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Epitaxial growth of celestite on barite (001) face at a molecular scale

Sánchez Pastor , Nuria and Pina Martínez, Carlos Manuel and Astilleros García-Monge, José Manuel and Fernández Díaz, Lourdes and Putnis, Andrew (2005) Epitaxial growth of celestite on barite (001) face at a molecular scale. Surface science, 581 . pp. 225-235. ISSN 0039-6028

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Abstract

In situ AFM experiments have been conducted in order to obtain information about kinetics of celestite epitaxial
growth on barite. Growth has been promoted by passing aqueous solutions supersaturated with respect to celestite over
freshly cleaved barite (001) surfaces. Solution supersaturation, bcelestite, was varied from 1 to 45.7 (βcelestite = a(Sr2+) . a(SO2-4)/Kspcel). At supersaturations below 10 neither two-dimensional nucleation neither step advancement
are observed on barite (001) surfaces. However, once the two-dimensional nucleation barrier is overcome (bcelestite
> 10), nuclei preferentially form on cleavage steps parallel to [100], [110] and [120] directions and more scarcely
on terraces. The subsequent growth of two-dimensional nuclei leads to the development of celestite ‘‘islands’’. Their
morphology is defined by (001) face and {210} and {100} forms and can be explained on the basis of PBCtheory.
The coalescence of such islands results in the formation of a homogeneous SrSO4 layer. Growth rates along [001] direction
have been measured for the whole supersaturation range. The growth rate equation for ‘‘Birth and Spread’’ crystal
growth mechanism has been successfully fitted to our experimental data. The fitting process has provided basic growth
parameters in a good agreement with theoretical ones. Both the high transitional supersaturation required for twodimensional
nucleation and the high interfacial energy value obtained from the fitting of the ‘‘Birth and Spread’’ equation (σ
cel–bar 001 = 0:137 J/m2) indicate low affinity of SrSO4 growth units for barite (001) faces. This is consistent with the
relative high mismatch between celestite and barite structure. The behaviour of the epitaxial growth described in this
work can help to interpret the oscillatory zoning frequently occurring in both natural and synthetic crystals of the
BaxSr1-xSO4 solid solution.

Item Type:Article
Uncontrolled Keywords:Surface topography; Atomic force microscopy; Epitaxy; Solid–liquid interfaces
Subjects:Sciences > Geology > Crystallography
ID Code:14050
Deposited On:12 Dec 2011 11:56
Last Modified:12 Dec 2011 11:56

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