Microstructure of NiO-CoO Solid Solution Sintered with Al2O3 Additive

The influence of (Ni, Co) Al2O4 spinel precipitates on the grain growth in (Ni, Co) O ceramics with 1.45mol%, Al2O3 was investigated in the temperature range 1280 to 1380°C. Smaller precipitates preferentially dissolved and larger precipitates grew with increasing temperature and holding time, therefore, the growth mechanism of spinel precipiates was considered to be Ostwald ripening. The matrix grain size increased linearly as a function of particle size of spinel at 1280°C and 1360°C. Furthermore, the slope increased with increasing temperature, which indicates that the grain growth inhibition effect became weak. It is believed that higher solubility of Al2O3 into the matrix at higher temperature decreases the volume fraction of the spinel precipitates inhibited the grain growth of matrix.