Effect of the powering frequency on the synthesis of carbon nanostructures by AC arc discharge at atmospheric pressure
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1142-JJ05-16
Effect of the powering frequency on the synthesis of carbon nanostructures by AC arc discharge at atmospheric pressure Marco Vittori Antisari, Daniele Mirabile Gattia, Renzo Marazzi, Emanuela Piscopiello1 and Amelia Montone ENEA, Department of Advanced Physical Technologies and New Materials, C.R. Casaccia Via Anguillarese 301, 00123, Rome, Italy 1 C.R.Brindisi, S.S. 7 Appia Km 706, 72100, Brindisi, Italy
ABSTRACT In this paper we report about the synthesis of single wall carbon nanohorns and highly convoluted graphite sheets by AC powered arc discharge carried out between pure graphite electrodes. The arc is ignited in air and the arched electrodes are surrounded by a cylindrical collector which collects the synthesized material and contributes to control the synthesis environment. With the purpose of studying the effect of the process variables, in this work we have explored the effect of the powering frequency on the structure of the synthesized material and on the yield of the process. Preliminary experimental results on tests carried out at constant voltage, show that the process yield is strongly influenced by the powering frequency and that higher yields are obtained at low frequency. The structure of the resulting soot has been characterized by transmission electron microscopy. Two kinds of microstructures are found by TEM observation constituted by highly convoluted graphene sheets, having locally the nanohorn morphology, and better organized nano-balls where also graphite nano-sheets can be locally found. The relative abundance of the two kinds of particles appears to depend on the powering frequency with a larger amount of the latter observed in samples synthesized at high frequency. INTRODUCTION Carbon nanostructures can be synthesized by the assembling of free carbon atoms in suitable experimental conditions. Arc discharge and impulsive laser ablation are the most explored experimental methods to produce carbon gas able to give rise to non-equilibrium nanostructures during the re-condensation process. In these methods carbon atoms are generated by graphite sublimation at high temperature, differently from CVD methods where the carbon supply is provided by the decomposition of a precursor molecule. Arc discharge has been used to produce for the first time fullerenes [1] and carbon nanotubes. This technique is useful to synthesize both Multi Wall Carbon Nanotubes (MWNT) [2] and Single Wall Carbon Nanotube (SWNT) [3] when electrodes constituted by a mixture of transition metal and carbon are ignited. In 1999 Iijima et al. [4] discovered another form of carbon nanostructures which can be produced starting from pure graphite: Single Wall Carbon Nanohorns (SWNH). This nanostructure is formed by single graphene curved in a “horn-like” shape with a fullerene at the tip. Synthesis experiments are generally carried out in controlled environment provided by a closed chamber which can be evacuated and filled with a gas at the desired pressure. However it has been shown that also un-conventional envir
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