Zirconium oxide and zirconia ceramics are extremely refractory compounds of zirconium and oxygen. They provide excellent chemical inertness and corrosion resistance at temperatures well above the melting point of alumina. Zirconia is more expensive than alumina, however, so zirconia ceramics are used mainly in applications where alumina is unsuitable.
Although zirconia ceramics are softer than alumina, zirconia additions in alumina abrasives can greatly enhance stainless steel grinding due to the development of a fine structure. The chemical inertness of zirconium oxide is also an advantage. Zirconia has low thermal conductivity and is an electrical conductor above 800° C.
How Zirconia Ceramics are Made
Zirconia ceramics are stabilized into a cubic crystal structure to avoid cracking and mechanical weakening during heating and cooling. Some products can also be transformed and toughened (tetragona-to-monoclinic phase change) under applied stress.
Zirconia ceramics increase in volume during this phase change, resulting in compressive stresses that may locally suppress crack growth. The development of a new phase may also slow crack propagation. High-density cubic zirconia can be made into a clear, crystal form used as substitute for diamonds.
The GlobalSpec SpecSearch database contains information about different types of zirconia.
Pure zirconia is used to enhance the properties of other oxide refractories. It promotes alumina’s sinterability, and is often used with high-fired alumina bodies. Monoclinic at room temperature, pure or unstabilized zirconia changes to a denser tetragonal form at about 1000° C.
Partially stabilized zirconia (PSZ) contains a stabilizer to bring its structure to a tetragonal phase at a temperature higher than 1000° C. PSZ refractories are used in the manufacture of ferrites, and as aerospace liners. Partially stabilized zirconia is also used in cylinder liners, piston caps and valve seats.
Fully stabilized zirconia is used in oxygen sensors and oxide fuel cell applications because of its high energy transfer efficiency.
Depending on their purity and density, zirconium oxide and zirconia ceramics are used in refractory tubes or cylinders, industrial crucibles, analytical labware, sensors, wear components, refractory cements, thermocouple protection tubes, furnace muffles, liners, and high-temperature heating element supports.