Role of Hydrodynamics, Li+ Addition and Transformation Kinetics on the Formation of Plate-Like {001} Calcite Crystals

Jasminka Kontrec,Damir Kralj,Branka Njegić Džakula,Nives Matijaković Mlinarić,Giuseppe Falini

doi:10.3390/cryst11030250

Abstract

Plate-like calcite crystals with expressed unstable {001} planes are interesting research model for investigations of interfacial interactions of different additive molecules, but also the crystal growth mechanisms. The aim of this study is to reproducibly prepare a significant amount of well-defined plate-like calcite crystals and to investigate the critical experimental parameters. Thus, in precipitation system c(NaHCO3) = c(CaCl2) = 0.1 mol dm−3, the influence of hydrodynamic parameters (mode of mixing of the reaction components) and a presence of lithium ions Li+ within a wide range of concentrations, 0.0 mol dm−3 < c(Li+) < 1.0 mol dm−3, have been studied. In addition, the kinetics of the solution mediated transformation of the initially formed metastable polymorph, vaterite, were followed in order to reproducibly describe the formation of stable calcite with expressed unstable morphology. The results indicate that the plate-like calcite is formed predominantly when the ultrasound irradiation is applied at c(Li+) ≥ 0.3 mol dm−3. On the other hand, when the magnetic and mechanical stirring are applied at higher Li+ concentrations, truncated rhombohedral crystals in a mixture with plate-like crystals are obtained. It was also found that the Li+ addition significantly prolonged the transformation, mainly by inhibiting the crystal growth of calcite.

Highlights

IntroductionThose of calcite, are interesting model systems for studying the interfacial interactions on crystal planes, namely, for any detailed analysis of crystal growth kinetics and mechanisms, or investigation of basic molecular interactions that may happen at the solid-liquid interfaces
The result showed that after 5 days of aging of the suspension, predominantly plate-like calcite has precipitated in the US system when the concentration of lithium ions was equal or higher than 0.3 mol dm−3, while in the mechanical propeller (MECH) and magnetically stirred (MAG) systems concentration has been as high as 1.0 mol dm−3
When the concentration of Li+ was lower than critical, truncated rhombohedral calcite crystals in a mixture with plate-like crystals have been obtained in all systems

Summary

Introduction

Those of calcite, are interesting model systems for studying the interfacial interactions on crystal planes, namely, for any detailed analysis of crystal growth kinetics and mechanisms, or investigation of basic molecular interactions that may happen at the solid-liquid interfaces. The morphology and shape of these highly ordered organic-inorganic composites are controlled by biologically active macromolecules that interact with specific crystal planes during their nucleation and crystal growth [8] These processes have been extensively studied on the molecular level in order to understand the respective interactions and mechanisms of preparation of highly functionalized composite materials [9,10,11,12,13,14,15,16]

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