Electric Conductance and Structure of Molten Oxide System PbO-SiO<sub>2</sub>-Fe<sub>2</sub>O<sub>3</sub>

Abstract

Electric conductivities of molten oxide system PbO-SiO2-Fe2O3 were measured over the temperature range from liquidus to 1200°C (Fig. 3-6). The mechanism of conduction was discussed and compared with that of system PbO-B2O3-Fe2O3 from the view point of the behaviour of ferric ion in the melt.The samples, containing Fe2O3 0-25mol%, were quenched from 1200°C, and most of them were glass. Some glasses were crystallized by heat-treatment. Measurements of Infra-red absorption spectra and X-ray diffraction were carried out of the samples quenched and then crystallized (Fig. 9, 10), and the structure of complex silicates in these samples was discussed.Based upon these measrements, the behaviou of ferric ions and structure of complex silicate ions in molten oxide were discussed, and the following results were obtained.(1) Specific conductivity increases with temperature, and obeys the Arrhenius equation (e.g. Fig. 2). The values of the apparent activation energy for conduction are about 10-25kcal/mol, and are nearly the same values as in the system PbO-SiO2. Specific conductivity increases when the SiO2 content decreases (Fig. 6), and increases with the Fe2O3 content when the ratio (PbO)/(SiO2) is constant (Fig. 4, 5). From these results, it is considered that the electric conduction in this system is ionic and that the electric charge is mainly carried by Pb2+ and Fe3+ ions.(2) The activation energy for conduction increases with the increase of effect of Fe3+ ion, because it seems to have larger interaction with silicate anion than Pb2+ ion. However, the activation energy decreases when the dissociation of chain or sheet (or ring) silicate ions occurs in the melts containing more Fe2O3, 10-20mol% (Fig. 8). The dissociation of silicate ions is caused by the dissociation of Fe2O3 into Fe3+ and O2- ions.(3) The complex anion, corresponding to the unknown ternary compound PbO-Fe2O3 SiO2, seems to exist in the molten oxide of this system which contains more than 20mol% of Fe2O3. The activation energy for conduction increases with the presence of this complex anion.