Effect of starting Si contents on the properties and structure of biomorphic SiC ceramics

Biomorphic SiC ceramics were prepared by infiltrating liquid Si into biocarbon templates derived from beech at 1550 °C for 1.5 h with different starting Si/C ratios. Microstructure observation and phase identification of the biocarbon templates and the resulting products were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Open porosity and density of the resulting products were measured by the Archimedes method. The bending strength and fracture toughness were tested by the three-point bending method and the single edge notched beam (SENB) method, respectively. The conversion degrees from biocarbon templates to biomorphic SiC ceramics were also discussed. Experimental results showed that, with increasing starting Si contents, the resulting products were biomorphic C/SiC, SiC and SiC/Si, the porosity decreased, and bending strength and fracture toughness increased. The key factors affecting properties of the resulting products were conversion degree and the amount of the residual silicon. The bending strength and toughness fracture of the axial samples were much higher than those of the radial samples because of loading direction and anisotropic pore orientation derived from microstructures of original wood.