C2 Temperature Effects on Carbon Morphology

Sammanfattning

This thesis investigates the synthesis of advanced carbon materials and clean hydrogen via non-thermal, plasma-assisted pyrolysis of hydrocarbons, offering a sustainable alternative to conventional thermal methods. The study aims to characterize the complex relationship between reactor process parameters, local plasma conditions, and the resulting solid carbon morphology. Experimentally, alternating electric field discharges were utilized to crack hydrocarbon gas. Local gas temperatures were monitored spectroscopically using the Swan band emission of diatomic carbon (C2) as a proxy, while electrical diagnostics and in-line mass spectrometry tracked power input and gas exhaust composition (hydrogen, acetylene, and ethylene). The structural quality and crystallite size (La) of the synthesized carbon particles were evaluated ex situ using Raman spectroscopy and automated least-squares curve fitting. The results demonstrate that lowering the driving frequency shifts the system toward localized thermal equilibrium, leading to higher C2 rovibrational temperatures. This thermal enhancement accelerates secondary dehydrogenation, yielding higher total hydrogen outputs and a reduced ethylene-to acetylene ratio. Fur- thermore, Raman analysis reveals that these higher local temperatures directly influence carbon morphology, significantly enhancing the yield of highly ordered turbostratic carbon. Finally, tuning the plasma driving frequency provides a critical control parameter for optimizing both material structure and energy yield in advanced material synthesis.