Thermochemical studies on SrFe12O19(s)

Abstract: The citrate–nitrate gel combustion route was used to prepare SrFe12O19(s) powder sample and the compound was characterized by X-ray diffraction analysis. A solid-state electrochemical cell of the type: (−)Pt, O2(g)/{CaO(s)+CaF2(s)}//CaF2(s)//{SrFe12O19(s)+SrF2(s)+Fe2O3(s)}/O2(g), Pt(+) was used for the measurement of emf as a function of temperature from 984 to 1151K. The standard molar Gibbs energy of formation of SrFe12O19(s) was calculated as a function of temperature from the emf data and is given by: (SrFe12O19, s, T)/kJmol−1 (±1.3)=−5453.5+1.5267×(T/K). Standard molar heat capacity of SrFe12O19(s) was determined in two different temperature ranges 130–325K and 310–820K using a heat flux type differential scanning calorimeter (DSC). A heat capacity anomaly was observed at 732K, which has been attributed to the magnetic order–disorder transition from ferrimagnetic state to paramagnetic state. The standard molar enthalpy of formation, (298.15K) and the standard molar entropy, (298.15K) of SrFe12O19(s) were calculated by second law method and the values are −5545.2kJmol−1 and 633.1JK−1 mol−1, respectively. [Copyright &y& Elsevier]