Abstract
The relationship between rate constant, activation energy and growth rate of crystallite for formation of acicular α-FeOOH particles, and FeCl3 concentration of colloidal mother liquid was discussed. Both rate constant and growth rate of crystallite decreased with increasing FeCl3 concentration at aging above 80°C. At below 55°C it did not almost show the concentration dependence. The activation energy monotonically decreased, and decreased rapidly for the case in which FeCl3 concentration is less than 0.1kmol/m3. The observed dependenCles on FeCl3 concentration can be explained in the following manner: crystal growth of side face parallel to c axis of acicular particles is restrained by singular adsorption of Cl-on the side face. It is considered that activation energy decreases with increasing FeCl3 concentration, because recrystallization process of Fe(OH)4- changes from the surface reaction controlled process to the diffusion controlled process. The crystallite size of acicular α-FeOOH. particles increased steeply with increasing FeCl3 concentration at aging above 80°C. At below 55°C it increased slightly. The particle size grew larger maintainning acicular shape with increasing FeCl3 concentration. The length of major axis and aspect ratio of acicular particles increased especially. It is considered that increasing their size is due to growth of crystallite by coalescence of each nuclei.
