The influence of raw material ratio and reaction conditions on in situ synthesis of SiC-ZrC composite powders using graphite as the carbon source

SiC-ZrC composite powders were synthesized in situ in a high-temperature tubular resistance furnace under an Ar gas atmosphere by carbothermic reduction using SiC, ZrO2 and graphite as starting materials. The effects of reaction temperature, Si/Zr ratio, and graphite dosage on the phase composition, mass loss rate and microstructure of the synthesized products were examined. The synthesized powders were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. The results indicate that the increase of the graphite content in the precursor mixture enhances the contact area between ZrO2 and C particles, thereby facilitating the synthesis reaction. When the Si/Zr molar ratio was 7:3 and graphite excess was 10%, SiC-ZrC composite powder with high purity was obtained by holding at 1600°C for 1.5 h. The powder consists mainly of short rod-like particles, quasispherical particles, flaky particles (with an average size of 50-200 nm) and whisker-like substances with a diameter of approximately 50 nm. The SiC and ZrC particles are intact, exhibit good crystallinity and have well-defined grain boundaries.