Sharing the hexagonal P6/mmm crystal structure of MgB2, ZrB2 combines a 3,246 °C melting point and high point-defect energies with metallic-like electrical and thermal conductivity.
Because covalent bonding and surface oxides impede densification, ZrB2 is hot-pressed or sintered with B4C and blended with ~30 vol% SiC to form a protective silica scale during hypersonic flight.
Carbon-fiber-reinforced ZrB2-SiC ultra-high-temperature ceramic matrix composites (UHTCMCs) are engineered for atmospheric re-entry leading edges and rocket motor nozzles.