Sintering properties and thermal depletion of boron in zirconia-zirconium diboride conductive ceramic

Zirconium diboride (ZrB2) as an ultrahigh temperature ceramic (UHTC) with excellent electrical conductivity is a potential candidate for harsh-environment devices. Fabrication of ZrB2-based materials however involves processing in the active oxidation regime (T>1200 K) leading to depletion of boron. We report a simple technique to prevent degradation during pressureless sintering of zirconia-matrix composites of ZrB2. The composites prepared using this method reach the percolation threshold at ~10 wt% ZrB2 and metal-like conductivity (~105 S/m) at 25 wt% ZrB2 in agreement with the general effective media theory. The improved mechanical properties are also discussed in terms of various toughening mechanisms.