State of the art of plasma chemical synthesis of homogenous and heterogenous products

Abstract

Since 1960 many studies have been devoted to physical and chemical transformations in plasmas. In this paper we do not propose to make an exhaustive overview but to underline the main development points of plasma chemistry. First after a brief historical review, we present the plasma chemical reactors and describe the different types of plasma generators. We discuss then of the two main parameters to be taken into account in plasma chemical reactor: mixing of the reactants and quenching. We examine models taking into account kinetics, diffusion and mixing of reactants and also the catalysis problems. Secondly we recall the energetic situation and the advantages of plasma chemical reactors. We review the actual industrial plasma processes, essentially surface treatment and spraying, spheroidization, ultrafine powders production, remelting, ozone production and we try to guess what will be the future tendencies in the industrial development of plasma processes either for high quantity production and for high commercial added value products. In the third part we deal with the diagnostic techniques. For the plasma, attention is given to the assumptions involved in each techniques specially with regard to the local thermodynamic equilibrium. We describe a few techniques of measurement of the temperature and population of excited species by emission and absorption, enhancing the advantages of laser light scattering. For the condenses particles injected in a plasma jet we present the most recent techniques to measure in flight their velocity (LDA), their temperature (statistical pyrometry), their diameter and their flux. In the last part, through four examples: nitric oxide synthesis, acetylene production, plasma spraying and extractive metallurgy we try to show, what progress the development of the measuring techniques and of the modelisation has brought and what is still to be made. © IUPAC