2. Materials and methods
2.1. Test specimens
A high purity alumina powder with 750 ppm MgO (AKS-3030 A,
Sumitomo Chemical Co., Japan) was uniaxially pressed at 45 MPa to
form discs in a cylindrical die (diameter of 52 mm). The discs were
then pressed at 200 MPa in a cold isostatic press and afterward
they were sintered at 1650 1C for 1 h in air using an electric
furnace. The flat surfaces were machined and then lapped with a
diamond suspension of 15 mm, which produced an isotropic surface
finishing.