Synthesis of nanocrystalline TiB2 powder from TiO2, B2O3 and Mg reactants through microwave-assisted self-propagating high-temperature synthesis method

Abstract

In this research work, microwave-assisted self-propagating high-temperature synthesis (SHS) process was employed for the fabrication of titanium diboride (TiB2) compound from TiO2-B2O3-Mg mixtures. Thermodynamic evaluations of this system and its relevant subsystems revealed that TiB2-MgO composite powder can be easily produced by a SHS reaction. However, experimental results of a TiO2: B2O3: 5Mg mixture heated in a domestic oven showed the formation of some intermediate compounds such as Mg3B2O6, presumably due to some degree of Mg loss. The optimum amount of Mg in TiO2: B2O3: xMg mixtures, yielding the highest amount of TiB2 phase, was found to be around 7 mol, i.e., 40 mol% more than the stoichiometric amount. Experimental results revealed that a pure TiB2 compound could be obtained by leaching the unwanted by-products in an HCl acid solution. Scanning electron microscopic observations and Scherrer calculations showed that the produced TiB2 contains sub-micron (150-200 nm) particles, where each particle consists of a number of nanosized (32 nm) crystallites.