New Frontiers in Material Processing Using Thermal Plasma Technology

Abstract

A review is made of the fundamental aspects involved in material processing using thermal plasma technology. The description of plasma generating devices covers d.c. plasma torches, d.c. transferred arcs, radio frequency (r.f.) inductively coupled plasma torches and hybrid combinations of them. Emphasis is given to the identification of the basic energy coupling mechanism involved in each case and the principal characteristics of the flow and temperature fields in the plasma. Materials processing techniques using thermal plasmas are grouped in two broad categories depending on the role played by the plasma in the process. The simplest and most widely used processes such as spheroidization, melting, deposition and spray-coating makes use of the plasma only as a high temperature energy source. Thermal plasma technology is also used in applications involving chemical synthesis in which the plasma is used as a source of chemically active species. Examples of such applications are, the synthesis of titanium dioxide pigment, high purity synthetic silica and a large number of high purity ultrafine ceramic powders such as Al₂O₃, SiC, Si₃N₄, TiN, TiBz.