Engineered Ceramics for Air Bearing Systems

The Challenge

Aerostatic bearings are critical components in ultra-precision manufacturing, metrology systems, and semiconductor processing. These bearings require porous ceramic materials with precisely controlled properties: enough porosity for uniform air distribution, sufficient permeability for bearing performance, yet adequate mechanical strength to withstand operational loads. Achieving this balance—high open porosity with interconnected pores while maintaining structural integrity—presents significant material development challenges.

The Solution

This research developed porous alumina ceramics by mixing γ-alumina with α-alumina powder in varying ratios. The γ-alumina addition served dual purposes: realizing pore transfixion (creating interconnected open porosity) while simultaneously enhancing compressive strength. The researchers established that permeability and open porosity follow a power-function relationship, providing a predictive tool for material design.

Impulse excitation testing measured the elastic modulus of these porous structures, essential for predicting bearing stiffness. The correlation between processing parameters (γ-alumina content), microstructural features (porosity, pore size), and mechanical properties (elastic modulus, compressive strength) enabled systematic optimization of the ceramic formulation.

Results

At 50 wt% γ-alumina content, the optimized ceramic achieved 25% open porosity, permeability of 3.2 × 10⁻¹⁵ m², compressive strength of 325 MPa, and elastic modulus of 145 GPa. The resulting aerostatic bearing demonstrated stiffness of 13.5 N/μm at 0.3 MPa supply pressure with a 7.5 μm film thickness—performance suitable for ultra-precision applications.