Nucleation of CaCO3 polymorphs from a colloidal alcoholic solution of Ca(OH)2 nanocrystals exposed to low humidity conditions

Abstract

A study of the stability of calcium carbonate polymorphs formed as a result of the carbonation process from an alcoholic colloidal solution of nanocrystals of Ca(OH) 2 in low relative humidity (RH) conditions (33% and 54% RH) is presented in this research. The crystalline behaviour, the time dependence of nucleation and the phases` transformations as a result of exposure to low humidity conditions are evaluated. The carbonation process is slow, starting with the nucleation of amorphous calcium carbonate, associated to an amorphization process that affects both the portlandite (Ca(OH) 2 ) and the initial unstable CaCO 3 polymorphs. The excess of alcohol in the solution decreases the surface tension and the nucleation is accelerated by the fast evaporation of the solvent, which avoids the particles to diffuse to their lowest energy sites, giving smaller particles with lower crystallinity as RH decreases.

Synthesis and morpho-structural characterization of nanostructured magnesium hydroxide obtained by a hydrothermal method

“…Recently, interest in magnesium hydroxide (Mg(OH) 2 ) nanoparticles has been increasing rapidly due to the fact that these nanoparticles have multiple applications in medicine [1], industry [2] and more recently, in the conservation of cultural heritage [3,4]. The reason why the nanoparticles have multiple applications is that crystalline Mg(OH) 2 offers several great advantages, such as a good thermal stability, good fire retardant properties, a low toxicity and a low cost [5,6].…”

Micro‐Raman spectroscopy investigation of the carbonation reaction in a lime paste produced with a traditional technology

“…Vaterite and/or metastable CaCO 3 polymorphs may also play a role as precursors of calcite. All these anhydrous CaCO 3 polymorphs were detected during the carbonation of nanolime suspensions . It is well known, that reactions conditions (e.g.…”

“…All these anhydrous CaCO 3 polymorphs were detected during the carbonation of nanolime suspensions. [15][16][17]38] It is well known, that reactions conditions (e.g. temperature, pH, humidity, presence of additives) play a crucial role in the precipitation of the CaCO 3 polymorphs.…”

“…The reaction rate is mainly controlled by two mechanisms: the diffusion of the atmospheric CO 2 gas into the pore structure of the lime specimens, and the chemical reaction between the dissolved CO 2 and Ca(OH) 2 . During the carbonation process, different CaCO 3 polymorphs can be formed . Calcium carbonate can occur as amorphous phase (ACC), crystalline hydrated forms (calcium carbonate hexahydrate (ikaite) and calcium carbonate monohydrate) and as anhydrous crystalline polymorphs—vaterite, aragonite, and the most thermodynamically stable calcite…”

“…[12] During the carbonation process, different CaCO 3 polymorphs can be formed. [12][13][14][15][16][17] Calcium carbonate can occur as amorphous phase (ACC), crystalline hydrated forms (calcium carbonate hexahydrate (ikaite) and calcium carbonate monohydrate) and as anhydrous crystalline polymorphs-vaterite, aragonite, and the most thermodynamically stable calcite. [18] In lime specimens, the carbonation progresses from the surface to the interior of the sample, with the onset of a concentration profile of the products which evolves in time, according to the CO 2 diffusion coefficient and steric hindrance, that may impact during crystal growth.…”