PREPARATION AND CHARACTERIZATION OF COLLOIDAL ALPHA-FEOOH WITH A NARROW SIZE DISTRIBUTION

Crystals of alpha-FeOOH with a narrow size distribution and maximum dimensions < 0.1-mu-m have been prepared by a two-step process. In the first stage, amorphous iron(III) hydroxide was converted to a crystalline, Fe(II)Fe(III) intermediate by interaction with a reducing organic ligand, L-cysteine. This intermediate phase was then oxidized to alpha-FeOOH. The initial crystals of alpha-FeOOH were poorly ordered. They transformed to a fully crystalline material by a dissolution/reprecipitation mechanism. The crystal morphology depended on the cysteine: Fe ratio, on the type of buffering agent used and on the presence of foreign cations in the system. alpha-FeOOH containing a few percent of Mn or Zn in the crystal structure could also be prepared by this method. Both the alpha-FeOOH and the crystalline intermediate phase were characterized using various techniques. alpha-FeOOH with a narrow size distribution has wide application as a model system for fundamental and technological studies.