Morphology Prediction of Gibbsite Crystals − An Explanation for the Lozenge-shaped Growth Morphology

Abstract

The morphology of gibbsite, γ-Al(OH)3, crystals is predicted on the basis of a complete connected net analysis. It turns out that the morphology cannot be explained on the basis of the attachment energy. Instead, it is shown by a Monte Carlo algorithm based on a 2D nucleation model, that the edge (free) energy of the flat faces is the relevant parameter that determines the growth morphology. The algorithm reveals that the morphological importance of the faces follows the sequence: {112}, {112̄} ≈ {101}, {101̄} < {200} < {110} ≪ {002}. At zero driving force, gibbsite has a hexagonal morphology with {002} basal faces, {200} and {110} side and {101}, {101̄}, {112} and {112̄} chamfered faces. At higher driving forces, the chamfered faces disappear first, followed by the {200} faces. This corresponds well to our experimental results and is explained in terms of the energies involved in the formation of 2D nuclei at the various surfaces. Thus, the various morphologies observed for gibbsite crystals depending on the driving force for crystallization can be explained.