ZrO2

Zirconium dioxide, commonly called zirconia, is a white ceramic with the chemical formula ZrO2. It is produced synthetically for engineering and medical use and occurs naturally as trace minerals. Zirconia combines a high melting point, hardness, wear resistance, and chemical stability, enabling applications that require durability at elevated temperatures and in demanding environments.

Zirconia exhibits three main polymorphs: monoclinic below approximately 1170 C, tetragonal from about 1170 to 2370 C, and cubic above 2370 C. Cooling tetragonal zirconia to room temperature induces volume expansion and potential cracking. Stabilizers such as yttria (Y2O3), calcium oxide, magnesium oxide, or ceria are added to retain a desired phase at room temperature, producing partially stabilized zirconia (PSZ) or fully stabilized zirconia. The common commercial form is yttria-stabilized tetragonal zirconia polycrystal (Y-TZP).

Stabilized zirconia offers high hardness and fracture toughness through transformation toughening, along with low thermal conductivity and chemical inertness. It is biocompatible, making it favorable for dental and orthopedic components. Processing can yield dense, fine-grained ceramics suitable for wear parts and structural applications.

Applications include structural ceramics, dental crowns and implants, thermal barrier coatings, and reinforcement in composites such as zirconia-toughened alumina. Synthetic cubic zirconia is used as a gemstone substitute in jewelry. Manufacturing typically involves powder synthesis, calcination, pressing, and sintering to achieve dense objects.