Abstract
α-FeOOH particles have been produced by the aging of amorphous ferric oxyhydroxide colloidal solution. The effects of addition of ions: OH-, Cl-, CO32-, PO43- and Co2+, on the process of formation and morphology of α-FeOOH particles have been clarified.(1) The mechanism of formation of α-FeOOH crystal particles is considered as the dissolution-recrystallization process. The formation reaction of a-FeOOH crystal particles from the amorphous ferric oxyhydroxide can be expressed by a rate equation of the first order reaction.(2) Since OH- and Cl- ions are selectively adsorptive to the side face parallel to c axis of α-FeOOH particles, the crystal growth of the side face is depressed.(3) Since CO32- ion is not selectively adsorptive to the specific crystal plane, but is adsorbed on each plane of the a, b and c crystal planes homogeneously, the crystal growth of those planes is depressed. The recrystallization process of Fe(OH)4- ion is shifted from the surface reaction control to the diffusion control with increasing CO32- and Cl- ion concentrations.(4) The asterisk type particles were produced in the limited narrow region of PO43- ion concentration. An asterisk type particle is heterogeneously junctioned particle of an α-Fe2O3 and several α-FeOOH crystals.
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