Advances in SiC-reinforced cementitious composites for aerostatic thrust bearings based on full factorial design

Aerostatic thrust bearings utilise air as a lubricant to support loads while minimising friction and wear. The airflow within these bearings is controlled by a restrictor, which can be constructed from various materials, including porous substances. The selection of a porous material for the restrictor is particularly influenced by factors such as permeability, stiffness, and homogeneity. This work proposes a microstructural design for air restrictors based on compacted cementitious composites. A novel cementitious composite, consisting of silicon carbide (SiC) particles and Portland cement, is fabricated through cold pressing at 10 MPa and a low water-to-cement ratio of 0.30. To evaluate the effects of SiC particle size and weight fraction on the physical and mechanical properties of the composites, a statistical design approach is employed. The response variables include apparent density, apparent porosity, oxygen permeability coefficient, compressive strength, flexural strength, and dynamic modulus. In general, a significant reduction in density, compressive strength, flexural strength, and dynamic modulus, along with an increase in porosity and oxygen permeability, is achieved by composites made with smaller SiC particles. A higher weight fraction of SiC reduces bulk density and compressive strength, while increasing porosity and oxygen permeability. Finally, composites made with 67 wt% of fine SiC particles exhibit promising characteristics for aerostatic bearings, particularly in terms of porosity and permeability.