PLASMA SYNTHESIS OF CERAMIC POWDERS

Production of high quality ceramic powders for high technology ceramics is becoming one of the most urgent issues in the ceramic industries. In particular, the development of fine ceramic powders with unusual and superior properties will be of great interest. Thermal plasmas with their unique processing capabilities will play an important role in these developments. High temperature gas-phase chemistry within thermal plasma environments provides an attractive and chemically unspecific route for powder synthesis. Furthermore, the supersaturation of vapor species which provides the driving force for particle condensation can be very large, leading to the production of ultrafine particles by homogeneous nucleation. Ceramic powders such as carbides, nitrides, oxides and solid solutions have been successfully synthesized in thermal plasma reactors based on high intensity arcs, plasma jets and rf inductively coupled discharges. Starting materials are either in the form of gases, liquids or solids. However, the availability of gas phase precursors for metals is severely limited. Therefore, the most commonly used reactants for plasma synthesis are solids. In this case the injection process is not trivial; in fact it is almost an insurmountable problem because of the high viscosity of the plasma. Recently, a liquid injection method has been developed to overcome the problems associated with solid injection and to realize the benefits of gaseous reactants. This paper will present an overview of recent advances in plasma synthesis of ceramic powders including liquid injection plasma synthesis. © 1990 IUPAC