Growth of Calcite in Confinement

Lei Li,Dag Dysthe,Felix Kohler,Anja Røyne

doi:10.3390/cryst7120361

Abstract

Slow growth of calcite in confinement is abundant in Nature and man-made materials. There is ample evidence that such confined growth may create forces that fracture solids. The thermodynamic limits are well known, but since confined crystal growth is transport limited and difficult to control in experiments, we have almost no information on the mechanisms or limits of these processes. We present a novel approach to the in situ study of confined crystal growth using microfluidics for accurate control of the saturation state of the fluid and interferometric measurement of the topography of the growing confined crystal surface. We observe and quantify diffusion-limited confined growth rims and explain them with a mass balance model. We have quantified and modeled crystals “floating” on a fluid film of 25–50 nm in thickness due to the disjoining pressure. We find that there are two end-member nanoconfined growth behaviors: (1) smooth and (2) rough intermittent growth, the latter being faster than the former. The intermittent growth rims have regions of load- bearing contacts that move around the rim causing the crystal to “wobble” its way upwards. We present strong evidence that the transition from smooth to rough is a generic confinement-induced instability not limited to calcite.

Highlights

A number of marine organisms mineralize calcium carbonate [1]
We report confined crystal growth experiments that differ from previous experiments in two respects: (1) instead of highly soluble crystals, we use calcite, which has a solubility of about four orders of magnitude smaller, and the growth rate is 3–4 orders smaller than NaClO3 ; (2) we study the evolution of the growing confined crystal surface in situ
We present in situ images of how the crystal surfaces confined by the glass surface evolve during stable growth conditions

Summary

Introduction

A number of marine organisms mineralize calcium carbonate [1]. The biomineralization processes are of great interest in themselves, and confinement in cellular compartments is thought to be important in the process of controlling biological mineral growth [2]. The organisms with calcium carbonate skeletons sediment to the sea floor, and the sediments undergo compaction where dissolution and recrystallization of calcite occur in confinement to form limestone [3]. Some such carbonate rocks are buried deeper and undergo recrystallization in confinement once more and emerge as marble. Both limestone and marble are used for construction and sculptures that deteriorate due to confined salt crystallization in the pore space [4]. Confined recrystallization of calcite in other environments has been shown to create forces that break other mineral grains [6] and lift rock overburden [7]

Results

Discussion

Conclusion