Microstructure, crystalline phases and electrical properties of aluminous porcelain containing different Fe ₂ O ₃ concentrations sintered in reducing and oxidizing atmosphere

Abstract

Aluminous porcelain containing different Fe₂O₃ concentrations were sintered in oxidizing and reducing atmosphere. The microstructure and crystalline phase formation were investigated by scanning electron microscopy and X-ray diffraction. Electrical properties were investigated by Impedance spectroscopy. The results indicated that all samples showed mullite and corundum as major phases and small fractions of quartz. The addition of Fe₂O₃ caused the appearance of hematite in samples sintered in oxidizing atmosphere and metallic iron for the samples containing > 3%wt. and sintered in reducing atmosphere. The impedance spectrum indicates that the glass phase and crystal/glassy phase interface govern the overall electrical behavior of the samples. However, different firing atmospheres cause opposite effect on the electrical resistivity of the porcelain containing Fe₂O₃. The presence of hematite was considered to be responsible for the decrease in resistivity for samples sintered in oxidizing atmosphere, whereas the increase in the resistivity of the sample sintered in a reducing atmosphere was attributed to the high amount of glassy phase and porosity. These results indicate that reducing atmosphere during firing may favor the use of raw materials with higher concentrations of Fe₂O₃, since all iron oxide have been dissolved into the melting phase during the sintering of porcelain bodies.

Keywords:
porcelain; impedance spectroscopy; Fe₂O₃ ; electrical resistivity