Kinetic asymmetry between crystal growth and dissolution: step movement at low temperatures

Abstract

The kinetics of crystal growth and dissolution due to step movement has been studied. Linear fitting of the rate vs. C/C_eq or σ(|C/C_eq– 1|) over a limited range of supersaturation and for dissolution was found. The plot of rate vs. σ/x₀(σ) was also found to be linear over a much wider range of distance from equilibrium. These two rate laws show kinetic asymmetry in growth and dissolution at a given distance from equilibrium in terms of concentration. An exception was found at high temperature for the plot of rate proportional to σ/x₀(σ), provided that the different forms of x₀(σ) for growth and dissolution are not considered.

Under the influence of 2D nucleation, the overall kinetics of growth and dissolution of the stepped surface appears to show deviation from linearity in the plot of rate vs. σ/x₀. Such deviation is greater for surfaces with lower step density. However, the presence of steps appears to have no effect on promoting 2D nucleation near equilibrium. Further from equilibrium, the presence of nucleation significantly diminishes the step contribution to the overall rate.

The activation energies for growth and dissolution were found to be independent of step density. The activation energy of dissolution is higher than growth and it increases with decreasing temperature. This qualitative trend is the same for the activation energy determined by both rate laws.