Abstract
The formation process of acicular α-FeOOH particles, which was prepared from the colloidal solution of amorphous ferric oxyhydroxide, was investigated with using IR, XRD and TEM measurements. The formation mechanism of crystal particles was considered to be by the dissolution-recrystallization process. The rate constant and activation energy of the process showed strong pH dependence of the mother liquid. The crystallite size of particles also showed pH dependence. The rate constants increased and reached maximum values, after that decreased with increasing pH. The maximum values showed a tendency to shift on the lower pH side with increasing aging temperature. The activation energy decreased and reached minimum values near pH12.5, and increased at higher pH region exceeding 12.5. On the other hand, the crystallite size of (110) of particles decreased with increasing pH. Their pH dependencies might be due to promotion of crystal growth depend on increasing the supersaturation of solute and inhibitory action of its crystal growth depend on singular adsorption of OH- on the side face parallel to c axis of particles.
