Home About us Contact
|
Home About us Contact | ||
|
|
||
Recrystallization
Selected AbstractsDecanuclear Manganese Isobutyrate Clusters Featuring a Novel MnII8MnIII2 CoreEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 28 2009Iurii L. Malaestean Abstract Recrystallization of freshly prepared MnII isobutyrate from PrOH or from EtOH/MeCN mixtures containing pyrazole (pyr) yields neutral mixed-valence decanuclear manganese(II/III) complexes, [Mn10O2(O2CCHMe2)18(HO2CCHMe2)2(PrOH)2] (1) and [Mn10O2(O2CCHMe2)18(pyr)4] (2). The Mn10 metal core of both 1 and 2 consists of eight MnII and two MnIII centers and represents a new motif in the structural organization of polynuclear mixed-valence manganese clusters. Both, 1 and 2 exhibit a net antiferromagnetic exchange coupling resulting in singlet ground states. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Solvent-Mediated Redox Transformations of Ytterbium Bis(indenyl)diazabutadiene ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2005Alexander A. Trifonov Abstract The reactions of diamagnetic [(C9H7)2Yb(THF)2] (2) and [rac -(CH2 -1-C9H6)2Yb(THF)2] (3) with tBuN=CH,CH=NtBu (DAD) in toluene result in the formation of the paramagnetic complexes [(C9H7)2Yb(DAD)] (4) and [rac- (CH2 -1-C9H6)2Yb(DAD)] (5), respectively. The IR, UV/Vis, and 1H NMR spectroscopic data, the magnetic properties, and the single-crystal X-ray diffraction studies of 4 and 5 indicate that in the solid state and in noncoordinating media both complexes are ytterbium(III) derivatives containing the DAD radical-anion, whereas the 1H NMR and UV/Vis spectra of solutions of 4 and 5 in the coordinating solvent THF give evidence for divalent ytterbium. Recrystallization of 4 and 5 from THF/hexane results in the recovery of the starting ytterbium complexes 2 and 3 due to an unusual redox substitution of the radical anion of diazabutadiene by THF in the coordination sphere of ytterbium. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] In Situ Observation of Dynamic Recrystallization in the Bulk of Zirconium Alloy (Adv. Eng.ADVANCED ENGINEERING MATERIALS, Issue 8 2009Mater. The cover shows the in-situ diffraction setup. A fine synchrotron beam transmits the sample situated in a (heated) load frame and scatters into Debye-Scherrer cones. Large crystallites map onto spots onto the 2D detector rather than continuous rings. In the background, the intensity distribution of one selected reflection - here beta-Zr 110 - is plotted in color scale as a function of azimuthal angle (horizontal axis) and time (vertical axis) revealing the different states during thermo-mechanical processing. More details can be found in the article by K.-D. Liss on page 637. [source] In Situ Observation of Dynamic Recrystallization in the Bulk of Zirconium Alloy,ADVANCED ENGINEERING MATERIALS, Issue 8 2009Klaus-Dieter Liss Dynamic recrystallization and related effects have been followed in situ and in real time while a metal undergoes rapid thermo-mechanical processing. Statistics and orientation correlations of embedded/bulk material grains were deduced from two-dimensional X-ray diffraction patterns and give deep insight into the formation of the microstructure. Applications are relevant in materials design, simulation, and in geological systems. [source] Recrystallization and Texture in a Ferritic Stainless Steel: an EBSD Study,ADVANCED ENGINEERING MATERIALS, Issue 8 2003C.W. Sinclair The recrystallization behavior of laboratory-processed AISI409 ferritic stainless steel sheet has been studied with a focus on texture inhomogeneity and "sluggish" recrystallization kinetics, mainly using EBSD in the scanning electron microscope. Pronounced texture gradients were observed in some grain orientations (see Figure for a TEM image of the , versus ,-grain border region) and correlated to the deformation-induced substructure. The strong pinning of some boundaries has been linked not only to textural effects, but also to the precipitation of fine titanium carbonitrides. [source] Influence of Deformation on Recrystallization of an Yttrium Oxide Dispersion-Strengthened Iron Alloy (PM2000),ADVANCED ENGINEERING MATERIALS, Issue 4 2003C. Capdevila Montes A two-fold effect of non-uniform deformation of the yttria-strengthened Fe alloy PM2000 has been revealed by analysis of the microstructure: Firstly, recrystallization temperature decreases, in accordance with the hypothesis that anything that makes the original microstructure more heterogeneous will encourage recrystallization; and secondly, the increase in number and density of recrystallization nuclei leads to fine grain structures which are more 3D isotropic. [source] Predicting the Mircostructure in Semi-Crystalline Thermoplastics using Software for the Simulation of Recrystallization in Metals,ADVANCED ENGINEERING MATERIALS, Issue 3 2003W. Michaeli A software for the simulation of spherulite growth during the cooling of a quiescent melt has been developed and tested vs. experimental data by the authors. The tests have verified good qualitative results: the calculated crystal microstructure and distribution (see Figure for a simulated pattern close to the mold surface) correspond well with the real morphology. [source] Purification, crystallization and X-ray diffraction analysis of the extracellular part of the human Fc receptor for IgA, Fc,RI (CD89)ACTA CRYSTALLOGRAPHICA SECTION D, Issue 12 2003Katja Wenig Fc,RI is the predominant receptor for IgA in the serum. Nevertheless, the interaction between the molecules that finally leads to an immune response is poorly understood. To investigate the structural requirements for IgA binding, the extracellular region of Fc,RI was cloned and overexpressed in Escherichia coli. The resulting inclusion-body protein was refolded and purified. Despite its deglycosylated state, this recombinant Fc,RI retained its ability to bind human IgA. The protein crystallized spontaneously as microcrystalline needles. Recrystallization yielded crystals belonging to a primitive monoclinic space group. A complete 2.8,Å resolution X-ray diffraction data set was collected using synchrotron radiation. [source] Sodium Cation Migration Above the Diimine ,-System of Solvent Coordinated dpp-BIAN Sodium Aluminum Complexes (dpp-BIAN=1,2-Bis[(2,6-diisopropylphenyl)imino]acenaphthene)CHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2007Herbert Schumann Prof. Abstract The reactions of the disodium salt of the 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-BIAN) ligand with one equivalent of Me2AlCl in diethyl ether, toluene, and benzene produced the complexes [Na(Et2O)2(dpp-BIAN)AlMe2] (1), [Na(,6 -C7H8)(dpp-BIAN)AlMe2] (2) and [Na(,6 -C6H6)(dpp-BIAN)AlMe2] (3), respectively. Recrystallization of 1 from hexane afforded solvent-free [{Na(dpp-BIAN)AlMe2}n] (4) or [Na(Et2O)(dpp-BIAN)AlMe2] (5) depending on the temperature of the solvent. The molecular structures of 1,5 have been determined by single-crystal X-ray diffraction. The sodium cation coordinates either one of the naphthalene rings (1) or the diimine part of the dpp-BIAN ligand (2,5). In the complexes 2 and 3, the sodium cation additionally coordinates the toluene (2) or benzene molecule (3) in an ,6 -fashion. [source] Recrystallization and Shape Control of Crystals of the Organic Dye Acid Green 27 in a Mixed SolventCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2007Huai-Ping Cong Abstract Recrystallization of the unstructured dye acid green 27 (AG27) in a mixed solvent of alcohol (ethanol or methanol) and water was systematically studied. The results demonstrated that AG27 crystals with uniform sizes and controllable shapes can be produced by simply changing the volume ratio of ethanol (or methanol) and deionized water (DIW). Rodlike and shuttlelike AG27 crystals can be selectively synthesized. The XRD analyses revealed the periodic structures of the organic crystals. Furthermore, crystallization in another mixed solvent of N,N -dimethylformamide (DMF) and DIW results in the formation of longer fibers with high aspect ratio, which further validates the remarkable effects of mixed solvent on the shape of the AG27 crystals. This method of recrystallization in a mixed solvent is expected to facilitate the synthesis of other functional organic crystals with unusual shapes. [source] Cationic Scandium Allyl Complexes Bearing Mono(cyclopentadienyl) Ligands: Synthesis, Novel Structural Variety, and Olefin-Polymerization CatalysisCHEMISTRY - AN ASIAN JOURNAL, Issue 8-9 2008Nan Yu Abstract The one-pot salt-metathesis reaction of ScCl3, cyclopentadienyl lithium salts, and allylmagnesium chlorides afforded with ease the corresponding base-free half-sandwich scandium di(,3 -allyl) complexes [(C5Me4SiMe3)Sc(C3H5)2] (1,a), [(C5Me5)Sc(C3H5)2] (1,b), and [(C5Me5)Sc(2-MeC3H4)2] (1,c) in high yields. Reaction of 1,a with 1,equivalent of [PhNMe2H][B(C6F5)4] in toluene gave rapidly the N,N -dimethylaniline-coordinated cationic mono(,3 -allyl) complex [(C5Me4SiMe3)Sc(,3 -C3H5)(,6 -PhNMe2)][B(C6F5)4] (2). The similar reaction of 1,a with [Ph3C][B(C6F5)4] yielded the analogous toluene-separated ion pair [(C5Me4SiMe3)Sc(,3 -C3H5)(,6 -PhMe)][B(C6F5)4] (3). When [PhNMe2H][BPh4] was treated with 1,a, the contact ion pair [(C5Me4SiMe3)Sc(,3 -C3H5)( ,,,6 -Ph)BPh3] (4) was obtained. Recrystallization of 2, 3, and 4 in THF yielded the corresponding thf-separated ion pair complexes [(C5Me4SiMe3)Sc(,3 -C3H5)(thf)2][B(C6F5)4] (5) and [(C5Me4SiMe3)Sc(,3 -C3H5)(thf)2][BPh4] (6). The N,N -dimethylaniline-coordinated cationic scandium allyl complex 2 and the toluene-coordinated analogue 3 showed high activity (activity: 3>2) toward the polymerization and copolymerization of isoprene and norbornene to afford random copolymers with a broad range of isoprene content (33,86,mol,%). The tight ion pair 4 and the thf-coordinated complexes 5 and 6 showed no activity under the same conditions. These results offer unprecedented insight into the structure,activity relationship of a cationic metal polymerization-catalyst system. [source] 1,3,5-Triazapentadiene Nickel(II) Complexes Derived from a Ketoxime-Mediated Single-Pot Transformation of NitrilesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2010Maximilian N. Kopylovich Abstract A series of cationic (2+) [Ni{HN=C(R)NHC(R)=NH}2](X)2 {R = 4-(Cl)C6H4 (1), 3-(NC)C6H4 (3), 4-(NC)C6H4 (4) and Me (7); X = Cl, (1, 3, 4) or MeCOO,·H2O (7)} and neutral [Ni{HN=C(R)NC(R)=NH}2](solvate) {R = 3-(Cl)-4-py (2), 3-py (5) and 4-py (6); solvate = MeOH and/or H2O; py = pyridyl} N,N -chelating bis(1,3,5-triazapentadiene/ato)nickel(II) [Ni(tap)2]2+/0 complexes has been easily generated by a ketoxime-mediated single-pot reaction of a nickel(II) salt [NiCl2·2H2O or Ni(MeCOO)2·4H2O] with 4-chlorobenzonitrile, isophthalonitrile, terephthalonitrile, acetonitrile, 2-chloro-4-cyanopyridine, 3-cyanopyridine or 4-cyanopyridine, respectively. The obtained compounds have been characterized by IR, 1H and 13C{1H} NMR spectroscopy, FAB-MS(+) or ESI-MS(+), elemental analyses and single-crystal X-ray diffraction [for 7 and solvated mono- {1a·(Me2CO)0.33·(MeOH)0.67} and bis-deprotonated (2b·2Me2CO, 4b·CHCl3, 5b·Me2CO and 6b·MeOH) products, formed upon recrystallization of 1, 2, 4, 5 and 6, respectively]. The crystal structures of all compounds bear similar monomeric Ni(tap)2 units with a nearly square-planar geometry. In addition, the structure of 7 features the formation of infinite 1D zig-zag water,acetate chains {[(H2O)2(MeCOO)2]2,}n, which multiply interact with the [Ni(tap)2]2+ cations to generate a 2D hydrogen-bonded supramolecular assembly. [source] Equal Channel Angular Pressing of a Mg,3Al,1Zn Alloy with Back Pressure,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Feng Kang Abstract An extruded Mg,3Al,1Zn alloy bar is subjected to 1,4 passes equal channel angular pressing (ECAP) with or without 125,MPa backpressure via route Bc at 200,°C. Both strength and ductility are significantly increased after ECAP with backpressure; this is in strong contrast to the case of ECAP without backpressure, where significant improvement in ductility is accompanied by obvious decrease in yield strength from texture softening. Compared to ECAP without backpressure, much enhanced grain refinement, and the split of the dominant texture component of (0002) pole were observed with scatter intensity peaks in the case after ECAP with backpressure. This turns out to be resulted mainly from the activation of new slip system together with enhanced dynamic recrystallization under the effect of backpressure. The improvement of both strength and ductility in Mg,3Al,1Zn alloy through ECAP with back pressure provides a better approach to meet the engineering requests on comprehensive performance of this light alloy. [source] Recrystallization Modeling of AA8XXX Alloys with Cellular Automata Considering Recovering Kinetics,ADVANCED ENGINEERING MATERIALS, Issue 3 2010Carmen Schäfer A through-process modeling scheme for the prediction of recrystallization textures and microstructures after final annealing, subsequent to cold rolling is proposed and applied to a commercial AlFeSi alloy. The heart of the setup is a cellular automaton for modeling of recrystallization which considers changes in dislocation density by recovery and changes in Zener and solute drag due to microchemistry evolution. However, recrystallization is the crucial point in the whole setup, since it leads to significant changes in microstructure and texture. The simulated results are compared to experiments. [source] Oriented Grain Growth Analyses With In Situ Annealing Experiments Using High Energy Synchrotron RadiationADVANCED ENGINEERING MATERIALS, Issue 3 2010Caterina Elisabetta Tommaseo The development of the recrystallization and annealing textures of Al,Mn alloys with 0.4, 0.7 and 1,wt.-% manganese is analyzed using specific techniques that allow the detection of changes in grain orientation during in situ annealing. In order to investigate the evolution of texture components during annealing, highly rolled samples were annealed from room temperature to 500,°C at a constant heating rate. The advantage of in situ annealing experiments using synchrotron radiation is the detection of grain orientations over time, which allows observation of the development of the recrystallization and annealing textures in a sample. In fact, the recrystallization and annealing textures in the Al,0.4Mn are characterized by an interruption in the detection of most of the grain orientations between 380 and 425,°C and by competition between the cube {001}<100>, {011}<1-33>, {011}<0-11> and rotated-cube {001}<110> grain orientations, where the latter is detected until the end of the experiment. In the Al,0.7Mn sample a competition between the cube {001}<100>, {011}<100>, and rotated cube {001}<110>, {011}<0,11> grain orientations is observed. In the sample with the highest manganese concentration (1,wt.-%) an unhindered grain growth of all possible grain orientations with a high amount of the {011}<0-11> grain orientation is observed. The evolution of the resulting local textures is discussed in terms of preferentially oriented grain growth depending on the temperature and manganese concentration. [source] Microstructure and Texture Formation During Near Conventional Forging of an Intermetallic Ti,45Al,5Nb Alloy,ADVANCED ENGINEERING MATERIALS, Issue 12 2009Andreas Stark Abstract Texture formation was studied in an intermetallic Ti-45at%Al-5at%Nb alloy after uniaxial compression and near conventional forging. Depending on the deformation conditions the texture of the , -TiAl phase is formed by pure deformation components, components related to dynamic recrystallization, or transformation components. This changing corresponds with microstructural observations. The ,2 -Ti3Al and the , -Ti(Al) phase show a similar texture as it is known for Ti and Ti-base alloys after compressive deformation at elevated temperatures. In contrast to the , texture, no significant change of the ,/,2 texture was observed in the temperature range between 800,°C and just below the , -transus temperature (T,,=,1295,°C). [source] PE-UHMW in Hip Implants: Properties of Conventional and Crosslinked Prosthetic ComponentsADVANCED ENGINEERING MATERIALS, Issue 10 2009Ruth Markut-Kohl Hip implants made of crosslinked ultra high molecular weight polyethylene,PE-UHMW,(different as-received conditions) are compared with a retrieval made from non-crosslinked PE-UHMW and a control PE-UHMW. Oxidation leads to recrystallization and the enhanced crystallinity corresponds to higher hardness values. These structure-property relations are discussed for conventional PE-UHMW and also for crosslinked material. [source] In Situ Observation of Dynamic Recrystallization in the Bulk of Zirconium Alloy,ADVANCED ENGINEERING MATERIALS, Issue 8 2009Klaus-Dieter Liss Dynamic recrystallization and related effects have been followed in situ and in real time while a metal undergoes rapid thermo-mechanical processing. Statistics and orientation correlations of embedded/bulk material grains were deduced from two-dimensional X-ray diffraction patterns and give deep insight into the formation of the microstructure. Applications are relevant in materials design, simulation, and in geological systems. [source] Mechanism of Selective and Unselective Enclathration by a Host Compound Possessing Open, Flexible Host FrameworksEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2003Kazunori Nakano Abstract Molecular recognition of o -, m -, and p -xylenes (oX, mX, and pX) through enclathration of cholic acid (CA) is described. All of the xylenes give lattice inclusion crystals with CA, and crystallographic studies reveal that they are included in different open host frameworks. In particular, oX has two polymorphs, depending on the recrystallization temperatures. Competitive recrystallization from mixtures of xylenes resulted in selective enclathrations and the formation of racemic mixed crystals. In the presence of an equimolar amount of oX, CA selectively includes mX or pX in the host frameworks, which are identical to those obtained from the pure mX or pX, respectively. The low affinity of oX is explained in terms of a lower stability of CA·oX than of the other two complexes, as judged from the low PCcavity, the volume ratio of the guest compound to the host cavity. Meanwhile, mixtures of mX and pX yield inclusion crystals that accommodate both of the guests. These have the same open host framework as obtained from pure mX, and the guest components are disordered statically in the host cavity. The ratios of the xylene mixtures in the single crystals are similar to those in the original recrystallization mixtures, and also in the bulk crystals, indicating that CA forms mixed crystals of mX and pX. This non-selectivity is attributed to the similar stabilities of CA·mX and CA·pX, according to the moderate PCcavity. The inclusion behavior of CA from mixtures of xylenes is quite similar to chiral recognition by diastereomer-salt methods. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Influence of Deformation on Recrystallization of an Yttrium Oxide Dispersion-Strengthened Iron Alloy (PM2000),ADVANCED ENGINEERING MATERIALS, Issue 4 2003C. Capdevila Montes A two-fold effect of non-uniform deformation of the yttria-strengthened Fe alloy PM2000 has been revealed by analysis of the microstructure: Firstly, recrystallization temperature decreases, in accordance with the hypothesis that anything that makes the original microstructure more heterogeneous will encourage recrystallization; and secondly, the increase in number and density of recrystallization nuclei leads to fine grain structures which are more 3D isotropic. [source] Engineering of a monomeric and low-glycosylated form of human butyrylcholinesteraseFEBS JOURNAL, Issue 2 2002Expression, characterization, crystallization, purification Human butyrylcholinesterase (BChE; EC 3.1.1.8) is of particular interest because it hydrolyzes or scavenges a wide range of toxic compounds including cocaine, organophosphorus pesticides and nerve agents. The relative contribution of each N-linked glycan for the solubility, the stability and the secretion of the enzyme was investigated. A recombinant monomeric BChE lacking four out of nine N-glycosylation sites and the C-terminal oligomerization domain was stably expressed as a monomer in CHO cells. The purified recombinant BChE showed catalytic properties similar to those of the native enzyme. Tetragonal crystals suitable for X-ray crystallography studies were obtained; they were improved by recrystallization and found to diffract to 2.0 Å resolution using synchrotron radiation. The crystals belong to the tetragonal space group I422 with unit cell dimensions a = b = 154.7 Å, c = 124.9 Å, giving a Vm of 2.73 Å3 per Da (estimated 60% solvent) for a single molecule of recombinant BChE in the asymmetric unit. The crystal structure of butyrylcholinesterase will help elucidate unsolved issues concerning cholinesterase mechanisms in general. [source] Speleothem preservation and diagenesis in South African hominin sites implications for paleoenvironments and geochronologyGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 5 2009Philip J. Hopley Plio-Pleistocene speleothems from australopithecine-bearing caves of South Africa have the potential to yield paleoenvironmental and geochronological information using isotope geochemistry. Prior to such studies it is important to assess the preservation of geochemical signals within the calcitic and aragonitic speleothems, given the tendency of aragonitic speleothems to recrystallize to calcite. This study documents the geochemical suitability of speleothems from the principal hominin-bearing deposits of South Africa. We use petrography, together with stable isotope and trace element analysis, to identify the occurrence of primary aragonite, primary calcite, and secondary calcite. This study highlights the presence of diagenetic alteration at many of the sites, often observed as interbedded primary and secondary fabrics. Trace element and stable isotopic values distinguish primary calcite from secondary calcite and offer insights into geochemical aspects of the past cave environment. ,13C values of the primary and secondary calcites range from +6 to ,9, and ,18O values range from ,4 to ,6,. The data are thus typical of meteoric calcites with highly variable ,13C and relatively invariant ,18O. High carbon isotope values in these deposits are associated with the effects of recrystallization and rapid outgassing of CO2 during precipitation. Mg/Ca and Sr/Ca ratios differ between primary and secondary calcite speleothems, aiding their identification. Carbon and oxygen isotope values in primary calcite reflect the proportion of C3 and C4 vegetation in the local environment and the oxygen isotope composition of rainfall. Primary calcite speleothems preserve the pristine geochemical signals vital for ongoing paleoenvironmental and geochronological research. © 2009 Wiley Periodicals, Inc. [source] The mechanism of fluid infiltration in peridotites at Almklovdalen, western NorwayGEOFLUIDS (ELECTRONIC), Issue 3 2002O. Kostenko Abstract A major Alpine-type peridotite located at Almklovdalen in the Western Gneiss Region of Norway was infiltrated by aqueous fluids at several stages during late Caledonian uplift and retrogressive metamorphism. Following peak metamorphic conditions in the garnet,peridotite stability field, the peridotite experienced pervasive fluid infiltration and retrogression in the chlorite,peridotite stability field. Subsequently, the peridotite was infiltrated locally by nonreactive fluids along fracture networks forming pipe-like structures, typically on the order of 10 m wide. Fluid migration away from the fractures into the initially impermeable peridotite matrix was facilitated by pervasive dilation of grain boundaries and the formation of intragranular hydrofractures. Microstructural observations of serpentine occupying the originally fluid-filled inclusion space indicate that the pervasively infiltrating fluid was characterized by a high dihedral angle (, > 60°) and ,curled up' into discontinuous channels and fluid inclusion arrays following the infiltration event. Re-equilibration of the fluid phase topology took place by growth and dissolution processes driven by the excess surface energy represented by the ,forcefully' introduced external fluid. Pervasive fluid introduction into the peridotite reduced local effective stresses, increased the effective grain boundary diffusion rates and caused extensive recrystallization and some grain coarsening of the infiltrated volumes. Grain boundary migration associated with this recrystallization swept off abundant intragranular fluid inclusions in the original chlorite peridotite, leading to a significant colour change of the rock. This colour change defines a relatively sharp front typically located 1,20 cm away from the fractures where the nonreactive fluids originally entered the peridotite. Our observations demonstrate how crustal rocks may be pervasively infiltrated by fluids with high dihedral angles (, > 60°) and emphasize the coupling between hydrofracturing and textural equilibration of the grain boundary networks and the fluid phase topology. [source] Finite element formulation for modelling large deformations in elasto-viscoplastic polycrystalsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 14 2004Karel Matou Abstract Anisotropic, elasto-viscoplastic behaviour in polycrystalline materials is modelled using a new, updated Lagrangian formulation based on a three-field form of the Hu-Washizu variational principle to create a stable finite element method in the context of nearly incompressible behaviour. The meso-scale is characterized by a representative volume element, which contains grains governed by single crystal behaviour. A new, fully implicit, two-level, backward Euler integration scheme together with an efficient finite element formulation, including consistent linearization, is presented. The proposed finite element model is capable of predicting non-homogeneous meso-fields, which, for example, may impact subsequent recrystallization. Finally, simple deformations involving an aluminium alloy are considered in order to demonstrate the algorithm. Copyright © 2004 John Wiley & Sons, Ltd. [source] Asymmetric Lithiation of Boron Trifluoride-Activated Aminoferrocenes: An Experimental and Computational InvestigationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Costa Metallinos Abstract Tertiary aminoferrocenes complexed to boron trifluoride (BF3) are shown to undergo asymmetric lithiation with alkyllithiums in the presence of bulky chiral 1,2-diaminocyclohexane ligands. This reaction represents the first BF3 -activated asymmetric lithiation of a prochiral aromatic amine and the first such transformation to be mediated by a chiral diamine other than (,)-sparteine. The process provides rapid access to a broad range of enantiomerically enriched 2-substituted-1-aminoferrocenes, including derivatives with uncommon substitution patterns that are of interest in catalysis. The enantioselectivity of the process is high enough (87:13 to 91:9 er) to allow for isolation of single enantiomers of several products after simple recrystallization as either the free aminoferrocenes or their ammonium fluoroborate salts. Both antipodes of the planar chiral 2-substituted-1-aminoferrocene products are accessible, as confirmed by single crystal X-ray diffraction analysis of two compounds with opposite relative stereochemistry. Single-point calculation of thirty-two different transition states of the reaction at the M06-2X/6-311+g(2d,2p) level produced a computational model that correctly predicted both the sense and extent of chiral induction. Three factors appeared to play important roles in determining enantioinduction during lithiation of BF3 -complexed tertiary aminoferrocenes: (i) the maintenance of a highly organized eight-membered ring transition state; (ii) the existence of a strong Li,,,F contact which placed the chiral diamine ligand in close proximity to the ferrocene substrate; (iii) the orientation of the sterically demanding N -alkyl groups of the chiral diamine additives, either away or towards, the aminoferrocene and the alkyllithium. The model may serve as a predictive tool for the rational design of new ligands for this and related asymmetric lithiations. [source] Three-dimensional finite strain analysis in the high-grade part of the Sanbagawa Belt using deformed meta-conglomerateISLAND ARC, Issue 2 2002Yoshinori Moriyama Abstract Regional ductile deformation of the Sanbagawa belt is generally thought to be characterized by constrictional strain, based on strain analysis using deformed radiolarians in the low-grade regions. Similar strain analysis could not be carried out in the medium- to high-grade zones, because it is very difficult to identify individual radiolarians after strong recrystallization. However, discovery of the first known meta-conglomerate in the high-grade region of the Sanbagawa Belt allows quantitative 3-D strain to be estimated in this region. Using a development of the Rf-, method, an evaluation of appropriate errors for this estimate can be determined. The principal strain ratios and estimated errors are X/Y = 5.4,6.6 and Y/Z = 3.8,3.9 implying deformation in the flattening field and refuting the idea of uniform constrictional strain. Semi-quantitative markers of the shape of the strain ellipse throughout the high-grade regions suggest that the deformation of the Sanbagawa Belt is dominantly in the flattening field. The difference with the earlier results may be due to late-stage overprinting by upright folding of the main ductile fabric in the low-grade region of western Shikoku. [source] Nanoparticles of CdCl2 with closed cage structuresISRAEL JOURNAL OF CHEMISTRY, Issue 1 2001Reshef Tenne Nanoparticles of various layered compounds having a closed cage or nanotubular structure, designated also inorganic fullerene-like (IF) materials, have been reported in the past. In this work IF -CdCl2 nanoparticles were synthesized by two methods. In one technique, a high temperature evaporation and subsequent condensation of dried cadmium chloride powder was used. In the other method, electron beam irradiation of the source powder led to its recrystallization into closed nanoparticles with a nonhollow core. The two methods are shown to produce nanoparticles of different topologies. While mostly spherical nested structures are obtained from the high temperature process, polyhedra with hexagonal or elongated rectangular characters are obtained by the electron beam induced process. The analysis also shows that, while the source (dried) powder is orthorhombic cadmium chloride monohydrate, the crystallized IF cage consists of the anhydrous 3R polytype which is not stable as bulk material in ambient atmosphere. Consistent with previous observations, this study shows that the seamless structure of the IF materials can stabilize phases, which are otherwise unstable in ambient conditions. [source] Enantioselective Michael Addition of Dicyanoolefins to ,,,-Unsaturated Aldehydes in Aqueous MediumADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2008Jun Lu Abstract A pool of water-compatible catalysts, namely dialkyl-(S)-prolinols, has been developed for the enantioselective direct vinylogous Michael addition reaction of vinylmalononitriles to ,,,-unsaturated aldehydes in aqueous medium. In many cases, the products can be obtained in almost optically pure form (>96% ee) after a single recrystallization. [source] Synchrotron texture analysis with area detectorsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2003H.-R. Wenk The wide availability of X-ray area detectors provides an opportunity for using synchrotron radiation based X-ray diffraction for the determination of preferred crystallite orientation in polycrystalline materials. These measurements are very fast compared to other techniques. Texture is immediately recognized as intensity variations along Debye rings in diffraction images, yet in many cases this information is not used because the quantitative treatment of texture information has not yet been developed into a standard technique. In special cases it is possible to interpret the texture information contained in these intensity variations intuitively. However, diffraction studies focused on the effects of texture on materials properties often require the full orientation distribution function (ODF) which can be obtained from spherical tomography analysis. In cases of high crystal symmetry (cubic and hexagonal) an approximation to the full ODF can be reconstructed from single diffraction images, as is demonstrated for textures in rolled copper and titanium sheets. Combined with area detectors, the reconstruction methods make the measurements fast enough to study orientation changes during phase transformations, recrystallization and deformation in situ, and even in real time, at a wide range of temperature and pressure conditions. The present work focuses on practical aspects of texture measurement and data processing procedures to make the latter available for the growing community of synchrotron users. It reviews previous applications and highlights some opportunities for synchrotron texture analysis based on case studies on different materials. [source] Effect of precipitate size and dispersion on recrystallization behavior in Ti-added ultra low carbon steelsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2003E. J. Shin The effect of coiling temperature on precipitates and solid solution was investigated in P-free and P-added Ti-stabilized ultra low carbon steels. The volume fractions of the fine precipitates smaller than 60 nm were evaluated by using small-angle neutron scattering technique. The solute P was quantified from the lattice parameters obtained from neutron diffraction patterns. In the P-free steels, TiC and Ti4C2S2 with various sizes ranging from 5~60 nm were observed. In addition to these precipitates, FeTiP precipitates of a size exceeding 50 nm were also observed in the P-added steel. The amount of fine precipitates smaller than 10 nm and the concentration of solute P was higher in the samples coiled at low temperature. The recrystallization temperature increases if the coiling temperature decreases in both, P-free and P-added steels. The recrystallization temperature of P-free steels is lower than that of P-added steels. In the P-free steels, the pinning effect of fine precipitates played a key role for the retardation of the recrystallization. In the P-added steels, the retardation of recrystallization is due to both, the pinning effect of fine precipitates and the solute drag effect of P in solid solution. [source] | ||||||||||||||||||||||||||||||||||||||||