Multifunctional silicon carbide/cement-based composites for porous aerostatic bearings

Composites based on silicon carbide (SiC) and Portland cement manufactured by uniaxial compaction with a low water-to-cement ratio (0.25) are designed and characterised to obtain a promising porous microstructure to be used as an air restrictor for aerostatic bearings. A 3141 full factorial design is used to investigate the effects of SiC amount (10, 20, 30 and 40 wt.%) and compacting pressure (10, 20 and 30 MPa) on bulk density, apparent porosity, flexural strength and modulus. A second statistical design (22) is carried out to verify the effects of SiC and pressure levels on oxygen permeability, compressive strength and modulus. Higher porosity levels (upper than 20%) are obtained by adding 40 wt.% of SiC for all pressures, but also by adding 30 wt.% of SiC and 10 MPa of compaction. In contrast, reduced flexural strength is obtained under these conditions. Cement-based composites reinforced with 30 wt.% SiC at 20 MPa achieve high mechanical performance combined with 15% of porosity and high permeability, being a promising material for aerostatic bearings.