Growth speeds and growth modes of sodium chloride : a quantitative two-dimensional phase-field study

Abstract

The understanding of crystal growth is beneficial to many different sectors, such as crystal engineering, drug manufacturing and life sciences. This phenomenon can be studied computationally on the molecular level, providing insights into the atomistic interactions of growth particles occurring at the solid-liquid interface. However, a significant amount of effort is often required to reveal information on spatial and temporal scales that are relevant in crystal growth experiments that are (usually) mesoscopic in nature. The Phase-field (PF) approach is a phenomenological model that can simulate, efficiently, the evolution of microstructures on length and time scales that are directly comparable to experiments but not many quantitative studies of precipitation crystal growth using the PF method are reported in the literature.

In this study, the precipitation PF model was employed to simulate and investigate, quantitatively, the crystal growth of sodium chloride, NaCl, in supersaturated solutions. More specifically, the accuracy of the model over a wide range of time scales is revealed by comparing the one-dimensional growth speeds of NaCl (simulated over periods of a few milliseconds up to several minutes) with experimental results from the literature. In addition, by simulating two-dimensional growth using circular crystals of different radii, it is shown that the PF model can be used to demonstrate the influence of curvature of a crystal surface on the growth speed. Lastly, by simulating anisotropic crystal growth of NaCl in two dimensions for a range of concentrations, the model predicted the transition from compact to non-compact growth to occur at a supersaturation coefficient of ~1.4, which is in good agreement with experimental observations of NaCl grown in microchannels.

The work described in this thesis demonstrates that the PF model can provide information about crystal growth on length and time scales that are not easily accessible with molecular methods.