Influence of Spodumene Added as a Fluxing Agent on the Properties of Alumina Porcelain Insulator

Abstract

Alumina porcelain electrical insulators were prepared using Li2O-bearing spodumene flux as a partial substitute for feldspar. The effects of spodumene on microstructure, crystalline phases, physical properties, modulus of rupture, dielectric breakdown strength and volume resistivity were investigated. The samples with spodumene content >5 mass-% sintered at 1350°C showed both zero percent water absorption (WA) and apparent porosity (AP). Density was found to decrease with increasing spodumene content from 2.39 g/cm3 (at 5 mass-% spodumene) to 2.37 g/cm3 (10 mass-%) to 2.33 g/cm3 (15 mass-%). This may be due to the irreversible phase transformation of α-spodumene to β-spodumene, which accompanies a change in density of spodumene from α-phase (3.20 g/cm3) to β-phase (2.35 g/cm3). The crystalline phases were characterised by X-ray diffraction and scanning electron microscope. They showed that spodumene favours crystallisation of elongated needle-like mullite and spodumene solid solution that coexist with alumina particles embedded in the glassy matrix of bodies sintered at 1350°C. This resulted in an increase in modulus of rupture and enhanced the electrical properties of the porcelain bodies. The maximum 71 N/mm2 modulus of rupture (MOR), dielectric strength of 21 KV/mm and electrical resistivity equal to 10×1012 Ω·cm were recorded with 10 mass-% spodumene.