Physical and chemical properties of sodium ferrates and equilibrium calculations in HO/CO environments

Huang, J.; Furukawa, Tomohiro  ; Aoto, Kazumi 

Thermodynamic data for most of the Na-Fe oxides with Fe+2 and Fe+3 have been evaluated in previous studies by the present authors; how- ever, crystal structureand thermodynamic data Na4feO11 (or Na2O1.5Fe2O3) have seldom been studied experimentally. To investigate its role in the Na-Fe-O system, sample Na4Fe6O11 was prepared by heating 2Na2CO3+3Fe2O3. The X-ray powder diffraction data of Nqa4Fe6O11 were indexed by a monoclinic system with the cell parameters a = 13.4622, b = 5.3886, c = 9.1317, = 90, = 96.35, = 90.0. By using Knudsen effu-sion mass spectrometry, the temperature dependence of CO2 partial pre-ssure overthe mixture 2Na2CO3+3Fe2O3 was determined as ln{p(CO2)/Pa}=29.4385-29015.4/T(913-1023K). Thermodynamic data of Na4Fe6O11 were then evaluated as, fH (298.15 K) = -3569.543.95 KJ/mol = (-37168392274.55) + (1200.162.35) T/K, fG(298) is recommended as -3255.312.4 KJ/mol. It is further found that Na4fe6O11is thermodynamically stable only at high temperatures over about 1200K