Morphological and crystallization process of CaCO3 in the presence of Aqua soft 330 (AS 330)

CaCO3 was crystallized from CaCl2 solution containing commercially available 1-hydroxyethylidene-1,1-diphosphonic acid, Aqua soft having a chelating value of 330 (AS 330). The effect of the concentration of AS 330 and the temperature of crystallization on the morphology and crystalline structure of CaCO3 was investigated. The samples were characterized using scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The presence of AS 330 favored ternary calcite–vaterite–aragonite mixture at 60 and 80 °C and a binary calcite–vaterite mixture at 100 °C. Rhomboidal calcite, needle/rod like aragonite and flower like vaterite were obtained under different conditions. In contradiction to the usual process of the transformation of amorphous CaCO3 into different polymorphic forms, the data confirmed calcite is the precursor for the flower structured vaterite. The mechanism of formation of the flower structured vaterite is discussed in detail.

Four stage mechanism for the formation of flower-like vaterite. Step 1. Formation of the core part from the rhomboidal calcite. Step 2. Agglomeration of bulbous units. Step 3. Dispersion of the second and further layers of spheres. Step 4. Spreading of layers ceases leading to the final sunflower structure.Figure optionsDownload as PowerPoint slideHighlights
► We report a unique flower like morphology for vaterite.
► The formation of this polymorph form more stable calcite is a novel concept.
► The mechanism of formation of this flower like morphology is discussed.