Spinel grain growth and microstructure characterisation by Scanning Electron Microscopy and Digital Image Analysis

The microstructure of sintered polycrystalline MgO·1.5Al2O3 ceramic is strongly affected by the sintering conditions due to the precipitation of α-alumina at a temperature lower than about 1400°C. Consequently, the mechanical properties, depending on grain size distribution, are greatly influenced. Three different microstructures were obtained by a two step sintering process adopting an intermediate sintering temperature of 1050°C, 1100°C and 1300°C respectively, and a final sintering temperature of 1500°C. Comparable samples obtained directly by firing at 1500°C were used. Digital image analysis (DIA) carried out on scanning electron microscope (SEM) images was performed in order to better describe the microstructural parameters. By DIA, it was possible to simultaneously characterize both grain morphology and pore size distribution, allowing us to obtain a parametrical classification which is of fundamental importance in automatic morphology recognition.