Universidad Complutense de Madrid
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The role of magnesium in the growth of calcite: An AFM study

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Astilleros García-Monge, José Manuel y Fernández Díaz, Lourdes y Putnis, Andrew (2010) The role of magnesium in the growth of calcite: An AFM study. Chemical geology, 271 . pp. 52-58. ISSN 0009-2541

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URL Oficial: doi:10.1016/j.chemgeo.2009.12.011



Resumen

The mechanisms that determine the inhibition of calcite growth by magnesium have remained unclear and
subject to controversy over decades. Although it has been long apparent that the inhibition mechanisms take
place at the crystal-solution interface, the molecular phenomena occurring at calcite surfaces in contact with
Mg-bearing solutions are still not completely understood. The main goal of this work is to contribute to
further clarify those phenomena. With this aim, we carried out in situ atomic force microscopy (AFM)
observations of the growth behaviour of calcite f10 1–
4g surfaces in contact with supersaturated aqueous
solutions (β=5) bearing different amounts of Mg (ranging from 0.05 to 4.00 mmol dm−3). Under the
conditions considered, growth occurred by monolayer spreading. Our observations revealed that only the
first elementary growth layer advancing on the original calcite surfaces grow normally, showing
characteristics nearly identical to the growth of pure calcite. However, subsequent monolayers behave
differently. Thus, as soon as one of these monolayers reaches areas of the surface that have grown
incorporating Mg and whose composition can consequently be described as MgxCa1-xCO3, the rate at which
this step advances significantly decreases. Moreover, the step becomes progressively rougher. A clear
relationship between the extent of the inhibition effect and the concentration of Mg in the aqueous solution
exists. Furthermore, our observations allow us to conclude that each newly formed monolayer exerts a
certain control on the development of the growth of subsequent monolayers. Such a control causes the
reproduction of the nanotopographic features of the original surface, producing the so called “template
effect”. This behaviour cannot be easily incorporated within the general framework of the currently accepted
impurity crystal growth models, which are based on either the pinning of elementary step motion by
impurities or changes in the solubility of the newly formed layers as a result of the incorporation of the
impurity into the lattice of the growing crystal. We discuss our results on the basis of the solid solution–
aqueous solution model and provide a complementary explanation for the development of “dead zones” in
the case of the growth of calcite f10 1–
4g surfaces from divalent cation-bearing aqueous solutions.


Tipo de documento:Artículo
Palabras clave:Solid solution–aqueous solution; Atomic force microscopy; Crystal growth inhibition; Calcite; Magnesium
Materias:Ciencias > Geología > Mineralogía
Código ID:18031
Depositado:29 Ene 2013 13:25
Última Modificación:16 Abr 2015 12:01

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