In situ optical microscopy and ex situ atomic force microscopy have been used to investigate the kinetics and surface evolution during the growth of single crystals of gibbsite at 80ºC as a function of supersaturation. The results of in situ optical microscopy reveal that growth on the basal face follows a spiral growth mechanism up to a relative supersaturation of 0.81 (0.65 A/C). Above that level, the growth of the basal face was found to follow the birth and spread mechanism. The edge free energy, calculated for a polynuclear birth and spread mechanism, is 6.0 ± 1.5 kJ/mole.
Similar studies have been carried out in a series of ex situ experiments in which the same crystal area was repeatedly located and imaged after immersion in synthetic liquor, using atomic force microscopy (AFM). The results of these experiments are in agreement with those of the optical microscopy, and show that growth on the basal face at a low relative supersaturation of 0.43 (0.50 A/C) occurs by a step flow mechanism, while growth was found to occur by continuous birth and spread mechanism at a higher supersaturation of 1.0 (0.70 A/C). Growth by continuous birth and spread mechanism and step flow were both observed to occur simultaneously on the basal face of different seed crystals at a relative supersaturation of 0.71 (0.60 A/C).