engleski

Formation of beta-FeOOH by forced hydrolysis of FeCl3 solutions and thermal decomposition of beta-FeOOH particles

Beta-FeOOH (akaganéite) particles are usually precipitated by slow or forced hydrolysis of FeCl3 solutions. Alpha-Fe2O3 particles can also be formed in dependence on FeCl3 concentration. In the present work we focused on the on the formation of beta-FeOOH by forced hydrolysis of 0.1 or 0.01 M FeCl3 solutions containing different contents of HCl. The presence of alfa-FeOOH, beta-FeOOH and alpha-Fe2O3 phases was observed, whereas exact phase composition depended on the concentration of HCl and time of Fe3+ hydrolysis. Size and shape of the particles were monitored by electron microscopy. beta-FeOOH particles, used in the investigation of their thermal decomposition in air, were prepared by a forced hydrolysis of the 0.1 M FeCl3 + 5x10-3 M HCl solution, whereas sulfated beta-FeOOH particles were prepared by forced hydrolysis of the 0.1 M FeCl3 solution containing 5x10-3 M quinine hydrogen sulfate (QHS). Beta-FeOOH particles, as well as sulfated beta-FeOOH particles, were thermally treated up to 600 oC. The samples were characterized using DTA, XRD, FT-IR and TEM. Beta-FeOOH particles showed a cigar-type morphology, whereas the bundles of beta-FeOOH needles were obtained in the presence of QHS. Heating of beta-FeOOH particles at 300 oC and above yielded alpha-Fe2O3 particles. Specific adsorption of sulfate groups showed a strong effect on the thermal decomposition of beta-FeOOH particles. Upon heating of sulfated particles between 300 and 500 oC the formation of an amorphous phase and a small fraction of alpha-Fe2O3 were observed. Needle-like morphology of amorphous particles in these samples was preserved. At 600 oC, alpha-Fe2O3 particles were obtained ; however, they were much smaller than those obtained by heating a pure beta-FeOOH.

forced hydrolysis; FT-IR; TEM; XRD; alpha-Fe2O3; beta-FeOOH

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