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 (11) Citing Articles via Google Scholar Google Scholar Articles by Majzlan, J. Articles by Casey, W. H. Search for Related Content GeoRef GeoRef Citation

SURFACE ENTHALPY OF BOEHMITE

¹ Thermochemistry Facility, Department of Geology, University of California at Davis, Davis, California 95616, USA
² Land, Water, and Air Resources, University of California at Davis, Davis, California 95616, USA

E-mail of corresponding author: jmajzlan{at}ucdavis.edu

The persistence of many seemingly metastable mineral assemblages in sediments and soils is commonly attributed to their sluggish transformation to the stable-phase assemblage. Although undoubtedly kinetics plays a major role, this study shows that thermodynamic factors, particularly surface energy, significantly influence the free energy. Enthalpies of formation of boehmite samples with variable surface area were derived using high-temperature oxide-melt calorimetry. The average surface enthalpy for all faces terminating boehmite particles was calculated at +0.52 ± 0.12 J/m². This value represents the surface enthalpy for surfaces exposed to vacuum assuming that H₂O adsorbed on the surface of boehmite is loosely bound. These results show that the enthalpy of formation of boehmite may vary by 8 kJ/mol as a function of particle size. An overview of published values of surface energies of gibbsite, -Al₂O₃, corundum, and the results here indicates that the hydrated phases (boehmite, gibbsite) have lower surface energies than the anhydrous phases (corundum, -Al₂O₃). Lower surface energies allow the hydrated phases to maintain high surface area, i.e., small particle size. Similar surface energies of boehmite and gibbsite suggest kinetic control favoring the crystallization of boehmite or gibbsite from aqueous solution. The enthalpy of formation of bulk boehmite from the elements was calculated at –994.0 ± 1.1 kJ/mol. Combining this result with the data in existing thermodynamic databases, we confirm that bulk boehmite is metastable with respect to bulk diaspore at ambient conditions.

Key Words: Boehmite • Enthalpy of Formation • Surface Enthalpy

This article has been cited by other articles:

				A. Navrotsky, L. Mazeina, and J. Majzlan Size-Driven Structural and Thermodynamic Complexity in Iron Oxides Science, March 21, 2008; 319(5870): 1635 - 1638. [Abstract] [Full Text] [PDF]

				L. Mazeina and A. Navrotsky SURFACE ENTHALPY OF GOETHITE Clays and Clay Minerals, April 1, 2005; 53(2): 113 - 122. [Abstract] [Full Text] [PDF]

				A. Navrotsky Energetic clues to pathways to biomineralization: Precursors, clusters, and nanoparticles PNAS, August 17, 2004; 101(33): 12096 - 12101. [Abstract] [Full Text] [PDF]

				S. Utsunomiya, S. Utsunomiya, S. C. Peters, J. D. Blum, and R. C. Ewing Nanoscale mineralogy of arsenic in a region of New Hampshire with elevated As-concentrations in the groundwater American Mineralogist, November 1, 2003; 88(11-12): 1844 - 1852. [Abstract] [Full Text] [PDF]