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Progress in Plasma Processing of Materials, 1999

ISBN:
1-56700-126-2 (Print)

ENTHALPY PROBE MEASUREMENTS: INTERACTION BETWEEN PLASMA JETS AND ENTRAINED ATMOSPHERE

O. Lagnoux
Equipe Plasma Laser Matériaux, ESA CNRS 6015, 87060 Limoges Cedex, France

Alain Denoirjean
Equipe Plasma Laser Matériaux, ESA CNRS 6015, 87060 Limoges Cedex, France

M. F. Elchinger
SPCTS University of Limoges, 123 av. A. Thomas, 87060 Limoges cedex, France

L. Bianchi
Commissariat a L'Energie Atomique, Le Ripault, B.P. 16, 37260 MONTS, FRANCE

Pierre Fauchais
Laboratoire Sciences des Procedes Ceramiques et de Traitements de Surface UMR CNRS 6638 University of Limoges 123 avenue Albert Thomas, 87060 LIMOGES - France

Abstract

Turbulent thermal plasma jets, such as those used for D.C. plasma spraying, are strongly affected by the ambient gas entrainment which cools down the jet and modifies its temperature, velocity and composition distributions when spraying in air. It can modify the thermomechanical properties of the sprayed coatings with the surface oxidation of the particles in flight and that of the "splats" and passes. To understand better the involved phenomena, the surrounding air entrainment in plasma jets has been studied for an Ar/H2 plasma forming gas mixture by using an enthalpy probe coupled with a mass spectrometer. The effect of a nozzle shield has been tested with a laboratory designed torch. The injection of air as carrier has also been studied. The used set-up has allowed the simultaneous determination of velocity, temperature and gas concentration distributions in the plume of plasma jets. Certain designs of nozzle shields allow to reduce the quantity of entrained air.