Thermal plasma jets interact intensively with the surrounding atmosphere. This interaction leads to strong changes of the plasma jet properties affecting the resulting products. Modification of the nozzle parameters and conditions at the exit of the torch helps to vary and better control the process of plasma jet – ambient air interaction.

In the present study the DC arc plasma torch was equipped with a modified anode nozzle (M2.5) and a surrounding shroud at the jet exit. The process of air entrainment was investigated when shroud gas was supplied producing a protecting envelope to reduce the air entrainment. Schlieren photography and enthalpy probe with mass spectrometer were applied to study the influence on plasma jet quality. The effect of the shroud nozzle geometry as well as the effect of the shroud gas nature and flow rate was studied.

Influence of both the nozzle geometry and gas shrouding on deposition efficiency, porosity and oxide content in the resulting coatings is discussed in particular for components of high temperature fuel cells of SOFC type.