Growth modification of hematite by phosphonate additives

Abstract

The hydroxylated surface structures of seven morphologically important crystallographic surfaces of hematite have been calculated ? allowing the determination of the surface energies and consequently the hematite equilibrium morphology. The docking of two organic phosphonate additives (methyl nitrilo dimethylenephosphonic acid ? MNDP, ethylenediamine tetraphosphonic acid ? EDTP) was then simulated on these surfaces and the replacement energies calculated. With these energies, the effect of MNDP and EDTP on the hematite equilibrium morphology can then be predicted. Results without the additive show a bipyramidal morphology of faces capped with faces at each end. The interaction with the EDTP additive predicts the stabilization of the face to be far more pronounced than for the MNDP additive. This leads to the appearance of faces in the morphology predicted in presence of EDTP. Experimental validation by means of electron microscopy shows morphologies close to those calculated, confirming that a computational approach can thus be used for the prediction of morphologies of crystals grown in the presence of additives.