Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Sugawara, T. Articles by Akaogi, M. Search for Related Content GeoRef GeoRef Citation

Calorimetry of liquids in the system Na₂O-Fe₂O₃-SiO₂

Department of Chemistry, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan

Transposed-temperature, drop-calorimetry measurements were performed in the systems Na₂SiO₃-Fe₂O₃-SiO₂ and Na₂SiO₃-NaFeSi₂O₆ at 1373 K to investigate thermodynamic properties of Fe³⁺-bearing silicate liquids. The results confirm previously measured enthalpy of Na₂SiO₃ and SiO₂ melts. No significant heats of mixing were observed in the Na₂SiO₃-SiO₂ liquids or in peralkaline liquids in the system Na₂SiO₃-Fe₂O₃. The enthalpy of mixing of peralkaline liquids in the system Na₂SiO₃-Fe₂O₃-SiO₂ was less than the standard deviation of drop calorimetry (approx. ±10 kJ/mol). From calorimetric data of Na₂SiO₃-Fe₂O₃ liquids extrapolated to hematite composition and published heat capacity, the enthalpy of fusion of hematite is estimated to be 83.3 ± 10.5 kJ/mol at 1373 K and 133.4 ± 10.5 kJ/mol at its melting point 1895 K. The Fe³⁺/Fe²⁺ ratio of the liquid was estimated from thermodynamic calculations using the fusion enthalpy of hematite and published data of FeO and O₂, and reproduced measured Fe³⁺/Fe²⁺ ratios in natural silicate liquids and in CaO-Al₂O₃-Fe₂O₃-FeO-SiO₂ liquids. No significant heats of mixing were observed in the Na₂SiO₃-NaFeSi₂O₆ liquids. The enthalpy of formation of NaFeSi₂O₆ (acmite) at 1bar and 298 K calculated from calorimetric data is –2546.9 ± 17 kJ/mol. The enthalpy and entropy of fusion of acmite are estimated to be 70.5 ± 9.4 kJ/mol and 51.3 ± 6.8 J/K-mol, respectively, at metastable congruent melting point, 1373 K. The entropy of fusion of acmite is similar to that of NaAlSi₂O₆ (jadeite), indicating that Fe³⁺ and Al³⁺ have analogous structural roles in pyroxene melts.

This article has been cited by other articles:

				V. E. Payne, R. E. M. Rickaby, L. G. Benning, and S. Shaw Calcite crystal growth orientation: implications for trace metal uptake into coccoliths Mineralogical Magazine, February 1, 2008; 72(1): 269 - 272. [Abstract] [Full Text] [PDF]