On the carbo-thermal reduction of silica for carbon nano-fibre formation via CVD
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On the carbo-thermal reduction of silica for carbon nano-fibre formation via CVD Alicja Bachmatiuk1, Felix Börrnert1, Imad Ibrahim1, Bernd Büchner1, and Mark H. Rümmeli1,2 1 2
IFW Dresden, P.O. Box 270116, 01069 Dresden, Germany Technische Universität Dresden, 01062 Dresden, Germany
ABSTRACT The formation of carbon nanostructures using silica nanoparticles from quartz substrates as a catalyst in an aerosol assisted chemical vapor deposition process was examined. The silica particles are reduced to silicon carbide via a carbothermal reduction process. The recyclability of the explored quartz substrates is also presented. The addition of triethyl borate improves the efficiency of the carbothermal reduction process and carbon nanotubes formation. Moreover, the addition of hydrogen during the chemical vapor deposition leads to the helical carbon nanostructures formation. INTRODUCTION It is well known that the graphitization process for carbon nanomaterials formation mostly use metal catalysts [1-6]. Which remain as impurities after the synthesis reaction. These metal impurities are for many applications unwanted and so strategies to eliminate or avoid them are being developed. The most popular method to remove metal impurities is through the use of post-synthesis chemical treatments, e.g. by acids [7, 8]. However, these treatments, on the whole, are not able to fully eliminate the metals and additionally such treatment can be destructive to the carbon structures themselves. Thus, there is interest to replace metal catalyst systems through non-metal synthesis routes. The implementation of the ceramic catalysts (SiO2, MgO, ZrO2, Al2O3, SiC) for the synthesis of carbon materials is a rapidly developing field [9-20]. In particular, the utilization of SiO2 for carbon nanomaterials synthesis is very attractive for further application in silicon based technology. In this article we present metal free synthesis of sp2 carbon nanomaterials from silicon carbide particles formed via carbothermal reduction of silica. The addition of triethyl borate as an acceleration agent for the carbon nanomaterials synthesis and hydrogen as a modifying carbon structure medium were also investigated. Moreover, the recycling potential for the substrates is also demonstrated. EXPERIMENT The chemical vapor deposition experiments were accomplished in a horizontal oven using an aerosol system to introduce the carbon source [9, 10]. The carbon nanostructures were formed at the centre of the furnace over pristine quartz substrates as well as over previously used substrates. The CVD experiments were performed using a temperature of 900 °C and the reaction time was 0.5 hour. The carbon source: ethanol or an ethanol/triethyl borate mixture was transported to the reactor via flowing argon (7200ml/min) through the spray injection system which forms a fine mist. In addition, nominal additions of H2 were investigated using the same flow rates. The recyclability processes consisted of two steps: initial burning of the previously
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