Wet powder spraying (WPS) is an easy and low-cost technology to coat planar or three dimensional surfaces. A suspension composed of solvent, powder and additives is sprayed by a nozzle. The thickness of the coating is adjusted by the amount of spraying regimes with intermediate drying steps. Various geometries, e.g planar-type or tubular-type SOFCs can be coated by a PC controlled x-y-axis system and a rotational system for the tubes. The thickness obtained so far varies between 5 and 100μm. The major parameters affecting the spray result are the spray pressure, the spray distance, the nozzle type (with varying aperture), the viscosity and the solid fraction of the suspension and the grain size distribution and grain morphology of the powder. The intermediate drying steps to obtain thicker layers are necessary to supress cracking during drying.
The major advantages of WPS compared to screen printing or plasma spraying are the low-cost fabrication, the flexibility concerning size and shape of the samples to be coated, and the easy integration into an industrial process chain.
For the  Jülich SOFC the double cathode layer consisting of  cathode functional layer and  cathode were wet powder sprayed. Additionally the cathode contact layer is applied on the metallic interconnects by WPS.
Limitations of the technology are the overspray (the amount of suspension which is sprayed besides the sample) and the formation of a suspension mist which needs to be extracted by suction. The overspray can be recycled.

Contact: Dr. N. H. Menzler,  n.h.menzler @fz-juelich.de