potential of chiral solvents in enantioselective crystallization

Magdeburg, Univ., Fak. für Verfahrens- und Systemtechnik, Diss., 2010

Formation and crystallization based separation of diastereomeric salts

Magdeburg, Univ., Fak. für Verfahrens- und Systemtechnik, Diss., 2012

Designing crystallization based-enantiomeric separation for chiral compound-forming systems in consideration of polymorphism and solvate formation

Magdeburg, Univ., Fak. für Verfahrens- und Systemtechnik, Diss., 2014

Continuous fluidized bed crystallization

Magdeburg, Univ., Fak. für Verfahrens- und Systemtechnik, Diss., 2015

Modeling of in-situ crystallization processes in the Permian mafic layered intrusion of Mont Collon (Dent Blanche nappe, western Alps)

The Mont Collon mafic complex is one of the best preserved examples of the Early Permian magmatism in the Central Alps, related to the intra-continental collapse of the Variscan belt. It mostly consists (> 95 vol.%) of ol+hy-nonnative plagioclase-wehrlites, olivine- and cpx-gabbros with cumulitic structures, crosscut by acid dikes. Pegmatitic gabbros, troctolites and anorthosites outcrop locally. A well-preserved cumulative, sequence is exposed in the Dents de Bertol area (center of intrusion). PT-calculations indicate that this layered magma chamber emplaced at mid-crustal levels at about 0.5 GPa and 1100 degrees C. The Mont Collon cumulitic rocks record little magmatic differentiation, as illustrated by the restricted range of clinopyroxene mg-number (Mg#(cpx)=83-89). Whole-rock incompatible trace-element contents (e.g. Nb, Zr, Ba) vary largely and without correlation with major-element composition. These features are characteristic of an in-situ crystallization process with variable amounts of interstitial liquid L trapped between the cumulus mineral phases. LA-ICPMS measurements show that trace-element distribution in the latter is homogeneous, pointing to subsolidus re-equilibration between crystals and interstitial melts. A quantitative modeling based on Langmuir's in-situ crystallization equation successfully duplicated the REE concentrations in cumulitic minerals of all rock facies of the intrusion. The calculated amounts of interstitial liquid L vary between 0 and 35% for degrees of differentiation F of 0 to 20%, relative to the least evolved facies of the intrusion. L values are well correlated with the modal proportions of interstitial amphibole and whole-rock incompatible trace-element concentrations (e.g. Zr, Nb) of the tested samples. However, the in-situ crystallization model reaches its limitations with rock containing high modal content of REE-bearing minerals (i.e. zircon), such as pegmatitic gabbros. Dikes of anorthositic composition, locally crosscutting the layered lithologies, evidence that the Mont Collon rocks evolved in open system with mixing of intercumulus liquids of different origins and possibly contrasting compositions. The proposed model is not able to resolve these complex open systems, but migrating liquids could be partly responsible for the observed dispersion of points in some correlation diagrams. Absence of significant differentiation with recurrent lithologies in the cumulitic pile of Dents de Bertol points to an efficiently convective magma chamber, with possible periodic replenishment, (c) 2005 Elsevier B.V. All rights reserved.

Enriched basaltic andesites from mid-crustal fractional crystallization, recharge, and assimilation (Pilavo Volcano, Western Cordillera of Ecuador)

The origin of andesite is an important issue in petrology because andesite is the main eruptive product at convergent margins, corresponds to the average crustal composition and is often associated with major Cu-Au mineralization. In this study we present petrographic, mineralogical, geochemical and isotopic data for basaltic andesites of the latest Pleistocene Pilavo volcano, one of the most frontal volcanoes of the Ecuadorian Quaternary arc, situated upon thick (30-50 km) mafic crust composed of accreted Cretaceous oceanic plateau rocks and overlying mafic to intermediate Late Cretaceous-Late Tertiary magmatic arcs. The Pilavo rocks are basaltic andesites (54-57 center dot 5 wt % SiO(2)) with a tholeiitic affinity as opposed to the typical calc-alkaline high-silica andesites and dacites (SiO(2) 59-66 wt %) of other frontal arc volcanoes of Ecuador (e.g. Pichincha, Pululahua). They have much higher incompatible element contents (e.g. Sr 650-1350 ppm, Ba 650-1800 ppm, Zr 100-225 ppm, Th 5-25 ppm, La 15-65 ppm) and Th/La ratios (0 center dot 28-0 center dot 36) than Pichincha and Pululahua, and more primitive Sr ((87)Sr/(86)Sr similar to 0 center dot 7038-0 center dot 7039) and Nd (epsilon(Nd) similar to +5 center dot 5 to +6 center dot 1) isotopic signatures. Pilavo andesites have geochemical affinities with modern and recent high-MgO andesites (e.g. low-silica adakites, Setouchi sanukites) and, especially, with Archean sanukitoids, for both of which incompatible element enrichments are believed to result from interactions of slab melts with peridotitic mantle. Petrographic, mineral chemistry, bulk-rock geochemical and isotopic data indicate that the Pilavo magmatic rocks have evolved through three main stages: (1) generation of a basaltic magma in the mantle wedge region by flux melting induced by slab-derived fluids (aqueous, supercritical or melts); (2) high-pressure differentiation of the basaltic melt (at the mantle-crust boundary or at lower crustal levels) through sustained fractionation of olivine and clinopyroxene, leading to hydrous, high-alumina basaltic andesite melts with a tholeiitic affinity, enriched in incompatible elements and strongly impoverished in Ni and Cr; (3) establishment of one or more mid-crustal magma storage reservoirs in which the magmas evolved through dominant amphibole and clinopyroxene (but no plagioclase) fractionation accompanied by assimilation of the modified plutonic roots of the arc and recharge by incoming batches of more primitive magma from depth. The latter process has resulted in strongly increasing incompatible element concentrations in the Pilavo basaltic andesites, coupled with slightly increasing crustal isotopic signatures and a shift towards a more calc-alkaline affinity. Our data show that, although ultimately originating from the slab, incompatible element abundances in arc andesites with primitive isotopic signatures can be significantly enhanced by intra-crustal processes within a thick juvenile mafic crust, thus providing an additional process for the generation of enriched andesites.

Cell size distribution in a random tessellation of space governed by the Kolmogorov-Johnson-Mehl-Avrami model: Grain size distribution in crystallization

The space subdivision in cells resulting from a process of random nucleation and growth is a subject of interest in many scientific fields. In this paper, we deduce the expected value and variance of these distributions while assuming that the space subdivision process is in accordance with the premises of the Kolmogorov-Johnson-Mehl-Avrami model. We have not imposed restrictions on the time dependency of nucleation and growth rates. We have also developed an approximate analytical cell size probability density function. Finally, we have applied our approach to the distributions resulting from solid phase crystallization under isochronal heating conditions

The duration of prograde garnet crystallization in the UHP eclogites at Lago di Cignana, Italy

The distinct core-to-rim zonation of different REEs in garnet in metamorphic rocks, specifically Sm relative to Lu, suggests that Sm-Nd and Lu-Hf isochron ages will record different times along a prograde garnet growth history. Therefore, REE zonations in garnet must be measured in order to correctly interpret the isochron ages in terms of the garnet growth interval, which could span several m.y. New REE profiles, garnet crystal size distributions, and garnet growth modeling, combined with previously published Sm-Nd and Lu-Hf geochronology on a UHP eclogite of the Zermatt-Saas Fee (ZSF) ophiolite, Lago di Cignana (Italy), demonstrate that prograde garnet growth of this sample occurred over a similar to 30 to 40 m.y. interval. Relative to peak metamorphism at 38 to 40 Ma, garnet growth is estimated to have begun at similar to 11 to 14 kbar pressure at similar to 70 to 80 Ma. Although such a protracted garnet growth interval is surprising, this is supported by plate tectonic reconstructions which suggest that subduction of the Liguro-Piemont ocean occurred through slow and oblique convergence. These results demonstrate that REE zonations in garnet, coupled to crystal size distributions, provide a powerful means for understanding prograde metamorphic paths when combined with Sm-Nd and Lu-Hf geochronology. (C) 2009 Elsevier B.V. All rights reserved.

Volatile transport during the crystallization of anatectic melts: Oxygen, boron and hydrogen stable isotope study on the metamorphic complex of Naxos, Greece

Crystallization of anatectic melts in high-temperature metamorphic terrains releases volatile-rich magmas that can be transported into adjacent lithologies. This study addresses the variations in the oxygen, boron and hydrogen isotopic composition of aplite-pegmatite dikes that formed during the crystallization of anatectic melts in regional high-temperature metamorphism on the island of Naxos, Greece, and propagated upward into the overlying sequences of metamorphic schist. The transport distance of these dikes was increased through a significant horizontal component of travel that was imposed by contemporaneous low-angle extensional shearing. Laser fluorination oxygen isotope analyses of quartz, tourmaline, garnet, and biotite mineral separates from the aplite-pegmatite dikes show a progressive rise in delta(18)O values with increasing distance from the core. Oxygen isotope fractionations among quartz, tourmaline, and garnet show temperature variations from > 700degreesC down to similar to400degreesC. This range is considered to reflect isotopic fractionation beginning with crystallization at high temperatures in water-undersaturated conditions and then evolving through lower temperature crystallization and retrograde sub-solidus exchange. Two processes are examined for the cause of the progressive increase in delta(18)O values: (1) heterogeneous delta(18)O sources and (2) fluid-rock exchange between the aplite/pegmatite magmas and their host rock. Although the former process cannot be ruled out, there is as yet no evidence in the exposed sequences on Naxos for the presence of a suitable high delta(18)O magma source. In contrast, a tendency for the delta(18)O of quartz in the aplite/pegmatite dikes to approach that of the quartz in the metamorphic rock suggests that fluid-rock exchange with the host rock may potentially be an important process. Advection of fluid into the magma is examined based on Darcian fluid flow into an initially water-undersaturated buoyantly propagating aplitic dike magma. It is shown that such advective flow could only account for part of the O-18-enrichment, unless it were amplified by repeated injection of magma pulses, fluid recycling, and deformation-assisted post-crystallization exchange. The mechanism is, however, adequate to account for hydrogen isotope equilibration between dike and host rock. In contrast, variations in the delta(11)B values of tourmalines suggest that B-11/B-10 fractionation during crystallization and/or magma degassing was the major control of boron geochemistry rather than fluid-rock interaction and that the boron isotopic system was decoupled from that of oxygen. Copyright (C) 2003 Elsevier Ltd.

Crystallization and preliminary crystallographic characterization of an SH3 domain from the IB1 scaffold protein.

IB1 is a mammalian scaffold protein that interacts with components of the c-Jun N-terminal kinase (JNK) signal-transduction pathway mainly via its protein-protein interaction domains. Crystallization of the key Src homology 3 (SH3) domain of IB1 has been achieved. Crystallization experiments with unmodified protein and deliberately oxidized protein have led to different crystal forms. X-ray data have been collected to 3.0 A resolution from a crystal form with rectangular prism morphology. These crystals are orthorhombic (P2(1)2(1)2(1)), with unit-cell parameters a = 45.9, b = 57.0, c = 145.5 A. These are the first crystallographic data on a scaffold molecule such as IB1 to be reported.

Structural and functional characterization of (110)-oriented epitaxial La2/3Ca1/3MnO3 electrodes and SrTiO3 tunnel barriers

La2/3Ca1/3MnO3 (LCMO) films have been deposited on (110)-oriented SrTiO3 (STO) substrates. X-ray diffraction and high-resolution electron microscopy reveal that the (110) LCMO films are epitaxial and anisotropically in-plane strained, with higher relaxation along the [1¿10] direction than along the [001] direction; x-ray absorption spectroscopy data signaled the existence of a single intermediate Mn3+/4+ 3d-state at the film surface. Their magnetic properties are compared to those of (001) LCMO films grown simultaneously on (001) STO substrates It is found that (110) LCMO films present a higher Curie temperature (TC) and a weaker decay of magnetization when approaching TC than their (001) LCMO counterparts. These improved films have been subsequently covered by nanometric STO layers. Conducting atomic-force experiments have shown that STO layers, as thin as 0.8 nm, grown on top of the (110) LCMO electrode, display good insulating properties. We will show that the electric conductance across (110) STO layers, exponentially depending on the barrier thickness, is tunnel-like. The barrier height in STO (110) is found to be similar to that of STO (001). These results show that the (110) LCMO electrodes can be better electrodes than (001) LCMO for magnetic tunnel junctions, and that (110) STO are suitable insulating barriers.

Strain-induced stabilization of new magnetic spinel structures in epitaxial oxide heterostructures.

We report here on the growth of NiFe2O4 epitaxial thin films of different thickness (3 nm ¿ t ¿ 32 nm) on single crystalline substrates having spinel (MgAl2O4) or perovskite (SrTiO3) structure. Ultrathin films, grown on any of those substrates, display a huge enhancement of the saturation magnetization: we will show that partial cationic inversion may account for this enhancement, although we will argue that suppression of antiparallel collinear spin alignment due to size-effects cannot be excluded. Besides, for thicker films, the magnetization of films on MAO is found to be similar to that of bulk ferrite; in contrast, the magnetization of films on STO is substantially lower than bulk. We discuss on the possible mechanisms leading to this remarkable difference of magnetization.

Epitaxial growth of biferroic YMnO3(0001) on platinum electrodes

Epitaxial films of the biferroic YMnO3 (YMO) oxide have been grown on platinum-coated SrTiO3(1 1 1) and Al2O3(0 0 0 1) substrates. The platinum electrodes, (1 1 1) oriented, are templates for the epitaxy of the hexagonal phase of YMO with a (0 0 0 1) out-of-plane orientation, which is of interest as this is the polarization direction of YMO. X-ray diffractometry indicates the presence of two crystal domains, 60° rotated in-plane, in the Pt(1 1 1) layers which subsequently are transferred on the upperlaying YMO. Cross-section analysis by high-resolution transmission electron microscopy (HRTEM) of YMnO3/Pt/SrTiO3(1 1 1) shows high-quality epitaxy and sharp interfaces across the structure in the observed region. We present a detailed study of the epitaxial growth of the hexagonal YMO on the electrodes.

Atomic diffusion induced by stress relaxation in InGaAs/GaAs epitaxial layers

The origin of the microscopic inhomogeneities in InxGa12xAs layers grown on GaAs by molecular beam epitaxy is analyzed through the optical absorption spectra near the band gap. It is seen that, for relaxed thick layers of about 2.8 mm, composition inhomogeneities are responsible for the band edge smoothing into the whole compositional range (0.05,x,0.8). On the other hand, in thin enough layers strain inhomogeneities are dominant. This evolution in line with layer thickness is due to the atomic diffusion at the surface during growth, induced by the strain inhomogeneities that arise from stress relaxation. In consequence, the strain variations present in the layer are converted into composition variations during growth. This process is energetically favorable as it diminishes elastic energy. An additional support to this hypothesis is given by a clear proportionality between the magnitude of the composition variations and the mean strain.