Carbonization of Wood-Silica Composites and Formation of Silicon Carbide in the Cell Wall

Wood-mineral composites (WMCs) impregnated with silica (SiO2) were carbonized at high temperature to form silicon carbide (SiC) directly using carbon from the wood with the impregnated silica. Carbonized composites were investigated using X-ray diffraction and EPMA (electron probe X-ray microanalysis). Water-saturated sapwood specimens of sugi, Japanese cedar (Cryptomeria japonica), were diffuse-penetrated with a colloidal silica solution or a water glass solution followed by drying to fix silica gel for preparing wood-SiO2 composites. The composites were burned at 600°C, 1000°C, and 1300°C for 30-120 minutes in a furnace in nitrogen gas. X-ray diffraction showed that the peak of SiO2 was recognized at 20 = 22°, and the peak became greater with an increase in burning temperature. The peak at 1300°C became very sharp, revealing the change of crystalline structure of SiO2 (cristobalite). In addition, the occurrence of the peak around 20 = 35° at 1300°C appeared, which confirmed the formation of silicon carbide (β-SiC) in the carbonized composites. EPMA observation showed the distribution of silicon in the cell walls that were carbonized at 1300°C. In conclusion, we showed that SiC was produced in the cell walls and the crystalline structure-changed SiO2 (cristobalite) existed in the cell lumina