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Matthias Heuer Alexandra L. Huber Geoffrey D. Bromiley Karl Thomas Fehr Klaus Bente 《Physics and Chemistry of Minerals》2005,32(8-9):552-563
Clinopyroxenes of the solid solution series hedenbergite (CaFeSi2O6)–petedunnite (CaZnSi2O6) were synthesized at temperatures of 825–1200°C and pressures of 0.5–2.5 GPa. Compositions were determined by electron microprobe analysis. Selected crystals were investigated by means of single crystal diffraction and structure refinement and the structural distortion was studied depending on the substitution of iron by zinc on the octahedral M1 site. It is shown that the coordination of the M1 site has the most significant effect on M–O bond lengths, with changes on the other sites accommodating this distortion. The mean quadratic elongation and the octahedral angle variance as quantitative measures of the distortion of the coordination polyhedron were correlated with former results of 57Fe Mössbauer spectroscopy at 298 K. The results presented now complete an earlier work on synthetic, crystalline powders of the same material and deliver exact structural data that were not possible to obtain by Rietveld refinements on powder data. 相似文献
13.
Isothermal solid state experiments on the diffusion of Cu, Fe, Zn and In and related effects have been carried out in sphalerite single crystals. The driving force for the diffusion and corresponding reactions are chemical potential gradients which are established by differences in sulfur fugacity, oxygen fugacity and the chemical activity between sulfide powders as metal sources and receptor crystals.Studies in the system ZnS-CuInS2 show replacement rims in sphalerite produced by the formation of solid solutions between ZnS and CuInS2. These differences reflect the extent of mutual solid solution. The composition profiles of these rims at different temperatures and sulfur fugacities are calculated to diffusion coefficients for the coupled substitution of Cu+ + In3+ versus 2 Zn2+. The interdiffusion coefficients of (Cu + In) in Fe-free sphalerite at the Fe/FeS sulfur fugacity of the sources obey to the relation: 相似文献
14.
Summary Metal substitution studies of the stability, structure and chemical bonding of sulfides and sulfosalts lead to significant results, which can be applied to natural parageneses and crystal chemical systematics. Comparison of experiments on stable and metastable phases with thin films provides data, which exceed known geometrical criteria of the sulfosalt systematics. Synthetic and natural phases have been studied with respect to their substitution, bonding chemistry and temperature dependent metal distribution as well as to the structure and orientation of thin films.
With 13 Figures
In memoriam Prof. Dr. V. Kupcik ( 1990) 相似文献
Zusammenfassung Die Untersuchung der Stabilität, Struktur und chemischen Bindung von Sulfosalzen führt zu aussagekräftigen auf natürliche Paragenesen sowie auf die Systematik dieser Verbindungen anwendbaren Resultaten, wenn systematische Substitutionsexperimente angesetzt werden. Diese liefern im Vergleich von stabilen und metastabilen Phasen sowie durch Vergleich mit dünnen Schichten Ergebnisse, die wesentlich über bekannte strukturgeometrische Ansätze zur Sulfosalzsystematik hinausgehen. Es werden synthetische und natürliche Verbindungen bezüglich ihrer Substitution, Bindungschemie und temperaturabhängigen Metallordnung sowie die Orientierung und Struktur von dünnen Schichten diskutiert.
With 13 Figures
In memoriam Prof. Dr. V. Kupcik ( 1990) 相似文献
15.
Jens Wenzel Andreasen Emil Makovicky Bente Lebech Sven Karup Møller 《Physics and Chemistry of Minerals》2008,35(8):447-454
Rietveld refinement of neutron powder diffraction data on four samples of synthetic, iron-bearing tetrahedrite (Cu12?xFexSb4S13) with x = 0.28, 0.69, 0.91, 2.19 and four samples of synthetic tennantite (Cu12?xFexAs4S13) with x = 0.33, 0.38, 0.86, 1.5 indicate unambiguously that iron is incorporated into tetrahedral M1 (12d) sites and not into triangular M2 (12e) sites in the cubic crystal structure (space group I $ \ifmmode\expandafter\bar\else\expandafter\=\fi{4} Rietveld refinement of neutron powder diffraction data on four samples of synthetic, iron-bearing tetrahedrite (Cu12−xFexSb4S13) with x = 0.28, 0.69, 0.91, 2.19 and four samples of synthetic tennantite (Cu12−xFexAs4S13) with x = 0.33, 0.38, 0.86, 1.5 indicate unambiguously that iron is incorporated into tetrahedral M1 (12d) sites and not into triangular M2 (12e) sites in the cubic crystal structure (space group I 3 m). The refinement results also confirm that M2 is a split (24g), flat-pyramidal site situated statistically on both sides of the S1−S1–S2 triangle. In tetrahedrite, this split is about
0.6 ?, in tennantite about 0.7 ?. Trends in bond lengths and magnitude of the M2 split were evaluated by means of linear regression
with Fe concentration as the independent variable. 相似文献
16.
Bente Aa. Lomstein Bo B. Jørgensen Jutta Niggemann 《Geochimica et cosmochimica acta》2006,70(12):2970-2989
The spatial distribution of total hydrolysable amino acids (THAA) and amino acid enantiomers (d- and l-forms) was investigated in sediments underlying two contrasting Chilean upwelling regions: at ∼23 °S off Antofagasta and at ∼36 °S off Concepción. The contribution of amino acids to total organic carbon (%TAAC: 7-14%) and total nitrogen (%TAAN: 23-38%) in surface sediments decreased with increasing water depth (from 126 to 1350 m) indicating that organic matter becomes increasingly decomposed in surface sediments at greater water depth. Changes in the ratio between the protein amino acid aspartate and its non-protein degradation product β-alanine confirmed this observation. Furthermore, estimates of THAA mineralization showed that sedimentary amino acid reactivity decreased with both increasing water depth as well as progressive degradation status of the organic matter that was incorporated into the sediment. Reactivity of organic matter in the sediment was also assessed using the Degradation Index (DI) developed by [Dauwe, B., Middelburg, J.J., 1998. Amino acids and hexosamines as indicators of organic matter degradation state in North Sea sediments. Limnol. Oceanogr.43, pp. 782-798.]. Off Concepción, DI was successfully applied to examine the degradation status of sedimentary organic matter at different water depths. However, unexpected results were obtained at the Antofagasta stations as DI increased with sediment depth, suggesting more degraded organic matter at the surface than deeper in the cores. The contribution of peptidoglycan amino acids to THAA was estimated from the concentrations of d-aspartate, d-glutamic acid, d-serine, and d-alanine. Peptidoglycan amino acids accounted for >18% of THAA in all investigated samples. In surface sediments peptidoglycan amino acids accounted for a progressively larger fraction of THAA at increasing water depths (up to >26%). Further, the contribution of peptidoglycan amino acids to THAA increased with increased sediment depth and age (up to 288-year-old) reaching up to 59%. Independent estimates based on d-amino acid concentrations in selected laboratory strains, bacterial counts and the sedimentary concentrations of d-amino acids indicate that a large fraction of the measured d-amino acids (>47 to >97%) originated from cell wall residues rather than from enumerated cells. 相似文献
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A. L.?Huber M.?Heuer K. T.?FehrEmail author K.?Bente E.?Schmidbauer G. D.?Bromiley 《Physics and Chemistry of Minerals》2004,31(2):67-79
Clinopyroxenes along the solid solution series hedenbergite (CaFeSi2O6)–petedunnite (CaZnSi2O6) were synthesized under hydrothermal conditions and different oxygen fugacities at temperatures of 700 to 1200 °C and pressures of 0.2 to 2.5 GPa. Properties were determined by means of X-ray diffraction, electron microprobe analysis and 57Fe Mössbauer spectroscopy at 298 K. Unit-cell parameters display a linear dependency with changing composition. Parameters a0 and b0 exhibit a linear decrease with increasing Zn content while the monoclinic angle increases linearly. Parameter c0 is not affected by composition and remains constant at a value of 5.248 Å. The molar volume can be described according to the equation Vmol (ccm mol–1)=33.963(16)–0.544(31)*Zn pfu. The isomer shifts of ferrous iron on the octahedral M1 site in hedenbergite are not affected by composition along the hedenbergite–petedunnite solid solution series and remain constant at an average value of 1.18 mm s–1. Quadrupole splittings of Fe2+ on the M1 are, however, strongly affected by composition, and they decrease linearly with increasing petedunnite component in hedenbergite, ranging from 2.25 mm s–1 for pure hedenbergite end member to 1.99 mm s–1 for a solid solution containing 84 mole% petedunnite. The half-widths of intermediate solid solutions vary between 0.26 and 0.33 mm s–1, indicating, in accordance with the microprobe analyses and X-ray diffraction, that samples are homogeneous and well-crystallized. The data from this study demonstrate that the crystallinity of hedenbergitic clinopyroxenes can be improved by using oxide mixtures as starting materials. Crystal sizes for intermediate compositions range up to 70 m, suitable for standard single-crystal X-ray analysis.This paper is dedicated to Prof. Dr. Georg Amthauer, Salzburg, on occasion of his 60th birthday 相似文献
18.
Groundwater-dependent ecology of the shoreline of the subtropical Lake St Lucia estuary 总被引：1，自引：0，他引：1
Ricky Taylor Bruce Kelbe Sylvi Haldorsen Greg A. Botha Bente Wejden Lars Været Marianne B. Simonsen 《Environmental Geology》2006,49(4):586-600
The ecology of the St Lucia estuary in South Africa is of unique international importance. During droughts the estuary experiences
high salinities, with values above that of seawater. Ion-poor groundwater flowing into the estuary from prominent sand aquifers
along its eastern shoreline forms low-salinity habitats for salt-sensitive biota. During droughts, plants and animals can
take refuge in the groundwater discharge zone until the condition in the estuary regains tolerable salinity. Simulations of
the groundwater discharge indicate that the flow can persist during droughts over at least a decade, and be of great important
for the resilience of the estuary. Anthropogenic activities have reduced the river inflow and made the St Lucia estuary more
sensitive to droughts. The groundwater has thereby become increasingly important for the estuary’s ecology. Protection of
the groundwater discharge along the shoreline itself and actions to increase the groundwater recharge are therefore important
management tasks. 相似文献
19.
Prof. Dr. K. Bente 《Mineralogy and Petrology》1987,36(3-4):205-217
Summary Three stabilization phenomena, 1: special e.g. hydrothermal conditions, 2: stabilization by replacements of ions, as e.g. Cu and Fe and 3: heterogeneous nucleation as, e.g., by epitaxy are tested for phases in the system Cu2S-CuS2-Bi2S3-FeS-FeS2. Hydrothermal solution and precipitation conditions can metastabilize or stabilize phases, which are not existent under dry conditions as Cu4Bi5S10 or CuS2-FeS2 mixed crystals, but are stable at high pressures. Stabilization by Cu-Fe substitution leads to the assumption that stabilization basically depends on the ionic radii similarity, but necessarily electronic interactions have to be involved. Stabilization by heterogeneous nucleation is tested for Pb-Bi sulfosalts, e.g. for the epitaxial growth of Bi2S3 on NaCl. In contrast to the normal orthorhombic Bi2S3, the epitaxial Bi2S3 shows a pseudotetragonal subcell correlated to NaCl. Satellite reflections indicate a modulation probably caused by a modulation of the metal vacancies.
With 10 Figures
Contribution to the Ore Mineralogy Symposium (IMA/COM) at the 14th General Meeting of the International Mineralogical Association, at Stanford, California, in July, 1986. 相似文献
Stabilisterung von Cu-Fe-Bi-Pb-Sn-Sulfiden
Zusammenfassung Im System Cu2S-CuS2-Bi2S3-FeS-FeS2 werden drei Stabilisierungsphänomene 1: spezielle Stabilisierungsbedingungen z. B. in hydrothermalen Lösungen, 2: Stabilisierungen durch Elemente- bzw. Ionenersatz am Beispiel von Cu und Fe und 3: heterogene Keimbildung anhand von Epitaxieversuchen verifiziert.Hydrothermale Ausscheidungsbedingungen können metastabile oder stabile Phasen bedingen, die z. B. unter trockenen Bedingungen nicht oder nur bei hohen Drucken stabil sind. Dies gilt z. B. für den Cu-Fe-Ersatz in Cu4Bi5S10 bzw. für CUS2-FeS2 Mischkristalle. Die Stabilisierung durch Cu-Fe-Substitution führt zu der Annahme, daß hierfür als notwendige Voraussetzung die Ähnlichkeit der Ionenradien gilt, jedoch als hinreichende Bedingung die elektronische Wechselwirkung zwischen den sich ersetzenden Ionen anzusehen ist.Die Stabilisierung durch heterogene Keimbildung wird für Pb-Bi-Sulfosalze am Beispiel der Epitaxie von Bi2S3 auf NaCI getestet. Im Gegensatz zum normalen orthorhombischen Bi2S3 zeigt die epitaktische Phase eine mit NaCl korrelierte tetragonale Subzelle. Satellitenreflexe deuten auf eine Modulation der Leerstellen der Metallionen hin.
With 10 Figures
Contribution to the Ore Mineralogy Symposium (IMA/COM) at the 14th General Meeting of the International Mineralogical Association, at Stanford, California, in July, 1986. 相似文献
20.