Abstract:
In-situ optical microscopy was used to measure the growth rate of gibbsite single crystals growing from aqueous sodium aluminate solutions. The growth rate was measured for various crystal faces, i.e., {100} and {001} faces in case of twinned hexagons and {110} faces for single crystalline lozenges. A considerable dispersion in crystal growth rate was measured: the growth rates varied from crystal to crystal within the same experiment as well as from experiment to experiment. They also fluctuated in time. The origin of this dispersion in growth rates is discussed. The results of the growth rates measured as a function of the driving force, which were averaged over several crystals, were fitted with growth rate equations for various growth mechanisms. It is shown that the birth and spread-type growth rate equation defined by Nielsen (J. Cryst. Growth 1984, 67, 289-310) as well as an equation derived in this paper for step nucleation growth at the intersection line of contacting crystallites can be used to describe the growth rates of gibbsite in all crystallographic directions.