PARTIAL HYDROLYSIS OF FERRIC NITRATE SALT - STRUCTURAL INVESTIGATION BY DYNAMIC LIGHT-SCATTERING AND SMALL-ANGLE X-RAY-SCATTERING

The structure of fresh sols of partially hydrolyzed ferric nitrate salt were investigated by dynamic light scattering and small-angle X-ray scattering. The size of the colloids formed vs the hydrolysis ratio n = (NaOH)/(Fe) varied with the age of the solutions. Just after the end of the mixing of NaOH with Fe-(NO3)3.9H2O (t < 10 min) the size distribution is bimodal in n = 2, n = 2.2, and n = 2.5 with size particles in the range 40-500 nm. At t > 10 min, the size distribution is monomodal without further evolution with time. The sizes are close to 10-20 nm. Small-angle X-ray scattering curves yield two results: (1) the colloids are linear at the semilocal range order when n = 1.5 or 2.0, but with n = 2.2 or 2.5, they are semilinear or with a structure of fractal aggregates formed by small subunits; (2) the size of the subunits varies from 7 angstrom (n = 1.5) up to 13.5 angstrom (n = 2.5). This size variation with n is contrary to observations when using ferric chloride salts. NO3- ions are rapidly exchanged for OH- or O- ligands in a homogeneous nucleation process.