Properties of gravity-free arc discharge and its application to production of high-quality carbon annotates

1)在无重力条件下，电弧的发射强度增强，电弧体积增大，电极上的电弧光斑稳定。2)流体模拟计算了实验条件下气体温度轮廓线和膨胀速度矢量的时间演化。在无重力条件下，热气体区单调缓慢地膨胀。温度梯度越低，反应时间越长。在正常重力条件下，在1 s内立即建立稳态热对流（速度约为1m /s）。计算结果与实验结果吻合较好。在无重力条件下，(a)烟尘的生成速率增加，(b)烟尘中单壁碳纳米管的含量增加约一倍，纳米管束的厚度增加，(c)长度估计为10-100微米，(d)纳米管变粗。氧等离子体净化纳米管样品。采用火花隙法去除导电碳颗粒。5)物理性质制备出纳米管颗粒，其硬度较强。研究结果在东京举行的“创新日本2005”（Innovation Japan 2005, 2005年9月）展览会上发表。

1)Experiment by a 12-m-high vertical-swing-tower Under the gravity-free condition, the emission intensity from the arc is enhanced, the volume of the arc is increased and the arc spot on the electrodes is stabilized.2)Fluid simulation Time evolution of the temperature contour and expansion velocity vectors of the gas was calculated under the experimental condition. Under the gravity-free condition, the hot gas region expands slowly and monotonically. As the temperature gradient is low, the reaction time is increased. Under the normal gravity condition, the steady-state heat convection (with speed of about 1 m/s) is immediately established within 1 s. These calculation results are in good agreement with the experimental results.3)Production of nanotubes under the gravity-free condition Under the gravity-free condition, (a)production rate of the soot increases, (b)content of single-walled carbon nanotubes in the soot is about twice, and the thickness of the nanotube-bundles increases, (c)the length is estimated to be 10-100 micro meter, (d)the nanotubes become fatter.4)Purification By the oxygen plasma the nanotube sample is purified. By using the spark-gap method, conductive carbon particles are removed.5)Physical properties The nanotube pellet is produced, and its hardness is strong.6)Presentation in an exhibition The results were presented in the exhibition (Innovation Japan 2005, Sep. 2005) held in Tokyo.