Quantitative 3D Visualization of the Growth of Individual Gypsum Microcrystals: Effect of Ca2+:SO42– Ratio on Kinetics and Crystal Morphology

Abstract

The kinetics of crystal growth of gypsum is determined by measuring the 3D time-evolution of isolated microcrystals (∼10 μm characteristic dimension) by in situ AFM. By coupling such measurements to a well-posed diffusion model, the importance of mass transport to the overall rate can be elucidated readily. Indeed, because microscale interfaces that act as source or sink sites are characterized by intrinsically high diffusion rates, it is possible to study crystal growth free from mass transport effects in many instances. In the present study, a particular focus is to elucidate how the ratio of Ca2+ to SO42– ions at constant supersaturation influences the rate of growth at the major crystal faces of gypsum. It is found that growth at the {100} and {001} faces, in particular, is highly sensitive to solution stoichiometry, resulting in needle-like crystals forming in Ca2+-rich solutions and plate-like crystals forming in SO42–-rich solutions. The maximum growth rate occurs with a stoichiometric solution of ...