Difficulties in determining the crystal growth mechanism from growth rate versus solution supersaturation dependence are discussed. Obtained results indicate that in the supersaturation range of 0.66−1.56%, sodium chlorate crystals grow in accordance with the spiral growth model. It is shown that in the supersaturation range of 0.44−1.32%, the growth mechanism depends on crystal growth history. Namely, the exponent n in the power law R = Kσ n depends on the manner of supersaturation changes (varied from 1.3 to 1.9%). This indicates that the overlapping of diffusion fields of neighboring steps depends on growth history.
Effects of partial dissolution and refaceting on growth rates of sodium chlorate and potassium dihydrogen phosphate (KDP) crystals are presented. Under the same external conditions, crystals of sodium chlorate and KDP exhibit growth rate dispersion (GRD), prior to dissolution and after refaceting. These GRDs were described by multiple normal distributions. Dissolution and refaceting reduce the GRD. A number of growth rates pertained to higher order maxima decreases, whereas a number of those pertained to lower order increases, that is, crystals continue to grow at leveled rates. Maxima positions are related to the activity of dominant dislocation groups emerging on the crystal surface. Many nongrowing {100} faces of sodium chlorate and KDP crystals, as well as the nongrowing roofs of KDP crystals, were also noticed before dissolution and after refaceting, which is related to a lattice strain effect. ■ INTRODUCTIONUnder the same solution and external conditions, different crystals of the same material grow at different rates. This phenomenon, termed as the growth rate dispersion (GRD), which occurs for a number of inorganic and organic crystals generated by primary or secondary nucleation, is still not understood well. 1−4 Also, it was shown that under the same external macroscopic conditions, specific crystal faces grow at different rates, that is, a GRD of crystal faces occurred. 5,6 Recently it was shown that in the first few hours of the growth period, the majority of the crystal growth rates decreased, and did not change significantly later. 7 Leveling of the growth rates during the growth occurred as well.The growth rate dispersion affects the crystal size distribution, and hence the industrial crystallizers product quality. Changing the growth temperature or the solution supersaturation is the usual way of altering the crystal growth rate (or size) distribution. Another way is to change the parameters influencing GRD at a specific temperature and supersturation. Therefore, studying the crystal growth rate distributions under the same external conditions is important, especially the ways that they affect them. It is shown that partial dissolution of crystals, and the subsequent resumption of their growth, changes these distributions. 6,8 Effects of the growth rate history on current growth rate was studied through the changes in the supersaturation, 9,10 and crystal dissolution and refaceting. 8 As is shown, GRD of sodium chlorate crystals in the ⟨100⟩ direction can be described by multiple normal distributions. 11 Recently we have shown that after the dissolution and refaceting, fast growing faces disappeared. 6 All faces either grow at rates that correspond to one GRD maximum, or they did not grow at all. These considerable changes in the growth rate distributions might be significant for the quality of products in industrial crystallizers. We test whether the same conclusion is valid for different supersaturations of sodium chlorate and potassium dihydrogen phosphate (KDP) solutions, and the results are p...
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