THE DISPERSION OF GROWTH-RATE AS A RESULT OF DIFFERENT CRYSTAL PERFECTION

The aim of the cooperative work of the above mentioned institutes was to find out the reason for growth rate dispersion (GRD). Measurements of growth rate (overall or face-specific), microhardness (HV), etch pi t density (EPD) and crystal perfection (X-ray topography and Laue X-ra y method) were carried out using KAI(SO4)(2) . 12H(2)O (PA) and KNO3 ( PN) crystals. The investigated crystals were grown under different con ditions and treated in different ways. It is possible to influence the growth rate by well-directed alternations of supersaturation (sigma 1 , sigma 2, sigma 1), strain, mechanical stress, annealing and surface roughening. Depending on observation time, the constant crystal growth model (CCG model)(a few hours) as well as the random fluctuation mode l (RF model; a few days up to a month) describe the growth behaviour o f PA. The growth of PN can only be described by the RF model. At const ant supersaturation, the average growth rate of small particles in the subsieve size range (up to 60 mu m) is considerably smaller than the average rate of larger crystals of the product size range (500 mu m) i n an MSMPR (mixed suspension mixed product removal) crystallizer.