Formation of uniform spherical magnetite particles by crystallization from ferrous hydroxide gels

The formation of iron (hydrous) oxides by aging ferrous hydroxide gels at elevated temperatures was studied as a function of various parameters. It was found that the composition and the morphology of the resulting solids depended strongly on the nature of the anions present in the system. Spherical magnetite particles of narrow size distribution, with mean diameters ranging between 0.03 and 1.1 μm, were obtained if FeSO4 was interacted with KOH in the presence of nitrate ion and the resulting gelatinous suspension was kept at 90°C for several hours. The particle size distribution of the magnetite sol was affected by the excess concentration of Fe(II) species in equilibrium with the ferrous hydroxide precipitate. If oxygen was present in addition to nitrate ion, rodlike α-FeOOH particles crystallized along with the magnetite on aging of some ferrous hydroxide gels. A mechanism of the magnetite formation under the conditions of these experiments is offered.