Åke Kvick

Crystal structure of the zeolite mutinaite, the natural analog of ZSM-5

We describe the crystal structure of the high-silica zeolite mutinaite, recently found at Mt. Adamson (Northern Victoria Land, Antarctica). Mutinaite is the natural counterpart of the synthetic zeolite ZSM-5. The new mineral, (Na 2.76 K 0.11 Mg 0.21 Ca 3.78 ) (Al 11.20 Si 84.91 ) · 6O H 2 O H 2 O, is orthorhombic, space group Pnma, with a = 20.201(2), b = 19.991(2), and c = 13.469(2) A. A single-crystal X-ray diffraction experiment was performed at the synchrotron radiation source ESRF (Grenoble). No Si-Al order in the framework has been detected. Large distances between ions in the channels and framework oxygens suggest weak interactions between the framework and extraframework species.

TiC-NiAl composites obtained by SHS: a time-resolved XRD study

Self-propagating high-temperature synthesis (SHS) has been performed in the quaternary Al–Ni–Ti–C system in order to obtain intermetallic–ceramic composites. These kind of reaction synthesis are very fast (linear velocity of the synthesis front is in the range 1–100 mm/s) and the productivity would be very high from the industrial point of view. Nevertheless,this characteristic is a negative point when synthesis mechanism and kinetics must be studied. There are only a few tools with enough time resolution in order to study these kinds of fast reactions. Synchrotron radiation (ESRF,Grenoble) has been employed to follow the reactions in situ on a time-scale of 100 ms. Powder diffraction patterns were recorded in this time-interval using a high-speed CCD camera coupled to an image intensifier X-ray sensitive detector with 10241024 pixels frames. As the reactions proceed patterns from the pre-heated, reaction front,post-heated and cooling zones of the reaction were sampled. The phases occurring during the reactions were identified and information of the reaction mechanism and the nucleation kinetics were obtained. SEM was used to characterize the final microstructure. # 2002 Published by Elsevier Science Ltd.

Metastable phases in Zr-based bulk glass-forming alloys detected using a synchrotron beam in transmission

Abstract Nucleation and crystallisation in Zr-based bulk metallic glasses has been directly detected using high intensity high energy monochromatic synchrotron beam diffraction in transmission during in-situ heat treatment. Previously, it was established that crystallisation of the amorphous phase occurs via initial nucleation and growth of metastable phases that transform to equilibrium tetragonal Zr 2 Cu before melting. However, no trace of nucleation of the metastable phase was obtained during cooling of the liquid alloy from above liquidus temperature T l and Zr 2 Cu forms directly from the liquid. The metastable crystalline nanostructure obtained during rapid heating was found to depend sensitively on the alloy composition. Ti addition suppresses the previously detected metastable state and leads to a new phase with structure close to that of tetragonal Zr 2 Ni phase but with a highly stressed nanostructure. On the other hand, increasing the Zr content to nearly 70xa0at.% allows easy preparation of the metastable state during rapid heating at rates of the order of 1xa0K/s as used in most DSC experiments.

The crystal structure of methyl β-cellotrioside monohydrate 0.25 ethanolate and its relationship to cellulose II

The crystal structure of methyl beta-cellotrioside (methyl O-beta-D-glucopyranosyl-(1-->4)-O-beta-d_guycopyranosyl-(1-->4)-be ta-D- glucopyranoside) complexed with water and ethanol, C19H34O16. H2O.0.25[C2H6O] was determined by combining Cu K alpha X-ray and synchrotron data collected at room temperature. The crystals have the monoclinic space group P21 with Z = 8 and unit cell parameters a = 7.9978(11), b = 76.38(4), c = 8.9908(6) A and beta = 116.40(1) degree. The structure, which was solved by direct methods and refined to a final R-factor of 0.067, contains four independent molecules of methyl beta-cellotrioside with an extended conformation. They are arranged parallel to the long b axis of the unit cell, and organized in two pairs of antiparallel molecules. Each beta-D-glucopyranosyl residue of the four independent molecules is in the 4C1 pyranose conformation, and each (O-6) primary hydroxyl group has the gt conformation. The crystal structure of methyl beta-cellotrioside has many points in common with that of cellotetraose hemihydrate as well as with the structure of cellulose II. Thus, it is likely that the precise atomic coordinates obtained in this study can be directly transposed to give an improved structure for cellulose II where, in particular, only the gt conformation would be present at the primary hydroxyl groups of both polysaccharide chains.

In situ crystallization of Zr55Cu30Al10Ni5 bulk glass forming from the glassy and undercooled liquid states using synchrotron radiation

Abstract Real-time detection of crystal nucleation and growth in amorphous Zr 55 Cu 30 Al 10 Ni 5 was performed for the first time. The experiments were performed at the European Synchrotron Radiation Facilities (ESRF) using monochromatic beam with energy of 90 keV corresponding to a X-ray wavelength of 0.137 A. Full X-ray spectra in transmission were obtained every 3 s. Crystallization was monitored both during heating of the amorphous alloy and during cooling of the liquid alloy to detect differences in the nucleating crystalline phases. We found that crystallization of the amorphous phase occurs via initial nucleation and growth of a metastable phase that transforms to equilibrium tetragonal Zr 2 Cu before melting. However, no trace of nucleation of the metastable phase was obtained during cooling of the liquid alloy from above T m and Zr 2 Cu formed directly from the liquid.

Self propagating high temperature synthesis of magnesium zinc ferrites (MgxZn1-xFe2O3): thermal imaging and time resolved X-ray diffraction experiments

Spinel ferrites of the form MgxZn1-xFe2O4 ( x = 0. 0.25, 0.50, 0.75, 1.00) were prepared by self-propagating high-temperature synthesis (SHS) from reactions of iron(III), zinc and magnesium oxides, iron powder and sodium perchlorate. The driving force for the reactions is the oxidation of iron powder. Reactions were carried out in the presence of an external magnetic field of 0.2 or 1.1 T. Reaction velocity and temperatures were obtained by thermal imaging camera. The transformation of reactants to products was studied by time resolved X-ray diffraction using Rietveld refinement for determination of phase percentages. Reactions typically reached temperatures in excess of 1150 degreesC with a timescale of complete conversion of reactant to products of 20 s. All materials were characterised by X-ray powder diffraction (XRD), energy dispersive X-ray analysis (EDXA), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Mossbauer spectroscopy and vibrating sample magnetometry (VSM).

Advanced Ways and Experimental Methods in Self-Propagating High-Temperature Synthesis (SHS) of Inorganic Materials

New experimental methods for investigations of phase formation during SHS have been established. First experiments using penetrating synchrotron radiation and energy dispersive detectors for different classes of complex inorganic materials were carried out at ESRF (Grenoble, France) and Daresbury (UK). A new and very sensitive thermal imaging method (Thermal Imaging Technique (TIT)) based on continuous registration of the whole combustion process by using highly sensitive IR-camera and software developed by MIKRON Instruments Co. (USA) was used for precise registration of the combustion parameters. SHS was performed on different types of pure and doped complex inorganic materials in pellet and powder form in a range of dc magnetic fields up to 20 T and in electrical field strengths up to ±220 kV/m. The dc magnetic field was applied during the reaction, supplied either by a permanent magnet (transverse, up to 1.1 T) or by an electromagnet (longitudinal, up to 20 T). The dc electrical field was applied along the direction of the combustion wave front propagation. The combined processes of SHS and SLS (Selective Laser Sintering) of 3D articles for different powdered compositions were optimized with laser irradiation power.

In‐Situ time‐resolved X‐ray diffraction: The current state of the art

This article outlines the recent progress in time-resolved diffraction using synchrotron radiation from the ESRF and the Daresbury synchrotron storage rings. The ESRF work is concentrated on the use of monochromatic high energy X-rays, whereas the Daresbury work is based on energy-dispersive methods. The aim of an in situ diffraction study of a solid-state reaction is the acquisition of kinetic data describing the formation of a crystalline material. On the simplest qualitative level, this can simply mean knowledge of the time-scale of the reaction; how long a reaction takes to reach completion, or how long is required for the first appearance of a crystalline material. Ideally, quantitative crystallization curves from which rate constants can be determined are required, and, if the time resolution is sufficient, this is made possible by continual monitoring of the diffraction pattern during a chemical change. Additional, and often unforeseen, information is possible to obtain, such as the direct observation of intermediate crystalline phases (see below). All of these pieces of information are vital to begin to understand the formation mechanism of solid materials. This is a requirement when these materials have industrially and commercially important characteristics such as microporosity, electrochemical activity, charge storage, magnetism and ferroelectricity.

Casting and Phase Transformations of Fe65.5Cr4Mo4P12C5B5.5 Bulk Metallic Glass

Bulk glassy Fe 65.5Cr4Mo4Ga4P12C5B5.5 rods with diameters of 1.5 3 mm were prepared by copper mold casting. Thermal stability measurements reveal a distinct glass transition, followed by a supercooled liquid region of 60 K. The casting temperature plays an important role for obtaining fully glassy material. The crystallization of the g lass as observed by in-situ X-ray diffraction measurements in transmission configuration occurs via the formation of a metastable intermediate phase. The crystalline phases observed after heatin g do not correspond to those occurring after slow cooling from the melt. Introduction The Fe-based amorphous alloys recently found by Inoue et al. [1-3] exhibit a large supercooled liquid region between the glass transition temperature Tg and the crystallization temperature Tx visible upon constant-rate heating to elevated temperatures. Beca use of the lack of crystal anisotropy, they have good soft magnetic properties charac terized by low coercive force and high permeability [4-7]. The high glass-forming ability of this ki nd of alloys allows the formation of bulk glassy samples [8-10]. Such alloys can be directly cast in f orm of bulk specimens, which could be used for magnetic cores using different techniques, such as copper mold casting or water quenching. However, the critical cooling rate of about 10 2 K/s required for glass formation is higher than the value of about 1-10 K/s characteristic for alloys with ver y good glass-forming ability [11,12]. Thus, the maximum achievable diameter of these Fe-based allo ys is limited to only a few millimeters [13]. The other hindrance that can influence bulk glass formation is the presence of impurities in the melt [14,15] that can be removed using fluxing techniqu es [16,17], or of crystalline inclusions that can form upon solidification of the melt. In the case of FeCrMoGaPCB alloys, Shen and Schwarz [15] used the flux-mel ting technique to remove the oxide inclusions from the melt and subsequent water quenching allows to produce rods with 4 mm diameter. From this class of alloys, the nominal c omposition Fe65.5Cr4Mo4Ga4P12C5B5.5 was chosen because the samples show the best thermal stability and soft magnetic properties. The present work focuses on the possibility to cast this alloy directly in bulk form using the copper mold casting technique, the correlation between t h casting conditions and the structure, as well as the crystallization behavior measured in-situ using a high intensity high-energy monochromatic X-Ray synchrotron beam. Journal of Metastable and Nanocrystalline Materials Online: 2002-08-01 ISSN: 2297-6620, Vol. 12, pp 77-84 doi:10.4028/www.scientific.net/JMNM.12.77

Materials science research at the European Synchrotron Radiation Facility

Abstract The Materials Science Beamline ID11 at the European Synchrotron Radiation Facility in Grenoble, France is dedicated to research in materials science notably employing diffraction and scattering techniques. Either an in-vacuum undulator with a minimum gap of 5 mm or a 10 kW wiggler giving high-flux monochromatic X-rays generates the synchrotron radiation in the energy range 5–100 keV. The dominant research is in the area of time-resolved diffraction, powder diffraction, stress/strain studies of bulk material, 3D mapping of grains and grain interfaces with a measuring gauge down ∼5×5×50 μm, and microcrystal diffraction. A variety of CCD detectors are used to give time-resolution down to the millisecond time regime.