Formation Process and Thermodynamic Poperties of Calcite

Abstract

The fast mixing of aqueous solutions of calcium chloride and sodium carbonate resulted in crystalline forms of vaterite and calcite under vigorous stirring. Then, the vaterite was transformed to pure calcite within about 180 min. The crystalline forms all grew with experimental time increase. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction spectroscopy (XRD) techniques were employed to characterize the as-prepared samples. The heat capacity of the stable as-synthesized calcite was determined by means of an adiabatic calorimeter from 80 to 390 K. The thermodynamic functions of the calcite were derived based on the relationships among the thermodynamic functions and the function of the measured heat capacity with respect to temperature.

Structure transition from aragonite to vaterite and calcite by the assistance of SDBS

“…The phase diagram of CaCO 3 shows that calcite is the stable style under ambient conditions, aragonite is the high-pressure polymorph, and vaterite is thermodynamically unstable [1][2][3][4]. Calcite and aragonite are the most common biologically formed CaCO 3 polymorphs, and have been applied in industry as fillers and pigments.…”

Removal of Cr (III) and Ni (II) from tannery effluent using calcium carbonate coated bacterial magnetosomes

“…The precipitated solid was collected and immediately filtered through cellulose nitrate membrane (0.2 µm) and dried under vacuum. 36 The CaCO 3 coated magnetosomes were fabricated by mixing equal volume of 0.33 M CaCl 2 solution and Na 2 CO 3 in the presence of vigorously stirred magnetosome (50 mg/mL). The precipitate was filtered through cellulose nitrate membrane (0.2 µm) and dried at 70°C for 30 min.…”

Précipitation de carbonates de cations divalents dans les systèmes lacustres : intérêt, état des connaissances des mécanismes et suggestions (Revue critique de la littérature)

“…La température et le rapport Mg:Ca déterminent la composition et la variété cristallographique de carbonate de calcium précipité : calcite, aragonite, solutions solides Ca 1-x Mg x CO 3 ont été ainsi décrites (DEAN, 2009;MORSE et al, 2007;MÜLLER ,1972;SHAPLEY et al, 2002). La calcite est la variété cristalline de carbonate de calcium la plus stable à température et pression ambiantes, l'aragonite étant stable à haute pression et la vatérite étant thermodynamiquement instable (CÖLFEN, 2003;JOHANESS et PUHAN, 1971;NAN et al, 2007). Cependant, ZHAODONG et al (2008), dans une étude récente ont obtenu la vatérite à partir de l'aragonite en présence d'un surfactant.…”