Zirconia: A Unique Multifunctional Ceramic Material

Abstract

Zirconia ceramics possess the unique combination of multi-functionality. There have been a number of landmark discoveries in the areas of its mechanical, electrical and thermal properties. The material is known to have a number of polymorphs like monoclinic at room temperature, tetragonal normally above around 1170 degrees C and cubic above around 2300 degrees C. The high-temperature cubic phase can be stabilized at room temperature by forming a solid solution with di-, tri- or tetravalent metal oxides. Its fracture toughness can be enhanced significantly by taking advantage of the stress-induced polymorphic transformation. Partially stabilized zirconia is known to have the highest toughness among all the monolithic ceramic materials. The addition of zirconia to other ceramics like alumina also toughens the ceramic composite. Stabilization of zirconia to its cubic form generates very large amount of oxygen ion vacancy, thereby enhancing the oxygen diffusivity and oxygen ion conductivity, which makes this material one of the most important solid-state high-temperature electrolytes suitable for electrochemical devices like solid oxide fuel cell, oxygen sensor and oxygen pump. Low thermal conductivity of the material makes it useful as thermal barrier coating for gas turbine blades in order to increase the operating temperature and therefore the efficiency of the turbines. High mechanical strength and high toughness together with excellent resistant to toxicity have made it emerge as a new material for biomedical prosthesis, particularly dental implants. Reinforcing with carbon nano-tube or graphene oxide enhances the mechanical properties and changes the nature of electrical conduction significantly.