Electron Microscopic Study of Heat-Treated Carbon Nanotubes

碳纳米管在中等真空度（-10 Torr<-4>）下，用钨加热器在250 ℃左右进行热处理，碳纳米管表面被复杂形貌的包覆。这看起来像是碳纳米管的再生。用能谱分析电子显微镜证实了W和O元素的存在。其原因是在低真空下通过钨加热器加热生成挥发性氧化钨，并将其蒸发到碳纳米管表面。在没有热处理的情况下，即在高电弧电流或高气压下，观察到类似的碳纳米管再生长的形貌。最近，我们发现在氢气中通过电弧放电蒸发制备了细而长的高质量碳纳米管。那么，碳纳米粒子共存的部分也是非常低的，非常理想的试样。在500 ℃的空气中，用红外辐射加热系统对样品进行30分钟的热辐照，可以很容易地去除共存的碳纳米颗粒。即，实现了碳纳米管的热纯化。此外，如果电弧放电1 min的第一蒸发是稳定的，则碳纳米管的取向与电场的平行方向对齐。结果，可以获得体积为1 mm^3的大量纯化的碳纳米管。与之前纯化碳纳米管相比，这个数量相当多。因此，这些纯化的碳纳米管在物理性质的测量和实际应用中是有希望的。

When carbon nanotrubes were heat-treated under intermediate vacuum (-10^<-4>Torr) at about 250ﾟC by using tungusten heater, all over the surface of carbon nanotubes are coated in complex morphology. It seems like regrowth of carbon nanotubes. The existence of elements, W and O,was confirmed by energy dispersive analytical electron microscope. The reason is that by heating of tungusten heater under low vacuum volatile tungusten oxide was made and it was evaporated to coat the surface of carbon nanotubes. Similar morphology of carbon nanotubes like regrowth was observed in cases of no heat-treating, namely at high arc current or at high pressure of atmospheric gas.Recently, we found that thin and long high quality carbon nanotubes were made by arc discharge evaporation in hydrogen gas. Then, the part of co-existing carbon nanoparticles is also very low and very desirable specimens. if we heat-irra diated the specimens by infrared radiation heating system in air at 500ﾟC for 30 minutes, we could easily removed the co-existing carbon nanoparticles. Namely, thermal purification of carbon nanotubes was realized. Moreover, if the first evaporation by arc discharge for lmin is stable, the orientation of carbon nanotubes is aligned to the parallel direction of electric field. As the result, a bulk of purified carbon nanotubes of 1mm^3 in volume could be obtained. This quantity is fairly much in the order compared with the previous purfication of carbon nanotubes. Therefore, these purified carbon nanotubes are expected in the measurement of physical properties and in practical application.