Improving the microstructural and physical properties of alumina electrical porcelain with Cr2O3, MnO2 and ZnO additives

The optimum concentrations of Cr₂O₃, MnO₂ and ZnO were added separately and combined to the basic composition of the alumina electrical porcelain body. The samples were prepared from wet and plastic porcelain bodies according to IEC standard methods. After drying and firing under appropriate conditions, the effects of added oxides on the microstructural and physical properties of sintered porcelain were studied. It was found that the microstructure of this material was remarkably improved compared to one without additives. The sintering temperature was decreased by 60 °C, and at the same time closed porosity decreased considerably resulting in a density increase. The mullite content increased slightly, but both the size and shape of its acicular crystals were limited to values providing formation of a very strong network connecting other crystalline phases in the glassy matrix without any significant internal microcracks. It was concluded that these oxides acted as densification catalysts, partly as mineralizers, and as crystal growth inhibitors causing significant improvement of mechanical, electrical and thermal properties of the alumina electrical porcelain investigated.