engleski

Microstructural properties of Fe-oxide powders obtained by precipitation from FeCl3 solutions

The precipitation of Fe-oxides was performed by adding NaOH or urotropin to FeCl3 solutions and aging the precipitation systems at 90oC. Phase composition and microstructural properties of Fe- oxide powders were investigated using Fourier transform infrared spectroscopy, Mössbauer spectroscopy, X-ray diffraction and transmission electron microscopy. b-FeOOH was obtained in all precipitation systems with final pH values up to 1.80. However, when the precipitation was for a long time at pH Ł 1.80 the appearance of a-Fe2O3 phase was also observed. In the presence of urotropin the size of submicrometer b-FeOOH rods increased with time of aging thus forming a fibril structure of near micrometer size. The crystallite size of b-FeOOH varied between 7 and 11 nm and this indicated that b-FeOOH fibrils possessed a substructure. After 30 days of aging, the presence of a a-Fe2O3 phase was also detected by XRD. a- Fe2O3 was obtained as a single phase by precipitation with NaOH at pH 4.20 and 4.40 and aging of the precipitation systems up to 3 days. When the pH of precipitation was increased to 6.00 and 6.50 the formation of a-FeOOH particles, in addition to a-Fe2O3, was observed. TEM showed that the size and morphology of particles strongly depended on the precipitation conditions. The mechanism of the formation of Fe-oxide phases is discussed.

akaganeite ; Ft-ir ; goethite ; hematite ; mossbauer ; tem ; urotropin ; Xrd

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