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Sintered reaction-bonded Si3N4 ceramics with equiaxed microstructure were prepared with TiO2–Y2O3–Al2O3 additions by rapid nitridation at 1400°C for 2 hours and subsequent post-sintering at 1850°C for 2 hours under N2 pressure of 3 MPa. It was found that α–Si3N4, β–Si3N4, Si2N2O, and TiN phases were formed by rapid nitridation of Si powders with single TiO2 additives. However, the combination of TiO2 and Y2O3–Al2O3 additives led to the formation of 100% β–Si3N4 phase from the nitridation of Si powders at such low temperature (1400°C), and the removal of Si2N2O phase. As a result, dense β–Si3N4 ceramics with equiaxed microstructure were obtained after post-sintering at high temperature.

Flexible synthesis of ultra-fine ZrB2 powders was achieved by borothermal reduction in a mixture of ZrO2, boron, and TiO2. Without TiO2 additive, coarse ZrB2 powders with particle size of 0.81 μm were obtained, presumably due to good wettability and solubility of ZrB2 in the byproduct B2O3. It was found that the particle growth of ZrB2 was effectively inhibited by the solid solution of TiB2 (≥1 mol%). The refinement mechanism was that the solid solution of in situ formed TiB2 presumably lowered the wettability and solubility of ZrB2 in the B2O3 liquid and significantly inhibited the coarsening of ZrB2. The average particle size of resulting powders decreased to 0.37 μm with the addition of 10 mol% TiO2.