Growth modification of hematite by phosphonate additives

The hydroxylated surface structures of seven morphologically important crystallographic surfaces of hematite were 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 could be predicted. Results without the additive show a bipyramidal morphology of (1 0 2) faces capped with (2 2 2) faces at each end. The interaction with the EDTP additive predicts the stabilization of the (1 0 (1) over bar) face to be far more pronounced than for the MNDP additive. This leads to the appearance of (1 0 (1) over bar) 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 be used for the prediction of morphologies of crystals grown in the presence of additives. (C) 2007 Elsevier B.V. All rights reserved.