Effect of growth rate history on current crystal growth. 2. Crystal growth of sucrose, Al(SO4)(2)center dot 12H(2)O, KH2PO4, and K2SO4

摘要

The current study investigated a potential mechanism of growth rate dispersion (GRD) by determining the effect of a crystal's "growth rate history" on its current crystal growth, for sucrose, potash alum, potassium dihydrogen phosphate (KDP), and potassium sulfate crystals, using a combination of growth kinetic analysis and surface analysis via atomic force microscopy (AFM) and scanning electron microscopy (SEM). The growth history of a crystal had a significant effect on the future crystal growth rate: if a crystal had a period of high growth in a high supersaturation environment, the subsequent growth of the crystal in a lower supersaturation had a lower rate than a crystal that had been kept in the lower supersaturation environment. These results can be explained by the effect of high growth rates on the growing surface of a crystal: crystals grown in high supersaturation solutions had a rougher surface (on a macroscopic rather than molecular scale) than those grown in low supersaturation solutions. This phenomenon occurs if growth occurs above a critical level of the supersaturation, which we term the roughening transition. The level of GRD is shown to be related to the surface energy of the crystal, with high surface energy species also displaying higher levels of growth rate dispersion at the same relative supersaturation.