Herein, we investigate the mechanism of soot formation produced by controlled-temperature pyrolysis of ethylene in Ar, He, or N2 and analyze the size distributions of soot particles to understand soot aggregation and nucleation behavior. Additionally, we probe the reactivity of soot, revealing that soot particles were highly unlikely to react with molecules of the above carrier gases. The use of Ar is demonstrated to promote soot production, facilitate crystalline growth, and increase the diameter of primary soot particles, while the use of He has an opposite effect, which is ascribed to the large size of the former molecules and the small size of the latter ones. Consequently, the soot generation mechanism is found to be affected by carrier gas type.
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