X-ray Diffraction Patterns (x-ray + diffraction_pattern)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of X-ray Diffraction Patterns

  • powder x-ray diffraction pattern

  • Selected Abstracts

    Rational, Facile Synthesis and Characterization of the Neutral Mixed-Metal Organometallic Oxides Cp*2MoxW6,xO17 (Cp* = C5Me5, x = 0, 2, 4, 6)

    Glnur Taban-al
    Abstract The reaction of the bis(pentamethylcyclopentadienyl)pentaoxidodimetal complexes Cp*2M2O5 with four equivalents of Na2M,O4 (M, M, = Mo, W) in acidic aqueous medium constitutes a soft and selective entry into neutral Lindqvist-type organometallic mixed-metal oxides Cp*2MoxW6,xO17 [x = 6 (1), 4 (2), 2 (3), 0 (4)]. The identity of the complexes is demonstrated by elemental analyses, thermogravimetric analyses and infrared spectroscopy. Thermal degradation of 1,4 up to above 500 C leads to Mox/6W1,x/6O3. The molecular identity and geometry of compound 2 is further confirmed by a fit of the powder X-ray diffraction pattern with a model obtained from previously reported single-crystal X-ray structures of 1 and 4, with which 2 is isomorphous. DFT calculations on models obtained by replacing Cp* with Cp (I,IV) validate the structural assignments and assist in the assignment of the M,M,,O vibrations. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Comparative analysis of triacylglycerol composition, melting properties and polymorphic behavior of palm oil and fractions

    Sabine Braipson-Danthine
    Abstract Palm oil is without doubt the most widely fractionated oil. Dry fractionation is based on differences in the melting points of triacylglycerols (TAG) which will crystallize selectively during the cooling process. Unfortunately, limitations due to intersolubility, closely linked to polymorphism, induce formation of co-crystals at each crystallization step. For this reason, only restricted TAG enrichments are observed. In this work, a series of samples (24) of palm oil, solid and liquid fractions (stearins, mid fractions, oleins and superoleins) have been selected and examined in terms of TAG composition (by HPLC), differential scanning calorimetry (DSC) melting profile and variable temperature powder X-ray diffraction pattern. Three major endotherms [low-melting, high-melting and very high-melting peaks (LMP, HMP and VHMP)] are detected in the DSC melting profiles (5,C/min). The VHMP is only recorded for palm stearin which contains more SSS components. The HMP contribution is weak for palm olein and even not observed for palm super oleins. The LMP is usually made up of UUU, SUU and SUS components; SUS components are observed in both LMP and HMP; the HMP is also made up of some SSS, except for palm oleins and super oleins. Sub-,2, sub-,1, ,, ,'2, ,'1 and , polymorphic forms are recorded; the LMP components preferentially crystallize in sub-,2, sub-,1 and ,,forms; the HMP components generally crystallize in ,'2 and ,'1, with a tendency to exhibit ,,crystals, depending on the SSS content. Components of the VHMP have an increased tendency to stabilize in the ,,form; in view of the results, we can assume that there is a clear relationship between TAG composition, melting properties and polymorphic behavior and of palm oil and fractions. [source]

    Study of Cation Ordering in Ba(Yb1/2Ta1/2)O3 by X-Ray Diffraction and Raman Spectroscopy

    Dibyaranjan Rout
    The complex perovskite Ba(Yb1/2Ta1/2)O3 has been prepared by the two-stage solid-state reaction method. Rietveld' refinement analysis indicates cubic perovskite phase with space group . The 1:1 cation ordering at the B-site is revealed by the presence of (111) superlattice reflection in the X-ray diffraction pattern and further evidenced by the presence of A1g and F2g vibrational modes in the Raman spectra. The dielectric constant is measured to be 29.1, the product of quality factor and resonant frequency (Qf) is found to be 32,000 GHz and the temperature coefficient of resonant frequency (,f) is 135 (ppm/C) in the temperature range 30,70C. [source]

    On the tetragonality of the room-temperature ferroelectric phase of barium titanate, BaTiO3

    Dean S. Keeble
    The room-temperature phase of the important ferroelectric material barium titanate, BaTiO3, was re-investigated by single-crystal X-ray diffraction on a sample grown by the top-seeded solution growth method, with the intention of demonstrating once again that the structure has tetragonal symmetry consistent with the space-group assignment P4mm and thus resolving recent controversy in the scientific community and literature [Yoshimura, Kojima, Tokunaga, Tozaki & Koganezawa (2006). Phys. Lett. A, 353, 250,254; Yoshimura, Morioka, Kojima, Tokunaga, Koganezawa & Tozaki (2007). Phys. Lett. A, 367, 394,401]. To this end, the X-ray diffraction pattern of a small (341,m3) sample of top-seeded solution-grown BaTiO3 was measured using an Oxford Diffraction Gemini CCD diffractometer employing Mo,K, radiation and an extended 120,mm sample-to-detector distance. More than 104 individual diffraction maxima observed out to a maximum resolution of 0.4, were indexed on two tetragonal lattices. These were identical to within the standard deviations on the lattice parameters and were related to each other by a single rotation of 119.7 about the [11] direction of the first tetragonal lattice (the major twin component), although the actual twinning operation that explains the observed diffraction pattern both qualitatively and quantitatively is shown to be conventional 90 twinning by the m[101] operation. Importantly, it is not necessary to invoke either monoclinic symmetry or a coexistence of tetragonal and monoclinic phases to explain the observed diffraction data. [source]

    Amorphous orientation and its relationship to processing stages of blended polypropylene/polyethylene fibers

    Amy M. Trottier
    Abstract Changes in the molecular orientation, melting behavior, and percent crystallinity of the individual components in a fibrous blend of isotactic polypropylene (iPP) and high-density polyethylene (HDPE) that occur during the melt extrusion process were examined using wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The crystalline orientation of each component was found using Wilchinsky's treatment of uniaxial orientation and described by the Hermans,Stein orientation parameter. The amorphous orientation was found by resolving the X-ray diffraction pattern in steps of the azimuthal angle into its iPP and HDPE crystalline and amorphous reflections. The utility of DSC and WAXD analyses to capture the effects of small differences in processing, and the use of these results as fingerprints of a particular manufacturing process were demonstrated. Major increases in the melting temperatures, percent crystallinities, and molecular orientations of the iPP and HDPE components occurred during the main stretching stage of the melt extrusion process. The annealing stage was found to have little to no effect on the melting behavior and molecular orientation of these components. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Effects of MgCl2 Crystallographic Structure on Active Centre Formation in Immobilized Single-Centre and Ziegler,Natta Catalysts for Ethylene Polymerization

    Rubin Huang
    Abstract The ability of a MgCl2 support to activate a transition metal catalyst has been found to depend both on the crystallographic structure of the support and on the nature of the catalyst. A high degree of crystallographic disorder can be very effective for the immobilization and activation of titanium and vanadium complexes, but is not necessarily effective for zirconocene activation. A highly disordered support prepared by the reaction of MgBu2 with HCl gave high activity with TiCl4 but low activity with (n -PrCp)2ZrCl2. High polymerization activities with the zirconocene were only obtained with supports of type MgCl2/AlRn(OEt)3,n prepared from the reaction of AlR3 with MgCl2,,1.1EtOH. These supports are characterized by additional peaks in the X-ray diffraction pattern, indicating the presence of a crystalline structure which is absent in the other supports and contains highly Lewis acidic sites able to generate the active metallocenium species. [source]

    Submicron resolution X-ray diffraction from periodically patterned GaAs nanorods grown onto Ge[111]

    Anton Davydok
    Abstract We present high-resolution X-ray diffraction pattern of periodic GaAs nanorods (NRs) ensembles and individual GaAs NRs grown catalyst-free throughout a pre-patterned amorphous SiNx mask onto Ge[111]B surfaces by selective-area MOVPE method. To the best of our knowledge this is the first report about nano-structure X-ray characterization growth on non-polar substrate. The experiment has been performed at home laboratory and using synchrotron radiation using a micro-sized beam prepared by compound refractive lenses. Due to the non-polar character of the substrate the shapes of NRs appear not uniform and vary between deformed hexagonal and trigonal in symmetry. Because the average diameter of NRs equals the experimental resolution certain cuts through slightly inclined edges or corners of individual NRs with lateral size of about 225,nm could be selected using spatially resolved reciprocal space mapping. [source]

    Effect of clay with different cation exchange capacity on the morphology and properties of poly(methyl methacrylate)/clay nanocomposites

    POLYMER COMPOSITES, Issue 11 2009
    Tsung-Yen Tsai
    PMMA/clay nanocomposites were successfully prepared by in situ free-radical polymerization with the organic modified MMT-clay using methyl methacrylate monomer and benzoyl peroxide initiator. Two clays with different cation exchange capacity have been used to prepare and compare the several properties. The clays have been modified using Amphoterge K2 by ion exchange reaction to increase the compatibility between the clay and polymer matrices. The modified clays have been characterized by wide-angle X-ray diffraction pattern, Fourier transform infrared spectroscopy, and thermogravimetric analysis (TGA). The powdered X-ray diffraction and transmission electron microscopy techniques were employed to study the morphology of the PMMA/clay nanocomposites which indicate that the modified clays are dispersed in PMMA matrix to form both exfoliated and intercalated PMMA/modified clay nanocomposites. The thermomechanical properties were examined by TGA, differential scanning calorimetry, and dynamic mechanical analysis. Gas permeability analyzer shows the excellent gas barrier property of the nanocomposites, which is in good agreement with the morphology. The optical property was measured by UV,vis spectroscopy which shows that these materials have good optical clarity and UV resistance. POLYM. COMPOS., 2009. 2008 Society of Plastics Engineers [source]

    Phase transition of triclinic hen egg-white lysozyme crystal associated with sodium binding

    Kazuaki Harata
    A triclinic crystal of hen egg-white lysozyme obtained from a D2O solution at 313,K was transformed into a new triclinic crystal by slow release of solvent under a temperature-regulated nitrogen-gas stream. The progress of the transition was monitored by X-ray diffraction. The transition started with the appearance of strong diffuse streaks. The diffraction spots gradually fused and faded with the emergence of diffraction from the new lattice; the scattering power of the crystal fell to a resolution of 1.5, from the initial 0.9, resolution. At the end of the transition, the diffuse streaks disappeared and the scattering power recovered to 1.1, resolution. The transformed crystal contained two independent molecules and the solvent content had decreased to 18% from the 32% solvent content of the native crystal. The structure was determined at 1.1, resolution and compared with the native structure refined at the same resolution. The backbone structures of the two molecules in the transformed crystal were superimposed on the native structure with root-mean-square deviations of 0.71 and 0.96,. A prominent structural difference was observed in the loop region of residues Ser60,Leu75. In the native crystal, a water molecule located at the centre of this helical loop forms hydrogen bonds to main-chain peptide groups. In the transformed crystal, this water molecule is replaced by a sodium ion with octahedral coordination that involves water molecules and a nitrate ion. The peptide group connecting Arg73 and Asn74 is rotated by 180 so that the CO group of Arg73 can coordinate to the sodium ion. The change in the X-ray diffraction pattern during the phase transition suggests that the transition proceeds at the microcrystal level. A mechanism is proposed for the crystal transformation. [source]

    Effect of Pb on the properties of Sr2YRu1-xCuxO6 crystals grown from PbO-PbF2 solutions at high temperatures

    S. M. Rao
    Abstract Single crystals of Sr2YRu1-xCuxO6 with x=0 and x=0.1 were grown using PbO-PbF2 based solutions at different temperatures in the range 1150,1350C. The influence of Pb from the solutions and the Cu from the solid solutions of Sr2YRu1-xCuxO6 on the resulting crystals was studied using microstructure and magnetic property measurements. The peaks in the powder X-ray diffraction patterns and Raman spectra do not change in the case of x=0 crystals but shift in the presence of Cu. A diamagnetic transition indicative of superconductivity was observed in the presence of Cu and an antiferromagnetic behavior with x=0. Based on these results it is concluded that Pb may not be incorporated in the crystals and even if it does the influence is not observed. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Thermoelectric properties of RE2,xMxCuO4 oxide sintering bulks

    Yusuke Ichino
    Abstract La2,xSrxCuO4 (LSCO) and Sm2,xCexCuO4 (SCCO) polycrystal bulks with x=0 to 0.10 were made by solid-phase reaction method. From the X-ray diffraction patterns, LSCO and SCCO were confirmed single phase. Seebeck coefficient, resistivity, and heat conductivity decreased with increasing amount of Sr2+ and Ce2+ substitution. We estimated ZT from these values and found that the highest value of ZT=0.034 at 323 K was achieved in the LSCO with x=0.02. As a result, we conclude that LSCO and SCCO showed high thermoelectric properties around room temperature. We can expect RE2,xMxCuO4 will be a very useful material for thermoelectric module operating at room temperature. 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 91(12): 24,28, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10003 [source]

    In Situ Observation of Dynamic Recrystallization in the Bulk of Zirconium Alloy,

    Klaus-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]

    Transformation of haematite and Al-poor goethite to Al-rich goethite and associated yellowing in a ferralitic clay soil profile of the middle Amazon Basin (Manaus, Brazil)

    E. Fritsch
    Summary The red and yellow colours of ferralitic soils in the tropics have for long intrigued pedologists. We have investigated the upward yellowing in a 10-m thick profile representative of the Ferralsols of the plateaux of the Manaus region of Brazil. We determined changes in the nature and crystal chemistry of their Fe oxides by optical and Mssbauer spectroscopy as well as Rietveld refinement of X-ray diffraction patterns. We attribute the upward yellowing of the soil to a progressive transformation of the Fe oxides at nearly invariant iron contents. Aluminium in contrast is strongly mobilized in the uppermost clay-depleted topsoil where there is preferential dissolution of kaolinite and crystallization of gibbsite. Haematite decreases from 35 to 10% of the Fe oxides from the bottom to the top of the profile and the particles become smaller (75,10 nm). Its Al for Fe-substitution remains almost unchanged (10,15 mol %). The average Al-substitution rate of goethite increases from 25 to 33 mol %, and its mean crystal diameter remains in the range 20,40 nm. The proportion of Al-rich goethite (33 mol %) increases at the expense of less Al-substituted Fe oxides (haematite and goethite). This conversion with restricted transfer of iron means that the amount of Al stored in Fe oxides gradually increases. Kaolinite, haematite and Al-poor goethite are thus witnesses of earlier stages of ferralitization of the soil. In contrast, Al-rich goethite and gibbsite initiate the alitization (or bauxitization) of the soil. They correspond to the last generation of soil minerals, which most likely reflects the present-day weathering conditions. The progressive replacement of kaolinite, haematite and Al-poor goethite by new generations of Al-rich goethite and gibbsite attests to greater activities of water and aluminium and smaller activity of aqueous silica in the topsoil than in the subsoil. We interpret this as a consequence of longer periods of wetting in the topsoil that could result from soil aging, more humid climate or both. [source]

    Electrochemical Method for Synthesis of a ZnFe2O4/TiO2 Composite Nanotube Array Modified Electrode with Enhanced Photoelectrochemical Activity

    Yang Hou
    Abstract An electrode with intimate and well-aligned ZnFe2O4/TiO2 composite nanotube arrays is prepared via electrochemical anodization of pure titanium foil in fluorine-containing ethylene glycol, followed by a novel cathodic electrodeposition method. The deposition of ZnFe2O4 is promoted in the self-aligned, vertically oriented TiO2 nanotube arrays but minimized at the tube entrances. Thus, pore clogging is prevented. Environmental scanning electron microscopy, energy-dispersive X-ray spectra, high-resolution transmission electron microscopy, X-ray diffraction patterns, and X-ray photoelectron spectroscopy indicate that the as-prepared samples are highly ordered and vertically aligned TiO2 nanotube arrays with ZnFe2O4 nanoparticles loading. The TiO2 nanotubes are anatase with the preferential orientation of <101> plane. Enhanced absorption in both UV and visible light regions is observed for the composite nanotube arrays. The current,voltage curve of ZnFe2O4 -loaded TiO2 nanotube arrays reveals a rectifying behavior. The enhanced separation of photoinduced electrons and holes is demonstrated by surface photovoltage and photocurrent measurements. Meanwhile, the photoelectrochemical investigations verify that the ZnFe2O4/TiO2 composite nanotube array modified electrode has a more effective photoconversion capability than the aligned TiO2 nanotube arrays alone. In addition, the photoelectrocatalytic ability of the novel electrode is found enhanced in the degradation of 4-chlorophenol. [source]

    Self-Assembled Nanostructures: Role of Water in Directing Diphenylalanine Assembly into Nanotubes and Nanowires (Adv. Mater.

    ADVANCED MATERIALS, Issue 5 2010
    The controllable assembly behavior of diphenylalanine molecules to form nanowires (NWs) and nanotubes (NTs) and their structural details are presented. Hyotcherl Ihee, Sang Ouk Kim and co-workers show on p. 583 that the nanoscale morphologies are closely related to molecular arrangements of diphenylalanine as revealed by Rietveld refinement of powder X-ray diffraction patterns and electron-density distributions in NTs and NWs via the maximum entropy method analysis. [source]

    Role of Water in Directing Diphenylalanine Assembly into Nanotubes and Nanowires

    ADVANCED MATERIALS, Issue 5 2010
    Jangbae Kim
    The controllable assembly behavior of diphenylalanine molecules to form nanowires (NWs) and nanotubes (NTs) and their structural details are presented (see figure). The nanoscale morphologies are closely related to molecular arrangements of diphenylalanine as revealed by Rietveld refinement of powder X-ray diffraction patterns and electron-density distributions in NTs and NWs via the maximum entropy method analysis. [source]

    Solid-State Supramolecular Organization of Polythiophene Chains Containing Thienothiophene Units

    ADVANCED MATERIALS, Issue 10-11 2009
    Patrick Brocorens
    Abstract We use molecular modeling and the simulation of X-ray diffraction patterns to determine the molecular packing of a thiophene-based polymer showing exceptionally high field-effect mobilities (up to 1,cm2,V,1,s,1). We focus on the organization of the polymer chains in lamellae and the orientation of these crystalline domains with respect to the substrate in thin films. The analysis is supported by XRD and NEXAFS experiments and is complemented by calculating intermolecular transfer integrals, which govern the charge mobility. [source]

    In-situ small-angle scattering study on the formation of a nanocrystalline soft-magnetic alloy

    D. R. Dos Santos
    A detailed study is presented on the nanocrystallization of the amorphous alloy Fe86Zr7Cu 1B6 (indices indicate at. %). Melt-spun ribbons were rapidly annealed by Joule heating, and the electrical resistance showed strong variations during thermal treatment. X-ray diffraction patterns indicate that these variations are related to the nucleation and growth of ,-Fe nanocrystals, and from peak profile analysis we obtained the average grain size and crystalline volume fraction for different annealing currents. The disorder-order transition was studied by in-situ small-angle X-ray scattering during conventional furnace treatments. SAXS intensity evolution for different temperatures, both below and above the crystallization temperature of the alloy, showed that a fast atomic rearrangement leads to the formation of atomic clusters before crystallization. The evolution of the size distribution function of these clusters as a function of time and temperature was obtained assuming a polydisperse system of spherical particles. [source]

    Polypropylene/clay nanocomposites prepared by in situ grafting-melt intercalation with a novel cointercalating monomer

    Pingan Song
    Abstract Polypropylene (PP)/clay nanocomposites were prepared by melt-compounding PP with organomontmorillonite (OMT), using maleic anhydride grafted polypropylene (PP- g -MA) as the primary compatibilizer and N -imidazol- O -(bicyclo pentaerythritol phosphate)- O -(ethyl methacrylate) phosphate (PEBI) as the cointercalating monomer. X-ray diffraction patterns indicated that the larger interlayer spacing of OMT in PP was obtained due to the cointercalation monomer having a large steric volume and the d -spacing further increased with the addition of PP- g -MA, as evidenced by transmission electron microscopy. Thermogravimetric analysis revealed that the PEBI-containing PP nanocomposites exhibited better thermal stability than PEBI-free PP composites. Dynamic mechanical analysis demonstrated that the storage modulus was significantly enhanced, and the glass transition temperature (Tg) shifted slightly to low temperature with the incorporation of clay for PP/OMT hybrids. PEBI-containing PP/OMT composites gave a lower Tg value because of the strong internal plasticization effect of PEBI in the system. Cone calorimetry showed that the flame-retardancy properties of PP nanocomposites were highly improved with the incorporation of PEBI. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Mechanical and morphological properties of organic,inorganic, hybrid, clay-filled, and cyanate ester/siloxane toughened epoxy nanocomposites

    S. Nagendiran
    Abstract Organic,inorganic hybrids involving cyanate ester and hydroxyl-terminated polydimethylsiloxane (HTPDMS) modified diglycidyl ether of bisphenol A (DGEBA; epoxy resin) filled with organomodified clay [montmorillonite (MMT)] nanocomposites were prepared via in situ polymerization and compared with unfilled-clay macrocomposites. The epoxy-organomodified MMT clay nanocomposites were prepared by the homogeneous dispersion of various percentages (1,5%), and the resulting homogeneous epoxy/clay hybrids were modified with 10% HTPDMS and ,-aminopropyltriethoxysilane as a coupling agent in the presence of a tin catalyst. The siliconized epoxy/clay prepolymer was further modified separately with 10% of three different types of cyanate esters, namely, 4,4,-dicyanato-2,2,-diphenylpropane, 1,1,-bis(3-methyl-4-cyanatophenyl) cyclohexane, and 1,3-dicyanato benzene, and cured with diaminodiphenylmethane as a curing agent. The reactions during the curing process between the epoxy, siloxane, and cyanate were confirmed by Fourier transform infrared analysis. The results of dynamic mechanical analysis showed that the glass-transition temperatures of the clay-filled hybrid epoxy systems were lower than that of neat epoxy. The data obtained from mechanical studies implied that there was a significant improvement in the strength and modulus by the nanoscale reinforcement of organomodified MMT clay with the matrix resin. The morphologies of the siloxane-containing, hybrid epoxy/clay systems showed heterogeneous character due to the partial incompatibility of HTPDMS. The exfoliation of the organoclay was ascertained from X-ray diffraction patterns. The increase in the percentage of organomodified MMT clay up to 5 wt % led to a significant improvement in the mechanical properties and an insignificant decrease in the glass-transition temperature versus the unfilled-clay systems. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source]

    Chemical Structure and Physical Properties of Mung Bean Starches Isolated from 5 Domestic Cultivars

    S.-H. Kim
    ABSTRACT:, Chemical structure and physical properties of starches isolated from 5 domestic mung bean cultivars (Gyungsun, Geumsung, Sunhwa, Eohul, and Jangan) were examined. The granules were jelly bean like in shape and smooth on surface, and the size was within 10 to 30 ,m. Mung bean starches displayed a CA -type crystalline structure when judged by the X-ray diffraction patterns. Branch chain-length distribution patterns of amylopectin (AP) revealed that peak chain length of APs was at either DP (degree of polymerization) 12 or DP13. Apparent amylose contents of 5 cultivars by iodine affinity test were 31.7% to 33.8%. Mung bean APs showed a unique molecular size distribution that has not been observed from other plant-derived starches. Two distinct peaks of AP fraction were identified on the size-exclusion chromatogram, and the ratios of these 2 peaks were different depending on the mung bean cultivars. Weight-average chain length (CLavg) of APs was in the range of 16.9 (Eohul) and 17.5 (Geumsung). The onset temperature (To) and enthalpy change (,Hgel) of starch gelatinization were 54.6 to 60.2 C and 11.6 to 13.2 J/g. The ,H of the retrograded mung bean starches was 5.5 to 6.6 J/g, which indicated 44.5% to 52.7% of recrystallization. The pasting temperature, peak viscosity, and setback were 66.1 to 69.2 C, 510 to 579 Rapid Visco Unit (RVU), and 66 to 90 RVU, respectively. [source]

    Crystallization Kinetics and X-ray Diffraction of Crystals Formed in Amorphous Lactose, Trehalose, and Lactose/Trehalose Mixtures

    Song Miao
    ABSTRACT: Effects of storage time and relative humidity on crystallization kinetics and crystal forms produced from freeze-dried amorphous lactose, trehalose, and a lactose/trehalose mixture were compared. Samples were exposed to 4 different relative water vapor pressure (RVP) (44.1%, 54.5%, 65.6%, 76.1%) environments at room temperature. Crystallization was observed from time-dependent loss of sorbed water and increasing intensities of peaks in X-ray diffraction patterns. The rate of crystallization increased with increasing storage humidity. Lactose crystallized as ,-lactose monohydrate, ,-anhydrous, and anhydrous forms of ,- and ,-lactose in molar ratios of 5:3 and 4:1 in lactose and lactose/trehalose systems. Trehalose seemed to crystallize as a mixture of trehalose dihydrate and anhydrate in trehalose and lactose/trehalose systems. The crystal forms in a mixture of lactose and trehalose did not seem to be affected by the component sugars, but crystallization of the component sugars was delayed. Time-dependent crystallization of lactose and trehalose in the lactose-trehalose mixture could be modeled using the Avrami equation. The results indicated that crystallization data are important in modeling of crystallization phenomena and predicting stability of lactose and trehalose-containing food and pharmaceutical materials. Keywords: crystallization, lactose, trehalose, crystal form, X-ray diffraction [source]

    The effect of disorder on the chemical reactivity of an organic solid, tetraglycine methyl ester: Change of the reaction mechanism

    Evgenyi Shalaev
    Abstract Many drugs undergo chemical changes in the solid state, and understanding chemical reactivity of organic crystals is a critical factor in the drug development process. In this report, the impact of milling on the thermal chemical reactivity of an organic solid, tetraglycine methyl ester, was studied using DSC, isothermal calorimetry, chemical analysis (HPLC and insoluble residue determination), and powder X-ray diffraction. Significant changes in both X-ray diffraction patterns and DSC curves were detected after very brief milling (5 s). The changes were interpreted as the formation of a disordered phase. The disordered phase was tentatively identified as a crystal mesophase that combines properties of both crystalline (i.e., long-range order) and amorphous (i.e., glass transition) states. In the disordered material, the reaction mechanism changed from the methyl transfer reaction, which was observed in the intact crystal, to a polycondensation reaction when the reaction was performed at 165C. Such changes in the reaction mechanism occurred in materials milled for >,30 s. 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91:584,593, 2002 [source]

    Crystal structure prediction for eniluracil

    Mark Sacchetti
    Abstract State-of-the-art molecular modeling tools were used to predict the crystal structure of eniluracil, a compound for which it has not been possible to grow a single crystal. Two methods were used, one that incorporates molecular structure and powder X-ray diffraction data and another that employs molecular structure and lattice energy calculations into the search algorithm. Two structures were identified, one with P21/c and the other with P21 symmetry, both of which are consistent with the infrared and Raman spectra. A detailed analysis of the simulated and experimental powder X-ray diffraction patterns indicates that the P21/c structure is the best representation of the crystal structure. 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1049,1055, 2001 [source]

    Effect of aniline formaldehyde resin on the conjugation length and structure of doped polyaniline: Spectral studies

    Ko-Shan Ho
    Abstract A DBSA (n -dodecylbenzene sulfate)-complexed aniline formaldehyde [AF(DBSA)1.0] was successfully synthesized with excess aniline (compared with formaldehyde) in the presence of n -dodecylbenzene sulfonic acid (HDBSA), which was complexed with aniline monomer before polymerization. The resin was carefully characterized with 1H and 13C NMR, electron spectroscopy for chemical analysis, and Fourier transform infrared and was demonstrated to be a polymer in which anilines were all complexed with HDBSA and became anilinium salts. A drastic decrease of the maximum absorption wavelength (ultraviolet,visible spectra) of DBSA-doped polyaniline [PANI(DBSA)0.5] was found when AF(DBSA)1.0 was mixed, and this resulted from the reduced conjugation length. A similar effect on PANI(DBSA)0.5 was found when free HDBSAs were mixed with PANI(DBSA)0.5. Visual inspection with an optical microscope revealed that PANI(DBSA)0.5/AF(DBSA)1.0 gave uniform morphologies in various compositions, showing possible miscibility for this system. X-ray diffraction patterns of PANI(DBSA)0.5/AF(DBSA)1.0 showed that the layered structure of PANI(DBSA)0.5 was still present but became shorter in the polyblend because of the presence of AF(DBSA)1.0. Solid-state 13C NMR spectra revealed that the reduced conjugation length was derived from the interaction of alkyl groups between HDBSA, complexed DBSA, and dopant DBSAs. 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3116,3125, 2005 [source]

    Biaxial Flexural Strength and Microstructure Changes of Two Recycled Pressable Glass Ceramics

    Mohammad Albakry BSc
    Purpose: This study evaluated the biaxial flexural strength and identified the crystalline phases and the microstructural features of pressed and repressed materials of the glass ceramics, Empress 1 and Empress 2. Materials and Methods: Twenty pressed and 20 repressed disc specimens measuring 14 mm 1 mm per material were prepared following the manufacturers' recommendations. Biaxial flexure (piston on 3-ball method) was used to assess strength. X-ray diffraction was performed to identify the crystalline phases, and a scanning electron microscope was used to disclose microstructural features. Results: Biaxial flexural strength, for the pressed and repressed specimens, respectively, were E1 [148 (SD 18) and 149 (SD 35)] and E2 [340 (SD 40), 325 (SD 60)] MPa. There was no significant difference in strength between the pressed and the repressed groups of either material, Empress 1 and Empress 2 (p > 0.05). Weibull modulus values results were E1: (8, 4.7) and E2: (9, 5.8) for the same groups, respectively. X-ray diffraction revealed that leucite was the main crystalline phase for Empress 1 groups, and lithium disilicate for Empress 2 groups. No further peaks were observed in the X-ray diffraction patterns of either material after repressing. Dispersed leucite crystals and cracks within the leucite crystals and glass matrix were features observed in Empress 1 for pressed and repressed samples. Similar microstructure features,dense lithium disilicate crystals within a glass matrix,were observed in Empress 2 pressed and repressed materials. However, the repressed material showed larger lithium disilicate crystals than the singly pressed material. Conclusions: Second pressing had no significant effect on the biaxial flexural strength of Empress 1 or Empress 2; however, higher strength variations among the repressed samples of the materials may indicate less reliability of these materials after second pressing. [source]

    Micro-Raman study of Zr-substituted Bi4Ti3O12 ceramics

    S. R. Das
    Abstract We have studied the lattice vibrational modes of Zr-substituted Bi4Ti3O12 ceramics using micro-Raman spectroscopy. Replacement of Zr at the Ti site in the perovskite block is found from the increase in the lattice parameters as a function of Zr contents. Combined X-ray diffraction patterns and Raman analysis suggested less than 40 mole% Zr solubility in Bi4Ti3O12. At 40 mole% of Zr substitution or above, the unreacted monoclinic-phase ZrO2 is observed in the X-ray diffraction patterns and the Raman spectra. The incorporation of Zr in Bi4Ti3O12 reduces the soft mode wavenumber and the transition temperature. Moreover, temperature dependent studies confirmed the ferroelectric to paraelectric transition in Bi4Ti3O12 at about 675 C. On increasing the Zr content up to 40% on the Ti sites of Bi4Ti3O12, a systematic decrease in the phase transition temperature from 675 to 630 C was observed. Copyright 2007 John Wiley & Sons, Ltd. [source]

    Microstructure and Microwave Dielectric Properties of xCa(Al0.5Nb0.5)O3+(1,x)SrTiO3 Solid Solutions

    Mingzhe Hu
    The crystal structure evolution and microwave (MW) dielectric properties of xCa(Al0.5Nb0.5)O3+(1,x)SrTiO3 (xCAN+(1,x)ST, 0,x,1.0, ) dielectric ceramics were investigated. X-ray diffraction patterns illustrated that a single perovskite solid solution could be formed between the two end members; however, minor amount of pyrochlore phase was also detected in the composition range of 0.5,x,0.9. With the increase of x value, the crystal structure gradually evolved from a simple Pm3m cubic to a monoclinic P21/n space group with the octahedral tilting and the B-site ordering structure transition subsequently developed. The MW dielectric properties of xCAN+(1,x)ST solid solutions were elaborately investigated and correlated to their crystal structures. The microscopic structure-related thermal parameters in the xCAN+(1,x)ST solid solution were analyzed in terms of the Claussius,Mossotti equation to reveal the original contributors in temperature coefficients. Temperature coefficient-compensated ceramic could be obtained in the xCAN+(1,x)ST system in the range of 0.5[source]

    Crystal Structure and Compressibility of Pb(Zr1,xTix)O3 Ceramics Under High Pressure

    Young Ho Ko
    X-ray diffraction patterns of Pb(Zr0.3Ti0.7)O3 and Pb(Zr0.7Ti0.3) O3 have been measured at pressures up to 36 GPa with good signal-to-noise ratio using synchrotron radiation. In order to refine the crystal structure, Rietveld analysis has been performed. The structure of Pb(Zr0.3Ti0.7)O3 is tetragonal in space group P4mm with lattice parameters a=b=3.98430.0003 and c= 4.15450.0003 at ambient pressure. A pressure-induced phase transition was found in the pressure range higher than ,7.4 GPa at room temperature. The high-pressure phase is cubic in space groupwith lattice parameter a=3.96000.0003 at 7.4 GPa. The Birch,Murnaghan equation of state fit to the experimental data yields B0=83.91.7 GPa (B,0=4.0 is fixed) for tetragonal phase and B0=102.54.4 GPa (B,0=4.0 is fixed) for cubic phase with V0=65.950.01 3. The structure of Pb(Zr0.7Ti0.3)O3 is monoclinic in space group Cc with lattice parameters a=10.06270.0164 , b=5.85110.0024 , c= 5.79490.0020 , and ,=125.1850.119 at ambient pressure. No pressure-induced phase transition for Pb(Zr0.7Ti0.3)O3 was observed over the pressure range of this study. The Birch,Murnaghan equation of state fit to the experimental data yields B0=73.618.9 GPa (B,0=4.0 is fixed) with V0= 278.810.63 3. [source]

    Enhanced Blue Emission from Transparent Oxyfluoride Glass,Ceramics Containing Pr3+:BaF2 Nanocrystals

    Kaushik Biswas
    Transparent glass,ceramics containing Pr3+:BaF2 nanocrystals in the chemical composition of SiO2,BaF2,K2CO3,La2O3,Sb2O3 oxyfluoride glass systems have been prepared from melt quenching and with a subsequent heat-treatment method. The luminescence and structural properties of these materials have been evaluated and the results are reported. Rietveld analysis of X-ray diffraction patterns and investigation of transmission electron microscopy confirmed the presence of BaF2 nanocrystals dispersed in the heat-treated glass matrices. Measured UV-Vis-NIR absorption spectra exhibited nine bands of the transitions 3H4,3P2, (1I6, 3P1), 3P0, 1D2, 1G4, 3F3, 3F2, 3H6, and 3H5 from all the samples with nondegenerated 1I6 and 3P1 levels in the glass,ceramics. The photoluminescence spectra show an enhancement in the intensities upon ceramization, indicating the incorporation of Pr3+ ions into BaF2 nanocrystals that possess a low phonon energy (346 cm,1). This has further been corroborated from the observation of a significant threefold increase in the relative intensity ratio of blue (3P0,3H4) to red (1D2,3H4, 3P0,3H6) emissions from glass,ceramics compared with the glass. This is due to a significant decrease of multiphonon nonradiative relaxation from the 3P0 to the 1D2 level of Pr3+ in glass,ceramics. Time-resolved spectra exhibit 3P0 -level decays faster than the 1D2 level. [source]