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

Abstract

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 degrees C and then heat-treated at 1650 degrees 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.