AN AFM INVESTIGATION OF THE MECHANISM OF SECONDARY NUCLEATION INDUCEDBY CONTACT

Although secondary nucleation is the main source of new crystal nuclei in an industrial crystallizer, the precise source of contact nuclei h as not yet been determined. To address the various theories presented in the literature, we have adopted the dual approach of using microsco py to characterize, at their earliest stages of growth, the secondary nuclei that are produced by contact and also the surface topography of the primary crystals before and after contact. AFM studies of a range of crystals, including isomorphous alums, combined with scanning and transmission electron microscopy experiments indicate that, at least f or the case of very gentle contact, transfer of crystallographic infor mation can occur through an ordered solute layer in a supersaturated s olution without the need for the transfer of solid materials from the primary crystal by microattrition. Knowledge about this mechanism has the potential to improve the quality of product from industrial crysta llizers, through control of crystal morphology and size distribution.