Spectroscopic and Photographic Evaluation of the Near-Surface Layer Produced by Arc-Induced Polymer Ablation

High-intensity plasmas can release material from the surface of polymers by a process known as arc-induced ablation. As consequence, the formation of a near-surface layer of polymeric vapor is generally assumed. In order to investigate the near-surface layer formed by the ablation of polyoxymethylene, high-speed photography and space-resolved optical emission spectroscopy are used. Transient arc plasmas generated under a 1.9-kA, 50-Hz current semicycle are used as ablation source in air. It is found that the near-surface ablation layer strongly scatters radiation emitted by the arc core. This effect is caused by light scattering of micrometer-size fragments released by the ablating polymer. This finding shows that the near-surface layer is not only composed of vapor but also contains a significant density of large-sized polymer fragments. These fragments are formed a few milliseconds after the ignition of the arc plasma, and their density rapidly decreases with the distance to the surface.