Cubic Zirconia (ZrO₂)

Zirconia is best known among ceramics as being both hard and fracture-tough at room temperature. Additionally, its fine (sub-micron) grain size enables excellent surface finishes and the ability to hold a sharp edge. Although it retains many properties including corrosion resistance at extremely high temperatures, zirconia does exhibit structural changes that may limit its use to perhaps only 500 °C. It also becomes electrically conductive as this temperature is approached. Zirconia is commonly blended with either MgO, CaO, or Yttria as a stabilizer in order to facilitate transformation toughening. This induces a partial cubic crystal structure instead of fully tetragonal during initial firing, which remains metastable during cooling. Upon impact, the tetragonal precipitates undergo a stress induced phase transformation near an advancing crack tip. This action expands the structure as it absorbs a great deal of energy, and is the cause of the high toughness of this material. Reforming also occurs dramatically with elevated temperature and this negatively affects strength along with 3-7% dimensional expansion. The amount of tetragonal can be controlled by additions of the blends above to balance toughness against loss of strength. Cubic Zirconia: This single crystal optically clear form of ZrO2 has a relatively low fracture toughness and strength, but very high thermal shock resistance. Zirconia PSZ: Cream colored blends with approximately 10% MgO, called partially stabilized zirconia (PSZ), are high in toughness, and retain this property to elevated temperatures. They are somewhat lower in cost but also have larger grain structure. Zirconia TZP: Yttria blends of approximately 3% are called tetragonal zirconia polycrystal (TZP) and have the finest grain size. These grades exhibit the highest toughness at room temperature, because they are nearly 100% tetragonal, but this degrades severely between 200 and 500°C as these irreversible crystal transformations also cause dimensional change.

PROPERTY UNITS VALUE REMARKS  Mechanical  Density  gm/cc  5.92    Hardness  Knoop  7.2    Tensile Strength  kpsi  -    Modulus of Elasticity  psi x 106  -  Young  Flexural Strength  kpsi -    Compressive  Strength  kpsi  -    Poisson's Ratio  -  -  Varies with  Orientation  Fracture Toughness  MPa m1/2  -    Electrical  Dielectric Strength  ac volts/mil  -    Dielectric Constant  (at 1 MHz)  -  parallel to the c-axis  Volume Resistivity  ohm-cm2/cm  - -  Thermal  Coefficient of  Thermal Expansion  x10-6/oC  8  parallel to the c-axis  Thermal Conductivity  W/moK  31.8  -  Specific Heat  cal/goC  -  -  Max Working Temp  oC  2500  -  Shock Resistance  oC diff.  Optical  Index of  Refraction  (Ordinary ray,  No,c-axis)  (Extraordinary ray,  Ne,c-axis)  2.1  -  -  -  Birefringence  (No-Ne)  -  -  Transmission Band  Wavelength of microns  -   All properties are at room temperature unless otherwise noted. Engineering data are representative, and are not intended as absolute nor warrantable. Manufacturer' s Data shown is blended from multiple sources and therefore illustrates the marketplace.