The appearance of single crystals and agglomerates of gibbsite during precipitation in Bayer liquor has been monitored using scanning electron microscopy. Definite growth features developed during the induction period. This stage was caused by the presence of Ca in the liquor and was practically eliminated in Ca free liquors. Whether the seed was added wet or dry had no effect on the induction period.
Different growth mechanisms appear to operate on different crystal faces. On the basal and prismatic planes, growth proceeds by a continuous, spreading mechanism, whereas on the bevelled edges and on abraded regions, numerous small crystallites develop initially. The growth behaviour has been discussed in terms of the Hartman-Perdok and surface roughness theories.