Characterization of akaganeite synthesized in presence of Al3+, Cr3+, and Cu2+ ions and urea

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 77 K 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 results may 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.