Thermodynamic Aspects of the Vaterite-Calcite Phase Transition |
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Authors: | G Wolf E Königsberger H G Schmidt L-C Königsberger H Gamsjäger |
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Institution: | (1) Department of Physical Chemistry, Technical University Bergakademie Freiberg, D-09596 Freiberg, Germany;(2) Department of Physical Chemistry, University of Leoben, A-8700 Leoben, Austria |
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Abstract: | Although vaterite is the least stable anhydrous calcium carbonate polymorph, it is formed as a metastable phase in some normal
and pathological biomineralisation processes. In this work, thermodynamic aspects of the vaterite-calcite phase transition
were comprehensively studied. Vaterite samples were prepared by different methods and characterised for the composition, crystal
structure, specific surface and grain size. All products were identified to be pure vaterite by careful X-ray diffraction
measurements. The enthalpy and Gibbs energy of transition were determined by precise calorimetric and potentiometric measurements.
The reliability of the thermodynamic data for the vaterite-calcite phase transition derived from this work was shown by the
use of different calorimetric methods to determine the enthalpy of transition and the independent measurements of heat capacity
and entropy of vaterite. Our recommended values are Δtrs
G*=−2.9±0.2 kJ mol−1 , Δ trs
H *=−3.4±0.2 kJ mol−1 and Δ trs
S *=−1.7±0.9 J K−1 mol−1 , where the uncertainties are given as twice the standard deviations.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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Keywords: | calcite calcium carbonate polymorphs phase transition thermodynamics vaterite |
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