In situ investigations of carbonate nucleation on mineral and organic surfaces
DE YOREO ; WAYCHUNAS ; JUN ; FERNANDEZ-MARTINEZ
Type de document
ARTICLE A COMITE DE LECTURE REPERTORIE DANS BDI (ACL)
Langue
anglais
Auteur
DE YOREO ; WAYCHUNAS ; JUN ; FERNANDEZ-MARTINEZ
Résumé / Abstract
Nucleation is the seminal event in formation of new mineral phases. The subject has a long history, finding its modern roots in the work of Gibbs in the late 1800’s (Gibbs 1876, 1878) and continuing through the efforts of Stransky and others in the mid-20th century (Gutzow 1997). What emerged has come to be known as classical nucleation theory (CNT). Within this model, mineral nucleation comes about through ion-by-ion addition to a growing cluster (Fig. 1A), whose origin lies in the inherent thermodynamic fluctuations of the solution. In recent years, this well-accepted theory has been called into question by an increasing number of studies, both experimental and theoretical, reporting so-called “non-classical” pathways of nucleation involving aggregation of clusters or nanoparticles that exist in equilibrium with the free ions (Fig. 1B). Moreover, such studies often report the nuclei consist of an amorphous precursor, which transforms to the more stable crystalline products only after nucleation has long ended. Presumably, if these cluster-based and multi-stage processes dominate, it is because they offer a lower barrier pathway to nucleation than does the pathway through ion-by-ion addition. Based on the many years of surface science research since the development of CNT, we now know that energy landscapes are unlikely to be flat; i.e., the free energy of a cluster of ions should depend on its size and/or configuration, and composition, including that of the solvent. The resulting peaks and valleys in the energy landscape will naturally create cluster populations, which could give rise to unexpected pathways. In the context of a geological reservoir, consideration of mineral surfaces, organic films, and pores is crucial, because both substrates and pores can reduce the classical barrier to nucleation and, hence, may play a large role in modifying energy landscapes, re-directing pathways, and determining nucleation rates.
Source
Reviews in Mineralogy & Geochemistry, num. 1, pp. 229-257 p.
Editeur
MINERALOGICAL SOCIETY OF AMERICA
