GROWTH-RATE ENHANCEMENT BY MICROCRYSTALS AND THE QUALITY OF RESULTINGPOTASH ALUM CRYSTALS

Growth rate enhancement resulting from the addition of ground powder c rystals to a growing larger crystal has been examined for the potash a lum-water system. The crystal quality of the large crystal after the a ddition and subsequent growth rate enhancement was evaluated in terms of the formation of inclusions and dislocations. Inclusions were obser ved with an optical microscope and the dislocations were analysed usin g X-ray transmission topography. It was found that the development of inclusions occurs at the time of the addition to the solution of the g round powder crystals and their attachment to the growing crystal surf ace. Simultaneously, dislocation bundles were generated. It is propose d that the inclusions form as the growing crystal surface envelopes th e adhering particles and that the dislocations form both as a conseque nce of the strain that develops and the lattice mismatch required to r efacet the surface. Both result in the development of additional growt h centres which cause the growth rate enhancement. (C) 1998 Elsevier S cience B.V. All rights reserved.