GROWTH-RATE DISPERSION OF SINGLE POTASSIUM ALUM CRYSTALS

The dispersion of growth rates is a lively discussed matter. However, still no acceptable explanation exists for the reason of the phenomenon describing that crystals of the same size growing under the same constant environmental conditions (as supersaturation, temperature and hydrodynamics) might grow with different rates. The individual face-specific growth rates of potassium aluminium alum crystals (diameter 1-3 mm) have been directly determined at different supersaturations (sigma = 0.5-5%). It was found that the order of growth rates of the appearing faces of unhurt and hurt crystals is {111} < {100} < {110}. Further experiments have shown that face-specific growth rates of unhurt crystals (out of evaporation crystallization) are lower than those of hurt crystals (out of batch crystallization experiments).