%0 Journal Article
%A Pina Martínez, Carlos Manuel
%A Enders, Michael
%A Putnis, Andrew
%T The composition of solid solutions crystallising from aqueoussolutions: the influence of supersaturation and growthmechanisms
%D 2000
%@ 0009-2541
%U https://hdl.handle.net/20.500.14352/57131
%X In this paper we present a new approach to the problem of the crystallisation in solid solution–aqueous solution (SS–AS)systems, in which two main controlling factors have been considered: (i) the supersaturation state of the multicomponentsolution in contact with the growing crystal and (ii) the growth mechanisms, operating at a molecular scale on the variousfaces of the crystal. Supersaturation has been evaluated as a function of the solid solution (the β function) and thetransitional supersaturation between spiral growth and two dimensional nucleation mechanisms has been considered as alinear function of the solid composition (the β* line). By superimposing β functions and β* line on a supersaturation–solidcomposition diagram, we can define compositional regions growing according to different growth mechanisms. In order totest our model, a number of in situ Atomic Force Microscope (AFM) experiments have been conducted in theBa2+–Sr 2+–SO24–H2O system, using barite (001) as the substrate. The general growth behaviour observed is consistent with the predictions given for a number of initial aqueous solution compositions. Microprobe analysis shows that the new(001) layers grown under conditions where the maximum supersaturation corresponded to intermediate compositions of the(Ba,Sr)SO4 solid are very Sr-rich. A qualitative explanation for such a compositional shift is given on the basis of nucleationrate calculations in the Ba2+–Sr 2+–SO424–H2O system. Finally we discuss the effect of the substrate on the formation anddistribution of two-dimensional (Ba,Sr)SO4 nuclei on a barite (001) surface.
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