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  • 1
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    Enthalpies of formation of rare earth niobates, RE3NbO7 (2015)
    Mineralogical Society of America
    Details
    Publication Date: 2015-07-02
    Description: High-temperature oxide melt solution calorimetry was used to investigate energetics of a series of rare earth niobates RE 3 NbO 7 . All of investigated compounds were found to be stable in enthalpy in respect to their oxides. The enthalpy of formation from oxides becomes more exothermic as the size of the RE cation increases, a trend seen previously in other RE compounds including pyrochlores, perovskites, and phosphates. For smaller RE cations the enthalpy of exchange of RE between niobates and titanates is close to zero, whereas larger RE are energetically favored in the titanate pyrochlores. Implications of the results from the geochemical and material engineering points of view are discussed.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 2
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    Energetics of lanthanide-doped calcium phosphate apatite (2014)
    Mineralogical Society of America
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    Publication Date: 2014-11-19
    Description: Lanthanides "Ln" (rare earths) are critical elements found in natural minerals such as calcium phosphate apatites, in sedimentary and igneous settings as well as in skeletal diagenesis. From a medical point of view, nanoparticles of lanthanide-doped apatites can be produced for conferring luminescence properties of interest in cancer cells detection. However, the impact of the substitution of Ln for Ca on the stability and solubility of related apatite phases is still essentially unknown. To investigate the thermochemical effects of such lanthanide substitution for calcium in apatite, we prepared and analyzed four series of apatites with up to 10% lanthanide substitution for calcium. After thorough physicochemical characterization via complementary techniques (XRD, FTIR, TG/DSC, and IPC-AES), high-temperature oxide melt solution calorimetry in molten sodium molybdate at 973 K was performed to determine their enthalpies of formation from constituent oxides and from the elements, at 298 K. Our results indicate that although enthalpies of formation are strongly exothermic in all cases, Ln-doping has a destabilizing effect, which increases with dopant concentration and with the size of the incorporated Ln 3+ ion. After estimating standard entropies, Gibbs free energies of formation and equilibrium constants for Ca 2+ /Ln 3+ exchange reactions in apatite were then evaluated, for the first time allowing access to quantitative thermodynamic data that may be used in various fields for stability calculations or partitioning estimates between fluids and solids.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
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  • 3
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    Thermochemistry of rare earth perovskites Na3xRE0.67-xTiO3 (RE = La, Ce) (2016)
    Mineralogical Society of America
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    Publication Date: 2016-05-03
    Description: High-temperature oxide melt solution calorimetry using sodium molybdate (3Na 2 O·4MoO 3 ) solvent at 973 K was performed for the Na 3 x RE 0 . 67– x TiO 3 (RE = La, Ce) perovskite series. The enthalpies of formation of lanthanum perovskites from oxides (La 2 O 3 , Na 2 O, TiO 2 ), are –107.25 ± 2.56, –93.83 ± 6.06, –80.68 ± 5.93, and –33.49 ± 4.26 kJ/mol and enthalpies of formation from elements are –1614.05 ± 5.37, –1596.44 ± 7.68, –1594.03 ± 7.58, and –1577.56 ± 6.36 kJ/mol for Na 0.459 La 0.522 Ti 0.999 O 3 , Na 0.454 La 0.523 Ti 0.994 O 3 , Na 0.380 La 0.567 Ti 0.980 O 3 , and La 0.692 Ti 0.979 O 3 , respectively. The enthalpies of formation of cerium perovskites are –99.98 ± 5.78 and –45.78 ± 3.30 kJ/mol from oxides (Ce 2 O 3 , Na 2 O, TiO 2 ), and –1611.34 ± 6.90 and –1602.06 ± 2.72 kJ/mol from elements for Na 0.442 Ce 0.547 Ti 0.980 O 3 and Ce 0.72 Ti 0.96 O 3 . The A- site defect perovskites become more stable relative to oxide components as sodium contents increase. Na 0.5 Ce 0.5 TiO 3 and Na 0.5 La 0.5 TiO 3 could be considered as thermodynamically stable end-members in natural loparite minerals, in which these end-members are in solid solution with CaTiO 3 and other components.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
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  • 4
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    Thermodynamics of NiAl2O4–NiFe2O4 Spinel Solid Solutions (2011)
    Wiley
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    Publication Date: 2011-11-24
    Description: NiAl 2 O 4 , NiFe 2 O 4 , and their solid solution Ni(Fe z Al 1− z ) 2 O 4 have been studied using high temperature oxide melt solution calorimetry in molten 2PbO·B 2 O 3 at 973 K. X-ray absorption near edge structure (XANES) measurements and Mössbauer spectroscopy investigation of the cation distribution showed that the Ni fraction in octahedral sites increases with increasing iron content. Despite the zero heat of mixing, the solid solution is not thermodynamically ideal in the sense of Raoult's law. The entropies of mixing are similar to those for a solid solution of two inverse spinels and the activities are approximated as the square of the mole fractions. The stability of the solid solutions relative to oxide components ( NiO , Al 2 O 3 , Fe 2 O 3 ) increases with increasing iron content. The solid solution is a suitable waste form for nickel from industrial processing with higher iron content potentially beneficial to its stability.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Wiley
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  • 5
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    Thermochemistry and aqueous solubilities of hydrotalcite-like solids (2002)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2002-04-27
    Description: Hydrotalcites are used in technology as catalysts and anion exchangers and are important sinks for environmental contaminants. Their compositional variability makes it important, but difficult, to estimate their aqueous solubility. We report calorimetric measurements of the heats of formation of cobalt-aluminum hydrotalcite phases. The heat and free energy of formation from the elements are equal to those of mechanical mixtures of binary compounds, namely hydroxides and carbonates. The interlayer anion is much more important than the cation in determining the solubility of the hydrotalcite phase and its ability to contain or release heavy metals to the environment. Because hydrotalcites do not have an unreactive polymer as a structural core, their aqueous stability will change dramatically with composition, particularly with anion content. This simple mechanical mixture model allows prediction of aqueous solubilities and trace metal retention in a variety of geochemical settings.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Allada, Rama kumar -- Navrotsky, Alexandra -- Berbeco, Hillary Thompson -- Casey, William H -- New York, N.Y. -- Science. 2002 Apr 26;296(5568):721-3.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Thermochemistry Facility, Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11976450" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 6
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    Negative Pressure-Temperature Slopes for Reactions Formign MgSiO3 Perovskite from Calorimetry (1990)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1990-09-14
    Description: A new and sensitive differential drop solution calorimetric technique was developed for very small samples. A single experiment using one 5.18-milligram sample of perovskite, synthesized at 25 gigapascals and 1873 Kelvin, gave 110.1 +/- 4.1 kilojoules per mole for the enthalpy of the ilmenite-pervoskite transition in MgSiO(3). The thermodynamics of the reaction of MgSiO(3) (ilmenite) to MgSiO(3) (perovskite) and of Mg(2)SiO(4) (spinel) to MgSiO(3) (pervoskite) and MgO (periclase) were assessed. Despite uncertainties in heat capacity and molar volume at high pressure and temperature, both reactions clearly have negative pressure-temperature slopes, -0.005 +/- 0.002 and -0.004 +/- 0.002 gigapascals per Kelvin, respectively. The latter may be insufficiently negative to preclude whole-mantle convection.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ito, E -- Akaogi, M -- Topor, L -- Navrotsky, A -- New York, N.Y. -- Science. 1990 Sep 14;249(4974):1275-8.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17835541" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 7
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    A clathrate reservoir hypothesis for Enceladus' south polar plume (2006)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2006-12-16
    Description: We hypothesize that active tectonic processes in the south polar terrain of Enceladus, the 500-kilometer-diameter moon of Saturn, are creating fractures that cause degassing of a clathrate reservoir to produce the plume documented by the instruments on the Cassini spacecraft. Advection of gas and ice transports energy, supplied at depth as latent heat of clathrate decomposition, to shallower levels, where it reappears as latent heat of condensation of ice. The plume itself, which has a discharge rate comparable to Old Faithful Geyser in Yellowstone National Park, probably represents small leaks from this massive advective system.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kieffer, Susan W -- Lu, Xinli -- Bethke, Craig M -- Spencer, John R -- Marshak, Stephen -- Navrotsky, Alexandra -- New York, N.Y. -- Science. 2006 Dec 15;314(5806):1764-6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Geology, University of Illinois at Urbana-Champaign, 1301 West Green Street, Urbana, IL 61801, USA. skieffer@uiuc.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17170301" target="_blank"〉PubMed〈/a〉
    Keywords: Carbon Dioxide ; Extraterrestrial Environment ; Gases ; *Ice ; Mathematics ; Methane ; Models, Theoretical ; Nitrogen ; Pressure ; *Saturn ; Spacecraft ; Temperature ; Water
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 8
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    Size-driven structural and thermodynamic complexity in iron oxides (2008)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2008-03-22
    Description: Iron oxides occur ubiquitously in environmental, geological, planetary, and technological settings. They exist in a rich variety of structures and hydration states. They are commonly fine-grained (nanophase) and poorly crystalline. This review summarizes recently measured thermodynamic data on their formation and surface energies. These data are essential for calculating the thermodynamic stability fields of the various iron oxide and oxyhydroxide phases and understanding their occurrence in natural and anthropogenic environments. The competition between surface enthalpy and the energetics of phase transformation leads to the general conclusion that polymorphs metastable as micrometer-sized or larger crystals can often be thermodynamically stabilized at the nanoscale. Such size-driven crossovers in stability help to explain patterns of occurrence of different iron oxides in nature.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Navrotsky, Alexandra -- Mazeina, Lena -- Majzlan, Juraj -- New York, N.Y. -- Science. 2008 Mar 21;319(5870):1635-8. doi: 10.1126/science.1148614.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Peter A. Rock Thermochemistry Laboratory and Nanomaterials in the Environment, Agriculture, and Technology Organized Research Unit, University of California, Davis, CA 95616, USA. anavrotsky@ucdavis.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18356516" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
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    Nuclear fuel in a reactor accident (2012)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2012-03-10
    Description: Nuclear accidents that lead to melting of a reactor core create heterogeneous materials containing hundreds of radionuclides, many with short half-lives. The long-lived fission products and transuranium elements within damaged fuel remain a concern for millennia. Currently, accurate fundamental models for the prediction of release rates of radionuclides from fuel, especially in contact with water, after an accident remain limited. Relatively little is known about fuel corrosion and radionuclide release under the extreme chemical, radiation, and thermal conditions during and subsequent to a nuclear accident. We review the current understanding of nuclear fuel interactions with the environment, including studies over the relatively narrow range of geochemical, hydrological, and radiation environments relevant to geological repository performance, and discuss priorities for research needed to develop future predictive models.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Burns, Peter C -- Ewing, Rodney C -- Navrotsky, Alexandra -- New York, N.Y. -- Science. 2012 Mar 9;335(6073):1184-8. doi: 10.1126/science.1211285.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Civil Engineering and Geological Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556, USA. pburns@nd.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22403382" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 10
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    Stability of peroxide-containing uranyl minerals (2003)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2003-11-15
    Description: Minerals containing peroxide are limited to studtite, (UO2)O2(H2O)4, and metastudtite, (UO2)O2(H2O)2. High-temperature oxide-melt solution calorimetry and solubility measurements for studtite (standard enthalpy of formation at 298 kelvin is -2344.7 +/- 4.0 kilojoules per mole from the elements) establishes that these phases are stable in peroxide-bearing environments, even at low H2O2 concentrations. Natural radioactivity in a uranium deposit, or the radioactivity of nuclear waste, can create sufficient H2O2 by alpha radiolysis of water for studtite formation. Studtite and metastudtite may be important alteration phases of nuclear waste in a geological repository and of spent fuel under any long-term storage, possibly at the expense of the commonly expected uranyl oxide hydrates and uranyl silicates.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kubatko, Karrie-Ann Hughes -- Helean, Katheryn B -- Navrotsky, Alexandra -- Burns, Peter C -- New York, N.Y. -- Science. 2003 Nov 14;302(5648):1191-3.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Civil Engineering and Geological Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/14615533" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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