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.