Effect of different carbon black types on single-walled carbon nanotube production by induction thermal plasma

Abstract

Carbon nanotubes (CNT) are important new class of technological materials that have numerous novel and useful properties. Single-Walled Carbon Nanotubes (SWCNTs) have exceptional electrical, mechanical and chemical properties. They are the best conductors of electricity and heat and the strongest and stiffest materials known to mankind. There are four methods commonly used to synthesize CNTS: arc discharge, chemical vapour deposition (CVD), laser Ablation and thermal plasma technique. Thermal plasma technology is extraordinarily well-suited for carbon nanotube synthesis because of its high temperature, high energy density and abundant contents of reactive species. Carbon nanotubes (CNTs) have been synthesized from different carbon sources. Large scale future uses of carbon nanotubes require a rapid, efficient, low cost method of synthesis, and do not require expensive starting material. Carbon black, due to its industrial availability and low cost, is an appropriate starting carbon source for carbon nanotube production. The work presented here is focused on the synthesis of SWCNTs by inductively coupled thermal plasma using carbon black as a carbon source. The main objectives of this research are; 1) Examining different grades of carbon black from different companies in order to find the best carbon black grade for SWCNTs production and 2) Studying different properties of carbon blacks which affect the quality of the SWCNTs. The methodology used in the experimental design is based on the direct evaporation of a mixture of carbon black and metallic catalyst inside the plasma plume. The experimental setup consisted of a continuous flow type reactor equipped with a high frequency plasma torch operated at 3 MHz. A serie of experimental tests were conducted to evaluate the ability of carbon blacks in producing high-quality SWCNTs. Eight grades of carbon blacks from three different companies were used as a carbon source in these experiments. A ternary mixture of nickel, cobalt, and yttrium oxide was used as a catalyst. Different properties of carbon blacks such as sulfur content, particle size, and degree of graphitization have been studied in order to find the impact they have on SWCNTs production and quality. A serie of experimental tests were performed to study the effect of mixing different grades on the behaviour of carbon black in SWCNTs synthesis and the impact of mixing on the quality of the product. Throughout the study, high resolution scanning electron microscopy (HRSEM), electron dispersive spectroscopy (EDS), and Raman spectroscopy, X-ray diffraction analysis (XRD), and thermo gravimetric analysis (TGA) were performed to evaluate the quality of the produced material. X-ray diffraction analysis was done to evaluate the microstructural data for the starting material. Overall, it has been found that carbon black grades with various properties such as particle size, sulphur content, and grain size will produce SWCNTs which differ in quality. In other words, different properties of carbon blacks have direct impact on the quality of SWCNTs. It has also been shown that properties of carbon blacks do not affect the size distribution of SWCNTs and under the same conditions, using different grades of carbon black will not change the diameter size of the product. Mixing different carbon black grades cannot improve the quality of synthesized soot. All the mixtures of different carbon blacks yielded in worse quality products comparing with the product obtained when mixtures were not used. However, it seems that mixing different grades can reduce clogging problems since no clogging interrupted the operation during the experiments in which mixtures were used as a feedstock.