Gas-phase combustion synthesis of titanium boride (TiB₂) nanocrystallites

Two techniques are described for synthesizing nanometer-sized TiB₂particles by gas-phase combustion reactions of sodium vapor with TiCl₄and BCl₃: a low-pressure, low-temperature burner and a high-temperature flow reactor. Both methods produce TiB₂particles that are less than 15 nm in diameter. The combustion by-product, NaCl, is efficiently removed from the TiB₂by water washing or vacuum sublimation. Material collected from the low-temperature burner and annealed at 1000 °C consists of loosely agglomerated particles 20 to 100 nm in size. Washed material from the high-temperature flow reactor consists of necked agglomerates of 3 to 15 nm particles. A thermodynamic analysis of the Ti/B/Cl/Na system indicates that near 100% yields of TiB₂are possible with appropriate reactant concentrations, pressures, and temperatures.