Determination of the thermodynamic stability of TiB2

The standard free energy of formation of titanium boride (TiB2) was measured by the Electro Motive Force (EMF) method (by using yttria doped thoria (YDT) as the solid electrolyte). Two galvanic cells viz. Cell (I): Pt, TiB2 (s), TiO2 (s), B (s) |YDT| NiO (s), Ni (s), Pt and cell (II): Pt, TiB2 (s), TiO2 (s), B (s) |YDT| FeO (s), Fe (s), Pt were constructed in order to determine the ΔfGo of TiB2. Enthalpy increments on TiB2 were measured by using inverse drop calorimetry over the temperature range 583-1769 K. The heat capacity, entropy and the free energy function have been derived from these experimental data in the temperature range 298-1800 K. The mean value of the standard enthalpy of formation of TiB2 (ΔfH2980 ) was obtained by combining these ΔfGo values and the free energy functions of TiB2 derived from the drop calorimetry data. The mean values of ΔfH2980 derived from the ΔfGo data obtained from cell I and II were -322 ± 1.2 kJ mol-1 and -323.3 ± 2.1 kJ mol-1, respectively. These values were found to be in very good agreement with the assessed data.