THE MECHANISM OF β-Fe_2O_3 FORMATION BY SOLID-STATE REACTION BETWEEN NaCl AND Fe_2(SO_4)_3

摘要

Moessbauer 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(SO_4)_3 in the oxidizing atmosphere (air). It was found that the reaction starts at 400°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(SO_4)_3=3:1. β-Fe_2O_3, NaFe(SO_4)_2, Na_3Fe(SO_4)_3 and Na_2SO_4 were identified as solid products of the initial reaction. At the second stage both the double sulfates were transformed into β-Fe_2O_3 and Na_2SO_4, the gaseous SO_3 was liberated simultaneously. Thermally less stable NaFe(SO_4)_2 decomposes before Na_3Fe(SO_4)_3. The hexagonal α-Fe_2O_3 is formed in this process only as the product of the structural transformation of β-Fe_2O_3. 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.