EXPERT-AL LLC, St. Petersburg, Russia:

E. S. Gorlanov, Deputy CEO, e-mail: gorlanove@yandex.ru

To determine the mechanism and conditions for the increased of product yield of titanium diboride TiB₂ lowtemperature synthesis, a thermodynamic assessment of the interaction in the TiО₂ – B₂О₃ – C system was performed. A numerical method was used to study a series of consequentially-parallel processes for the reduction of titanium oxide to its non-stoichiometric oxycarbide phase and its subsequent interaction with gaseous boron oxides. The Gibbs energy was estimated for oxycarbide TiC_xO_{1 – x} and titanium borate TiBO₃ at 1027 ^oC, which are related as G⁰_{TiCxO1 – x} >> G⁰_TiBO3. This energy ratio of intermediate products of the titanium diboride synthesis allowed to make essential corrections in providing conditions and final results of synthesis. At the first stage of the process, it was established that fluorine-doped titanium oxide TiO_{2 – x}F_x is reduced to oxycarbide TiC_xO_{1 – x} with a deficient carbon content of x < 0.5. At the final stage, exposure of isolated system at a fixed temperature requires moderate kinetic stimulation of TiB2 synthesis by periodic vacuuming. This is due to the need to create conditions for the disproportionation of gaseous boron oxide B₂O_3(gas) to its suboxides (B₂O_2(gas), BO_2(gas)) in the volume of the reaction mixture TiО₂ – B₂О₃ – C and to suppress the “parasitic” reaction of the titanium borate TiBO₃ formation. The established mechanism assumes observance of balance between temperature and duration of phase transformations during the exposure of the system at the first stage, a balance between the increased P_B2O2/P_CO ratio in the gas phase and the temperature at the final stage of the titanium diboride synthesis. The mechanism and conditions for the TiB₂ synthesis are confirmed by laboratory experiments, the implementation of which allows to obtain titanium diboride powders of technical purity at 1030–1050 ^oC.

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