Fe-57 Mossbauer, 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 co mpletely or partially neutralized by addition of concentrated NaOH solution , and then aged at various temperatures and times. The oxide phases were in vestigated using Mossbauer spectroscopy, FT-IR spectroscopy and transmissio n 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 Mossbauer spectrum of this sample at 298 K showed sup erposition of the central quadrupole doublet and a collapsing sextet, while at 80 K a sextet corresponding to alpha-FeO(OH) was recorded. In the highl y 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 p rolonged 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 alkaline medium, nucleation and crystallization of alpha-Fe2O3 occurred inside the a morphous gel, while alpha-FeOOH crystallized by a dissolution/reprecipitati on mechanism. After neutralization of 90% of 1 M Fe(NO3)(3) solution, lemon -shaped alpha-Fe2O3 particles were produced at 398 K between 6 and 24 h. In terpretations of the spectroscopic and electron microscopic measurements ar e given.