Zirconia PSZ

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  5.75    Hardness  Knoop  1120-1300    Tensile Strength  kpsi  65    Modulus of Elasticity  psi x 106  29-30  Young  Flexural Strength  kpsi 100    Compressive  Strength  kpsi  268    Poisson's Ratio  -  0.23-0.31  Varies with  Orientation  Fracture Toughness  MPa m1/2  12    Electrical  Dielectric Strength  ac volts/mil  250    Dielectric Constant  (at 1 MHz)  -  parallel to the c-axis  Volume Resistivity  ohm-cm2/cm  >108 -  Thermal  Coefficient of  Thermal Expansion  x10-6/oC  10.1  parallel to the c-axis  Thermal Conductivity  W/moK  1.8-3.0  -  Specific Heat  cal/goC  0.1  -  Max Working Temp  oC  1100  -  Shock Resistance  oC diff. 400 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.