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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of agricultural and food chemistry 2 (1954), S. 970-976 
    ISSN: 1520-5118
    Source: ACS Legacy Archives
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Analytical chemistry 22 (1950), S. 215-221 
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 172 (1953), S. 166-167 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Pursuing these studies further, specimens of the Suket Shales (containing well-preserved specimens of Fermoria) belonging to the upper part of the Semri series1 of the Lower Vindhyans, near Rampura (lat. 24 28'; long. 75 26'), Central India (now Madhya Bharat), were treated with hydrofluoric acid ...
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  • 4
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A composition-graded solid electrolyte has been used to determine the standard Gibbs free energy of formation of lanthanum zirconate (La2Zr2O7) from the component oxides lanthana (La2O3) (A-rare earth) and zirconia (ZrO2) (monoclinic) in the temperature range of 870–1240 K. The cell used for measurement can be represented as Pt, O2, CaO + CaF2∥ CaF2| (LaF3)x(CaF2)1-x∥LaF3+ La2Zr2O7+ ZrO2, O2, Pt x=0 x=0.32 A composition-graded electrolyte has been introduced to compensate the solubility effects of the electrode material (lanthanum fluoride, LaF3) in the solid electrolyte (calcium fluoride, CaF2). The ability of the graded electrolyte to gen-erate a Nernstian response is demonstrated, using electrodes with known fluorine chemical potentials. For the reaction La2O3 (A-rare earth) + 2ZrO2 (monoclinic) → La2Zr2O7 (pyrochlore), the Gibbs free energy change (ΔG°f,ox) is given by the formula −133800 −10.32T (±4500) (in units of J/mol). The enthalpy and entropy of formation of La2Zr2O7 obtained in this study are in good agreement with calorimetric data. The “third-law” enthalpy of formation of La2Zr2O7, from the component oxides at 298.15 K, is −133.8 ± 5 kJ/mol.
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  • 5
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Solid-state miscibility gap in the pseudo-binary calcium oxide-strontium oxide (CaO-SrO) system is delineated by X-ray diffractometry studies on samples equilibrated either under vacuum or in a flowing inert-gas atmosphere at temperatures of 973-1273 K. For the CaxSr1−xO solid solution, an asymmetric phase boundary that is characterized by a critical temperature of 1173 (±3) K and a composition of x= 0.53 (±0.01) is obtained. The excess Gibbs energy of mixing of the solid solution, which is derived from the experimental phase-boundary compositions and temperatures, can be represented by the expression ΔGE=x (1−x)[(27040 − 5.82 T) x+ (24915 − 5.34 T)(1 −x)] (in units of J/mol). It is necessary to include excess entropy terms to obtain a good fit to the experimental data. The chemical spinodal curve is computed from the thermodynamic parameters. The results obtained in this study are compared with phase-diagram and calorimetric information that is available in the literature.
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  • 6
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The standard Gibbs energy of formation of the spinel MgAl2O4 from component oxides, MgO and α-Al2O3, has been determined in the temperature range 900 to 1250 K using a solid-state cell incorporating single-crystal CaF2 as the solid electrolyte. The cell can be represented as—Pt,O2,MgO+MgF2|CaF2|MgF2+MgAl2O4+α-Al2O3,O2,Pt—The standard Gibbs energy of formation from binary oxides, computed from the reversible emf, can be represented by the expression—capdeltaG°f,ox=−23600 − 5.91T(±150) J/mol—The ‘second-law’ enthalpy of formation of MgAl2O4 obtained in this study is in good agreement with high-temperature solution calorimetric studies reported in the literature.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Geologische Rundschau 85 (1996), S. 19-28 
    ISSN: 0016-7835
    Keywords: Key words Anastomoses ; Crystal zoning ; Snow bands ; Liesegang rings ; Ostwald ripening ; Self organization ; Siderite ; Supersaturation theory ; Zebra rock
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Morphological instabilities in periodic patterns occurring both in precipitation and crystallization processes (Liesegang rings and crystal zoning) are investigated and compared with similar patterns in geological samples (zebra rocks and mud bands in snow sediments). In classical Liesegang systems, undisturbed parallel or concentric precipitation bands are emanated from even or concentric diffusion sources in homogeneous diffusion matrices of gelatine or other gels. In the case of superposing diffusion sources, sources with undulatory curvatures or local diffusion barriers there may occur several types of instabilities within the sequence of regular patterns: (a) gaps within the bands forming radial alleys free of precipitate, (b) transition from broken bands to speckled patterns and (c) apparent branching of bands linked together by so-called anastomoses. Calculations with a competitive particle growth (CPG) model show that lateral instabilities in Liesegang bands (gaps and radial alleys of gaps) are the result of Ostwald ripening effects taking place after precipitation. Apparent branching of bands or formation of anastomoses can be simulated with a prenucleation model according to Ostwald's supersaturation theory. Similar irregularities can be observed in zebra rocks (e.g. banded siderite) whose bandings are commonly explained by sequential sedimentation processes. A very different mechanism is assumed to be responsible for the origin of mud bands in snow sediments. An initially homogeneous distribution of intrinsic mud in snow sediments can be arranged into parallel bands according to a crystal zoning mechanism which is based on repeated thawing and freezing of the snow sediment due to the daily alternation of sun and darkness.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Geologische Rundschau 85 (1996), S. 29-37 
    ISSN: 0016-7835
    Keywords: Key words Banded mineralization ; Harz mountains ; Self-organization ; Iron ; manganese ; ferrihydrite ; birnessite ; Time-series analysis ; Aquatic systems ; Iron bacteria ; Ostwald ripening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  A recent early diagenetic banded iron–manganese mud has been forming underground in a closed lead–zinc mine for approximately 40 years. The processes leading to the banded structure of the precipitate were studied during a period of 2 years. Therefore, 19 physical and chemical parameters were measured regularly in short intervals. The resulting time series were analysed with respect to the data sets of the monthly chemical analyses of the descendent mine water, the daily rainfall and the mineral content. The results reveal that the precipitated material undergoes internal self-organization due to interaction of redox, colloid-chemical, microbial, electrical and ripening processes, and not exclusively produced by seasonal fluctuations of material input. Thus, the primary banding of the material, caused by externally forced fluctuations of the redox conditions within the mine water, is reorganized after a short time. The finally observed bands are controlled by non-linear coupling of reaction and transport processes within the mud. A genetic model for the banded mineralization was developed and verified by numerical simulation.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    International journal of earth sciences 85 (1996), S. 19-28 
    ISSN: 1437-3262
    Keywords: Anastomoses ; Crystal zoning ; Snow bands ; Liesegang rings ; Ostwald ripening ; Self organization ; Siderite ; Supersaturation theory ; Zebra rock
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Morphological instabilities in periodic patterns occurring both in precipitation and crystallization processes (Liesegang rings and crystal zoning) are investigated and compared with similar patterns in geological samples (zebra rocks and mud bands in snow sediments). In classical Liesegang systems, undisturbed parallel or concentric precipitation bands are emanated from even or concentric diffusion sources in homogeneous diffusion matrices of gelatine or other gels. In the case of superposing diffusion sources, sources with undulatory curvatures or local diffusion barriers there may occur several types of instabilities within the sequence of regular patterns: (a) gaps within the bands forming radial alleys free of precipitate, (b) transition from broken bands to speckled patterns and (c) apparent branching of bands linked together by so-called anastomoses. Calculations with a competitive particle growth (CPG) model show that lateral instabilities in Liesegang bands (gaps and radial alleys of gaps) are the result of Ostwald ripening effects taking place after precipitation. Apparent branching of bands or formation of anastomoses can be simulated with a prenucleation model according to Ostwald's supersaturation theory. Similar irregularities can be observed in zebra rocks (e.g. banded siderite) whose bandings are commonly explained by sequential sedimentation processes. A very different mechanism is assumed to be responsible for the origin of mud bands in snow sediments. An initially homogeneous distribution of intrinsic mud in snow sediments can be arranged into parallel bands according to a crystal zoning mechanism which is based on repeated thawing and freezing of the snow sediment due to the daily alternation of sun and darkness.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    International journal of earth sciences 85 (1996), S. 29-37 
    ISSN: 1437-3262
    Keywords: Banded mineralization ; Harz mountains ; Self-organization ; Iron, manganese, ferrihydrite, birnessite ; Time-series analysis ; Aquatic systems ; Iron bacteria ; Ostwald ripening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract A recent early diagenetic banded iron-manganese mud has been forming underground in a closed lead-zinc mine for approximately 40 years. The processes leading to the banded structure of the precipitate were studied during a period of 2 years. Therefore, 19 physical and chemical parameters were measured regularly in short intervals. The resulting time series were analysed with respect to the data sets of the monthly chemical analyses of the descendent mine water, the daily rainfall and the mineral content. The results reveal that the precipitated material undergoes internal self-organization due to interaction of redox, colloid-chemical, microbial, electrical and ripening processes, and not exclusively produced by seasonal fluctuations of material input. Thus, the primary banding of the material, caused by externally forced fluctuations of the redox conditions within the mine water, is reorganized after a short time. The finally observed bands are controlled by non-linear coupling of reaction and transport processes within the mud. A genetic model for the banded mineralization was developed and verified by numerical simulation.
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