Zirconia (ZrO2)

Zirconia or zirconium oxide (ZrO2) is an extremely refractory compound of zirconium and oxygen. Zirconia may have additions of calcia, magnesia or baria to stabilize the structure into a cubic structure and/or improve dielectric characteristics. Zirconia stabilized in the cubic crystal structure avoids cracking and mechanical weakening during heating and cooling. Certain zirconia materials have the ability to transformation toughen (tetragonal to monoclinic phase change) under applied stress and it is frequently used in wear applications requiring improved fracture toughness and stiffness over alumina. Zirconia ceramics possess excellent chemical inertness and corrosion resistance at temperatures well above the melting point of alumina. Zirconia is more costly than alumina, so it is only where alumina will fail. Zirconia has low thermal conductivity and it is an electrical conductor above 800°C. Zirconia is used to fabricate oxygen sensors or fuel cell membranes because zirconia possesses the unique ability to allow oxygen ions to move freely through the crystal structure above 600°C. Zirconia products should not be used in contact with alumina above 1600°C. Depending on the purity and density zirconia is used for refractory tubes, industrial crucibles, analytical labware, sensors, wear components, refractory cements, thermocouple protection tubes, furnace muffles, liners and high temperature heating element supports.