Fabrication and Characterization of Partially Reduced NiO-YSZ Cermets

10 or 40 vol% Ni-YSZ cermets were prepared by die pressing. The XRD results show that the solid solubility of NiO in YSZ should be less than 5 mol% when sintering at 1300℃/1 h. The sintered NiO-YSZ or reduced Ni-YSZ cermets show a uniform two-phase microstructure, consisting of NiO/Ni grains dispersed in the continuous YSZ matrix. When increasing the sintering temperature from 1300℃ to 1600℃, the evaporation of NiO phases takes place at high temperature and condensation of NiO occurs during the cooling process. Ni-YSZ cermets were then annealed at 1000℃ for 1 h to 10 h under 5vol% H2 atmosphere. After the reduction, the denser NiO-YSZ cermets resulted in the formation of partially reduced NiO particles and thus the formation of core-shell microstructures, showing the nano-sized Ni crystals and defect clustering of NiO. The size of nano-sized Ni crystals in the shell structure is in the range of 20-30 nm. No inter-diffusion or reaction between Ni/NiO and YSZ is found in the present research after annealing at 1000℃ for 10 h under 5vol% H2 atmosphere.