FORMATION OF COLLOIDAL DISPERSIONS FROM SUPERSATURATED IRON(III) NITRATE SOLUTIONS .5. SYNTHESIS OF MONODISPERSE GOETHITE SOLS

Based on our knowledge of nucleation, growth and aging processes in supersaturated acid iron(III) solutions, methods are presented for the preparation of sols of monodisperse colloidal goethite particles having a well-defined crystal habit. One method involves controlled dialysis of dispersions of primary particles (amorphous iron hydroxide). This procedure yields monodisperse and stable sols provided the growth of the secondary particles (goethite) has not yet begun in the partially neutralized iron(III) solutions at the instant of dialysis. In another method, seeds of goethite crystals are added to supersaturated iron-bearing solutions. These experiments confirm an earlier observation that goethite grows in the left bracket 001 right bracket direction by incorporation of low-moleculer-weight species from solution.