Drying process of low-oxygen boron carbide superfine ceramic powder

Abstract

The invention belongs to the field of compound drying, and particularly relates to a drying process of low-oxygen boron carbide superfine ceramic powder, which comprises the following steps of: putting muddy boron carbide powder subjected to purification, neutralization, washing and filter pressing into a multilayer rotatable high-temperature-resistant polytetrafluoroethylene dryer, heating to 50-70 DEG C, drying by microwave and vacuumizing at the same time, and drying to obtain the low-oxygen boron carbide superfine ceramic powder. And scattering by adopting airflow to obtain the superfine boron carbide ceramic powder. By optimizing the drying process and the crushing process of the muddy boron carbide powder, not only can the oxygen content in the superfine boron carbide powder be effectively reduced, but also the powder purity and the production efficiency can be improved, and the obtained product powder is low in oxygen content, high in purity and production efficiency and more environmentally friendly and has remarkable economic benefits and social benefits.

Description

Technical Field

[0001] The invention belongs to the field of compound drying, and in particular relates to a drying process for low-oxygen boron carbide ultrafine ceramic powder. Background Art

[0002] In industry, boron carbide is generally produced by carbothermal reduction process, which first dehydrogenates boric acid to produce water and B2O3, then reacts B2O3 with CO to produce element B, and then reacts element B and C to produce boron carbide. The chemical amount of each raw material in this process is difficult to control, making it difficult to fix the product size, and more impurities will be introduced in the process of crushing into the desired particle size powder.

[0003] The high oxygen content in boron carbide powder is introduced by oxidation reactions during the preparation and storage process. During the preparation process, boron carbide powder undergoes oxidation reactions with oxygen and moisture in the atmosphere. Especially at high temperatures, the oxidation reaction will be more intense, resulting in an increase in the oxygen content in the boron carbide powder. For example, flash drying and ordinary oven drying are currently used to dry the obtained muddy boron carbide powder. The drying process is: gradually increase the temperature from room temperature to 120℃-200℃ at 1℃ / min, and keep it at 120℃-200℃ for 8h. During the drying process, due to the long drying time and the presence of a large amount of oxygen in the air, coupled with high temperature, boron carbide is easily oxidized. The oxidation reaction formula is: B4C+3O2→2B2O3+CO2. In this reaction, boron carbide (B4C) reacts with oxygen (O2) to generate boron oxide (B2O3) and carbon dioxide (CO2). This reaction is an exothermic reaction that generates a lot of heat. At the same time, due to the presence of B2O3, the oxygen content in the boron carbide powder increases, which can reach 2.0%-2.5%. In addition, boron carbide powder will also undergo oxidation reactions with oxygen and moisture in the air during storage, especially ultrafine powders. Due to their large specific surface area and high powder activity, they are very easy to absorb oxygen and oxidize during production, storage and transportation. As ceramic powders, the presence of oxygen and increased oxygen content are fatal to the production of ceramic products, causing the performance of ceramic products to decline and affecting their performance.

[0004] The existing production technology of ultrafine boron carbide ceramic powder is becoming more mature, and the above problems are expected to be solved by optimizing the drying and crushing processes. Summary of the invention

[0005] In view of the above defects or improvement needs of the prior art, the present invention provides a drying process for low-oxygen boron carbide ultrafine ceramic powder, which can not only effectively reduce the oxygen content in the ultrafine boron carbide powder, but also improve the powder purity and improve production efficiency.

[0006] In order to achieve the above purpose, the present invention provides a drying process for low-oxygen boron carbide ultrafine ceramic powder. The boron carbide powder after purification, neutralization, washing and filter pressing is placed in a multi-layer rotatable high-temperature resistant polytetrafluoroethylene dryer, and then heated to 50°C-70°C and then dried by microwave and vacuumed, and then air flow is used to break up the powder to obtain ultrafine boron carbide powder. Specifically, the boron carbide powder with a particle size of D is obtained after air flow pulverization of the 20-200 mesh particle. 50 The powder is then wet ground to obtain submicron-sized boron carbide powder. 50 The boron carbide ultrafine ceramic powder with a size of 0.5 μm to 2 μm is then purified by conventional acid washing, neutralized, rinsed and filtered to obtain the muddy boron carbide powder of the present invention.

[0007] The present invention optimizes the drying process and crushing process of muddy boron carbide powder, adopts a microwave drying method, has uniform heating, low energy consumption, high efficiency and easy control, and simultaneously vacuums and empties the air in the equipment during the drying process, which can not only remove impurities and impurities such as water vapor, free carbon, B2O3, free B and the like generated by microwave bombardment, but also effectively prevent oxygen doping, thereby improving the purity of the boron carbide ceramic powder; in addition, microwave drying has high efficiency, and a lower drying temperature can be selected, which can further prevent boron carbide from being oxidized to generate B2O3, thereby effectively preventing the increase of oxygen content; an air flow breaking process is adopted for crushing, which can be operated in conjunction with microwave drying, so that the ceramic powder is less polluted, the original morphology of the particles is not damaged, and the particle size reduction rate is high.

[0008] Furthermore, in the above technical solution, the heating rate is 5°C / min-10°C / min.

[0009] Furthermore, in the above technical solution, the microwave frequency output by microwave drying is 2450±25 MHz, and the drying rate is 24±2 kg water / h.

[0010] Microwave is a very high frequency electromagnetic wave, which has the wave characteristics of electromagnetic waves such as reflection, transmission interference, diffraction, polarization and electromagnetic wave energy transmission. The principle of microwave drying is to use the interaction between microwaves and material molecules in a rapidly changing high-frequency electromagnetic field to make polar molecules rotate at high speed and generate heat by friction, thereby achieving rapid and uniform drying of materials. The present invention adopts high-frequency microwave drying, which is fast, efficient, greatly shortens the drying cycle, and has low energy consumption. It can achieve more than 4 times the efficiency of conventional drying technology, and at the same time, its heating is uniform and easy to control.

[0011] Furthermore, in the above technical solution, a vacuum pump is used to evacuate the cavity of the polytetrafluoroethylene dryer during microwave drying to maintain a vacuum degree of 1000±20 Pa. In the present technical solution, vacuum treatment during microwave drying can remove impurities and impurities such as water vapor, free carbon, B2O3, and free B generated by microwave bombardment while excluding air, thereby improving the purity of the ceramic powder and reducing the oxygen content.

[0012] Furthermore, in the above technical solution, the moisture content of the powder after microwave drying is 0.5%-1.0%.

[0013] Furthermore, in the above technical solution, the air flow is dispersed by a nitrogen source with a pressure of 0.8±0.05MPa. In this technical solution, an air flow dispersion process that can protect the original morphology of the particles is used for crushing, and a nitrogen source is used as the dispersion air flow, which can effectively prevent oxygen from being absorbed into the ceramic powder during the process and maintain a low oxygen content.

[0014] Furthermore, in the above technical solution, the oxygen content in the ultrafine boron carbide powder is 1.5%-2.0%.

[0015] Furthermore, in the above technical solution, the particle size D of the ultrafine boron carbide ceramic powder is 50 0.5μm-2μm.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention adopts a microwave drying method, making full use of the advantages of microwave drying, such as uniform heating, low energy consumption, high efficiency and easy control. At the same time, vacuum treatment is performed during the drying process, which can not only remove impurities and impurities such as water vapor, free carbon, B2O3, free B, etc. generated by microwave bombardment, but also effectively prevent oxygen adsorption and doping, improve the purity of boron carbide ceramic powder, and reduce the oxygen content; in addition, due to the high efficiency of microwave drying, a lower drying temperature can be selected to achieve high efficiency, and the low temperature can prevent boron carbide from being oxidized to generate B2O3, further effectively preventing the increase of oxygen content; the air flow dispersion process is combined with microwave drying, and high-pressure nitrogen is introduced for air flow dispersion after drying is completed, which can prevent the ceramic powder from being contaminated and oxygen from being inhaled, further improve the purity of the ceramic powder and reduce the oxygen content.

[0017] 2. The present invention greatly reduces the oxygen content in the product powder and improves the purity by optimizing the drying and crushing processes. It has high production efficiency and is more environmentally friendly. The obtained ultrafine boron carbide ceramic powder has an oxygen content between 1.5% and 2.0% and a purity between 98.8% and 99.3%, which has significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1The present invention is a production process flow chart of the ultrafine boron carbide ceramic powder. DETAILED DESCRIPTION

[0019] The experimental methods in the following examples are conventional methods unless otherwise specified. The raw materials involved in the following examples are common commercial products and can be purchased from the market unless otherwise specified.

[0020] The above-mentioned technical features of the present invention and the technical features specifically described below (such as implementation cases) can be combined with each other to form a new or preferred technical solution.

[0021] The present invention adopts conventional production process to prepare ultrafine boron carbide ceramic powder. The production process flow chart is as follows: Figure 1 The specific method is as follows: the coarse boron carbide powder of 20-200 mesh is crushed by air flow to obtain a particle size D 50 The obtained micron-sized boron carbide ceramic powder is wet-ground to obtain a submicron-sized boron carbide ultrafine ceramic powder (D 50 0.5μm-2μm); then through acid washing, purification, neutralization, washing, plate and frame filter pressing and other processes (conventional method), muddy boron carbide powder is obtained for subsequent processes.

[0022] Example 1 A drying process for low-oxygen boron carbide ultrafine ceramic powder comprises the following steps: 60 kg of muddy boron carbide powder was placed in a multi-layer rotatable high-temperature resistant polytetrafluoroethylene dryer. The temperature was raised from room temperature to 60°C at a rate of 7°C / min, and then the temperature was maintained. Microwaves with a frequency of 2450 MHz were used for drying for 30 minutes. During the drying process, a vacuum pump was used to evacuate the polytetrafluoroethylene dryer cavity and the vacuum degree was maintained at 1000 Pa to obtain boron carbide ceramic powder blocks. Then, the microwave and vacuum were stopped, and nitrogen with a pressure of 0.8 MPa was introduced to break up the powder blocks to obtain ultrafine boron carbide ceramic powder.

[0023] Example 2 A drying process for low-oxygen boron carbide ultrafine ceramic powder comprises the following steps: 60 kg of muddy boron carbide powder was placed in a multi-layer rotatable high-temperature resistant polytetrafluoroethylene dryer. The temperature was increased from room temperature to 50°C at a rate of 5°C / min, and then the temperature was maintained. Microwaves with a frequency of 2460 MHz were used for drying for 30 minutes. During the drying process, a vacuum pump was used to evacuate the polytetrafluoroethylene dryer cavity and the vacuum degree was maintained at 1020 Pa to obtain boron carbide ceramic powder blocks. Then, the microwave and vacuum were stopped, and nitrogen with a pressure of 0.85 MPa was introduced to break up the powder blocks to obtain ultrafine boron carbide ceramic powder.

[0024] Example 3 A drying process for low-oxygen boron carbide ultrafine ceramic powder comprises the following steps: 60 kg of muddy boron carbide powder was placed in a multi-layer rotatable high-temperature resistant polytetrafluoroethylene dryer. The temperature was increased from room temperature to 70°C at a rate of 10°C / min, and then the temperature was maintained. Microwaves with a frequency of 2440 MHz were used for drying for 30 minutes. During the drying process, a vacuum pump was used to evacuate the polytetrafluoroethylene dryer cavity and the vacuum degree was maintained at 990 Pa to obtain boron carbide ceramic powder blocks. Then, the microwave and vacuum were stopped, and nitrogen with a pressure of 0.75 MPa was introduced to break up the powder blocks to obtain ultrafine boron carbide ceramic powder.

[0025] Comparative Example 1 A drying process for low-oxygen boron carbide ultrafine ceramic powder comprises the following steps: 60 kg of muddy boron carbide powder was placed in a multi-layer rotatable high-temperature resistant polytetrafluoroethylene dryer, and the temperature was increased from room temperature to 60°C at a rate of 7°C / min. The temperature was maintained and the drying was carried out for 30 minutes using a microwave with a frequency of 2450 MHz to obtain a boron carbide ceramic powder block. The microwave was then stopped and nitrogen with a pressure of 0.8 MPa was introduced to break up the powder block to obtain an ultrafine boron carbide ceramic powder.

[0026] Comparative Example 2 A drying process for low-oxygen boron carbide ultrafine ceramic powder comprises the following steps: 60 kg of muddy boron carbide powder was placed in a multi-layered rotatable high-temperature resistant polytetrafluoroethylene dryer. The temperature was increased from room temperature to 200°C at a rate of 7°C / min, and then the temperature was maintained. Microwaves with a frequency of 2450 MHz were used for drying for 30 minutes. During the drying process, a vacuum pump was used to evacuate the polytetrafluoroethylene dryer cavity and the vacuum degree was maintained at 1000 Pa to obtain boron carbide ceramic powder blocks. Then, the microwave and vacuum were stopped, and nitrogen with a pressure of 0.8 MPa was introduced to break up the powder blocks to obtain ultrafine boron carbide ceramic powder.

[0027] Comparative Example 3 A drying process for low-oxygen boron carbide ultrafine ceramic powder comprises the following steps: 60 kg of muddy boron carbide powder was placed in a multi-layered rotatable high-temperature resistant polytetrafluoroethylene dryer. The temperature was raised from room temperature to 60°C at a rate of 7°C / min, and then the temperature was maintained. Microwaves with a frequency of 2450 MHz were used for drying for 30 minutes. During the drying process, a vacuum pump was used to evacuate the polytetrafluoroethylene dryer cavity and the vacuum degree was maintained at 1000 Pa to obtain boron carbide ceramic powder blocks. Then, the microwave and vacuum were stopped, and air with a pressure of 0.8 MPa was introduced to break up the powder blocks to obtain ultrafine boron carbide ceramic powder.

[0028] Comparative Example 4 A drying process for ultrafine boron carbide ceramic powder comprises the following steps: 60kg of muddy boron carbide powder was placed in a common oven for drying. The drying process was as follows: gradually heating from room temperature to 200°C at a rate of 1°C / min and keeping the temperature at 200°C for 8 hours; then the powder was placed in a crusher at a speed of 500r / min for crushing to obtain ultrafine boron carbide ceramic powder.

[0029] Test example 1. The particle size distribution, purity, oxygen content and B2O3 content of the final product of the ultrafine boron carbide ceramic powder in Examples 1-3 and Comparative Examples 1-4 were tested. The results are shown in Table 1.

[0030] Table 1

[0031] From the results in Table 1, it can be seen that the final product of the ultrafine boron carbide ceramic powder obtained by the microwave low-temperature drying combined with high-pressure nitrogen dispersion process of the present invention has a uniform particle size distribution, can well maintain the original morphology, has a purity of more than 98.88%, an oxygen content as low as 1.5%, and a B2O3 content as low as 0.09%. In Comparative Example 1, no vacuum was drawn during microwave drying, and the impurity content increased significantly; in Comparative Example 2, high-temperature treatment was used, which not only increased the impurity content but also consumed energy; in Comparative Example 3, air was used for dispersion, and since the air contained oxygen, the oxygen content in the final product also increased to a certain extent; in Comparative Example 4, conventional oven drying was used, and the temperature was high, which not only caused a large change in particle size distribution, but also high oxygen content and B2O3 content, which directly affected its purity.

[0032] 2. Compare the production efficiency of the drying methods of Example 1 and Comparative Example 4. According to calculations, Example 1 uses a 24kW microwave box drying device, a drying cycle of 30 minutes, an output of 60kg, and a daily production capacity of about 600kg, while Comparative Example 4 uses a traditional oven drying, two 10kW devices, and a daily production capacity of about 200kg. Therefore, it can be seen that the optimized drying process of the present invention can greatly reduce energy consumption and cost, and greatly improve production capacity and production efficiency.

[0033] In summary, the invention optimizes the drying and crushing process, adopts the microwave low-temperature drying method, and performs vacuum treatment during the drying process, which has low energy consumption, high efficiency and easy control. At the same time, high-pressure nitrogen is used to break up the powder, which retains the original powder morphology. The obtained product powder has low oxygen content, high purity and production efficiency, is more environmentally friendly, and has significant economic and social benefits.

[0034] Finally, it should be emphasized that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A drying process for low-oxygen boron carbide ultrafine ceramic powder, characterized in that: The drying process is as follows: the muddy boron carbide powder after purification, neutralization, washing and filter pressing is placed in a multi-layer rotatable high-temperature resistant polytetrafluoroethylene dryer, heated to 50°C-70°C, then dried by microwave and vacuumized at the same time, and then dispersed by air flow to obtain ultrafine boron carbide ceramic powder.

2. The drying process of a low-oxygen boron carbide ultrafine ceramic powder according to claim 1, characterized in that: The heating rate is 5°C / min-10°C / min.

3. The drying process of a low-oxygen boron carbide ultrafine ceramic powder according to claim 1, characterized in that: The microwave frequency output by microwave drying is 2450±25 MHz, and the drying rate is 24±2 kg water / h.

4. The drying process of a low-oxygen boron carbide ultrafine ceramic powder according to claim 1, characterized in that: During the microwave drying process, a vacuum pump is used to evacuate the cavity of the polytetrafluoroethylene dryer to maintain a vacuum degree of 1000±20Pa.

5. The drying process of a low-oxygen boron carbide ultrafine ceramic powder according to claim 1, characterized in that: The moisture content of the powder after microwave drying is 0.5%-1.0%.

6. The drying process of low-oxygen boron carbide ultrafine ceramic powder according to claim 1, characterized in that: The air flow is dispersed using a nitrogen source with a pressure of 0.8±0.05MPa.

7. The drying process of low-oxygen boron carbide ultrafine ceramic powder according to claim 1, characterized in that: The oxygen content in the ultrafine boron carbide powder is 1.5%-2.0%.

8. The drying process of low-oxygen boron carbide ultrafine ceramic powder according to claim 1, characterized in that: The particle size D of the ultrafine boron carbide ceramic powder 50 0.5μm-2μm.

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