Plasma Chemistry and Plasma Processing, Vol. 12, No. 4, 1992 Thermodynamic and Transport Properties of Ar-H~ and At-He Plasma Gases Used for Spraying at Atmospheric Pressure. I: Properties of the Mixtures B. Pateyron, ~ M.-F. Elchinger, 1 G. Delluc, 1 and P. Fauchais 1 Received May 14, 1991; revised March 12, 1992 The transport properties of argon~helium and argon~hydrogen mixtures used for plasma spraying were calculated according to the Chapman-Enskog theoo, with the following approximations: third for electrical conductivity and for electron translational thermal conductivity, second for heavy species translational thermal conductivity and internal thermal conductivity, and first for reactional thermal conductivi O, and viscosity. The results are as follows: -- for electrical conductivity for T< 14,00OK, that of At/He is almost unaffected by the mole percent I-t,, while that of Ar/He is almost that of Ar up to 80 mole % He. --for viscosity, that of Ar-H2 is between those of pure Ar and pure H2, while for Ar-He mixtures an "'anomalous" behavior is observed with higher values of the mixture viscosity compared to those of the components, in the temperature range 6000-10,000 K. Such behavior is due to the value of the Ar-He interaction potential proposed and experimentally verified by Aziz et al. The simplified mLxing rule of Wilke must be used ve~ cautiously especially for Ar-He where it predicts higher values for the mixture. The addition of hydrogen or helium to argon increases its thermal conductivity drastically. When considering the mean integrated thermal conductivity, the addition of hydrogen results in a step variation when dissociation occurs, while the increase is more regular when adding He. KEY WORDS: Plasma; transport properties; argon; helium; hydrogen. 1. INTRODUCTION Plasma spraying is now part of mechanical engineering and is in full development (for example, in the last five years sales increased about t Equipe Thermodynamique et Plasma, U.A. 320 CNRS and Universit~ de Limoges, 123 Avenue Albert Thomas, 87060 Limoges Cedex, France. 421 0272-4324/92/1200-0421506.50/0 © 1992PlenumPublishing Corporation