Experimental study on preparation of spherical alumina powder by laminar plasma jet
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摘要: 为研究非转移弧层流等离子体制备面向新材料领域的μm级球形氧化铝粉末的能力，使用自制的非转移弧分段式阳极层流等离子体球化设备，以载气送粉的方式，对η相的不规则μm级三氧化二铝粉末进行等离子体球化处理，并采用均匀设计法，研究等离子体发生器和送粉器不同的工作参数对氧化铝粉末球化率的影响规律。结果表明，实验所采用的直流非转移弧层流等离子体发生器能有效制备球化率接近100%的高球化率球形氧化铝粉末。实验发现，高球化率、高分散性和粒径大小均匀的球形氧化铝粉末可在不同工艺参数组合下制备，并证明了采用非转移弧分段式阳极层流等离子体发生器可实现较低功率下制备较高球化率球形氧化铝的可行性。实验还通过XRD与PDF卡片索引技术对球化前后的氧化铝粉末进行了物相定性分析，发现η相的氧化铝粉末经射流作用转化成了Corundum型的氧化铝粉末。Abstract: For preparing micro-sized spherical alumina powder, the micro-sized η phase irregular alumina powders with large pore volume were spheroidized in laminar plasma jet generated by a segmented anode non-transferred arc laminar plasma torch using nitrogen as plasma gas. The effect of different working parameters of the plasma torch and a powder feeder on the spheroidization rate of the treated powders was investigated. The spheroidization rate was obtained by counting the number of the spherical particles over the total particles shown in images taken by an optical microscope, using reflection method. The spheroidization rate of the treated powders was close to 100%, showing a good performance of the laminar plasma torch. The alumina powders with high spheroidization rate, high dispersion and uniform particle size can be obtained using different combinations of the working parameters of the plasma torch and the powder feeder. In addition, it was shown that high spheroidization rate of the alumina powders can be achieved with the laminar plasma torch working at low power. The main phases of the raw and treated alumina are η and α, respectively, characterized by the XRD based on PDF card matching method.
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图 1 分段式阳极层流等离子体发生器结构示意图
Figure 1. Schematic diagram of a laminar plasma torch with a segmented anode
图 2 层流等离子体射流图片(I=80 A; Qw=14 L/min)
Figure 2. Image of a laminar plasma jet
(working current I=80 A; working gas flow Qw=14 L/min)
图 3 层流等离子体球化系统示意图
Figure 3. Schematic diagram of a laminar plasma spheroidization system
图 4 在光学显微镜下原料氧化铝粉末的表面形貌
Figure 4. Surface morphology of the raw alumina powder under the optical microscope
图 5 球化率高于接近100%的球形粉末在光学显微镜下的表面形貌
Figure 5. Microscopic images of the treated powders with spheroidization rate(Rs) close to 100%
图 8 球化率随等离子体发生器和送粉器工作参数变化的变化规律
Figure 8. Change of Rs with the working parameters of plasma torch and powder feeder
表 1 送粉器送粉速率
Table 1. Powder feeding rate of the powder feeder
Qc/(L/h) U/V vp(g/min) 50 1 6.2 50 2 11.2 50 3 16.6 100 1 8.6 100 2 10.4 100 3 15.3 200 1 7.6 200 2 11.8 200 3 15.3 
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