Thermodynamic Prediction and Synthesis of a Titanium Diboride Powder by Reduction of Titanium Dioxide with Boron Carbide in Argon Atmosphere

An extreme case reaction, the formation of fine titanium diboride (TiB2) powder by the reduction of titanium oxide (TiO2) with boron carbide (B4C) (molar ratio of B4C/TiO2 = 0.714 without carbon black (C)) in the Argon atmosphere, was confirmed through both thermodynamical calculation and experimental results. Because the intermediate product boron-oxide (B2O3) produced in the extreme case reaction and those of general boro/carbothermal reaction (i.e., molar ratio B4C/TiO2 = 0.5 with 1.5 molar of C) and intermediate reaction (molar ratio of B4C/TiO2 = 0.833 without C) was volatile, excess boron (B) should be added, as in the extreme case reaction, to compensate for the B loss in order to prepare high-purity TiB2 powder. The experimental results and the reaction mechanism indicate that the formation of TiB2 powder occurs in the following steps: Firstly, the TiO2 reduced to titanium carbide (TiC), titanium borate (TiBO3), B2O3, C and TiB2. Secondly, the by-product C and B2O3 reacted together to form B4C at temperature as high as 1562 °C. Finally, the by-product TiC, TiBO3 and B4C reacted together to complete the TiB2 formation reaction. The sole suitable situation for obtaining purified fine TiB2 powder was the extreme case reaction. Experiments indicated that the optimum synthesis temperature and firing time for the extreme case reaction were about 1580 °C and 1 h, respectively. The morphology of the TiB2 powder that was synthesized resembled a hexagonal shape.