High-efficiency aerosol filters based on silicon carbide foams coated with ceramic nanowires

This work describes the evaluation of the performance of ceramic foams coated with nanowires as high-efficiency aerosol filters. A process of catalyst-assisted pyrolysis was employed to grow Si2N2O nanowires in situ on the cell walls of commercial α-SiC foams. The resulting bodies presented a hierarchical reticulated structure comprised of large cells (0.5-5 mm) with struts coated with a layer (8-207 μm thick) of nanowires of 200-400 nm in diameter. Permeability to air flow and particle collection efficiency of coated foams were experimentally assessed and compared with those of filter groups defined by the European standards EN 779:2002 and EN 1822:2009. Coated foams were more permeable than filters from the Coarse and Fine groups, but possessed a collection efficiency for NaCl nanoparticles typical of filter groups EPA (E12) and HEPA (H13). The progressive stacking of samples to increase filter thickness promoted a linear increase in pressure drop, but with an exponential improvement in collection efficiency by the diffusion and interception mechanisms. The integrity of nanowires was maintained after exposure to air flow at 679 °C. These features indicate the applicability of ceramic foams coated with nanowires as aerosol filters with enhanced performance to operate under aggressive airflow conditions, in which conventional glass fiber media are not recommended.