%0 Journal Article
%A Pina Martínez, Carlos Manuel
%T Nanoscale dissolution and growth on anhydrite cleavage faces
%D 2009
%@ 0016-7037
%U https://hdl.handle.net/20.500.14352/49787
%X In situ atomic force microscopy (AFM) was used to study the molecular-scale reactivity of anhydrite (1 0 0), (0 1 0), and(0 0 1) faces exposed to water and CaSO4 aqueous solutions at room temperature. In pure water, dissolution occurs by stepretreat and etch pit nucleation and growth. Both the kinetics of the step retreat and the shape of the etch pits are surface-specificand crystallographically controlled. In CaSO4 aqueous solutions with concentrations ranging from 0.030 mol/l to0.075 mol/l, the growth kinetics on anhydrite (1 0 0) and (0 1 0) faces was studied. Growth is also strongly controlled by crystallographicconstraints and occurs exclusively from pre-existing step edges by highly anisotropic spreading of monolayers(3.5A ˚ in height). The AFM observations demonstrate that monolayer growth can occur on anhydrite (0 1 0) and (1 0 0)faces even from slightly supersaturated solutions. In addition, the comparison of the step kinetics on anhydrite faces showsthat the mechanisms of step dissolution and growth are essentially the same, with the direction of migration of crystal buildingunits being reversed at the anhydrite saturation point. Moreover, the analysis of both high resolution AFM images and lateralforce microscopy (LFM) images confirms that the newly-formed monolayers are anhydrite growing in structural continuitywith the original (1 0 0) and (0 1 0) surfaces. However, the formation of the first monolayers is metastable and two-dimensionalnucleation and further multilayer growth of anhydrite are strongly inhibited even at high supersaturations.
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