Electrical behavior of platinum-group metals in glass-forming oxide melts

This paper presents an experimental study of the electrical conduction mechanisms in glass-forming oxide melts containing RuO2 needles. The composites were obtained by melting calcine in an industrial-scale induction-heated cold crucible melter. The temperature dependence of the conductance was measured by complex impedance spectroscopy, using a four-electrode cell, from 1200 °C to 400 °C. Direct current analysis revealed that even with low RuO2 content, electronic and ionic transport occurred over a wide temperature range. The RuO2 particle dispersion significantly enhances the total electrical conductivity up to 1200 °C. Percolation theory associated with tunneling conduction models is used to describe the electronic contribution to the conductivity. An equivalent circuit is proposed to describe the mixed ionic-electronic transport. The electronic conductivity not only depends on the RuO2 content, but on the particle length-to-diameter ratio and the RuO2 solubility.