Thin and Dense Ceramic Coatings by Plasma Spraying at Very Low Pressure

The Very Low Pressure Plasma Spray (VLPPS) process is operating at a pressure range towards 100 Pa. At this, the plasma jet interaction with the surrounding atmosphere is only weak. Thus, the plasma velocity is almost constant over a large distance from the nozzle exit. Furthermore, at these low pressures the collision frequency is distinctly reduced and the mean free path is strongly increased. As a consequence, at low pressure the specific enthalpy of the plasma is substantially higher.
These particular plasma characteristics offer enhanced possibilities to spray thin and dense ceramics compared to conventional processes in the pressure range between 5 and 20 kPa. The paper presents some examples of gas-tight and electrically insulating coatings with low thickness below 50 µm for solid oxide fuel cell (SOFC) applications. Furthermore, plasma spraying of oxygen conducting membrane materials like perowskites is discussed.