Microstructural changes in particles detected during the transformation from β-FeOOH to α-Fe2O3 in dense aqueous suspensions

The hydrothermal transformation from β-FeOOH to α-Fe2O3 in dense aqueous suspensions, obtained by partial neutralization of concentrated FeCl3 solution with concentrated NaOH solution, was investigated. Mössbauer spectroscopy was used for the phase analysis of samples, as well as the complementary techniques XRD and FT-IR. The size and morphology of the particles were inspected with FE-SEM. At the beginning of the crystallization process very fine β-FeOOH particles were formed, which transformed to α-Fe2O3 (end-product) with a prolonged time of heating. A small amount or traces of α-FeOOH as an intermediate phase were detected by FT-IR and FE-SEM. Gradual formation of α-Fe2O3 double spheres with ring was monitored. Double spheres with ring were formed by the aggregation mechanism. The orientation effect of α-Fe2O3 subunits in double spheres with ring was observed. α-Fe2O3 double spheres with ring also showed two narrow particle size distributions.