Abstract
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, γ-Al2O3, corundum, and the results here indicates that the hydrated phases (boehmite, gibbsite) have lower surface energies than the anhydrous phases (corundum, γ-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.
Similar content being viewed by others
References
Anovitz, L.M., Allard, L.F., Porter, W.D., Coffey, D.W., Benezeth, P., Palmer, D.A., and Wesolowski, D.J. (1999) Microstructural characterization of water-rich boehmite (AlO(OH)): TEM correlation of apparently divergent XRD and TGA results. Microscopy and Microanalysis: Proceedings of Microscopy and Microanalysis’ 99, Volume 5, Supplement 2, 540–541.
Anovitz, L.M., Perkins, D., and Essene, E.J. (1991) Metastability in near-surface rocks of minerals in the system Al, Or SiO2-H2O. Clays and Clay Minerals, 39, 225–233.
Apps, J.A., Neil, J.M., and Jun, C.-H. (1989) Thermochemical Properties of Gibbsite, Bayerite, Boehmite, Diaspore, and the Aluminate Ion Between 0 and 350°C. U.S. Nuclear Regulatory Commission, Washington, D.C., 98 pp.
Baker, B.R. and Pearson, R.M. (1974) Water content of pseudoboehmite: A new model for its structure. Journal of Catalysis, 33, 265–278.
Bardossy, G. and Aleva, G.J.J. (1990) Lateritic bauxites. Developments in Economic Geology, Volume 27, Elsevier, 624 pp.
Bellotto, M., Rebours, B., and Euzen, P. (1998) Mechanism of pseudo-boehmite dehydration: Influence of reagent structure and reaction kinetics on the transformation sequence. Materials Science Forum Volumes, 278–281, 572–577.
Blonski, S. and Garofalini, S.H. (1993) Molecular dynamics simulation of a-alumina and y alumina surfaces. Surface Science, 295, 263–274.
Bloom, P.R. and Weaver, R.M. (1982) Effect of removal of reactive surface material on the solubility of synthetic gibbsites. Clays and Clay Minerals, 30, 281–286.
Bradley, S.M., Kydd, R.A., and Howe, R.F. (1993) The structure of Al-gels formed through base hydrolysis of Al3+ aqueous solutions. Journal of Colloid Interface Science, 159, 405–412.
Bradley, S.M. and Hanna, J.V. (1994)27 Al and 23Na MAS NMR and powder X-ray diffraction studies of sodium aluminate spéciation and the mechanistics of aluminum hydroxide precipitation upon acid hydrolysis. Journal of the American Chemical Society, 116, 7771–7783.
Buol, S.W., Hole, F.D., and McCracken, R.J. (1989) Soil Genesis and Classification. Iowa State University Press, 446 pp.
Brunauer, S., Emmett, P.H., and Teller, E. (1938) Adsorption of gases in multimolecular layers. Journal of the American Chemical Society, 60, 309–319.
Causa, M., Dovesi, R., Pisani, C., and Roetti, C. (1989) Ab initio characterization of the (0001) and (1010) crystal faces of a-alumina. Surface Science, 215, 259–271.
Chesworth, W. (1972) The stability of gibbsite and boehmite at the surface of the Earth. Clays and Clay Minerals, 20, 369–374.
Dyer, C., Hendra, P.J., Forsling, W., and Ranheimer, M. (1993) Surface hydration of aqueous γ-Al2O3, studied by Fourier transform Raman and infrared spectroscopy-I. Initial results. Spectrochimica Acta, 49A, 691–705.
Efron, B. and Tibshirani, R.J. (1993) An Introduction to the Bootstrap. Chapman and Hall, 436 pp.
Fleming, S., Rohl, A., Lee, M.-Y., Gale, J., and Parkinson, G. (2000) Atomistic modeling of gibbsite: Surface structure and morphology. Journal of Crystal Growth, 209, 159–166.
Fu, G., Lazar, L.F., and Bain, A.D. (1991) Aging processes of alumina sol-gels: Characterization of new aluminum polycations by 27A1 spectroscopy. Chemistry of Materials, 3, 602–610.
Gregg, S.J. and Sing, K.S.W. (1982) Adsorption, Surface Area and Porosity. Academic Press, 303 pp.
Gribb, A.A. and Banfield, J.F. (1997) Particle size effects on transformation kinetics and phase stability in monocrystalline TiO2. American Mineralogist, 82, 717–728.
Haas, K.C., Schneider, W.F., Curioni, A., and Andreoni, W. (1998) The chemistry of water on alumina surfaces: Reaction dynamics from first principles. Science, 282, 265–268.
Hemingway, B.S., Robie, R.A., and Apps, J.A. (1991) Revised values for the thermodynamic properties of boehmite, AlO(OH), and related species and phases in the system Al-H-O. American Mineralogist, 76, 445–457.
Langel, W. and Parrinello, M. (1995) Ab initio molecular dynamics of H2O adsorbed on solid MgO. Journal of Chemical Physics, 103, 3240–3252.
Lindan, P.J.D., Harrison, N.M., Holender, J.M., and Gillan, M.J. (1996) First-principles molecular dynamics simulation of water dissociation on TiO2 (110). Chemical Physics Letters, 261, 246–252.
Mackrodt, W.C., Davey, R.J., and Black, S.N. (1987) The morphology of α-Al2O3, and α-Fe2O3: The importance of surface relaxation. Journal of Crystal Growth, 80, 441–446.
McHale, J.M., Auroux, A., Perrotta, A.J., and Navrotsky, A. (1997a) Surface energies and thermodynamic phase stability in nanocrystalline aluminas. Science, 277, 788–791.
McHale, J.M., Navrotsky, A., and Perrotta, A.J. (1997b) Effects of increased surface area and chemisorbed H2O on the relative stability of nanocrystalline γ-Al2O3 and α-Al2O3. The Journal of Physical Chemistry B, 101, 603–613.
McHardy, W.J. and Thomson, A.P. (1971) Conditions for the formation of bayerite and gibbsite. Mineralogical Magazine, 38, 358–368.
May, H.M., Helmke, P.A., and Jackson, M.L. (1979) Gibbsite solubility and thermodynamic properties of hydroxy-aluminum ions in aqueous solutions at 25°C. Geochimica et Cosmochimica Acta, 43, 861–868.
National Bureau of Standards Certificate: Standard Reference Material 720 (1982) Synthetic sapphire (α-Al2O3). Washington, D.C., April 1982.
Navrotsky, A. (1997) Progress and new directions in high temperature calorimetry revisited. Physics and Chemistry of Minerals, 24, 222–241.
Navrotsky, A., Rapp, R.P., Smelik, E., Burnley, P., Circone, S., Liang, C., and Kunal, B. (1994) The behavior of H2O and CO2 in high-temperature lead borate solution calorimetry of volatile-bearing phases. American Mineralogist, 79, 1099–1109.
Packter, A. (1979) Studies on recrystallized aluminium trihydroxide precipitates: The energetics of dissolution by sodium hydroxide solutions. Colloid and Polymer Science, 257, 977–980.
Penn, R.L., Banfield, J.F., and Kerrick, D.M. (1999) TEM investigation of Lewiston, Idaho, fibrolite: Microstructure and grain boundary energetics. American Mineralogist, 84, 152–159.
Peryea, F.J. and Kittrick, J.A. (1988) Relative solubility of corundum, gibbsite, boehmite, and diaspore at standard state conditions. Clays and Clay Minerals, 36, 391–396.
Robie, R.A. and Hemingway, B.S. (1995) Thermodynamic Properties of Minerals and Related Substances at 298.15 K and 1 bar (105 pascals) and at Higher Temperatures. U.S. Geological Survey Bulletin 2131, Washington, D.C., 461 pp.
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 (HP pascals) and at Higher Temperatures. U.S. Geological Survey Bulletin 1452, Washington, D.C., 456 pp.
Russell, A.S., Edwards, J.D., and Taylor, C.S. (1955) Solubility of hydrated aluminas in NaOH solutions. Journal of Metals, 203, 1123–1128.
Seichter, W., Mögel, H.-J., Brand, P., and Saleh, D. (1998) Crystal structure and formation of the aluminum hydroxide chloride [All3(OH)24)(H2O)24]Cl15·13H2O. European Journal of Inorganic Chemistry, 1998, 795–797.
Smith, R.W. and Hem, J.D. (1972) Effect of Aging on Aluminum Hydroxide Complexes in Dilute Aqueous Solutions. Geological Survey Water-Supply Paper 1827-D, Washington, D.C., 51 pp.
Tasker, P.W. (1984) Surfaces of magnesia and alumina. In Structure and Properties of MgO and Al2O3 Ceramics, Advances in Ceramics, Volume 10, W.D. Kingery, ed., 176–189.
Tettenhorst, R.T. and Hofmann, D.A. (1980) Crystal chemistry of boehmite. Clays and Clay Minerals, 28, 373–380.
Tosi, M.P. (1964) Cohesion of ionic solids in the Bom model. Solid State Physics, 16, 1–120.
Tsukada, T., Segawa, H., Yasumori, A., and Okada, K. (1999) Crystallinity of boehmite and its effect on the phase transition temperature of alumina. Journal of Materials Chemistry, 9, 549–553.
Wesolowski, D.J. and Palmer, D.A. (1994) Aluminum spéciation and equilibria in aqueous solution: V. Gibbsite solubility at 50°C and pH 3–9 in 0.1 molal NaCl solutions (a general model for aluminum spéciation; analytical methods). Geochimica et Cosmochimica Acta, 58, 2947–2969.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Majzlan, J., Navrotsky, A. & Casey, W.H. Surface Enthalpy of Boehmite. Clays Clay Miner. 48, 699–707 (2000). https://doi.org/10.1346/CCMN.2000.0480611
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1346/CCMN.2000.0480611