Analysis of atmospheric pressure plasma torch and the effects of multiple gas compositions on plasma chemistry and its interaction with high density polyethylene

Summary form only given. Atmospheric plasma torches with compressed air feed gas are currently being evaluated as an alternative to grit blasting for the removal of paint coatings on naval and air vessels. Although these systems have demonstrated the ability to remove coatings at a moderate rate, the mechanisms by which the paint is removed are not well understood. It is widely postulated that the oxidizing dissociated species formed in the plasma torch provide a chemical pathway for enhanced removal of coatings; however, this mechanism has not been confirmed. In this work, we seek to elucidate mechanisms that drive paint removal with an atmospheric plasma torch. Specifically, the influence of reactive species, thermal energy dissipation, and energetic plasma species on coating removal rates need to be quantified. To this end, an atmospheric pressure plasma torch operating at 100 kHz and approximately 1 kW delivered power is studied under different feed gases. High density polyethylene (HDPE) samples are used as a surrogate for a generic paint matrix. Operating the plasma torch with compressed air as the feed gas, this system has been shown to remove HDPE up to a rate of approximately 100 mg/s. Preliminary results indicate the removal of HDPE with a nitrogen plasma in ambient and inert environments, suggesting that the removal mechanism is not solely oxidation. We compare these results with removal rates obtained with different gases including nitrogen, carbon dioxide, and nitrogen-oxygen mixtures. Removal rates are also compared to optical emission spectroscopy to identify the reactive plasma constituents. This work exhibits a complex plasma chemistry comprised of energetic metastable and reactive species that portends the feasibility of anaerobic removal under ambient conditions with comparable rates.