The high-temperature heat capacity of natural calcite (CaCO3) |
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Authors: | Gary K. Jacobs Derrill M. Kerrick Kenneth M. Krupka |
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Affiliation: | 1. Department of Geosciences, The Pennsylvania State University, 16802, University Park, Pennsylvania, USA
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Abstract: | The heat capacity (C P) of a natural sample of calcite (CaCO3) has been measured from 350 to 775 K by differential scanning calorimetry (DSC). Heat capacities determined for a powdered sample and a single-crystal disc are in close agreement and have a total uncertainty of ±1 percent. The following equation for the heat capacity of calcite from 298 to 775 K was fit by least squares to the experimental data and constrained to join smoothly with the low-temperature heat capacity data of Staveley and Linford (1969) (C P in J mol?1 K?1, T in K): $$begin{gathered} C_p = - 184.79 + 0.32322T - 3,688,200T^{ - 2} hfill {text{ }} - (1.2974{text{ }} times {text{ 10}}^{ - {text{4}}} )T^2 + 3,883.5T^{ - 1/2} hfill end{gathered} $$ Combining this equation with the S 298 0 value from Staveley and Linford (1969), entropies for calcite are calculated and presented to 775 K. A simple method of extrapolating the heat capacity function of calcite above 775 K is presented. This method provides accurate entropies of calcite for high-temperature thermodynamic calculations, as evidenced by calculation of the equilibrium: CaCO3 (s)=CaO(s)+CO2 (s). |
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