Materials Processing With Thermal Plasmas

Abstract

Thermal plasmas in which the plasma state approaches local thermodynamic equilibrium may be produced by high-intensity arcs (current I > 100 A) or by radio-frequency (rf) discharges at high-power densities and at pressures exceeding 10 kPa (0.1 atm). In such plasmas, electron and heavy-particle temperatures are identical, and particle densities are only a function of the temperature (chemical equilibrium).Thermal-plasma technology has passed through a drastic transition stage from primarily space-related activities in the 1960s to a more and more materials-oriented focus in the 1980s and 1990s, and thermal-plasma processing of materials is now attracting increasing interest for industrial applications.Thermal-plasma processing of materials however must be viewed in the context of much broader technology trends, some of which are visible today. There is no question that materials and materials processing will be one of the most important technical issues as we approach the turn of the century. This trend will not be restricted to the development of new materials but will also include the refining of materials, the conservation of materials (by hard facing, coating, etc.), and the development of new processing routes that are more energy-efficient, more productive, and less damaging to our environment. Thermal-plasma processing is already playing an important role in these developments. Its potential for developing new materials-related technologies is increasingly recognized, and many research laboratories all over the world are engaged in advancing the frontiers of our knowledge in this exciting field. As a result of these efforts, thermal-plasma processing has emerged as a powerful technology that is finding numerous industrial applications.