Zirconia Crucibles (ZrO2) offer three advantages over their alumina crucible counterparts: they are more refractory, having a melting point some 500oC above alumina. They are readily machined and give a high quality surface finish and are a useful oxygen anion conductor for use in sensors and fuel cells. However, they are considerably more expensive than alumina.
Zirconium dioxide has the complication of being metastable and needs to be stabilised before it can be put to use. The addition of small quantities of stabilising oxides such as CaO, MgO and best of all Y2O3 allow the high temperature cubic phase to stabilise itself. Partially stabilised zirconia can also be used as a toughening agent in alumina.
Zirconia-toughened alumina (ZTA) shows a considerable improvement in strength and more importantly toughness. As a result, these ceramics can be used in areas of extreme mechanical abrasion and thermal shock.
Fully stabilised zirconia (FSZ) produces a high-density ceramic on sintering. The grain size is relatively large at 10-40m m and the ceramics are often translucent in appearance. Recent optimisation of zirconia powders have resulted in a readily sinterable high purity product.
Please note that the information set forth herein is offered for comparison only, and is not to be construed as absolute engineering data or constituting a warranty or representation for which we assume legal responsibility.
|Property||Unit||Test||Zirconia Toughened Alumina||Partially Stabilised Zirconia||Fully Stabilised Zirconia|
|Elastic Modulus||GPa||ASTM C848||360||200||200|
|Flexural Strength||MPa||ASTM F417||450||620||900|
|Compressive Strength||MPa||ASTM C773||2900||1750||2500|
|Fracture Toughness Range||MPa||NOTCHED BEAM||5-6||11||13|
|Thermal Conductivity||W/mK||ASTM C20||27||2.2||2.2|
|CTE 25-100||10(-6)/0C/||ASTM C372||8.2||10.1||10.3|
|Thermal Shock||delta Tc||NOTE3||300||350||350|
|Dielectric Strength||ac-kv/mm (6.25mm)||ASTM D116||9.0||9.4||9.4|
|Dielectric Loss||250C@1MHz||ASTM D2520||0.0005||0.001||0.001|
|Volume Resistivity||1000C ohm-cm||ASTM D1829||10^6||<10^2||<10^1|
- DATA MEASUREMENTS – All data measurements are typical and made at room temperature unless otherwise noted.
- THERMAL SHOCK RESISTANCE – Tests are run by quenching samples into water from various elevated temperatures. The change in temperature where a sharp decrease in flexural strength is observed is listed as ‘delta Tc’.
- CHEMICAL RESISTANCE – Although all alumina and zirconia ceramics are highly resistant to chemical attack, it is recommended that specific applications are discussed with Almath Crucibles to ensure optimum ceramic selection.