Kunihiro Maeda

Preparation of NiO–YSZ tubular support with radially aligned pore channels

Abstract A porous NiO–YSZ tubular support with radially aligned pore channels was prepared by freeze-drying of a water-based slurry. The slurry was frozen, controlling the growth direction of the ice, and it was sublimated at a reduced pressure. After sintering, the support tube showed radially aligned large pore channels parallel to the ice growth direction, and fine pores are formed around the outer surface of the tube. Bilayer consisting of dense thin electrolyte film of YSZ onto the support has been successfully fabricated using a slurry-coating process followed by co-firing. It is regarded that such a unique bilayer structure is suitable for constructing electrode-supported type electrochemical cells.

Degradation of Zinc Oxide Varistors

The effect of ambient gases on degradation and rejuvenation of ZnO varistors was investigated from the viewpoint of voltage-current characteristics. Ambient oxygen gas suppressed increases in the leakage current during ac biasing, while it rejuvenated degraded samples. The time dependence of rejuvenation indicated that ion migrations, possibly the desorption and adsorption of oxygen ions at the grain boundaries, occur reversibly in degradation and rejuvenation. Moreover, a noticeable difference was observed between V–I curve shapes after ac biasing in nitrogen and in oxygen atmospheres.