Thermal plasma processing in the nineties
In the context of materials which are expected to be one of the major technical issues in the nineties, an attempt is made to describe the role which thermal plasma processing may play in these years. Newer developments in plasma melting/remelting, extractive metallurgy, plasma deposition, plasma synthesis, and plasma densification are briefly described since it is anticipated that these developments will carry over and expand in the nineties. The major research needs associated with these developments are delineated and it is concluded that some areas in thermal plasma processing will develop into viable technologies in the nineties. In this paper, an attempt will be made to forecast developments in the field of thermal plasma processing in the nineties. Forecasts are always risky, unless there are trends already pointing towards such developments. Fortunately, this is the case for most of the newer developments. It should be realized that thermal plasma processing must be viewed in the context of much broader technology trends; some of them are clearly visible today. There is no question that materials and materials processing will be one of the most important technical issues in the nineties. This 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 which are more energy efficient, more productive, and less damaging to our environment. Thermal plasma processing will play 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. An interesting example of the utility of plasma processing has been recently demonstrated in connection with a breakthrough in the field of high temperature superconductors. It has been shown that superconducting films of these new materials can be deposited by plasma spraying 111. In spite of great strides over the past 20 years, the number of successful industrial applications in thermal plasma processing is still relatively small. There are two major reasons for the relatively slow growth of this technology. First of all, industrial efforts have not been sufficiently paralleled by basic studies at universities and, as a consequence, the required engineering base for many processes is still poorly developed or non-existent. This problem is directly linked with the nature of thermal plasma processing as a highly interdisciplinary field which cannot succeed without extensive interdisciplinary endeavors. Knowledge in plasma physics, gaseous electronics, fluid dynamics, and heat transfer has to be paired with experience in surface chemistry, electrochemistry, and material science. Universities are usually not structured for this type of interdisciplinary cooperation. And secondly, the potential of thermal plasma processing has been frequently overestimated, resulting in widespread disappointment and, even more damaging, in cuts in R & D funding. For a realistic assessment of the potential of thermal plasma processing it is essential to take competing technologies into account. The tirst part of this paper will focus on some of the more recent developments in the field of plasma melting/remelting, plasma extractive metallurgy, plasma deposition, plasma synthesis, and plasma consolidation. It is felt that these developments provide guidance for what may be