Temporally and spatially resolved study of laser-induced plasma generated on coals with different volatile matter contents

Abstract

Volatile matter content is one of the important characteristics of coal, which would inevitably influence the laser-coal interaction process. In this work, the coal samples with different volatile matter contents were carried out by laser induced breakdown spectroscopy (LIBS) in argon atmosphere. The temporal and spatial evolution of spectra was captured along with the plasma evolution to investigate the mechanism of the volatile matter effects. The results showed that the spectral emissions for the species that abundant in volatile matter were intense at the plasma front, which indicated that the volatile matter vaporized preferentially as laser irradiating and pushed toward the upper part of the plasma. The distribution characteristics of the atomic carbon emission and ionic calcium emission of different coals demonstrated that the amount of vaporization increased with the volatile content. The more abundant dissociated volatile matter in the plasma plume benefited the generation of molecular carbon (CN and C2) formed by several pathways, resulting in an enhancement on the corresponding emissions. Moreover, effects of volatile content on ablation process contributed to the difference in plasma structure and composition, which would be magnified during the plasma expansion and fluctuation process, contributing to greatly diverse plasma morphology and parameter distribution. Consequently, a conceptual laser-coal interaction model was proposed based on the comprehensive analysis of the measurements to describe the initiation and propagation of the effects of volatile matter on coal plasma.