Microstructural evolution and grain boundary structure during static recrystallization in synthetic polycrystals of Sodium Chloride containing saturated brine   总被引：1，自引：0，他引：1  

Oliver?SchenkEmail author  Janos?L.?Urai 《Contributions to Mineralogy and Petrology》2004,146(6):671-682

The effects of brine on recrystallization in halite are well known. However, properties of brine such as morphology, connectivity, diffusivity and the resulting influences on deformation mechanisms are still a matter of debate. This paper presents a microstructural study of dense, statically recrystallizing synthetic polycrystalline halite containing small amounts of brine. We used powders of two different grain size classes: <10 µm and 200–355 µm. The aggregates were compacted to brine-filled porosities less than about 2% and annealed at room temperature, without an external stress field.Coarse-grained samples undergo recrystallization manifested by the growth of large (up to 300 µm) strain-free grains into the deformed old grains. The new grains are frequently euhedral, with mobile grain boundaries moving at rates up to 6 nm/s. Their mobility is interpreted to be high due to the presence of water. Grain surfaces are smooth and the width of the water-rich zones is usually below the resolution of the SEM (less than 50 nm).The evolution of fine-grained samples starts with primary recrystallization and a reorganization of grain boundaries. After this stage, which lasts a few hours, normal grain growth effectively stops, and no significant increase of grain size is observed even after several months. Microstructural observations indicate contact healing at the grain boundaries, with dihedral angles ranging between 20 and 110°. We interpret these boundaries to be fluid-free, with the brine residing in a network of triple junction tubes. This system of triple junctions is interconnected and associated with significant permeability.While grain growth is inhibited in the fine-grained samples, after a few hours of annealing exaggerated grain growth is commonly initiated. This is manifested by the growth of large, euhedral grains replacing the fine-grained matrix. These grains also grow with low-index facets and their boundaries are also interpreted to be mobile due to the existence of a water-rich phase.Editorial Responsibility: J. Hoefs  相似文献   

Local structural heterogeneity,mixing behaviour and saturation effects in the grossular–spessartine solid solution     

U.?RodehorstEmail author  M. A.?Carpenter  T. Boffa?Ballaran  C. A.?Geiger 《Physics and Chemistry of Minerals》2004,31(7):387-404

Local structural heterogeneities in crystals of the binary grossular–spessartine solid solution have been analyzed using powder IR absorption spectroscopy. Wavenumber shifts of the highest energy Si–O stretching mode in spectra collected at room temperature are consistent with variations in Si–O bond length from structural data. They show a smaller positive deviation from linearity across the join than is seen for the grossular–pyrope and grossular–almandine binaries. The effective line widths, corr, of three selected wavenumber regions all deviate positively from linear behaviour. An empirical calibration of this excess spectroscopic property, obtained by comparison with calorimetric enthalpy of mixing data, gives an estimate for the symmetric Margules parameter of W^H_spec = 14.4(7) kJ mol^–1 in H^mix = W^H_specX_GrX_Sp. W^H_spec values derived on the same basis for four aluminosilicate garnet solid solutions analyzed by IR spectroscopy vary with V², where V represents the difference in molar volume between the end members of each binary system. Measurements of lattice parameters and IR spectra were made over a range of temperatures for seven samples with different compositions. Positive excess molar volumes of mixing at low temperature (30 K) may be larger than the excess molar volumes at room temperature. The saturation temperatures of the molar volumes show no correlation with composition, however, in contrast with what had been expected on the basis of data for the grossular–pyrope binary. Saturation temperatures for spectroscopic parameters and lattice parameters of samples with compositions Gr15Sp85 and Gr60Sp40 seem to be outliers in all experiments. It is concluded that the data hint at systematic changes in saturation temperatures across the solid solution, with implications for both the excess entropy of mixing and the excess volume of mixing, but more precise data or further sample characterization are needed to prove that this composition dependence is real in garnet solid solutions.  相似文献   

Determination of the spatial and temporal variation of tropospheric water vapour using CGPS networks   总被引：1，自引：0，他引：1  

M. Troller  A. Geiger  E. Brockmann  H.-G. Kahle 《Geophysical Journal International》2006,167(2):509-520

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Crystal chemistry, cation ordering and thermoelastic behaviour of CoMgSiO4 olivine at high temperature as studied by in situ neutron powder diffraction     

Romano Rinaldi  G. D. Gatta  G. Artioli  K. S. Knight  C. A. Geiger 《Physics and Chemistry of Minerals》2005,32(8-9):655-664

The thermal expansion, structural changes and the site partitioning of Co and Mg in synthetic CoMgSiO₄ olivine have been studied by in situ time-of-flight neutron powder diffraction as a function of temperature, between 25 and 1,000°C. Thermal expansion of the unit cell dimensions and volume are linear within this temperature range and give no indications of a phase transition, although the thermoelastic behaviour indicates a slight strain minimum around 700°C. Co²⁺ shows a strong preference for the M1 site throughout this temperature range with an oscillatory behaviour; it decreases slightly at about 300°C, climbing up to nearly its original value at around 800°C and then decreasing by about 30% at 1,000°C. This behaviour is in contrast with that of (Fe, Mg)₂SiO₄ olivine, in which the initial Fe²⁺ site preference for the M1 site switches to the M2 site beyond a cross-over temperature. The oscillatory site preference in (CoMg)-olivine as a function of temperature is reflected in the M–O polyhedral volume changes and M–O bond lengths, as well as, thermoelastic strain and atomic thermal displacement parameters. The imbalance between the increasing vibrational and decreasing configurational entropy contributions, together with covalent bonding effects rather than crystal field contributions, seem to drive the cation partitioning in (CoMg)-olivine.  相似文献   

Recent vertical movements from precise levelling in the vicinity of the city of Basel, Switzerland     

Andreas Schlatter  Dieter Schneider  Alain Geiger  Hans-Gert Kahle 《International Journal of Earth Sciences》2005,94(4):507-514

The southern end of the Upper Rhine Graben is one of the zones in Switzerland where recent crustal movements can be expected because of ongoing seismotectonic processes as witnessed by seismicity clusters occurring in this region. Therefore, in 1973 a control network with levelling profiles across the eastern Rhine Graben fault was installed and measured in the vicinity of the city of Basel in order to measure relative vertical movements and investigate their relationship with seismic events. As a contribution to EUCOR-URGENT, the profiles were observed a third time in the years 2002 and 2003 and connected to the Swiss national levelling network. The results of these local measurements are discussed in terms of accuracy and significance. Furthermore, they are combined and interpreted together with the extensive data set of recent vertical movements in Switzerland (Jura Mountains, Central Plateau and the Alps). In order to be able to prove height changes with precise levelling, their values should amount to at least 3–4 mm (1). The present investigations, however, have not shown any significant vertical movements over the past 30 years.  相似文献   

The crystal chemistry of pumpellyite: An X-ray Rietveld refinement and 57Fe Mössbauer study     

G. Artioli  C. A. Geiger 《Physics and Chemistry of Minerals》1994,20(7):443-453

Pumpellyite of the general formula W₈X₄Y₈-Z₁₂O_56-n(OH)_n contains Fe, Al and Mg in two crystallographically different octahedral sites. Three different pumpellyite samples covering the known compositional field from Al- to Fe-rich have been studied to determine the valence state and intracrystalline partitioning of the Fe cations between the two independent octahedral sites. Fe⁺² and Fe⁺³ cation partitioning is interpreted on the basis of results obtained by ⁵⁷Fe Mössbauer spectroscopy at 293 and 77 K and from Rietveld structure analysis performed on powder X-ray diffraction data. Pumpellyite from low-grade metamorphic rocks typically contains a majority of iron in the Fe⁺³ oxidation state, which is found in the smaller and less symmetrical octahedral Y-site. Fe⁺² was also present in all pumpellyite samples studied and it is located in the larger and more symmetrical octahedral X-site.  相似文献   

MELIMEX,an experimental heavy metal pollution study: Behaviour of heavy metals in an aquatic food chain     

Dr. René Gächter  Dr. Wolfgang Geiger 《Aquatic Sciences - Research Across Boundaries》1979,41(2):277-290

Phytoplankton, periphyton and zooplankton samples, chironomid andSialis sp. larvae, and fry of trout and bream collected from unpolluted and artificially metal-polluted limno-corrals were analyzed for mercury, copper, cadmium, zinc and lead. The results indicate that these metals are not accumulated through the food chain and suggest that increased metal concentrations in the environment favor the growth of phytoplankton organisms with a low metal sorption capacity.  相似文献   

Recent crustal movements in the Alpine-Mediterrane an region analyzed in the Swiss ALPS     

A. Geiger  H.-G. Kahle  E. Gubler 《Tectonophysics》1986,130(1-4):289-292

The most recent results of uplift rates determined by repeated precise levelling, are analyzed in terms of geodynamic processes still going on in the region of the Alpine-Mediterranean plate boundary. Special emphasis is focused on levelling nets in the Swiss Alps which have been remeasured for the second time. A comparison of these geodetic results with geophysical information, such as gravity anomalies and explosion seismic results, as well as seismicity, provides further evidence that these sets of data are interrelated with each other. An attempt is made to estimate the strain energy associated with the crustal deformation by introducing first-order stress-strain relationships.  相似文献   

Raman spectra of silicate garnets   总被引：2，自引：1，他引：1  

B. A. Kolesov  C. A. Geiger 《Physics and Chemistry of Minerals》1998,25(2):142-151

The single-crystal polarized Raman spectra of four natural silicate garnets with compositions close to end-members almandine, grossular, andradite, and uvarovite, and two synthetic end-members spessartine and pyrope, were measured, along with the powder spectra of synthetic pyrope-grossular and almandine-spessartine solid solutions. Mode assignments were made based on a comparison of the different end-member garnet spectra and, in the case of pyrope, based on measurements made on additional crystals synthesized with ²⁶Mg. A general order of mode frequencies, i.e. R(SiO₄)>T(metal cation)>T(SiO₄), is observed, which should also hold for most orthosilicates. The main factors controlling the changes in mode frequencies as a function of composition are intracrystalline pressure (i.e. oxygen-oxygen repulsion) for the internal SiO₄-vibrational modes and kinematic coupling of vibrations for the external modes. Low frequency vibrations of the X-site cations reflect their weak bonding and dynamic disorder in the large dodecahedral site, especially in the case of pyrope. Two mode behavior is observed for X-site cation vibrations along the pyrope-grossular binary, but not along the almandine-spessartine join. Received: 3 December 1996 / Revised, accepted: 13 April 1997  相似文献   

Possibility for subdividing apparently homogeneous depositional sequences by combined use of sedimentological,palaeontological and mathematical methods     

B. Molnár  J. Geiger 《GeoJournal》1995,36(2-3):169-177

Sedimentologists often find such depositional sequences, which visually, but even for microscopic examinations look homogeneous, and their fossil-content is very low. These sequences can be subdivided into genetic units only with great difficulties or not at all, and their correlation may be problematical.An experiment is presented here, aiming at a subdivision of loess profiles by a combined use of sedimentological, palaeontological and mathematical methods. The loess samples selected for this examination were characterised by their grain size parameters as suggested by Folk and Ward (1957) and by their carbonate content. Using a Q-type cluster analysis these samples were classified into different groups by their similarity. After arranging the samples with their cluster symbols into their real stratigraphic position, the genetic units of the depositional sequence were delimited by an analysis of the vertical series of the previously established cluster-groups. Finally, a method of discriminant analysis was applied to establish the stability, ie the probability, of the existence of the vertical genetic units obtained by this zonation method.Parallel to it the sequence was subdivided from a faunistic point of view, too. These units correlate well with the results of the numeric approach.  相似文献