Thermal plasmas in material processing

Abstract

Thermal plasmas are partially ionized gases at atmospheric pressures, characterized by temperatures in the range of 2000–20,000 K and charged particle number densities in the range of 10¹⁹–10²¹ per m³. Thermal plasmas are produced by plasma torches as a highly constricted jet. The high temperatures, enthalpies and heat fluxes in the plasma jet make it amenable to many chemical and metallurgical processes of industrial importance. The processing environment can be inert as in the case of argon or nitrogen plasmas or can be made reactive by introducing suitable gases. Reactive thermal plasma processing is a novel technique, wherein the plasma enters the reaction scheme, with ions and excited species opening up new channels. This technique is versatile in producing a wide variety of materials like oxides, carbides, borides, aluminides and coatings of diamond, superconductors and bioceramics. In this paper, the basic design of the plasma devices and some of the significant materials-related activities carried out recently at BARC are reported.