A study of surface-coated SiC whiskers on carbon fiber substrates and their properties for diesel particulate filter applications

β-Silicon carbide (β-SiC) whiskers were synthesized on carbon fiber substrates using a chemical vapor infiltration (CVI) vapor-solid (VS) growth mechanism. An additional SiC surface coating process was utilized after whisker deposition by controlling the input gas ratio of the source gas flow and changing the H₂ (hydrogen) diluent gas to N₂ (nitrogen) under the same deposition temperature of 1,300 °C. As the surface coating deposition time increased, whiskers thickness and spherical blunt tips which were seen at the top edge of the whiskers went thicker. Observing the microstructure of the resulting tips by transmission electron microscopy (TEM) revealed that uncoated whiskers showed few stacking faults, whereas surface-coated whiskers were completely filled with stacking faults. The effect of surface coating deposition time was also evaluated by measuring the properties of a filtration system. Specifically, as the surface coating deposition time increased, gas permeability decreased; however, even at 30 min, the gas permeability of the thickest surface coated whisker filters was five times higher than that of cordierite honeycomb, which is currently used in commercial diesel particulate filter (DPF) devices. A specimen that had been surface coated for more than 20 min almost completely maintained its prime line density under high-pressure (5 MPa) gas. Moreover, we confirmed that SiC surface coating on whiskers and carbon fiber substrates enhanced oxidation resistance and filtration efficiency.