Ignition and chemical mechanisms of volume combustion synthesis of titanium diboride

Reaction ignition and chemical mechanisms in volume combustion synthesis of TiB2 via TiO2–B2O3–Mg precursors were studied using in-situ differential thermal analysis, X-ray diffraction, scanning electron microscopy and thermochemical modeling. Mg–TiO2 samples ignited at 607 °C through a sudden single step solid-solid reaction while Mg–B2O3 samples ignited at 810 °C after melting of magnesium. X-ray diffraction analysis revealed that reduction of TiO2 occurs in multiple steps and forms intermediate compounds. Results showed that heat released from the first reaction between TiO2 and Mg ignites the reactions between Mg, Ti and B2O3 resulting in the formation of TiB2. Samples with larger TiO2 particle size or a higher sample surface to volume ratio showed a two-step reaction behavior and the released heat in the first solid state reaction was insufficient for the propagation of the reaction throughout the sample. In addition, Mg3B2O6 undesired by-product was formed as a result of this two-step reaction.