Thermodynamic characterization of Fe2TeO6

The standard Gibbs energy of formation of iron tellurate, Fe2TeO6 (s), was determined by measuring the vapour pressure of TeO2 (g) over the phase mixture Fe2TeO6 (s) + Fe2O3 (s) in the temperature range of 1103-1203 K by employing a thermogravimetry-based transpiration technique. The temperature dependence of the vapour pressure of TeO2 (g) generated by the incongruent vapourization reaction obtained from this study could be represented as log (p (TeO2 (g)/Pa +/- A 0.03) = 17.53-19,836/T (1103-1203 K). The temperature dependence of the Gibbs energy of formation of Fe2TeO6(s) derived from the above expression could be represented as {Delta G (f) (o) (Fe2TeO6, (s)) (kJ mol(-1)) +/- A 6.0} = -1276.3 + 0.507 T (1103-1203 K). An inverse drop calorimeter was used for measuring the enthalpy increments of Fe2TeO6 (s) for the first time in the temperature range of 483-1083 K. The thermodynamic functions, viz. heat capacity, entropy and Gibbs energy functions of Fe2TeO6 (s), were derived from the experimentally measured enthalpy increment values. A mean value of -1318.1 +/- A 0.9 kJ mol(-1) was obtained for by third-law analysis of vapour pressure data.