Microscopic and Spectroscopic Observations of Plasma Generation in the Microwave Heating of Powder Material

Abstract

Structure formation during the plasma ignition was experimentally investigated under microwave irradiation of magnetite (Fe₃O₄) and graphite composite powder. It was found from microscopic images that there are stepwise structure formations: (i) a luminous layer, (ii) hotspots, (iii) flare like emissions, and (iv) a luminous body above the powder. The 1D-spatially resolved emission spectra show that the light of the luminous layer of (i) has CO bands, and the luminous body of (iv) has iron atomic spectra superimposed on the continuum spectrum. The structure formation indicates a process of plasma-material mixing through chemical reduction of the magnetite powder.