Electrical resistivity of ceramic–metal composite materials: application in crucibles for induction furnaces

A study was conducted of the electrical properties of partially-stabilized zirconia ceramic matrix composites with 0 to 40 vol% of titanium, niobium, nickel, and titanium and cristobalite, over temperatures ranging from 25 to 800°C. Composites containing metallic inclusions above 25 vol% show the predominance of electronic type conduction. For metallic inclusions bellow 25 vol%, a typical ionic conduction behavior has been observed. Due to the percolation effect, partially-stabilized zirconia containing 25 vol% of titanium, or nickel, shows an insulator to conductor transition, and cristobalite containing 30 vol% of titanium shows a conductor to insulator transition as the temperature is raised. Crucibles of composites of partially stabilized zirconia containing titanium were made by slip casting and sintering. Tests performed in an induction furnace showed that both pellets and crucibles containing metallic inclusions above 25 vol% had self-heated. The maximum temperature reached by fixing the power to 2 kw was 1350°C without any charge. X-ray diffraction, energy dispersive spectroscopy, scanning electron and optical microscopy were performed to provide a full microstructure characterization. Continuous paths formed by metallic clusters can be seen for materials containing metallic concentration over 25 vol%.