Effect of sintering temperature on nanostructure and grain boundary diffusion of plasma sprayable calcined NiO-8YSZ cermet particles

The plasma spray technique was employed to produce an anode layer for solid oxide fuel cells (SOFCs) using calcined micro-sized nickel oxide-8 mol% yttria-stabilized zirconia (NiO-8YSZ) cermet particles as stock powder. The nanostructure of calcined micro-sized NiO-8YSZ cermet particles (CMCEP) generated through the sintering process is closely related to SOFC performance and varied with sintering conditions. Thus, the present study was conducted to analyze the effect of the sintering temperature on the diffusion and nanostructure of particles during the production of CMCEP for SOFC anode material. The distributions of Ni and Zr in grain boundary caused by molecular diffusion were quantified at different sintering temperatures in the range 1,100 °C-1,300 °C. The effects of sintering on nanosurface and structural properties of CMCEP were analyzed through scanning electron and back-scattered electron microscopies and specific surface area. The crystallinity of CMCEP was found to increase with increasing sintering temperature. Smoothing, neck formation, shrinkage, and densification of nano-sized NiO-8YSZ composite granules occurred due to the acceleration of molecular diffusion at sintering temperatures above 1,200 °C, resulting in distinct grain boundary formation. The width of interfacial transition gap between Ni and Zr measured with respect to the grain boundary increased by 69.1% as molecular diffusion accelerated with increasing sintering temperature from 1,100 to 1,300 °C. The results of the nanostructural analysis of the CMCEP surface showed a decrease in the specific surface area (measured by the Brunauer Emmett Teller (BET) method) with increasing calcination temperature. The results of this study are expected to contribute to performance optimization in the future via the control of the porosity, electrical conductivity, and triple phase boundary generation during SOFC anode layer production using plasma sprays.