Hydrogen bond studies. 85. A very short, asymmetrical, intramolecular hydrogen bond: A neutron diffraction study of pyridine‐2,3‐dicarboxylic acid (C7H5NO4)

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/jcp/60/10/10.1063/1.1680831.A neutron diffraction study of pyridine‐2,3‐dicarboxylic acid (quinolinic acid) has been carried out. The intensities for 3780 reflexions were measured at the Brookhaven High Flux Beam Reactor. The structure was refined to an R(F 2) of 0.054 using starting parameters from a previous x‐ray study. The short intramolecular hydrogen bond [O ··· O: 2.398(3) Å] has no symmetry restriction operating on the hydrogen atom position and is asymmetric. The two O ··· H distances are 1.163(5) and 1.238(5) Å, respectively, and the O–H–O angle is 174.4(4)°. The asymmetry of the bond can be explained by the intramolecular environment. The strain in the molecule caused by the short hydrogen bond results in long carbon‐carbon bonds to the carboxyl groups [1.516(2) and 1.541(2) Å]. The C–O bond lengths [1.219(3), 1.263(2), 1.222(3), and 1.270(2) Å] vary depending on the hydrogen‐bond involvement of the oxygen atoms. The mean C–H distance is 1.087 Å and the N–H distance is 1.036(4) Å. The nitrogen atom is involved in an intermolecular N–H ··· O hydrogen bond [N ··· O: 2.725(2), H ··· O: 1.845(4) Å and angle N–H ··· O: 140.5(2)°]. There are a number of short intermolecular O ··· H–C contacts. The refined neutron scattering length for the nitrogen atom is b̄ N=0.925(4)×10−12 cm

Materials science at the European Synchrotron Radiation Facility.

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 m, and microcrystal diffraction. A variety of CCD detectors are used to give time-resolution down to the millisecond time regime

Time-resolved XRD study of TiC-TiB2 composites obtained by SHS

Composites of TiC and TiB2 were prepared by self-propagating high-temperature synthesis (SHS). Two routes were attempted; from the elements and from a mixture of anatase, boron oxide, graphite and magnesium. The reactions were monitored in situ by synchrotron X-ray diffraction ( lambda = 0. 26102 Angstrom). The powder mixtures were compacted as cylindrical pellets and upon ignition diffraction patterns were collected every 65 ms with a CCD camera. TiC was the first phase to form, followed by TiB2. The reactions take place in time scales of 0.1 s. The temperature profile for the first route was established from the peak position and the known thermal expansion coefficients. The microstructure of the final products was different: particles of 10 mum for the first and submicron for the second. The viability of the second route to produce ceramic powders in a cheaper way was confirmed. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

(K4Li4)Al8Ge8O32 8H(2)O, an Li+-exchanged potassium alumino-germanate with the zeolite gismondine (GIS) topology

The title compound, lithium potassium dialuminium diger-manium octaoxide dihydrate, (K,Li)-(Al,Ge)-GIS (GIS is gismondine), is the result of a 50% Li+ exchange into the K-(Al,Ge)- GIS structure. The (K,Li)-(Al,Ge)-GIS structure was determined from a 4 x 4 x 2 m m octahedral single crystal at the ESRF synchrotron X-ray source. The ion exchange results in a symmetry transformation from I2/a for K-(Al,Ge)-GIS to C2/c for (K,Li)-(Al,Ge)-GIS. The structural change is due to disordering of K+ ions with Li+ ions along the [001] channel and ordering of water molecules in the [101] channels. The distance between sites partially occupied by K+ ions increases from 2.19 (3) Angstrom in K-(Al,Ge)-GIS to 2.94 (3) Angstrom in (K,Li)-(Al, Ge)-GIS. The Li+ ions occupy positions along the twofold axis at the intersection of the eight-membered-ring channels in a twofold coordination with water molecules. For the four closest framework O2- anions, the Li ... O distances are 3.87 (4) Angstrom

In situ accelerated leaching of cement paste by application of electrical fields monitored by synchrotron X-ray diffraction

An external dc voltage was applied to a cured cement paste to simulate its natural degradation as a function of time. The electrical treatment was monitored in situ by simultaneous acquisition of diffraction patterns every 10 min. The analysis of the diffraction patterns has confirmed that the microstructure of the whole paste changes during the treatment, with precipitation and dissolution of several phases. This work contributes to the understanding of the fundamentals of the microstructure alterations that take place upon application of an electrical field, allowing the establishment of a first approach to the understanding of the mechanism of these changes.Peer reviewe

Synchrotron Radiation Diffraction Study of the Microstructure Changes in Cement Paste due to Accelerated Leaching by Application of Electrical Fields

An external dc voltage was applied to cured cement pastes to simulate their natural degradation over time; i.e. migration of ions and dissolution of solid phases. The presence of crystalline phases before and after applying a voltage was quantified by powder diffraction using synchrotron X-ray radiation. The results were refined by the Rietveld method. The specimens were also analysed by mercury intrusion porosimetry. Results indicated that a portion of the crystalline phases dissolved and later precipitated as amorphous phases in smaller pores. This accelerated treatment led to the formation of a larger proportion of amorphous phases in the specimens studied.Peer reviewe

Properties of FeNiB-based metallic glasses with primary BCC and FCC crystallisation products.

FeSiB tapes have long been commercialised for their excellent soft-magnetic properties but do not manifest a glass transition temperature Tg as crystallisation intervenes. In this work, we present the crystallisation and properties of two Fe-based glasses, which show a glass transition before crystallisation. Using Ni and Co substitution, we can design glasses that form primary FCC or BCC FeNiCo solutions in their first stage of crystallisation followed by the formation of the metastable (FeNiCo)4B (C6Cr23-type cF116) intermetallic phase. Thermal and structural and magnetic properties were compared during heat treatment

The new macromolecular crystallography stations at MAX-lab: The MAD station

A new beamline, Cassiopeia, at MAX II is about to come into operation. It consists of an energy-tunable station and four side stations intended for macromolecular crystallography. The X-ray source is a 3.5 T superconducting multipole wiggler installed in the 1.5 GeV MAX II storage ring. The energy-tunable station use grazing incidence Rh-coated silicon mirrors and an internally water-cooled Si(111) double-crystal monochromator while the four side stations use bent diamond and germanium monochromators and multilayer mirrors. This paper concentrates on the optics design of the energy-tunable station and also briefly describes other beamline component