Study on purification of flaky graphite by argon arc plasma torch
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摘要: 石墨材料作为一种工业原料，特别是纯度在99.9%以上的高纯石墨被应用在各大高科技领域，现有物理法和化学法的石墨提纯技术成本高、酸碱对设备和环境破坏严重、工艺流程复杂，因此开发一种优良有效的石墨提纯技术，已成为近年来国内外研究的热点。建立了一种利用非转移电弧等离子体炬提纯大鳞片石墨的方法，利用电弧可快速产生高温的特性，对黑龙江省鸡西市纯度为94.18%的大鳞片石墨样品进行高温处理。研究显示在本文电弧装置下提纯石墨的最佳放电参数范围气流量为25 L/min、电流为400 A、功率为10 kW，此时的电弧表面温度高达3350 ℃，利用扫描电子显微镜等对电弧处理前后石墨样品的微观结构对比发现石墨样品出现粉碎、断裂等特点，根据石墨化学分析方法国家标准GB/T 3521 2008对石墨纯度及其杂质进行研究分析，经电弧处理后石墨纯度提高到99.21%。Abstract: High purity graphite with purity above 99.9%, as an industrial raw material, plays an important role in the high-tech field. The existing physical and chemical methods of graphite purification technology has high cost serious damage to equipment and environment by acid and alkali, and complex processes. Thus the development of an excellent and effective graphite purification technology has become a research hotspot in recent years at home and abroad. A purification method of flaky graphite by arc plasma is established in this paper. The characteristics of high temperature which can be produced quickly by using arc plasma is used to treat the flaky graphite samples with a purity of 94.18% from Jixi City of Heilongjiang Province, under high temperature. The results show that the optimal discharge parameters are air flow rate 25 L/min, current 400 A and power 10 kW. At this point, the surface temperature of the arc plasma is up to 3350 ℃. Scanning electron microscope is used to compare the microstructure of graphite samples before and after arc processing to find the characteristics of shredding and breaking of graphite samples. The graphite purity and impurities are analysed according to national standard chemical analysis method of GB/T 3521 2008. After arc treatment, the purity of graphite is increased to 99.21%.
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图 1 鸡西大鳞片石墨样品扫描电镜照片
Figure 1. Scanning electron micrograph of flaky graphite samples from Jixi
图 2 电弧等离子体炬提纯石墨实验系统示意图
Figure 2. Experimental system of arc plasma torch purification graphite
图 5 氩气电弧等离子体炬伏安特性曲线
Figure 5. Voltage-current characteristics of argon arc plasma torch
图 8 加入石墨样品后电弧等离子体炬的伏安特性曲线
Figure 8. Diagram of the voltage-current characteristic of arc plasma torch after adding the graphite sample
图 9 电弧等离子体炬最高温度随电流变化
Figure 9. Arc plasma torch’s maximum temperature varies with the current
图 11 送粉速5 g/min时外送粉提纯后石墨纯度
Figure 11. Graphite purity by outer shipping at 5 g/min of delivery speed
图 12 送粉速10 g/min时外送粉提纯后石墨纯度
Figure 12. Graphite purity by outer shipping at 10 g/min of delivery speed
图 13 送粉速15 g/min时外送粉提纯后石墨纯度
Figure 13. Graphite purity by outer shipping at 15 g/min of delivery speed
表 1 鸡西大鳞片石墨主要元素及质量分数
Table 1. Composition and mass fraction of main elements of flaky graphite from Jixi city
element mass fraction/% melting point/℃ boiling point/℃ C 94.18 3850 4830 Si 1.12 1723 2230 Al 0.27 2045 2980 Fe 0.17 1565 3414 S 0.06 112 444 Ca 0.05 2572 2850 Mg 0.004 2800 3600 
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表 2 电弧等离子体炬放电参数表
Table 2. Discharge parameters of arc plasma
current/A power/kW flow rate/(nL·min−1) voltage/V 200～500 2.4～18.0 10～30 20～30
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表 3 处理前后石墨主要元素及质量分数
Table 3. Changes of composition and proportion of the main elements of graphite before and after purification
element mass fraction before process/% mass fraction after process/% C 94.18 99.21 Si 1.12 0.52 Al 0.27 0.07 Fe 0.17 0.17 S 0.06 0.001 Ca 0.05 0.003 Mg 0.004 0.001
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