Natural alumina is corundum with a Mohs hardness of 9. The Mohs hardness of cubic zirconia is 8.5. Therefore, in terms of pure alumina and zirconia, the hardness of alumina is higher and it is more wear-resistant.
But alumina ceramic is a mixture, which is artificially blended and then sintered, not pure and brittle corundum. Therefore, depending on the alumina content of the ceramics, some manufacturers have 95% alumina ceramics, 97% alumina ceramics, 99% alumina, 99.7% alumina ceramics and other ceramics. But what is certain is how to make abrasive materials. The hardness is great.
It is worth mentioning that if the grinding media material working under centrifugal force is best selected from zirconia, its monoclinic density is 5.85. The density of alumina is only 3.9-4.0. Therefore, choosing zirconia as the grinding medium will produce greater shear force and improve the grinding efficiency. If it is used as a material for grinding pots or bearings, it is better to choose high-purity alumina ceramics with higher hardness.