An overview of crystallization in gels

Abstract

Considerable experimental and theoretical work concerning crystallisation in gels can be found in the scientific literature. After the pioneer book by Henish [1], crystal growth in gels has shown to be a simple and suitable method for making single crystals of sparingly soluble salts, small-molecule compounds, and macromolecules, e.g.: [2,3]. The gel medium suppresses convection and advection only allowing diffusion of the aqueous species, which eventually can react to form solids. From experimental data it is abundantly clear that gels reduce the nucleation chance and, in that sense, offer certain research opportunities that crystallization from ’’free’’ aqueous solutions cannot provide. So, in the context of purposeful crystal growth, the suppression of nucleation is the principal function of the gel because a lower nucleation density favours the development of larger crystals. However, a more fundamental interest of gels arises from their possibilities to explore crystallisation behaviour in a variety of environments, including microgravity, and to simulate a diversity of unusual crystallization phenomena, e.g.: [4-10]. Here, we present a brief review of previous work carried out with this kind of systems, which includes a miscellany of topics, such as 1) nucleation behaviour of stoichiometric compounds and solid solutions in porous media, 2) reaction paths and generation of patterns during the growth process, 3) metastable crystallization and subsequent solvent-mediated phase transformations, 4) simulation of biomineralization processes and generation of biomimetic crystalline aggregates, 5) sorption of pollutants by surface precipitation of pollutantbearing phases on minerals embedded in gel media, and 6) simulation of mineral replacement and other mineral-fluid interaction phenomena.