Hydrothermal synthesis of β-FeO(OH) rod-like particles with uniform size distribution

β-FeO(OH) particles were prepared by a two-step hydrothermal precipitation. First, the hydrolysis of 0.25 mol dm−3 FeCl3 acidic solution at 90°C produced β-FeO(OH) fine seed crystallites. Next, an appropriate amount of urea was added to the β-FeO(OH) acidic suspension, then heated to the pre-determined temperature for further hydrolytic precipitation. The effects of the [(NH2)2CO]/[Fe3+] molar ratio and the hydrothermal temperature on both the precipitation rate and the particle size were studied. The precipitation rate increased with the [(NH2)2CO]/[Fe3+] molar ratio and with the hydrothermal temperature, and a simple model for the hydrolysis reaction was supposed on these experimental results. The particle size of β-FeO(OH) precipitates was almost independent of both the molar ratio and the hydrothermal temperature, and their particle size distribution was relatively narrow. It was thought to be attributed to the separation between the nucleation and the particle growth via the two-step hydrolysis reaction. In addition, it was found that the remaining chloride amount in the obtained β-FeO(OH) precipitates were remarkably low.