Study of plasma properties in pulsed plasma spraying of liquid feedstock

Summary form only given. Plasma spraying of liquid feedstock has opened the perspective of nanostructured ceramic materials deposition with intermediate thicknesses (1-20μm) for aeronautic, photocatalytic or electronic applications. Submicron particles can be injected in the plasma by the use of liquid as carrier medium forming a ceramic suspension. Solution precursor can also be injected which produces the in-flight formation of nanostructured materials. This implies to control heat and momentum transfers between material and the arcjet. Many efforts are then devoted to stabilize the arc in multi-electrode segmented plasma torches. In this paper, an alternative method is presented which consists in amplifying arc oscillations to obtain a self-sustained pulsed arc. A pulsed and synchronous piezoelectric injection of droplet containing material to deposit is then implemented. The control of the injection timing with respect to plasma oscillation permits to ensure a reproducible injection and to adjust heat and momentum transfers between plasma and materials. Pulsed arc plasma torch operates at atmospheric pressure with pure nitrogen as plasma forming gas. The modulation of specific enthalpy and plasma speed is highlighted by means of optical emission spectroscopy (OES) and speed measurements. The latter are also interpreted with an analytical model which permits to have better understanding on plasma properties oscillations. The injection of droplets of titanium dioxide ceramic particles and aluminum nitrate solution is studied by OES and imaging. It is shown that their plasma treatment (fragmentation, evaporation and trajectories) depends on the injection timing. The structural and microstuctural features of the as-sprayed coatings are also shown.