Growth mechanisms of NaClO3 and KBr from aqueous solutions under relatively high supersaturation ranges

Normal growth rates of {100} faces of NaClO3 and KBr crystals in aqueous solutions have been measured under relatively high supersaturation regions, using a specially designed cell for in-situ observation. The growth rates versus supersaturation relations are examined in order to investigate the growth mechanisms, based on BCF and two dimensional nucleation growth theories. As the most plausible growth mechanism, the birth and spread model in two dimensional nucleation growth theory is suggested for both crystals in the supersaturation ranges investigated. Based on this mechanism, the growth rate constant A and relative edge free energy γ′⁄kT are calculated to be in the order of 4×10−4 cm/sec and 0.2 for NaClO3, and 3×10−3 cm/sec and 0.2 for KBr, respectively. These values are reasonable in comparison with the values for other ionic compounds. The growth mechanism of NaClO3 and KBr in aqueous solutions from low to high supersaturation ranges is also discussed, based on the present results and the previously published data, which lead to a conclusion that BCF mechanism is applicable under the low supersaturation region, whereas two dimensional nucleation growth will predominate up to the supersaturation range where dendritic growth occurs.