Ceria-zirconia oxides is thermodynamically favorable in a wide range of solid solution compositions, which means that ceria-zirconia is metastable with respect to phase separation. Ceria-zirconia is widely used as a component in current three-way catalytic converters. The ceria-based component of the converter has several functions, including promoting the dispersion of the noble metals in the catalyst, but also storing and releasing oxygen. The incorporation of zirconium in modern converters, forming ceria-zirconia, improves the performance of the catalyst by enhancing the resistance of the material to sintering, and simultaneously increasing the ability of the oxide to accommodate oxygen vacancies in its structure.
Zirconia Toughened Alumina offers several key properties. The mechanical robustness compared to alumina is attributed to the displacive phase transformation of the metastable tetragonal ziroconia grains when the material is stressed. The stress concentration at a crack tip can cause a transformation from a tetragonal crystal structure to a monoclinic one, which has an associated volume expansion of ziroconia. This volume expansion effectively pushes back the propagation of the crack and results in higher toughness and strength. A common specimen of Zirconia Toughened Alumina will have 10-20% zirconium oxides. The 20-30% increase in strength often meets the design criteria needed at a much