Hostname: page-component-586b7cd67f-dlnhk Total loading time: 0 Render date: 2024-11-26T11:07:08.914Z Has data issue: false hasContentIssue false
  • English
  • Français

Heat capacity of lazulite, MgAl2(PO4)2(OH)2, from 35 to 298 K and a (S–V) value for P2O5 to estimate phosphate entropy

Published online by Cambridge University Press:  05 July 2018

F. Brunet ,
D. Morineau  and
P. Schmid-Beurmann
F. Brunet*
Affiliation:
Laboratoire de Géologie, CNRS-UMR 8538, Ecole normale supérieure, 24 rue Lhomond, F-75005 Paris, France
D. Morineau
Affiliation:
Laboratoire de Chimie Physique, UMR 8000, Université Paris-sud, Bat. 349, F-91405 Orsay, France
P. Schmid-Beurmann
Affiliation:
Institut für Geowissenschaften, Universität Kiel, Olshausenstr. 40, D-24118 Kiel, Germany
*
*E-mail: [email protected]
Get access Rights & Permissions [Opens in a new window]

Abstract

The heat capacity of synthetic lazulite, MgAl2(PO4)2(OH)2, has been measured between 35 and 298 K by means of low-temperature adiabatic calorimetry. A lazulite third-law entropy (S2980) value of 204(3) J K–1 mol–1 was retrieved after extrapolation of the lazulite heat capacity by a cubic temperature function, down to absolute temperature. Identical measurements on α-Al2O3 yielded S2980 = 51.2 J mol–1 K–1 instead of the recommended 50.94 J mol–1 K–1 value. This new lazulite third-law entropy along with other phosphate entropy data either derived from low-temperature adiabatic calorimetry or experimental phase equilibria under pressure and temperature, were computed to retrieve a (S–V)P2O5 value of 57.4(2.9) to predict phosphate entropies from oxide summation. The predicted third-law entropy for trolleite, Al4(PO4)3(OH)3, amounts to 285.4(8.5) J mol–1 K–1 ~13% higher than the previously published value. We propose a new formation enthalpy from the elements of –6504.2 kJ mol–1 and a new third-law entropy of 281.7 J mol–1 K–1 for trolleite, compatible with the predicted entropy from oxide summation as well as with the published brackets on the trolleite = berlinite + corundum + water reaction.

Keywords

heat capacitylazulitephosphateentropytrolleite
Type
Research Article
Information
Mineralogical Magazine , Volume 68 , Issue 1 , February 2004 , pp. 123 - 134
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2004

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Abernathy, S.A. and Blanchard, N.F. (1982) Variation in unit cell parameters and in the X-ray diffraction intensity ratio I(200)/I(100) in the lazulite-scorzalite series. American Mineralogist, 67, 610–614.Google Scholar
Amthauer, G. and Rossman, G.R. (1984) Mixed valence of iron in mineral with cation clusters. Physics and Chemistry of Minerals, 11, 37–51.CrossRefGoogle Scholar
Andrut, M., Hammer, V.M.F., Lengauer, C.L., Ntaflos, T. and Redhammer, G.J. (2001) Schleifwü rdiger grü ner Lazulith aus Pakistan. Zeitschrift der deutsche n Gemmologischen Gesellschaft, 50, 65–74.Google Scholar
Bass, J.D. and Sclar, C.B. (1979) The stability of trolleite and the Al2O3-AlPO4-H2O phase diagram. American Mineralogist, 64, 1175–1183.Google Scholar
Brunet, F. and Chopin, C. (1995) Bear thite, Ca2Al(PO4)2OH: synthesis, stability and thermodynamic properties. Contributions to Mineralogy and Petrology, 121, 258–266.CrossRefGoogle Scholar
Brunet, F. and Vielzeuf, D. (1996) The farringtonite/ Mg3(PO4)2-II transformation: a new curve for pressure calibration in piston-cylinder apparatus. European Journal of Mineralogy, 8, 349–354.CrossRefGoogle Scholar
Brunet, F., Chopin, C. and Seifert, F. (1998) Phase relations in the MgO-P2O5-H2O system and the stability of phosphoellenbergerite. Petrological implications. Contribut ions to Mineralogy and Petrology, 131, 54–70.CrossRefGoogle Scholar
Cemič, L. and Schmid-Beurmann, P. (1995) Lazulite stability relations in the system Al2O3-AlPO4-Mg3(PO4)2-H2O. Euopean Journal of Mineralogy, 7, 921–929.CrossRefGoogle Scholar
Cortesogno, L., Gagerro, L. and Lucchetti, G. (1987) Phosphate mineralizations in a permo-triassic sequence (Giogo di Toirano, Italy). Neues Jahrbuch für Mineralogie Monatshefte, 1987, 305–313.Google Scholar
Furukawa, G.T., Douglas, T.B., McCoskey, R.E. and Ginnings, D.C. (1956) Thermal Properties of Aluminum Oxide From 0° to 1,200° K. Journal of Research of the National Bureau of Standards, 57, 67–82.CrossRefGoogle Scholar
Gottfried, J.M., Schmidt, K.J., Schroeder, S.L.M. and Christmann, K. (2002) Spontaneous and electroninduced adsorption of oxygen on Au(110)-(162). Surface Science, 511, 65–82.CrossRefGoogle Scholar
Holland, T.J.B. (1989) Dependence of entropy on volume for silicate and oxide minerals: A review and a predictive model. American Mineralogist, 74, 5–13.Google Scholar
Lengauer, C.L. (1993) HILL8. Institut für Mineralogie, Kristallographie und Strukturchemie der Universität Wien, Austria.Google Scholar
Leyx, C., Chopin, C. and Brunet, F. (2002) Towards a thermodynamic database for phosphate minerals: Elastic properties of Mg-phosphates and phase relations in the system MgO-Al2O3-P2O5-SiO2- H2O. EMPG IX (Zürich), Journal of Conference Abstracts, 7, 64.Google Scholar
Morteani, G. and Ackermand, D. (1996) Aluminium phosphates in muscovite-kyanite metaquartzites from Passo di Vizze (Alto Adige, Italy). European Journal of Mineralogy, 8, 853–859.CrossRefGoogle Scholar
Oetting, F.L. and McDonald, R.A. (1963) The thermodynamic properties of magnesium orthophosphate and magnesium pyrophosphate. Journal of Physical Chemistry, 67, 2737–2743.CrossRefGoogle Scholar
Robie, R.A., Hemingway, B.S. and Fisher, J.R. (1978) Thermodynamic properties of minerals and related substances at 298.15 K and 1 bar (105 pascals) pressure and at higher temperatures. US Geological Survey Bulletin, 1452, (reprinted with corrections 1979, 456 pp.).Google Scholar
Schmid-Beurmann, P., Morteani, G. and Cemič, L. (1997) Experimental determination of the upper stability of scorzalite, FeAl2[OH/PO4]2, and the occurrence of minerals with a composition intermediate between scorzalite and lazulite(ss) up to the conditions of the amphibolite facies. Mineralogy and Petrology, 61, 211–222.CrossRefGoogle Scholar
Schmid-Beurmann, P., Brunet, F. and Lathe, C. (2002) Thermodynamic properties of Mg-Al phosphates: Polymorphism and stability of MgAlPO4O, a key phase in the MgO-Al2O3-P2O5-H2O lazulite system. EMPG IX (Zürich), Journal of Conference Abstracts, 7, 94.Google Scholar
Wise, W.S. and Loh, S.E. (1976) Equilibria and origin of minerals in the system Al2O3-AlPO4-H2O. American Mineralogist, 61, 409–413.Google Scholar