Feasibility analysis of carbon nanofiber synthesis and morphology control using a LPG premixed flame

Flame synthesis using liquefied petroleum gas (LPG) as the precursor gas to produce carbon nanofibers (CNFs) is an economical alternative to conventional chemical vapor deposition methods using single-component fuels such as methane and ethylene. Though LPG is a commercially viable source for carbon-based nanomaterials, the understanding of the effects of a LPG flame on CNF growth is very limited. Therefore, the present study is to analyze the feasibility of CNF growth in a premixed LPG flame using a one-dimensional flame at varying equivalence ratios. The effects of flame equivalence ratio on the CNF morphology and crystallinity are then analyzed systematically. In the present study, a diffusion flame was used to check the stability of the flame at different flow rates, followed by establishing a premixed flat flame of LPG. An optimum height above burner of 10 mm at which the temperature is around 650 °C was used in the synthesis process. Zirconia beads impregnated with nickel nitrate catalyst have been employed. Dense CNF growth with an average diameter of 77.9 nm was observed at an equivalence ratio of 1.8; as the equivalence ratio was reduced to 1.6, the average diameter of CNF increased by 46% to 114 nm, with amorphous carbon observed. The said observation is due to the effects of the increased flame temperature as the equivalence ratio approaches stoichiometry conditions from the rich side. This increases the nucleation rate, which in turn increases the catalyst particle size and the amount of free carbon atoms, producing CNFs with larger diameters and amorphous carbon. According to Raman analysis, the grown CNFs have a high number of defects, which may be good for applications where defective nanomaterials are desirable to improve the component performance. The work has proven that flame synthesis of CNFs using commercial LPG is feasible, paving the way for further exploration into cost-efficient CNF production with potential industrial applications.