.The bulk density of the SPSed specimens
was measured according to the Archimedean principle
and by using distilled water as the medium. The relative
density was calculated using the theoretical density of β-
SiAlON (z¼1) (3.168 g/cm3
). The Vickers hardness of the
polished SPSed compact was measured using a Vickers
hardness tester under the load of 19.6 N (2.0 kg) at room
temperature for 20 s. Ten readings were performed on average
at different locations of the specimen surfaces.