U. Schwertmann

Technical University of Munich

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E. Murad

Bayerische Staatssammlung für Paläontologie und Geologie

R. M. Taylor

Commonwealth Scientific and Industrial Research Organisation

Darrell G. Schulze

Purdue University West Lafayette

Helge Stanjek

RWTH Aachen University

L. Carlson

Technical University of Munich

J. Torrent

University of Córdoba

H. Fechter

Technical University of Munich

R. W. Fitzpatrick

University of Adelaide

Vidal Barrón

University of Córdoba

G. Pfab

Technical University of Munich

Cooperative Institutions

Technical University of Munich

The Ohio State University

ETH Zurich

Leibniz University Hannover

Centre National de la Recherche Scientifique

Stanford University

University of Hohenheim

Weihenstephan-Triesdorf University of Applied Sciences

Technische Universität Berlin

University of California, Davis

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Influence of Al Substitution and Crystal Size on the Room-Temperature Mössbauer Spectrum of Hematite

Clays and Clay Minerals (1986)

E. Murad U. Schwertmann

Substitution (logic)

Crystal (programming language)

10.1346/ccmn.1986.0340101

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Citations (78)

Schwertmannite and the chemical modeling of iron in acid sulfate waters

Geochimica et Cosmochimica Acta (1996)

Jerry M. Bigham U. Schwertmann Samuel J. Traina Ronald Lee Winland Moritz Wolf

Schwertmannite

Ferrihydrite

Jarosite

Acid Mine Drainage

Lepidocrocite

10.1016/0016-7037(96)00091-9

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Citations (1,003)

PROPERTIES OF GOETHITE AND HEMATITE IN KAOLINITIC SOILS OF SOUTHERN AND CENTRAL BRAZIL

Soil Science (1985)

U. Schwertmann Nestor Kämpf

Iron oxides in clay fractions of Inceptisols, Ultisols, and Oxisols from Rio Grande do Sul and Goias State in southern and central Brazil, respectively, were essentially goethite and hematite. Their Al substitution was around 10 mole % for hematites and between 15 to 25 mole % for goethites in southern Brazil and around 15 and 33 mole %, respectively, for those in central Brazil. The ratio of the Al substitution of hematite and goethite in the same sample is concentrating around 0.5:1. The size of the hematite crystals as measured by XRD-line broadening was between 10 to 15 nm thick (along the z axis) and 20 to 30 nm wide (along the x axis). The goethite crystals generally appeared to be smaller, as judged from the speClfic surface area obtained from a correlation between line broadening and surface area of 42 synthetic goethites. Under the electron microscope goethite and hematite crystals look very much alike: they appear mainly as subrounded, isodimensional particles. Hexagonal (hematite) and aClcular (goethite) particles are rare. The Fe-oxide crystals appeared not to be closely assoClated with kaolinite crystals, but were aggregated among themselves.

10.1097/00010694-198504000-00008

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Citations (183)

Electron Micrographs of Soil Lepidocrocites

Clay Minerals (1973)

U. Schwertmann

An abstract is not available for this content so a preview has been provided. Please use the Get access link above for information on how to access this content.

Electron micrographs

Micrograph

Content (measure theory)

10.1180/claymin.1973.010.1.08

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Citations (7)

Die Tonminerale in einigen Marschen und ihr Verhalten gegenüber Kalium

Zeitschrift für Pflanzenernährung Düngung Bodenkunde (1961)

U. Schwertmann U. Politz

Der letzte Beitrag einer Serie von Arbeiten über die chemischen Eigenschaften einiger Marschprofile des Ems- und Weser-Jade-Gebietes (15) befaßte sich mit der Kaliumfixierung und -nachlieferung. Dabei ergaben sich zum Teil erhebliche Unterschiede zwischen den einzelnen Profilen, als deren Ursache Unterschiede im Tonmineralbestand vermutet wurden. Im folgenden wird diese Vermutung geprüft. Zu diesem Zweck wurden aus den eingehend beschriebenen 5 Marschprofilen (13, 14) von den 13 untersuchten Proben eine repräsentative Probe aus jedem Profil näher auf den Mineralbestand der Tonfraktion und dessen Reaktion auf die Zufuhr von Kalium untersucht.

10.1002/jpln.19610920305

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Citations (13)

The influence of crystallinity on the Mössbauer spectrum of lepidocrocite

Mineralogical Magazine (1984)

E. Murad U. Schwertmann

Abstract Particle morphology can result in very pronounced effects of crystallinity on the Mössbauer spectra of lepidocrocite. Such effects can noticeably increase the quadrupole splitting of poorly crystallized paramagnetic lepidocrocites, making it necessary to fit two doublets of different quadrupole splittings to Mössbauer spectra of such samples, and may lower the onset of magnetic ordering from the bulk Néel temperature of 77 ±1 K to about 50 K. At 4.2 K, distributions of magnetic hyperfine fields with a limiting upper field of 460 kOe are observed. The contributions of lower fields to such distributions increase with decreasing crystallinity, producing asymmetrically broadened resonant lines.

Lepidocrocite

Quadrupole splitting

Limiting

Diamagnetism

10.1180/minmag.1984.048.349.04

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Citations (74)

The influence of aluminium on iron oxides: XIII. Properties of goethites synthesised in 0·3 M KOH at 25°C

Clay Minerals (1987)

Darrell G. Schulze U. Schwertmann

Abstract Aluminium-substituted goethites were synthesised in 0·3 M KOH at either 25° or 70°C. The 25°C goethites had unit-cell a and c dimensions about 0·1–0·2% larger than the 70°C goethites of comparable Al substitution. Unit-cell b dimensions were similar regardless of synthesis temperature. The 25°C goethites contained larger amounts of Al in their structures than the 70°C goethites synthesised at the same initial Al/(Al + Fe) mole ratio in solution. The 25°C goethites had lower dehydroxylation temperatures and smaller differences between the two OH-bending bands than comparable 70°C goethites. These differences between the two sets of goethites are believed to be caused by the presence of more structural defects in the 25°C goethites than in the 70°C goethites. Goethites with the lowest Al substitutions consisted of crystals with several coherently diffracting domains, while at high Al substitutions the crystals were mainly monodomainic. Surface areas of the 25°C goethites varied in a complex manner as a function of thickness along [100], character of the domains, and physical size.

10.1180/claymin.1987.022.1.07

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Citations (81)

Thermodynamics of iron oxides: Part III. Enthalpies of formation and stability of ferrihydrite (similar to Fe(OH)(3)), schwertmannite (similar to FeO(OH)(3/4)(SO4)(1/8)), and epsilon-Fe2O3

Geochimica et Cosmochimica Acta (2004)

Juraj Majzlan A. Navrotsky U. Schwertmann

Schwertmannite

Ferrihydrite

Chemical Stability

Source

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The Formation of Green Rust and Its Transformation to Lepidocrocite

Clay Minerals (1994)

U. Schwertmann H. Fechter

Abstract The formation of Fe II,III hydoxy salts (green rusts) from Fe II sulphate and chloride solutions and their transformation to lepidocrocite, γ-FeOOH, was studied at ambient temperature, constant pH of ∼7.0 and under controlled air flow. The formation of green rust and its subsequent transformation to lepidocrocite could be distinguished by the reaction rate and solution chemistry. The SO 4 2− and Cl − concentrations in solution attain a minimum at the break between the two reaction steps and are completely restored to their initial values after complete transformation to lepidocrocite. While the green rust is being formed, its Fe II /Fe III ratio shows a minor decrease and its Fe III /anion ratio a minor increase. These ratios, however, deviate from the ideal pyroaurite-type structure ( M 2+ / M 3+ = 3; M 3+ / A − = 1; M : metal; A − : anion) and possibilities to accommodate this deviation are discussed. A period during which no protons were produced (i.e. no base consumed) was found to separate the two reactions in the chloride, but not in the sulphate system. During this period a partial solid state oxidation of the green rust took place, leading to its destabilization and eventual decomposition.

Lepidocrocite

Rust (programming language)

Base (topology)

10.1180/claymin.1994.029.1.10

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Citations (168)

Microaggregates from Oxisols and Inceptisols: dispersion through selective dissolutions and physicochemical treatments

Geoderma (1996)

Déborah Pinheiro Dick U. Schwertmann

Oxisol

Dithionite

Inceptisol

10.1016/s0016-7061(96)00047-x

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Citations (123)