Growth kinetics of sintered NiO/ZrO2 (5 mol.% Y2O3) composites

This work uses X-ray diffraction and scanning electron microscopy to investigate the solution of NiO in ZrO2 (with 5 mol% Y2O3, mainly in a metastable t′ phase as plasma sprayed powders) and the resultant growth kinetics of the NiO/ZrO2 composite at 1600°C. The t′-ZrO2 transforms into cubic (c-) ZrO2 within 1 h upon firing, and room temperature X-ray lattice parameter results indicate that the solubility of NiO in c-ZrO2 is about 3 mol%. Within the solubility limit, both sintering and growth of c-ZrO2 grains were enhanced by NiO addition. A further increase in the NiO content results in the formation of NiO particles which hinder the grain growth of c-ZrO2. For specimens with 10 mol% NiO the c-ZrO2 grains were found to follow the t1/3 growth kinetics, i.e. bulk diffusion controlled, while the intergranular and intragranular NiO particles coarsen according to tQTR and r1/5 laws respectively. The interfacial energy of NiO/c-ZrO2 is about 0.48 ± 0.1 J m2, inferred from the geometry of the NiO particles at the grain boundary.