Tetragonal Zirconia Polycrystal (TZP)

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Zirconia Yttria blends of approximately 3% are called tetragonal zirconia polycrystal or TZP, and have the finest grain size. These grades of Zirconia 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.

Zirconia is best known among ceramics as being both hard and fracture-tough at room temperature. Additionally, its fine (sub-micron) grain size enablesexcellent 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.

PropertyValue
General
Chemical Formula

ZrO2-Y2O3

Mechanical
Density
6.04 gm/cc
Hardness

1300-1600 Knoop

Modulus of Elasticity

29 - 30 x 106 psi

Flexural Strength
130 - 150 kpsi
Compressive Strength
360 - 700 kpsi
Poisson's Ratio
0.23 - 0.32
Fracture Toughness
7 - 13 MPa m<sup>½</sup>
Electrical
Dielectric Strength
50 ac V/mil
Dielectric Constant
26.0 (@ 1 MHz)
Volume Resistivity

> 1013 ohm-cm

Thermal
Coefficient of Thermal Expansion

5.7 - 11 x 10-6/°C

Thermal Conductivity
1.8 - 2.9 W/mK
Shock Resistance
350 °C Diff.
Maximum Working Temperature
2400 °C

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.

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