Zirconia Or Alumina Which To Specify

Most enquiries we receive name a shape but not a material. Zirconia and alumina cover the large majority of industrial ceramic parts between them, and the published property tables make the choice fairly mechanical once you know which property the part is actually failing on.

Where Zirconia Wins

• Fracture toughness is 9.0 MPam1/2 against 4 for 99% alumina. A zirconia part tolerates handling, press fits and impact that would chip alumina.
• Flexural strength is 800 MPa against 330 MPa. In bending, zirconia carries more than twice the load.
• Thermal expansion is 9.6 x 10-6/C, close to that of steel, so a zirconia part clamped in a steel housing stays clamped through a temperature swing.
• Thermal shock resistance is 250 dT C against 200 dT C.
• It is non-magnetic, with a smooth ground surface, which is why plungers, shafts, guide rails and clipper blades are usually zirconia.

Where Alumina Wins

• Maximum use temperature is 1650C. Zirconia is not offered for that duty.
• Thermal conductivity is 27.5 W(m.K) against 2.5 for zirconia, an order of magnitude better, which is the whole point of a substrate.
• Dielectric strength above 10 KV/mm with volume resistivity above 10^14 ohm.cm.
• Hardness is higher: Mohs grade 9 and 92 HRA, with a Vickers value of 15.7 GPa against 11.5 GPa for zirconia.
• Density is 3.85 g/cm3 against 6.0, so an alumina part of the same size is lighter.

A Short Decision Rule

• If the part is failing by chipping, cracking or impact, move to zirconia.
• If the part is failing by softening, conducting or not shedding heat, stay with alumina and raise the purity.
• If the part runs above about 1200C, alumina is the only one of the two on the list.
• If the part has to be non-magnetic and slide against a seal, zirconia.