Differential thermal analysis and infrared studies on the effect of impurities on aragonite–calcite transformation

Abstract

CHEBROLU RAMA MOHAN RAO and PRATAP NARAIN MEHROTRA. Can. J. Chem. 56.32 (1978).The transformation of aragonite to calcite (A-C) is an irreversible reconstructive transformation involving a change from 6 to 9 in the primary coordination. Cationic impurities like N a + , Mg2+, Zn2+, Y3 +, La3+, Nd3+, Gd3+, Dy3+ have been doped in pure aragoniteand their effect on the kinetics and energetics of its transformation to calcite is studied. By employing a DTA technique, the enthalpy and energy of activation for the transformation have been calculated. The ir spectra of aragonite and calcite in pure form and with various impurities have been studied and the effect of impurities on absorption bands discussed.

Thermal Decomposition of CaC2O4·H2O Studied by Thermo-Raman Spectroscopy with TGA/DTA

“…They are for CaCO 3 , which has two forms, aragonite and calcite. 21,22 These spectra were similar except for the weak band at 160 cm -1 and the strong Rayleigh scattering. No spectral band appears in the last spectrum measured at 730 °C, as shown in Figure 2h.…”

“…These indicated a phase transformation of CaCO 3 from anagonite to calcite around spectrum 596 (616 °C), higher than the reported 513 °C. 21 The reason might be the different experimental conditions and the property of this transformation. It is irreversible, reconstructive, and sluggish.…”

“…They were consistent with the variations in TGA/DTA. Furthermore, phase transformations or changes in crystal symmetry of I and II forms of CaC 2 O 4 ‚H 2 O, 10,[16][17][18][19][20] R, β, and γ forms of CaC 2 O 4 , 3,16,17 and two forms of CaCO 3 21,22 were observed in this work by Raman spectroscopy which were not detectable in TGA/DTA. Thus, we illustrate in this work that Raman spectroscopy can be operated alone in thermal analysis to provide much direct and valuable information.…”

Variation in the diagenetic response of aragonite archives to hydrothermal alteration

“…In contrast, the incorporation of Mg 2+ is by far non-ideal and still hotly debated (Finch and Allison, 2007). For Mg 2+ , the change of coordination from six in the aqueous ion to nine, if it is assumed to be replacing structural Ca (Rao and Mehrotra, 1978), is unlikely to occur. In contrast to calcite, aragonite is known to preferentially incorporate metal ions with ion radii larger than Ca 2+ (Böttcher and Dietzel, 2010).…”

Phase transformation studies on pure and doped strontium carbonate

“…cation vacancy, etc. ; these changes markedly effect phase transformation of solids (Subba Rao et al 1968;Rao and Mehrotra 1978). In the present investigation, the kinetics and energetics of orthorhombic-hexagonal transformation of strontium carbonate with known amounts of different impurity cations have been studied.…”