Spinning up the polymorphs of calcium carbonate

Dino Spagnoli,Ramiz A. Boulos,Colin L. Raston,Adam D. Martin,Fei Zhang,Edwin S. Tjandra

doi:10.1038/srep03616

Abstract

Controlling the growth of the polymorphs of calcium carbonate is important in understanding the changing environmental conditions in the oceans. Aragonite is the main polymorph in the inner shells of marine organisms, and can be readily converted to calcite, which is the most stable polymorph of calcium carbonate. Both of these polymorphs are significantly more stable than vaterite, which is the other naturally occurring polymorph of calcium carbonate, and this is reflected in its limited distribution in nature. We have investigated the effect of high shear forces on the phase behaviour of calcium carbonate using a vortex fluidic device (VFD), with experimental parameters varied to explore calcium carbonate mineralisation. Variation of tilt angle, rotation speed and temperature allow for control over the size, shape and phase of the resulting calcium carbonate.

Highlights

Controlling the growth of the polymorphs of calcium carbonate is important in understanding the changing environmental conditions in the oceans
We have investigated the effect of high shear forces on the phase behaviour of calcium carbonate using a vortex fluidic device (VFD), with experimental parameters varied to explore calcium carbonate mineralisation
While the conditions here are much more extreme and different to those likely to be encountered in the environment in the future, the results highlight the conditions required for selective preparation of different polymorphs of calcium carbonate

Summary

Introduction

Controlling the growth of the polymorphs of calcium carbonate is important in understanding the changing environmental conditions in the oceans. The rising concentration of carbon dioxide in the atmosphere, estimated to be 40% higher than preindustrial levels and higher than at any point in the last 800,000 years[1], has led to a shift in the equilibrium of dissolved CO2 in seawater This has lowered the pH of seawater and along with increasing temperatures, has greatly affected the optimum conditions for calcium carbonate (CaCO3) mineralisation[2,3]. Controlling the formation of CaCO3 polymorphs is important in understanding the mineralisation process with such changing environmental conditions, and for this purpose we used the recently developed, continuous flow processing, vortex fluidic device (VFD)[10,11,12,13]. Important is gaining control over the interconversion of the different polymorphs of calcium carbonate where particular applications demand the presence of one phase of www.nature.com/scientificreports specific particle size and morphology (e.g. paper coating)[25] while another application may require the in situ conversion of CaCO3 from one phase to another, such as in drug delivery[26]

Methods

Results

Conclusion