Thermochemical study of natural pollucite

  • Ogorodova L
  • Melchakova L
  • Kiseleva I
 et al. 
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Abstract

Experimental data on the heat capacities, enthalpies of formation from the oxides and elements of the natural pollucites: Cs0.77Na0.14Rb0.04Al0.91Si2.08O6·0.34H2O (Minas Gerais, Brazil) (I) and Cs0.84Na0.11Al0.88Si2.10O6·0.17H2O (East Siberia, Russia) (II) have been determined. The heat capacities of the pollucite (II) were measured by differential scanning calorimetry (DSC) method from T = 250 to 810K. A value of C°p,m(298.15K) = 172.2 J K-1mol-1was obtained and the resultant C°p,m(T) equation in the interval T = 298.15-610 K was calculated: C°p,m= 131.37 + 181.97 × 10-3T - 11.84 × 105T-2J K-1mol-1(±0.36%). The standard enthalpies of formation were determined by a set of thermochemical cycles using decomposition and subsequent dissolution of the dehydration products in molten lead borate at T = 973 K. Values of ΔfH°m(298.15 K) are found to be -3104 ± 13 kJ mol-1(pollucite I) and -3090 ± 14 kJ mol-1(pollucite II). The values of ΔfG°m(298.15 K) were calculated as -2921 kJ mol-1(pollucite I) and -2911 kJ mol-1(pollucite II). © 2003 Elsevier Science B.V. All rights reserved.

Author-supplied keywords

  • Enthalpy of formation
  • Heat capacity
  • Pollucite
  • Thermochemistry

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Authors

  • L. P. Ogorodova

  • L. V. Melchakova

  • I. A. Kiseleva

  • I. A. Belitsky

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