Microstructure and electrical conductivity of Ni/YSZ and NiO/YSZ composites for high-temperature electrolysis prepared by mechanical alloying

Nickel and yttria stabilized zirconia (Ni/YSZ) composite powders for a cathode that can be used in high-temperature electrolysis are synthesized by the ball milling of Ni and YSZ powder and by the ball-milling of NiO and YSZ powder. The influence of ball milling parameters such as milling environment and milling time on the microstructure and electrical conductivity are investigated. Microstructural analysis of the ball-milled powder shows that the milling time and environment affect the crystal structure and particle size of the composites. A NiO/YSZ composite composed of crystalline NiO and YSZ particles changed to an amorphous phase after milling for 90 h. As the milling time is increased, there is little change in the particle size of dry-milled powder whereas the particle size decreases with wet-milled powder. After subsequent cold-pressing and annealing at 900 °C for 2 h, the particle size is increased in the wet-milled powder. The electrical conductivity increases after sintering at 900 °C. Well-connected particles are thought to be the reason for the enhanced electron conductivity after sintering.