The effects of additives of sodium phosphate, potassium phosphate, citric acid, tartaric acid, sodium hydrogen carbonate, oxalic acid, and acetic acid, when monodispersed hematite particles were prepared by forced hydrolysis from aqueous ferric solutions, were determined by measuring the size and shape of the particles by transmission electron microscope and scanning electron microscope.
The basic shapes of particles prepared from 0.02M of ferric chloride, after two days incubation at $100\circ{C}$ were spherical and rounded-cubic, but the effects of additives and their concentrations on the shapes, sizes, compositions were significant. Among the additives used, sodium phosphate, potassium phosphate, citric acid and tartaric acid had induced the change of particles, but retarded the growth of hematite as their concentrations were increased. Cubic-like particles were obtained at $1\times 10^{-4}$M solution fo tartaric acid.
Oxalic acid and sodium hydrogen carbonate changed the shape of particles to be spherical but did not delay the growth of hematite, while acetic acid increased the polydispersity in size though its growth was not retarded. In comparison with chloride and nitrate solutions, the variation of the morphology of particles in chloride solutions may be due to the adsorption of the additives in the stage of phase transformation of β-FeOOH → α-$Fe_2O_3$.
