Preparation of nanohorn particles by pulsed arc discharge

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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.