Crystallographic, chemical, and physical properties of akaganeite formed in the presence of Al3+, Cr3+,
and Cu2+ ions and urea when it is obtained by the hydrolysis of FeCl3 solutions were investigated by
different techniques. X-ray diffraction (XRD), RT and 77K Mössbauer spectrometry, Fourier transformed
infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) demonstrate that akaganeite is the
only compound being formed independent of the type and concentration of the metallic cations and urea.
Very small differences in some of the crystallographic, Mössbauer and infrared parameters for samples
obtained in the presence of Cr, Cu, and Al ions at concentrations less than 10 mol%,were observed.However
at 30 mol%, the presence of Al is able to reduce the average grain size of the final products. The presence
of urea does not help to incorporate in an appreciable amount the Al into the akaganeite structure at least
in the concentration ranges studied here. In contrast, they drastically affect the grain size of the products
by reducing them. The present resultsmay suggest that, because the properties of akaganeite are slightly
affected by most alloying elements at low concentrations, this compound when formed as corrosion
product of weathering and carbon steels should exhibit very similar properties to that of akaganeite
obtained synthetically pure. |
