Appearance of a conductive carbonaceous coating in a dielectric barrier discharge and its influence on the electrical properties and the conversion efficiency Plasma sources science and technology / Institute of Physics -

No abstract

Dielectric Barrier Discharges operating in CO and CO 2 form solid products at atmospheric pressure. The main differences between both plasmas and their deposits were analyzed, at similar energy input. GC measurements revealed a mixture of CO 2 , CO, and O 2 in the CO 2 DBD exhaust, while no O 2 was found in the CO plasma. A coating of nanoparticles composed of Fe, O, and C was produced by the CO 2 discharge, whereas, a microscopic dendrite-like carbon structure was formed in the CO plasma. Fe 3 O 4 and Fe crystalline phases were found in the CO 2 sample. The CO deposition was characterized as an amorphous structure, close to polymeric CO (p-CO). Interestingly, p-CO is not formed in the CO 2 plasma, in spite of the significant amounts of CO produced (up to 30% in the reactor exhaust).

O 2 and CO 2 Dielectric Barrier Discharges (DBD) were studied at elevated (i.e., above atmospheric) pressure regimes (1-3.5 bar). It was demonstrated that these operational conditions significantly influence both the discharge dynamics and the process efficiencies of O 2 and CO 2 discharges. For the case of the O 2 DBD, the pressure rise results in the amplification of the discharge current, the appearance of emission lines of the metal electrode material (Fe, Cr, Ni) in the optical emission spectrum and the formation of a granular film of the erosion products (10-300 nm iron oxide nanoparticles) on the reactor walls. Somewhat similar behavior was observed also for the CO 2 DBD. The discharge current, the relative intensity of the CO Angstrom band measured by Optical Emission Spectroscopy (OES) and the CO 2 conversion rates could be stimulated to some extent by the rise in pressure. The optimal conditions for the O 2 DBD (P = 2 bar) and the CO 2 DBD (P = 1.5 bar) are demonstrated. It can be argued that the dynamics of the microdischarges (MD) define the underlying process of this behavior. It could be demonstrated that the pressure increase stimulates the formation of more intensive but fewer MDs. In this way, the operating pressure can represent an additional tool to manipulate the properties of the MDs in a DBD, and as a result also the discharge performance.

No abstract