Perspectives of suspension plasma spraying of palladium nanoparticles for preparation of thin palladium composite membranes

Suspension plasma spraying (SPS) of Pd nanoparticles was evaluated as a new method for coating of dense Pd films for H2 separation on porous substrates. The substrates were prepared by coating porous sinter metal disks with a porous yttria stabilized zirconia (YSZ) layer acting as a barrier against intermetallic diffusion between the sinter metal and the Pd membrane (diffusion barrier layer, DBL). Before applying the Pd coating, the sinter metal substrates were characterized by N2 permeance measurements. The maximum pore sizes before and after coating of the DBL were determined. For SPS of Pd, particles with diameters in the range between 250 nm and 550 nm were suspended in ethyl cellulose containing diethylene glycol monobutyl ether solution. A wide process parameter field was tested in the SPS. After Pd coating, the membrane morphology was characterized with scanning electron microscopy (SEM) and electron probe microanalysis (EPMA), and the membrane performance was evaluated with N2 and H2 permeation measurements. The thickest Pd layer (9.5 µm) showed an ideal H2/N2 permselectivity of 60 at 350 °C and a H2 permeability of 1.2×10−7exp(−1392/T) mol m−1 s−1 Pa−0.5. Yet rather thick Pd layers of around 10 µm were required to close the pores of the rough YSZ layers, but with further optimizations, SPS appears to be a promising new way for the fabrication of robust Pd coatings on porous substrates. A particular advantage is seen in the very quick deposition.