Synthesis and sintering of ZrB₂-SiC based composites have been carried out in a single-step pressureless reaction sintering (PLRS) of ZrO₂, B₄C, and Si. Y₂O₃ and Al₂O₃ were used as sintering additives. The effect of ratios of ZrO₂/B₄C, ZrO₂/Si, and sintering additives (Y₂O₃ and Al₂O₃), was studied by sintering at different temperatures between 1500 and 1680 ℃ in argon atmosphere. ZrB₂, SiC, and YAG phases were identified in the sintered compacts. Density as high as 4.2 g/cm³, micro hardness of 12.7 GPa, and flexural strength of 117.6 MPa were obtained for PLRS composites. Filler material was also prepared by PLRS for tungsten inert gas (TIG) welding of the ZrB₂-SiC based composites. The shear strength of the weld was 63.5 MPa. The PLRS ZrB₂-SiC composites exhibited: (i) resistance to oxidation and thermal shock upon exposure to plasma flame at 2700 ℃ for 600 s, (ii) thermal protection for Cf-SiC composites upon exposure to oxy-propane flame at 2300 ℃ for 600 s.

ZrB₂ and ZrB₂-SiC powders have been produced by reducing ZrO₂ and ZrSiO₄ with B₄C without using any furnace. Magnesium was added to the mixtures of (ZrO₂+B₄C) and (ZrSiO₄+B₄C). The reaction has been assisted by a floral thermite packed around the compacts. By introducing elemental Si into (ZrO₂+B₄C) mixture, composite powders of ZrB₂-SiC formed. After leaching out MgO with suitable HCl water solution, the product was analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect of Si, B₄C, and Mg on the extent of formation of ZrB₂, ZrB₂-SiC, and other phases has been studied. Formation of nano-sized ZrB₂ and ZrB₂-SiC composite powders was identified. The adaptability of the process for bulk production was examined.