Phase and microstructure evolution of carbon black-derived SiC-$ \mathrm{ZrB_2} $ powders: Effects of Si/Zr ratio and calcination temperature

SiC- \mathrm{ZrB_2} composites are promising for aerospace and high-temperature industries, yet conventional mechanical mixing leads to uneven powder distribution and severe agglomeration. This work prepares uniform composite powders via carbothermal reduction to overcome these drawbacks. Silica sol, zirconia, boric acid and carbon black were used as raw materials, and synthesis was carried out at 1400~1650°C under Ar for 1 h. The influences of calcination temperature and Si/Zr molar ratio on phase composition, mass loss rate and microstructure were systematically investigated. The two factors strongly regulate phase transformation, grain size and particle morphology. Near full reaction is achieved at 1550°C. At Si/Zr=7:3, ultrafine powders (50~200 nm) with spherical, short rod, columnar and whisker shapes are obtained, featuring high SiC/ \mathrm{ZrB_2} crystallinity, homogeneous element distribution and negligible agglomeration. SiC grows via combined VS and VLS mechanisms, where liquid B2O3 catalyzes whisker formation. Directional growth of ZrB2 in B2O3 liquid yields rod-like and columnar grains.