Effect of the precursor aggregate state on the synthesis of CNTs in a DC plasma jet

• Published in: Diamond and related materials Vol. 123; p. 108844
• Main Authors: Shavelkina, M.B., Ivanov, P.P., Amirov, R.Kh, Bocharov, A.N.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.03.2022; Elsevier BV
• Subjects: Acetylene; Argon plasma; Carbon; Carbon nanotubes; DC plasma torch; Ethanol; Local thermodynamic equilibrium; Phase composition; Plasma; Plasma composition; Plasma jet synthesis; Plasma jets; Precursors; Production methods; Pyrolysis; Soot; Substrates; Thermal analysis; Thermal stability; Thermodynamic analysis; Vapor phases; Carbon nanotubes; Plasma composition; Thermodynamic analysis; Plasma jet synthesis; Thermal stability; DC plasma torch
• ISSN: 0925-9635; 1879-0062
• DOI: 10.1016/j.diamond.2022.108844

The transformation of various carbonaceous substances into ordered carbon nanostructures is a fundamental process in nanotechnology. Since this structural transformation is a common property of various methods for producing CNTs, understanding the mechanism of this process in the bulk of a plasma jet will be extremely important, since no substrates are used here. We present an experimental and numerical study of the synthesis of CNTs with and without external catalysts for the pyrolysis of soot, acetylene, and ethanol in a DC argon plasma at a pressure of 350 Torr. By combining various physical methods, including simultaneous thermal analysis, diffraction analysis, electron microscopy, and energy dispersive analysis, we will show that the aggregation state of the precursor significantly affects the structural and morphological properties of CNTs. Theoretical calculations under the assumption of local thermodynamic equilibrium made it possible to study the gas phase composition of a plasma flow in which the CNT precursor is nucleated. It was found that during the pyrolysis of soot (C), the condensation temperature of solid carbon is 3672 K, with the hydrogen in precursor (C2H2) it is lower and equals 3353 K, with the addition of oxygen (C2H5OH) its value becomes even <3141 K. At the lowest condensation temperature, the most thermally stable CNTs are formed. [Display omitted] •Carbon precursor in three states of aggregation was used for the synthesis of CNTs.•Synthesis was carried out in a stream of argon afterglow plasma at 350 Torr.•A DC plasma torch was used as a plasma jet generator.•CNTs synthesized from different precursors have different thermal stability.•The modeling revealed differences in the gas phase composition during the pyrolysis.