs to be carried out slowly to prevent the generation of large heat, and the particle size of the precursor powder after grinding should be maintained at 125-425 μm.

[0064] (III) Technical Effect

[0065] Compared with the prior art, the preparation system for controlling the boron carbide crystal growth environment of the present invention has the following beneficial and significant technical effects:

[0066] (1) Compared with the prior art, the boron carbide prepared by the preparation system for controlling the boron carbide growth environment of the present invention has higher purity, smaller particle size, contains high-density twins, and has a lower free carbon content.

[0067] (2) The preparation system for controlling the boron carbide crystal growth environment of the present invention has a lower reaction temperature and a shorter preparation time than the prior art. The reaction temperature is 200 to 300° C. lower than the prior art, and the equipment time can be shortened by about 10%, greatly improving the preparation efficiency.

[0068] (3) The preparation system for controlling the boron carbide crystal growth environment of the present invention has lower energy consumption than the prior art. Due to the shortened reaction preparation time, the energy consumption in the preparation process is greatly reduced and no hazardous waste is generated during the preparation process, and the environmental protection performance is also greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 It is a schematic diagram of a preparation system for controlling a boron carbide crystal growth environment of the present invention;

[0070] Figure 2 It is a partial structural schematic diagram of a preparation system for controlling a boron carbide crystal growth environment of the present invention;

[0071] Figure 3 The present invention is a schematic flow chart of a preparation method for controlling a boron carbide crystal growth environment. DETAILED DESCRIPTION

[0072] In order to better understand the present invention, the content of the present invention is further explained in conjunction with the embodiments below. In the accompanying drawings, the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be understood as limitations on the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention. The structure and technical solution of the present invention are further described in detail below in conjunction with the accompanying drawings, and an embodiment of the present invention is given.

[0073] like Figure 1 As shown, the preparation system for controlling the boron carbide crystal growth environment of the present invention includes a raw material preparation unit 10, a raw material mixing unit 20, a precursor drying unit 30, a precursor calcining unit 40, a precursor crushing unit 50, a precursor conveying unit 60, a crystal growth reaction unit 70, and a separation device 80.

[0074] The raw material preparation unit 10 of the present invention comprises at least a boron source and a carbon source, wherein the boron source is high-purity boric acid or boron oxide, and the carbon source is highly active carbon black or graphite. The raw material component mass ratio between the boron source and the carbon source after metering and weighing should be maintained in the range of 10:7 to 10:8.5 to ensure the completeness of the subsequent reaction between the two and the purity of the product.

[0075] The raw material mixing unit 20 comprises at least a first container and a second container which are arranged adjacent to each other, wherein the boron source is dispersed in deionized water in a stirring manner in the inner cavity of the first container to form a boron slurry; the carbon source is dispersed in deionized water in a stirring manner in the inner cavity of the second container and a surfactant is added to form a carbon slurry; the carbon slurry is poured into the first container and fully stirred and mixed with the boron slurry, and the mixture is heated during the stirring process so that the water in the mixture is fully evaporated to form a carbon-boron paste. Preferably, the first container and the second container are both open containers with an open top and a closed bottom, wherein at least one heating device is provided on the outer wall of the first container and at least one stirring device is provided in its inner cavity, and the boron source is dispersed in deionized water in a stirring manner with the help of the first stirring device under a temperature environment of about 80°C in the inner cavity of the first container and forms a boron slurry; at least one lifting and tilting device is provided at the bottom of the second container and at least one second stirring device is provided in its inner cavity, and the carbon source is dispersed in deionized water in the inner cavity of the second container with the help of the second stirring device in a stirring manner and forms a carbon slurry after adding a surfactant; after the carbon source is formed into the carbon slurry, the carbon slurry in the second container is slowly poured into the first container at a small inclination angle under the action of the lifting and tilting device and is fully stirred and mixed with the boron slurry under the action of the first stirring device, and the heating device is in an activated state during the stirring process, and the heating time should at least ensure that the water in the mixture evaporates to form a carbon-boron paste. In addition, the surfactant added when forming the carbon slurry is a polyethylene glycol ether nonionic surfactant, a polyoxyethylene ether surfactant, a fatty alcohol polyethylene glycol ether surfactant, a sodium dodecyl sulfate salt ionic surfactant or a hexadecyl trimethyl ammonium salt ionic surfactant. The stirring time of the boron source and the carbon source in the inner cavity of the first and second containers is about 30 minutes, so that the boron source and the carbon source are fully dispersed in the deionized water; the heating degree of the heating device does not exceed 100°C.

[0076] The precursor drying unit 30 includes at least one low-temperature oven, which is connected to the first container via a material transport pipeline I. The carbon-boron paste formed in the first container is transported to the low-temperature oven via the material transport pipeline I and is fully dried and heated under the temperature environment to form a dry precursor. Preferably, the drying and heating temperature of the oven is between 120°C and 140°C, and the drying time is not less than 12 hours.

[0077] The precursor calcining unit 40 includes at least one medium-temperature calcining box, the inner cavity of which is an inert gas atmosphere. After the dry precursor formed in the low-temperature oven is transported to the medium-temperature calcining box, it is fully calcined in a medium-temperature environment and under the action of a constant inert gas flow to remove various organic substances and excess carbon and oxygen remaining in the dry precursor, and finally forms a calcined block. Preferably, the medium-temperature calcining box is a closed box and forms an airflow circulation loop with an inert gas source through a gas pipeline, so that the inner cavity of the medium-temperature calcining box is an inert gas atmosphere, and the medium-temperature calcining box is connected to the low-temperature oven through a material conveying pipeline II. After the dry precursor formed in the low-temperature oven is transported to the medium-temperature calcining box through the material conveying pipeline II, it is fully calcined in a medium-temperature environment and under the action of a constant inert gas flow to remove various organic substances including surfactants and excess carbon and oxygen remaining in the dry precursor, and finally forms a calcined block. In addition, the medium temperature calcination box is a tubular electric furnace, the inert gas is argon, and the dry precursor is calcined under a constant argon flow in the tubular electric furnace. The calcination temperature does not exceed 600°C, and the calcination time does not exceed 10 minutes to remove various organic substances including surfactants and excess carbon and oxygen remaining in the dry precursor, while not significantly affecting the crystal structure and chemical composition of subsequent boron carbide products.

[0078] The precursor crushing unit 50 includes at least one grinding and crushing device. The calcined blocks in the medium temperature calcining box are cooled to room temperature and then transported to the grinding and crushing device through a transfer device to be crushed into precursor powder with a particle size of 100 microns. Preferably, the grinding and crushing device is a quartz mortar or a ceramic mortar. During the grinding process, force needs to be applied slowly to prevent the generation of large heat. The particle size after grinding should be maintained at 125 to 425 μm.

[0079] like Figure 1 , 2 As shown, the precursor conveying unit 60 of the present invention comprises at least a screw feeder 62, a sealed hopper 61 and a cold tube feeder 63, wherein the screw feeder 62 is arranged in a horizontal state as a whole and comprises a feed end and a discharge end; the sealed hopper 61 is used to store precursor powder that meets the particle size requirements, and is in a closed and sealed structure as a whole, and its bottom is connected to the feed end of the screw feeder 62 through a gate valve; the cold tube feeder 63 is arranged in a vertical state as a whole, and is a hollow tubular component as a whole, and its top is connected to an inert gas source through a pipeline, and a feed port connected to the discharge end of the screw feeder 62 is provided on the side wall near the top, and a cooling medium sleeve is arranged on the outer wall of the side wall, and the cooling medium sleeve is connected to a low-temperature cooling medium source through a connecting pipeline to form a cooling medium circulation loop, and the bottom open end of the cold tube feeder 63 forms its discharge port.

[0080] Preferably, the cold tube feeder 63 is cooled by its cooling medium sleeve, and the temperature in the hollow tubular cavity is controlled at 400-500°C. After the temperature in the inner cavity of the high-temperature arc furnace reaches at least 1600°C, the gate valve at the bottom of the sealed hopper 61 is opened, and the precursor powder is transported to the cold tube feeder by the action of the screw feeder 62, and passed into the inner cavity of the high-temperature arc furnace under the entrainment of the inert gas.

[0081] like Figure 1 , 2 As shown, the crystal growth reaction unit 70 of the present invention comprises a vertical high-temperature electric arc furnace which is in a closed state as a whole, wherein two arc-shaped plate-like graphite electrodes 71 are arranged oppositely in the side walls of the inner cavity of the high-temperature electric arc furnace, a disc-shaped support base is provided at the bottom of the center of the inner cavity of the high-temperature electric arc furnace, and at least one cylindrical high-temperature isolation container 72 which is arranged concentrically with the support base and has an open top is fixedly provided on the top surface of the support base, and at least one heat-resistant crucible 73 which is arranged concentrically with the support base and has an open top is fixedly provided in the high-temperature isolation container 72, and a radial gap is provided between the heat-resistant crucible 73 and the high-temperature isolation container 72, and the bottom of the high-temperature isolation container 72 is provided with an air vent connected to the inner cavity of the disc-shaped support base, and the bottom of the disc-shaped support base is provided with an exhaust port connected to its inner cavity, and the exhaust port is connected to the outside through an exhaust pipeline. The cold tube feeder 63 passes through the top of the high-temperature arc furnace and extends into the top opening of the heat-resistant crucible 73. The precursor powder in the cold tube feeder 63 falls into the heat-resistant crucible 73 under the action of gravity and reacts in a high-temperature environment to generate boron carbide crystals. The boron carbide crystal powder generated by the reaction accumulates in the heat-resistant crucible 73. The gaseous by-products generated by the reaction, including carbon monoxide and excess boron oxide gas, and the inert gas leave the system in sequence through the gap between the heat-resistant crucible 73 and the high-temperature isolation container 72, the vent holes at the bottom of the high-temperature isolation container 72, the exhaust port at the bottom of the disc-shaped support base, and the exhaust pipeline.

[0082] Preferably, before the temperature in the inner cavity of the high-temperature electric arc furnace stabilizes at above 1600°C, the precursor powder is kept in the sealed hopper 61. After the furnace temperature stabilizes at above 1600°C, the gate valve at the bottom of the sealed hopper 61 is opened, and the precursor powder is transported to the cold pipe feeder 63 under the action of the screw feeder 62 to maintain a relatively low temperature, and is passed into the high-temperature electric arc furnace under the entrainment of inert gas. After the furnace temperature of the high-temperature electric arc furnace stabilizes at above 1600°C, the precursor powder is transported to the cold pipe feeder 63 under the action of the screw feeder 62 at a feeding rate of 1.5 to 3 g / min, and is passed into the high-temperature electric arc furnace under the entrainment of inert gas. The two graphite electrodes in the high-temperature arc furnace are electrically connected to a high-power power source through a wire, so that a high-power arc is generated between the two graphite electrodes 71, and the position of the cold pipe feeder 63 extending into the high-temperature arc furnace should ensure that the precursor powder discharged from its discharge port is in the hot zone of the high-temperature plasma flow between the high-power arcs, and the inert gas entrained by the precursor powder is used to prevent the precursor powder from oxidizing and facilitate heat transfer, and finally the precursor powder enters the hot zone with a temperature of 10 3 -10 5 The heating rate of K / s reaches a reaction temperature of more than 1600°C. In addition, the ventilation rate of the inert gas in the cold tube feeder 63 is 400-600 ml / min. On the one hand, the inert gas in the passage carries the precursor powder into the hot zone in the high-temperature arc furnace and matches the heating rate of the hot zone to achieve the precursor powder Fully converted into boron carbide crystals, on the other hand, prevents the oxidation of the precursor powder and facilitates heat transfer, and prevents the accumulation of gas byproducts produced by the reaction in the hot zone from affecting the reaction.

[0083] As can be seen from Table 1 below, the boron carbide powder prepared by the present invention has a smaller particle size, lower free carbon and impurity content, higher grain boundary twin density, and higher relative density and microhardness than the existing commercial boron carbide powder. These performance advantages indicate that the boron carbide preparation method and system of the present invention can achieve higher purity, better stoichiometric control, finer grain size, and more defect introduction.

[0084] Table 1 Various properties of boron carbide powder prepared by the present invention

[0085]

[0086]

[0087] Through the above embodiments, the purpose of the present invention is fully and effectively achieved. Those skilled in the art can understand that the present invention includes but is not limited to the contents described in the drawings and the above specific embodiments. Although the present invention has been described with respect to the most practical and preferred embodiments currently considered, it should be understood that the present invention is not limited to the disclosed embodiments, and any modification that does not deviate from the functional and structural principles of the present invention will be included in the scope of the claims.

Claims

1. A preparation system for controlling the boron carbide crystal growth environment, comprising at least a raw material preparation unit, a raw material mixing unit, a precursor drying unit, a precursor calcining unit, a precursor crushing unit, a precursor conveying unit, and a crystal growth reaction unit, characterized in that: The raw material preparation unit comprises at least a boron source and a carbon source, wherein the boron source is high-purity boric acid or boron oxide, and the carbon source is highly active carbon black or graphite; The raw material mixing unit comprises at least a first container and a second container which are arranged adjacent to each other, wherein the boron source is dispersed in deionized water in a stirring manner in the inner cavity of the first container to form a boron slurry; the carbon source is dispersed in deionized water in a stirring manner in the inner cavity of the second container and a surfactant is added to form a carbon slurry; the carbon slurry is poured into the first container and fully stirred and mixed with the boron slurry, and the mixture is heated during the stirring process so that the water in the mixture is fully evaporated to form a carbon-boron paste; The precursor drying unit comprises at least one low-temperature oven, which is connected to the first container via a material transport pipeline I. The carbon-boron paste formed in the first container is transported to the low-temperature oven via the material transport pipeline I and is fully dried and heated under the temperature environment to form a dry precursor. The precursor calcining unit comprises at least one medium-temperature calcining box, the inner cavity of which is an inert gas atmosphere. After the dry precursor formed in the low-temperature oven is transported to the medium-temperature calcining box, it is fully calcined in a medium-temperature environment and under the action of a constant inert gas flow to remove various organic substances and excess carbon and oxygen remaining in the dry precursor, and finally forms a calcined block; The precursor crushing unit includes at least one grinding and crushing device. The calcined blocks in the medium-temperature calcining box are cooled to room temperature and then transported to the grinding and crushing device through a transfer device to be crushed into precursor powders with a particle size of 100 microns. The precursor delivery unit comprises at least a screw feeder, a sealed hopper and a cold tube feeder, wherein: The screw feeder is arranged in a horizontal state as a whole and includes a feeding end and a discharging end. The sealed hopper is used to store precursor powder that meets the particle size requirements. The sealed hopper is a closed sealed structure as a whole, and its bottom is connected to the feeding end of the screw feeder through a gate valve. The cold pipe feeder is arranged in a vertical state as a whole, and is a hollow tubular component as a whole. The top of the cold pipe feeder is connected to an inert gas source through a pipeline. A feed port connected to the discharge end of the screw feeder is provided on the side wall near the top, and a cooling medium sleeve is provided on the outer side of the side wall. The cooling medium sleeve is connected to a low-temperature cooling medium source through a connecting pipeline to form a cooling medium circulation loop. The bottom open end of the cold pipe feeder forms its discharge port; The crystal growth reaction unit comprises a vertical high-temperature electric arc furnace which is in an overall closed state, wherein: The inner cavity side wall of the high temperature electric arc furnace is provided with two arc-shaped plate-shaped graphite electrodes arranged opposite to each other. A disc-shaped support base is provided at the bottom of the inner cavity center of the high-temperature electric arc furnace, and at least one cylindrical high-temperature insulation container which is arranged concentrically with the support base and has an open top is fixedly provided on the top surface of the support base, and at least one heat-resistant crucible which is arranged concentrically with the support base and has an open top is fixedly provided in the high-temperature insulation container, and a radial gap is provided between the heat-resistant crucible and the high-temperature insulation container, and the bottom of the high-temperature insulation container is provided with an air vent which is connected to the inner cavity of the disc-shaped support base, and the bottom of the disc-shaped support base is provided with an exhaust port which is connected to the inner cavity thereof, and the exhaust port is connected to the outside through an exhaust pipeline, The cold tube feeder extends through the top of the high-temperature electric arc furnace into the top opening of the heat-resistant crucible. The precursor powder in the cold tube feeder falls into the heat-resistant crucible under the action of gravity and reacts in a high-temperature environment to generate boron carbide crystals. The boron carbide crystal powder generated by the reaction accumulates in the heat-resistant crucible. The gaseous byproducts including carbon monoxide and excess boron oxide gas and the inert gas generated by the reaction sequentially leave the system through the gap between the heat-resistant crucible and the high-temperature isolation container, the vent hole at the bottom of the high-temperature isolation container, the exhaust port at the bottom of the disc-shaped support base, and the exhaust pipeline. And among them, In the precursor conveying unit, the cold tube feeder is cooled by its cooling medium sleeve, and the temperature in the hollow tubular cavity is controlled at 400-500°C. After the temperature in the inner cavity of the high-temperature arc furnace reaches at least 1600°C, the gate valve at the bottom of the sealing hopper is opened, and the precursor powder is conveyed to the cold tube feeder under the action of the screw feeder, and is passed into the inner cavity of the high-temperature arc furnace under the entrainment of the inert gas; Before the temperature in the inner cavity of the high-temperature electric arc furnace is stabilized at above 1600° C., the precursor powder is kept in the sealed hopper. After the furnace temperature is stabilized at above 1600° C., the gate valve at the bottom of the sealed hopper is opened, and the precursor powder is transported to the cold pipe feeder under the action of the screw feeder to maintain a relatively low temperature, and is introduced into the high-temperature electric arc furnace under the entrainment of inert gas; After the furnace temperature of the high-temperature electric arc furnace stably reaches above 1600°C, the gate valve at the bottom of the sealed hopper is opened, and the precursor powder is transported to the cold tube feeder at a feeding rate of 1.5~3 g / min under the action of the screw feeder, and is passed into the high-temperature electric arc furnace under the entrainment of inert gas.

2. The preparation system for controlling the boron carbide crystal growth environment according to claim 1, characterized in that: In the raw material preparation unit, the raw material component mass ratio between the boron source and the carbon source after metering and weighing should be maintained in the range of 10:7 to 10:8.5 to ensure the completeness of the subsequent reaction between the two and the purity of the product.

3. The preparation system for controlling the boron carbide crystal growth environment according to claim 1, characterized in that: In the raw material mixing unit, the first container and the second container are both open containers with an open top and a closed bottom, wherein: At least one heating device is provided on the outer wall of the first container and at least one first stirring device is provided in the inner cavity thereof, and the boron source is dispersed in deionized water by stirring with the aid of the first stirring device at a temperature of about 80° C. in the inner cavity of the first container to form a boron slurry; At least one lifting and tilting device is provided at the bottom of the second container and at least one second stirring device is provided in the inner cavity thereof, and the carbon source is dispersed in deionized water in the inner cavity of the second container by stirring with the aid of the second stirring device and a surfactant is added to form a carbon slurry; After the carbon source is formed into carbon slurry, the carbon slurry in the second container is slowly poured into the first container at a small inclination angle under the action of the lifting and tilting device and is fully stirred and mixed with the boron slurry under the action of the first stirring device. During the stirring process, the heating device is in a started state, and the heating time should at least ensure that the water in the mixture is fully evaporated to form a carbon-boron paste.

4. The preparation system for controlling the boron carbide crystal growth environment according to claim 3, characterized in that: In the raw material mixing unit, the surfactant added when forming the carbon slurry is a polyethylene glycol ether nonionic surfactant, a polyoxyethylene ether surfactant, a fatty alcohol polyethylene glycol ether surfactant, a sodium dodecyl sulfate salt ionic surfactant or a hexadecyl trimethyl ammonium salt ionic surfactant.

5. The preparation system for controlling the boron carbide crystal growth environment according to claim 3, characterized in that: In the raw material mixing unit, the boron source and the carbon source are stirred in the inner cavities of the first and second containers for about 30 minutes, so that the boron source and the carbon source are fully dispersed in the deionized water; the heating degree of the heating device does not exceed 100°C.

6. The preparation system for controlling the boron carbide crystal growth environment according to claim 1, characterized in that: In the precursor drying unit, the drying heating temperature of the oven is between 120° C. and 140° C., and the drying time is not less than 12 h.

7. The preparation system for controlling the boron carbide crystal growth environment according to claim 1, characterized in that: In the precursor calcining unit, the medium-temperature calcining box is a closed box and forms an airflow circulation loop with an inert gas source through a gas pipeline, so that the inner cavity of the medium-temperature calcining box is an inert gas atmosphere, and the medium-temperature calcining box is connected to the low-temperature oven through a material conveying pipeline II. After the dry precursor formed in the low-temperature oven is transported to the medium-temperature calcining box through the material conveying pipeline II, it is fully calcined in a medium-temperature environment and under the action of a constant inert gas flow to remove various organic substances including surfactants and excess carbon and oxygen remaining in the dry precursor, and finally forms a calcined block.

8. The preparation system for controlling the boron carbide crystal growth environment according to claim 7, characterized in that: In the precursor calcination unit, the medium-temperature calcination box is a tubular electric furnace, the inert gas is argon, and the dry precursor is calcined under a constant argon flow in the tubular electric furnace. The calcination temperature does not exceed 600°C, and the calcination time does not exceed 10 minutes, so as to remove various organic substances including surfactants and excess carbon and oxygen remaining in the dry precursor, while not significantly affecting the crystal structure and chemical composition of subsequent boron carbide products.

9. The preparation system for controlling the boron carbide crystal growth environment according to claim 1, characterized in that: In the precursor pulverizing unit, the grinding and pulverizing device is a quartz mortar or a ceramic mortar. During the grinding process, force needs to be applied slowly to prevent the generation of large heat. The particle size of the precursor powder after grinding should be maintained at 125-425 μm.

10. The preparation system for controlling the boron carbide crystal growth environment according to claim 1, characterized in that: The two graphite electrodes in the high-temperature arc furnace are electrically connected to a high-power power supply through a wire, so that a high-power arc is generated between the two graphite electrodes, and the position of the cold pipe feeder extending into the high-temperature arc furnace should ensure that the precursor powder discharged from its discharge port is in the hot zone of the high-temperature plasma flow between the high-power arcs, and the inert gas entrained by the precursor powder is used to prevent the precursor powder from oxidizing and facilitate heat transfer, and finally the precursor powder enters the hot zone at a speed of 10 3 -10 5 K / s heating rate to achieve reaction temperatures above 1600 °C.

11. The preparation system for controlling the boron carbide crystal growth environment according to claim 10, characterized in that: The ventilation rate of the inert gas in the cold tube feeder is 400-600 ml / min. On the one hand, the inert gas in the passage carries the precursor powder into the hot zone in the high-temperature arc furnace and matches the heating rate of the hot zone to achieve sufficient conversion of the precursor powder into boron carbide crystals. On the other hand, it prevents oxidation of the precursor powder and facilitates heat transfer, and prevents the accumulation of gas by-products produced by the reaction in the hot zone from affecting the reaction.

12. The preparation system for controlling the boron carbide crystal growth environment according to claim 1, characterized in that: In the crystal growth reaction unit, the high-temperature isolation container is made of graphite, ceramic or silicon-carbon high-temperature refractory materials.

13. A method for controlling a boron carbide crystal growth environment, based on the system for controlling a boron carbide crystal growth environment according to any one of claims 1 to 12, characterized in that: The preparation method comprises at least the following steps: SS1. Raw material preparation Providing high-purity boric acid or boron oxide as a boron source, providing highly active carbon black or graphite as a carbon source, the raw material component mass ratio between the boron source and the carbon source after metering and weighing should be maintained in the range of 10:7 to 10:8.5 to ensure the completeness of the subsequent reaction between the two and the purity of the product; SS2. Raw material mixing First, the boron source is dispersed in deionized water in a first container in a stirring manner to form a boron slurry; and the carbon source is dispersed in deionized water in a second container in a stirring manner and a surfactant is added to form a carbon slurry; Secondly, pouring the carbon slurry into the first container and fully stirring and mixing with the boron slurry, and heating during the stirring process so that the water in the mixture is fully evaporated to form a carbon-boron paste; SS3. Precursor drying The carbon-boron paste formed in the first container is transported to a low-temperature oven via a material transport pipeline I and fully dried and heated under the temperature environment to form a dry precursor; SS4. Precursor calcination After the dried precursor prepared in step SS3 is transported to a medium-temperature calcination box in an inert gas atmosphere, it is fully calcined in a medium-temperature environment and under the action of a constant inert gas flow to remove various organic substances and excess carbon and oxygen remaining in the dried precursor, and finally formed into a calcined block; SS5. Precursor crushing The calcined blocks in the medium-temperature calcination box of step SS4 are cooled to room temperature and then transported to the grinding and crushing device through a transfer device to be crushed into precursor powders with a particle size of 100 microns; SS6. Precursor delivery and high temperature crystal growth First, the precursor powder is kept in the sealed hopper, and the high temperature arc furnace is started and preheated until the temperature in the inner cavity thereof is stabilized at above 1600° C.; Secondly, when the furnace temperature of the high-temperature electric arc furnace is stabilized at above 1600°C, the gate valve at the bottom of the sealed hopper is opened, and the precursor powder is conveyed to the cold tube feeder at a feeding rate of 1.5-3 g / min to maintain a relatively low temperature under the action of a screw feeder while the inner cavity temperature of the cold tube feeder is controlled at 400-500°C, and is then introduced into the high-temperature electric arc furnace under the entrainment of an inert gas at a ventilation rate of 400-600 ml / min; Then, after the precursor powder completes the boron carbide reaction under high temperature conditions, an inert gas is continuously introduced into the furnace body and the precursor powder is stopped from being transported to the high-temperature electric arc furnace, and the high-temperature electric arc furnace is continuously cooled in an inert gas atmosphere to reduce its furnace temperature; Finally, after the temperature of the high-temperature electric arc furnace is lowered to room temperature, the boron carbide crystal powder in the heat-resistant crucible is collected by cyclone separation and filtration, and impurities and gases therein are removed.

14. The method for controlling the boron carbide crystal growth environment according to claim 13, characterized in that: In the above step SS2, the boron source is dispersed in deionized water by stirring with the help of a first stirring device under a temperature environment of about 80°C in the inner cavity of the first container and forms a boron slurry; the stirring time of the boron source and the carbon source in the inner cavities of the first and second containers is about 30 minutes, so that the boron source and the carbon source are fully dispersed in the deionized water; the heating degree of the heating device does not exceed 100°C.

15. The method for controlling the boron carbide crystal growth environment according to claim 13, characterized in that: In the above step SS2, after the carbon source is formed into carbon slurry, the carbon slurry in the second container is slowly poured into the first container at a small inclination angle under the action of the lifting and tilting device and is fully stirred and mixed with the boron slurry under the action of the first stirring device. During the stirring process, the heating device is in a started state, and the heating time should at least ensure that the water in the mixture is fully evaporated to form a carbon-boron paste.

16. The method for controlling the boron carbide crystal growth environment according to claim 13, characterized in that: In the above step SS3, the carbon-boron paste is dried and heated in a low-temperature oven at a temperature between 120° C. and 140° C., and the drying time is not less than 12 h.

17. The method for controlling the boron carbide crystal growth environment according to claim 13, characterized in that: In the above step SS4, the dried precursor is transported to the medium-temperature calcining box via the material transport pipeline II, and is fully calcined in a medium-temperature environment and under the action of a constant inert gas flow to remove various organic substances including surfactants and excess carbon and oxygen remaining in the dried precursor, and finally forms a calcined block.

18. The method for controlling the boron carbide crystal growth environment according to claim 13, characterized in that: In the above step SS4, the dried precursor is calcined under a constant argon flow in the medium temperature calcination box, the calcination temperature does not exceed 600 ° C, and the calcination time does not exceed 10 min, so as to remove various organic substances including surfactants and excess carbon and oxygen remaining in the dried precursor, while not significantly affecting the crystal structure and chemical composition of subsequent boron carbide products.

19. The method for controlling the boron carbide crystal growth environment according to claim 13, characterized in that: In the above step SS5, the grinding process needs to be carried out slowly to prevent the generation of large heat, and the particle size of the precursor powder after grinding should be maintained at 125-425 μm.

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