The mechanism of β-Fe2O3 formation by solid-state reaction between NaCl and Fe2(SO4)3

Mossbauer spectroscopy, x-ray powder diffraction, thermal analysis and elemental analysis were used for the study of the mechanism of reaction between NaCl and Fe-2(SO4)(3) in the oxidizing atmosphere (air). It was found that the reaction starts at 400 degrees C in isothermal conditions and is accompanied by the liberation of Cl-2. The initial reaction proceeds in the molar ratio of NaCl:Fe-2(SO4)(3)=3:1. beta-Fe2O3, NaFe(SO4)(2), Na3Fe(SO4)(3) and Na(2)So(4) were identified as solid products of the initial reaction. At the second stage both the double sulfates were transformed into beta-Fe2O3 and Na2SO4, the gaseous SO3 was liberated simultaneously. Thermally less stable NaFe(SO4)(2) decomposes before Na3Fe(SO4)(3). The hexagonal alpha-Fe2O3 is formed in this process only as the product of the structural transformation of beta-Fe2O3. This beta-alpha transformation accompanies both the initial reaction and the secondary conversions of the intermediates. The Mossbauer parameters of the reaction products are enlisted.