Zirconium oxide - ZrO2

Zirconium oxide is, next to aluminium oxide, the most widely used oxide ceramic for structural and, in particular, functional applications. The most important technical modifications of ZrO₂ are polycrystallines, tetragonal zirconium oxide (TZP) and partially stabilised zirconium oxide (PSZ). Cubic fully-stabilised ZrO₂ (FSZ or CSZ) plays a less important role, due to its unfavourable mechanical properties. Diffusants are added to zirconium oxide to stabilise these thermodynamic phases (which are unstable below 1170°C). These are mainly magnesium oxide, calcium oxide, yttrium oxide or ceroxide and are added in differing quantities. This avoids conversion to the stable monoclinic phase encountered at low temperatures and, consequently, the volumetric leap associated with this process which would otherwise lead to destruction during production or use.

The addition of stabilisers creates oxygenic defects in the zirconium oxide structure which considerably favour the conveying of ions. This leads to a high level of oxygen ion conductivity at higher temperatures. Zirconium oxide is also distinguished by a high resistance to breakage when compared to other ceramics and glasses, along with excellent strength, a high degree of resistance to wear and corrosion and low thermal conductivity.

Positive thermal resistance and high-temperature strength mean that zirconium oxide is widely used as a refractory ceramic and structural ceramic in mechanical engineering. The high degree of resistance to fracturing enables the manufacture of knives and cutting tools with zirconium oxide blades and cutting edges. The material is used in medicine for manufacturing dental crowns, bridges, root pins and non-metallic implants, along with the production of hip joint implants. The capacity of diffused ZrO₂ to conduct oxygen ions at higher temperatures is exploited for the measurement of oxygen partial pressures (e.g. in exhaust gases with lambda oxygen sensors). Zirconium oxide is also used as a solid electrolyte in high-temperature fuel cells (SOFC).