Aqueous processing routes for new SOFC materials

This paper discusses the development of new polar inks for screen printing onto green tapes, which have been produced by aqueous methods. Conventional organic inks have shown incompatibility with these aqueous tapes, due to de-wetting. Here it is shown that moving to a more polar system, improves the wetting characteristics of the prints. The new screen printing inks are based on glycerol-water and propylene glycol-water based solvent systems, with PVP (polyvinyl pyrrolidone) as binder. Rheological data is presented for both polar ink vehicles, as well as inks and comparisons are made with a typical organics based vehicle. A large degree of pseudoplasticity was found in all polar inks. Some thixotropy is also found in binary glycerol-water based inks as well as the polypropylene glycol based inks. This thixotropy is believed to be beneficial in obtaining uniformly thick prints. More studies are required to understand the interaction between solvents and binder, as this seems key in the different levels of thixotropy observed. Optimising the rheological behaviour and in particular the degree of thixotropy in these inks should lead to further improvements in printing quality. Currently, best printing results are obtained for inks based on propylene glycol with PVP binder.