Synthesis of All Crystalline Phases of Anhydrous Calcium Carbonate

Abstract

Usually, the metastable vaterite phase transforms to the thermodynamically most stable calcite phase. We report here the phase transformation of vaterite to aragonite, which is seldom observed in the synthetic processes of calcium carbonate. The vaterite, upon equilibration with distilled water at room temperature, gradually transforms to aragonite. This transformation process is further accelerated when the vaterite sample is refluxed in distilled water. Under a different set of conditions, when equilibrated in the mother liquor, the same vaterite sample transforms to calcite without going through aragonite as an intermediate phase. The formation of all three crystalline polymorphs of calcium carbonate is achieved without the use of any additive. These polymorph transformations have been monitored using powder X-ray diffraction and FTIR spectroscopy. The morphological changes of the calcium carbonate samples isolated during the course of phase transformation processes are captured using scanning electron microscopy. The transformation either to aragonite or to calcite has been explained based on the dissolution-recrystallization mechanism.

Morphology control by flow-driven self-organizing precipitation

“…The comparison of the most intensive peaks presented in Table 2 reveals that rhombohedrals are calcite, while the spherical polycrystalline particles are vaterite in accordance with other studies [32]. It is important to point out that the slow phase transition of vaterite into calcite does not occur within the time frame of our experiments [33].…”

Vibrational spectroscopic characterization of growth bands in Porites coral from South China Sea

“…3, the peak at $133 cm À1 in XL1-1 showed a transition phase indicating which peak of vaterite at $120 cm À1 shifts to peak at $141 cm À1 of aragonite. Similarly, the peak at $178 cm À1 in XL1-1 showed a [19,[34][35][36]. In the present work, it is proposed that the vaterite could be the precursor of aragonite phase of coral skeleton from South China Sea.…”

Characterization of vaterite synthesized at various temperatures and stirring velocities without use of additives

“…Pure vaterite (≥ 99 wt.%) was found at 60°C. Only few studies can be found that deal with the synthesis of vaterite with the same reactants [28,29]. Sarka et al [29] have synthesized pure vaterite at 30°C with 200 rpm stirring velocity.…”

“…Only few studies can be found that deal with the synthesis of vaterite with the same reactants [28,29]. Sarka et al [29] have synthesized pure vaterite at 30°C with 200 rpm stirring velocity. This difference is probably caused by the modified experimental set up, mainly by the usage of a smaller volume of reactants, which actually diminishes the total reaction time, and variant impeller.…”