Microstructure and mechanical properties of porous SiC ceramics by carbothermal reduction and subsequent recrystallization sintering
Jianfei Zhang, Xiaonan Zhou, Qiang Zhi, Shan Zhao, Xin Huang, Nanlong Zhang, Bo Wang, Jianfeng Yang, Kōzō Ishizaki
Abstract
Porous SiC ceramics were prepared by a new approach combination of carbothermal reduction and subsequent recrystallization sintering. Firstly, micro-sized SiC particles were used as the skeleton, and SiC spherical nanocrystals were in-situ synthesized by the vapor-solid reaction between carbon nanoparticles and silicon monoxide vapor. The shape and diameter of SiC nanocrystals are related to the pristine carbon nanoparticles, showing a shape memory effect. After recrystallization sintering, high purity α-SiC porous ceramics with tailored necking area were obtained by the evaporation-condensation of SiC nanocrystals. A linear relation was revealed between the flexural strength and the value of d/d0 of porous recrystallized SiC (RSiC) ceramics (the neck diameter to coarse micron-sized grains diameter ratio). The necking area and d/d0 value increased with the SiC nanocrystals content, due to the higher saturated vapor pressure resulted in high mass mobility to neck area of SiC nanoparticles. As a result, a remarkable value of d/d0 ~ 99% and outstanding flexural strength of 75.7 MPa could be achieved for the porous RSiC ceramics with ~42% porosity by adding 20 wt.% nano-sized SiC sintered at 1950°C for 2 h.