engleski

57Fe Moessbauer, FT-IR and TEM observations of oxide phases precipitated from concentrated fe(NO3)3 solutions

Concentrated Fe(NO3)3 solutions (final Fe3+ concentration of 1 M) were completely or partially neutralized by addition of concentrated NaOH solution, and then aged at various temperatures and times. The oxide phases were investigated using Moessbauer spectroscopy, FT-IR spectroscopy and transmission electron microscopy. In a highly alkaline medium, single phase alpha-FeO(OH) was obtained by the aging of Fe(OH)3 suspension at room temperature (RT) for 135 days. The Moessbauer spectrum of this sample at 298 K showed superposition of the central quadrupole doublet and a collapsing sextet, while at 80 K a sextet corresponding to alpha-FeO(OH) was recorded. In the highly alkaline medium, an amorphous material was obtained after heating the Fe(OH)3 suspension at 333 K for 1 day. Spectroscopic investigations provided a certain evidence of the presence of alpha-Fe2O3 in this material. With prolonged time of heating, alpha-FeO(OH) appeared at 333 K and its fraction showed a tendency to increase. It was suggested that, in a highly alklaine medium, nucleation and crystallization of alpha-Fe2O3 occured inside the amorphous gel, while alpha-FeOOH crystallized by a dissolution/reprecipitation mechanism. After neutralization of 90% of 1 M Fe(NO3)3 solution...

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