Preparation and properties of porous alumina ceramics for ultra-precision aerostatic bearings

γ-alumina powder was mixed with α-alumina powder to fabricate porous ceramics. With an increase in the γ-alumina content, the porosity of the ceramics first increased and then decreased. The open porosity of the ceramics was the same as their total porosity when the γ-alumina content was equal to or greater than 20 wt%. The permeability and open porosity of the porous alumina had a power-function relationship. The addition of γ-alumina not only realised pore transfixion, but also effectively enhanced the compressive strength of the ceramics. The maximum pore size of the ceramics increased with an increase in the γ-alumina content, which contributed to the increase in the bearing capacity and stiffness. When the γ-alumina content was 50 wt%, the porous alumina exhibited an open porosity of 25% and a permeability of 3.2 × 10−15 m2, while the compressive strength and elastic modulus were 325 MPa and 145 GPa, respectively. The bearing stiffness of the film with a thickness of 7.5 μm reached 13.5 N/μm at the air supply pressure of 0.3 MPa. These ceramics showed potential for application in ultra-precision aerostatic bearings.