Preparation of nanohorn particles by pulsed arc discharge

碳纳米角颗粒的生长区域需要保持较高的温度。为了在中等规模的电弧放电室中实现这一条件，我们首先设计了一种仪器，它配备了完全覆盖电弧羽流的石英管。这种石英管是有效的，但我们的进一步研究优化纳米角颗粒的产生条件告诉石英管并不总是必要的。相反，我们控制其他因素，以产生高产量和高纯度的纳米角颗粒。我们发现最重要的参数是引入约20%的氧气，并且该氧气浓度不是那么严重，而是广泛地分布在约10和30%之间。因此，空气可用作工作气体。其次是电弧放电的电流密度。本装置的最佳条件是对直径为5 mm的碳棒使用100 A的电弧电流（约5 A/mm^2）。当我们设定较低的电流密度时，许多无定形碳颗粒开始包含在样品中。另一方面，随着电弧电流从最佳值增加，巨型石墨球（GG球）开始生长。此外，在高纯度纳米角生成的最佳条件下，纳米角颗粒的生成率最高。透射电子显微镜观察表明，纳米角颗粒的尺寸大多小于约100 nm。100 nm，并且隔离的纳米角尖端结构材料的浓度将随着电弧电流的增加而增加，其中GG球的产生加速。通过使用纳米角在乙醇中的胶体悬浮液进行离心分离，可以很容易地从样品中去除这种GG球成分。作为进一步的材料研究，我们计划研究孤立的纳米角尖结构材料。

Growing region of carbon nanohorn particles is needed to keep high temperature. To archive this condition in medium scale arc discharge chamber, we first design the instrument by equipping the quartz tube that entirely covers the arc plume. This quartz tube was effective but our further study for optimizing the generation condition of nanohorn particles tells that the quartz tube is not always necessary. Instead, we control other factors in order to generate nanohorn particles with high yield and high purity. Most important parameter that we found is to introduce about 20 % of oxygen gas, and this oxygen concentration is not so severe but widely distributed approximately between 10 and 30 %. Therefore, air is available as a working gas. Next important condition is the current density of arc discharge. Optimal conditions for the present apparatus is to use 100 A of arc current for a 5 mm in diameter carbon rod (ca.5 A/mm^2). When we set lower current density, many amorphous carbon particles come to be included in the sample. On the other hand, giant graphite balls (GG balls) are started to grow as the arc current increased from the optimal value. In addition, the production rates of nanohorn particles become the highest at the optimal condition of high purity nanohorn generation. According to the transmission electron microscopy, sizes of the nanohorn particles are mostly smaller than ca. 100 nm, and the concentration of isolated nanohorn-tip-structured materials is going to increase as increasing the arc current much more where the generation of GG balls accelerates. Such GG balls component can be easily removed from the sample by the centrifugal separation using the colloidal suspension of nanohorn in ethanol. We now plan to study the isolated nanohorn-tip-structured materials as the further materials research.