In situ synthesis of B₄C–SiC, B₄C–TiB₂, and B₄C–ZrB₂ composites from organic–inorganic hybrid precursor via a simple bottom-up approach

Boron carbide (B₄C) and its in situ composites were synthesized via a simple bottom-up process using low-cost boric acid and a sucrose-based precursor solution with silicon (Si), titanium (Ti), or zirconium (Zr) species. The precursor solution was first dried at 250 °C and then heat-treated at 1650 °C for 90 min under argon and hydrogen gas flow. Free boron oxide phases appeared in the boric acid-rich precursor compositions, whereas free carbon appeared in the sucrose-rich compositions. The B₄C particles exhibited a coarser and elongated morphology with boron-rich stoichiometric compositions (B/C:4/1), whereas the particles had a finer equiaxed morphology in carbon-rich compositions (B/C:2/1). As the carbon concentration increased in the precursor solution, the hexagonal lattice parameters of B₄C and its corresponding lattice volume decreased. On the other hand, the addition of Si, Ti, or Zr species into the precursor solution resulted in the formation of a silicon carbide (SiC), a titanium diboride (TiB₂), or a zirconium diboride (ZrB₂) phase along with the B₄C phase and was associated with an overall reduction in the average particle size and a more uniform size distribution. Moreover, the addition of these species increased the B₄C lattice parameter with a corresponding increase in the lattice volume; this was most likely due to an elemental substitution into the B₄C lattice. In addition, the data provide evidence that the formation of an ideal B₄C lattice is possible when synthesized from carbon-rich precursors using this method, despite the potential presence of free carbon. [Figure not available: see fulltext.].