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1

Radiation damage in the alkali halide crystals  

International Nuclear Information System (INIS)

A general review is given of the experimental data on radiation damage in the alkali halide crystals. A report is presented of an experimental investigation of irradiation produced interstitial dislocation loops in NaCl. These loops are found to exhibit the usual growth and coarsening behaviour during thermal annealing which operates by a glide and self-climb mechanism. It is shown that the recombination of defects in these crystals is a two stage process, and that the loss of interstitials stabilized at the loops is caused by extrinsic vacancies. The theoretical techniques used in simulating point defects in ionic crystals are described. Shell model potentials are derived for all the alkali halide crystals by fitting to bulk crystal data. The fitting is supplemented by calculations of the repulsive second neighbour interactions using methods based on the simple electron gas model. The properties of intrinsic and substitutional impurity defects are calculated. The HADES computer program is used in all the defect calculations. Finally the report returns to the problems of irradiation produced interstitial defects. The properties of H centres are discussed; their structure, formation energies, trapping at impurities and dimerization. The structure, formation energies and mobility of the intermediate and final molecular defects are then discussed. The thermodynamics of interstitial loop formation is considered for all the alklai halide crystals. The nucleation of interstitial loops in NaCl and NaBr is discussed, and the recombination of interstitial and vacancy defects. The models are found to account for all the main features of the experimental data. (author)

1975-01-01

2

Dielectric and anharmonic behaviour of alkali halide crystals  

International Nuclear Information System (INIS)

The dielectric and anharmonic behaviour of alkali halide crystals is studied by determining the volume derivatives of low frequency dielectric constant and polarizability. An interionic force model which takes into account the contributions arising from the short range overlap repulsion and the van der Waals interactions is used in calculations. The implicit and explicit temperature derivatives of low frequency and high frequency dielectric constants are obtained separately for all the alkali halide crystals with NaCl and CsCl structures. The anharmonic contribution to the dielectric constant is calculated using theoretical models due to Szigeti and Havinga. The recent analysis of pressure dependence of effective charge parameter and dielectric constant of ionic crystals performed by Varotsos is shown to be invalid. (author)

1982-12-01

3

THEORY OF PLASTICO ML IN ?–IRRADIATED ALKALI HALIDE CRYSTALS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The present paper reports the results of some theoretical approach made to the studies of mechanoluminescence (ML) in coloured alkali halide crystals. It is shown that moving dislocations produced during plastic deformation of crystalline materials cause light emission due to several processes like mechanical or electrostatic interaction of dislocations with defect centres, the dielectric breakdown of adsorbed gaseous molecules by the surface accumulated dislocation charges, the generation of...

2011-01-01

4

Self-trapped holes in alkali silver halide crystals  

Energy Technology Data Exchange (ETDEWEB)

{gamma}-Ray irradiation at 77 K induces defects in M{sub 2}AgX{sub 3} (M=Rb, K and NH{sub 4}; X=Br and I) crystals. The irradiation induces self-trapped holes of the form of I{sup 0} in the case of alkali silver iodides, and (halogen){sub 2}{sup -} and (halogen){sup 0} in the case of ammonium silver halides. The (halogen){sup 0} is weakly coupled with the nearest alkali metal ion or ammonium ion. It is able to be denoted as RbI{sup +}, KI{sup +}, NH{sub 4}I{sup +} or NH{sub 4}Br{sup +}. The directions of hole distribution of (halogen){sub 2}{sup -} and (halogen){sup 0} were different in each case of the alkali silver iodides, ammonium silver halides and mixed crystal of them. The (halogen){sup 0} decayed at 160 K in annealing process. The (halogen){sub 2}{sup -} was converted into another form of (halogen){sub 2}{sup -} at 250 K and this decayed at 310 K. A formation of metallic layers was observed on the crystal surface parallel with the c-plane of (NH{sub 4}){sub 2}AgI{sub 3} irradiated at room temperature. (author).

Awano, T. [Tohoku Gakuin Univ., Tagajo, Miyagi (Japan). Faculty of Engineering; Ikezawa, M.; Matsuyama, T.

1995-03-01

5

Analysis of the dielectric behaviour of alkali halide crystals  

International Nuclear Information System (INIS)

An analysis of the dielectric data at low temperature (2K) and at room temperature (290 K) is performed for the entire family of NaCl and CsCl structure alkali halide crystals. The recent data on dielectric constants and their pressure and temperature derivatives are used to study the nature of some important physical quantities like the energy gap between bonding and antibonding states, the Phillips-van Vechten electronegativity parameter and the Szigeti effective charge parameter. Some interesting results are obtained using the Penn model for the electronic dielectric constant and the Lawaetz relation between electronegativity and effective charge parameters. (author)

1980-09-01

6

THEORY OF PLASTICO ML IN ?–IRRADIATED ALKALI HALIDE CRYSTALS  

Directory of Open Access Journals (Sweden)

Full Text Available The present paper reports the results of some theoretical approach made to the studies of mechanoluminescence (ML in coloured alkali halide crystals. It is shown that moving dislocations produced during plastic deformation of crystalline materials cause light emission due to several processes like mechanical or electrostatic interaction of dislocations with defect centres, the dielectric breakdown of adsorbed gaseous molecules by the surface accumulated dislocation charges, the generation of holes during decay of mobile dislocations on the surfaces of crystals, etc. On the basis of rate equations, expressions are derived for the rise and decay of ML intensity at a given strain rate. The estimated values of ML intensities for different crystals are found to be comparable with the experimentally observed values. The expression derived are able to explain the dependence of ML intensity on several parameters like strain-rate, defect centre density, temperature, applied stress, crystal- size etc.

NAMITA RAJPUT

2011-06-01

7

Time-Resolved Femtosecond Laser Desorption from Alkali Halide Crystals  

International Nuclear Information System (INIS)

The positive ion yield as a function of delay between ultraviolet femtosecond pulse pairs for four alkali halide single crystals has been measured. Two-pulse correlation allows direct observation of solid state and surface dynamics on an ultrafast timescale. The ion yield from 265nm irradiated NaBr, KC1, KBr, and K1 depends critically on the time delay between the two sub-threshold pulses. Following irradiation of single crystal NaBr and KC1, the positive ion desorption yield displays three distinct features; a coherence peak, followed by rise, and decay features. In contrast, the yield of K+ from KBr displays only the coherence peak and picosecond decay features while the yield from K1 shows only the coherence feature. The data suggest that although the nanosecond ion desorption mechanism may be dominated by defect photoabsorption, significant electron-hole pair production may contribute to the desorption mechanism following femtosecond excitation

2004-04-25

8

Synthetic Alkali Halides  

Science.gov (United States)

This complex experimental investigation uses alkali halides (NaCl, KCl, and mixtures of both) to simulate the melting of alkali feldspars which melt at too high of temperatures to work with in lab. Three hypotheses are tested: It is possible to crystallize alkali-chloride salts from a magma with any composition between NaCl and KCl. Because K+ and Na+ do not have the same ionic size, the atomic spacing in alkali chlorides will vary systematically with composition. Alkali chlorides are equally stable at high (just below liquidus) and low (subsolidus)temperatures. This project takes more than one class period, depending on how many students are in the class, because there will be lines at the scales, oven, and XRD. It is advisable to introduce the lab in class and have students complete various parts on their own time. There are three main parts. Part one: Synthesize all alkali halide compositions at high temperature (hopefully above the solvus. Part two: Put grown crystals back in an oven at lower temperature to see if they will unmix. Part three: Write a report evaluating and interpreting all results, relevant graphs, and the above three hypothesis.

Perkins, Dexter

9

Empirical energy parameters for structural modeling of alkali halide crystals in standard formalisms  

Energy Technology Data Exchange (ETDEWEB)

Potential energy parameters, describing Coulombic, van der Waals, and repulsion energies, have been established for each of the nine common alkali halide ions in two forms of the exp-6 potential, with use of the standard, ambient-stable alkali halide crystal structures for reference. The derived potential parameters fir the lattice energies of the stable NaCl-type structures to better than 1 kcal/mol and predict the lattice energies of the stable CsCl-type structures to better than 3 kcal/mol. For the unstable alkali halide structures, lattice constants are predicted to better than 0.2 {angstrom}, in general, while the lattice energies obtained are more positive than for the corresponding stable strucures and agree well with published values where available.

Brink, G.; Glasser, L.; Mboweni, R.C. (Univ. of the Witwatersrand, Johannesburg (South Africa))

1989-04-20

10

SINGLE-SITE APPROXIMATION VIA IDEAL CRYSTAL GREEN'S FUNCTION : XANES OF ALKALI HALIDES  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The ideal crystal Green's function method is applied to XANES problem. This scheme allows to treat simultaneously two important aspects of the problem : band effects (multiple scattering) and core hole potential. The calculated K-spectra of alkali halides agree well with the experimental ones.

Gegusin, I.; Datsyuk, V.

1986-01-01

11

Mechanoluminescence response to the plastic flow of coloured alkali halide crystals  

International Nuclear Information System (INIS)

The present paper reports the luminescence induced by plastic deformation of coloured alkali halide crystals using pressure steps. When pressure is applied onto a ?-irradiated alkali halide crystal, then initially the mechanoluminescence (ML) intensity increases with time, attains a peak value and later on it decreases with time. The ML of diminished intensity also appears during the release of applied pressure. The intensity Im corresponding to the peak of ML intensity versus time curve and the total ML intensity IT increase with increase in value of the applied pressure. The time tm corresponding to the ML peak slightly decreases with the applied pressure. After tm, initially the ML intensity decreases at a fast rate and later on it decreases at a slow rate. The decay time of the fast decrease in the ML intensity is equal to the pinning time of dislocations and the decay time for the slow decrease of ML intensity is equal to the diffusion time of holes towards the F-centres. The ML intensity increases with the density of F-centres and it is optimum for a particular temperature of the crystals. The ML spectra of coloured alkali halide crystals are similar to the thermoluminescence and afterglow spectra. The peak ML intensity and the total ML intensity increase drastically with the applied pressure following power law, whereby the pressure dependence of the ML intensity is related to the work-hardening exponent of the crystals. The ML also appears during the release of the applied pressure because of the movement of dislocation segments and movements of dislocation lines blocked under pressed condition. On the basis of the model based on the mechanical interaction between dislocation and F-centres, expressions are derived for the ML intensity, which are able to explain different characteristics of the ML. From the measurements of the plastico ML induced by the application of loads on ?-irradiated alkali halide crystals, the pinning time of dislocations, diffusion time of holes towards F-centres, the energy gap Ea between the bottom of acceptor dislocation band and the energy level of interacting F-centres, and work-hardening exponent of the crystals can be determined. As in the elastic region the strain increases linearly with stress, the ML intensity also increases linearly with stress, however, as in the plastic region, the strain increases drastically with stress and follows power law, the ML intensity also increases drastically with stress and follows power law. Thus, the ML is intimately related to the plastic flow of alkali halide crystals.

2010-02-01

12

Acoustic and photon emissions during mechanical deformation of coloured alkali halide crystals  

International Nuclear Information System (INIS)

Acoustic and photon emissions take place in the elastic and plastic as well as the fracture region of x-irradiated KBr, KCl and NaCl crystals. The rate of photon emission is linear with the strain rate: however, the RMS value of the acoustic emission is proportional to the square root of the strain rate. The acoustic emission is maximum for x-irradiated NaCl crystals; however, the photon emission is maximum for x-irradiated KBr crystals. From the similarity between the acoustic emission and the photon emission, it seems that mobile dislocations are responsible for the acoustic emission in coloured alkali halide crystals. (author)

1984-01-14

13

Helium irradiation of alkali halides  

International Nuclear Information System (INIS)

An investigation has been made of radiation damage in alkali halide crystals induced by heavy bombardment of 1 MeV helium ions. The channeling technique has been employed and three processes have been monitored simultaneously to explain the apparent reduction of damage at high doses. It is shown that the initial rise and fall of the back-scattered yield from different alkali halides can be related to the Pooley mechanism coupled with the aggregation of interstitials to form dislocation loops through the intermediate stage of clusters

1979-01-01

14

Analogy between temperature dependent radiation effects in alkali halide crystals and crystalline ammonia  

International Nuclear Information System (INIS)

Pikaev, Ershov, and Makarov recently reported the characteristic shape of Arrhenius-type dependence for F-centers slow part (millisecond) decay in alkali halide crystals irradiated at different temperatures. The decay rate is constant when the temperature is below the limiting value (T/sub lim/) and exhibits constant activation energy (E/sub A/) at temperatures above T/sub lim/ up to the melting point. A similar dependence has been observed for crystalline ammonia radiolysis yields (H2 and N2) in the temperature range from 77 to 1950K (ammonia melting point) with a limiting value of 1050K for N2 and 1190K for H2. The coincidence between the alkali halide and ammonia data does not seem to be formal and there are indications showing a closer analogy between these two cases

1977-01-13

15

Electron-acceptor impurity effect on formation of positronium-like states in alkali halide crystals  

Energy Technology Data Exchange (ETDEWEB)

The positron annihilation in alkali halide crystals (AHC) KCl, KBr, alloyed by Ag impurities (O.1 mol %), Tl (1 mol %) OH (0.5 mol %) has been studied. The fraction of formed Ps states has been determined by changes in angular distribution of annihilation photons (ADAP) in a static magnetic field (H=10 kGc) and by data of time distribution measurement of positron annihilation. The data obtained testify in favour of blast-hole mechanism of Ps-states formation in AHC.

Aref' ev, K.P.; Kuznetsov, P.V.; Galanov, Yu.I. (Tomskij Politekhnicheskij Inst. (USSR))

1984-01-01

16

An optical criterion to obtain miscible mixed crystals in alkali halides  

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: English Abstract in spanish Este trabajo ofrece un nuevo criterio para predecir la formación de soluciones sólidas en halogenuros alcalinos cristalinos y discute algunos resultados obtenidos en el desarrollo de mezclas dieléctricas cristalinas miscibles de halogenuros alcalinos ternarias y cuaternarias. Estas mezclas son misci [...] bles en cualquier concentración de sus componentes. Tener el resultado de estas mezclas cristalinas está relacionado al centro F a través del comportamiento observado en la banda F de absorción en función de la constante de red de los halogenuros alcalinos donde el defecto fue formado (centro F). Dando un vistazo a la gráfica de Energía de banda F versus constante de red (ley de Mollwo-Ivey), se observa un conjunto de puntos, que dan la pauta (tal como KCl, KBr, RbCl), de posibles mezclas de materiales correspondientes a puntos adyacentes y una solución sólida podría formarse, significando un cristal de una sola fase, que dan por resultado cristales ternarios y cuaternarios. Así, la banda F de absorción nos permite tener un criterio numérico, basado en el porcentaje de cambio de la energía de la banda F que permite obtener soluciones sólidas. Encontramos información experimental, usando difractogramas de las mezclas cristalinas, se obtienen las constantes de red y se comparan con la obtenida teóricamente a través de la generalización de la Regla de Vegard, finalmente se discute la posibilidad de crecer cristales partiendo de cinco componentes, tomando cinco puntos consecutivos en la grafica de la Ley de Mollwo-Ivey. Abstract in english This work gives a novel criterion to predict the formation of alkali halide solid solutions and discusses some results obtained in the development of ternary and quaternary miscible crystalline dielectric mixtures of alkali halides. These mixtures are miscible in any concentration of their component [...] s. The miscibility of these mixed crystals is quite related to the F center through the behavior observed in the spectral position of the optical absorption F band as a function of the lattice constant of the alkali halide where the F center was formed. By inspection of an energy graph of the F band energy versus lattice constant (Mollwo-Ivey law), a set of points is observed corresponding to several pure alkali halides (such as KCl, KBr, RbCl), which gives a notion of possible mixed materials that would correspond to adjacent points and a solid solution could be obtained, meaning a single phase crystal, which result in ternary and quaternary mixed crystals. Thus, the optical absorption F band allows have a numerical criterion, based on the percentage respective of the F band energy, in order to predict possible solid solutions. We obtained experimental information using diffractograms of the mixed crystals, from which the lattice constant was obtained and compared with a theoretical calculus using a generalization of Vegard's law, finally it is discussed the case of a crystal growing, starting from five components, picking up five consecutive dots from the graph of Mollwo-Ivey's law.

R, Rodríguez-Mijángos; G, Vázquez-Polo; J.J., Palafox; R, Pérez-Salas.

17

New AIG method of growing alkali halide crystals and potential application to CZT  

International Nuclear Information System (INIS)

The new AIG (Advance Interface Growth) method has been successfully applied to alkali halide scintillation crystals at PhotoPeak, Inc. for the last four years. It produces single, stress-free crystals having a low level of defects and has resulted in increasing the yield of usable CsI(Tl) crystals to 75-85%. Essentially it is a low gradient method but has the capability to adapt the gradient to that needed by an individual crystal for the most successful growth. High quality crystals have been supplied to national laboratories and the nuclear medicine market. For example, a blank CsI(Tl) crystal 2 in diameter and 2 in length was produced having a measured energy resolution of 6.5% at 662 keV on a 2 -diameter PMT having a standard blue bialkali photocathode. This far exceeds the best resolution, 8.5-9.5%, obtained for CsI(Tl) crystals grown by the conventional Bridgman method. It is expected that this method can be successfully applied to grow high quality CZT crystals with substantially higher yield, 25-35%, than the presently existing 5-10%. The reasons for the expected improved yield of CZT crystals are that the phase diagram of CZT material has a narrow range of stability and CZT crystals should benefit from growth in a low gradient environment. Since the AIG method does not involve any moving parts, the temperature control and stability are much higher than for the conventional Bridgman method. The experience with CsI crystals indicates that imperfections like twinning, sparks, and multiplicities can be substantially reduced or even eliminated in CZT crystals. The expected higher yield and improved spectroscopic quality of CZT should allow many commercial applications to become a reality

2002-10-10

18

The influence of low temperature uniaxial stress on self trapped excitons' structure in alkali halide crystals  

International Nuclear Information System (INIS)

Full text: According to contemporary conceptions the alkali halide crystals (AHC) intrinsic luminescence can be classified by three different configurations of self trapped exciton (STE) with a core of molecular formation (Hal2-): central symmetric (I-type, on) exciton is Vk center localized in its field with electron without mass center removal of electron and hole subsystems of Hal2- ion. According to mass center removal (Vk - center) STE are subdivided into configurations of II-type (weak off - weak asymmetric) and Ill-type (strong off - strong asymmetric). The structure of all STE types (I, II, III) for FCC is orientated on crystallographic direction and for BCC on . In this connection uniaxial stress influence on different STE configurations in AHC at their radiative relaxation is investigated. With an increase of uniaxial stress degree at 100 K in KI crystal Ex luminescence is converted into ?-luminescence, and or RbI crystal the situation is vice versa - ?- luminescence is converted into Ex luminescence. Usually ?-luminescence for many crystals (for example, KCl, RbCl, RbBr) appears in visible spectral region with a large Stokes shift - SR =0.6. But in some crystals, for example NaBr and NaI, ?- luminescence appears in ultraviolet spectral region with a relatively small Stokes shift - SR =0.25-0.3, what is typical for ?-luminescence. That means ?-luminescence in AHC can have different STE structure, as weak off and strong off-configurations (I, II, Ill-types) as distinct from ?--luminescence which can have on-configuration only (I-type). NaCl initially has symmetric structure in comparison with Rbl. That is why the uniaxial stress only intensifies without redistribution effect. The same picture is observed in NaBr crystal where there is only one STE luminescence band with symmetric configuration. Thus analyzing radiation spectra redistributions of KI and RbI crystals and also NaCl and NaBr crystals we came to conclusion: uniaxial stress effectively acts in the direction that brings asymmetric STE to symmetric configuration (strong?weak?on or III?II?I - types). If the uniaxial stress is applied on crystallographic direction then except compression there can be stretching between self trapped excitons' components. Such a situation is observed for KBr and CsI crystals. Thus at low temperature uniaxial stress in face centered AHC luminescence redistribution takes place in favor of symmetric configuration, and in volume centered vice versa - in favor of STE asymmetric configuration

2004-01-01

19

CO_2 laser absorption and saturation studies of molecular impurities in alkali halide crystals  

International Nuclear Information System (INIS)

The objective of this research program has been to explore the equilibrium and non-equilibrium dynamical properties of ReO_4"- molecules embedded in alkali halide lattices using electromagnetic radiation. Both incoherent sources and CO_2 laser radiation have been used to explore the full dynamic range of the molecular vibrational modes. To achieve this objective stable molecular dopant - alkali halide combinations have been fabricated which have vibrational modes near the CO_2 laser frequencies. In order to uncouple the molecular modes from the lattice modes, to simplify the analysis as much as possible, low temperature spectroscopic measurements were required. In general, it was found that the molecular vibrational modes in the low temperature quiescent lattice had extremely narrow linewidths (less than 0.1 cm"-"1) so that most of the coincidences with the CO_2 laser lines were eliminated

1980-01-01

20

Defect production in alkali halide crystals by monochromatic x and uv radiation  

International Nuclear Information System (INIS)

The spectral dependence of the F-center production efficiency of several alkali halides was observed in diverse parts of the electromagnetic spectrum. Using low flux monochromatic sources, this efficiency was measured in the hard x-ray region at the K-edge of bromine in KBr and in the near-ultraviolet part of the spectrum corresponding to the exciton region of the alkali halide. A significant increase in the production efficiency was observed at the K-edge, indicating a new F-center production mechanism. In the ultraviolet, maxima in the F-center production efficiency were observed in the long wavelength tail of the first exciton peak and even in the region of the alpha band, providing the first direct measurements of the F-center production efficiency in this region. These studies were made possible by the development of an extremely sensitive new method of detecting F-centers in ultralow concentrations, which utilizes the luminescent properties of these centers. This laser-induced luminescence method enables detection of concentrations of F-centers that are five orders of magnitude smaller than can be detected by optical absorption measurements. Thus, a new regime of F-center production, the early part of the so-called stage I region, could be studied; it was observed to be linear for about four orders of magnitude

1985-01-01

 
 
 
 
21

Evaluation of the first- and higher-order volume and pressure derivatives of dielectric constants of alkali halide crystals  

International Nuclear Information System (INIS)

An analysis of first and higher order volume and pressure derivatives of low frequency or static dielectric constant is presented for sixteen alkali halide crystals with NaCl structure using seven different potential forms for the short range overlap repulsive energy. The potential parameters are calculated using recent values of van der Waals potentials and taking proper account of the thermal contribution derived from consistent experimental ultrasonic data. Calculated values of volume derivatives of dielectric constant and optic mode Grueneisen parameters are compared with available experimental data. The results obtained from some potential forms present distinctly better agreement with experiment in comparison of others. The usefulness of such potential forms is demonstrated in predicting the higher order pressure derivatives of dielectric constants of ionic crystals. (author)

1985-11-01

22

Solid state vibrational lasers using F-center/molecular-defect pairs in alkali halides  

Energy Technology Data Exchange (ETDEWEB)

A laser is described having a laser action in the infrared wavelength region comprising: an alkali halide crystal having dilute diatomic molecular defects; F-center defects in the alkali halide crystal associated with the molecular defects; cooling means for cooling the crystal below about 77KAPPA; optical pumping means for pumping the F-center/molecular defect pairs in the visible wavelength range.

Gellermann, W.; Yang, Y.; Luty, F.

1987-01-20

23

Electron scattering from alkali halide molecules  

International Nuclear Information System (INIS)

The low energy electron scattering from molecules belonging to alkali halide matrix is studied. The modified Born-Eikonal Series method is employed to calculate rotational excitation cross sections. The curves are plotted for the incident electron energy versus total cross section for each column of alkali halide matrix. The conclusion is drawn regarding dependence of the total cross section with the electron-negativity difference of the molecules. (author)

1983-04-01

24

Defects induced melting in alkali halides  

International Nuclear Information System (INIS)

In the present paper we study the pressure dependence of melting of NaCl and CsCl crystals. A formulation has been presented for the pressure dependence of melting temperature on the basis of the vacancy model using the expression for the pressure dependence of the volume of Schottky defects from the Roy-Roy equation of state. Values of pressure derivatives of melting temperature have been calculated at elevated pressures to determine the rate of change of melting temperature with increase in pressures using the data of vacancy formation energy and effective volume of Schottky defects. The vacancy model revised in the present study takes into account the variation of bulk modulus with pressure, whereas in the Ksiazek and Gorecki model, it was treated constant. Results for pressure derivative of melting temperature are calculated for the solids under study. The melting curves have also been obtained and found to compare well with results based on molecular dynamics simulation and experimental data reported in recent literature. -- Research Highlights: ? We have studied the pressure dependence of melting in alkali halides on the basis of the vacancy model. ? We have taken into account the pressure dependence of volume of Schottky defects. ? The pressure derivatives of melting temperature are calculated for the alkali halide solids. ? The results have been found to compare well with the corresponding experimental data. ? This work will be useful in the analysis of thermal equation of state for solids.

2011-02-01

25

Moments of the phonon spectra in alkali halides  

International Nuclear Information System (INIS)

The results of a systematic calculation of the moments of the phonon spectra for 20 alkali halides are reported. The relevant phonon spectra needed are taken from the Green's function compilations by Haridasan et al. The calculated moments show good agreement with the available experimental data for sodium, potasium and caesium halides. The moments deduced from Debye-Waller factor data and from specific heat data are mutually consistent. A critical inter-comparison of these moments in these crystals is made. (author)

1976-06-01

26

The influence of dislocation charge on the cleavage surface charge of alkali halide crystals  

International Nuclear Information System (INIS)

In order to study the role of charged dislocations in the formation of charge of the fresh surface of ionic crystals the investigated samples were cleaved from single crystals of NaCl, KCl, and LiF with various impurity (Ca) contents or from ?-irradiated single crystals. The dislocation charge per unit length was measured with the aid of indentation of the crystal surface, that was neutralized before testing. The indentor penetration depth was maintained approximately constant by load variation from 10 to 40 N from different crystals. To estimate the dynamic surface charge during fast specimen cleavage under the action of impact load both the electric field intensity around the specimen and the crack length were simultaneously measured. The residual surface charge was measured 1 min after the sample cleavage by the aid of an electrometer

1985-11-16

27

Effect of impurities on the hardness of alkali halide single crystals  

Science.gov (United States)

Micro hardness number of KCl, KBr and KCl-Br grown by Czocharlski technique, in the presence of homovalent and aliovalent ions of different ionic radii were measured in the indentation load range from 5 to 80*10-3 N. The measured data showed that there is an indentation size effect and classical Meyer's law was used for the characterization of crystal hardness of these crystals. The Meyer's index was also found to be smaller than 2 indicating brittle material characteristic. The P.R.S. model was used for the determination of the load independent micro hardness value. Result can be explained on the basis of interaction between created dislocation and point defect. It was found that hardness of these crystals is depending on the type of impurity.

Verma, Ashok K.; Ojha, Chaturbhuj; Shrivastava, A. K.

2014-04-01

28

Evaluation of electronic dielectric constant and fractional ionic character of mixed alkali halide crystals  

International Nuclear Information System (INIS)

The electronic dielectric constant and fractional ionic character of the chemical bond are calculated for the mixed crystals NaCl-NaBr, KCl-KBr, KBr-KI, CsCl-CsBr, CsCl-RbCl, and CsCl-KCl for the entire range of composition. The first four solid solutions are with common cations whereas the last two are formed of substances with common anions. For the electronic dielectric constant a comparison is given of the values calculated from the Clausius-Mossotti relation and the Pantelides formulation. For evaluating the fractional ionic character application is made of Phillips' and Pauling's theories. The calculated values are found to depend sensitively on the composition parameter of mixed crystals. (author)

1986-08-01

29

Electron localization in alkali-halide clusters  

International Nuclear Information System (INIS)

The quantum path-integral molecular-dynamics method was applied to explore the structure, energetics, and dynamics of an excess electron interacting with an alkali-halide cluster. Four distinct modes of electron localization were established, which depend on the cluster composition, size, and structure; they involve an internal F-defect, an external surface state, dissociative detachment of an alkali atom, and structural isometrization induced by electron attachment

1985-04-22

30

On the nature of defects responsible for thermal expansion of irradiated alkali halide crystals  

International Nuclear Information System (INIS)

To determine defect nature responsible for thermal expansion of irradiated AHC, effect of electron excitation on variation of linear expansion temperature coefficient and on accumulation of F-, X3--centers, devacancies in KBr crystals in the absorbed dose range of 3x104-5x108 rad has been studied. Specimen irradiation was performed with 1.2 MeV electrons at room temperature. Divacancies are shown to play a determining role in the process of AHC radiation expansion

1986-09-01

31

Interaction between dislocation and defects induced by X-irradiation in alkali halide crystals  

International Nuclear Information System (INIS)

Interaction between dislocation and defect induced by X-irradiation has been investigated in NaCl and KCl single crystals by strain rate cycling tests under superimposition of ultrasonic oscillation during plastic deformation. The interaction energy between dislocation and radiation-induced defect has been obtained by fitting Barnett model to experimental results, assuming that the defect is tetragonal. The interaction energies between dislocation and defect were determined to be 0.39 and 0.87 eV for NaCl and KCl, respectively. The larger interaction energy for KCl presents its larger tetragonality of defect induced by X-irradiation than NaCl.

2011-12-01

32

Temperature dependence of compressibility of alkali halides  

International Nuclear Information System (INIS)

Calculations are done to compute the temperature dependence of the isothermal compressibility for alkali halides at room temperature and atmospheric pressure. All the calculated data are tabulated together with other relevant parameters needed for the purpose. The results obtained are in good agreement with the experimental data taken from the literature

1981-08-01

33

Recombination of radiation defects in alkali halide crystals at low temperature  

International Nuclear Information System (INIS)

The complex investigation of the ionic-electronic processes of the charge transport and thermally stimulated luminescence of colour centres (I, ?, F, F', Vsub(K) and H) in X-irradiated KBr, NaCl, NaI and KCl crystals at 4.2 K has been carried out. The experiment has been performed on X-irradiated KBr at 4.2 K by a complex of thermally stimulated methods. A number of substages of temperature annealing of different defects was studied. The effect of electron tunneling ''recharge'' in the excited defect pair (F-H) during photostimulation in the F-band of KBr is observed which results in the charged Frenkel defect pair formation (?-I). The conclusion is drawn that the tunneling ''recharge'' of the non-excited F-H pair is unlikely. It was observed that the Frenkel defect (I, ?, ''H-Vsub(K)'', F, H') accumulation efficiencies increases by 10% or more if the X-irradiation at 4.6 K is carried out under an applied DC field of 3 kV/cm. Two competitive mechanism of the primary generation of the anion Frenkel defects are discussed. The formation of the self-trapped excitons and their luminescence as a result of the H and F centers direct recombination could be noneffective. It is found that anion exciton dissociation into the electron- hole pair is a process competitive to the exciton decay into the Frenkel defect pair

1981-01-01

34

Growth of pure single crystals of alkali halides and alkaline earth fluorides  

Science.gov (United States)

The final report covers the design of ion selective filters and development of an ion exchange purification system for potassium bromide. The system consists of an ion selective filter for passage of potassium ions and a bromide anion exchange system for reduction of anionic impurities. Because of the high ionic strength of the solutions used and particularly their ability to hydrolyze amide and ester bonds, limitations are imposed on the materials that can be used for construction of those parts of the systems that contact these solutions. Certain addition polymers are more promising for construction of the components of such a system than others, these are discussed in the body of the report. A special group of components have been designed and assembled to provide the fittings, valves, electrode chambers, sampling valves, columns and filters necessary for a closed purification system. The preparation of the resins for use in such a system required that their conversion to the forms required for purification of KBr, require that the reactions for this conversion go almost to completion. The extent of conversion of the resins affect the operational characteristics of the system and are discussed in this report. The product of the initial purification is a strongly acid KBr solution and the techniques were developed to minimize external contamination during reduction of the purified salt solution to a solid. The final purification step made during the growth of the crystal is treatment with a reactive gas. A greaseless reactive gas manifold was constructed and several reactive gas treatments were used in an attempt to purify the KBr.

Fredericks, W. J.

1981-05-01

35

Complexes in polyvalent metal - Alkali halide melts  

International Nuclear Information System (INIS)

Experimental evidence is available in the literature on the local coordination of divalent and trivalent metal ions by halogens in some 140 liquid mixtures of their halides with alkali halides. After brief reference to classification criteria for main types of local coordination, we focus on statistical mechanical models that we are developing for Al-alkali halide mixtures. Specifically, we discuss theoretically the equilibrium between (AlF6)3- and (AlF4)- complexes in mixtures of AlF3 and NaF as a function of composition in the NaF-rich region, the effect of the alkali counterion on this equilibrium, the possible role of (AlF5)2- as an intermediate species in molten cryolite, and the origin of the different complexing behaviours of Al-alkali fluorides and chlorides. We also present a theoretical scenario for processes of structure breaking and electron localization in molten cryolite under addition of sodium metal. (author). 26 refs, 2 tabs

1991-01-01

36

Optical radiation from electron sputtering of alkali halides  

International Nuclear Information System (INIS)

Electron-surface collisions have been observed to result in the emission of optical radiation from excited atoms and molecules desorbed from alkali halide single crystal surfaces. The detected radiation included Na and Li resonance lines, hydrogen Balmer emission, and OH molecular radiation. Much previous experimental and theoretical effort has been devoted to electron stimulated desorption (ESD) of ground state neutrals and ions, and in particular from alkali halides. The few studies concerned with excited particles have dealt primarily with ejected metastable neutrals. In one case involving electron bombardment fluorescence of ice, a tentative identification has been made of OH molecular radiation. The results reported here include a) the first definitive work on optical radiation from electron bombardment induced emission of excited free substrate particles, and b) the first observations of characteristic radiation from previously adsorbed free atoms and molecules. (orig.)

1980-09-19

37

Ionic alkali halide XUV laser feasibility study  

Energy Technology Data Exchange (ETDEWEB)

The objective of this work is to assess the feasibility of a select set of ionic alkali halide XUV laser concepts by obtaining the relevant kinetic and spectroscopic parameters required for a proof-of-principle and conceptual design. The proposed lasers operate in the 80--200 nm spectral region and do not require input from outside radiation sources for their operation. Frequency up-conversion and frequency mixing techniques and therefore not considered in the work to be described. An experimental and theoretical study of a new type of laser operating in the extreme ultraviolet wavelength region has been conducted. The lasing species are singly ionized alkali halide molecules such as Rb{sup 2+}F{sub {minus}}, Rb{sup 2+}Br{sup {minus}} and Cs{sup 2+}F{sup {minus}}. These species are similar in electronic structure to the rare gas halide excimers, such as XeF and Krf, except that the ionic molecules emit at wavelengths of 80--200 nm, much shorter than the conventional rare-gas halide excimer laser. The radiative lifetime of these molecules are typically near 1 ns, which is about an order of magnitude shorter than that for rare-gas halide systems. The values of the cross section for stimulated emission are on the order of 1 {times} 10{sup {minus}16}cm{sup 2}. Because of the fundamental similarity to existing UV lasers, these systems show promise as a high power, efficient XUV lasers. 55 refs., 50 figs., 5 tabs.

Yang, T.T.; Gylys, V.T.; Bower, R.D.; Harris, D.G.; Blauer, J.A.; Turner, C.E.; Hindy, R.N.

1989-11-10

38

Analysis of the relative stability of the NaCl, CsCl, and cubic ZnS structures in alkali halide crystals  

International Nuclear Information System (INIS)

The effect has been investigated of including the van der Waals interaction, second-neighbour repulsive interactions, and three-body interactions in predicting the stability of alkali halides. Four different interionic force models have been used for the calculation of cohesive energies in different possible structures (NaCl, CsCl and cubic ZnS)

1982-01-01

39

Investigating and Supplying Halid Flux-Grown KTP Crystals.  

Science.gov (United States)

The original purpose of this contract was to supply KTiOPO(4) (KTP) crystals grown by Cristal Laser S.A. by flux of alkali metal halide. Therefore, the experiments were performed on crystals from Cristal Laser S.A. The main tests provided for in the contr...

D. Lupinski

1995-01-01

40

Structured alkali halides for medical applications  

International Nuclear Information System (INIS)

Image plates based on storage phosphors are a major application of radiation defects in insulators. Storage phosphors absorb X-ray quanta creating trapped electron-hole pairs in the material. Optical stimulation of the electron causes recombination leading to light emission. Application of image plates requires an optimal compromise between resolution (represented by the modulation transfer function (MTF)) and sensitivity. In our paper we present a new solution of the problem of combining a high MTF with a high sensitivity by structuring the image plates in form of thin needles acting as light guides. This suppresses the lateral spread of light which is detrimental to resolution. As doped CsBr, e.g. CsBr:Ga [Physica Medica XV (1999) 301], can pose a good storage phosphor evaporated layers are of interest in computed radiography. Needle structured CsI:Tl is used as scintillator in direct radiography [IEEE Trans. Nucl. Sci. 45 (3) (1998)]. CsBr layers have been produced by evaporation in vacuum and in inert gas atmosphere varying pressure and temperature. The resulting structures are of fibrous or columnar nature being in good agreement with the zone model of Thornton [Ann. Rev. Mater. Sci. 7 (1977) 239]. A zone model for CsBr has been developed. Measurements on doped alkali halide image plates having needle structure show good MTF at high sensitivity making a significant progress in image plate technology

2002-05-01

 
 
 
 
41

Electron stimulated desorption thresholds for excited atoms desorbed from alkali-halides  

International Nuclear Information System (INIS)

We have investigated the thresholds for the generation of desorbed excited alkali atoms under electron bombardment for LiF, KCl and KBr in the energy range from 10 to 120 eV, and from room temperature up to 4500C. The dependence of the yield of excited atoms on the electron energy shows features which are in good agreement with the excitation energies of alkali core-excitons in the alkali-halide crystal. This suggests the production of an alkali core-exciton as an initial step for the desorption of excited alkali metal atoms under electron bombardment. The dependence of the yield of excited alkali atoms on either the temperature of the crystal or the electron density in the irradiated surface area gives additional support for that model. (author)

1988-09-19

42

Theoretical study of Tl"0 and Pb"+ centers in alkali halide and alkaline earth fluoride type crystals  

International Nuclear Information System (INIS)

A theoretical study has been carried out on the hfi of Pb"+ defects in KCl, CaF_2 and BaF_2 using an earlier developed crystal field model. Experimental results can be explained in the same way as was done for Tl"0 in KCl. However some parameters seem to have a less physical meaning than in the case of Tl"0. A new method is in progress using the ASW band structure procedure in order to estimate genuine solid state effects. Preliminary results are encouraging. (orig.)

1987-04-01

43

Characteristic features on Ag-centers in KCl:Ag single alkali halide crystals grown by Czochralski method  

International Nuclear Information System (INIS)

Single crystals of KCl and KCl:Ag were grown with different Ag as a dopant by Czochralski method. A study was made on absorption spectra of point defects like Ag-centers, which stablished by Gamma radiation. By inspecting the absorption spectra in addition to basic F-band, three new bands, named A, B and C were found, too. These are ascribed to transitions ISO? 3p1, 3p2 and 1p1, respectively. It is concluded that the linear electron-lattice coupling approximation and energy parameters are quite satisfactory for Ag-centers in the other results so far studied

2003-02-01

44

Laser-synchrotron studies of the dynamics of UV-photon-stimulated desorption in alkali halides  

International Nuclear Information System (INIS)

Laser-synchrotron studies of neutral alkali emission from alkali halide crystals are yielding new insights into the dynamics of energy absorption, energy localization and bond-breaking in photon-stimulated desorption. The ground-state neutral desorption is triggered by the thermal diffusion of photon-induced electronic defects; however, the excited-state neutral alkalis are formed in a surface-specific process on an extremely short time scale. In addition, there is new evidence for a surface overlayer which retards substrate desorption, thus suggesting a new approach to the optical damage problem at ultraviolet wavelengths. 8 references

1986-01-01

45

Laser-synchrotron studies of the dynamics of UV-photon-stimulated desorption in alkali halides  

International Nuclear Information System (INIS)

Laser-synchrotron studies of neutral alkali emission from alkali halide crystals are yielding new insights into the dynamics of energy absorption, energy localization and bond-breaking in photon-stimulated desorption. The ground-state neutral desorption is triggered by thermal diffusion of photon-induced electronic defects; however, the excited-state neutral alkalis are formed in a surface-specific process on an extremely short time scale. In addition, there is new evidence for a surface overlayer which retards substrate desorption, thus suggesting a new approach to the optical damage problem at ultraviolet wavelengths

1986-09-10

46

Electronic structure, lattice energies and Born exponents for alkali halides from first principles  

Directory of Open Access Journals (Sweden)

Full Text Available First principles calculations based on DFT have been performed on crystals of halides (X = F, Cl, Br and I of alkali metals (M = Li, Na, K, Rb and Cs. The calculated lattice energies (U0 are in good agreement with the experimental lattice enthalpies. A new exact formalism is proposed to determine the Born exponent (n for ionic solids. The values of the Born exponent calculated through this ab-initio technique is in good agreement with previous empirically derived results. Band Structure calculations reveal that these compounds are wide-gap insulators that explains their optical transparency. Projected density of states (PDOS calculations reveal that alkali halides with small cations and large anions, have small band gaps due to charge transfer from X ? M. This explains the onset of covalency in ionic solids, which is popularly known as the Fajans Rule.

C. R. Gopikrishnan

2012-02-01

47

Molten Alkali Halides: Straightforward Prediction of Surface Tension  

Science.gov (United States)

This article provides a new model for predicting the surface tension of molten alkali halides, because the subject is worthy of investigation. A relationship exists between the surface tension ( ?) at the melting point ( T m ), molar volume ( V), internuclear distance ( D), and radius ratio The basic idea results from the assumption that all of the parameters are constants. The relation depends on the reliability and accuracy of all the constants on which it is based. The formula was examined and showed remarkable agreement between the calculated surface tension and experimental data within a difference of less than 10 pct for most of the salts studied.

Aqra, Fathi

2014-05-01

48

Debye-Waller factors of alkali halides  

International Nuclear Information System (INIS)

Using very-high-intensity (?70 Ci) 183Ta Moessbauer sources, we have measured the Debye-Waller factors (DWF close-quote s) of sodium chloride, potassium chloride, and potassium bromide single crystals for several of the (h00) and (nnn) Bragg reflections. We have used an approach which properly accounts for thermal expansion over the temperature range of our experiment, from 90 K to 900 K, about 100 K below the melting point of our crystals. We have found that a procedure used to analyze data by earlier workers leads to incorrect parameters in the Debye-Waller factor exponent, and our procedure does not require empirical parameters to account for the effects of thermal expansion. Additionally, we find three items of significance. Contrary to earlier results, we observe that the cations and the anions have identical DWF close-quote s in NaCl and also in KBr. We observe terms in the expansion of the DWF exponential which are quartic in the scattering wave vector rvec Q in NaCl and KCl, with some evidence for a Q4 term in KBr. The size of the Q4 contribution is reported and varies with the direction of momentum transfer. We also observe that the Debye temperature and the coefficient of the anharmonic Q2 term also vary with the direction of momentum transfer. We believe our data are the definitive evidence for a nonspherical thermal cloud in a cubic crystal; the ions have a larger amplitude of oscillation in the [h00] direction than in the [nnn] direction, contrary to the commonly held view of crystallographers that the most general form of the mean-square thermal motion is of an ellipsoid shape. copyright 1998 The American Physical Society

1998-01-01

49

Thermal conductivity of molten alkali halides and their mixtures  

International Nuclear Information System (INIS)

Thermal conductivity of molten alkali halides and their mixtures with common anions is measured as a function of temperature. Use is made of the most reliable method of coaxial cylinders made of platinum, with radiation heat transfer being taken into account. It is found to vary directly with temperature. Expressions for its temperature dependence are derived from the experimental observations. Linear relations of the thermal conductivity to the molar volume are established for molten alkali fluorides, chlorides, bromides, iodides and their mixtures with common anions. Deviations from the additive quantities towards smaller values are observed in the case of the mixtures. They are in a good accordance with inverse deviations of their adiabatic compressibility. The heat conduction of ionic melts is semiquantitatively examined. Elementary quantities of heat transferred from cations to anions and vice versa are estimated. (author)

1987-01-01

50

Correlation between standard enthalpy of formation, structural parameters and ionicity for alkali halides  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The standard enthalpy of formation (?Ho) has been considered to be an interesting and useful parameter for the correlation of various properties of alkali halides. The interrelation between ?Ho and structural parameters for the halides of Li, Na, K and Rb has been thoroughly analyzed. When cationic component element is kept constant in a homologous series of alkali halides, the negative value of ?Ho has been observed to decrease linearly with increase of interionic distance (d) and a...

Nasar Abu

2013-01-01

51

OPTICAL ABSORPTION SPECTRA OF LIQUID ALKALI HALIDES-F-CENTER GENERATION AT VERY HIGH TEMPERATURES  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have measured optical absorption coefficients of liquid alkali halides such as NaCl, KCl and CsCl up to very high temperatures and found that there appears a new absorption band originated from F-center even in "pure" alkali halides by raising temperature, which is known to be generated usually by the addition of small amount of alkali metals to liquid alkali halides. The measurements have been performed using sapphire cell, the use of which is necessary to avoid a chemical reactio...

1991-01-01

52

Epitaxial growth of alkali halides on stepped metal surfaces  

International Nuclear Information System (INIS)

We present a growth study of the alkali halides NaCl and KCl on the stepped metal surfaces Cu(311) and Cu(221) using high resolution low energy electron diffraction. For all systems studied it was found that the alkali halide deposit forms (100)-terminated epitaxial layers which have essential structural features in common: The interfacial arrangement between the ionic adlayer and the stepped metal substrate is characterized by an alignment of the polar in-plane Cl ion rows parallel and perpendicular to the intrinsic Cu steps. For low coverages (?1 ML) the Cl ions are in registry with the intrinsic substrate steps causing uniaxial strain in the direction perpendicular to the steps. In contrast, parallel to the steps the Cl ions are free to adjust their optimum Cl-Cl spacing. For coverages >3 ML, the strain perpendicular to the intrinsic Cu steps is accommodated which suggests the incorporation of monoatomic Cu defect steps at the interface in this regime of higher coverage

2005-09-15

53

Response of alkali halide scintillators to neutrons from 5 to 100 MeV  

Energy Technology Data Exchange (ETDEWEB)

The response of three alkali halide scintillator`s to neutrons in the range 5 to 100 MeV was investigated with the spallation neutron source at LAMPF/WNR. Scintillating crystals were Nal(Tl), Kl(Tl) and Csl(Tl), each 2.5 cm in diameter and 1.2 cm thick. Pulse shapes that depend on particle type were observed for Nal(Tl) and Csl(Tl) but not for Kl(Tl). Pulse height spectra for are reported as a function of neutron energy, and, where pulse shape discrimination was observed, for individual charged-particle groups.

Bartle, C.M. [Inst. of Geophysical and Nuclear Sciences, Lower Hutt, (New Zealand); Haight, R.C. [Los Alamos National Lab., NM (United States)

1994-07-01

54

Fabrication of alkali halide UV photocathodes by pulsed laser deposition  

Energy Technology Data Exchange (ETDEWEB)

A technique has been proposed for the fabrication of atmospheric corrosion resistant alkali halide UV photocathodes by pulsed laser deposition. We produced photocathodes with a highly homogeneous photoemissive layer well-adherent to the substrate. The photocathodes were mounted in a vacuum photodiode, and a tungsten grid was used as an anode. Using pulsed UV lasers, we carried out experiments aimed at evaluating the quantum efficiency of the photocathodes. With a dc voltage applied between the photocathode and anode grid, we measured a shunt signal proportional to the total charge emitted by the cathode exposed to UV laser light. The proposed deposition technique enables one to produce photocathodes with photoemissive layers highly uniform in quantum efficiency, which is its main advantage over thin film growth by resistive evaporation. (laser technologies)

Brendel' , V M; Bukin, V V; Garnov, Sergei V; Bagdasarov, V Kh; Denisov, N N; Garanin, Sergey G; Terekhin, V A; Trutnev, Yurii A

2012-12-31

55

M-center growth in alkali halides: computer simulation  

International Nuclear Information System (INIS)

The heterogeneous interstitial nucleation model previously proposed to explain F-center growth curves in irradiated alkali halides has been extended to account for M-center kinetics. The interstitials produced during the primary irradiation event are assumed to be trapped at impurities and interstitial clusters or recombine with F and M centers. For M-center formation two cases have been considered: (a) diffusion and aggregation of F centers, and (b) statistical generation and pairing of F centers. Process (b) is the only one consistent with the quadratic relationship between M and F center concentrations. However, to account for the F/M ratios experimentally observed as well as for the role of dose-rate, a modified statistical model involving random creation and association of F+-F pairs has been shown to be adequate. (author)

1983-06-01

56

"Textbook" adsorption at "nontextbook" adsorption sites: Halogen atoms on alkali halide surfaces  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Density-functional theory and second order Moller-Plesset perturbation theory calculations indicate that halogen atoms bond preferentially to halide substrate atoms on a series of alkali halide surfaces, rather than to the alkali atoms as might be anticipated. An analysis of the electronic structures in each system reveals that this novel adsorption mode is stabilized by the formation of textbook two-center three-electron covalent bonds. The implications of these findings to, for example, nan...

Li, B.; Michaelides, A.; Scheffler, M.

2006-01-01

57

Desorption and surface topography changes induced by He+ ion bombardment of alkali halides  

International Nuclear Information System (INIS)

Desorption fluxes from alkali halide (RbI, KBr) crystals under 5 keV He+ bombardment and the corresponding surface topography evolution were investigated by means of quadruple mass spectroscopy (QMS) and dynamic force microscopy (DFM) in UHV. Although, for the energy range of He+ ions used, desorption of alkali halides occurs predominantly via electronic processes, there are significant differences between the ion-stimulated desorption (ISD) and the electron-stimulated desorption (ESD). The latter proceeds in a layer-by-layer mode and, as a result, oscillating desorption fluxes are observed. For ISD the DFM images show that the surface erosion does not follow the layer-by-layer scheme and no oscillation in desorption fluxes are found but they exhibit monotonic decrease to some saturation level. We suggest that these differences between electron- and ion-stimulated desorption are caused by ballistic processes disturbing the perfect lattice and introducing defects in the bulk and at the surface. Such lattice defects can act as recombination centres for diffusing Frenkel defects and inhibit the desorption process. Additionally, projectiles colliding violently with top-layer ions introduce additional nucleation centres for vacancies on the surface which lead to the surface erosion in the multi-layer mode

2004-12-01

58

Desorption and surface topography changes induced by He{sup +} ion bombardment of alkali halides  

Energy Technology Data Exchange (ETDEWEB)

Desorption fluxes from alkali halide (RbI, KBr) crystals under 5 keV He{sup +} bombardment and the corresponding surface topography evolution were investigated by means of quadruple mass spectroscopy (QMS) and dynamic force microscopy (DFM) in UHV. Although, for the energy range of He{sup +} ions used, desorption of alkali halides occurs predominantly via electronic processes, there are significant differences between the ion-stimulated desorption (ISD) and the electron-stimulated desorption (ESD). The latter proceeds in a layer-by-layer mode and, as a result, oscillating desorption fluxes are observed. For ISD the DFM images show that the surface erosion does not follow the layer-by-layer scheme and no oscillation in desorption fluxes are found but they exhibit monotonic decrease to some saturation level. We suggest that these differences between electron- and ion-stimulated desorption are caused by ballistic processes disturbing the perfect lattice and introducing defects in the bulk and at the surface. Such lattice defects can act as recombination centres for diffusing Frenkel defects and inhibit the desorption process. Additionally, projectiles colliding violently with top-layer ions introduce additional nucleation centres for vacancies on the surface which lead to the surface erosion in the multi-layer mode.

Krok, F. [Regional Laboratory of Physicochemical Analyses and Structural Research, Jagiellonian University, Ingardena 3, 30-059 Cracow (Poland)]. E-mail: ufkrok@if.uj.edu.pl; Kolodziej, J.J. [Institute of Physics, Jagiellonian University, Reymonta 4, 30-060 Cracow (Poland); Such, B. [Institute of Physics, Jagiellonian University, Reymonta 4, 30-060 Cracow (Poland); Czuba, P. [Institute of Physics, Jagiellonian University, Reymonta 4, 30-060 Cracow (Poland); Piatkowski, P. [Institute of Physics, Jagiellonian University, Reymonta 4, 30-060 Cracow (Poland); Struski, P. [Institute of Physics, Jagiellonian University, Reymonta 4, 30-060 Cracow (Poland); Szymonski, M. [Regional Laboratory of Physicochemical Analyses and Structural Research, Jagiellonian University, Ingardena 3, 30-059 Cracow (Poland); Institute of Physics, Jagiellonian University, Reymonta 4, 30-060 Cracow (Poland)

2004-12-01

59

Correlation between standard enthalpy of formation, structural parameters and ionicity for alkali halides  

Directory of Open Access Journals (Sweden)

Full Text Available The standard enthalpy of formation (?Ho has been considered to be an interesting and useful parameter for the correlation of various properties of alkali halides. The interrelation between ?Ho and structural parameters for the halides of Li, Na, K and Rb has been thoroughly analyzed. When cationic component element is kept constant in a homologous series of alkali halides, the negative value of ?Ho has been observed to decrease linearly with increase of interionic distance (d and accordingly following empirical equation ?Ho = ? + ?d (where ? and ? are empirical constants has been established. However, for common anionic series of alkali halides an opposite nonlinear trend has been observed with the exception of common fluorides. The correlation study on the standard enthalpy of formation has been extended in term of radius ratio and also discussed in the light of ionization energy of the metal, electron affinity of the halogen, size of the ions, ionic character of bond and lattice energy of the compound.

Nasar Abu

2013-01-01

60

First-principal calculations of physical properties of F-centers in alkali-halide crystals with CsCl structure  

International Nuclear Information System (INIS)

The results of theoretical simulation of F-centers in CsCl, CsBr and CsI crystals which has been carried out from first principles in CRYSTAL06 program system in representation of linear combination of atomic orbitals are given. The CRYSTAL program allows to simulate electronic structure both within the framework of the Hartree-Fock approximation and on the base of density functional theory. Microscopic spatial defect structure is obtained in periodic model for 250-atomic supercell with complete account of relaxation. Energies of optical transition are calculated after Franck-Condon principle with respect to difference of complete energies of corresponding states. Obtained theoretical data agree well with known experimental ones

2010-10-02

 
 
 
 
61

Investigation of condensation and evaporation of alkali halide crystals by molecular beam methods. VIII. Molecular beam pulse experiments with lithium flouride  

Science.gov (United States)

Experiments with molecular beam pulses allow the determination of the relaxation times of monomeric, dimeric, and trimeric molecules of lithium fluoride on (100) surfaces of LiF as functions of the crystal temperature T and of the molecular flux jon impinging onto the surface. At high T and low jon the relaxation times increase exponentially with 1/ T. The corresponding activation energies are 0.79, 0.77, and 1.14 eV for the monomers, dimers, and trimers. At lower T and higher jon they become independent of T but increase with decreasing jon. The experiments were performed with different lithium isotopes: 6Li for the impinging molecular beam and 7Li for the crystal. Measurements with dimers and trimers of differing isotopic composition show that the measured relaxation times are independent of the isotope exchange on the surface. Therefore, the Li exchange times are immeasurably small ( < 10 ?s).

Dabringhaus, H.; Meyer, H. J.

1983-02-01

62

Aggregating of mercury-like rare-earth ions in the alkali halide crystals as model of clusterization in lava-like fuel-containing materials  

International Nuclear Information System (INIS)

On the basis of results of spectral-luminescent characteristics research for dielectric crystals of different structure, activated by lead ions, possibility of creation of lead-containing nanocrystals is shown, that can model mechanism and reasons of creation of different crystalline inclusions into lava-like fuel-containing materials. Mechanical destruction of lava under influence of alpha-, beta-, gamma-rays may promote going out of lava the crystalline inclusions

2008-01-01

63

Fractal characteristics of metal clusters self-assembled in alkali halide matrices  

Energy Technology Data Exchange (ETDEWEB)

Metal nanoclusters of Ag and Au were obtained in alkali halide crystals (NaCl, KBr and KCl). The fractal character of the structures is proved by the fractal dimensions calculated using a home made computer program. The self aggregation of the metallic structures is governed in both cases (Ag and Au) by the DLA mechanism. This is proved by the values of the fractal dimension calculated using two methods, sandbox and box-counting, which are between 1.7 and 1.8 for Ag and for Au between 1.7 and 1.9. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Enculescu, M.; Enculescu, I. [National Institute for Materials Physics, P.O. Box MG-7, Magurele-Bucharest 077125 (Romania)

2007-03-15

64

A two-accelerator facility and its use for radiation damage studies in alkali halides  

International Nuclear Information System (INIS)

An experimental system is described in which heavy ions, of energies 50-100 MeV, and light ions of energies 0.5-2 MeV, may be transported alternately from different accelerators into a common scattering chamber. The beam-transport and scattering-chamber details are described, the latter being designed to make in-beam studies of different modes of radiation damage in the target material. Experimental studies are described of simultaneous detection of back-scattered helium ions, X-rays and optical absorption in single-crystal alkali halide samples, done during continuous irradiation by a 1 MeV He beam; also back-scattered protons following intermittent irradiation by a 60 MeV oxygen beam. Analysis of the relative damage by these two beams is discussed in relation to a damage mechanism due to Pooley

1980-01-01

65

EPR study of the relaxed excited state of F-centres in alkali halides  

International Nuclear Information System (INIS)

EPR spectra in the relaxed excited state (RES) of F-centres in isotope-enriched crystals "4"1KCl, "3"9KCl, "8"5RbCl, and "8"7RbCl are studied by means of an optical detection technique. The EPR linewidth is established to be due to the hyperfine interactions of the F-centre electron with the ligand nuclei. It is shown that the EPR data for the RES of F-centres in alkali halides can be accounted for with a rather localised RES wavefunction. A hydrogenlike 2s wavefunction with the extremum in the region of the first coordination sphere is used as an envelope function. Additional lines in the optically detected spectra of F-centres are studied. (author)

1982-03-01

66

Physics and Nanofriction of Alkali Halide Solid Surfaces at the Melting Point  

CERN Document Server

Alkali halide (100) surfaces are anomalously poorly wetted by their own melt at the triple point. We carried out simulations for NaCl(100) within a simple (BMHFT) model potential. Calculations of the solid-vapor, solid-liquid and liquid-vapor free energies showed that solid NaCl(100) is a nonmelting surface, and that the incomplete wetting can be traced to the conspiracy of three factors: surface anharmonicities stabilizing the solid surface; a large density jump causing bad liquid-solid adhesion; incipient NaCl molecular correlations destabilizing the liquid surface, reducing in particular its entropy much below that of solid NaCl(100). Presently, we are making use of the nonmelting properties of this surface to conduct case study simulations of hard tips sliding on a hot stable crystal surface. Preliminary results reveal novel phenomena whose applicability is likely of greater generality.

Zykova-Timan, T; Tartaglino, U; Tosatti, E

2006-01-01

67

Why Are Alkali Halide Solid Surfaces Not Wetted By Their Own Melt?  

CERN Document Server

Alkali halide (100) crystal surfaces are anomalous, being very poorly wetted by their own melt at the triple point. We present extensive simulations for NaCl, followed by calculations of the solid-vapor, solid-liquid, and liquid-vapor free energies showing that solid NaCl(100) is a nonmelting surface, and that its full behavior can quantitatively be accounted for within a simple Born-Meyer-Huggins-Fumi-Tosi model potential. The incomplete wetting is traced to the conspiracy of three factors: surface anharmonicities stabilizing the solid surface; a large density jump causing bad liquid-solid adhesion; incipient NaCl molecular correlations destabilizing the liquid surface. The latter is pursued in detail, and it is shown that surface short-range charge order acts to raise the surface tension because incipient NaCl molecular formation anomalously reduces the surface entropy of liquid NaCl much below that of solid NaCl(100).

Zykova-Timan, T; Tartaglino, U; Tosatti, E

2005-01-01

68

On the origin of atomistic mechanism of rapid diffusion in alkali halide nanoclusters  

Science.gov (United States)

To elucidate the atomistic diffusion mechanism responsible for the rapid diffusion in alkali halide nano particles, called Spontaneous Mixing, we execute molecular dynamics simulations with empirical models for KCl-KBr, NaCl-NaBr, RbCl-RbBr and KBr-KI. We successfully reproduce essential features of the rapid diffusion phenomenon. It is numerically confirmed that the rate of the diffusion clearly depends on the size and temperature of the clusters, which is consistent with experiments. A quite conspicuous feature is that the surface melting and collective motions of ions are inhibited in alkali halide clusters. This result indicates that the Surface Peeling Mechanism, which is responsible for the spontaneous alloying of binary metals, does not play a dominant role for the spontaneous mixing in alkali halide nanoclusters. Detailed analysis of atomic motion inside the clusters reveals that the Vacancy Mechanism is the most important mechanism for the rapid diffusion in alkali halide clusters. This is also confirmed by evaluation of the vacancy formation energy: the formation energy notably decreases with the cluster size, which makes vacancy formation easier and diffusion more rapid in small alkali halide clusters.

Niiyama, Tomoaki; Sawada, Shin-ichi Sawada; Ikeda, Kensuke S.; Shimizu, Yasushi

2014-04-01

69

Molecular beam scattering from clean surfaces of alkali halides  

International Nuclear Information System (INIS)

Molecular beam scattering of light gases from in situ cleaved alkali halide surfaces has been studied as a means of developing molecular beam scattering as a surface characterization tool and as a means of obtaining information about the gas atom-solid surface potential interaction. For 4He scattering from LiF carried out under improved resolution the main results are: (1) there are four bound states in the surface potential well, as energies of -5.8, -2.2, -0.6 and -0.1 MeV. (2) Most of the structure designated as ''fine structure'' is due either to transitions to these four levels via various small reciprocal lattice vectors or to the opening of diffraction channels. (3) The transitions involving the (01) and (0 anti 1) reciprocal lattice vectors (i.e., the ones nearly perpendicular to the incident wavevector) are strong; as much as 85 percent of the specular intensity may be removed. Transitions via the other small reciprocal lattice vectors are much weaker. (4) The widths of the lines are consistent with the velocity distribution, which has a half-width of about 2 percent. (5) The observed energies agree fairly well with those calculated for a zeta-function potential, but are not consistent with a Morse potential. The preliminary results for 4He/NaF scattering are that there are three bound-states in the surface potential well and are quite similar to the LiF results. These energies are -5.0, -1.9, and -0.5 MeV. 4He/NaF selective adsorption also shows ''fine structure'' and a more detailed analysis is called for here

1975-01-01

70

Efficient destruction of CF4 through in situ generation of alkali metals from heated alkali halide reducing mixtures.  

Science.gov (United States)

Perfluorocarbons (PFCs) are the most potent green house gases that are very recalcitrant at destruction. An effective way of converting PFCs using hot solid reagents into safe products has been recently introduced. By investigating the thermal reductive destruction of tetrafluoromethane (CF4) we provided new insight and more physicochemical consideration on this novel process. The complete destruction of CF4was successfully achieved by flowing the gas through a heated reagent bed (400-950 degrees C) that contained powder mixtures of alkali halides, CaO, and Si. The silicon acted as a reducing agent of alkali halides for the in-situ production of alkali metals, and the calcium oxide played the role of a halide ion acceptor. The absence of any single component in this ternary mixture drastically reduced the destruction efficiency of CF4. The CF4 destruction efficiencies with the solid reagent containing the alkali halide, MX, increased in the order of Li approximately Na SiF4 formation were detected in the exhaust gas. PMID:11944694

Lee, Myung Churl; Choi, Wonyong

2002-03-15

71

Halide electroadsorption on single crystal surfaces  

Energy Technology Data Exchange (ETDEWEB)

The structure and phase behavior of halides have been investigated on single crystals of Ag and Au using synchrotron x-ray scattering techniques. The adlayer coverages are potential dependent. For all halides studied the authors found that with increasing potential, at a critical potential, a disordered adlayer transforms into an ordered structure. Often these ordered phases are incommensurate and exhibit potential-dependent lateral separations (electrocompression). The authors have analyzed the electrocompression in terms of a model which includes lateral interactions and partial charge. A continuous compression is not observed for Br on Ag(100). Rather, they find that the adsorption is site-specific (lattice gas) in both the ordered and disordered phases. The coverage increases with increasing potential and at a critical potential the disordered phase transforms to a well-ordered commensurate structure.

Ocko, B.M. [Brookhaven National Lab., Upton, NY (United States). Dept. of Physics; Wandlowski, T. [Univ. of Ulm (Germany). Dept. of Electrochemistry

1997-07-01

72

The electronic structure of the F-center in alkali-halides-The Bethe cluster - lattice  

International Nuclear Information System (INIS)

The electronic structure of the F-center in alkali-halides with the NaCl structure has been studied using the Bethe Cluster lattice method. The central cluster has been taken as constituted by the vacancy and the nearest- and second-neighbors to it, respectively cations and anions. The optical transitions have been calculated and compared to experimental data on the location of the peak of the F-absorption band. The agreement obtained indicates that this method may be used to study properties of this defect in alkali halides. (Author)

1977-01-01

73

Electronic properties of metal-induced gap states formed at alkali-halide/metal interfaces  

CERN Document Server

The spatial distribution and site- distribution of metal induced gap states (MIGS) are studied by thickness dependent near edge x-ray absorption fine structure (NEXAFS) and comparing the cation and anion edge NEXAFS. The thickness dependent NEXAFS shows that the decay length of MIGS depends on rather an alkali halide than a metal, and it is larger for alkali halides with smaller band gap energy. By comparing the Cl edge and K edge NEXAFS for KCl/Cu(001), MIGS are found to be states localizing at anion sites.

Kiguchi, M; Ikeda, S; Saiki, K; Kiguchi, Manabu; Yoshikawa, Genki; Ikeda, Susumu; Saiki, Koichiro

2005-01-01

74

A Cluster-Bethe lattice treatment for the F-center in alkali-halides  

International Nuclear Information System (INIS)

The electronic structure of the F-center in alkali-halides with the NaCl structure has been studied using the Cluster-Bethe lattice method. The central cluster has been taken as constituted by the vacancy and the nearest- and second- neighbors to it, respectively, cations and anions. The optical transitions have been calculated and compared to experimental data on the location of the peak of the F-absorption band. The agreement obtained indicates that this method may be used to study properties of this defect in alkali halides

1977-12-01

75

The electronic structure of F-centers in allkali halide crystals  

International Nuclear Information System (INIS)

A method is presented for estimating the number of bound states of different orbital angular momentum quantum number for an F-centre residing in an alkali halide crystal through the introduction of a spherically symmetric potential well of finite depth. The method is illustrated through its application to the F-centre in sodium chloride, and the results for F-centres in various alkali halide lattices are tabulated. The results provide a good account of the experimental features of the F-centre including the K-band which we suggest is due to transitions from the 2p to excited levels. Values for the effective range of penetration of the defect electron with the neighbouring cation in different crystals are determined by requiring that the well depth be independent of orbital angular momentum quantum number. The technique is applied to estimate the Madelung constant and Madelung potential for the host crystal. (Author)

1982-01-01

76

Ionic alkali halide excimers excited by a laser-produced plasma  

Energy Technology Data Exchange (ETDEWEB)

We have observed ultraviolet (UV) and vacuum ultraviolet (VUV) emission from ionic alkali halide molecules and ionic rare gas alkali metal molecules excited by the soft x-rays from a laser-produced plasma and relativistic electron beams. The excitation process of the ionic excimer has been investigated using a simple kinetic model. The emission behavior of those ionic excimers in the UV and VUV region has been experimentally studied.

Kubodera, S.; Wisoff, P.J.; Sauerbrey, R. (Department of Electrical and Computer Engineereing Rice University, Houston, Texas 77251-1892 (US))

1989-10-20

77

Electron localization and the nonmetal-metal transition in alkali-alkali halide solutions  

International Nuclear Information System (INIS)

We evaluate and extend an earlier proposal for a microscopic theory of the nonmetal-to-metal (NM-M) transition which occurs on dissolving an alkali metal in its molten halide. The transition is viewed as involving a balance between the free energy gain from the binding of valence electrons into localization centres and the excess free energy of the ionic assembly screened by the electrons. Using parameters estimated for solutions of potassium in potassium chloride and assuming that the elementary process of electronic trapping is the formation of F-centre-like clusters, Thomas-Fermi screening by metallic electrons is shown to lead to a very sharp NM-M transition at a concentration in the range of 25-30% added metal. Thermally activated hopping of the localized electrons and the evolution of the localization centres with composition are next crudely taken into account by allowing for an additional contribution to the inverse screening length, which is estimated from the electronic localization length. This is shown to lead to a progressive break-up of the localization clusters, accelerating into a NM-M transition in the same concentration range. This simplified theoretical scenario is consistent with the available experimental evidence. (author). 18 refs, 5 figs

1995-01-01

78

Cluster-Bethe lattice calculation for the electronic structure of hydrogen centers in alkali-halides  

International Nuclear Information System (INIS)

The Cluster-Bethe lattice (CBL) method to calculate the electronic structure of the hydrogen centers U, U_1, U_2, U_3 in alkali-halides has been used. The results show the adequacy of the CBL in the interpretation of the nature of the optical transitions. (author)

1979-07-01

79

Two-Photon Absorption in Alkali Halides. Calculation of Nonlinear Optical Absorption Coefficients.  

Science.gov (United States)

Values of the two-photon absorption coefficient have been predicted for nine of the alkali halides. There are indications that RbI and NaBr are more sensitive to two-photon absorption than materials studied previously. These findings have implications for...

H. F. Taylor

1969-01-01

80

Lattice parameters of alkali halides by the Simons-Parr-Finlan technique  

International Nuclear Information System (INIS)

The lattice parameters of the twenty alkali halides are evaluated by using the Rittner potential through the Simons-Parr-Finlan technique. It is found that the values obtained are better than those obtained by earlier methods and further dispense the dependence of the potential on arbitrary and sensitive exponents encountered in the Woodcock potential. (author)

1982-06-16

 
 
 
 
81

Measurement of velocity of Ultrasonic sound in alkali halide R R solutions with different Normality  

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Full Text Available Velocity of sound in solutions is very large as compared to that in air, and this velocity is density dependent. In this experiment the alkali halide solutions of different normality was prepared and the velocity of sound was observed using Ultrasonic Interferometer at 2 M Hz of frequency. The velocity of sound was observed to be increasing with increasing Normality of solutions except for the potassium iodide solution, where this change is marginal. As an extension to this experiment sodium halide solutions were tested, and again the change in Sodium iodide was observed to be much less. This showed that the velocity of sound in alkali halide solutions was observed to be frequency dependent also that is at certain frequency for a solution velocity remains almost constant with change in normality.

M. N. Nyayate

2012-06-01

82

Reactions between cold methyl halide molecules and alkali-metal atoms  

CERN Document Server

We investigate the potential energy surfaces and activation energies for reactions between methyl halide molecules CH$_{3}X$ ($X$ = F, Cl, Br, I) and alkali-metal atoms $A$ ($A$ = Li, Na, K, Rb) using high-level {\\it ab initio} calculations. We examine the anisotropy of each intermolecular potential energy surface (PES) and the mechanism and energetics of the only available exothermic reaction pathway, ${\\rm CH}_{3}X+A\\rightarrow{\\rm CH}_{3}+AX$. The region of the transition state is explored using two-dimensional PES cuts and estimates of the activation energies are inferred. Nearly all combinations of methyl halide and alkali-metal atom have positive barrier heights, indicating that reactions at low temperatures will be slow.

Lutz, Jesse J

2013-01-01

83

Reactions between cold methyl halide molecules and alkali-metal atoms  

Science.gov (United States)

We investigate the potential energy surfaces and activation energies for reactions between methyl halide molecules CH3X (X = F, Cl, Br, I) and alkali-metal atoms A (A = Li, Na, K, Rb) using high-level ab initio calculations. We examine the anisotropy of each intermolecular potential energy surface (PES) and the mechanism and energetics of the only available exothermic reaction pathway, CH3X + A ? CH3 + AX. The region of the transition state is explored using two-dimensional PES cuts and estimates of the activation energies are inferred. Nearly all combinations of methyl halide and alkali-metal atom have positive barrier heights, indicating that reactions at low temperatures will be slow.

Lutz, Jesse J.; Hutson, Jeremy M.

2014-01-01

84

Correlations for calculating the surface tension and enthalpies of sublimation of alkali halides  

Science.gov (United States)

The capability of a new model on predicting the surface tension of molten alkali halides is described. A relationship, with a simple form of calculation, exists between the surface tension (?) at the melting point, molar volume (V), inter-nuclear distance (D) and the enthalpy of sublimation (Es). The basic idea results from the assumption that all the parameters are constants that are usually easy to acquire. Moreover, two previous models (Furth and Schytil equations) were also checked and applied for calculating surface tension of molten salts. The three formulas have been examined for 20 salts and showed remarkable agreement between calculated and experimental data with a difference of less than 10% for most of the salts studied. The heats of sublimation of alkali halides were, theoretically, calculated and compared to literature values.

Aqra, Fathi

2014-05-01

85

Heterogeneous reactions of alkali halides in the troposhere: Kinetics and mechanisms  

Energy Technology Data Exchange (ETDEWEB)

Reactions of alkali halides in airborne sea salt particles with gases are believed to generate photochemically active halogen-containing gases. Upon photolysis, these generate atomic halogens such as Cl and Br, which may play a significant role in the chemistry of the marine boundary layer under certain conditions. At the present time, both the kinetics and the mechanisms of the heterogeneous reactions of alkali halides with atmospherically relevant gases such as the oxides of nitrogen are controversial. The results of ongoing studies of the reactions of NaCl and NaBr with oxides of nitrogen such as NO{sub 2} and HNO{sub 3} in this laboratory will be presented, with emphasis on the observation of unique reactive intermediates. The implications for the chemistry of the marine boundary layer will be discussed.

Finlayson-Pitts, B.J. [Univ. of California, Irvine, CA (United States)

1996-10-01

86

Famed Bulgarian physicists. I. St. Petroff's Goettingen research of the photostimulated interconversions of color centers in alkali halides: the discovery of the photostimulated aggregation  

CERN Multimedia

This essay tells briefly of the life and work of one of the most successful scientists originating from a Balkan settlement whose name and popularity have greatly exceeded its realm. The word is of a discovery during WWII of the photostimulated aggregation of the F centers (else alkali atoms) dissolved from the vapor into an alkali halide crystal. Using optical absorption techniques while a grantee of Humboldt's Foundation in Goettingen, Germany between 1943-1944, he found new absorption bands pertaining to small-size F center aggregates and followed their interconversions. A primary photochemical solid state reaction was evidenced for the first time leading to nanoscale products.

Georgiev, Mladen

2008-01-01

87

Halide, Ammonium, and Alkali Metal Ion Parameters for Modeling Aqueous Solutions  

DEFF Research Database (Denmark)

A complete set of Lennard Jones parameters for the halide ions, F-, Cl-, Br-, and I-, ammonium ion, and the alkali metal ions is reported. The parameters have been optimized using Monte Carlo simulations and free energy perturbation theory with the TIP4P water model to reproduce experimental free energies of hydration and locations of the first maxima of the ion-oxygen radial distribution functions, to provide water coordination numbers consistent with experimental ranges, and to exhibit gas-phase monohydrate energies in reasonable agreement with ab initio values. Average errors for absolute and relative free energies of hydration for the ions are ca. 1 kcal/mol. For the halides, this is the first self-consistent set of parameters that has been optimized for aqueous-phase performance. The good results for relative free energies of hydration are particularly auspicious for use of the new parameters in a wide variety of liquid-phase simulations where halide and alkali cations are systematically varied.

Kepp, Kasper Planeta; Jorgensen, William L.

2006-01-01

88

Making Solid Solutions with Alkali Halides (and Breaking Them)  

Science.gov (United States)

In this exercise, the class will grow a variety of crystals of the same mineral, but with different chemical compositions. These crystals will be made from mixtures of halite (NaCl)and sylvite (KCl) that are melted and cooled. Because K+1 is significantly larger than Na+1,the unit cell is larger in sylvite than in halite. Intermediate compositions have intermediate unit cell sizes. Thus, a measurement of the lattice spacing of the crystalline products of your experiments can be used to determine their chemical composition. The principle goal of these experiments is to demonstrate that solid solutions do occur and that their physical properties vary with their chemical composition. Additional goals include studying the effect of composition on melting, exploring the process of exsolution as a function of temperature, and seeing the effect of fluids and deformation on crystallization kinetics.

Brady, John

89

EXAFS STUDY OF RELAXATION OF Cu+ IMPURITIES IN ALKALI HALIDES  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Cu K-edge EXAFS measurements have been done for NaCl : Cu+ in order to study the lattice relaxation around a cuprous ion. It was found that the bond length of Cu+ and Cl- in NaCl takes almost the same value as that of CuCl crystal. This suggests a very large distortion of the latice around a cuprous ion.

1986-01-01

90

Mass and orientation effects in dissociative collisions between rare gas atoms and alkali halide molecules  

International Nuclear Information System (INIS)

The collision induced dissociation of alkali halide molecules to ion pairs upon impact with hyperthermal rare gas atoms has been investigated using the crossed molecular beam method. Relative total cross sections for the dissociation of CsI, CsBr, RbI, and KI to ion pairs upon collision with xenon and krypton have been measured over a relative collision energy range from threshold to 10 and 8 eV, respectively. In addition, complete angular and energy distributions of both dissociated ions from Xe+CsI, CsBr, and RbI collisions and from Kr+CsI and CsBr collisions have been obtained at several collision energies within the above energy range. Mass, collision orientation, and energy dependence effects observed throughout this work define two limiting case dissociation mechanisms for the Xe(Kr)+MX?Xe(Kr)+M++X- processes. The dominant dissociation configuration consists of the rare gas atom incident on the light atom end of the alkali halide molecule in a near collinear collision. The less preferred dissociation mechanism results when the rare gas atom is incident in a near collinear configuration on the heavy atom end of the alkali halide molecule. Experimental measurements of the percentage of energy transfer from the relative kinetic energy between Xe(Kr) and MX to the relative motion of M+--X- range as high as 95%; these percentage energy transfers correlate well with the predictions of an impulsive collision model. Three-dimensional classical trajectory calculations using realistic interaction potentials have been performed and they verify the dynamical interpretation suggested by the experiments

1980-11-01

91

Thermoluminescence in alkali halides irradiated at 80K  

International Nuclear Information System (INIS)

The thermoluminescence, the thermally stimulated currents and the thermal stability of the F centres induced in pure NaCl and KC1 crystals by X irradiation at 80K have been studied in detail, in the range between 80 and 300K. The thermoluminescent processes induced by illumination at 80K with F light in samples previously irradiated at room temperature has also been studied. It has been clearly observed the existence of thermoluminescent processes due to electrons and holes thermally released from traps, in which the F centres are not involved. The existence of hole-F centre recombination has not been observed. There are several thermoluminescent processes in both materials which are scribed to the recombination of F centres with mobile interstitial halogen atoms thermally released from traps, which are likely monovalent impurities in this temperature interval. The light emitting stage in these processes is originated by the formation of self trapped excitons. (Author) 66 refs

1978-01-01

92

Oriented Silver Halide Nanocrystals Embedded in Crystalline Alkali Halide Matrix as Studied by EPR and ODMR.  

Science.gov (United States)

Shallow electron centers self-trapped holes and self-trapped excitons in small AgCl crystals embedded in KCl matrix were investigated by optical spectroscopy optically detected magnetic resonance (ODMR), and electron paramagnetic resonance (EPR) technique...

A. G. Badalyan N. G. Romanov P. G. Baranov R. A. Babunts V. A. Khramtsov

2000-01-01

93

Nanometer-scale patterning of alkali halide surfaces by ion bombardment  

Energy Technology Data Exchange (ETDEWEB)

Structural properties of alkali halide surfaces (KBr, KI, and RbI) have been modified by low energy Ar{sup +} ion beam bombardment. The morphology developed on the irradiated surfaces was investigated by the atomic-force microscopy (contact mode) under UHV conditions. The results indicate that for the incidence angles between 30{sup o} and 40{sup o} a periodic ripple morphology is developed with the ripple vector parallel to the beam direction, whereas for the angles larger than 60{sup o} the vector is perpendicular to the beam. The average surface roughness and the wavelength of the ion-induced periodic structures were measured as a function of the ion fluence (10{sup 13}-10{sup 18} ions/cm{sup 2}), the beam energy (1-5 keV), and the sample temperature (from 300 K to 600 K). The results are explained in terms of a new atomic-scale model taking into account the fact that ion sputtering of alkali halides in the investigated energy range is dominated by electronic processes rather than ballistic collisions.

Saeed, S.R.; Sinha, O.P.; Krok, F. [Research Center for Nanometer-Scale Science and Advanced Materials (NANOSAM), Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, ul. Reymonta 4, 30-059 Krakow (Poland); Szymonski, M. [Research Center for Nanometer-Scale Science and Advanced Materials (NANOSAM), Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, ul. Reymonta 4, 30-059 Krakow (Poland)], E-mail: ufszymon@cyf-kr.edu.pl

2008-12-30

94

Calculation of the melting point of alkali halides by means of computer simulations  

CERN Document Server

In this manuscript we study the liquid-solid coexistence of NaCl-type alkali halides, described by interaction potentials such as Tosi-Fumi (TF), Smith-Dang (SD) and Joung-Cheatham (JC), and compute their melting temperature (Tm) at 1 bar via three independent routes: 1) liquid/solid direct coexistence, 2) free-energy calculations and 3) Hamiltonian Gibbs-Duhem integration. The melting points obtained by the three routes are consistent with each other. The calculated Tm of the Tosi-Fumi model of NaCl is in good agreement with the experimental value as well as with other numerical calculations. However, the other two models considered for NaCl, SD and JC, overestimate the melting temperature of NaCl by more than 200 K. We have also computed the melting temperature of other alkali halides using the Tosi-Fumi interaction potential and observed that the predictions are not always as close to the experimental values as they are for NaCl. It seems that there is still room for improvement in the area of force-fields...

Aragones, J L; Valeriani, C; Vega, C; 10.1063/1.4745205

2012-01-01

95

Potential differences between chlorine and bromine electrode and between chlorine and iodine electrode in melts of the corresponding alkali-metal halides  

International Nuclear Information System (INIS)

Halogen electrodes, according to the authors, are the most convenient electrodes for thermodynamic studies of reactions involving halogens in molten alkali metal halides when the emf method is used. The authors measured the potential differences between the chlorine and bromine electrode and between the chlorine and iodine electrode in cells described here. From the results of measurements at different temperatures, the authors generalized interpolation relations between the potentials of the bromine and iodine electrode in molten alkalimetal bromides and iodides and their mixtures relative to the chlorine electrode in chlorides of the same metals, on one hand, and the temperature and cation's crystal radius on the other hand

1986-06-01

96

Quantitative determination of elements and identification of compounds of alkali halides by depth-sensitive secondary neutral mass spectrometry  

International Nuclear Information System (INIS)

In the development of a depth-sensitive analysis of saline microparticles, alkali halide salts were studied by plasma-based SNMS in an effort to check on the quantitative determination of elements and the detection of compounds for the example of salts. (orig./BBR)

1991-01-01

97

From unexpected reactions to a new family of ionic co-crystals: the case of barbituric acid with alkali bromides and caesium iodide  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Pressing solid barbituric acid with KBr to prepare samples for IR spectroscopy leads to the formation of an ionic co-crystal, in which the co-former is a classical ionic salt; co-crystal formation is also obtained with the other alkali bromides (LiBr, NaBr, RbBr and CsBr) and with caesium iodide. The simultaneous presence of alkali and halide ions affects the dissolution properties of barbituric acid in water.

Gobetto, Roberto; Chierotti, Michele Remo

2010-01-01

98

Identification of a Tl dimer centre in alkali halides by ODMR. [Ionising radiation  

Energy Technology Data Exchange (ETDEWEB)

In Tl/sup +/-doped alkali halides laser-active centres can be produced by ionising irradiation. This treatment inevitably produces other Tl-associated centres, which might degrade the laser performance. One of these centres that absorbs in the wavelength region where the laser centre is pumped was identified in the hosts KCl, RbCl and KBr by measuring its magnetic circular dichroism (MCD) tagged by electron spin resonance (ESR). The positions of the lowest-energy absorption and emission bands as well as sign and magnitude of the MCD resemble closely those of the laser centre. From the analysis of the optically detected ESR the structure of this new centre was determined. It consists of two neighbouring Tl/sup +/ cations adjacent to an anion vacancy, which share an electron. The ESR spectrum is explained be a fast hopping of the unpaired electron between the two Tl/sup +/ positions.

Ahlers, F.J.; Lohse, F.; Spaeth, J.M.

1985-07-20

99

Identification of a Tl dimer centre in alkali halides by ODMR  

International Nuclear Information System (INIS)

In Tl+-doped alkali halides laser-active centres can be produced by ionising irradiation. This treatment inevitably produces other Tl-associated centres, which might degrade the laser performance. One of these centres that absorbs in the wavelength region where the laser centre is pumped was identified in the hosts KCl, RbCl and KBr by measuring its magnetic circular dichroism (MCD) tagged by electron spin resonance (ESR). The positions of the lowest-energy absorption and emission bands as well as sign and magnitude of the MCD resemble closely those of the laser centre. From the analysis of the optically detected ESR the structure of this new centre was determined. It consists of two neighbouring Tl+ cations adjacent to an anion vacancy, which share an electron. The ESR spectrum is explained be a fast hopping of the unpaired electron between the two Tl+ positions. (author)

1985-07-20

100

F2+ center stabilization and tuneable laser operation in OH- doped alkali halides  

International Nuclear Information System (INIS)

Doping of alkali halides with large amounts (10-3 to 10-2) of OH- defects can be used to drastically increase the production and stabilization of F2+ centers. Under electron irradiation, the coloration efficiency and F2:F ratio is increased, and the OH- defect is decomposed into various substitutional and interstitial hydrogen and oxygen defects, part of which work as electron traps. As a consequence, optical ionization of F2 centers leads to stable F2+ center production, as tested in LiF, NaF, NaCl, KCl, and KBr hosts. Tuneable laser operation is achieved for the first time for F2+ centers in NaCl and KCl using this technique. A systematic study into the decomposition kinetics of OH- defects is started, which reveals the existence of a new hydrogen defect, identified by its ir local mode absorption, which may play the crucial role in the F2+ stabilization. (author)

1980-01-16

 
 
 
 
101

Effects of alkali halide doping on hydrogen bonding interaction in brown coal  

Energy Technology Data Exchange (ETDEWEB)

The effects of alkali halide doping on hydrogen bonding interactions in brown coal have been investigated by means of thermogravimetric analysis, FT-IR and UV-visible spectroscopy, differential scanning calorimeter (DSC) and solvent swelling. With lithium iodide (LiI) doping, volatile matter evolution of brown coal increased from 24.6 wt% to 43.9%, and the activation energy decreased from 54 kJ/mol to 31 kJ/mol. FT-IR spectra of pyrolysis residue obtained from raw and LiI doped brown coal indicate that LiI doped in coal control the formation of cross-link structures, such as ether linkage (-C-O-C-), during pyrolysis. Since LiI interacts with hydroxyl functional group, it can be concluded that doping coal with LiI results in declining hydrogen bonding interaction and increasing evolution of volatile matter. 4 refs., 5 figs., 3 tabs.

Kumagai, H.; Sato, N.; Sanada, Y.; Nakamura, K.; Sasaki, M.; Kotanigawa, T. [Hokkaido University, Sapporo (Japan)

1994-12-31

102

Chemical effects induced by dissolving ?-irradiated alkali halides in aqueous nitrate, permanganate and chromate solutions  

International Nuclear Information System (INIS)

Dissolution of ?-irradiated alkali halides in aqueous solutions of sodium nitrate, potassium permanganate and potassium chromate at neutral pH induces chemical changes leading to the formation of NO_2"- in nitrate, Mn(IV) and Cr(III) species in permanganate and chromate solutions, respectively. Further, the studies on nitrate and permanganate systems show that the amount of NO_2"- and Mn(IV) formed grows by increasing the dose of ?-irradiation of the salt and the amount of irradiated salt. Moreover, the extent of chemical changes effected by irradiated chlorides has been found to be more than that of bromides. The mesh size of the irradiated salt and the presence of scavengers like I"- and methanol in the system, affects the yield of NO_2"-. (author)

1982-02-25

103

Studies of Non-Proportionality in Alkali Halide and Strontium Iodide Scintillators Using SLYNCI  

Energy Technology Data Exchange (ETDEWEB)

Recently a collaboration of LLNL and LBNL has constructed a second generation Compton coincidence instrument to study the non-proportionality of scintillators [1-3]. This device, known as SLYNCI (Scintillator Light-Yield Non-proportionality Characterization Instrument), has can completely characterize a sample with less than 24 hours of running time. Thus, SLYNCI enables a number of systematic studies of scintillators since many samples can be processed in a reasonable length of time. These studies include differences in nonproportionality between different types of scintillators, different members of the same family of scintillators, and impact of different doping levels. The results of such recent studies are presented here, including a study of various alkali halides, and the impact of europium doping level in strontium iodide. Directions of future work area also discussed.

Ahle, L; Bizarri, G; Boatner, L; Cherepy, N J; Choong, W; Moses, W W; Payne, S A; Shah, K; Sheets, S; Sturm, B W

2009-05-05

104

Studies of non-proportionality in alkali halide and strontium iodide scintillators using SLYNCI  

Energy Technology Data Exchange (ETDEWEB)

Recently a collaboration of LLNL and LBNL has constructed a second generation Compton coincidence instrument to study the non-proportionality of scintillators. This device, known as SLYNCI (Scintillator Light-Yield Non-proportionality Characterization Instrument), has can completely characterize a sample with less than 24 hours of running time. Thus, SLYNCI enables a number of systematic studies of scintillators since many samples can be processed in a reasonable length of time. These studies include differences in nonproportionality between different types of scintillators, different members of the same family of scintillators, and impact of different doping levels. The results of such recent studies are presented here, including a study of various alkali halides, and the impact of europium doping level in strontium iodide. Directions of future work area also discussed.

Ahle, Larry; Bizarri, Gregory; Boatner, Lynn; Cherepy, Nerine J.; Choong, Woon-Seng; Moses, William W.; Payne, Stephen A.; Shah, Kanai; Sheets, Steven; Sturm, Benjamin, W.

2010-10-14

105

Reaction-rate approach to the dipolar relaxation in alkali halides  

Science.gov (United States)

An alternative reaction-rate approach is suggested for dealing with the relaxation times of dipolar defects in alkali halides. It rests on an occurrence-probability definition of the transition rate, accounting for both classical and quantal effects. A simple model Hamiltonian is postulated to describe the reorientational motion of a dipole within the framework of the adiabatic approximation. Two infamous examples are considered from this point of view. In one of these, the OH- dipole is assumed to couple only electronically to the neighboring cations, while all its remaining reorientational characteristics are, to a first approximation, independent of the host lattice. Assuming further that a single local oscillator drives the reorientational motion, this model agrees well with the experimental temperature dependence of the OH- relaxation time in four host halides up to 10 K, as measured by Kapphan and Lüty. The other example is the off-center Ag+ ion in RbBr and RbCl where a formal application of the reaction-rate method has been found to fit closely, over the entire range, the experimental temperature dependence of the relaxation time for 90° reorientation, measured by the same authors.

Georgiev, M.; Gochev, A.

1985-04-01

106

Silicon halide-alkali metal flames as a source of solar grade silicon. Seventh quarterly report  

Energy Technology Data Exchange (ETDEWEB)

This program is aimed at determining the feasibility of using high temperature reactions of alkali metals and silicon halides to produce low cost solar-grade silicon. Experiments are being performed to evaluate product separation and collection processes, measure heat release parameters for scaling purposes, and determine the effects of the reactants and/or products on materials of reactor construction. Prior work has demonstrated continuous separation of silicon from the byproduct alkali salt at a production rate of 0.5 kg h/sup -1/ in a graphite reactor using the reaction of Na with SiCl/sub 4/. Silicon of similar purity is obtained from Na + SiF/sub 4/ flames although yields are lower and product separation and collection are less thermochemically favored. During the current reporting period the results of heat release experiments have been used to design and construct a new type of thick-walled graphite reactor to produce larger quantities of silicon. A new reactor test facility has been constructed. Material compatibility tests have been performed for NA in contact with graphite and several coated graphites. All samples were rapidly degraded at T = 1200 K, while samples retained structural strength at 1700 K. Pyrolytic graphite coatings cracked and separated from substrates in all cases.

Olson, D.B.; Gould, R.K.

1979-04-01

107

Silicon halide-alkali metal flames as a source of solar grade silicon. Final report  

Energy Technology Data Exchange (ETDEWEB)

The object of this program was to determine the feasibility of using continuous high-temperature reactions of alkali metals and silicon halides to produce silicon in large quantities and of suitable purity for use in the production of photovoltaic solar cells. Equilibrium calculations showed that a range of conditions were available where silicon was produced as a condensed phase but the byproduct alkali metal salt was a vapor. A process was proposed using the vapor phase reaction of Na with SiCl/sub 4/. Low pressure experiments were performed demonstrating that free silicon was produced and providing experience with the construction of reactant vapor generators. Further experiments at higher reagent flow rates were performed in a low temperature flow tube configuration with co-axial injection of reagents. Relatively pure silicon was produced in these experiments. A high temperature graphite flow tube was built and continuous separation of Si from NaCl was demonstrated. A larger-scaled well-stirred reactor was built. Experiments were performed to investigate the compatibility of graphite-based reactor materials of construction with sodium. At 1100 to 1200 K none of these materials were found to be suitable. At 1700 K the graphites performed well with little damage except to coatings of pyrolytic graphite and silicon carbide which were damaged.

Olson, D.B.; Miller, W.J.; Gould, R.K.

1980-01-01

108

Silicon halide-alkali metal flames as a source of solar grade silicon  

Science.gov (United States)

The feasibility of using alkali metal-silicon halide diffusion flames to produce solar-grade silicon in large quantities and at low cost is demonstrated. Prior work shows that these flames are stable and that relatively high purity silicon can be produced using Na + SiCl4 flames. Silicon of similar purity is obtained from Na + SiF4 flames although yields are lower and product separation and collection are less thermochemically favored. Continuous separation of silicon from the byproduct alkali salt was demonstrated in a heated graphite reactor. The process was scaled up to reduce heat losses and to produce larger samples of silicon. Reagent delivery systems, scaled by a factor of 25, were built and operated at a production rate of 0.5 kg Si/h. Very rapid reactor heating rates are observed with wall temperatures reaching greater than 2000 K. Heat release parameters were measured using a cooled stainless steel reactor tube. A new reactor was designed.

Olsen, D. B.; Miller, W. J.

1979-01-01

109

Environmentally Benign Electrophilic Halogenation of Naphthalenes by H2O2Alkali Metal Halides in An Aqueous Cationic Micellar Media  

Directory of Open Access Journals (Sweden)

Full Text Available An efficient and greener protocol for the synthesis of 1-halo-naphthols by the action of hydrogen peroxide and alkali metal halides in aqueous micellar media is been described in the present work. This is an environmentally clean and safe procedure, which involved insitu generation of the active halogen in presence of alkali halides. Cationic surfactants such as cetyltrimethylammoniumbromide (CTAB and cetyltrimethylammoniumchloride (CTAC were found to facilitate efficiency of halogenation in aqueous media.

Kancharla Rajendar Reddy

2012-09-01

110

Vacuum Ultraviolet Emissions from Alkali-Halide Ionic Excimer (CsF)+ by Electron Beam Excitation  

Science.gov (United States)

The vacuum ultraviolet (VUV) fluorescence from an ionic alkali-halide excimer (CsF)+ was observed by electron beam excitation. A gas mixture of helium or neon with a hot vapor of cesium fluoride was excited to obtain two diffuse emission bands centered at 185 and 152 nm from the ionic excimer Cs2+F-, which is isoelectronic to the XeF excimer. The strong continuum emission centered at 185 nm was attributed to the B2\\varSigma+?X2\\varSigma+ bound-free band of (CsF)+, and the continuum from 145 to 155 nm was identified as the (CsF)+ D2\\varPi?{X}2\\varSigma+ bound-free transition. The formation mechanisms of these upper states were proposed to be a two-body or a three-body collisional charge transfer of He+ or Ne+ and Penning ionization of He* with neutral ground-state CsF molecules.

Xing, Da; Ueda, Ken-ichi; Takuma, Hiroshi

1992-08-01

111

Dynamics of nuclear wave packets at the F center in alkali halides  

Energy Technology Data Exchange (ETDEWEB)

The F center in alkali halides is a well-known prototype of a strongly coupled localized electron-phonon system. This colour center is one of the long studied targets in the field of photophysics because it is simple but rich in variety. Steady-state spectroscopy, such as modulation spectroscopy and Raman scattering spectroscopy, has elucidated the strength of the electron-phonon coupling in the (meta-)stable state, i.e. the ground state and the relaxed excited state. Picosecond spectroscopy has improved understanding of the state mixing in the transient state. Owing to recent developments of ultrafast lasers with pulse widths shorter than oscillation periods of phonons, it has been possible to perform real-time observation of lattice vibration, and the understanding of the transient state has been remarkably expanded. In this paper, we review early and present studies on dynamics of electron-phonon coupling at the F center, especially recent real-time observations on the dynamics of nuclear wave packets in the excited state of the F center in KI, KBr, KCl and RbCl. These real-time observations reveal (i) spatial extension of the electronic wave function of a trapped electron, (ii) the difference between the coupled phonons in the ground state and the excited state, (iii) diabatic transition between the adiabatic potential energy surfaces and (iv) anharmonicity of the potential energy surface.

Koyama, Takeshi; Suemoto, Tohru, E-mail: koyama@nuap.nagoya-u.ac.jp [Institute for Solid State Physics, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa-shi, Chiba 277-8581 (Japan)

2011-07-15

112

Physics of Solid and Liquid Alkali Halide Surfaces Near the Melting Point  

CERN Document Server

This paper presents a broad theoretical and simulation study of the high temperature behavior of crystalline alkali halide surfaces typified by NaCl(100), of the liquid NaCl surface near freezing, and of the very unusual partial wetting of the solid surface by the melt. Simulations are conducted using two-body rigid ion BMHFT potentials, with full treatment of long-range Coulomb forces. After a preliminary check of the description of bulk NaCl provided by these potentials, which seems generally good even at the melting point, we carry out a new investigation of solid and liquid surfaces. Solid NaCl(100) is found in this model to be very anharmonic and yet exceptionally stable when hot. It is predicted by a thermodynamic integration calculation of the surface free energy that NaCl(100) should be a well ordered, non-melting surface, metastable even well above the melting point. By contrast, the simulated liquid NaCl surface is found to exhibit large thermal fluctuations and no layering order. In spite of that, ...

Zykova-Timan, T; Tartaglino, U; Tosatti, E

2005-01-01

113

Excitonic absorption edge in alkali halides and the Urbach-Martienssen rule studied by three-photon difference-frequency generation  

Science.gov (United States)

Three-photon difference-frequency generation (TP-DFG) is used to excite resonances on the lower exciton-polariton branch in alkali halides. The line shape of the resonances is investigated in KI and RbI for temperatures between 1.5 and 800 K. A drastic variation of the linewidth ranging from 0.2 to about 50 meV is observed as a function of temperature and polariton energy. The experimental results are interpreted in the framework of polariton response theory, which links the shape of the TP-DFG resonance to the complex dielectric function. From the measured positions and widths of the resonance peaks, accurate data on dispersion and absorption are obtained for the region of the exponential tail of the excitonic absorption edge. The method allows us to determine the parameters of the Urbach-Martienssen rule by measurements on large single crystals.

Fröhlich, D.; Köhler, P.; Nieswand, W.; Rappen, T.; Mohler, E.

1991-05-01

114

H_2O- center in alkali halides with OH-: properties and formation kinetics-destruction after radiation damage  

International Nuclear Information System (INIS)

In order to understand the basic mechanisms that are responsible for the thermal formation and thermal destruction of the primary and secondary defects after low energy radiation damage in alkali halide crystals doped with OH-, the production of defects by pulse annealing in KCl:OH- and KBr:OH- was studied. These thermal processes were studied over a wide range of temperatures (52-300 K), and the several hydrogen reaction products were identified by their characteristic electronic absorption (visible-ultraviolet). Besides the well known substitucional and interstitial H"0 sub(i) and H"- defects, a new hydrogen defect, U_2 sub(x) center, was discovered after the thermal destruction of the U_2 centers. It is characterized by a new structureless eletronic absorption band (UV) at 45000 cm"-"1 in KCl and 40000 cm"-"1 in KBr. From this experimental observations it was proposed that the U_2 sub(x) center is constituted by one H"0 sub(i) center trapped by a substitucional OH"-, without disturbing the electronic transition of the OH"-. H_2O"- centers in KCl or H_2O"- and U centers in KBr are produced by thermal destruction of the U_2 sub(x) centers. Furthermore, it was observed that thermal desctruction of H_2O"- centers produced: F(15%), U(60%) and OH"- (25%) centers in KCl and F (approximated 100%) in KBr. At the end of this thermal process (at 300 K), 90 to 95% of the iitial OH"- centers were restored at the expenses of F and U centers. Several new properties of the H_2O"- defect were found and studied. (Author)

1979-03-01

115

Photodissociation comprehensive study of OH- on alkali halides and their interaction with colour centers  

International Nuclear Information System (INIS)

This work shows that the OH- defect induces changes in the electronics processes of the alkali halides such as in radiation damage and optical cycles of colour centers. Two cases were considered: with the presence of an OH- ion in the (1) excited state and (2) in the ground state; 1) the comprehensive study of resonant OH- photodissociation in several hosts showed that deep traps (for electrons) can be produced from the OH- dissociation. These traps can be effective for the capture of electrons produced in the radiation damage of the lattice as well as for trapping electrons from ionized color centers. It was observed a second channel (new) for the de-excitation of the (OH-)* molecule in KI and RbI. This effect can be effective only when the lattice around the molecule holds a large enough interstitial space. This new mechanism is responsible for the strong production at LNT of F centers and OH0 molecules at the expenses of OH- defects. Considering the complete investigation of the full cycle it was proposed a phenomenological model that would explain the observed behaviour when one covers a wide variation of lattice parameters (KCl -> RbI); 2) It was verified that the OH- ion present in the lattice induces strong changes in the de-excitation processes of electronic defects with a spread out wave function (like F centers). A change in the reorientation behaviour of excited F2 and F+2 centers was also verified. Two main effects should be mentioned: A) The induced de-excitation is very fast and non-radiative on F centers. B) Another type of system investigated (F2 and F+2) has shown an intense increase of the speed of reorientation of the F2 and F+2 excited centers. (autor)

1985-01-01

116

The enhancement effect of the lattice barrier of nonradiative decay of excitons at non-axial stress of alkali halides  

International Nuclear Information System (INIS)

Full text: According to the modern notions the formation processes of radiation defects and the luminescence of alkali halides (AH) are explained by the non-radiative and radiative relaxations of electronic excitons through various excitonic slates. In AH the luminescence of self-trapped excitons (STE) at 80 K has a small quantum efficiency, but its intensity sharply increases at elastic deformation when in contrast to STE luminescence the formation process of radiation defects decreases. This effect was interpreted by the increasing of exciton self-trapping probability in the regular lattice sites wi:b radiative annihilation. The enhancement of the STE luminescence intensity due to possible decreasing of the non-radiative decay efficiency of excitons with creation of radiation detects can be estimated by registration of the temperature dependence of luminescence of deformed AH at 80 K. The basic regularity of the intrinsic luminescence of AH are studied in less detail than the impurity luminescence. For the first time we studied the influence of the elastic deformation on the temperature quenching of the STE emission. The STE luminescence can be considered as a local interaction of excitons with lattice vibrations in analogy with the impurity luminescence according to the Mott model. At such an approach by determining the dependence of X-luminescence on temperature can be judged on the probability of the non-radiative annihilation of excitons and from the slope of straightforward lg(1/?-1)-(1/T) can be determined the activation energy required for the creation of primary radiation defects before (Q) and at (Q') elastic lattice deformation. Experimental results show that for crystals in which the luminescence efficiency close to unity (? ?1, CsI) or zero (??0.1, KCl) before and at the elastic deformation, the activation energies for non-radiative transitions of STE are not essentially different (Q?Q'). For other crystals (KI, RbI, KBr. NaCl) at their elastic deformation the activation energies for non-radiative annihilation of excitons are sharply increased (Q'>Q). The enhancement of the STE luminescence intensity in the presence of the elastic lattice deformation, caused by the decreasing of the non radiative decay efficiency of excitons or by the reduction of a barrier for exciton self-trapping or by the increasing of the probability of tunneling luminescence between the radiation defects are discussed

2001-06-04

117

Photography: enhancing sensitivity by silver-halide crystal doping  

Energy Technology Data Exchange (ETDEWEB)

The physical chemistry of the silver photography processes, exposure, development and fixing, is briefly summarized. The mechanism of the autocatalytic development by the developer of the clusters produced in silver bromide crystals during the exposure which is controlled by the critical nuclearity of these clusters was understood from pulse radiolysis studies. The effective quantum yield PHI{sub eff} of photoinduced silver cluster formation in silver halide microcrystals is usually much lower than the photoionization theoretical limit PHI{sub theor}=1 electron-hole pair per photon absorbed, owing to a subsequent very fast intra-crystal recombination of a part of the electron-hole pairs. In order to inhibit this recombination and favor the silver reduction by photo-electrons, the AgX crystals were doped with the formate HCO{sub 2}{sup -} as a specific hole scavenger. First, the dopant scavenges the photoinduced hole, thus enhancing the electron escape from the pair recombination. Second, the CO{sub 2}{sup {center_dot}}{sup -} radical so formed transfers an electron to another silver cation, so that the PHI{sub eff} limit may be of 2Ag{sup 0} per photon. This Photoinduced Bielectronic Transfer mechanism is strictly proportional to the light quanta absorbed and induces an exceptional efficiency for enhancing the radio- or photographic sensitivity insofar as it totally suppresses the electron-hole recombination.

Belloni, Jacqueline

2003-06-01

118

Dichroic infrared absorption of dipole centers in cadmium halide crystals  

International Nuclear Information System (INIS)

Dichroic infrared (IR) absorption measurements on CN- or OH- centers in cadmium halide crystals were carried out at 6 K with a high spectral resolution of 0.025 cm-1 at 2000 cm-1, by using a FT-IR spectrometer. Several sharp absorption lines with widths less than 0.1 cm-1 are observed in the energy region of the stretching vibration, i.e. 2000-2250 cm-1 for CN- and 2500-4500 cm-1 for OH-. These lines are classified into three groups attributed to: (1) an isolated center simply substituted for a halogen ion, (2) an interstitial center located between the cadmium and halogen ion sheets and (3) a coupled center with an anion vacancy. A doublet structure is observed in CdI2 which comes from different halogen-ion sites in the 4H-polytype crystal. The isolated CN- centers in CdCl2 and CdBr2 align toward Cd2+ ions, away from the direction of the c-axis. Almost all of the coupled center with a vacancy lies in a halogen-ion plane. The doublet structure of the coupled center in CdCl2 and CdBr2 is connected to the tunneling splitting of a vibrational level

2004-06-01

119

Conditions leading to the epitaxial growth of vacuum evaporated Ag thin films onto doped alkali halide substrate  

Energy Technology Data Exchange (ETDEWEB)

Thin Ag films up to 1800 A in thickness were vacuum evaporated onto freshly air cleaved doped NaCl substrates at constant temperature and deposition rate (T = 150 +- 20 deg C and R = 11 +- 0.5 Assup(-1)). The structural features of these films (growth stage, grain size and morphology, epitaxial orientation degree, densities of pinholes, dislocations, microtwins and stacking-faults etc.) induced by some deposition conditions (preheating treatment of air cleaved substrates and postdeposition vacuum annealing and by the nature and amount of NaCl substrate impurities Ag, Cu, Pb, Ca) are determined by means of electron-microscopy and electron diffraction. A parallel survey concerning the conditions leading to the epitaxial growth of continuous Ag and Au thin films onto deoped alkali halide substrates is also made.

Birjega, M.I.; Florescu, I.T.; Sarbu, C.; Topa, V. (Institutul de Fizica si Tehnologia Aparatelor cu Radiatii, Bucharest (Romania))

1980-01-01

120

Integrating 2-D position sensitive X-ray detectors with low-density alkali halide storage targets  

Science.gov (United States)

For the use in scattering experiments with synchrotron radiation, integrating position sensitive X-ray detectors are discussed. These detectors store the photon number equivalent charge (PNEC) in low-density alkali halide targets. Performance tests are given for a detector which uses a Gd 2O 2S fluorescence screen for X-ray detection and the low-density KCl storage target of a television SEC vidicon tube for photon integration. Rather than directly by X-rays, this target is charged by 6 keV electrons from the image intensifier section of the vidicon. Its excellent storage capability allows measurements of extremely high-contrast, high-flux X-ray patterns with the same accuracy as achieved with any single photon detection system if the discussed readout techniques are applied.

Haubold, H.-G.; Hoheisel, W.; Hiller, P.

1986-05-01

 
 
 
 
121

Integrating 2-D position sensitive X-ray detectors with low-density alkali halide storage targets  

International Nuclear Information System (INIS)

For the use in scattering experiments with synchrotron radiation, integrating position sensitive X-ray detectors are discussed. These detectors store the photon number equivalent charge (PNEC) in low-density alkali halide targets. Performance tests are given for a detector which uses a Gd_2O_2S fluorescence screen for X-ray detection and the low-density KCl storage target of a television SEC vidicon tube for photon integration. Rather than directly by X-rays, this target is charged by 6 keV electrons from the image intensifier section of the vidicon. Its excellent storage capability allows measurements of extremely high-contrast, high-flux X-ray patterns with the same accuracy as achieved with any single photon detection system if the discussed readout techniques are applied. (orig.)

1986-05-15

122

Studies of Non-Proportionality in Alkali Halide and Strontium Iodide Scintillators Using SLYNCI 6-16-2009  

Energy Technology Data Exchange (ETDEWEB)

Recently a collaboration of LLNL and LBNL has constructed a second generation Compton coincidence instrument to study the non-proportionality of scintillators. This device, known as SLYNCI (Scintillator Light-Yield Non-proportionality Characterization Instrument), has can completely characterize a sample with less than 24 hours of running time. Thus, SLYNCI enables a number of systematic studies of scintillators since many samples can be processed in a reasonable length of time. These studies include differences in non-proportionality between different types of scintillators, different members of the same family of scintillators, and impact of different doping levels. The results of such recent studies are presented here, including a study of various alkali halides, and the impact of europium doping level in strontium iodide. Directions of future work area also discussed.

Ahle, Larry [Lawrence Livermore National Laboratory (LLNL); Bizarri, Gregory [Lawrence Berkeley National Laboratory (LBNL); Boatner, Lynn A [ORNL; Cherepy, Nerine [Lawrence Livermore National Laboratory (LLNL); Choong, Woon-Seng [Lawrence Berkeley National Laboratory (LBNL); Moses, W. W. [Lawrence Berkeley National Laboratory (LBNL); Payne, Stephen A. [Lawrence Livermore National Laboratory (LLNL); Shah, Kanai [Radiation Monitoring Devices, Watertown, MA; Sheets, Steven [Lawrence Livermore National Laboratory (LLNL); Sturm, Benjamin [Lawrence Livermore National Laboratory (LLNL)

2009-01-01

123

Alkali atoms, dimers, exciplexes and clusters in 4He crystals  

International Nuclear Information System (INIS)

Full text: A closed-shell He atom and a single-electron alkali atom strongly repel each other because of the Pauli principle. As a consequence, an alkali atom immersed into condensed (superfluid or solid) 4He forms a spherical bubble state, in which the alkali repels the He quantum fluid/solid by imposing its own symmetry on the local He environment. For 15 years we have investigated such atomic bubbles in solid 4He using optical and magnetic resonance spectroscopy. In this talk I will first review our high resolution magnetic resonance studies performed on solid He matrix-isolated alkali atoms in the radio-frequency and microwave domains with special emphasis on their sensitive dependence on the crystalline structure (body-centered cubic, bcc, versus hexagonally close-packed, hcp) of the helium matrix. In recent years we have extended the purely atomic studies to larger bound complexes, such as exciplexes, dimers and clusters. I will present some of our intriguing recent results: in their respective ground states, alkali and He atoms are the worst enemies in the periodic table and strongly repel each other. Excited alkali atoms, however, attract He atoms and form bound states (so-called exciplexes), in which up to 7 He atoms can be attached to one alkali atom. Cs2 and Rb2 dimers in solid He can be excited via a large variety of absorption bands, and the deexcitation proceeds either by photodissociation or by emission of radiation. We made the strange observation that, irrespective of the excitation band, dimer fluorescence is only emitted on the (1)3?u ? X1?g triplet-singlet transition which is forbidden in the free dimer. When the first excited P1/2 state of an alkali atom is populated by direct atomic excitation, it fluoresces at 879 nm (1.7 % blueshifted from the free atomic transition at 894 nm), a quantitatively well explained fact. However, when the same state is populated by photodissociation of the dimer, the emission wavelength is 885 nm. We attribute this effect to the formation of an entangled diatomic bubble state. The doped region of the He crystal has a bluish color that originates from Mie scattering by alkali clusters, the size distribution of which can be inferred from the extinction spectrum. When the doped He crystal is molten by lowering the He pressure, the doped (column-shaped) region remains solid at pressures, where pure He is superfluid. We present experimental support for our hypothesis that this new form of solid He is an amorphous or crystalline ionic structure formed by snowballs (nanoscopic solid He structures formed around positive ions) and electron bubbles. (author)

2008-07-02

124

Tunable Crystal-to-Crystal Phase Transition in a Cadmium Halide Chain Polymer  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The chain polymer [{Cd(?-X)2py2}1?] (X = Cl, Br; py = pyridine) undergoes a fully reversible phase transition between a monoclinic low-temperature and an orthorhombic high-temperature phase. The transformation can be directly monitored in single crystals and can be confirmed for the bulk by powder diffraction. The transition temperature can be adjusted by tuning the composition of the mixed-halide phase: Transition temperatures between 175 K up to the decomposition of the material at ca. 3...

Kevin Lamberts; Irmgard Kalf; Amr Ramadan; Paul Müller; Richard Dronskowski; Ulli Englert

2011-01-01

125

Lattice model calculation of elastic and thermodynamic properties at high pressure and temperature. [for alkali halides in NaCl lattice  

Science.gov (United States)

The elastic constants and the entire frequency spectrum were calculated up to high pressure for the alkali halides in the NaCl lattice, based on an assumed functional form of the inter-atomic potential. The quasiharmonic approximation is used to calculate the vibrational contribution to the pressure and the elastic constants at arbitrary temperature. By explicitly accounting for the effect of thermal and zero point motion, the adjustable parameters in the potential are determined to a high degree of accuracy from the elastic constants and their pressure derivatives measured at zero pressure. The calculated Gruneisen parameter, the elastic constants and their pressure derivatives are in good agreement with experimental results up to about 600 K. The model predicts that for some alkali halides the Grunesen parameter may decrease monotonically with pressure, while for others it may increase with pressure, after an initial decrease.

Demarest, H. H., Jr.

1972-01-01

126

Ca-Fe and Alkali-Halide Alteration of an Allende Type B CAI: Aqueous Alteration in Nebular or Asteroidal Settings  

Science.gov (United States)

Ca-Fe and alkali-halide alteration of CAIs is often attributed to aqueous alteration by fluids circulating on asteroidal parent bodies after the various chondritic components have been assembled, although debate continues about the roles of asteroidal vs. nebular modification processes [1-7]. Here we report de-tailed observations of alteration products in a large Type B2 CAI, TS4 from Allende, one of the oxidized subgroup of CV3s, and propose a speculative model for aqueous alteration of CAIs in a nebular setting. Ca-Fe alteration in this CAI consists predominantly of end-member hedenbergite, end-member andradite, and compositionally variable, magnesian high-Ca pyroxene. These phases are strongly concentrated in an unusual "nodule" enclosed within the interior of the CAI (Fig. 1). The Ca, Fe-rich nodule superficially resembles a clast that pre-dated and was engulfed by the CAI, but closer inspection shows that relic spinel grains are enclosed in the nodule, and corroded CAI primary phases interfinger with the Fe-rich phases at the nodule s margins. This CAI also contains abundant sodalite and nepheline (alkali-halide) alteration that occurs around the rims of the CAI, but also penetrates more deeply into the CAI. The two types of alteration (Ca-Fe and alkali-halide) are adjacent, and very fine-grained Fe-rich phases are associated with sodalite-rich regions. Both types of alteration appear to be replacive; if that is true, it would require substantial introduction of Fe, and transport of elements (Ti, Al and Mg) out of the nodule, and introduction of Na and Cl into alkali-halide rich zones. Parts of the CAI have been extensively metasomatized.

Ross, D. K.; Simon, J. I.; Simon, S. B.; Grossman, L.

2012-01-01

127

Electronic properties of metal induced gap states at insulator/metal interfaces -- dependence on the alkali halide and the possibility of excitonic mechanism of superconductivity  

CERN Multimedia

Motivated from the experimental observation of metal induced gap states (MIGS) at insulator/metal interfaces by Kiguchi {\\it et al.} [Phys. Rev. Lett. {\\bf 90}, 196803 (2003)], we have theoretically investigated the electronic properties of MIGS at interfaces between various alkali halides and a metal represented by a jellium with the first-principles density functional method. We have found that, on top of the usual evanescent state, MIGS generally have a long tail on halogen sites with a $p_z$-like character, whose penetration depth ($\\lambda$) is as large as half the lattice constant of bulk alkali halides. This implies that $\\lambda$, while little dependent on the carrier density in the jellium, is dominated by the lattice constant (hence by energy gap) of the alkali halide, where $\\lambda_{\\rm LiF} < \\lambda_{\\rm LiCl} < \\lambda_{\\rm LiI}$. We also propose a possibility of the MIGS working favorably for the exciton-mediated superconductivity.

Arita, R; Kuroki, K; Aoki, H; Arita, Ryotaro; Tanida, Yoshiaki; Kuroki, Kazuhiko; Aoki, Hideo

2003-01-01

128

Conductometric study of some alkali metal halides in (dimethyl sulfoxide + acetonitrile) at T = 298.15 K  

Energy Technology Data Exchange (ETDEWEB)

Electrolytic conductivities of some alkali metal halides, MX (M{sup +} = Li{sup +}, Na{sup +}, and K{sup +}; X{sup -} = Cl{sup -}, Br{sup -}, and I{sup -}), NaBPh{sub 4} and Bu{sub 4}NBr have been investigated in (20, 40, and 60) mass% {l_brace}dimethyl sulfoxide (DMSO) in DMSO + acetonitrile{r_brace} at T = 298.15 K. The conductance results have been analyzed by the Fuoss-conductance-concentration equation in terms of the limiting molar conductance {lambda}{sup o} the association constant K{sub A} and the association diameter R. The ionic contributions to the limiting molar conductance have been estimated using Bu{sub 4}NBPh{sub 4} as the 'reference electrolyte'. The association constant K{sub A} tends to increase in the order mass percent 20 < 40 < 60 DMSO in (DMSO + acetonitrile) which is explained by the thermodynamic parameter {delta}G{sup o} and Walden product {lambda}{sup o}{eta}. The results have been interpreted in terms of ion-solvent interactions and structural changes in the mixed solvents.

Roy, Mahendra Nath [Department of Chemistry, North Bengal University, Darjeeling 734013 (India)], E-mail: mahendraroy2002@yahoo.co.in; Banerjee, Ashis; Das, Rajesh Kumar [Department of Chemistry, North Bengal University, Darjeeling 734013 (India)

2009-11-15

129

Growth and Hardening of Alkali Halides for Use in Infrared Laser Windows.  

Science.gov (United States)

Several KCl crystals have been pulled from melts of reagent grade KCl, RAP treated reagent grade KCl, and HCl/Cl2 treated KCl. The OH(-) concentrations and the 10.6 micrometers optical absorption of these crystals were evaluated. The results indicate that...

W. A. Sibley C. T. Butler J. R. Hopkins J. J. Martin

1974-01-01

130

Growth and Studies of Halides doped Zinc Tris-Thiourea Sulphate(HZTS) Crystals  

Science.gov (United States)

Single crystals of Sodium chloride and Potassium iodide (Halides) doped Zinc tris-thiourea sulphate (ZTS) were grown from low temperature solution growth technique by slow evaporation method using water as solvent. The powder X-Ray diffraction pattern were recorded and indexed. The UV transmittance spectrum has been recorded. The optical band gap was estimated using Taucís plot. The TGA/DTA studies show the thermal properties of the crystals.

Suveetha, P.; Sathya, T.; Sudha, S.; Raj, M. B. Jessie

2012-10-01

131

Photostimulated luminescence in alkali halides induced by excitation with ionizing radiation  

International Nuclear Information System (INIS)

The photostimulated luminescence (PSL) phenomenon induced in copper-doped sodium chloride (NaCl : Cu) and europium-doped potassium chloride (KCl : Eu) phosphor crystals by excitation with ionizing radiation such as X-rays is studied. The emission mechanism of the PSL in both phosphor crystals is discussed in terms of the recombination of electrons optically stimulated from the radiation-induced F centers with the luminescence centers such as Cu2+ in NaCl and Eu3+ ions in KCl. The potentiality of both phosphor crystals as a material for two-dimensional X-ray imaging sensors utilizing the PSL phenomenon is also discussed. ((orig.))

1994-06-01

132

Photochemistry and reactions of OH"- defects and F centers in alkali halides  

International Nuclear Information System (INIS)

Aditively colored KCl:OH"- crystals showed under a combined UV and VIS irradiation, a nearly complete and irreversible destruction of all F centers and visible absorption in the crystal. Only upon heating the crystal above 650"0C the F center coloration becomes partially restored. The photodissociation of the OH"-(under UV light) together with the photoionization of the F center (under VIS light) produces a not effects where all the F centers are converted into U centers. These photoreactions produces high contrast visible images that are completely stable under light at RT. Besides the optical information storage aspect of this effect these photoreaction s can also be used for controlled production of Usub(A) centers if the crystal also contains a foreign metallic impurity such a Na"+ ion

1978-04-01

133

Electron paramagnetic resonance, optical transmission spectra and DC conductivity studies of vanadyl-doped alkali halide borate glasses  

International Nuclear Information System (INIS)

Electron paramagnetic resonance, optical transmission spectra and DC conductivity of the glasses 2xMX·(0.30-x)M2O·0.70B2O3 (M=Na or K; X=Cl or Br) (0.01?x?0.10) containing 2.0 mol% of V2O5 have been studied. The spin-Hamiltonian parameters (SHP) of the VO2+ ions, the dipolar hyperfine parameter, P, the Fermi contact interaction parameter, K, and the molecular orbital coefficients (?2 and ?2) have been calculated. It is observed that in KX·K2O·B2O3 (X=Cl or Br) glasses, the tetragonal nature of V4+O6 complex decreases with KBr for x?0.05. An increase in the 2KX:K2O ratio (x?0.05) also results in the contraction of 3dxy orbit of the unpaired electron in the vanadyl ion, whereas in case of NaX·Na2O·B2O3 (X=Cl or Br) glasses, the SHP are independent of change in 2NaX:M2O ratio. It is observed that the SHP in these alkali halide borate glasses are independent of the theoretical optical basicity, ?th. It is also observed that the DC conductivity increases with increase in temperature. The order of conductivity is 10-6 ?-1 m-1 at low temperatures and 10-4 ?-1 m-1 at high temperatures. In MCl·M2O·B2O3 (M=Na or K) glasses, the conductivity increases and the activation energy decreases with an increase in mol% of the NaCl or KCl content whereas, in MBr·M2O·B2O3 (M=Na or K) glasses, the conductivity first increases and then decreases with mol% of the MBr content

2003-07-01

134

Crystallization of iron phosphate glass containing mixed alkali oxides  

International Nuclear Information System (INIS)

Iron phosphate glass (IPG) is a versatile alternate glass matrix for immobilization of high level nuclear waste. In the present work, 20 wt % mixed alkali oxides (added in the form of eutectic chlorides, LiCl-55 wt % KCl) were immobilized in IPG and the glass waste form was characterized by X-ray diffraction (XRD) technique. Crystallization behavior was studied by using Differential Scanning Calorimetry (DSC). Good glass forming characteristics, high % of waste loading and good chemical durability are the superior salient features of a versatile iron phosphate glass (IPG) as a host for nuclear waste immobilization. In the present work, the possibility of vitrification of 20 wt % of LiCl-KCl eutectic in IPG was explored along with its crystallization studies in order to study the feasibility of immobilizing pyrometallurgical chloride waste

2010-12-01

135

Effect of halides addition on the ligand field of chromium in alkali borate glasses  

International Nuclear Information System (INIS)

Highlights: •The 10 KM–64.7 B2O3–25 Na2O–0.3 Cr2O3 (M = Cl, Br and I) glassy system was prepared by a quenching method. •Optical basicity, ligand field theory optical band gap energy, refractive index, ESR and IR were studied. •The electronegativity plays an important role in deforming the crystal field around the transition metal ions. •The crystal-field sites of KCl or KBr sample are very strong compared to the very weak one in the KI sample. -- Abstract: Borate oxide glass system of composition 10 KM–64.7 B2O3–25 Na2O–0.3 Cr2O3 (M = Cl, Br and I) was prepared by conventional melt quenching technique. The amorphous nature of the investigated glasses was checked by the X-ray diffraction (XRD) technique. The optical basicity of the system has been calculated, and was found to increase by going from KCl to KBr and to KI. Optical absorption spectra were recorded in the UV–visible range. Through a careful analysis of the data, the ligand field parameters (crystal field strength Dq, Racah parameters B and nephelauxetic functions h) and the optical parameters (optical band gap, Urbach tail band width, and refractive index) have been estimated. The obtained results reveal a strong correlation between that ligand field parameters and the type of halogen atom; the crystal-field strength of KCl or KBr samples are very pronounced but it is rather weak in the KI sample. Electron spin resonance (ESR) has been used to probe the valency of the Chromium ions. The resulting ESR parameters revealed that chromium ions are predominantly in the trivalent state with traces of hexavalent state. Using Infrared spectroscopy (IR) information on the boron structural units has been obtained. The N4 ratio increases by replacing the KCl by KBr or KI, and it was found that the tetrahedral coordination of Cr+ ions becomes preferential in the host glasses with increasing the optical basicity

2013-10-15

136

Effect of halides addition on the ligand field of chromium in alkali borate glasses  

Energy Technology Data Exchange (ETDEWEB)

Highlights: •The 10 KM–64.7 B{sub 2}O{sub 3}–25 Na{sub 2}O–0.3 Cr{sub 2}O{sub 3} (M = Cl, Br and I) glassy system was prepared by a quenching method. •Optical basicity, ligand field theory optical band gap energy, refractive index, ESR and IR were studied. •The electronegativity plays an important role in deforming the crystal field around the transition metal ions. •The crystal-field sites of KCl or KBr sample are very strong compared to the very weak one in the KI sample. -- Abstract: Borate oxide glass system of composition 10 KM–64.7 B{sub 2}O{sub 3}–25 Na{sub 2}O–0.3 Cr{sub 2}O{sub 3} (M = Cl, Br and I) was prepared by conventional melt quenching technique. The amorphous nature of the investigated glasses was checked by the X-ray diffraction (XRD) technique. The optical basicity of the system has been calculated, and was found to increase by going from KCl to KBr and to KI. Optical absorption spectra were recorded in the UV–visible range. Through a careful analysis of the data, the ligand field parameters (crystal field strength Dq, Racah parameters B and nephelauxetic functions h) and the optical parameters (optical band gap, Urbach tail band width, and refractive index) have been estimated. The obtained results reveal a strong correlation between that ligand field parameters and the type of halogen atom; the crystal-field strength of KCl or KBr samples are very pronounced but it is rather weak in the KI sample. Electron spin resonance (ESR) has been used to probe the valency of the Chromium ions. The resulting ESR parameters revealed that chromium ions are predominantly in the trivalent state with traces of hexavalent state. Using Infrared spectroscopy (IR) information on the boron structural units has been obtained. The N{sub 4} ratio increases by replacing the KCl by KBr or KI, and it was found that the tetrahedral coordination of Cr{sup +} ions becomes preferential in the host glasses with increasing the optical basicity.

Hassan, M.A., E-mail: moukhtar_hassan@yahoo.com

2013-10-15

137

Remarkable properties of alkali halides and new techniques for determining Debye-Waller factors  

International Nuclear Information System (INIS)

We have used 70 Ci 183Ta Moessbauer sources to measure the Debye-Waller factors of NaCl, KCl, and KBr single crystals for several of the (h00) and (nnn) Bragg reflections. We have found that the procedure used to analyze data by earlier workers leads to incorrect parameters in the Debye-Waller factor exponent, and we use a procedure that eliminates the need to introduce an empirical parameter to account for thermal expansion effects. We observe that both the cations and anions in NaCl and KBr have identical Debye-Waller factors in the [nnn] direction. We observe Q4 terms in NaCl and KCl, with some evidence for a Q4 term in KBr. The size of this contribution varies with the direction of momentum transfer and will be reported. We observe that the Debye temperature and the coefficient of the anharmonic Q2 term also vary with direction of momentum transfer. We believe this to be the first definitive evidence for a non-spherical thermal cloud in a cubic crystal; the ions have a larger amplitude of oscillation in the [h00] direction than in the [nnn] direction. This effect is temperature dependent and greater at lower temperatures

1997-09-01

138

Remarkable properties of alkali halides and new techniques for determining Debye-Waller factors  

Energy Technology Data Exchange (ETDEWEB)

We have used 70 Ci {sup 183}Ta Moessbauer sources to measure the Debye-Waller factors of NaCl, KCl, and KBr single crystals for several of the (h00) and (nnn) Bragg reflections. We have found that the procedure used to analyze data by earlier workers leads to incorrect parameters in the Debye-Waller factor exponent, and we use a procedure that eliminates the need to introduce an empirical parameter to account for thermal expansion effects. We observe that both the cations and anions in NaCl and KBr have identical Debye-Waller factors in the [nnn] direction. We observe Q{sup 4} terms in NaCl and KCl, with some evidence for a Q{sup 4} term in KBr. The size of this contribution varies with the direction of momentum transfer and will be reported. We observe that the Debye temperature and the coefficient of the anharmonic Q{sup 2} term also vary with direction of momentum transfer. We believe this to be the first definitive evidence for a non-spherical thermal cloud in a cubic crystal; the ions have a larger amplitude of oscillation in the [h00] direction than in the [nnn] direction. This effect is temperature dependent and greater at lower temperatures.

Shepard, C.K.; Mullen, J.G. [Purdue University, Department of Physics (United States); Schupp, G. [University of Missouri Research Reactor (United States)

1997-09-15

139

In-situ investigation of surface reactions on alkali halides by atomic force microscopy  

International Nuclear Information System (INIS)

In-situ AFM images have been produced of dissolution processes on NaCl and KBr single crystals under different organic solvents. Using a home-built sample holder stable imaging conditions have been achieved and atomic resolution could be obtained on both materials. Dissolution rates have been determined quantitatively from the AFM images and compared with empirical solvent parameters such as acceptor number AN and ET(30) value. The AFM results are in agreement with the expected behaviour of the liquids. Dissolution rates could be controlled using mixtures of polar and non polar solvents. The results are a basis for further investigations of other systems and technologically important processes such as corrosion and surface modification. (orig.)

1994-05-01

140

Differential calorimeter and temperature controller for stored energy measurements in irradiated alkali halides  

International Nuclear Information System (INIS)

The design and performance of a simple temperature-controlled differential calorimeter are presented. This system allows to measure radiation-induced stored energy in insulators, above room temperature with a differential thermal analysis method. With platelets of KC1 single crystals, the base lines obtained for T2 T1 (with T2: irradiated sample temperature and T1: reference sample temperature) show a smooth drift less of 0,2 degree centigree in the interval from 25 to 400 degree centigree. The discrepancy between two consecutive base lines is less than ± 0,02 degree centigree which implies a calorimeter sensitivity of about ±0,004 cal/g. This sensitivity allows to measure stored energy release in samples with a color center concentration low enough to be directly measured with a spectrophotometer so that a search for correlations among the features of the stored energy spectrum and the color center annealing can be made. (Author) 13 refs

1977-01-01

 
 
 
 
141

Structure and molar refraction and its wavelength dependence at different alkali and ammonium halides  

International Nuclear Information System (INIS)

The wavelength dependence of the molar refraction of AB-compounds, crystallizing in the NaCl- or CsCl-structure type, is analysed by use of a two-term Sellmeier dispersion formula. In the range of the validity of a single-oscillator model a clear distinction between series with NaCl or CsCl structure is possible on the base of the influence of the parameters lambda1, the resonance wavelength of the electronic absorption, and n/sub eff/, the effective number of electrons involved in the elctron transition, on the molar refraction and its slope. The Sellmeier model is compared with the dispersion model of Wemple. (author)

1984-09-16

142

A generalized rule of average for glow peak temperature of ternary alkali halide systems  

Scientific Electronic Library Online (English)

Full Text Available SciELO Mexico | Language: English Abstract in spanish Se estudia la dependencia de la temperatura en la curva de brillo con la composición de los aniones en mezclas cristalinas impurificadas con Europio: KCl0.50KBr0.25RbX0.25:Eu2+ (X = Cl, Br). Cada material muestra una curva de brillo termoluminiscente consistente en dos picos de brillo principales co [...] n temperatura entre la del KCl:Eu2+ y la del KBr:Eu2+. El pico más intenso está relacionado con la destrucción del centro F, como ocurre en el caso de cristales de KCl:Eu2+ y su temperatura característica depende fuertemente de la composición del halogeno. El comportamiento confirma que la temperatura de la recombinación de los centros F-H en este tipo de materiales depende en gran medida de la proporción de los aniones. De estos resultados se propone una regla generalizada para obtener la temperatura, promediando la temperatura característica en función de la composición. Abstract in english The anion composition dependence of the characteristic glow peak temperature of europium doped KCl0.50KBr0.25RbX0.25:Eu2+ (X=Cl, Br) mixed crystals are studied. Each material shows a thermoluminescence glow curve consisting of two main glow peaks with a temperature is between KCl:Eu2+ and KBr:Eu2+. [...] The most intense is related to the F center destruction as occur in the case of KCl:Eu2+ crystals and its characteristic temperature depends strongly on the halogen composition. This behavior confirms that the temperature of the F-H centers recombination in this type of materials depends more on the proportion of anions. From these results, a generalized rule to obtain the temperature from averaging the characteristic temperature as function of the composition is discussed.

G., Moroyoqui-Estrella; R., Pérez-Salas; R., Rodriguez-Mijangos.

143

Heteroepitaxial strain in alkali halide thin films: KCl on NaCl  

DEFF Research Database (Denmark)

We have pet-formed Monte Carlo simulations of the properties of a NaCl (001) surface covered by full or partial layers of KCl, for coverages up to 5 monolayers (ML). A wide variety of structures of the film is found. For integer ML coverages we find the continuous, so-called floating mode rumple structure, as was previously found in the KBr/NaCl system. However, for a coverage of similar to 2.1 ML, we find a discrete structure of periodicity 3:4 of small regularly spaced KCl pyramids. It has the same scattering characteristics as the structure observed by Henzler et al. [Phys. Rev. B 52, 17 060 (1995)], but it is two-dimensional modulated, rather than the rowlike stacking fault structure proposed by Henzler et al. Also, at a coverage of similar to 0.8 ML there is a stable 3:4 structure. Other structures are found at intermediate coverages, corresponding to regular arrays of dislocation lines with periodicity 9:10. A further growth from such structures would give rise to growth of a similar to 5 degrees miscutKCl crystal relative to the NaCl lattice. The reciprocal space patterns corresponding to the continuous and the discrete film deformations are also calculated.

Lindgård, Per-Anker

1999-01-01

144

Epitaxial growth of pentacene on alkali halide surfaces studied by Kelvin probe force microscopy.  

Science.gov (United States)

In the field of molecular electronics, thin films of molecules adsorbed on insulating surfaces are used as the functional building blocks of electronic devices. Control of the structural and electronic properties of the thin films is required for reliably operating devices. Here, noncontact atomic force and Kelvin probe force microscopies have been used to investigate the growth and electrostatic landscape of pentacene on KBr(001) and KCl(001) surfaces. We have found that, together with molecular islands of upright standing pentacene, a new phase of tilted molecules appears near step edges on KBr. Local contact potential differences (LCPD) have been studied with both Kelvin experiments and density functional theory calculations. Our images reveal that differently oriented molecules display different LCPD and that their value is independent of the number of molecular layers. These results point to the formation of an interface dipole, which may be explained by a partial charge transfer from the pentacene to the surface. Moreover, the monitoring of the evolution of the pentacene islands shows that they are strongly affected by dewetting: Multilayers build up at the expense of monolayers, and in the Kelvin images, previously unknown line defects appear, which reveal the epitaxial growth of pentacene crystals. PMID:24601525

Neff, Julia L; Milde, Peter; León, Carmen Pérez; Kundrat, Matthew D; Eng, Lukas M; Jacob, Christoph R; Hoffmann-Vogel, Regina

2014-04-22

145

Middle-infrared luminescence of Nd ions in silver halide crystals  

Energy Technology Data Exchange (ETDEWEB)

The optical absorption and the luminescence emission in the middle infrared (mid-IR) were investigated in AgCl {sub x} Br{sub 1-} {sub x} crystals doped with Nd{sup 3+} ions. Strong luminescence emission, in the spectral range 4.5-5.8 {mu}m, in mid-IR was observed for the first time in Nd{sup 3+}-doped silver halide crystals. Various optical parameters were calculated for the Nd{sup 3+}-doped crystals, using the Judd-Ofelt approximation. The measured results and the calculated parameters indicate that these doped crystals could be used for the development of mid-IR solid-state lasers or mid-IR fiber lasers.

Shafir, I. [Raymond and Beverly Sackler Faculty of Exact Science, School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 69978 (Israel)]. E-mail: lyakhovs@post.tau.ac.il; Gayer, O. [Raymond and Beverly Sackler Faculty of Exact Science, School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 69978 (Israel); Nagli, L. [Raymond and Beverly Sackler Faculty of Exact Science, School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 69978 (Israel); Shalem, S. [Raymond and Beverly Sackler Faculty of Exact Science, School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 69978 (Israel); Katzir, A. [Raymond and Beverly Sackler Faculty of Exact Science, School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 69978 (Israel)

2007-10-15

146

Photofragmentation of metal halides  

International Nuclear Information System (INIS)

The author deals with photodissociation of molecules of alkali halides. It is shown that the total absorption cross section consists of two contributions arising from transitions to excited states of total electronic angular momentum ?=0"+ and ?=1. From the inversion of the absorption continua potential energy curves of the excited states can be constructed in the Franck-Condon region. It is found that for all alkali halides the 0"+ state is higher in energy than the ?=1 state. Extensive studies are reported on three thallium halides, TlI, TlBr and TlCl at various wavelengths covering the near ultraviolet region. (Auth.)

1980-01-01

147

Optical properties and stable, broadly tunable cw laser operation of new F A-type centers in Tl +-doped alkali halides  

Science.gov (United States)

A new group of complex color centers with F A-type properties, involving simple center production and high thermal and optical stabilities, has been found in six Tl +-doped alkali halides: NaCl, KCl, RbCl, KBr, RbBr and RbI. In its first tested examples, KCl and KBr, broadly tunable cw laser operation over the 1.4 to 1.7 ?m range has been obtained, with output powers in the 100 mW range. In contrast to already existing F +2 and F +2-like centers, operating in the same wavelength range, the new F A(Tl +) lasers are optically stable and do not show any bleaching effects under laser operation.

Gellermann, W.; L?y, F.; Pollock, C. R.

1981-11-01

148

Interaction of dislocations with radiation defects in alkaline-halide crystals  

International Nuclear Information System (INIS)

The studies on interaction of dislocations with point defects in the alkaline-halide crystal are carried out with the purpose of clarifying the nature of the deformation-stimulated luminescence (DSL) and radiation strengthening mechanism. The KCl monocrystals were irradiated by the gamma-quanta (the absorbed dose is of 2 MGy). The information on the hole centers is obtained by analysis of the thermostimulated luminescence curves within the temperature range of 300-540 K. The load on the sample was registered simultaneously with studying the DSL luminescence intensity. It is established that at the room temperature of the DSL crystals the KCl is conditioned by the Vz and V2 hole centers. Dislocations destroy the Vz and V2 centers, which results in the VF- and H-centers, recombining with the F-type centers formation. Thus, the DSL is the consequence of destroying the V2 and Vz hole centers

2000-02-01

149

Configurational coordinate diagram of Ni{sup 2+} doped silver halide crystals, as determined by optical and luminescence measurements  

Energy Technology Data Exchange (ETDEWEB)

Optical and luminescence measurements were carried out on Ni{sup 2+} doped silver halide crystals. The configurational coordinates of the ground and the first excited states made it possible to explain the important optical properties, such as the Stokes shift between the ground and excited states, the broadening of the bands with temperature and the thermal quenching. Determining the configurational coordinate diagram of the ground and first excited states is the first step for the design and fabrication of solid state and fiber lasers which are based on Ni{sup 2+} doped silver halides and which operate in the middle infrared. - Highlights: Black-Right-Pointing-Pointer Optical and luminescence measurements were carried out on Ni{sup 2+} doped silver halide crystals. Black-Right-Pointing-Pointer Configurational coordinates of the ground and the first excited state were calculated. Black-Right-Pointing-Pointer Optical properties of Ni{sup 2+} doped silver halide crystals can be obtained from the configurational coordinate diagram. Black-Right-Pointing-Pointer No emission signal was found above 220 K.

Zakosky-Neuberger, I., E-mail: yifat_z2@hotmail.com [Raymond and Beverly Sackler Faculty of Exact Sciences, School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 69978 (Israel); Shafir, I.; Nagli, L.; Katzir, A. [Raymond and Beverly Sackler Faculty of Exact Sciences, School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 69978 (Israel)

2012-08-15

150

IR laser power transmission through silver halide crystals and polycrystalline fibers  

Energy Technology Data Exchange (ETDEWEB)

Laser-induced breakdown (LIB) thresholds in AgC{sub x},Br{sub 1-x} crystals and fibers were studied under CO{sub 2} laser pulsed and CW excitation. The value of LIB threshold P{sub c} of the bulk crystals is about 7.2{center_dot}10{sup 8} W/cm{sup 2} for AgCl and 4{center_dot}10{sup 9} W/cm{sup 2} for AgBr under 60 ns TEA laser excitation. The LIB threshold in fibers is much smaller; about 2{center_dot}10{sup 8} W/cm{sup 2}. The absorption of the crystals at 10.6 {mu}m changes from 8{center_dot}10{sup -5} cm{sup -1} for AgCl to 2{center_dot}10{sup -5 }cm{sup -1} for AgBr; for fibers with the same composition absorption is much greater (3{center_dot}10{sup -4 }cm{sup -1} for AgCl; 2{center_dot}10{sup -4} cm{sup -1} for AgBr). The dependence of the LIB and IR absorption on composition, and mechanical and temperature treatments suggests that the LIB in silver halide crystals and fibers is due to the avalanche electrons in a high electric field. The initial free electrons for this process are supplied by ionization of the cation vacancy - charged dislocation complexes. The relatively lower optical stability of the fibers is due to the increased concentration of defects formed in the hot extrusion of the crystal. A simple thermal annealing method for reduction of the IR absorption is proposed.

Nagli, L.; Burstein, D.; Shalem, S.; German, A. [Tel-Aviv Univ. (Israel)] [and others

1997-12-01

151

Band-structure calculations of noble-gas and alkali halide solids using accurate Kohn-Sham potentials with self-interaction correction  

Energy Technology Data Exchange (ETDEWEB)

The optimized-effective-potential (OEP) method and a method developed recently by Krieger, Li, and Iafrate (KLI) are applied to the band-structure calculations of noble-gas and alkali halide solids employing the self-interaction-corrected (SIC) local-spin-density (LSD) approximation for the exchange-correlation energy functional. The resulting band gaps from both calculations are found to be in fair agreement with the experimental values. The discrepancies are typically within a few percent with results that are nearly the same as those of previously published orbital-dependent multipotential SIC calculations, whereas the LSD results underestimate the band gaps by as much as 40%. As in the LSD---and it is believed to be the case even for the exact Kohn-Sham potential---both the OEP and KLI predict valence-band widths which are narrower than those of experiment. In all cases, the KLI method yields essentially the same results as the OEP.

Li, Y.; Krieger, J.B. (Department of Physics, Brooklyn College, City University of New York, Brooklyn, New York 11210 (United States)); Norman, M.R. (Material Sciences Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)); Iafrate, G.J. (U.S. Army Research Office, Research Triangle Park, North Carolina 27709-2211 (United States))

1991-11-15

152

Characterization of an Alkali- and Halide-Resistant Laccase Expressed in E. coli: CotA from Bacillus clausii.  

Science.gov (United States)

The limitations of fungal laccases at higher pH and salt concentrations have intensified the search for new extremophilic bacterial laccases. We report the cloning, expression, and characterization of the bacterial cotA from Bacillus clausii, a supposed alkalophilic ortholog of cotA from B. subtilis. Both laccases were expressed in E. coli strain BL21(DE3) and characterized fully in parallel for strict benchmarking. We report activity on ABTS, SGZ, DMP, caffeic acid, promazine, phenyl hydrazine, tannic acid, and bilirubin at variable pH. Whereas ABTS, promazine, and phenyl hydrazine activities vs. pH were similar, the activity of B. clausii cotA was shifted upwards by ?0.5-2 pH units for the simple phenolic substrates DMP, SGZ, and caffeic acid. This shift is not due to substrate affinity (KM) but to pH dependence of catalytic turnover: The kcat of B. clausii cotA was 1 s-1 at pH 6 and 5 s-1 at pH 8 in contrast to 6 s-1 at pH 6 and 2 s-1 at pH 8 for of B. subtilis cotA. Overall, kcat/KM was 10-fold higher for B. subtilis cotA at pHopt. While both proteins were heat activated, activation increased with pH and was larger in cotA from B. clausii. NaCl inhibited activity at acidic pH, but not up to 500-700 mM NaCl in alkaline pH, a further advantage of the alkali regime in laccase applications. The B. clausii cotA had ?20 minutes half-life at 80°C, less than the ?50 minutes at 80°C for cotA from B. subtilis. While cotA from B. subtilis had optimal stability at pH?8, the cotA from B. clausii displayed higher combined salt- and alkali-resistance. This resistance is possibly caused by two substitutions (S427Q and V110E) that could repel anions to reduce anion-copper interactions at the expense of catalytic proficiency, a trade-off of potential relevance to laccase optimization. PMID:24915287

Brander, Søren; Mikkelsen, Jørn D; Kepp, Kasper P

2014-01-01

153

Characterization of an Alkali- and Halide-Resistant Laccase Expressed in E. coli: CotA from Bacillus clausii  

Science.gov (United States)

The limitations of fungal laccases at higher pH and salt concentrations have intensified the search for new extremophilic bacterial laccases. We report the cloning, expression, and characterization of the bacterial cotA from Bacillus clausii, a supposed alkalophilic ortholog of cotA from B. subtilis. Both laccases were expressed in E. coli strain BL21(DE3) and characterized fully in parallel for strict benchmarking. We report activity on ABTS, SGZ, DMP, caffeic acid, promazine, phenyl hydrazine, tannic acid, and bilirubin at variable pH. Whereas ABTS, promazine, and phenyl hydrazine activities vs. pH were similar, the activity of B. clausii cotA was shifted upwards by ?0.5–2 pH units for the simple phenolic substrates DMP, SGZ, and caffeic acid. This shift is not due to substrate affinity (KM) but to pH dependence of catalytic turnover: The kcat of B. clausii cotA was 1 s?1 at pH 6 and 5 s?1 at pH 8 in contrast to 6 s?1 at pH 6 and 2 s?1 at pH 8 for of B. subtilis cotA. Overall, kcat/KM was 10-fold higher for B. subtilis cotA at pHopt. While both proteins were heat activated, activation increased with pH and was larger in cotA from B. clausii. NaCl inhibited activity at acidic pH, but not up to 500–700 mM NaCl in alkaline pH, a further advantage of the alkali regime in laccase applications. The B. clausii cotA had ?20 minutes half-life at 80°C, less than the ?50 minutes at 80°C for cotA from B. subtilis. While cotA from B. subtilis had optimal stability at pH?8, the cotA from B. clausii displayed higher combined salt- and alkali-resistance. This resistance is possibly caused by two substitutions (S427Q and V110E) that could repel anions to reduce anion-copper interactions at the expense of catalytic proficiency, a trade-off of potential relevance to laccase optimization.

Brander, S?ren; Mikkelsen, J?rn D.; Kepp, Kasper P.

2014-01-01

154

Surface and zeta-potentials of silver halide single crystals: pH-dependence in comparison to particle systems.  

Science.gov (United States)

We have carried out surface and zeta-potential measurements on AgCl and AgBr single crystals. As for particle systems we find that, surprisingly and previously unnoted, the zeta-potential exhibits pH-dependence, while the surface potential does not. A possible interpretation of these observations is the involvement of water ions in the interfacial equilibria and in particular, stronger affinity of the hydroxide ion compared to the proton. The pH-dependence of the zeta-potential can be suppressed at sufficiently high silver concentrations, which agrees with previous measurements in particle systems where no pH-dependence was found at high halide ion concentrations. The results suggest a subtle interplay between the surface potential determining the halide and silver ion concentrations, and the water ions. Whenever the charge due to the halide and silver ions is sufficiently high, the influence of the proton/hydroxide ion on the zeta-potential vanishes. This might be related to the water structuring at the relevant interfaces which should be strongly affected by the surface potential. Another interesting observation is accentuation of the assumed water ion effect on the zeta-potential at the flat single crystal surfaces compared to the corresponding silver halide colloids. Previous generic MD simulations have indeed predicted that hydroxide ion adsorption is accentuated on flat/rigid surfaces. A thermodynamic model for AgI single crystals was developed to describe the combined effects of iodide, silver and water ions, based on two independently previously published models for AgI (that only consider constituent and background electrolyte ions) and inert surfaces (that only consider water and background electrolyte ions). The combined model correctly predicts all the experimentally observed trends. PMID:24863080

Selmani, Atiða; Lützenkirchen, Johannes; Kallay, Nikola; Preo?anin, Tajana

2014-06-18

155

Surface and zeta-potentials of silver halide single crystals: pH-dependence in comparison to particle systems  

Science.gov (United States)

We have carried out surface and zeta-potential measurements on AgCl and AgBr single crystals. As for particle systems we find that, surprisingly and previously unnoted, the zeta-potential exhibits pH-dependence, while the surface potential does not. A possible interpretation of these observations is the involvement of water ions in the interfacial equilibria and in particular, stronger affinity of the hydroxide ion compared to the proton. The pH-dependence of the zeta-potential can be suppressed at sufficiently high silver concentrations, which agrees with previous measurements in particle systems where no pH-dependence was found at high halide ion concentrations. The results suggest a subtle interplay between the surface potential determining the halide and silver ion concentrations, and the water ions. Whenever the charge due to the halide and silver ions is sufficiently high, the influence of the proton/hydroxide ion on the zeta-potential vanishes. This might be related to the water structuring at the relevant interfaces which should be strongly affected by the surface potential. Another interesting observation is accentuation of the assumed water ion effect on the zeta-potential at the flat single crystal surfaces compared to the corresponding silver halide colloids. Previous generic MD simulations have indeed predicted that hydroxide ion adsorption is accentuated on flat/rigid surfaces. A thermodynamic model for AgI single crystals was developed to describe the combined effects of iodide, silver and water ions, based on two independently previously published models for AgI (that only consider constituent and background electrolyte ions) and inert surfaces (that only consider water and background electrolyte ions). The combined model correctly predicts all the experimentally observed trends.

Selmani, Atiða; Lützenkirchen, Johannes; Kallay, Nikola; Preo?anin, Tajana

2014-06-01

156

Residual gas analysis of volatile impurities in halide precursors for scintillator crystals  

Science.gov (United States)

Alkaline-earth halides can be made into bright scintillators if purity is maintained during synthesis and growth. In order to investigate precursor purity, beaded halide precursors were heated under vacuum and evolved gas was assessed by residual gas spectroscopy. These precursors included cesium chloride, lithium chloride, yttrium chloride, cerium chloride, strontium iodide, europium iodide, barium bromide, and europium bromide. Water and CO2 desorption, sulfur release, argon release, and halide dissociation was observed in samples. Triply-oxidized precursors showed multiple paths to decomposition. The data inform approaches toward purification and growth.

Swider, S.; Motakef, S.; Datta, A.; Higgins, W. M.

2013-09-01

157

Effect of large gamma-irradiation doses on conversion efficiency and light output of alkali halide scintillators  

International Nuclear Information System (INIS)

It is shown that the effect of large irradiation doses on scintillation properties is mainly connected with bubbles which grow due to irradiation-induced diffusion of created vacancies, the number of bubbles remaining approximately constant. To all appearance, some structure defects initially present in a crystal act as coalescence centers for vacancies. Under this assumption, a significant straggling of the examined samples in the sensitivity to gamma-irradiation can be attributed to the difference in the number of coalescence centers

1996-11-02

158

Single-Crystal Growth of Bi-Sb-Te Thermoelectric Materials by Halide Chemical Vapor Transport Technique  

Science.gov (United States)

This report describes synthesis of binary Bi2Te3 and ternary Bi0.5Sb1.5Te3 single crystals using the halide chemical vapor transport technique. For synthesis of ternary Bi0.5Sb1.5Te3, BiBr3 is a more effective transport agent compared with iodine I2. The single crystal includes a few atomic percent of Br. The Bi0.5Sb1.5Te3 crystal shows p-type conduction and has a comparatively large residual resistivity ratio. The crystal exhibits relatively high electrical resistivity and high Seebeck coefficient. These high values are attributed to decrease of the hole concentration p due to doping of the transport agent Br.

Koyano, Mikio; Tanaka, Junya; Suekuni, Koichiro; Ariga, Tomoki

2012-06-01

159

Alkali metals  

International Nuclear Information System (INIS)

The discussion is presented under the following section headings: introduction; effect of contaminants; reactions of alkali metals with oxygen and nitrogen (sections on Li, Na, K, Rb, Cs); reactions of alkali metals with hydrogen; sample storage; sampling (sections on liquid metals in dynamic and static syystems and solid metals; methods for determination of oxygen (amalgamation, alkyl halide, fluorination, methanol solution and Karl Fischer titration, liquid ammonia for oxygen in lithium, distillation, plugging meter, electrochemical oxygen meter, freezing-point depression, resistivity, activation analysis); methods for determination of hydrogen (diffusion gasometric procedure, vacuum fusion and similar methods, amalgamation, isotope dilution, and miscellaneous); and,determination of nitrogen. (105 references.) (U.S.)

1974-01-01

160

Thermochemistry of Charge-Unsymmetrical Binary Fused Halide Systems. Ii. Mixtures of Magnesium Chloride with the Alkali Chlorides and with Silver Chloride.  

Science.gov (United States)

The integral enthalpies of mixing of the liquid mixtures of magnesium chloride with the alkali chlorides and with silver chloride were determined calorimetrically. The magnesium chloride-silver chloride system is slightly endothermic, while the alkali chl...

O. J. Kleppa F. G. McCarty

1965-01-01

 
 
 
 
161

Creation of molecular defects in alkali iodide crystals by irradiation with fast heavy ions  

International Nuclear Information System (INIS)

We show for the first time that irradiation at room temperature of alkali iodide crystals by fast heavy ions (40Ar14+ ions of 5.53 MeV/A at a fluence of 1013 ions/cm2) leads to the formation of V-type defects. By means of UV visible optical absorption and resonant Raman scattering measurements, we have identified I3-, I5- and (I2)n in Kl and only I3- and I5- in RbI irradiated under similar conditions. These preliminary results are consistent with previous investigations obtained in iodide crystals after exposure to X or ? rays at room temperature. (orig.)

1992-01-01

162

DFT-D study of 14N nuclear quadrupolar interactions in tetra-n-alkyl ammonium halide crystals.  

Science.gov (United States)

The density functional theory-based method with periodic boundary conditions and addition of a pair-wised empirical correction for the London dispersion energy (DFT-D) was used to study the NMR quadrupolar interaction (coupling constant CQ and asymmetry parameter ?Q) of (14)N nuclei in a homologous series of tetra-n-alkylammonium halides (C(x)H(2x+1))4N(+)X(-) (x = 1-4), (X = Br, I). These (14)N quadrupolar properties are particularly challenging for the DFT-D computations because of their very high sensitivity to tiny geometrical changes, being negligible for other spectral property calculations as, for example, NMR (14)N chemical shift. In addition, the polarization effect of the halide anions in the considered crystal mesophases combines with interactions of van der Waals type between cations and anions. Comparing experimental and theoretical results, the performance of PBE-D functional is preferred over that of B3LYP-D. The results demonstrated a good transferability of the empirical parameters in the London dispersion formula for crystals with two or more carbons per alkyl group in the cations, whereas the empirical corrections in the tetramethylammonium halides appeared to be inappropriate for the quadrupolar interaction calculation. This is attributed to the enhanced cation-anion attraction, which causes a strong polarization at the nitrogen site. Our results demonstrated that the (14)N CQ and ?Q are predominantly affected by the molecular structures of the cations, adapted to the symmetry of the anion arrangements. The long-range polarization effect of the surrounding anions at the target nitrogen site becomes more important for cells with lower spatial symmetry. PMID:24758512

Dib, Eddy; Alonso, Bruno; Mineva, Tzonka

2014-05-15

163

Introducing alkali impurities into BaFBr:Eu{sup 2+} crystals and their effect on photo-stimulated luminescence  

Energy Technology Data Exchange (ETDEWEB)

In alkali doped BaFBr:Eu{sup 2+} a considerable increase of photostimulated luminescence (PSL) intensity is observed. Upon Na doping the intensity of the PSL is increased by a factor of 15 in contrast to undoped samples. Moreover, the PSL peak shifted on 0.08 eV in the red region of spectrum upon Na doping. The potassium and rubidium doping results in the same effects, but with less efficiency. We prepared undoped BaFBr:Eu{sup 2+} crystals and those doped with varied concentrations of NaF, KF, RbF. The concentrations of alkali, which we doped before growth, were in the region of 0.1-5%. Atomic-Emission Analysis shows that the real alkali concentrations in the crystals are 0.0002-0.0025%. However, even such a small alkali doping concentration in BaFBr:Eu{sup 2+} influences effectively the PSL process.

Shalaev, A. E-mail: alshal@igc.irk.ru; Radzhabov, E.A.; Shabanova, E

2002-06-21

164

Introducing alkali impurities into BaFBr:Eu2+ crystals and their effect on photo-stimulated luminescence  

International Nuclear Information System (INIS)

In alkali doped BaFBr:Eu2+ a considerable increase of photostimulated luminescence (PSL) intensity is observed. Upon Na doping the intensity of the PSL is increased by a factor of 15 in contrast to undoped samples. Moreover, the PSL peak shifted on 0.08 eV in the red region of spectrum upon Na doping. The potassium and rubidium doping results in the same effects, but with less efficiency. We prepared undoped BaFBr:Eu2+ crystals and those doped with varied concentrations of NaF, KF, RbF. The concentrations of alkali, which we doped before growth, were in the region of 0.1-5%. Atomic-Emission Analysis shows that the real alkali concentrations in the crystals are 0.0002-0.0025%. However, even such a small alkali doping concentration in BaFBr:Eu2+ influences effectively the PSL process

2002-06-21

165

Growth of silver halides from the molecule to the crystal. Pulse radiolysis study  

Energy Technology Data Exchange (ETDEWEB)

Halide ions were produced in situ by pulse radiolysis, via electron transfer to dihalomethanes from solvated electrons or hydrogen atoms, and were then used to generate silver halide molecules and larger aggregates. This evolution of silver halide aggregates was studied for the case of silver iodide on the time scale of 10/sup /minus/6/-10/sup 2/ s. Conductivity detection allows determination of the rate of formation of the first AgI molecule. Spectrophotometric detection of the growth of the particles from the stage of the molecular species to colloidal particles of bulk electronic properties is then possible. When the aggregates thus formed approach sizes of ca. 50/degrees/ /angstrom/, their detection by light scattering provides an independent method of size determination. In the region where such measurements are possible, the sizes determined by light scattering agree with sizes calculated assuming confinement excitons in small particles and their electron-hole coulomb screening. A similar approach is suggested for growth studies of other insoluble materials. 13 references, 3 figures.

Schmidt, K.H.; Patel, R.; Meisel, D.

1988-07-20

166

Creation of molecular defects in alkali iodide crystals by irradiation with fast heavy ions  

Energy Technology Data Exchange (ETDEWEB)

We show for the first time that irradiation at room temperature of alkali iodide crystals by fast heavy ions ({sup 40}Ar{sup 14+} ions of 5.53 MeV/A at a fluence of 10{sup 13} ions/cm{sup 2}) leads to the formation of V-type defects. By means of UV visible optical absorption and resonant Raman scattering measurements, we have identified I{sub 3}{sup -}, I{sub 5}{sup -} and (I{sub 2}){sub n} in Kl and only I{sub 3}{sup -} and I{sub 5}{sup -} in RbI irradiated under similar conditions. These preliminary results are consistent with previous investigations obtained in iodide crystals after exposure to X or {gamma} rays at room temperature. (orig.).

Rzepka, E.; Wery, J.; Lefrant, S. (Lab. de Physique Cristalline, Univ. de Nantes, 44 (France)); Ramstein, B.; Tamisier, R.; Hourdequin, E. (Lab. de Physique Nucleaire de Nantes, Univ. de Nantes, 44 (France)); Bouffard, S. (C.I.R.I.L., 14 - Caen (France))

1992-02-01

167

New di-ferrocenyl-ethynylpyridinyl triphenylphosphine copper halide complexes and related di-ferricenyl electro-crystallized materials.  

Science.gov (United States)

Three new neutral di-ferrocenyl-ethynylpyridinyl copper complexes, [L2(CuCl)2(PPh3)2] (), [L2(CuBr)2(PPh3)2] (), and [L2(CuI)2(PPh3)2] () were synthesized from the ferrocenyl-ethynylpyridine ligand (L) (), the appropriate copper halide CuX (with X = Cl(-), Br(-), I(-)) and triphenylphosphine. These neutral complexes were fully characterized by spectroscopic methods and by single crystal X-ray crystallography. Cyclic voltammetry in dichloroethane revealed chemically reversible ferrocenyl oxidation signals followed by characteristic "stripping reduction peaks" showing evidence for oxidation-product electro-crystallization. Scanning electron microscopy confirmed spontaneous formation of crystalline oxidation products with three distinct morphologies for X = Cl(-), Br(-), I(-). Energy dispersive X-ray elemental analysis data show Fe?:?P ratios of 1?:?2.0, 1?:?2.1 and 1?:?2.1 for electro-crystallization products of complexes , , and , respectively, indicating the presence of two [PF6](-) anions in the vicinity of the dioxidized complexes, and suggesting product formulae [](2+)[PF6](-)2, [](2+)[PF6](-)2 and [](2+)[PF6](-)2. PMID:24824939

Shah, Hakikulla H; Al-Balushi, Rayya A; Al-Suti, Mohammed K; Khan, Muhammad S; Marken, Frank; Sudlow, Anna L; Kociok-Köhn, Gabriele; Woodall, Christopher H; Raithby, Paul R; Molloy, Kieran C

2014-06-01

168

Silver alkali halide glasses and a vitreous analog of the RbAg/sub 4/I/sub 5/ superionic conductor  

Energy Technology Data Exchange (ETDEWEB)

We report the existence of silver halide-rich glasses of a type not previously recognized. These contain only monovalent halides and represent perhaps the simplest ionic glasses yet realized. Despite the lack of the usual oxyanion matrix the new glasses show room temperature conductances which equal or exceed those of the best Ag/sup +/ glasses yet reported. Cu/sup +/ analogues have also been prepared. At the high conducting extreme apparently lies a vitreous state analog of the well-known crystalline conductor RbAg/sub 4/I/sub 5/. A crystalline analog of the latter FIC, CsAg/sub 4/(I /SUB 0.45/ C1 /SUB 0.55/ )/sub 5/ forms metastably on careful devitrification of the glass. Like its prototype, it has a very high conductivity and exhibits a sharp C /SUB p/ anomaly at low temperatures, -77/sup 0/C, in the vicinity of which the activation energy for conductance changes abruptly.

Liu, C.; Angell, C.A.; Sundar, H.G.K.

1985-05-01

169

Stability diagrams for complexes in molten mixtures of halide salts  

International Nuclear Information System (INIS)

The stability of local fourfold coordination for divalent and trivalent metal ions in liquid mixtures of polyvalent metal halides and alkali halides is classified by means of structural coordinates obtained from properties of the elements. In parallel with earlier classifications of compound crystal structures and molecular shapes, the elemental properties are taken from first-principles calculations of valence electron orbitals in atoms, in the form of (i) the nodal radii of Andreoni, Baldereschi and Guizzetti or (ii) the pseudo-potential radii of Zunger and Cohen. As a third alternative we also consider a classification based on Pettifor's phenomenological chemical scale of the elements. The alternative structural classification schemes that are developed from these elemental properties are very successful in distinguishing molten mixtures in which the available experimental evidence indicates stability of ''complexes'', i.e. long-lived fourfold coordination of polyvalent metal ions. (author). 55 refs, 3 figs

1988-01-01

170

Structure of luminescence spectra of UO_2"+"2 impurity ions in halide salt solid solutions  

International Nuclear Information System (INIS)

Luminescence spectra of impurity polyatomic ions of UO"2_2"+ in water and aqueous solutions of alkali-halide salts are studied in the 1.62-77 K temperature range. The emission spectra of these solutions at 77 K are characterized by a pronounced vibrational structure specified by the interaction of an electron transition with an impurity ion intramolecular vibration #betta#"1. At 1.62-4.2 K individual vibrational bands are splitted to phononless lines and structural phonon wings (FW). The PW structure is defined by an excitation of crystalline vibrations of a solution solid matrix. For the H"2O-UO"2_2"+ solution the PW maximum frequences are shown to be comparable with the main critical points of the vibration spectrum of an orientation-disorded ice crystal. In case of aqueous solutions of alkali-halide salts with UO"2_2"+ impurity ions the PW luminescence spectra are compared with the density functions of undistorted vibrations of alkali-halide salt crystals and ice

1982-10-01

171

ESR spectra on single crystals of alkali metal fulleride complexes by means of wet-chemical synthesis  

Science.gov (United States)

The facile and simple wet-chemical synthesis of single crystals of alkali metal doped fullerenes was developed by means of diffusion in organic solvents of C 60 and alkali metal tetraphenylborate. The single crystals M xC 60(THF) y (M = Na, K) posess a hexagonal unit cell and ESR showed the existence of a typical broad C 60 anion radical signal, in addition to a small sharp signal which is amenable to microwave power saturation. The existence of the spike signal is almost always involved in fullerene anion radical systems. The solid-state 23Na and solid-state 13C NMR on Na xC 60(THF) y also revealed the homogeneity of the single crystal.

Moriyama, Hiroshi; Kobayashi, Hayao; Kobayashi, Akiko; Watanabe, Tokuko

1995-05-01

172

Tabular silver halide crystals prepared by controlled Ostwald growth in the presence of dimethyl sulphoxide  

Energy Technology Data Exchange (ETDEWEB)

The results of research in the size and shape of silver bromide crystals precipitated by the Ostwald controlled growth method at the presence of dimethyl sulphoxide were presented in the paper. The silver bromide crystals were produced in the form of microcrystal suspension stabilised by gelatine. In the course of the synthesis of crystals, the constant concentration of dimethyl sulphoxide, concentration of excessive bromide ions and the constant ionic strength were achieved. The tabular crystals of silver bromide with their average size of 50 {mu}m and their aspect ratio equal to 100 were obtained by means of this method. The suspensions of flat silver bromide crystals produced in this manner can be used in the production of high-sensitivity materials. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Dyonizy, A.; Nowak, P.; Mora, C.; Krol-Gracz, A.; Michalak, E. [Institute of Physical and Theoretical Chemistry, Wroclaw University of Technology, Wybrzeze St. Wyspianskiego 27, 50-370 Wroclaw (Poland)

2010-03-15

173

Associated equilibria with participation of single and mixed silver, lead and cadmium halide complexes in mixtures of molten alkali and alkaline earth metal nitrates  

Energy Technology Data Exchange (ETDEWEB)

Associated equilibria in the systems, which contain single and mixed silver, cadmium and lead halide complexes in the KNO/sub 3/-Ba(N0/sub 3/)/sub 2/ (87.6:12.4 and 89:11 mol.%) and NaNO/sub 3/-Ba(NO/sub 3/)/sub 2/ (94.2-5.8 mol%) melts in the temperature range from 568.2 up to 698.2 K are investigated. Applicability of equations derivated on the base of quasi-lattice model to description of temperature coefficients of association constants is analyzed.

Gouk, Kh.S.; Gupta, R.K.; Vekma, K.V. (Delhi Univ. (India))

1983-01-01

174

Photoluminescence and EPR studies on gamma irradiated Ce{sup 3+} doped potassium halide single crystals  

Energy Technology Data Exchange (ETDEWEB)

Electron Paramagnetic Resonance(EPR), Photoluminescence(PL), Thermoluminescence (TL) and other optical studies of {gamma}-irradiated KBr, KCl:Ce{sup 3+} single crystals. Cerium when doped into the KBr, KCl is found to enter the host lattice in its trivalent state and act as electron trap during {gamma}-irradiation, thereby partially converting itself to Ce{sup 2+}. The Photoluminescence(PL) spectra of both KCl and KBr crystals doped with Ce exhibit the strong blue emissions of Ce corresponding to {sup 5}d({sup 2}D){yields}{sup 2}F{sub 5/2} and {sup 5}d({sup 2}D){yields}{sup 2}F{sub 7/2} transitions. The defect centers formed in the Ce{sup 3+} doped KBr and KCl. Crystals are studied using the technique of EPR. A dominant TL glow peak at 374, 422 K and KCl:Ce{sup 3+} at 466, 475 K is observed in the crystal. EPR studies indicate the presence at two centers at room temperature. Spectral distribution under the thermoluminescence emission(TLE) and optically stimulated emission(OSL) support the idea that defect annihilation process to be due to thermal release of F electron in KBr, KCl:Ce{sup 3+} crystals. Both Ce{sup 3+} and Ce{sup 2+} emissions were observed in the thermoluminescence emission of the crystals.

Bangaru, S., E-mail: ssbangaru@yahoo.co.i [Department of Physics, Arignar Anna Government Arts College, Namakkal 637002, Tamilnadu (India)

2011-01-15

175

Cluster models of doped ionic crystal scintillators. Quantum calculations  

International Nuclear Information System (INIS)

The authors have performed quantum electronic ab initio calculations of clusters of alkali halides, both pure and doped. In order to estimate the pure crystal energy gap and the dopant excitation, they have considered a central cation and four shells of ions surrounding it. They have studied KCl, NaI, NaCl and KI, both pure and with a Tl+ ion replacing the central alkali cation. Encouraging results are presented for absorption and emission

1994-04-04

176

Zirconium tungstate hydroxide hydrate revisited: Crystallization dependence on halide and hydronium ions  

International Nuclear Information System (INIS)

The formation of zirconium tungstate hydroxide hydrate, a precursor to the negative thermal expansion material cubic zirconium tungstate, shows a strong dependence on hydrothermal reaction conditions. It was found that not only the acid concentration, but also the acid counterion plays a significant role in the crystallization of ZrW2O7(OH)2.2H2O. High temperatures, high acid concentrations, and the presence of chloride or bromide ions promote the formation of well-crystallized ZrW2O7(OH)2.2H2O. For low acid concentrations, a new zirconium tungstate hydrate polymorph is observed, which transforms to tetragonal ZrW2O7(OH)2.2H2O at longer reaction times. A study of crystallization kinetics in hydrochloric acid is presented. - Graphical abstract: The formation of ZrW2O7(OH)2.2H2O shows a strong dependence on reaction conditions. Both acid concentration and acid counterion play a significant role in the crystallization. High temperatures, high acid concentrations, and the presence of chloride or bromide ions promote the formation of well-crystallized ZrW2O7(OH)2.2H2O. For low acid concentrations, a new zirconium tungstate hydrate polymorph is observed

2007-12-01

177

The radiation defect accumulation in scintillative crystals of caesium halides under intense electron beam irradiation  

CERN Document Server

The characteristics of defect accumulation and radiolysis at CsI crystals under mean energies of electron irradiation at wide dose rates and ranges of doses have been investigated by such methods: thermostimulated exoelectron emission (TSEE), Auger electron spectroscopy (AES) and optical absorption spectroscopy (OAS). The limit dose rates and absorbed doses of electron irradiation that lead to defects accumulation at room temperature in crystals volume and also surface stoichiometry violation have been evaluated. The doses of electron irradiation that lead to CsI radiolysis, with caesium coagulation in metallic phase have been determined. Some quasi periodic connection of such process with irradiation dose was observed.

Galiy, P V

1999-01-01

178

Chemiluminescence (lyoluminescence) during dissolution of crystals containing electron centers  

International Nuclear Information System (INIS)

Lyoluminescence of irradiated inorganic fluorides in concentrated acids is detected. Using the method of a rotating disk the intensity of lyoluminescence depending on the concentration of sulfuric acid aqueous solutions, dissolution rate of irradiated lithium fluoride and concentration of F centres in lithium fluoride, is studied. Mechanism of the appearance of lyoluminescence of irradiated alkali metal halide crystals is discussed

1981-01-01

179

Role of monovalent alkali ions in the Yb3+ centers of CaF2 laser crystals  

International Nuclear Information System (INIS)

Yb3+ and M+ monovalent alkali ions (M+ = Li+, Na+, K+)-co-doped CaF2 cubic laser crystals were grown by the micro-pulling-down method (?-PD) under CF4 atmosphere. Structural and spectroscopic characterizations of Yb3+ in substitution of Ca2+ (absorption, emission and decay curves) were carried out to study the effect of M+ ions as charge compensators.

2009-07-08

180

EPR detected via magnetic circular dichroism of optical absorption in irradiated alkali halide crystals doped with cadmium  

International Nuclear Information System (INIS)

Results are reported which were obtained by applying the optically detected magnetic resonance (ODMR) technique via magnetic circular dichroism (MCD) to Cd+ centers in X-irradiated KCl and NaCl doped with 111Cd and 113Cd. Using a simple non-resonant microwave circuit very strong ODMR of Cdc+ and AF(Cd) centers at 35 and 77 GHz were obtained. The ODMR technique enables to study the wavelength dependence of the ODMR and spin-lattice relaxation time

1988-06-01

 
 
 
 
181

Structure of polyvalent metal halide melts  

International Nuclear Information System (INIS)

A short review is given of recent progress in determining and understanding the structure of molten halide salts involving polyvalent metal ions. It covers the following three main topics: (i) melting mechanisms and types of liquid structure for pure polyvalent-metal chlorides; (ii) geometry and stability of local coordination for polyvalent metal ions in molten mixtures of their halides with alkali halides; and (iii) structure breaking and electron localization on addition of metal to the melt. (author). 28 refs, 3 figs, 1 tab

1990-01-01

182

Nonmetal-metal transition in molten potassium-potassium halide solutions  

International Nuclear Information System (INIS)

It is suggested, in the light of the available experimental evidence, that the nonmetal-to-metal transition in solutions of potassium in molten potassium halides may be viewed as a volume-percolation transition. The critical concentration is estimated and differences between alkali-alkali halide and metal-ammonia solutions are discussed. (author)

1984-01-01

183

Isotopic Ligand Exchange of Some Hexa-Coordinated Inorganic Complexes with Halide Ions in Solution and in Crystals  

International Nuclear Information System (INIS)

The kinetics of isotopic exchange reactions give information about the lability of complexes in solution and about the mechanisms of substitution. The exchange of 82Br-labelled [Rh(NH3)5Br]2+ and [Ii(NH3)5Br]2+ complexes with Br- ions, of trans-[Rh(en)2Cl2]+ and trans- [Co(en)2 Cl2]+]+ with Cl- ions, of trans- [Co(en)2Br2]+ with Br- and of [OSCl6]2- and [OsI6]2- with Cl- and I- ions, respectively, was investigated in acid solutions. The iridium pentamminebromo complex exchanges about 60 times slower than the corresponding rhodium pentamminebromo complex. The rate constant for the Rh- complex was found to be k = (1.03 ± 0,02) x 10-2 min-1 at 100°C, for the Ir-complex k100°C = 1.7 x 10-4 min-1. For both complexes the exchange rate R is first-order in the complex concentration; in acid solution R is nearly independent of the bromide and hydrogen concentration as well as of the ionic strength. This indicates that the exchange takes place by a dissociation mechanism. Activation energies of 24 and 23 kcal/ mole forthe Rh- and Ir-complex, respectively, were calculated. Rate constants of the 36Cl isotopic exchange between 60 and 100°C were measured for the trans- [Rh(en)2 Cl2]+ complex and an Arrhenius activation energy of 25 kcal/mole was determined. Here again the increase of the rate R is of first order in the complex concentration; but it is only slightly dependent on the hydrogen and chloride concentration. The exchange seems to occur by aquation. In methanolic HCl solution the exchange rate of this complex is immeasurably slow at 60°C. The halide exchanges of trans-[Co(en)2 Cl2]+ and trans [Co(en)2 Br2]+ were measured in methanolic solutions between 30 and 60°C. Further , the halide exchange of [OsCl6]2- and [Osl6]2- was investigated in hydrochloric acid and hydroiodic acid, respectively, in methanolic acid and in ethanolic acid solution. The rates measured are compared with earlier results of the isotopic exchange of the corresponding hexabromo complex. Beside these investigations of the dissolved complexes, displacement reactions of labelled cis- and trans-[Co(en)2Cl*2] Cl and trans- [Rh(en)2Cl*2] Cl in the lattice were studied. The half-time of the exchange for both solid isomeric Co complexes is about 4 h at 150°C. For the Rh complex a half-time of about 26 h was found at 225°C. Activation energies of 30-35 kcal/mole were calculated. X-ray irradiation leads to an exchange increasing with the dose. In addition, the thermal exchange of irradiated crystals is accelerated. In contrast to the ethylenediamine complexes, the solid Rh and Ir pentamminebromo bromides or chlorides exchange only very slowly by raising the temperature even to 210°C. But in these solid complexes ''activated'' exchange reactions take place if the complex receives excitation energy from a nuclear process such as the 80mBr -> 80Br isomeric transition. This phenomenon was investigated in some detail. (author)

1965-10-01

184

Characterization of an Alkali- and Halide-Resistant Laccase Expressed in E. coli: CotA from Bacillus clausii  

DEFF Research Database (Denmark)

The limitations of fungal laccases at higher pH and salt concentrations have intensified the search for new extremophilic bacterial laccases. We report the cloning, expression, and characterization of the bacterial cotA from Bacillus clausii, a supposed alkalophilic ortholog of cotA from B. subtilis. Both laccases were expressed in E. coli strain BL21(DE3) and characterized fully in parallel for strict benchmarking. We report activity on ABTS, SGZ, DMP, caffeic acid, promazine, phenyl hydrazine, tannic acid, and bilirubin at variable pH. Whereas ABTS, promazine, and phenyl hydrazine activities vs. pH were similar, the activity of B. clausii cotA was shifted upwards by ,0.5â??2 pH units for the simple phenolic substrates DMP, SGZ, and caffeic acid. This shift is not due to substrate affinity (KM) but to pH dependence of catalytic turnover: The kcat of B. clausii cotA was 1 s21 at pH 6 and 5 s21 at pH 8 in contrast to 6 s21 at pH 6 and 2 s21 at pH 8 for of B. subtilis cotA. Overall, kcat/KM was 10-fold higher forB. subtilis cotA at pHopt. While both proteins were heat activated, activation increased with pH and was larger in cotA from B. clausii. NaCl inhibited activity at acidic pH, but not up to 500â??700 mM NaCl in alkaline pH, a further advantage of the alkali regime in laccase applications. The B. clausii cotA had ,20 minutes half-life at 80uC, less than the ,50 minutes at 80uC for cotA from B. subtilis. While cotA from B. subtilis had optimal stability at pH,8, the cotA from B. clausii displayed higher combined salt- and alkali-resistance. This resistance is possibly caused by two substitutions (S427Q and V110E) that could repel anions to reduce anion-copper interactions at the expense of catalytic proficiency, a trade-off of potential relevance to laccase optimization.

Brander, Søren; Mikkelsen, Jørn Dalgaard

2014-01-01

185

Evaluation of third-order and fourth-order elastic constants of cesium halides and thallium halides  

International Nuclear Information System (INIS)

The third-order and fourth-order elastic constants for CsCl, CsBr, CsI, TlCl, and TlBr crystals are calculated taking into account the effect of Lundqvist's three body potential. The nearest neighbour and next-nearest neighbour repulsive interactions and the Van der Waals interactions are also included according to a recent scheme developed for NaCl-structure alkali halides. The three body charge transfer parameter and its derivatives are evaluated using an exponential form suggested by Cochran. The pressure derivatives of second-order and third-order elastic constants are also calculated for the crystals under study. The results obtained are found to be in reasonable agreement with available experimental data. (author)

1981-05-01

186

Alkali-ions diffusion, mullite formation, and crystals dissolution during sintering of porcelain bodies: Microstructural approach  

DEFF Research Database (Denmark)

The effect of alkali-silicate glassy matrix as replacement for feldspar in soft and hard porcelain compositions was studied. SEM and X-ray diffraction analysis were used to evidence phase evolution. For each composition, the influence of soaking time was evaluated. The difference in chemical composition (amount of alkali and alumina) between the two types of porcelain studied influenced the final microstructure: density, pore size and shape, and mullite content. Quartz dissolution was more important in soft porcelain where the mullitization was limited by the low amount of alumina compared to hard porcelain. Replacing the feldspar by alkali-silicate glassy matrices with similar chemical composition, the amount of secondary mullite and mechanical properties increased in both soft and hard compositions.

Leonelli, C.; Kamseu, E.

2009-01-01

187

Stability diagrams for fourfold coordination of polyvalent metal ions in molten mixtures of halide salts  

International Nuclear Information System (INIS)

The stability of local fourfold coordination for divalent and trivalent metal ions in liquid mixtures of polyvalent metal halides and alkali halides is classified by means of structural coordinates obtained from properties of the elements. In parallel with earlier classifications of compound crystal structures and molecular shapes, the elemental properties are taken from first-principles calculations of valence electron orbitals in atoms, in the form of (i) the nodal radii of Andreoni, Baldereschi and Guizzetti or (ii) the pseudopotential radii or Zunger and Cohen. As a third alternative a classification based on Pettifor's phenomenological chemical scale of the elements is also considered. The alternative structural classification schemes that are developed from these elemental properties are generally successfully in distinguishing molten mixtures in which the available experimental evidence indicates long-lived fourfold coordination of polyvalent metal ions. In addition, Pettifor's chemical scale scheme is useful in sorting out finer details of local coordination in the liquid state. 3 figs., 71 refs

1988-01-01

188

Differential calorimeter and temperature controller for stored energy measurements in irradiated alkali halides; Calorimetro diferencial y controlador de temperatura para medidas de energia almacenada en haluros alcalinos irradiados  

Energy Technology Data Exchange (ETDEWEB)

The design and performance of a simple temperature-controlled differential calorimeter are presented. This system allows to measure radiation-induced stored energy in insulators, above room temperature with a differential thermal analysis method. With platelets of KC1 single crystals, the base lines obtained for T{sub 2} T{sub 1} (with T{sub 2}: irradiated sample temperature and T{sub 1}: reference sample temperature) show a smooth drift less of 0,2 degree centigree in the interval from 25 to 400 degree centigree. The discrepancy between two consecutive base lines is less than {+-} 0,02 degree centigree which implies a calorimeter sensitivity of about {+-}0,004 cal/g. This sensitivity allows to measure stored energy release in samples with a color center concentration low enough to be directly measured with a spectrophotometer so that a search for correlations among the features of the stored energy spectrum and the color center annealing can be made. (Author) 13 refs.

Delgado Martinez, L.

1977-07-01

189

Phase equilibria of the oxide hydroxide halide systems of Sm, Eu, and Gd. The crystal structure of Gd 3O(OH) 5Br 2  

Science.gov (United States)

An investigation of hydrothermal phase equilibria in the halide-containing (Cl, Br, I) systems of Sm, Eu, and Gd has shown that diversities in behavior occur across the lanthanide ( Ln) series and within the halide group. In the chloride systems, the trihydroxide, two phases at a {Cl}/{Ln} ratio of 0.4, and Ln(OH) 2Cl phases are found. Equilibria in the bromide systems are more complex; Ln(OH) 3, Ln7(OH) 18Br 3, a high-temperature phase at {Br}/{Ln} = 0.45, Ln 3O(OH) 5Br 2, and Ln(OH) 2Br are observed. A single iodide-containing phase, Ln(OH) 2.67I 0.33, is found. X-Ray diffraction data are reported for all the previously unreported phases and the thermal decomposition behaviors of representative phases are described. The results of a single-crystal X-ray structure determination of orthorhombic ( Pmmn) Gd 2O(OH) 5Br 2 are reported and discussed.

Lance-Gomez, Edward Theodore; Haschke, John M.

1980-12-01

190

PLENARY SESSIONMatter transport in ionic crystals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The analysis of transport measurements on ionic crystals in terms of defect models is facilitated if some of the defect parameters can be determined from separate experiments, such as NMR measurements, or from theoretical calculations. This paper shows how the calculation of point defect parameters has proved useful in resolving a number of transport problems in the alkali and silver halides. The growing measure of concurrence between the results of analyses based on macroscopic (ionic conduc...

1980-01-01

191

Carbon monoxide adsorption on alkali and proton-exchanged chabazite: an ab-initio periodic study using the CRYSTAL code  

Science.gov (United States)

Ab initio periodic calculations based on local Gaussian basis sets as coded in the CRYSTAL program have been performed to investigate the structure, the binding energy and the vibrational features of carbon monoxide adsorbed on H+, Li+, Na+ and K+-exchanged chabazite (Si/Al = 11/1, i.e. one Al atom per unit cell). The hybrid B3LYP functional has been adopted for all calculations with a polarized double-zeta quality basis set. The B3LYP binding energies (BSSE corrected) are 16.0, 24.6, 20.4 and 5.1 kJ/mol for H+, Li+, Na+ and K+-exchanged chabazite, respectively. Corresponding CO hypsochromic stretching frequency shifts are 47, 68, 43 and 33 cm-1, respectively. Comparison with the case of CO interacting with bare alkali cations and the available experimental data on a variety of zeolites has also been addressed.

Ugliengo, P.; Busco, C.; Civalleri, B.; Zicovich-Wilson, C. M.

192

Ultraviolet laser ablation of halides and oxides  

International Nuclear Information System (INIS)

We compare and contrast recent measurements of the behavior of ions and excited ions desorbed from samples of alkali halides and oxide ferroelectrics by an excimer laser at 308 nm wavelength. At the intensities used in these experiments, the density of local electronic excitation is low in the halides and high in the ferroelectrics, corresponding to two- and one-photon band-to-band transitions, respectively. The observed desorption yields and changes in the sample surfaces are discussed in terms of the density of electronic excitation, the relative strengths of electron-lattice coupling, and the role of thermal relaxation processes in the two materials. (orig.)

1992-03-01

193

Electrodepositions on Tantalum in Alkali Halide Melts  

DEFF Research Database (Denmark)

Surface layers of tantalum metal were electrodeposited on steel from K2TaF7-LiF-NaF-KF melts. With careful control of the oxide contents dense and adherent deposits could be obtained by pulse plating. In NaCl-KCl-NaF-Na2CO3 and NaCl-KCl-Na2CO3 melts carbonate ions seems to be reduced to carbon in a single 4 electron step. By electrolyses at a constant potential of â?? 1.4 V vs. Pt in a NaCl-KCl-NaF-Na2CO3 melt at 800 oC coherent carbon containing surface layers could be obtained on tantalum substrates, when a CO2 atmosphere was applied

Barner, Jens H. Von; Jensen, Annemette Hindhede

2013-01-01

194

Sputtering of alkali halides under ion bombardment  

International Nuclear Information System (INIS)

New measurements prove the point that under any circumstances the halogen is primarily sputtered, and this at a very high rate. This high yield was found to be proportional to the electronic stopping power and to be far in excess of what can be explained by 'normal' collision cascades or replacement collision sequences (following a Pooley process). These 'giant' sputtering yields can only be explained by contributions from deeper layers of the bulk (a few thousand aengstroems, depending on temperature). The only theoretical model consistent with the above observations, and the fact that the sputtered atoms are found in a cosine angular distribution and in a Maxwell energy distribution, proves to be the following: H centers as defects of lowest energy and longest lifetime migrate in a random walk until eventually getting trapped at the surface, where they provide the neutral halogen atom which can be removed thermally. This mechanism will be explained in some detail. (orig.)

1982-07-01

195

High Temperature Thermal Expansion of Alkali Halides.  

Science.gov (United States)

Thermal expansion data for 11 sodium chloride structure-type solids have been evaluated with an empirical modified quasi-harmonic model for thermal expansion. Earlier it was shown for Group 4 elements and 10 Grimm-Sommerfeld compounds that an empirical qu...

K. Wang R. R. Reeber

1995-01-01

196

Crystal structure and magnetic properties of two new cobalt selenite halides: Co5(SeO3)4 X 2 (X=Cl, Br)  

International Nuclear Information System (INIS)

Two new isostructural cobalt selenite halides Co5(SeO3)4Cl2 and Co5(SeO3)4Br2 have been synthesized. They crystallize in the triclinic system space group P-1 with the following lattice parameters for Co5(SeO3)4Cl2: a=6.4935(8) A, b=7.7288(8) A, c=7.7443(10) A, ?=66.051(11)o, ?=73.610(11)o, ?=81.268(9)o, and Z=1. The crystal structures were solved from single-crystal X-ray data, R1=3.73 and 4.03 for Co5(SeO3)4Cl2 and Co5(SeO3)4Br2, respectively. The new compounds are isostructural to Ni5(SeO3)4Br2. Magnetic susceptibility measurements on oriented single-crystalline samples show anisotropic response in a broad temperature range. The anisotropic susceptibility is quantitatively interpreted within the zero-field splitting schemes for Co2+ and Ni2+ ions. Sharp low-temperature susceptibility features, at T N=18 and 20 K for Co5(SeO3)4Cl2 and Co5(SeO3)4Br2, respectively, are ascribed to antiferromagnetic ordering in a minority magnetic subsystem. In isostructural Ni5(SeO3)4Br2 magnetically ordered subsystem represents a majority fraction (T N=46 K). Nevertheless, anisotropic susceptibility of Ni5(SeO3)4Br2 is dominated at low temperatures by a minority fraction, subject to single-ion anisotropy effects and increasing population of Sz =0 (singlet) ground state of octahedrally coordinated Ni2+. - Graphical abstract: Two new iso-structural cobalt selenite halides Co5(SeO3)4Cl2 and Co5(SeO3)4Br2 have been synthesized which are iso-structural to Ni5(SeO3)4Br2. Magnetic susceptibility measurements on oriented single-crystalline samples show anisotropic response in a broad temperature range, revealing significant single-ion anisotropy effects

2007-03-01

197

Subvalent bismuth monocation Bi+ photoluminescence in ternary halide crystals KAlCl4 and KMgCl3  

International Nuclear Information System (INIS)

Monocation Bi+ isomorphically substitutes potassium in KAlCl4 and KMgCl3 chlorides. Having the unique 6p2 open-shell electronic configuration, Bi+ possesses a number of low-lying excited states, and displays broadband long-lived NIR photoluminescence in ternary chloride crystals. - Highlights: ? Monocation Bi+ can isomorphically substitute K+ in ternary chloride crystals. ? Bi+ doped ternary chlorides can be crystallized from Lewis acidic melts. ? Bi+ doped ternary chlorides possess broadband NIR luminescence.

2013-02-01

198

Dynamics of Defects in X-Ray Irradiated Alkali Chloride Crystals Studied by Positron Annihilation.  

Science.gov (United States)

This thesis reports first data on the time dependence of positron-electron annihilation characteristics in single crystals of the homologous series NaCl, KCl, RbCl, and CsCl after large doses of x irradiation. A new instrument, the (pi)-radian coincidence apparatus (PICA), recorded the coincidence count rate P of the two 0.5-MeV annihilation (gamma) rays emerging 180(DEGREES) apart from the crystal during isothermal and isochronal heating conditions. In most crystals one observes an initial rapid increase of P to a maximum followed by a slow decline toward the coincidence count rate corresponding to the pre-irradiation state of the crystal. Positron-annihilation data were completed by independent measurements of the optical absorption in KCl and NaCl crystals after various durations of isothermal heating. Absorption spectrophotometry revealed enhancement of the M band in KCl, of the R and N bands in NaCl, at the expense of the F band during the interval of increasing P. The PICA results are consistent with the interpretation that positrons are trapped by radiation-induced color centers in which they annihilate with a higher P than in the bulk of the crystal. The dynamics associated with the incipient rise of P during the initial heating period is attributable to the agglomeration of F centers into aggregate centers. The rise times of P give access to the diffusion rates for agglomeration. At equal temperatures, we observe a strong dependence of the rate of defect diffusion on the size of the cation. For example, it is 100 times faster in CsCl than in NaCl at 120(DEGREES)C. The data must be corrected for the effects of decoloration of the crystals by the positrons during the measurements. Activation energies for defect diffusion annealing are extracted. They test the hypotheses underlying the theories of macroscopic transport properties in these crystals in that they are indicative of the dominant microscopic lattice processes and their dependence on the crystal composition.

Stern, Stanley Hy.

199

An electron spin resonance study of cubic Fe"3"+ in alkali chloride crystals  

International Nuclear Information System (INIS)

Cubic Fe"3"+ is formed by X-irradiating LiCl:Fe crystals grown in a reactive atmosphere. Thin spin Hamiltonian parameters are consistent with the Fe/sub cub/"3"+ center, earlier observed in AgCl and NaCl, consisting of an interstitial Fe"3"+ forming a tetrahedral (FeCl_4)"- complex, the four nearest-neighbour cation sites being vacant. The superhyperfine structure analysis in samples containing "5"7Fe enriched iron gives the hyperfine splitting "5"7A = (9.4 +- 0.5) x 10"-"4 cm"-"1. No such center is found in KCl:Fe and RbCl:Fe crystals. (author)

1986-11-01

200

Measurement of the index of refraction of ?m crystals by a confocal laser microscope - Potential application for the refractive index mapping of ?m scale  

Science.gov (United States)

A conventional laser microscope can be used to derive the index of refractivity by the ratio of geometrical height of the transparent platelet to the apparent height of the normal incident light for very small crystals in the wide size range. We demonstrate that the simple method is effective for the samples from 100 ?m to 16 ?m in size using alkali halide crystals as a model system. The method is also applied for the surface fractured micro-crystals and an inclined crystal with microscopic size regime. Furthermore, we present two-dimensional refractive index mapping as well as two-dimensional height profile for the mixture of three alkali halides, KCl, KI, and NaCl, all are ?m in size.

Kimura, Keisaku; Sato, Seiichi

2014-05-01

 
 
 
 
201

Persistent vibrational spectral hole burning and dephasing properties of orientationally aligned CN- defects in cesium halide crystals  

Science.gov (United States)

Persistent spectral hole burning was used to study the dephasing mechanism of vibrationally excited K+:CN- pair defects in cesium chloride crystals. The K+:CN- pair defects are formed by statistical association of CN- and K+ doping impurities. They occur in two nonequivalent oppositely oriented configurations (CN-:K+ or NC-:K+) with corresponding spectrally separated transitions. Continuous optical excitation of either configuration in its second-harmonic transition (near 4000 cm-1) with a narrow-linewidth color-center laser leads to 180° CN- flips in spectrally selected K+:CN- defects. This produces, with efficiencies in the 10-5 range, a spectral hole in the laser-excited transition and a corresponding (slightly broadened) antihole in the other transition. The spectral holes were burned, and both the holes and antiholes were probed with the same single-mode-tunable color-center laser. Measurements of the holewidth under variation of defect concentration and crystal temperature reveal that the excited-state dephasing of the K+:CN- pair defects is strongly influenced by the motional behavior (tunneling, hindered rotation) of the isolated, i.e., not K+-associated, CN- molecules. The low-temperature (T=5 K) residual holewidth (as low as 20 MHz) is attributed to an elastic dipole-dipole interaction between the excited K+:CN- defect and the isolated CN- molecules. We discuss this mechanism in an elastic-continuum model where the isolated CN- molecules, which tunnel rapidly at this temperature between their eight equilibrium orientations, are the source of fluctuating strain fields in the crystal and cause ``dynamic strain broadening.'' The holewidth varies linearly with the concentration of the isolated CN- molecules, in agreement with the model. Under temperature increase the homogeneous linewidth broadens with a T2 dependence up to the ~40 K thermal-stability limit of the spectral holes. This T2 behavior far below the Debye temperature (TD=165 K for CsCl) indicates a non-Debye effective phonon density of states with a large number of low-frequency modes participating in the dephasing of the K+:CN- defects. In fact, the experimental data are consistent with theory for Raman scattering of phonons peaking in their density of states in the 10-cm-1 range. Candidates for this excitation are hindered-rotor levels of isolated CN- molecules or possibly an internal low-frequency mode of the K+:CN- defect itself.

Schrempel, M.; Gellermann, W.; Luty, F.

1992-05-01

202

Halide Adsorption on Single-crystal Silver Substrates Dynamic Simulations and ab-initio Density-functional Theory  

CERN Multimedia

We investigate the static and dynamic behaviors of a Br adlayer electrochemically deposited onto single-crystal Ag(100) using an off-lattice model of the adlayer. Unlike previous studies using a lattice-gas model, the off-lattice model allows adparticles to be located at any position within a two-dimensional approximation to the substrate. Interactions with the substrate are approximated by a corrugation potential. Using Density Functional Theory (DFT) to calculate surface binding energies, a sinusoidal approximation to the corrugation potential is constructed. A variety of techniques, including Monte Carlo and Langevin simulations, are used to study the behavior of the adlayer. The lateral root-mean-square (rms) deviation of the adparticles from the binding sites is presented along with equilibrium coverage isotherms, and the thermally activated Arrhenius barrier-hopping model used in previous dynamic Monte Carlo simulations is tested.

Mitchell, S J; Rikvold, P A; Wang, Sanwu

2002-01-01

203

Framework solids based on copper(II) halides (Cl/Br) and methylene-bridged bis(1-hydroxybenzotriazole): synthesis, crystal structures, magneto-structural correlation, and density functional theory (DFT) studies.  

Science.gov (United States)

A methylene-bridged 1-hydroxybenzotriazole derived ligand L [L = 1, 3-bis(benzotriazol-1-yl)-1,3-dioxapropane] has been synthesized and characterized by spectroscopic and structural methods. Reaction of L with two different copper(II) halides [CuX(2); X = Br, Cl] in an identical condition yields two different compounds of similar compositions, {[Cu(?-Br)(Br)(?-L)](2)}(n)·2nH(2)O (1) and {[Cu(?-Cl)(Cl)(?-L)](2)}(n)·2nH(2)O (2), both being characterized by various physicochemical techniques. Single crystal X-ray studies reveal that they appear as 2D coordination polymers with similar bridging fashion of L. Low temperature magnetic susceptibility measurements reveal antiferromagnetic and ferromagnetic behaviors for 1 and 2 with magnetic coupling constants J = -15.2 and +1.7 cm(-1), which are in a reasonable agreement with their calculated values (J = -9.79 and +0.68 cm(-1) respectively, for 1 and 2). The role of bridging halides in the structure and magnetic properties of the complexes are investigated, and a possible magneto-structural correlation has been established. Influence of spin density of bridging halides on the magnitude of coupling constants has been discussed with the help of density functional theory (DFT) calculations. PMID:22974283

Sasmal, Ashok; Shit, Shyamapada; Rizzoli, Corrado; Wang, Hongfeng; Desplanches, Cédric; Mitra, Samiran

2012-10-01

204

Self-Trapped Excitons in Ionic-Covalent Silver Halide Crystals and Nanostructures: High-Frequency EPR, ESE, ENDOR and ODMR Studies.  

Science.gov (United States)

Silver halides have unique features in solid state physics because their properties are considered to be of borderline nature between ionic and covalent bonding. In AgCl, the self-trapped hole (STH) is centered and partly trapped in the cationic sublattice, forming an Ag(2+) ion inside of a (AgCl(6))(4-) complex as a result of the Jahn-Teller distortion. The STH in AgCl can capture an electron from the conduction band forming the self-trapped exciton (STE). Recent results of a study of STE by means of high-frequency electron paramagnetic resonance, electron spin echo, electron-nuclear double resonance (ENDOR) and optically detected magnetic resonance (ODMR) are reviewed. The properties of the STE in AgCl crystals, such as exchange coupling, the ordering of the triplet and singlet sublevels, the dynamical properties of the singlet and triplet states, and the hyperfine interaction with the Ag and Cl (Br) nuclei are discussed. Direct information about the spatial distribution of the wave function of STE unpaired electrons was obtained by ENDOR. From a comparison with the results of an ENDOR study of the shallow electron center and STH, it is concluded that the electron is mainly contained in a hydrogen-like 1s orbital with a Bohr radius of 15.1 ± 0.6 Å, but near its center the electron density reflects the charge distribution of the hole. The hole of the STE is virtually identical to an isolated STH center. For AgCl nanocrystals embedded into the KCl crystalline matrix, the anisotropy of the g-factor of STE and STH was found to be substantially reduced compared with that of bulk AgCl crystals, which can be explained by a considerable suppression of the Jahn-Teller effect in nanoparticles. A study of ODMR in AgBr nanocrystals in KBr revealed spatial confinement effects and allowed estimating the nanocrystal size from the shape of the ODMR spectra. PMID:21151483

Baranov, P G; Romanov, N G; Poluektov, O G; Schmidt, J

2010-12-01

205

Syntheses and crystal structures of quaternary chalcogenides containing rare earth and coinage metals : with an appendix on alkali metal thiotellurates  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The main purpose of this work was to extend the knowledge about quaternary rare-earth metal coinage-metal chalcogenides containing alkali-metals toward heavy chalcogens, and then to explore the possibility of accommodating other possible metal(I)-cations instead of the alkalimetals.

Babo, Jean-marie

2010-01-01

206

Effect of alkali metal Oxides on viscosity and crystallization of the MgO–Al2O3–SiO2 glasses  

International Nuclear Information System (INIS)

MgO–Al2O3–SiO2 glasses were prepared by using TiO2 and ZrO2 as nucleation agents, and 2% (wt%, the same as below) content of alkali metal oxide was added. The viscosity of MAS glass melt was investigated by the rotating crucible viscometer, and the melting temperature and activation energy for viscous flow of the melt were derived by the Arrhenius equation. After melting and casting, the glass samples were crystallized in the temperature range from 880 to 1145 °C. The prepared glass-ceramics presented transparent to opaque with the increasing of crystallization temperature, which had been investigated by X-ray diffraction and field emission–environment scanning electron microscope. The results showed that the melting temperature of glass containing 2% Na2O was about 1585 °C. The MgAl2O4, ZrTiO4 and the sapphirine crystalline phases precipitated from matrix glass successively as the crystallization temperature raising. When 1% Na2O was replaced by Li2O, the melting temperature of the glasses decreased to 1508 °C, meanwhile, the main crystal phase changed from MgAl2O4 to high-/low—quartz solid solution, therefore, the crystallization behavior was uncontrollable and the transparent glass ceramic cannot be obtained. As 1% K2O substituted for Na2O, the melting temperature decreased to 1573 °C. The adding of K2O could broaden the crystallization temperature range of preparing transparent glass-ceramics. After crystallized at the range from 900 °C to 1000 °C, the fine spinel (MgAl2O4) crystals which had average size about 25 nm precipitated from matrix glasses, and the specimens kept transparent

2013-04-15

207

Effect of alkali metal Oxides on viscosity and crystallization of the MgO–Al{sub 2}O{sub 3}–SiO{sub 2} glasses  

Energy Technology Data Exchange (ETDEWEB)

MgO–Al{sub 2}O{sub 3}–SiO{sub 2} glasses were prepared by using TiO{sub 2} and ZrO{sub 2} as nucleation agents, and 2% (wt%, the same as below) content of alkali metal oxide was added. The viscosity of MAS glass melt was investigated by the rotating crucible viscometer, and the melting temperature and activation energy for viscous flow of the melt were derived by the Arrhenius equation. After melting and casting, the glass samples were crystallized in the temperature range from 880 to 1145 °C. The prepared glass-ceramics presented transparent to opaque with the increasing of crystallization temperature, which had been investigated by X-ray diffraction and field emission–environment scanning electron microscope. The results showed that the melting temperature of glass containing 2% Na{sub 2}O was about 1585 °C. The MgAl{sub 2}O{sub 4}, ZrTiO{sub 4} and the sapphirine crystalline phases precipitated from matrix glass successively as the crystallization temperature raising. When 1% Na{sub 2}O was replaced by Li{sub 2}O, the melting temperature of the glasses decreased to 1508 °C, meanwhile, the main crystal phase changed from MgAl{sub 2}O{sub 4} to high-/low—quartz solid solution, therefore, the crystallization behavior was uncontrollable and the transparent glass ceramic cannot be obtained. As 1% K{sub 2}O substituted for Na{sub 2}O, the melting temperature decreased to 1573 °C. The adding of K{sub 2}O could broaden the crystallization temperature range of preparing transparent glass-ceramics. After crystallized at the range from 900 °C to 1000 °C, the fine spinel (MgAl{sub 2}O{sub 4}) crystals which had average size about 25 nm precipitated from matrix glasses, and the specimens kept transparent.

Wang, Jing, E-mail: wangjing7683@sina.com [State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070 (China); Cheng, Jin-shu; Deng, Zhen-lu [State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070 (China)

2013-04-15

208

Theoretical and experimental study of the Stark effect in the ground state of alkali atoms in helium crystals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis work describes a detailed study of the Stark interaction in the ground state of cesium atoms trapped in a solid helium matrix. The motivation for the investigation of electric field effects on alkali species implanted in solid helium is related to the original main goal of our experimental activities, i.e., the measurement of a permanent atomic electric dipole moment (EDM). The existence of an atomic EDM simultaneously violates the discrete symmetries of time reversal (T) and pari...

Ulzega, Simone; Weis, Antoine

2007-01-01

209

Photochemistry of Phenyl Halides  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have studied fundamental aspects of photo-induced dissociation kinetics and dynamics in several phenyl halides. By combining femtosecond pump-probe measurements with ab initio calculations we are able to account for several observations. In mixed phenyl halides, the dissociation kinetics is found to be dependent on the nature, the number, and the position of the substituents, and also on the excitation wavelength. A surprisingly large reduction in the dissociation time constant, compared t...

Karlsson, Daniel

2008-01-01

210

Weak itinerant ferromagnetism and electronic and crystal structures of alkali-metal iron antimonides: Na Fe4 Sb12 and K Fe4 Sb12  

Science.gov (United States)

The synthesis, chemical, structural, and magnetic properties of alkali-metal compounds with filled-skutterudite structure, NaFe4Sb12 and KFe4Sb12 , are described. X-ray and neutron diffraction and elemental analysis established the crystal structure without defects and disorder on the cation site. The temperature and pressure dependence of the cubic unit cell of NaFe4Sb12 and the displacement parameter of Na are investigated. The electronic structure is calculated by density functional methods (LMTO, FPLO). Quantum chemical calculations (electron localization function) reveal the covalent character of both Fe-Sb and Sb-Sb interactions. Electronic structure calculations within the local density approximation exhibit a band ferromagnetic ground state and predict a half-metallic behavior. In contrast to isostructural alkaline-earth compounds ( CaFe4Sb12 and BaFe4Sb12 ), the alkali-metal skutterudites are itinerant electron ferromagnets with small magnetic moments ( ?0.25?B/Fe atom) and TC?85K . Yet the paramagnetic moments of all four compounds are between 1.5?B and 1.7?B per Fe atom, indicating similar Stoner factors. Temperature-dependent Fe57 and Sb121 Mössbauer spectroscopies confirm the ferromagnetic state in the sodium compound with very small hyperfine fields at the iron and antimony sites.

Leithe-Jasper, A.; Schnelle, W.; Rosner, H.; Baenitz, M.; Rabis, A.; Gippius, A. A.; Morozova, E. N.; Borrmann, H.; Burkhardt, U.; Ramlau, R.; Schwarz, U.; Mydosh, J. A.; Grin, Y.; Ksenofontov, V.; Reiman, S.

2004-12-01

211

Stability diagrams for fourfold coordination of polyvalent metal ions in molten mixtures of halide salts  

Energy Technology Data Exchange (ETDEWEB)

The stability of local fourfold coordination for divalent and trivalent metal ions in liquid mixtures of polyvalent metal halides and alkali halides is classified by means of structural coordinates obtained from properties of the elements. In parallel with earlier classifications of compound crystal structures and molecular shapes, the elemental properties are taken from first-principles calculations of valence electron orbitals in atoms, in the form of (i) the nodal radii of Andreoni, Baldereschi and Guizzetti or (ii) the pseudopotential radii or Zunger and Cohen. As a third alternative a classification based on Pettifor's phenomenological chemical scale of the elements is also considered. The alternative structural classification schemes that are developed from these elemental properties are generally successfully in distinguishing molten mixtures in which the available experimental evidence indicates long-lived fourfold coordination of polyvalent metal ions. In addition, Pettifor's chemical scale scheme is useful in sorting out finer details of local coordination in the liquid state. 3 figs., 71 refs.

Akdeniz, Z. (International Centre for Theoretical Physics, Trieste (Italy) Istanbul Univ. (Turkey). Dept. of Physics); Tosi, M.P. (Trieste Univ. (Italy). Dipt. di Fisica Teorica Argonne National Lab., IL (USA))

1988-11-01

212

Ternary molybdenum sulfides of the heavy alkali metals  

International Nuclear Information System (INIS)

Two series of ternary molybdenum sulfides, Asub(x)Mo4S6(A = K,Rb,Cs) and A2Mo15S20(A = K,Rb), were prepared by reduction of molybdenum disulfide with alkali metals in alkali halide melts at 1100-1300 K. All compounds are hexagonal and show electronic conductivity; structural characteristics suggest isolated [Mo/S]sup(x)-sub(infinity) chains as lattice elements for Asub(x)Mo4S6. (orig.)

1980-01-01

213

Theoretical characterization of dihydrogen adducts with halide anions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The interaction between a hydrogen molecule and the halide anions F-, Cl-, Br-, and I- has been studied at different levels of theory and with different basis sets. The most stable configurations of the complexes have a linear geometry, while the t-shaped complexes are saddle points on the potential energy surface, opposite to what is observed for alkali cations. An electrostatic analysis conducted on the resulting adducts has highlighted the predominance of the electrostatic term in the comp...

Zecchina, Adriano; Damin, Alessandro Ali; Ricchiardi, Gabriele; Vitillo, Jenny Grazia

2006-01-01

214

Self-Trapped Excitons in Ionic-Covalent Silver Halide Crystals and Nanostructures: High-Frequency EPR, ESE, ENDOR and ODMR Studies  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Silver halides have unique features in solid state physics because their properties are considered to be of borderline nature between ionic and covalent bonding. In AgCl, the self-trapped hole (STH) is centered and partly trapped in the cationic sublattice, forming an Ag2+ ion inside of a (AgCl6)4? complex as a result of the Jahn–Teller distortion. The STH in AgCl can capture an electron from the conduction band forming the self-trapped exciton (STE). Recent results of a study of STE by m...

Baranov, P. G.; Romanov, N. G.; Poluektov, O. G.; Schmidt, J.

2010-01-01

215

Bio-conventional bleaching of kadam kraft-AQ pulp by thermo-alkali-tolerant xylanases from two strains of Coprinellus disseminatus for extenuating adsorbable organic halides and improving strength with optical properties and energy conservation.  

Science.gov (United States)

Two novel thermo-alkali-tolerant crude xylanases namely MLK-01 (enzyme-A) and MLK-07 (enzyme-B) from Coprinellus disseminatus mitigated kappa numbers of Anthocephalus cadamba kraft-AQ pulps by 32.5 and 34.38%, improved brightness by 1.5 and 1.6% and viscosity by 5.75 and 6.47% after (A)XE(1) and (B)XE(1)-stages, respectively. The release of reducing sugars and chromophores was the highest during prebleaching of A. cadamba kraft-AQ pulp at enzyme doses of 5 and 10 IU/g, reaction times 90 and 120 min, reaction temperatures 75 and 65°C and consistency 10% for MLK-01 and MLK-07, respectively. MLK-07 was more efficient than MLK01 in terms of producing pulp brightness, improving mechanical strength properties and reducing pollution load. MLK-01 and MLK-07 reduced AOX by 19.51 and 42.77%, respectively at 4% chlorine demands with an increase in COD and colour due to removal of lignin carbohydrates complexes. A. cadamba kraft-AQ pulps treated with xylanases from MLK-01 to MLK-07 and followed by CEHH bleaching at half chlorine demand (2%) showed a drastic reduction in brightness with slight improvement in mechanical strength properties compared to pulp bleached at 4% chlorine demand. MLK-01 reduced AOX, COD and colour by 43.83, 39.03 and 27.71% and MLK-07 by 38.34, 40.48 and 30.77%, respectively at half chlorine demand compared to full chlorine demand (4%). pH variation during prebleaching of A. cadamba kraft-AQ pulps with strains MLK-01 and MLK-07 followed by CEHH bleaching sequences showed a decrease in pulp brightness, AOX, COD and colour with an increase in mechanical strength properties, pulp viscosity and PFI revolutions to get a beating level of 35 ± 1 °SR at full chlorine demand. PMID:22805918

Lal, Mohan; Dutt, Dharm; Tyagi, C H

2012-04-01

216

Optical properties and radiation damages of cerium fluoride crystals doped with alkali-earth and rare-earth elements  

International Nuclear Information System (INIS)

The most essential contribution in the investigation of CeF3 crystals having the goal to construct high precision electromagnetic calorimeters has been done by Crystal Clear Collaboration. Study of optical properties and radiation damages of Cerium Fluoride crystals doped with Ca, Ba, Sr, La, Nd, Zr and Hf in the wide range of concentrations has been performed with the goal to obtain high optical transparency of crystals at different cumulative doses under ?-irradiation. Time decay curves and relative light yields of scintillators as a function of doping level were measured using X-ray excitation of samples and single photon counting method

1994-04-04

217

Electrically excited mercury halide laser  

Energy Technology Data Exchange (ETDEWEB)

An improved electric-discharge-excited mercury halide dissociation laser operable on the (B-x) transitions in HgCl, HgBr and HgI at 558, 502 and 443 nm respectively is described. The laser discharge cell is elongated and made from temperature-resistant silicon-glass laminate or any other suitable material and includes separate ceramic crucibles for containing mercuric dihalide crystals. A pair of electrodes, each having external terminals, extend along the linear axis of the cell in parallel relationship with the linear axis and each other. Ultraviolet discharge means is also provided for preionizing a buffer gas of helium to which nitrogen has been added. The improvement comprises the addition of about 10% nitrogen to the buffer gas of helium which is admitted to the laser cell prior to excitation. The addition of nitrogen may act to selectively remove the terminal levels of the mercury halide laser transitions, thereby permitting more efficient extraction of the optical energy from the laser media. Thus improvements in both efficiency and output energy are obtained. The laser cavity is completed by a fully and a partially reflective surface for the wavelength of operation. The gases are preionized and excited by pulsed electrical energy from separate sources.

Burnham, R. L.

1980-10-28

218

Ternary halides of the A3MX6 type. V. Synthesis, crystal structures, and sodium ionic conductivity of the ternary iodides Na3MI6 (M=Sm,Gd-Dy) and of the solid solution halides Na3GdBr6-xIx  

International Nuclear Information System (INIS)

The system Na3GdBr6-xIx exhibits a complete solid solution. The influence of the successive substitution of iodide for bromide on structure and ionic conductivity has been investigated systematically. X-ray structure determination from single crystal and powder data shows that the cryolite-type of structure is observed for x 3GdBr5.1I0.9, monoclinic, P21/n, Z = 2, a = 734.6(10), b = 779.5(9), c = 1101(2) pm, ? = 90.8(2) [. For x > 3 the new Na3GdI6 type is observed [monoclinic, C2/m, Z = 2, a = 787.5(1), b 1353.4(2), c = 778.3(1) pm, ? = 110.14(1) ; for Na3GdBr2.4I3.6: a 772.7(4), b = 1323.3(7), c = 765.8(4) pm, ? = 110.14(3) [. In between, an ordered variant of the Na3GdI6 structure type is found with a doubled c axis [for Na3GdBr4.8I1.2: monoclinic, C2/c, Z = 4, a = 751.5(4), b 1285.7(6), c = 1413.7(7) pm, ? = 99,65(2) [. Ionic conductivity measurements by impedance spectroscopy exhibt a decline of the activation energies for Na+ conductivity for halides with unchanged crystal structures with increasing substitution by iodide. (orig.)

1997-05-01

219

Single crystal X-ray structure of Lawsone anion: Evidence for coordination of alkali metal ions and formation of naphthosemiquinone radical in basic media  

Science.gov (United States)

2-hydroxy-1,4-naphthoquinone; Lawsone (Lw) is a natural compound found in henna leaves. The reaction of lawsone with 'Na' metal (Lw-1), CH3COONa (Lw-2), NaOH (Lw-3), KOH (Lw-4), K2CO3 (Lw-5) and Tris(hydroxymethyl)aminomethane (Lw-6) were studied. Red orange solids obtained for Lw-1 to Lw-6 are characterized by Elemental Analysis, FTIR, 1HNMR and EPR studies. The results reveal the coordination of alkali metals 'Na' and 'K' to lawsone anion. The single crystal X-ray structure of Lw-6 was solved and it crystallizes in triclinic space group P-1 with extensive hydrogen bonding network of Csbnd H⋯O, Nsbnd H⋯O and Osbnd H⋯O between cations and anions. Polycrystalline powder X-band EPR spectra of Lw-1 to Lw-5 shows signals ˜2.004 at 133 K, while Lw-6 is EPR silent. The naphthosemiquinone (NSQ-rad ) radical formed in Lw-2 to Lw-5, is due to disproportion reaction of catechol and naphthoquinone.

Salunke-Gawali, Sunita; Kathawate, Laxmi; Shinde, Yogesh; Puranik, Vedavati G.; Weyhermüller, Thomas

2012-02-01

220

Metallic Halide Thiourea Compounds.  

Science.gov (United States)

Divalant metal halide-thiorea compounds are effective as extreme pressure additives in various lubricating compositions which include synthetic and mineral oil base lubricants. An intermediate N,N' or N,N,N'N', substituted thiourea is first synthesized an...

J. Ryer P. M. Kerschner W. C. Bradbury

1965-01-01

 
 
 
 
221

Thermochemical investigations to the high-temperature corrosion of polycrystalline alumina (PCA) by metal halides  

International Nuclear Information System (INIS)

The accomplished investigations in the context of the available work concerning the high-temperature corrosion of polycrystalline alumina (PCA) by halides of the alkalis and the lanthanides are from special interest in the lamp industry. Mixtures from alkali halides and halides of the lanthanides are an indispensable component of modern metal halide lamps. The halides of the lanthanides produce a very line-rich emission spectrum in the arc of the gas-discharge lamp within the visible range which is very close to that of the natural sunlight. Caused by the high temperatures and temperature gradients in a burner vessel chemical reactions between the lamp filling and the wall of the discharge vessel as well as the electrodes take place. Chemical transport can be observed, which can finally lead to a reduction of the wall thickness and to a failure of the lamp. The goal of this work is the clearing-up of the so far not understood mechanisms of the corrosion processes observed in metal halide lamps with PCA burners. For the improvement of the lamp characteristics it is finally the goal of describing these lamps in a computer-model in order to be able to make statements concerning the corrosion behavior. Apart from the understanding of the corrosion mechanisms it is important for the modelling to identify the formed corrosion phases and to determine their thermochemical data. The available work makes a contribution to this. (orig.)

2002-01-01

222

Optical properties of halide and oxide scintillators  

Energy Technology Data Exchange (ETDEWEB)

Knowledge of optical properties of scintillators is important both for the optimization of scintillator systems and the development of new materials particularly ceramic scintillators. Recent theoretical developments, especially new density functionals that enable accurate prediction of band gaps, have made it possible to perform quantitative calculations of the optical properties of scintillator materials. We used these techniques to obtain optical properties of a large number of high light output halide scintillators. These calculations showed that many halide scintillators have remarkably little optical anisotropy and may be good candidates for development as ceramic scintillators. These include materials such as CaI{sub 2}:Eu{sup 2+} that have very high light output and other favorable properties but are difficult to develop due to crystal growth issues. We review some of our recent results and present new results for CeCl{sub 3}.

Singh, David J [ORNL

2011-01-01

223

Crystallographic and fluorescence studies of the interaction of haloalkane dehalogenase with halide ions. Studies with halide compounds reveal a halide binding site in the active site.  

Science.gov (United States)

Haloalkane dehalogenase from Xanthobacter autotrophicus GJ10 catalyzes the conversion of 1,2-dichloroethane to 2-chloroethanol and chloride without use of oxygen or cofactors. The active site is situated in an internal cavity, which is accessible from the solvent, even in the crystal. Crystal structures of the dehalogenase enzyme complexed with iodoacetamide, chloroacetamide, iodide, and chloride at pH 6.2 and 8.2 revealed a halide binding site between the ring NH's of two tryptophan residues, Trp-125 and Trp-175, located in the active site. The halide ion lies on the intersection of the planes of the rings of the tryptophans. The binding of iodide and chloride to haloalkane dehalogenase caused a strong decrease in protein fluorescence. The decrease could be fitted to a modified form of the Stern-Volmer equation, indicating the presence of fluorophors of different accessibilities. Halide binding was much stronger at pH 6.0 than at pH 8.2. Assuming ligand binding to Trp-125 and Trp-175 as the sole cause of fluorescence quenching, dissociation constants at pH 6.0 with chloride and iodide were calculated to be 0.49 +/- 0.04 and 0.074 +/- 0.007 mM, respectively. Detailed structural investigation showed that the halide binding site probably stabilizes the halide product as well as the negatively charged transition state occurring during the formation of the covalent intermediate. PMID:8369276

Verschueren, K H; Kingma, J; Rozeboom, H J; Kalk, K H; Janssen, D B; Dijkstra, B W

1993-09-01

224

First examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands  

International Nuclear Information System (INIS)

Two new organic–inorganic compounds based on polyoxometalates, metal halide clusters and organic ligands: [BW12O40]2[Cu2(Phen)4Cl](H24, 4?-bpy)4·H3O·5H2O (1) and [HPW12O40][Cd2(Phen)4Cl2](4, 4?-bpy) (2) (Phen=1, 10-phenanthroline, bpy=bipyridine), have been prepared and characterized by IR, UV–vis, XPS, XRD and single crystal X-ray diffraction analyses. Crystal structure analyses reveal that compound 1 is constructed from [BW12O40]5?, metal halide clusters [Cu2(Phen)4Cl]+and 4, 4?-bpy ligands, while compound 2 is constructed from [PW12O40]3?, metal halide cluster [Cd2(Phen)4Cl2]2+ and 4, 4?-bpy ligands. Compound 1 and compound 2 are not common hybrids based on polyoxometalates and metal halide clusters, they also contain dissociated organic ligands, therefore, compound 1 and 2 are the first examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. - Graphical Abstract: Two new compounds have been synthesized and characterized. Structure analyses revealed that the two compounds are the first examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. Highlights: ? First examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. ? Two different kinds of metal halide clusters. ? Supramolecular structures based on polyoxometalates, metal halide clusters and organic ligands. ? Hybridization of three different of building blocks.

2012-07-01

225

Phase separation of crystal surfaces a lattice gas approach  

CERN Multimedia

We consider both equilibrium and kinetic aspects of the phase separation (``thermal faceting") of thermodynamically unstable crystal surfaces into a hill--valley structure. The model we study is an Ising lattice gas for a simple cubic crystal with nearest--neighbor attractive interactions and weak next--nearest--neighbor repulsive interactions. It is likely applicable to alkali halides with the sodium chloride structure. Emphasis is placed on the fact that the equilibrium crystal shape can be interpreted as a phase diagram and that the details of its structure tell us into which surface orientations an unstable surface will decompose. We find that, depending on the temperature and growth conditions, a number of interesting behaviors are expected. For a crystal in equilibrium with its vapor, these include a low temperature regime with logarithmically--slow separation into three symmetrically--equivalent facets, and a higher temperature regime where separation proceeds as a power law in time into an entire one-...

Shore, J D; Shore, Joel D; Bukman, Dirk Jan

1994-01-01

226

Preparation and characterization of cadmium(II) halide complexes with N-substituted glycines, and the crystal structures of dichloro(N-methylglycine)cadmium(II) and diaquadichloro(N,N-dimethylglycine)cadmium(II)  

International Nuclear Information System (INIS)

Eight cadmium(II) halide complexes with N-methylglycine (sarcosine, Hsar), N,N-dimethylglycine (Hdmgly), and N,N,N-trimethylglycine (betaine, Hbet) have been prepared and characterized by using their infrared absorption spectra and thermal analyses. In addition, the crystal and molecular structures of [CdCl2(Hsar)] (1) and [CdCl2(Hdmgly)(H2O)2] (2) were determined by a single-crystal X-ray diffraction method. The crystal data for these two complexes are as follows: Complex (1): monoclinic, space group P21/n, a=7.960(2), b=13.844(1), c=6.917(1) A, ?=92.42(2)deg, Z=4. Complex (2): monoclinic, space group P21/a, a=7.696(2), b=21.854(4), c=6.253(2) A, ?=103.69(2)deg, Z=4. These structures were solved by the heavy-atom method and refined by full-matrix least-square methods to final R values of 0.043 for 2533 reflections about 1 and 0.068 for 3615 reflections about 2, respectively. For 1 the structure consists of a one-dimensional polymer bridged by two chlorine atoms. The cadmium atom is hexa-coordinated, being ligated with two oxygen atoms of a carboxyl group and four chlorine atoms. For 2 the cadmium atom is in a distorted octahedral geometry, ligated by a carboxylato oxygen atom, two water molecules, and three chlorine atoms, in which one is terminal and the other two are bridging cadmium atoms to make a polymer. (author)

1994-12-01

227

Subvalent bismuth monocation Bi{sup +} photoluminescence in ternary halide crystals KAlCl{sub 4} and KMgCl{sub 3}  

Energy Technology Data Exchange (ETDEWEB)

Monocation Bi{sup +} isomorphically substitutes potassium in KAlCl{sub 4} and KMgCl{sub 3} chlorides. Having the unique 6p{sup 2} open-shell electronic configuration, Bi{sup +} possesses a number of low-lying excited states, and displays broadband long-lived NIR photoluminescence in ternary chloride crystals. - Highlights: Black-Right-Pointing-Pointer Monocation Bi{sup +} can isomorphically substitute K{sup +} in ternary chloride crystals. Black-Right-Pointing-Pointer Bi{sup +} doped ternary chlorides can be crystallized from Lewis acidic melts. Black-Right-Pointing-Pointer Bi{sup +} doped ternary chlorides possess broadband NIR luminescence.

Romanov, Alexey N., E-mail: alexey.romanov@list.ru [Research Computer Center of M.V. Lomonosov Moscow State University, 1 Leninskie Gory, Build. 4, 119991 Moscow (Russian Federation); Dimonta Ltd., 15 Nagornaya Str., Build. 8, 117186 Moscow (Russian Federation); Veber, Alexander A. [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, 38 Vavilov Str., 119991 Moscow (Russian Federation); Fattakhova, Zukhra T. [N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 4 Kosygina Str., 119991 Moscow (Russian Federation); Usovich, Olga V. [Department of Chemistry, M.V. Lomonosov Moscow State University, 1 Leninskie Gory, Build. 3, 119991 Moscow (Russian Federation); Haula, Elena V. [N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 4 Kosygina Str., 119991 Moscow (Russian Federation); Trusov, Lev. A.; Kazin, Pavel E. [Department of Chemistry, M.V. Lomonosov Moscow State University, 1 Leninskie Gory, Build. 3, 119991 Moscow (Russian Federation); Korchak, Vladimir N. [N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 4 Kosygina Str., 119991 Moscow (Russian Federation); Tsvetkov, Vladimir B. [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, 38 Vavilov Str., 119991 Moscow (Russian Federation); Sulimov, Vladimir B. [Research Computer Center of M.V. Lomonosov Moscow State University, 1 Leninskie Gory, Build. 4, 119991 Moscow (Russian Federation); Dimonta Ltd., 15 Nagornaya Str., Build. 8, 117186 Moscow (Russian Federation)

2013-02-15

228

Photolytic ?-elimination of organic halides from organotellurium (IV) halides  

International Nuclear Information System (INIS)

Irradiation of organotellurium (IV) halides in benzene affords the corresponding organic halide by ?-elimination, the carbon-halogen bond being formed at ipso-position and in some case retentively. The reaction is not affected by the presence or absence of oxygen and t-butoxy radical. (author)

1980-01-01

229

Dynamics of early stage defect production in irradiated alkali halides  

International Nuclear Information System (INIS)

The growth of F, H_D and V_2"m centres in X-irradiated KCl (0.01 mol% SrCl_2) has been studied as a function of temperature in the range 140 K to 185 K. The results show a dynamic, temperature-dependent saturation concentration of H_D centres, which decreases with increasing temperature of irradiation and partially recovers on re-irradiation at a lower temperature. The growth of F and V_2"m centres has a temperature dependence quite different from that obtained for irradiations performed at higher temperatures. The model of Comins and Carragher is in good agreement with the experimental results and accounts in detail for the complex, interrelated defect growth. Analysis of the rate equations of the model shows that in the limit of sufficiently high temperature the form of solution F(t)= sum _i?_i(1-e"-"?"_i"t) is obtained; this has been used in the past to provide empirical fits to F centre growth curves and demonstrates an overall unity in the approaches used. ((orig.))

1994-06-01

230

Temperature jump induction of isomerization dynamics of alkali halide clusters  

Energy Technology Data Exchange (ETDEWEB)

The time resolved dynamics of diffusionless cube->ring isomerization of the Na{sub 4}Cl{sub 4} cluster was interrogated by constant energy molecular dynamics simulations, utilizing the first passage time method. The nonreactive isomerization induced by nonselective vibrational excitation is well accounted for in terms of the statistical RRK theory, opening avenues for experimental exploration of time-resolved cluster isomerization dynamics. (orig.).

Heidenreich, A.; Schek, I.; Scharf, D.; Jortner, J. (Tel Aviv Univ. (Israel). School of Chemistry)

1991-01-01

231

Temperature jump induction of isomerization dynamics of alkali halide clusters  

International Nuclear Information System (INIS)

The time resolved dynamics of diffusionless cube?ring isomerization of the Na4Cl4 cluster was interrogated by constant energy molecular dynamics simulations, utilizing the first passage time method. The nonreactive isomerization induced by nonselective vibrational excitation is well accounted for in terms of the statistical RRK theory, opening avenues for experimental exploration of time-resolved cluster isomerization dynamics. (orig.)

1991-01-01

232

Single crystal growth by self-flux method of the mixed valence gold halides Cs2[AuIX2][AuIIIX4] (X=Br,I)  

Science.gov (United States)

High quality single crystals of Cs2Au2X6 (X=Br,I) were grown using a ternary self-flux method. Structural refinements based on single crystal X-ray diffraction measurements show that both materials have a distorted perovskite structure belonging to the I4/mmm space group with full site occupancy. Transport measurements reveal a large bandgap of 550±100 meV for Cs2Au2I6 and 520±80 meV for Cs2Au2Br6. Initial attempts at chemical substitution are described.

Riggs, Scott C.; Shapiro, M. C.; Corredor, F.; Geballe, T. H.; Fisher, I. R.; McCandless, Gregory T.; Chan, Julia Y.

2012-09-01

233

A Convenient Synthetic Strategy toward Heavy Alkali Metal Bis(trimethylsilyl)phosphides: Crystal Structures of the Ladder-Type Polymers [A(thf)P(SiMe(3))(2)](infinity) (A = K, Rb, Cs).  

Science.gov (United States)

A series of highly reactive heavy alkali metal phosphides was prepared by treating trimethylsilyl-substituted phosphines with alkali metal tert-butyl alcoholates. The compounds are formed in excellent yield and purity, and the side product can be easily removed in a vacuum. The high synthetic potential of this reaction route was further shown by utilizing excess alkali metal tert-butyl alcoholates in reaction with silyl substituted phosphines. In all cases, only monometalated products were isolated. In the course of this work the crystal structures of the bis(trimethylsilyl)phosphides [K(thf)P(SiMe(3))(2)](infinity), 1a, [Rb(thf)P(SiMe(3))(2)](infinity), 1b, and [Cs(thf)P(SiMe(3))(2)](infinity), 1c, were obtained. The compounds display polymeric ladder-type structures. Compounds 1a,b are isomorphous, while compound 1c displays a slightly altered local geometry. Despite small differences in local geometry, the coordination spheres for the phosphorus atoms and the alkali metal are fairly similar. The five coordinate phosphorus atoms are connected to three alkali metal centers in addition to two trimethylsilyl groups. The alkali metals are four coordinate with ligations to three phosphorus centers in addition to one thf oxygen donor. Compounds 1a-c were characterized using elemental analysis, NMR spectroscopy, and X-ray crystallography. Crystal data with Mo Kalpha (lambda = 0.710 73 Å) at 150 K are as follows: 1a, a = 6.4261(2) Å, b = 12.4119(2) Å, c = 21.5447(4) Å, V = 1718.41(7) Å(3), Z = 4, orthorhombic, space group P2(1)2(1)2(1), 3427 independent reflections, R1 (all data) = 0.0351; 1b, a = 6.5338(2) Å, b = 12.5664(3) Å, c = 21.5537(5) Å, V = 1769.70(8) Å(3), Z = 4, orthorhombic, space group P2(1)2(1)2(1), 4195 independent reflections, R1 (all data) = 0.0776; 1c, a = 11.3515(1) Å, b = 22.3445(3) Å, c = 7.2501(1) Å, beta = 96.017(1) degrees, V = 1828.81(4) Å(3), Z = 4, monoclinic, space group P2(1)/c, 4343 independent reflections, R1 (all data) = 0.0811. PMID:11670439

Englich, Ulrich; Hassler, Karl; Ruhlandt-Senge, Karin; Uhlig, Frank

1998-07-13

234

Exciton-relaxation dynamics in lead halides  

International Nuclear Information System (INIS)

We survey recent comprehensive studies of exciton relaxation in the crystals of lead halides. The luminescence and electron-spin-resonance studies have revealed that excitons in lead bromide spontaneously dissociate and both electrons and holes get self-trapped individually. Similar relaxation has been also clarified in lead chloride. The electron-hole separation is ascribed to repulsive correlation via acoustic phonons. Besides, on the basis of the temperature profiles of self-trapped states, we discuss the origin of luminescence components which are mainly induced under one-photon excitation into the exciton band in lead fluoride, lead chloride, and lead bromide

2003-05-01

235

Exciton-relaxation dynamics in lead halides  

Energy Technology Data Exchange (ETDEWEB)

We survey recent comprehensive studies of exciton relaxation in the crystals of lead halides. The luminescence and electron-spin-resonance studies have revealed that excitons in lead bromide spontaneously dissociate and both electrons and holes get self-trapped individually. Similar relaxation has been also clarified in lead chloride. The electron-hole separation is ascribed to repulsive correlation via acoustic phonons. Besides, on the basis of the temperature profiles of self-trapped states, we discuss the origin of luminescence components which are mainly induced under one-photon excitation into the exciton band in lead fluoride, lead chloride, and lead bromide.

Iwanaga, Masanobu E-mail: iwanaga@phys.h.kyoto-u.ac.jp; Hayashi, Tetsusuke

2003-05-01

236

Exciton-relaxation dynamics in lead halides  

CERN Document Server

We survey recent comprehensive studies of exciton relaxation in the crystals of lead halides. The luminescence and electron-spin-resonance studies have revealed that excitons in lead bromide spontaneously dissociate and both electrons and holes get self-trapped individually. Similar relaxation has been also clarified in lead chloride. The electron-hole separation is ascribed to repulsive correlation via acoustic phonons. Besides, on the basis of the temperature profiles of self-trapped states, we discuss the origin of luminescence components which are mainly induced under one-photon excitation into the exciton band in lead fluoride, lead chloride, and lead bromide.

Iwanaga, M; Iwanaga, Masanobu; Hayashi, Tetsusuke

2003-01-01

237

Studies on multiphased mixed crystals grown from NaBr and KCl  

International Nuclear Information System (INIS)

We have grown multiphased binary and ternary mixed crystals by the melt method using the miscible alkali halides, viz. NaBr and KCl and physically characterized. Thermal parameters like Debye-Waller factor, Debye temperature, Debye frequency and mean square amplitude of vibration were determined using the X-ray powder diffraction intensity data. DC and AC electrical measurements were carried out by using the parallel plate capacitor method at various temperatures. Activation energies (DC and AC), mean jump frequency, compressibility and mean sound velocity were also determined. The results obtained are reported here

2008-05-01

238

Studies on multiphased mixed crystals grown from NaBr and KCl  

Energy Technology Data Exchange (ETDEWEB)

We have grown multiphased binary and ternary mixed crystals by the melt method using the miscible alkali halides, viz. NaBr and KCl and physically characterized. Thermal parameters like Debye-Waller factor, Debye temperature, Debye frequency and mean square amplitude of vibration were determined using the X-ray powder diffraction intensity data. DC and AC electrical measurements were carried out by using the parallel plate capacitor method at various temperatures. Activation energies (DC and AC), mean jump frequency, compressibility and mean sound velocity were also determined. The results obtained are reported here.

Padma, C.M. [Physics Research Centre, S.T. Hindu College, Nagercoil 629 002, Tamilnadu (India); Mahadevan, C.K. [Physics Research Centre, S.T. Hindu College, Nagercoil 629 002, Tamilnadu (India)], E-mail: mahadevan58@yahoo.co.in

2008-05-01

239

Oscillatory rule in the energy spectrum of traps in KCl and NaI crystals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The thermoluminescence (TL) method is used for the investigation of the energy spectrum of traps in KCl and NaI crystals in the temperature range 80-500 K. It is shown that the thermal activation energies of traps in KCl and NaI form one oscillatory series E=hwn with vibrational quantum energies of 0.121 eV in KCl and 0.061 eV in NaI. In this case, the quantum number n assumes half-integer and integer values. Based on the generalized data on the investigated alkali-halide cr...

Gumenyuk, A. F.; Kutovyi, S. Yu; Stanovyi, O. P.; Pashchenko, V. G.; Tomylko, S. V.

2010-01-01

240

Solution enthalpies of trivalent defects in alkali chlorides  

Energy Technology Data Exchange (ETDEWEB)

Calculations of the heat of formation of dilute solid solutions of AlCl/sub 3/, ScCl/sub 3/, GaCl/sub 3/, YCl/sub 3/, and InCl/sub 3/ in each of the three alkali chlorides NaCl, KCl, and RbCl are reported. The Born-Mayer repulsive parameters (B-M RPs) for nearest-neighbour interaction and the solution enthalpies of trivalent defects in alkali halides have been derived from the correlation between B-M RPs and the charge density overlap parameters of the interacting ions.

Bandyopadhyay, S.; Deb, S.K. (Kalyani Univ. (India). Dept. of Physics)

1984-12-01

 
 
 
 
241

Stability analysis for complexes in calcium-alkali bromide solutions  

International Nuclear Information System (INIS)

We discuss the dependence of the stability of tetrahedral complexes in molten halide mixtures on the halogen species. This is done by calculating the equilibrium concentration of (CaBr4)2- complexes in calcium-alkali bromide solutions as a function of composition, in comparison with earlier calculations on the calcium-alkali chloride systems. The comparison supports a possible trend of increasing stability from chlorides to bromides, provided that halogen polarizability or chemical bonding contribute appreciably to the binding of a complex. Supporting evidence is noted and further experiments are suggested. (author). 10 refs, 2 figs

1988-01-01

242

Chemical ionization of pentacarbonylrhenium halides in vapors of water, methanol and ethanol  

International Nuclear Information System (INIS)

The behaviour of pentacarbonylrhenium (PCR) halides at the chemical ionization in vapors of water, methanol and ethanol is studied by the method of mass-spectrometry. Energy of ionizing electron beam is 90 eV, temperature of ionizing chamber is 170-200 deg C. It is found out that ?-linked with metal halide atom is the most active group in Re(Co)_5X complexes, with tendency to detachment and displacement in ionizing water vapors as well as in vapors of some simplest alkalies

1985-01-01

243

Effect of the nature of alkali and alkaline-earth oxides on the structure and crystallization of an alumino-borosilicate glass developed to immobilize highly concentrated nuclear waste solutions  

International Nuclear Information System (INIS)

A complex rare-earth rich alumino-borosilicate glass has been proved to be a good candidate for the immobilization of new high level radioactive wastes. A simplified seven-oxides composition of this glass was selected for this study. In this system, sodium and calcium cations were supposed in other works to simulate respectively all the other alkali (R+ = Li+, Rb+, Cs+) and alkaline-earth (R2+ = Sr2+, Ba2+) cations present in the complex glass composition. Moreover, neodymium or lanthanum are used here to simulate all the rare-earths and actinides occurring in waste solutions. In order to study the impact of the nature of R+ and R2+ cations on both glass structure and melt crystallization tendency during cooling, two glass series were prepared by replacing either Na+ or Ca2+ cations in the simplified glass by respectively (Li+, K+, Rb+, Cs+) or (Mg2+, Sr2+, Ba2+) cations. From these substitutions, it was established that alkali ions are preferentially involved in the charge compensation of (AlO4)- entities in the glass network comparatively to alkaline-earth ions. The glass compositions containing calcium give way to the crystallization of an apatite silicate phase bearing calcium and rare-earth ions. The melt crystallization tendency during cooling strongly varies with the nature of the alkaline-earth. (authors)

2008-05-19

244

Intrinsic luminescence of alkali silicate glasses  

International Nuclear Information System (INIS)

This study obtains additional information on L centers and their role in electron excitation and intrinsic luminescence of a whole series. (Li, Na, K, Rb, and Cs) of alkali silicate glasses. The authors compare the features of the interaction with radiation of specimens of glass and crystal of a similar chemical composition, since silicates of alkali metals can be obtained in both the glassy and crystalline states

1986-09-01

245

Alkali metal intercalates of molybdenum disulfide.  

Science.gov (United States)

Study of some of the physicochemical properties of compounds obtained by subjecting natural molybdenite and single crystals of molybdenum disulfide grown by chemical vapor transport to intercalation with the alkali group of metals (Li, Na, K, Rb, and Cs) by means of the liquid ammonia technique. Reported data and results include: (1) the intercalation of the entire alkali metal group, (2) stoichiometries and X-ray data on all of the compounds, and (3) superconductivity data for all the intercalation compounds.

Somoano, R. B.; Hadek, V.; Rembaum, A.

1973-01-01

246

Synthesis, characterization, crystal structure determination and computational study of the two new bidentate O, N Schiff bases derived from bromosalicylaldehyde and amines containing alkyl halide pendant groups  

Science.gov (United States)

Two new Schiff base compounds 2-{(E)-[2-(bromoethyl)imino]methyl}-4-bromophenol (1) and 2-{(E)-[2-(chloroethyl)imino]methyl}-4-bromophenol (2) have been synthesized and characterized by FT-IR and 1H NMR spectroscopy, elemental analysis, thermal studies and single-crystal X-ray diffraction. They crystallize in the triclinic system, space group P-1. Both Schiff base compounds 1 and 2 display a trans configuration with respect to the CN double bond. Quantum theory of atoms in molecules (QTAIM) has been also used to find intramolecular interactions and investigate their chemical nature. The results show that in both of the compounds 1 and 2, there is a hydrogen bonding between nitrogen of imine and oxygen of phenol which is considerably stronger than normal hydrogen bonds. In addition, it has been shown that these hydrogen bonds are partially covalent and partially electrostatic in nature, in contrast to normal hydrogen bonds, which are usually considered as electrostatic interactions.

Grivani, Gholamhossein; Tahmasebi, Vida; Eskandari, Keiamars; Khalaji, Aliakbar Dehno; Bruno, Giuseppe; Rudbari, Hadi Amiri

2013-12-01

247

Specificity of structure of zinc(2) halides with cyclic tetraaminne ligands. Crystal structures of ZnCyclamX2, X=Cl, Br, I  

International Nuclear Information System (INIS)

Crystal structure of ZnCyclamX2, X=Cl, Br, I, Cyclam(C10H24N4)=1,4,8,11-tetraazacyclotetradecane, was defined. The complexes are monomer tetragonally-bipyramid structures with meso-planar conformation Cyclam. Metal atoms is statistically shifted from equatorial plane by 0.24 A in case X=Cl; 0.33 A - X=Br; and 0.40 A - X=I. Secondary (elongated) axial bonds are nonequilibrium: Zn-Cl 2.424(8) and 2.0905(8) A, Zn-Br 2.555(4) and 3.214(4) A; Zn-I 2.753(1) and 3.543(1) A. Judging by geometry of the complexes and 13C[1H]NMR data statistical shift of Zn is dynamic character. The assumption is made that intramolecular motion increases stability of the complexes and characterizes specific type of binding, inherent of d10-metal complexes. It is shown that antibate correlation in the lengths of equatorial and axial bonds ascertained for slightly distorted octahedral complexes is just both for pyramid and bipyramid complexes with axial long-range action

1994-03-01

248

Actinide halide complexes  

Energy Technology Data Exchange (ETDEWEB)

A compound of the formula MX.sub.n L.sub.m wherein M is a metal atom selected from the group consisting of thorium, plutonium, neptunium or americium, X is a halide atom, n is an integer selected from the group of three or four, L is a coordinating ligand selected from the group consisting of aprotic Lewis bases having an oxygen-, nitrogen-, sulfur-, or phosphorus-donor, and m is an integer selected from the group of three or four for monodentate ligands or is the integer two for bidentate ligands, where the sum of n+m equals seven or eight for monodentate ligands or five or six for bidentate ligands, a compound of the formula MX.sub.n wherein M, X, and n are as previously defined, and a process of preparing such actinide metal compounds including admixing the actinide metal in an aprotic Lewis base as a coordinating solvent in the presence of a halogen-containing oxidant, are provided.

Avens, Larry R. (Los Alamos, NM); Zwick, Bill D. (Santa Fe, NM); Sattelberger, Alfred P. (Los Alamos, NM); Clark, David L. (Los Alamos, NM); Watkin, John G. (Los Alamos, NM)

1992-01-01

249

Elastic properties of cubic crystals: Every's versus Blackman's diagram  

International Nuclear Information System (INIS)

Blackman's diagram of two dimensionless ratios of elastic constants is frequently used to correlate elastic properties of cubic crystals with interatomic bondings. Every's diagram of a different set of two dimensionless variables was used by us for classification of various properties of such crystals. We compare these two ways of characterization of elastic properties of cubic materials and consider the description of various groups of materials, e.g. simple metals, oxides, and alkali halides. With exception of intermediate valent compounds, the correlation coefficients for Every's diagrams of various groups of materials are greater than for Blackaman's diagrams, revealing the existence of a linear relationship between two dimensionless Every's variables. Alignment of elements and compounds along lines of constant Poisson's ratio v((100), m), (m arbitrary perpendicular to (100)) is observed. Division of the stability region in Blackman's diagram into region of complete auxetics, auxetics and non-auxetics is introduced. Correlations of a scaling and an acoustic anisotropy parameter are considered

2008-03-01

250

Coacervation of Aqueous Solutions of Tetraalkylammonium Halides.  

Science.gov (United States)

The coacervation of aqueous solutions of tatraalkylammonium halides in the presence of not of inorganic halides and acids has been studied, considering thermodynamic and spectroscopic aspects. The importance of dispersion forces as well as forces resultin...

A. Mugnier de Trobriand

1979-01-01

251

Research Update: Physical and electrical characteristics of lead halide perovskites for solar cell applications  

Directory of Open Access Journals (Sweden)

Full Text Available The field of thin-film photovoltaics has been recently enriched by the introduction of lead halide perovskites as absorber materials, which allow low-cost synthesis of solar cells with efficiencies exceeding 16%. The exact impact of the perovskite crystal structure and composition on the optoelectronic properties of the material are not fully understood. Our progress report highlights the knowledge gained about lead halide perovskites with a focus on physical and optoelectronic properties. We discuss the crystal and band structure of perovskite materials currently implemented in solar cells and the impact of the crystal properties on ferroelectricity, ambipolarity, and the properties of excitons.

Simon A. Bretschneider

2014-04-01

252

Polar binary Zn/Cd-rich intermetallics: Synthesis, crystal and electronic structure of A(Zn/Cd){sub 13} (A = alkali/alkaline earth) and Cs{sub 1.34}Zn{sub 16}  

Energy Technology Data Exchange (ETDEWEB)

The binary alkali/alkaline earth (A) zinc and cadmium (M) compounds that form the NaZn{sub 13} structure type (cubic, space group Fm3-bar c), which were known only from indexed X-ray powder diagrams, have been synthesized from stoichiometric mixtures of the elements and have been structurally characterized using a combination of single crystal data and the Rietveld method. The alkali zinc phases A{sup I}Zn{sub 13} are only formed with the lighter alkali elements sodium to rubidium (A{sup I}=Na: a -bar =-bar 1227.3(2)-bar pm, R1=0.0205;A{sup I}=K: a -bar =-bar 1237.9(3)-bar pm, R1=0.0154;A{sup I}=Rb: a -bar =-bar 1245.19(1)-bar pm, R{sub p}=0.0250), whereas the cadmium compounds A{sup I} Cd{sub 13} are stable only for the heavier alkali metals potassium to cesium (A{sup I}=K: a -bar =-bar 1379.2(4)-bar pm, R1=0.0118;A{sup I}=Rb: a -bar =-bar 1384.5(2)-bar pm, R1=0.0139;A{sup I}=Cs: a -bar =-bar 1392.0(3)-bar pm, R1=0.0381). In the crystal structures M-centered M(2)M(1){sub 12} icosahedra are connected via strong exobonds (forming tetrahedral stars, stella quadrangula) to form a 3D net, in the interstices of which the alkali metals are located in a snub cube 24 coordination. In contrast, the alkaline earth (A{sup II}) zinc compounds with calcium, strontium and barium (A{sup II}=Ca: a -bar =-bar 1215.4(1)-bar pm, R1=0.0274;A{sup II}=Sr: a -bar =-bar 1222.2(2)-bar pm, R1=0.0154;A{sup II}=Ba: a -bar =-bar 1235.8(2)-bar pm, R1=0.0227) show statistical defects at the Zn(2) position centering the Zn(1) icosahedra. Both the geometric and the electronic stability of the NaZn{sub 13} structure type, which can be assessed from the pseudo-bandgap calculated using FP-LAPW-DFT methods, are discussed. In contrast to the aforementioned systems, the NaZn{sub 13} type ceases to exist in the binary system Cs-Zn. In this case a phase Cs{sub 1.36}Zn{sub 16} with a new structure type but very similar stoichiometry emerges. This compound is the first and only known phase in the system Cs-Zn and crystallizes with a new incommensurably modulated structure: its average structure (orthorhombic, space group Imma, a=264.2(5) -bar pm,b=720.8(14) -bar pm,c=1760(5) -bar pm, R1=0.0198) already indicates the representative structural features: in a 3D net of Zn atoms tubular channels filled by the Cs atoms are formed. This Cs filling is, due to geometric requirements, not commensurate with the Zn host structure resulting in a modulated structure with satellite reflections that can be indexed with a q-> vector of (0,-bar 0,-bar 0.2755). The final refinement in the superspace group (Pcn2(00g)sso,a=1760(5) -bar pm,b=720.8(14) -bar pm,c=264.2(5) -bar pm, wR{sub main}=0.0550,wR{sub satellites}=0.140) shows a strong occupational and a weak positional modulation of Cs in the channels formed by the Zn partial structure.

Wendorff, Marco [Institut fuer Anorganische und Analytische Chemie, Universitaet Freiburg/Brsg. (Germany); Roehr, Caroline [Institut fuer Anorganische und Analytische Chemie, Universitaet Freiburg/Brsg. (Germany)]. E-mail: caroline@ruby.chemie.uni-freiburg.de

2006-09-14

253

Hall Determination of Atomic Radii of Alkali Metals  

Science.gov (United States)

I will propose here an alternative method for determining atomic radii of alkali metals based on the Hall measurements of their free electron densities and the knowledge of their crystal structure. (Contains 2 figures.)

Houari, Ahmed

2008-01-01

254

Alkali metal hydride formation  

International Nuclear Information System (INIS)

The present invention relates to a method of producing alkali metal hydrides by absorbing hydrogen gas under pressure into a mixture of lower alkyl mono amines and alkali metal alkyl amides selected from sodium and potassium amides formed from said amines. The present invention also includes purification of a mixture of the amines and amides which contain impurities, such as is used as a catalytic exchange liquid in the enrichment of deuterium, involving the formation of the alkali metal hydride

1975-03-27

255

Growth, Morphology and Solid State Miscibility of Alkali Nitrates  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This PhD thesis is focused in structural aspects of alkali nitrates. In the first chapter, we recollected the most important advancement in this field in alkali nitrates compounds published since 1970. Along this lines, crystal structure, polymorphism and phase transition is discussed first; second, crystal growth, and third, the morphology. And, finally a section concerning solid state miscibility and binary phase diagrams between these compounds is presented.

Benages Vilau, Rau?l

2013-01-01

256

Growth, Morphology and Solid State Miscibility of Alkali Nitrates  

Digital Repository Infrastructure Vision for European Research (DRIVER)

[eng] This PhD thesis is focused in structural aspects of alkali nitrates. In the first chapter, we recollected the most important advancement in this field in alkali nitrates compounds published since 1970. Along this lines, crystal structure, polymorphism and phase transition is discussed first; second, crystal growth, and third, the morphology. And, finally a section concerning solid state miscibility and binary phase diagrams between these compounds is presented. The following chapters pr...

Benages Vilau, Rau?l

2013-01-01

257

Effect of the nature of alkali and alkaline-earth oxides on the structure and crystallization of an aluminoborosilicate glass developed to immobilize highly concentrated nuclear waste solutions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A complex rare-earth rich aluminoborosilicate glass has been proved to be a good candidate for the immobilization of new high level radioactive wastes. A simplified seven-oxides composition of this glass was selected for this study. In this system, sodium and calcium cations were supposed in other works to simulate respectively all the other alkali (R+=Li+, Rb+, Cs+) and alkaline-earth (R'2+=Sr2+, Ba2+) cations present in the complex glass composition. Moreover, neodymium or lanthanum are use...

Quintas, Arnaud; Caurant, Daniel; Maje?rus, Odile; Charpentier, Thibault; Dussossoy, Jean-luc

2008-01-01

258

Liquid + liquid equilibrium in mixtures of lithium fluoride with potassium and rubidium halides  

International Nuclear Information System (INIS)

Highlights: ? We measured electrical conductivity of the dissolving melts of LiF with KBr, KI, RbBr, and RbI along the saturation line. ? We studied a transient layer between the coexisting phases. ? The difference between the conductivities of phases increases as the radius of ion grows. ? An essential reorganisation of the light phase was found near the critical solution point. - Abstract: The liquid + liquid phase equilibrium of molten mixtures of lithium fluoride with potassium and rubidium halides was investigated over an extended temperature range in the two-phase region along the saturation line by the electrical conductivity method. In the overwhelming majority of mixtures, the electrical conductivity for coexisting equilibrium phases increased when the temperature increased. For mixtures with only potassium bromide, it decreased because of the extensive solubility of potassium bromide in lithium fluoride. The electrical conductivity for the light phase was half the value of the conductivity of the pure lithium fluoride. The electrical conductivity of the heavy phase did not differ enough from the conductivity of the pure heavy alkali halides. At the same time, the solubility of the heavy component in LiF was many times less than the lithium fluoride solubility in the lower phase. This contradiction points to essential reorganisation of the structure of the light phase. The difference between the conductivities of the coexisting phases at equal temperatures increased as the radius of the halide anion or alkali cation grew. The temperature growth led to the increase in the conductivity difference along the saturation line for mixtures of LiF with RbI. For mixtures of LiF with lighter alkali halides, it decreased up to zero at the critical mixing point for LiF + KBr mixtures as the temperature increased. Between the coexisting equilibrium phases, a transient layer was revealed, where a conductivity gradient exists. The thickness of this layer decreased as the temperature decreased and the sum of the ionic radii of the mixtures increased.

2012-08-01

259

Thermochemical investigations to the high-temperature corrosion of polycrystalline alumina (PCA) by metal halides; Thermochemische Untersuchungen zur Hochtemperaturkorrosion von polykristallinem Aluminiumoxid (PCA) durch Metallhalogenide  

Energy Technology Data Exchange (ETDEWEB)

The accomplished investigations in the context of the available work concerning the high-temperature corrosion of polycrystalline alumina (PCA) by halides of the alkalis and the lanthanides are from special interest in the lamp industry. Mixtures from alkali halides and halides of the lanthanides are an indispensable component of modern metal halide lamps. The halides of the lanthanides produce a very line-rich emission spectrum in the arc of the gas-discharge lamp within the visible range which is very close to that of the natural sunlight. Caused by the high temperatures and temperature gradients in a burner vessel chemical reactions between the lamp filling and the wall of the discharge vessel as well as the electrodes take place. Chemical transport can be observed, which can finally lead to a reduction of the wall thickness and to a failure of the lamp. The goal of this work is the clearing-up of the so far not understood mechanisms of the corrosion processes observed in metal halide lamps with PCA burners. For the improvement of the lamp characteristics it is finally the goal of describing these lamps in a computer-model in order to be able to make statements concerning the corrosion behavior. Apart from the understanding of the corrosion mechanisms it is important for the modelling to identify the formed corrosion phases and to determine their thermochemical data. The available work makes a contribution to this. (orig.)

Markus, T.

2002-01-01

260

Reactivity of 2-pyridinecarboxylic esters with cadmium(II) halides: study of (113)Cd NMR solid state spectra and crystal structures of hexacoordinated complexes [CdI(2)(C(5)H(4)NCOOMe)(2)] and [CdI(2)(C(5)H(4)NCOOPr(n))(2)].  

Science.gov (United States)

The series of complexes [CdX(2)(C(5)H(4)NCOOR)] (X = Cl or Br; R = Me, Et, Pr(n)() or Pr(i)()) and [CdX(2)(C(5)H(4)NCOOR)(2)] (X = I; R = Me, Et, Pr(n)(), or Pr(i)()) have been obtained by the addition reaction of esters of 2-pyridinecarboxylic acid to cadmium(II) halides. X-ray crystal structures of two complexes [CdI(2)(C(5)H(4)NCOOR)(2)], R = Me (10) and R = Pr(n)() (12), have been determined. In both cases, the structure consists of discrete neutral monomeric units where the cadmium atom has a distorted octahedral coordination with CdI(2)N(2)O(2) core, two halides being in cis disposition. Structural information is compared with that deduced from (113)Cd CPMAS NMR experiments. Chemical shift anisotropies are discussed in terms of distortions produced in cadmium octahedra. The orientation of the principal axes of (113)Cd shielding tensor is also analyzed and related to the disposition of ligands in the structures of two analyzed compounds. PMID:14606835

March, Ricard; Pons, Josefina; Ros, Josep; Clegg, William; Alvarez-Larena, Angel; Piniella, Joan Francesc; Sanz, Jesus

2003-11-17

 
 
 
 
261

Analytical applications of alkali metal tetrahydridoborates  

Energy Technology Data Exchange (ETDEWEB)

The analysis of physicochemical, thermodynamic and analytical properties of alkali metal tetrahydridoborates is made. The crystal structure of the compounds, their state in different solutions, ways of their preparation are considered. A conclusion is made that alkali metal tetrahydridoborates are of interest as reagents able to reduce ions of many elements to different oxidation degrees. They also can be used as titrants. The use of the reactions with the participation of NaBH/sub 4/ and KBH/sub 4/ to develop highly sensitive methods of kinetic determination of ultralow amounts of alements is very prospective.

Khain, V.S. (Ukhtinskij Industrial' nyj Inst. (USSR))

1981-05-01

262

Charged-soft-sphere potentials for trivalent metal halides  

International Nuclear Information System (INIS)

Octahedral-type coordination by halogens in the liquid state has been reported for a number of trivalent metal ions from diffraction and Raman scattering experiments on their molten trihalides and from Raman scattering spectroscopy of liquid mixtures of trihalides with alkali halides. We analyze the available data on bond lengths and Raman frequencies by treating an isolated (MX_6)"3"- species within a model which adopts charged-soft-sphere interionic potentials supplemented by an account of ionic polarization. The trivalent metal ions that we consider are M = La, Ce, Pr, Nd, Sm, Gd, Dy and Y for X = Cl and M = Al for X = F. The main result of the analysis is the prediction of trends in the soft-sphere repulsive parameters for the trivalent metal ions, leading to estimates of all the vibrational frequencies and the binding energy of such octahedral species. (author). 26 refs, 1 fig., 4 tabs

1991-01-01

263

Structure and properties of lanthanide halides  

Science.gov (United States)

Lanthanum and cerium bromides and chlorides form isomorphous alloy systems with the UCl 3 type structure. These scintillating alloys exhibit high luminosity and proportional response, making them the first scintillators comparable to room temperature semiconductors for gamma spectroscopy; Ce(III) activated lanthanum bromide has recently enabled scintillating gamma ray spectrometers with < 3% FWHM energy resolutions at 662 keV. However brittle fracture of these materials impedes development of large volume crystals. Low fracture stress and perfect cleavage along prismatic planes cause material cracking during and after crystal growth. These and other properties pose challenges for material production and post processing; therefore, understanding mechanical behavior is key to fabricating large single crystals, and engineering of robust detectors and systems. Recent progress on basic structure and properties of the lanthanide halides is reported here, including thermomechanical and thermogravimetric analyses, hygroscopicity, yield strength, and fracture toughness. Observations including reversible hydrate formation under atmospheric pressure, loss of stoichiometry at high temperature, anisotropic thermal expansion, reactivity towards common crucible materials, and crack initiation and propagation under applied loads are reported. The fundamental physical and chemical properties of this system introduce challenges for material processing, scale-up, and detector fabrication. Analysis of the symmetry and crystal structure of this system suggests possible mechanisms for deformation and crack initiation under stress. The low c/a ratio and low symmetry relative to traditional scintillators indicate limited and highly anisotropic plasticity cause redistribution of residual process stress to cleavage planes, initiating fracture. This proposed failure mechanism and its implications for scale up to large diameter crystal growth are also discussed.

Doty, F. P.; McGregor, Douglas; Harrison, Mark; Findley, Kip; Polichar, Raulf

2007-10-01

264

Organic halide electroreduction on silver  

Energy Technology Data Exchange (ETDEWEB)

Silver, whose extraordinary electrolytically properties for organic halide reduction have been recently evidenced, has been used as cathode material for systematic preparative electrolyses in membrane-divided cells. To better elucidate the substrate role on the remarkable positive shift of reduction potentials, and on the cage effect i. e. the promotion of intermolecular reaction on adsorbed intermediates, three halide substrate patterns are here compared in terms of both voltammetric characterization and preparative electroreduction products: aliphatic halides (adamantanes), aromatic halides (phenols) and anomeric glycosyl halides. The preparative electroreductions result mainly in dimerization in the case of glycosyl halides, in H {yields} Br substitution in the case of bromophenols, in dimerization + substitution in the case of haloadamantanes. The product analysis, both at the end of the reaction and at intermediate times, allows discussing the reaction pathways in terms of intermediate stability and of active surface accessibility. The possibility of complete dehalogenation on a wider substrate variety with remarkably lower energy consumption and almost quantitative current yields makes the process potentially very interesting for environmental purposes. [Italian] L'argento, di cui sono state recentemente evidenziate straordinarie proprieta' elettrocatalitiche per la riduzione degli alogenuri organici, e' stato utilizzato come materiale catodico per sistematiche elettrolisi preparative in celle a membrana. Per mettere in risalto il ruolo del substrato organico sul notevole anticipo del potenziale di riduzione e sull'effetto gabbia, ovvero la promozione di reazioni intermolecolari su intermedi adsorbiti, vengono qui confrontate, in termini sia di caratterizzazione voltammetrica sia di prodotti di elettroriduzioni preparative, tre tipologie di alogenuri: alifatici (adamantani), aromatici (fenoli) e glicosidici. Le elettroriduzioni preparative danno luogo principalmente a dimerizzazione nel caso di glicosilalogenuri, a H {yields} Br sostituzione nel caso di bromofenoli, a dimerizzazione + sostituzione nel caso degli alogenoadamantani. L'analisi dei prodotti, sia al termine della reazione, sia a tempi intermedi e di accessibilita' della superficie attiva. La possibilita' di completa dealogenazione di una piu' vasta categoria di substrati con notevole riduzione del consumo energetico e rendimento di corrente pressoche' unitario conferisce al processo un potenziale notevole interesse ambientale.

Fiori, G.; Mussini, P.; Rondinini, S.; Vertova, A. [Milan Univ., Milan (Italy). Dept. of Physical Chemistry and Electrochemistry

2001-04-01

265

Correlations between entropy and volume of melting in halide salts  

International Nuclear Information System (INIS)

Melting parameters and transport coefficients in the melt are collated for halides of monovalent, divalent and trivalent metals. A number of systems show a deficit of entropy of melting relative to the linear relationships between entropy change and relative volume change on melting that are found to be approximately obeyed by a majority of halides. These behaviours are discussed on the basis of structural and transport data. The deviating systems are classified into three main classes, namely (i) fast-ion conductors in the high-temperature crystal phase such as AgI, (ii) strongly structured network-like systems such as ZnCl2, and (iii) molecular systems melting into associated molecular liquids such as SbCl3. (author). 35 refs, 1 fig., 3 tabs

1991-01-01

266

Melting and liquid structure of polyvalent metal halides  

International Nuclear Information System (INIS)

A short review is given of recent progress in determining and understanding liquid structure types and melting mechanisms for halides of polyvalent metals. The nature of the preferred local coordination for the polyvalent metal ion in the melt can usually be ascertained from data on liquid mixtures with halogen-donating alkali halides. The stability of these local coordination states and the connectivity that arises between them in the approach to the pure melt determines the character of its short-range and possible medium-range order. A broad classification of structural and melting behaviours can be given on the basis of measured melting parameters and transport coefficients for many compounds, in combination with the available diffraction data on the liquid structure of several compounds. Correlations have been shown to exist with a simple indicator of the nature of the chemical bond and also with appropriate parameters of ionic models, wherever the latter are usefully applicable for semiquantitative calculations of liquid structure. Consequences on the mechanisms for valence electron localization in solutions of metallic elements into strongly structured molten salts are also briefly discussed. (author). 46 refs, 4 figs, 2 tabs

1992-01-01

267

Materials discovery by crystal growth: Lanthanide metal containing oxides of the platinum group metals (Ru, Os, Ir, Rh, Pd, Pt) from molten alkali metal hydroxides  

International Nuclear Information System (INIS)

This review addresses the process of materials discovery via crystal growth, specifically of lanthanide metal containing oxides of the platinum group metals (Ru, Os, Ir, Rh, Pd, Pt). It provides a detailed overview of the use of hydroxide fluxes for crystal growth. The melt chemistry of hydroxide fluxes, specifically, the extensive acid base chemistry, the metal cation solubility, and the ability of hydroxide melts to oxidize metals are described. Furthermore, a general methodology for the successful crystal growth of oxides is provided, including a discussion of experimental considerations, suitable reaction vessels, reaction profiles and temperature ranges. Finally, a compilation of complex platinum group metal oxides recently synthesized using hydroxide melts, focusing on their crystal growth and crystal structures, is included. - Graphical abstract: A review that addresses the process of materials discovery via crystal growth using hydroxide fluxes. It provides a detailed overview of the use of hydroxide fluxes for crystal growth and describes the melt chemistry of hydroxide fluxes, specifically, the extensive acid base chemistry, the metal cation solubility, and the ability of hydroxide melts to oxidize metals. In addition, a compilation of complex platinum group metal oxides recently synthesized using hydroxide melts is included.

2009-07-01

268

K3[C3N3(COO)3] ? 2 H2O – Crystal Structure of a New Alkali Derivative of the Multidentate Ligand Triazine Tricarboxylate  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract Potassium-1,3,5-triazine-2,4,6-tricarboxylate dihydrate K3[C3N3(COO)3] · 2 H2O was obtained by saponification of the respective ethyl ester in aqueous solution under mild conditions and subsequent crystallization at 4 °C. The crystal structure of the molecular salt was elucidated by single-crystal X-ray diffraction (P-1, a = 6.9663(14), b = 17.485(3), c = 17.560(3) pm, ? = 119.73(3), ? = 91.96(3), ? = 93.84(3)°, V = 1847.6(6) · 106 pm3, Z = 6, T = 200 K). Perpendicu...

2010-01-01

269

Fine structures in the optical absorption spectra of photochemical silver in silver halides? A call for further research  

CERN Multimedia

A survey is presented of the work done so far to check earlier claims that a fine structure may be observed to occur under certain circumstances in the impurity spectral range of the optical absorption spectra of silver halides following photostimulation in the intrinsic range. This structure, associated with the photochemical formation of silver specks, has been questioned over the years. We now weigh carefully the experimental evidence on the silver halides against a background of similar data on the alkali halides, where competing processes run slower. We come to the conclusion that present day advances in experimental techniques may be quite adequate for providing a solid experimental basis to solve the problem unambiguously.

Georgiev, Mladen

2007-01-01

270

Pulse radiolysis of molten fluorides of alkali metals  

International Nuclear Information System (INIS)

Melts of mixtures of alkali metal flourides were investigated by pulse radiolysis with optical recording. The parameters of the optical spectra and radiation chemical yields of solvated electrons in these systems are close to the corresponding values in melts of other halides. The optical absorption of the oxidative component of radiolysis was detected; its parameters were substantially different from those in molten chlorides, bromides, and iodides, which may be associated with a rapid reaction of F3- formation. 9 refs., 4 figs., 1 tab

1992-11-01

271

Separation of alkali metals  

International Nuclear Information System (INIS)

A new environmentally friendly method of separation and purification of alkali metals, according to which gallium intermetallic compound (IC) with alkali metal is used instead of amalgam, while separation of alkali metal pairs occurs as a result of exchange between IC and aqueous solution of the metal hydroxide, has been developed. Influence of temperature and concentration of the exchanging phases on separation factor in the system LiGa - NaOH and LiGa - KOH is considered. Kinetic parameters of lithium, sodium and potassium exchange are ascertained. Comparison is made of characteristics of gallium IC base and amalgam-exchange systems studied

2003-06-01

272

First examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands  

Science.gov (United States)

Two new organic-inorganic compounds based on polyoxometalates, metal halide clusters and organic ligands: [BW12O40]2[Cu2(Phen)4Cl](H24, 4'-bpy)4·H3O·5H2O (1) and [HPW12O40][Cd2(Phen)4Cl2](4, 4'-bpy) (2) (Phen=1, 10-phenanthroline, bpy=bipyridine), have been prepared and characterized by IR, UV-vis, XPS, XRD and single crystal X-ray diffraction analyses. Crystal structure analyses reveal that compound 1 is constructed from [BW12O40]5-, metal halide clusters [Cu2(Phen)4Cl]+and 4, 4'-bpy ligands, while compound 2 is constructed from [PW12O40]3-, metal halide cluster [Cd2(Phen)4Cl2]2+ and 4, 4'-bpy ligands. Compound 1 and compound 2 are not common hybrids based on polyoxometalates and metal halide clusters, they also contain dissociated organic ligands, therefore, compound 1 and 2 are the first examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands.

Wang, La-Mei; Fan, Yong; Wang, Yan; Xiao, Li-Na; Hu, Yang-Yang; Peng, Yu; Wang, Tie-Gang; Gao, Zhong-Min; Zheng, Da-Fang; Cui, Xiao-Bing; Xu, Ji-Qing

2012-07-01

273

Synthesis of aryl halides via organoborane chemistry  

Energy Technology Data Exchange (ETDEWEB)

A method for the rapid synthesis of a variety of substituted aryl halides by the reaction of organoboranes with halide ions in the presence of chloramine-T is described in detail. The products were purified by column chromatography on silica gel using a mixture of petroleum ether-ethyl acetate as eluent.

Kabalka, G.W.; Sastry, K.A.R.; Sastry, U.; Somayaji, V.

1982-01-01

274

New layered manganese oxide halides.  

Science.gov (United States)

The first layered manganese(III) oxide chlorides, Sr2MnO3Cl and Sr4Mn3O8-yCl2, have been synthesised; Sr2MnO3Cl adopts a K2NiF4 type structure with sheets of MnO5 square based pyramids linked through oxygen and separated by SrCl layers; it is the end member of a new family of Ruddlesden-Popper type manganese oxide halides which includes the three-layer member Sr4Mn3O8-yCl2 also reported herein. PMID:12120392

Knee, Christopher S; Weller, Mark T

2002-02-01

275

Methods of recovering alkali metals  

Energy Technology Data Exchange (ETDEWEB)

Approaches for alkali metal extraction, sequestration and recovery are described. For example, a method of recovering alkali metals includes providing a CST or CST-like (e.g., small pore zeolite) material. The alkali metal species is scavenged from the liquid mixture by the CST or CST-like material. The alkali metal species is extracted from the CST or CST-like material.

Krumhansl, James L; Rigali, Mark J

2014-03-04

276

Structural and functional analysis of a novel haloalkane dehalogenase with two halide-binding sites.  

Science.gov (United States)

The crystal structure of the novel haloalkane dehalogenase DbeA from Bradyrhizobium elkanii USDA94 revealed the presence of two chloride ions buried in the protein interior. The first halide-binding site is involved in substrate binding and is present in all structurally characterized haloalkane dehalogenases. The second halide-binding site is unique to DbeA. To elucidate the role of the second halide-binding site in enzyme functionality, a two-point mutant lacking this site was constructed and characterized. These substitutions resulted in a shift in the substrate-specificity class and were accompanied by a decrease in enzyme activity, stability and the elimination of substrate inhibition. The changes in enzyme catalytic activity were attributed to deceleration of the rate-limiting hydrolytic step mediated by the lower basicity of the catalytic histidine. PMID:25004965

Chaloupkova, Radka; Prudnikova, Tatyana; Rezacova, Pavlina; Prokop, Zbynek; Koudelakova, Tana; Daniel, Lukas; Brezovsky, Jan; Ikeda-Ohtsubo, Wakako; Sato, Yukari; Kuty, Michal; Nagata, Yuji; Kuta Smatanova, Ivana; Damborsky, Jiri

2014-07-01

277

Alkali elemental and potassium isotopic compositions of Semarkona chondrules  

Science.gov (United States)

We report measurements of K isotope ratios in 28 Semarkona chondrules with a wide range of petrologic types and bulk compositions as well as the compositions of CPX-mesostasis pairs in 17 type I Semarkona chondrules, including two chondrules with radial alkali zonation and 19 type II chondrules. Despite the wide range in K/Al ratios, no systematic variations in K isotopic compositions were found. Semarkona chondrules do not record a simple history of Rayleigh-type loss of K. Experimentally determined evaporation rates suggest that considerable alkali evaporation would have occurred during chondrule formation. Nevertheless, based on Na CPX-mesostasis distribution coefficients, the alkali contents of the cores of most chondrules in Semarkona were probably established at the time of final crystallization. However, Na CPX-mesostasis distribution coefficients also show that alkali zonation in type I Semarkona chondrules was produced by entry of alkalis after solidification, probably during parent body alteration. This alkali metasomatism may have gone to completion in some chondrules. Our preferred explanation for the lack of systematic isotopic enrichments, even in alkali depleted type I chondrule cores, is that they exchanged with the ambient gas as they cooled. ?? The Meteoritical Society, 2005.

Alexander, C. M. O'D.; Grossman, J. N.

2005-01-01

278

Spectra of alkali atoms  

International Nuclear Information System (INIS)

Emission spectra of alkali atoms has been determined by using spectrometer at the ultraviolet to infra red waves range. The spectra emission can be obtained by absorption spectrophotometric analysis. Comparative evaluations between experimental data and data handbook obtained by spark method were also presented. (author tr.)

1980-01-01

279

Electron thermalization and trapping rates in pure and doped alkali and alkaline-earth iodide crystals studied by picosecond optical absorption  

Science.gov (United States)

Although light continues to be emitted from insulating crystals used as scintillators over a period of nanoseconds to microseconds after stopping of an energetic particle, much of what determines the nonlinearity of response goes on in the first picoseconds. On this time scale, free carriers and excitons are at high density near the track core and thus are subject to nonlinear quenching. The hot (free) electrons eventually cool to low enough energy that trapping on holes, dopants, or defects can commence. In the track environment, spatial distributions of trapped carriers determined on the picosecond time scale can influence the proportionality between light yield and the initial particle energy throughout the whole light pulse. Picosecond spectroscopy of optical absorption induced by a short pulse of above-gap excitation provides a useful window on what occurs during the crucial early evolution of excited populations. The laser excitation can be tuned to excite carriers that are initially very hot (˜3 eV) relative to the band edges, or that are almost thermalized (˜0.1 eV excess energy) at the outset. Undoped and doped samples of NaI:Tl(0%, 0.1%), CsI:Tl(0%, 0.01%, 0.04%, 0.3%), and SrI2:Eu(0%, 0.2%, 0.5%, 3%) are studied in this work.

Ucer, K. B.; Bizarri, G.; Burger, A.; Gektin, A.; Trefilova, L.; Williams, R. T.

2014-04-01

280

ICES studies on 99mTc-halide complexes: formation, hydrolysis and ligand exchange  

International Nuclear Information System (INIS)

The Internal Conversion Electron Spectroscopy (ICES) method was employed to study the products of reduction of no-carrier-added [99mTc]pertechnetate by concentrated hydrochloric, hydrobromic and hydroiodic acids. The reductions were carried out in vacuum with subbsequent evaporation of the solution to dryness. In the solid deposits, containing ? 10-9 g Tc, chemical shifts of 99mTc electron binding energies were measured and the results were compared with known data of x-ray photoelectron spectroscopy for defined technetium compounds. It was evidenced that all reduction/evaporation procedures yielded 99mTc(IV)-halide complexes. Another technique of reduction by vapours of halogen acids was proposed to prepare thin radioactive sources for physics studies. The reduction power of alkali halides in absence of acids was examined and a partial reduction of pertechnetate by iodide was found. The product was a hydrolysed species. The hydrolysis of halide complexes yielded the same product. In the absence of acids, dissolved species were partly oxidised to Tc(VII) by air. Oxidation was most apparent for the chloride and negligible for the iodide system. Ligand exchange of chloro and bromo complexes to chelate with DTPA at pH 3 was found to be uncomplete. Tc(IV) hydrolysed species, Tc(IV)DTPA and Tc(VII) were evidenced. Tc(V)DTPA was also observed which arises from partially oxidised products. (author)

1988-01-01

 
 
 
 
281

Reactive scattering of electronically excited alkali atoms with molecules  

International Nuclear Information System (INIS)

Representative families of excited alkali atom reactions have been studied using a crossed beam apparatus. For those alkali-molecule systems in which reactions are also known for ground state alkali and involve an early electron transfer step, no large differences are observed in the reactivity as Na is excited. More interesting are the reactions with hydrogen halides (HCl): it was found that adding electronic energy into Na changes the reaction mechanism. Early electron transfer is responsible of Na(5S, 4D) reactions, but not of Na(3P) reactions. Moreover, the NaCl product scattering is dominated by the HCl- repulsion in Na(5S, 4D) reactions, and by the NaCl-H repulsion in the case of Na(3P). The reaction of Na with O2 is of particular interest since it was found to be state specific. Only Na(4D) reacts, and the reaction requires restrictive constraints on the impact parameter and the reactants' relative orientation. The reaction with NO2 is even more complex since Na(4D) leads to the formation of NaO by two different pathways. It must be mentioned however, that the identification of NaO as product in these reactions has yet to be confirmed

1987-09-14

282

Modelling current transfer to cathodes in metal halide plasmas  

International Nuclear Information System (INIS)

This work is concerned with investigation of the main features of current transfer to cathodes under conditions characteristic of metal halide (MH) lamps. It is found that the presence of MHs in the gas phase results in a small decrease of the cathode surface temperature and of the near-cathode voltage drop in the diffuse mode of current transfer; the range of stability of the diffuse mode expands. Effects caused by a variation of the work function of the cathode surface owing to formation of a monolayer of alkali metal atoms on the surface are studied for particular cases where the monolayer is composed of sodium or caesium. It is found that the formation of the sodium monolayer affects the diffuse mode of current transfer only moderately and in the same direction that the presence of metal atoms in the gas phase affects it. Formation of the caesium monolayer produces a dramatic effect: the cathode surface temperature decreases very strongly, the diffuse-mode current-voltage characteristic becomes N-S-shaped

2005-09-07

283

IR analysis of polyvinylidene fluoride doped with transition metal halides  

Science.gov (United States)

Pure and doped polyvinylidene fluoride (PVDF) films were prepared by casting. Films with various concentrations of transition metal halides TMHs (AlCl3, ZnCl2, and CoCl2) were prepared. The microstructure and physical properties of these films were studied by IR analysis. The two factors affecting the interaction between the PVDF and MHs are (i) the dopant weight fraction (Hc) (0.05% -30%) by weght, and (ii) precasting time (tpc) which is the time during which the PVDF pellets are maintained solved with the halides added before casting. From the IR quantitative analysis, it is evident that the addition of the three MH to the undoped PVDF film makes ?-phase as the dominant crystalline structures in the doped films without the need for mechanical drawing treatment. The precasting time plays a role for new crystalline structures to appear which becomes strong for CoCl2 doping, moderate in ZnCl2 doping and weak in AlCl3 doping. This phase is maximum for the relatively low doping levels ZnCl2 and AlCl3. This result is extremely important hence the ?-phase is that one which is electrically active compared with the other two phases and it is needed in all the samples used in the useful applications of the PVF2 films. Remembering, that ?-phase is obtained in the crystallization from melt samples by the uneasy mechanical stress and elevated temperature, it becomes evident the importance of the present result.

El Hefnawy, Somia M.; Aboelkher, Mervet M.; Abdelkader, H.

2009-05-01

284

Structure of alkali metal fluorouranates (3)  

International Nuclear Information System (INIS)

X-ray analytical characteristics are presented, and the data on the structure of ternary uranium (3) fluorides and alcali metals obtained by inducing roentgenograms of polycrystals, are discussed. It is established that potassium, rubidium and cesium hexafluorouranates are crystallized in tetragonal cryolite-like lattices. The rest of fluorouranates (3) have lattices derived from the fluorite structure. For them, the correlation of the coordinate numbers of atoms of alkali metals and uranium Zsub(M)/Zsub(U) is 1.0+-0.2, and the structure is isodesmic

1981-04-01

285

Line shape of the low-energy tail of exciton absorption in molecular crystals  

Science.gov (United States)

The influence of crystal defects and phonons on the line shape of the low-energy tail of exciton absorption is calculated for molecular crystals with the lower limit of their exciton band at k-->=0. The exciton Hamiltonian for a crystal with lattice defects is derived from that for a perfect crystal with lattice vibrations. Calculation of the line shape is done assuming that the individual lattice defects have independent effects on the unperturbed exciton band. Three examples of the molecular exciton energy bands are considered: (1) one-dimensional tight-binding exciton band, (2) the exciton bands with Hubbard's model of density of states, and (3) exciton bands with density of states independent of the exciton energies. At very low temperatures where the influence of the defects is dominant, we have found the asymmetric low-energy tail due to defects, acting as shallow traps, in all the three examples. The observed asymmetric line shape in 1,2-dibromonaphthalene single crystals is, therefore, attributed to such shallow traps and analogous to the Urbach-Martienssen tail observed in alkali halides. As the temperature increases and phonons become more active, the line shape becomes symmetric due to the dominant influence of thermal broadening.

Singh, Jai

1981-02-01

286

Interaction of halides in ternary mutual systems in melt  

International Nuclear Information System (INIS)

The character of halides interaction in ternary mutual systems of diagonal type is analyzed. It is shown that the direction of exchange reaction and equilibrium state in the melt are determined by a halide solubility ratio. The interaction parameter (mixing heat) of the halides is calculated. Difficulty soluble salts in the melt are noted to behave as weak electrolytes

2001-01-01

287

Chlor-alkali electrolysis  

International Nuclear Information System (INIS)

The chlor-alkali industry produces simultaneously chlorine (Cl2) and caustic soda (NaOH) by decomposition of a salt solution in water. Additionally to the chlorine and caustic soda, hydrogen (H2) is produced. The global production capacity of chlorine in 1995 was approximately 44 million tons. The development of the chlorine production capacity in Western Europe since 1960 is presented. The most important chlorine producer in Western Europe is Germany with 38 % of the annual chlorine capacity of Western Europe. The chlorine capacity in 1997 in different Western European countries and their share an the total capacity in Western Europe is also presented. World-wide several processes are available for the production of chlorine and caustic soda. The most important routes are the following: ion exchange membrane process; mercury cell process; diaphragm process. Several other processes are available but do not have a significant contribution to the total production. The geographical distribution of the processes differs widely. In Japan the membrane process is predominate with 73 %, in the United States the diaphragm process with 75 %, whereas in Western Europe the mercury cell process is the most important one (64 %) [EIPPCB, 2000]. Approximately 65 % of the global chlorine capacity is located in these three regions. A comparison of the relative contribution of different production technologies to the chlor-alkali capacity in these three regions and in the world in 1994 is given. The distribution of processes and capacities of chlor-alkali plants in some European countries is presented (October 1999). Note that any one plant can have more than one cell technology installed. (author)

2001-01-01

288

Alkali metal vapor detector  

International Nuclear Information System (INIS)

This detector is characterized by a sensor including an electricity conductor element in gold and antimony, whose ends are related to two electric conductors; it includes also detection means, related to these conductors, of an important variation of the gold or antimony conductor electric resistance or of another electric quantity depending of this resistance; this variation results from the gold or antimony reaction with alkali metal vapors; it includes at last a safety device controlled by those detection means. This is used noticeably in the nuclear field and sodium cooled furnaces

1985-01-07

289

Infrared evanescent field sensing with quantum cascade lasers and planar silver halide waveguides.  

Science.gov (United States)

We demonstrate the first midinfrared evanescent field absorption measurements with an InGaAs/AlInAs/InP distributed feedback (DFB) quantum cascade laser (QCL) light source operated at room temperature coupled to a free-standing, thin-film, planar, silver halide waveguide. Two different analytes, each matched to the emission frequency of a QCL, were investigated to verify the potential of this technique. The emission of a 1650 cm(-1) QCL overlaps with the amide absorption band of urea, which was deposited from methanol solution, forming urea crystals at the waveguide surface after solvent evaporation. Solid urea was detected down to 80.7 microg of precipitate at the waveguide surface. The emission frequency of a 974 cm(-1) QCL overlaps with the CH3-C absorption feature of acetic anhydride. Solutions of acetic anhydride in acetonitrile have been detected down to a volume of 0.01 microL (10.8 microg) of acetic anhydride solution after deposition at the planar waveguide (PWG) surface. Free-standing, thin-film, planar, silver halide waveguides were produced by press-tapering heated, cylindrical, silver halide fiber segments to create waveguides with a thickness of 300-190 microm, a width of 3 mm, and a length of 35 mm. In addition, Fourier transform infrared (FT-IR) evanescent field absorption measurements with planar silver halide waveguides and transmission absorption QCL measurements verify the obtained results. PMID:16013852

Charlton, Christy; Katzir, Abraham; Mizaikoff, Boris

2005-07-15

290

Ternary halides of the A{sub 3}MX{sub 6} type. V. Synthesis, crystal structures, and sodium ionic conductivity of the ternary iodides Na{sub 3}MI{sub 6} (M=Sm,Gd-Dy) and of the solid solution halides Na{sub 3}GdBr{sub 6-x}I{sub x}; Ternaere Halogenide vom Type A{sub 3}MX{sub 6}. V. Synthese, Kristallstrukturen und Natrium-Ionenleitfaehigkeit der ternaeren Iodide Na{sub 3}MI{sub 6} (M=Sm,Gd-Dy) sowie der Mischkristalle Na{sub 3}GdBr{sub 6-x}I{sub x}  

Energy Technology Data Exchange (ETDEWEB)

The system Na{sub 3}GdBr{sub 6-x}I{sub x} exhibits a complete solid solution. The influence of the successive substitution of iodide for bromide on structure and ionic conductivity has been investigated systematically. X-ray structure determination from single crystal and powder data shows that the cryolite-type of structure is observed for x < 1 [Na{sub 3}GdBr{sub 5.1}I{sub 0.9}, monoclinic, P2{sub 1}/n, Z = 2, a = 734.6(10), b = 779.5(9), c = 1101(2) pm, {beta} = 90.8(2) ]. For x > 3 the new Na{sub 3}GdI{sub 6} type is observed [monoclinic, C2/m, Z = 2, a = 787.5(1), b = 1353.4(2), c = 778.3(1) pm, {beta} = 110.14(1) ; for Na{sub 3}GdBr{sub 2.4}I{sub 3.6}: a = 772.7(4), b = 1323.3(7), c = 765.8(4) pm, {beta} = 110.14(3) ]. In between, an ordered variant of the Na{sub 3}GdI{sub 6} structure type is found with a doubled c axis [for Na{sub 3}GdBr{sub 4.8}I{sub 1.2}: monoclinic, C2/c, Z = 4, a = 751.5(4), b = 1285.7(6), c = 1413.7(7) pm, {beta} = 99,65(2) ]. Ionic conductivity measurements by impedance spectroscopy exhibt a decline of the activation energies for Na{sup +} conductivity for halides with unchanged crystal structures with increasing substitution by iodide. (orig.)

Bohnsack, A. [Hannover Univ. (Germany). Inst. fuer Anorganische Chemie]|[Hannover Univ. (Germany). Sonderforschungsbereich 173; Meyer, G. [Hannover Univ. (Germany). Inst. fuer Anorganische Chemie]|[Hannover Univ. (Germany). Sonderforschungsbereich 173

1997-05-01

291

Multi-wavelength metal halide lasers  

Energy Technology Data Exchange (ETDEWEB)

This patent describes a laser, emitting energy at selected, characteristic wavelengths within the visible and near infra-red regions of the spectrum, by dissociation of selected metal dihalides. The laser consists of: (a) enclosure means; (b) at least two metal halides from group II-B of the Periodic Table, present within the enclosure means; (c) an inert buffer gas, present within the enclosure means; (d) a heat source, for vaporization of the metal halides, capable of maintaining the enclosure means at a temperature of at least about 370/sup 0/C; (e) a source of pulsed dissociative energy, located in proximity to the enclosure means and in communication therewith, for effecting dissociation of the vaporized metal halide; (f) pre-ionization means, located in proximity to the enclosure means and in communication therewith, for effecting ionization of the vaporized metal halides in concert with and during the pulsed dissociation; and (g) an optical cavity disposed about the enclosure means, comprising a reflective surface and a partially reflective surface, each aligned to permit pulsed emission of a portion of the laser energy.

Eden, J.G.; McCown, A.W.; Ediger, M.N.; Greene, D.P.

1986-08-19

292

Multiline Operation of Mercury Halide Lasers,  

Science.gov (United States)

Emission spectrum of the (B-X) band system of HgX-radicals (X=Chlorine, Bromine, Iodine) has been observed by passing electrical discharge through flowing vapors of mercury halides. The emission intensity of the most intense band of the (B-X) system of th...

M. Kushawaha M. Mahmood

1988-01-01

293

Barium halide nanocrystals in fluorozirconate based glass ceramics for scintillation application  

International Nuclear Information System (INIS)

Europium (Eu)-activated barium halide nanocrystals in fluorozirconate based glass ceramics represent a promising class of Xray scintillators. The scintillation in these glass ceramics is mainly caused by the emission of divalent Eu incorporated in hexagonal BaCl2 nanocrystals which are formed in the glass matrix upon appropriate annealing. Experiments with cerium (Ce)-activated fluorozironate glass ceramics showed that Ce is an interesting alternative. In order to get a better understanding of the scintillation mechanism in Eu- or Ce-activated barium halide nanocrystals, an investigation of the processes in the corresponding bulk material is essential. The objective of this thesis is the investigation of undoped, Eu-, and Ce-doped barium halides by X-ray excited luminescence (XL), pulse height, and scintillation decay spectra. That will help to figure out which of these crystals has the most promising scintillation properties and would be the best nanoparticles for the glass ceramics. Furthermore, alternative dopants like samarium (Sm) and manganese (Mn) were also investigated. Besides the above-mentioned optical investigation electron paramagnetic resonance (EPR) and Moessbauer measurements were carried out in order to complete the picture of Eu-doped barium halides. The EPR data of Eu-doped BaI2 is anticipated to yield more information about the crystal field and crystal structure that will help to understand the charge carrier process during the scintillation process. The main focus of the Moessbauer investigations was set on the Eu-doped fluorochlorozirconate glass ceramics. The results of this investigation should help to improve the glass ceramics. The Eu2+/Eu3+ ratio in the glass ceramics should be determined and optimize favor of the Eu2+. We also want to distinguish between Eu2+ in the glass matrix and Eu2+ in the nanocrystals. For a better understanding of Moessbauer spectroscopy on Eu also measurements on Eu in a CaF2 host lattice were carried out. (orig.)

2007-01-01

294

Synthesis, characterization and thermal properties of small R2R?2N+X--type quaternary ammonium halides  

Science.gov (United States)

Twenty-one R2R'2N +X- -type ( R=methyl or ethyl, R'=alkyl, X=Br or I) quaternary ammonium (QA) halides have been prepared by using a novel one-pot synthetic route in which a formamide (dimethyl-, diethylformamide, etc.) is treated with alkyl halide in the presence of sodium or potassium carbonate. The formation of QA halides was verified with 1H-NMR, 13C-NMR, MS and elemental analysis. The crystal structures of four QA halides (two bromide and two iodide) were determined using X-ray single crystal diffraction, and the powder diffraction method was used to study the structural similarities between the single crystal and microcrystalline bulk material. The thermal properties of all compounds were studied using TG/DTA and DSC methods. The smallest compounds decomposed during or before melting. The decreasing trend of melting points was observed when the alkyl chain length was increased. The liquid ranges of 120-180 °C were observed for compounds with 5-6 carbon atoms in the alkyl chain. The low melting points and wide liquid ranges suggest potential applicability of these compounds for example as ionic liquids precursors.

Busi, Sara; Lahtinen, Manu; Mansikkamäki, Heidi; Valkonen, Jussi; Rissanen, Kari

2005-06-01

295

Alkali metal ion source  

International Nuclear Information System (INIS)

An alkali metal ion source the operation of which is based on surface ionization is described. The source is designed for investigation of ion-photon emission. The ion source unit comprises a casing, a bin, an ionization unit, a quasipierce system of ion beam formation, heating spirals of the bin and ionizer, light-protective screens, accelerating electrode and a cylindrical capacitor. The source casing is a cylindrical 10 mm long chamber with 3.5 mm internal diameter, where the bin with a working substance is placed and 15 mm long steam pipeline with 2.5 mm internal diameter along which steam of the working substance is fed to the ionizer. Under the optimum mode of operation the ion source produces the 4 keV and approximately 20-30 ?A direct current of Cs+ ions

1982-01-01

296

Selective separation of molybdenum as volatile halides from deep-sea ferromanganese nodules  

International Nuclear Information System (INIS)

A simple and rapid method for a selective separation of Mo from deep-sea ferromanganese nodules is described. Sulfation of the ground nodule material with a gas mixture of SO2 and O2 at elevated temperatures results in the sublimation of the Mo therein. The sublimates are mainly composed of pure MoCl4 and MoO2Cl2 which are readily soluble in water. Addition of alkali metal halides to the nodules prior to sulfation increases the Mo recovery to over 95% in 30 min sulfation at 400 to 5000C. The sulfation process, developed primarily for the selective separation of Mn, Cu, Ni, and Co, can be effectively used for Mo separation without complication. 4 figures, 12 tables

1980-01-01

297

Structure and bonding in metal-rich compounds: pnictides, chalcides and halides  

International Nuclear Information System (INIS)

The subject is reviewed under the following headings: introduction (compounds included in the review; purpose of the review); MX compounds with M = transition metal and X = O,N,S or P; sulfides and selenides of the transition metals; transition-metal phosphides; alkali oxides; transition-metal oxides and nitrides with X/M < 1; metal-rich halides; conclusion. The references number 238. Compounds of the following principal elements of nuclear interest are included in the tables and text: Am, Ce, Cs, Eu, Gd, Hf, La, Mo, Np, Nb, Pu, Pr, Pa, Re, Ru, Sc, Ta, Tb, Th, W, U, V, Y, Zr. The information in the tables is presented under: structure type, space group, lattice parameters and remarks. (U.K.)

1978-01-01

298

Elastic properties of cubic crystals: Every's versus Blackman's diagram  

Science.gov (United States)

Blackman's diagram of two dimensionless ratios of elastic constants is frequently used to correlate elastic properties of cubic crystals with interatomic bondings. Every's diagram of a different set of two dimensionless variables was used by us for classification of various properties of such crystals. We compare these two ways of characterization of elastic properties of cubic materials and consider the description of various groups of materials, e.g. simple metals, oxides, and alkali halides. With exception of intermediate valent compounds, the correlation coefficients for Every's diagrams of various groups of materials are greater than for Blackaman's diagrams, revealing the existence of a linear relationship between two dimensionless Every's variables. Alignment of elements and compounds along lines of constant Poisson's ratio v(lang100rang, m), (m arbitrary perpendicular to lang100rang) is observed. Division of the stability region in Blackman's diagram into region of complete auxetics, auxetics and non-auxetics is introduced. Correlations of a scaling and an acoustic anisotropy parameter are considered.

Paszkiewicz, T.; Wolski, S.

2008-03-01

299

Thermodynamic properties of pure and dilute alkali cyanides: short range order effects  

International Nuclear Information System (INIS)

The alkali-cyanides NaCN and KCN, both pure and mixed in alkali-halides are studied, in the low temperature phases (paraelectric and antiferroelectric). Experimental results on the dielectric properties of these systems indicate that short-range order effects are important. These effects are investigated using the Kikuchi method in the limit of the pair correlation approximation (Bethe approximation). The results for the temperature dependence of the dielectric constant, for the pure systems, are adjusted to the experimental data available to obtain the three relevant parameters of the model: coordination number, coupling interaction and electric dipole moment of the CN- molecular ion. This parametrization is used in the study of the dielectric constants of the mixed systems and the critical temperature as a function of the CN- dipole concentration is obtained. The results are in good qualitative agreement with the experimental ones. (Author)

1984-01-01

300

Configuration and migration of point defects in alkali metals  

International Nuclear Information System (INIS)

A computer calculation of vacancy and interstitial migration using a pair interaction potential deduced from the theory of pseudo-potentials is described. The parameters involved in the expression of the potential are adjusted so as to reproduce the elastic constants and the phonon spectrum of the perfect crystal. One obtains the relaxation energies at equilibrium configuration and at the saddle point and the migration energy of a vacancy and an interstitial in the alkali metals. For Na, K and Rb, the vacancy mechanism is the most probable whereas in Li, there is a possibility of an interstitial mechanism, which would explain the experimental results. The diffusion of alkali solutes in alkali metals is analysed by means of a pair interaction potential deduced from the physical properties of the pure solvent and solute crystals. For solute atoms bigger than the solvent, the substitutional mechanism explains the experimental results whereas an interstitial mechanism is more probable for small impurities. This phenomenon may explain the experimental results observed for the diffusion of Na in K and K in Na. The ?Q values are given for several combinations of the four alkali metals Li, Na, K and Rb. (authors)

1969-01-01

 
 
 
 
301

Alkali removal from PFBC exhaust  

Energy Technology Data Exchange (ETDEWEB)

The objectives of this work are to reliably measure the alkali-vapor (Na and K) concentration in a pressurized fluidized-bed combustion (PFBC) exhaust and to demonstrate a fixed granular-bed sorber for the control of alkali vapors from the actual PFBC exhaust. During this reporting period, Test Series No. 8 with the PFBC/alkali sorber unit was conducted to demonstrate the AASB technique and to quantify the level of alkali vapors in the PFBC exhaust. In Test Series No. 8, Beulah lignite (North Dakota) was combusted with Tymochtee dolomite at average bed temperatures ranging from 850 to 875/degree/C and a system pressure of 9.2 atm absolute. Beulah lignite has a low potassium but a very high sodium content (0.024 and 0.67 wt %, respectively, on a moisture-free basis); therefore, our effort was concentrated on the vapor-phase sodium for this test. 2 refs.

Lee, S.H.D.; Carls, E.L.

1989-01-01

302

Reduction of Methylene Blue and related dyes by gamma-irradiated alkali halides  

International Nuclear Information System (INIS)

A spectrophotometric study is reported of the reduction of some dyes with methylene blue structure used in bacteriological staining. The reduction is effected by the species liberated during the dissolution of ?-irradiated sodium chloride. The G values for the two modes of the reduction are compared and the effects of radical scavengers on the reactions are studied. Results are found to be similar to the chemically and biologically induced reduction. The dyes studied include, in addition to Methylene Blue, Janus Green B and Nile Blue sulfate. (author) 9 refs.; 5 figs.; 2 tabs

1989-01-01

303

A generalized rule of average for glow peak temperature of ternary alkali halide systems  

Directory of Open Access Journals (Sweden)

Full Text Available Se estudia la dependencia de la temperatura en la curva de brillo con la composición de los aniones en mezclas cristalinas impurificadas con Europio: KCl0.50KBr0.25RbX0.25:Eu2+ (X = Cl, Br. Cada material muestra una curva de brillo termoluminiscente consistente en dos picos de brillo principales con temperatura entre la del KCl:Eu2+ y la del KBr:Eu2+. El pico más intenso está relacionado con la destrucción del centro F, como ocurre en el caso de cristales de KCl:Eu2+ y su temperatura característica depende fuertemente de la composición del halogeno. El comportamiento confirma que la temperatura de la recombinación de los centros F-H en este tipo de materiales depende en gran medida de la proporción de los aniones. De estos resultados se propone una regla generalizada para obtener la temperatura, promediando la temperatura característica en función de la composición.

R. Rodriguez-Mijangos

2011-01-01

304

Alkali Halide Opacity in Brown Dwarf and Cool Stellar Atmospheres: A Study of Lithium Chloride  

Science.gov (United States)

Recent thermochemical equilibrium calculations have revealed the important role played by lithium chloride in the lithium chemistry of cool dwarf atmospheres (K. Lodders 1999, ApJ 519, 793). Indeed, LiCl appears to be the dominant Li-bearing gas over an extended domain of the (P,T) diagram, typically for temperatures below 1500 K. LiCl has a large dipole moment in its ground electronic state which can give rise to intense rovibrational line spectra. In addition, LiCl can make dipole transitions to several low-lying unbound excited states, causing dissociation of the molecule. For these reasons, LiCl may be a significant source of line and continuum opacity in brown dwarf and cool stellar atmospheres. In this work, we report calculations of complete lists of line oscillator strengths and photodissociation cross sections for the low-lying electronic states of LiCl. We have performed single- and double-excitation configuration interaction calculations using the ALCHEMY ab initio package (Mc Lean et al. 1991, MOTECC 91, Elsevier, Leiden) and obtained the potential curves and the corresponding dipole transition moment functions between the X 1? ^+ ground state and the B 1? ^+ and A 1? excited states. The resulting line oscillator strengths and molecular photodissociation cross sections have been included in the PHOENIX stellar atmosphere code (Hauschildt & Baron 1999, J. Comput. App. Math. 102, 41). The new models, calculated using spherical geometry for all gravities considered, also incorporate our latest database of nearly 670 million molecular lines, and updated equations of state (EOS). This work was supported in part by NSF grants AST-9720704 and AST-0086246, NASA grants NAG5-8425, NAG5-9222, and NAG5-10551 as well as NASA/JPL grant 961582.

Kirby, K.; Weck, P. F.; Schweitzer, A.; Stancil, P. C.; Hauschildt, P. H.

2003-12-01

305

Role of cation impurities on radiation-induced processes in alkali halides  

International Nuclear Information System (INIS)

Experimental data on the energy levels' spectrum of defects produced by _3_0Si"+ ions' implantation into the Si-SiO"2 interface regions of MOS-structures are presented. The energy spectrum consists of a continuum (background) and discrete bands. The maxima, which are repeated for both N and P-type Si, mostly correspond to the known energy levels of radiation-induced defects in Si, and thus can be concluded that the levels belong to point defects and complexes produced in Si near Si-SiO"2, interface during Si"+ ions' implantation. The dependence of the interface states' density (ISD) on implantation dose is presented and the results of annealing are given for the continuum and discrete ISD. The continuum annealing is bimolecular with the activation energy of 0.4 +- 0.02 eV. (author)

1982-01-01

306

Equation-of-state data for CsCl-type alkali halides  

International Nuclear Information System (INIS)

Energy-dispersive x-ray diffraction (EDXD), with synchrotron radiation and diamond anvil cells (DAC), is used with different pressure sensors to determine the lattice parameters and equations of state (EOS) at room temperature, and pressures up to typically 40 GPa, for KBr, KI, RbCl, RbBr, RbI, CsCl, and CsBr. A comparison with previous literature data obtained by various techniques, and for different ranges of pressure indicates that all of the data fit to a recently proposed 'simple' first-order EOS form. (author)

1997-06-30

307

Metal-Induced Gap States at Well Defined Alkali-Halide/Metal Interfaces  

CERN Document Server

In order to search for states specific to insulator/metal interfaces, we have studied epitaxially grown interfaces with element-selective near edge X-ray absorption fine structure (NEXAFS). An extra peak is observed below the bulk edge onset for LiCl films on Cu and Ag substrates. The nature of chemical bonds as probed by X-ray photoemission spectroscopy and Auger electron spectroscopy remains unchanged, so we regard this as evidence for metal-induced gap states(MIGS) formed by the proximity to a metal, rather than local bonds at the interface. The dependence on the film thickness shows that the MIGS are as thin as one monolayer. An ab initio electronic structure calculation supports the existence of the MIGS that are strongly localized at the interface.

Kiguchi, M; Yoshikawa, G; Tanida, Y; Katayama, M; Saiki, K; Koma, A; Aoki, H; Kiguchi, Manabu; Arita, Ryotaro; Yoshikawa, Genki; Tanida, Yoshiaki; Katayama, Masao; Saiki, Koichiro; Koma, Atsushi; Aoki, Hideo

2003-01-01

308

Two-electron F' centers in alkali halides: A negative-U analysis  

CERN Document Server

The existence of bound excited states of two-electron centers loosely trapped in an anion vacancy, the F' centers, is a long-standing problem of color center physics. Optical absorption bands attributed to F' centers in NaI and NaBr as observed by Baldacchini et al. seem to confirm the existence of F' bound snglet states. Nevertheless, a paper by Zhang et al. published not long ago reports extended ion calculations predicting bound excited states for F' centers in NaI alone while the evidence for NaBr is only marginal. For the first time we apply the negative-U mechanism in order to see whether bound excited F' states do not arise by virtue of the lattice polarization produced by the two trapped charge carriers. The result is positive for NaI and less so for NaBr, in agreement with Zhang et al. Other hosts, such as CsI and RbI also show a tendency towards sustaining F' bound excited states. However, the lack of entry data for LiI makes it presently too hard to obtain a complete negative-U picture for the iodi...

Georgiev, M

2005-01-01

309

Role of Farben centers in electron- and photon-stimulated desorption from alkali halides  

International Nuclear Information System (INIS)

Measurements of the time history of ground-state neutral lithium desorption from LiF during pulsed electron irradiation have resulted in a new model for the lithium-desorption mechanism. We show that the slow diffusion to the surface of bulk Farben (F) centers created by the electron-beam is the rate-controlling factor responsible for most of the time history of the lithium desorption rather than the thermal evaporation of the metal from the surface. Comparison between theoretical and experimental time dependencies yields values for the F center diffusion constant and its activation energy

1987-01-01

310

Lanthanide-halide based humidity indicators  

Energy Technology Data Exchange (ETDEWEB)

The present invention discloses a lanthanide-halide based humidity indicator and method of producing such indicator. The color of the present invention indicates the humidity of an atmosphere to which it is exposed. For example, impregnating an adsorbent support such as silica gel with an aqueous solution of the europium-containing reagent solution described herein, and dehydrating the support to dryness forms a substance with a yellow color. When this substance is exposed to a humid atmosphere the water vapor from the air is adsorbed into the coating on the pore surface of the silica gel. As the water content of the coating increases, the visual color of the coated silica gel changes from yellow to white. The color change is due to the water combining with the lanthanide-halide complex on the pores of the gel.

Beitz, James V. (Hinsdale, IL); Williams, Clayton W. (Chicago, IL)

2008-01-01

311

Reactivity of Pt0 complexes toward gallium(III) halides: synthesis of a platinum gallane complex and oxidative addition of gallium halides to Pt0.  

Science.gov (United States)

The reaction of [Pt(PCy 3) 2] and GaCl 3 resulted in quantitative formation of the adduct [(Cy 3P) 2Pt-GaCl 3], the first known platinum gallane complex. Although similar reactivity with GaBr 3 and GaI 3 was expected, NMR spectroscopic data revealed a different reaction course. Crystal structure determination proved that, in the latter case, the product of the oxidative addition was formed. The resulting platinum gallyl complexes represent the first example of an oxidative addition of gallium(III) halides to low-valent transition metals. PMID:18785731

Braunschweig, Holger; Gruss, Katrin; Radacki, Krzysztof

2008-10-01

312

Computational screening of mixed metal halide ammines  

DEFF Research Database (Denmark)

Metal halide ammines, e.g. Mg(NH3)6Cl2 and Sr(NH3)8Cl2, can reversibly store ammonia, with high volumetric hydrogen storage capacities. The storage in the halide ammines is very safe, and the salts are therefore highly relevant as a carbon-free energy carrier in future transportation infrastructure. In this project we are searching for improved mixed materials with optimal desorption temperatures and kinetics, optimally releasing all ammonia in one step. We apply Density Functional Theory, DFT, calculations on mixed compounds selected by a Genetic Algorithm (GA), relying on biological principles of natural selection. The GA is evolving from an initial (random) population and selecting those with highest fitness, a function based on e.g. stability, release temperature and storage capacity. The search space includes all alkaline, alkaline earth, 3d and 4d metals and the four lightest halides. In total the search spaces consists of millions combinations, which makes a GA ideal, to reduce the number of necessarycalculations. We are screening for a one step release from either a hexa or octa ammine, and we have found promising candidates, which will be further investigated ? both computationally and experimentally.

Jensen, Peter Bjerre; Lysgaard, Steen

313

Photoexcitation, photoionisation and photofragmentation of molecular rubidium halides  

Energy Technology Data Exchange (ETDEWEB)

Photoionisation and photofragmentation of molecular rubidium halides following photoexcitation in the vacuum ultraviolet region are investigated. For this purpose total and partial ion yield spectra are measured from the vapours of RbF, RbCl, RbBr and RbI. Two different decay channels - spectator and participator type - are studied in different rubidium halide molecules. It is demonstrated that the opening of the spectator channel takes place at different excitation energies, depending on the halide atom in the molecule.

Kisand, V. [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia); Nommiste, E. [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia)]. E-mail: ergo@fi.tartu.ee; Kukk, E. [Department of Physical Sciences, University of Oulu, P.O. Box 3000, FIN-90014 Oulu (Finland); Calo, A. [Department of Physical Sciences, University of Oulu, P.O. Box 3000, FIN-90014 Oulu (Finland); Aksela, H. [Department of Physical Sciences, University of Oulu, P.O. Box 3000, FIN-90014 Oulu (Finland); Aksela, S. [Department of Physical Sciences, University of Oulu, P.O. Box 3000, FIN-90014 Oulu (Finland)

2005-06-15

314

Process and composition for drying of gaseous hydrogen halides  

Energy Technology Data Exchange (ETDEWEB)

A process for drying a gaseous hydrogen halide of the formula HX, wherein X is selected from the group consisting of bromine, chlorine, fluorine, and iodine, to remove water impurity therefrom, comprising: contacting the water impurity-containing gaseous hydrogen halide with a scavenger including a support having associated therewith one or more members of the group consisting of: (a) an active scavenging moiety selected from one or more members of the group consisting of: (i) metal halide compounds dispersed in the support, of the formula MX.sub.y ; and (ii) metal halide pendant functional groups of the formula -MX.sub.y-1 covalently bonded to the support, wherein M is a y-valent metal, and y is an integer whose value is from 1 to 3; (b) corresponding partially or fully alkylated compounds and/or pendant functional groups, of the metal halide compounds and/or pendant functional groups of (a); wherein the alkylated compounds and/or pendant functional groups, when present, are reactive with the gaseous hydrogen halide to form the corresponding halide compounds and/or pendant functional groups of (a); and M being selected such that the heat of formation, .DELTA.H.sub.f of its hydrated halide, MX.sub.y.(H.sub.2 O).sub.n, is governed by the relationship: .DELTA.H.sub.f .gtoreq.n.times.10.1 kilocalories/mole of such hydrated halide compound wherein n is the number of water molecules bound to the metal halide in the metal halide hydrate. Also disclosed is an appertaining scavenger composition and a contacting apparatus wherein the scavenger is deployed in a bed for contacting with the water impurity-containing gaseous hydrogen halide.

Tom, Glenn M. (New Milford, CT); Brown, Duncan W. (Wilton, CT)

1989-08-01

315

10 CFR 431.322 - Definitions concerning metal halide lamp ballasts and fixtures.  

Science.gov (United States)

...concerning metal halide lamp ballasts and fixtures. 431.322 Section 431.322...EQUIPMENT Metal Halide Lamp Ballasts and Fixtures § 431.322 Definitions concerning metal halide lamp ballasts and fixtures. Ballast efficiency...

2010-01-01

316

75 FR 5544 - Energy Conservation Program: Energy Conservation Standards for Metal Halide Lamp Fixtures: Public...  

Science.gov (United States)

...Conservation Standards for Metal Halide Lamp Fixtures: Public Meeting and Availability of...standards for certain metal halide lamp fixtures. This document announces that the period...conservation standards for metal halide lamp fixtures and provide docket number...

2010-02-03

317

Lead Halide Perovskites and Other Metal Halide Complexes As Inorganic Capping Ligands for Colloidal Nanocrystals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Lead halide perovskites (CH3NH3PbX3, where X = I, Br) and other metal halide complexes (MX, where M = Pb, Cd, In, Zn, Fe, Bi, Sb) have been studied as inorganic capping ligands for colloidal nanocrystals. We present the methodology for the surface functionalization via ligand-exchange reactions and the effect on the optical properties of IV-VI, II-VI, and III-V semiconductor nanocrystals. In particular, we show that the Lewis acid base properties of the solvents, in addition to the solvent di...

2014-01-01

318

Selective endo and exo binding of alkali metals to corannulene.  

Science.gov (United States)

The ion size matters: the structures of corannulene monoanions crystallized with Cs(+) and Rb(+) ions in the presence of [18]crown-6 reveal the intrinsic binding preferences of alkali metals and allow evaluation of the bowl deformation caused by negative charge distribution and metal binding. The large cesium cation coordinates exclusively to the concave face of C(20) H(10)(-), whereas the smaller rubidium cation exhibits convex binding. PMID:21748832

Spisak, Sarah N; Zabula, Alexander V; Filatov, Alexander S; Rogachev, Andrey Yu; Petrukhina, Marina A

2011-08-22

319

Annealing of chemical radiation damage in alkali metal nitrates  

International Nuclear Information System (INIS)

Annealing of chemical radiation damage in ?-irradiated alkali metal nitrates is presented. The order of annealing, LiNO3 > RbNO3 > CsNO3, is in the reverse order of free space in these crystals. Sodium and potassium nitrates are less susceptible to thermal annealing. The annealing data have been analysed on the models of simple interstitial vacancy recombination and also on the basis of conventional chemical kinetics. (author)

1981-01-01

320

sup 79 Br solid state NMR studies of surfaces, point defects and dislocations in silver halides  

Energy Technology Data Exchange (ETDEWEB)

Pure and mixed silver halide crystals form the basis of chemical photography. The authors have used {sup 79}Br solid state NMR at 4.7 T to characterize the structure and dynamics of defects and surface effects that may be involved in determining the photographic properties of these materials. The influence of free and bound vacancies on bromine spin-lattice relaxation in doped AgBr single crystals and microcrystals was studied and interpreted within the context of the space charge model. Microcrystals subjected to compressive strain have a higher dislocation density as reflected in linewidths and 'missing' Br signal intensity. For crystals under one micron in size, the integrated Br signal intensity is a function of a crystallite size. We have established that the electric field gradient deviates from cubic symmetry within 200 A of the crystal surface. (author). 26 refs.; 4 tabs.

Zumbylyadis, N.; Marchetti, P. (Eastman Kodak Co., Rochester, NY (USA))

1990-04-01

 
 
 
 
321

Structure and Chemistry in Halide Lead-Tellurite Glasses  

Energy Technology Data Exchange (ETDEWEB)

A series of TeO2-PbO glasses were fabricated with increasing fractions of mixed alkali, alkaline earth, and lanthanide chlorides. The glass and crystal structure was studied with Raman spectroscopy, nuclear magnetic resonance (NMR), X-ray diffraction, and electron microscopy. As the chloride fraction increased, the medium-range order in the glass decreased up to a critical point (~14 mass% of mixed chlorides), above which the glasses became phase-separated. Resulting phases are a TeO2/PbO-rich phase and a crystalline phase rich in alkali chlorides. The 125Te NMR indicates, contrary to previous studies, that Te site distribution did not change with increased concentrations of M+, M2+, and M3+ cations, but rather is controlled by the Te/Pb molar ratio. The 207Pb NMR shows that two Pb species exist and their relative concentration changes nearly linearly with addition of the mixed chlorides, indicating that the additives to the TeO2-PbO glass are accommodated by changing the Pb species. The 23Na and 35Cl NMR indicate that Na and Cl are distributed in the single-phase glass phase up to the critical point, and at higher concentrations partition to crystalline phases. Transmission electron microscopy shows that the sample at the critical point contains ~10 nm seed nuclei that increase in size and concentration with exposure to the electron beam.

McCloy, John S.; Riley, Brian J.; Lipton, Andrew S.; Windisch, Charles F.; Washton, Nancy M.; Olszta, Matthew J.; Rodriguez, Carmen P.

2013-02-11

322

Dimensional reductions from 2-D Nb 4P 2S 21 to 1-D ANb 2PS 10 ( A=Na, K, Rb, Cs, Tl) and to 0-D Tl 5[Nb 2S 4C l8]Cl using halide molten salts  

Science.gov (United States)

We found new synthetic routes to obtain 1-D quaternary thiophosphate compounds and a 0-D molecular complex containing a Nb 2S 4 core from a 2-D ternary thiophosphate, Nb 4P 2S 21. When Nb 4P 2S 21 was reacted with alkali metal halides ( ACl; A=Na, K, Rb, Cs) or TlCl at 500-700 °C, the -S-S-S- bridges in 2-D Nb 2PS 10-S-S 10PNb 2 were excised to form a 1-D chain, and cations were inserted between the chains to form ANb 2PS 10 ( A=Na, K, Rb, Cs, Tl). We also found that thallium chloride (TlCl) is an excellent reagent for further excision, and it substitutes chloride ligands for the sulfur ligands of 2-D Nb 4P 2S 21 to form the molecular complex Tl 5[Nb 2S 4Cl 8]Cl. Crystal data for TlNb 2PS 10: monoclinic, Pn, a=6.9452(11) Å, b=7.3761(12) Å, 12.873(2) Å, ?=104.472(3)°, and Z=2. Crystal data for Tl 5[Nb 2S 4Cl 8]Cl: orthorhombic, Immm, a=7.001(5) Å, b=9.509(7) Å, c=15.546(11) Å, and Z=2.

Bang, Hyunjin; Kim, Youngmee; Kim, Seri; Kim, Sung-Jin

2008-08-01

323

FTIR Studies of Internal Water Molecules of Bacteriorhodopsin: Structural Analysis of Halide-bound D85S and D212N Mutants in the Schiff Base Region  

Science.gov (United States)

Bacteriorhodopsin (BR), a membrane protein found in Halobacterium salinarum, functions as a light-driven proton pump. The Schiff base region has a quadropolar structure with positive charges located at the protonated Schiff base and Arg82, and counterbalancing negative charges located at Asp85 and Asp212 (Figure 1A). It is known that BR lacks a proton-pumping activity if Asp85 or Asp212 is neutralized by mutation. On the other hand, binding of C1- brings different effects for pumping functions in mutants at D85 and D212 position. While C1--bound D85T and D85S pump C1-, photovoltage measurements suggested that C1--bound D212N pumps protons at low pH. In this study, we measured low-temperature FTIR spectra of D85S and D212N containing various halides to compare the halide binding site of both proteins. In the case of D85S, the N-D stretching vibrations of the Schiff base were halide-dependent. This result suggests that the halide is a hydrogen-bond acceptor of the Schiff base, being consistent with the X-ray crystal structure. On the other hand, no halide dependence was observed for vibrational bands of the retinal skeleton and the Schiff base in the D212N mutant. This result suggests that the halide does not form a hydrogen bond with the Schiff base directly, unlike the mutation at D85 position. Halide-dependent water bands in the Schiff base region also differ between D85S and D212N. From these results, halide binding site of both proteins and role of two negative charges in BR will be discussed.

Shibata, Mikihiro; Kandori, Hideki

2007-12-01

324

Actinide halides and their complexes  

International Nuclear Information System (INIS)

Papers are reviewed published since late 1967 to middle 1970. Problems involving the availability of actinoid halogenides with oxidation degrees from +6 to +2, actinoid oxihalogenides, and also halogenous actinoid complexes with oxidation degrees from +6 to +3, oxihalogenous actinoid complexes with valencies from +6 to -6. The NpF+L5, BKF4, CfF4, BKF3, CfF3 BKBr3, PaF5.2H2O and Pa2OF8 compounds with rhombic pseudocell with the parameters of a0=6.894A, b0=4.014A, c0=4.143A have been obtained for the first time. The process is described of the hew- synthesised ThOF with the face-centered lattice (a0=5.68A), hydrated U(5)-MU2F12 complexes where M=Co, Mi, Cu, and also MUF7 complexes where M=K1Rb, Cs. Csub(s)UFsub(7) is characterized by cubic symmetry with a0=5.54A. The crystal structure of the formally-divalent actinoid compound, ThI2, has been examined. In fact, this compound should be regarded as Th4+(e-)2I2. An interesting method for obtaining UOCl3 through a reaction between UO3 and MoCl5; UOF2.H2O from aqueous solution, and also a simple method for obtaining UCl5 by UO3 reduction with the silicon tetrachloride. The results of investigation of infrared spectra of halogenous and oxihalogenous actinoid complexes (valency from +6 to +4) with donor ligands

1977-01-01

325

The association of ammonia with halide ions in the gas phase  

International Nuclear Information System (INIS)

The enthalpy changes, ?H"0, and entropy changes, ?S"0, for the gas-phase association of ammonia to Cl"-, Br"-, and I"- have been measured using high pressure mass spectrometry. The -?H"0 were determined to be 8.2, 7.7, and 7.4 kcal/mole (0.36, 0.33, and 0.32 eV) and the -?S"0 were 15.4, 19.1, and 20.9 cal/K-mole, respectively, for "3"5Cl"-, "8"1Br"-, and I"-. The -?H"0 values are considerably smaller than those for the association of ammonia to alkali ions and also of water and sulfur dioxide to both halide and alkali ions. One explanation can be based on electrostatic considerations. The quadrupole moment of ammonia leads to a repulsive interaction (considerably greater than that of water) when the ion-dipole orientation is most favorable for a negative ion. Similarly, these opposing interactions may be responsible for the relatively little variation in the enthalpy change for ammonia association between Cl"- and I"-

1984-01-01

326

Comparison of the morphology of alkali–silica gel formed in limestones in concrete affected by the so-called alkali–carbonate reaction (ACR) and alkali–silica reaction (ASR)  

International Nuclear Information System (INIS)

The morphology of alkali–silica gel formed in dolomitic limestone affected by the so-called alkali–carbonate reaction (ACR) is compared to that formed in a siliceous limestone affected by alkali–silica reaction (ASR). The particle of dolomitic limestone was extracted from the experimental sidewalk in Kingston, Ontario, Canada that was badly cracked due to ACR. The siliceous limestone particle was extracted from a core taken from a highway structure in Quebec, affected by ASR. Both cores exhibited marked reaction rims around limestone particles. The aggregate particles were polished and given a light gold coating in preparation for examination in a scanning electron microscope. The gel in the ACR aggregate formed stringers between the calcite crystals in the matrix of the rock, whereas gel in ASR concrete formed a thick layer on top of the calcite crystals, that are of the same size as in the ACR aggregate

2013-05-01

327

Comparison of the morphology of alkali–silica gel formed in limestones in concrete affected by the so-called alkali–carbonate reaction (ACR) and alkali–silica reaction (ASR)  

Energy Technology Data Exchange (ETDEWEB)

The morphology of alkali–silica gel formed in dolomitic limestone affected by the so-called alkali–carbonate reaction (ACR) is compared to that formed in a siliceous limestone affected by alkali–silica reaction (ASR). The particle of dolomitic limestone was extracted from the experimental sidewalk in Kingston, Ontario, Canada that was badly cracked due to ACR. The siliceous limestone particle was extracted from a core taken from a highway structure in Quebec, affected by ASR. Both cores exhibited marked reaction rims around limestone particles. The aggregate particles were polished and given a light gold coating in preparation for examination in a scanning electron microscope. The gel in the ACR aggregate formed stringers between the calcite crystals in the matrix of the rock, whereas gel in ASR concrete formed a thick layer on top of the calcite crystals, that are of the same size as in the ACR aggregate.

Grattan-Bellew, P.E., E-mail: p.grattan-bellew@sympatico.ca [Materials and Petrographic Research G-B Inc., 472 Edison Avenue, Ottawa, ON, Canada K2A 1T9 (Canada); Chan, Gordon [NRC Construction, Bldg., M20, 1200 Montreal Road, Ottawa, ON, Canada K1A 0R6 (Canada)

2013-05-15

328

Characterization of a novel alkali metal and transition metal plasma source  

International Nuclear Information System (INIS)

Results of characterization studies of a metal vapor plasma, and potentially an ion source, are presented. The source is well suited to solids having dielectric and thermal properties which permit rapid heating of the solid by a high-frequency (2-3 GHz) signal. By proper placement in a resonant cavity, the conductively and dielectrically heated solid surface emits a vapor stream which is then ionized in the near-surface region, yielding a metal ion rich plasma. The work presented here concerns plasmas produced from two alkali metal halides, NaCl and KBr, as well as from graphite, titanium dioxide, and iron oxide. The power densities involved are characteristic of high-frequency plasmas and range from 1 to 30 W/cm3. The factor of two or three difference between the ionization potentials of the metals and of the halides or oxygen results in an enrichment of the metal ion content of the plasma and in the presence of the halides or oxygen as atoms rather than ions. In addition to the description of the novel source, its operation, and that of the plasmas produced in it, results of preliminary attempts at extraction and characterization of a beam are presented

1989-05-22

329

crystals  

Science.gov (United States)

A novel combined interferometric-mask method for the formation of micro- and nanometric scale three-dimensional (3D) rotational symmetry quasi-crystalline refractive lattice structures in photorefractive materials is demonstrated experimentally. The method is based on micrometric scale spatial modulation of the light by amplitude mask in the radial directions and along the azimuthal angle and the use of counter-propagating beam geometry building up Gaussian standing wave, which defines the light modulation in the axial direction with half-wavelength periodicity. 3D intensity pattern can be represented as numerous mask-generated 2D quasi-periodic structures located in each anti-node of the standing wave. The formed 3D intensity distributions of the optical beams can be imparted into the photorefractive medium thus creating the micro- and sub-micrometric scale 3D refractive index volume lattices. The used optical scheme allows also the formation of 2D lattices by removing the back-reflecting mirror. 2D and 3D refractive lattices were recorded with the use of 532 nm laser beam and rotational symmetry mask in doped lithium niobate crystals and were tested by the probe beam far-field diffraction pattern imaging and direct observation by phase microscope. The formed rotational symmetry 3D refractive structures have the periods of 20-60 ?m in the radial directions, 60 ?m along the azimuthal angle and half-wavelength 266 nm in the axial direction.

Badalyan, A.; Hovsepyan, R.; Mantashyan, P.; Mekhitaryan, V.; Drampyan, R.

2014-07-01

330

Positron ionization of alkali atoms  

Energy Technology Data Exchange (ETDEWEB)

The authors have extended their distorted wave model previously used to calculate positron scattering from hydrogen atoms to treat positron ionization of the alkali atoms. In this method the distortion potential in the final channel represents the sum of Coulomb interactions between the nucleus and both the positron and free electron. The strength of these interactions are given by effective charges which vary with the energies of the two free particles. Two different sets of effective charges are used. Both cases effectively exclude positronium formation. Details of the models will be given along with values of the cross sections for various alkali atoms.

Stauffer, A.D. [York Univ., Toronto (Canada)

1994-12-31

331

Improved processing for silver halide pulse holography  

Science.gov (United States)

Using of an improved developer with optical latensification allowed to significantly increase exposure sensitivity of currently in use silver halide materials. Transmission large-scale holograms (30 X 40 cm2) of diffused objects have been recorded under pulse exposure of about 6.5 X 10-6 J/cm2 for VRP and of about 2 X 10-6 J/cm2 for Agfa-Gavaert 8E56HD, in both cases without appreciable contrast deterioration. Results of the first experiments on pulse reflection holography are also discussed.

Mikhailov, Viktor N.; Son, Jung-Young; Grinevitskaya, Olga V.; Lee, Hyuk-Su; Choi, Y.-J.

1996-04-01

332

Electrolytic method to make alkali alcoholates using ion conducting alkali electrolyte/separator  

Energy Technology Data Exchange (ETDEWEB)

Alkali alcoholates, also called alkali alkoxides, are produced from alkali metal salt solutions and alcohol using a three-compartment electrolytic cell. The electrolytic cell includes an anolyte compartment configured with an anode, a buffer compartment, and a catholyte compartment configured with a cathode. An alkali ion conducting solid electrolyte configured to selectively transport alkali ions is positioned between the anolyte compartment and the buffer compartment. An alkali ion permeable separator is positioned between the buffer compartment and the catholyte compartment. The catholyte solution may include an alkali alcoholate and alcohol. The anolyte solution may include at least one alkali salt. The buffer compartment solution may include a soluble alkali salt and an alkali alcoholate in alcohol.

Joshi, Ashok V. (Salt Lake City, UT); Balagopal, Shekar (Sandy, UT); Pendelton, Justin (Salt Lake City, UT)

2011-12-13

333

A negative ion source for alkali ions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An ion source is described which delivers negative alkali ions. With this source, which consists of a duoplasmatron and a charge exchange canal with alkali vapour, negative Li, Na and K ions are produced. The oven in which alkali metals are evaporated can reach temperatures up to 575°C.

1980-01-01

334

A negative ion source for alkali ions  

International Nuclear Information System (INIS)

An ion source is described which delivers negative alkali ions. With this source, which consists of a duoplasmatron and a charge exchange canal with alkali vapour, negative Li, Na and K ions are produced. The oven in which alkali metals are evaporated can reach temperatures up to 5750C. (orig.)

1980-09-15

335

Palladium-Catalyzed Coupling of Vinylferrocene with Aromatic Halides - A Highly Efficient Route to (Ferrocenylvinyl)arenes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

(Ferrocenylvinyl)arenes 3, 5, and 7 are obtained from vinylferrocene (1) and substituted aromatic and heteroaromatic halides by palladium-catalyzed Heck-type reactions. Up to three ferrocene units are introduced in one step by the multi-fold reaction of 1,2-dibromo- (4) or 1,3,5-tribromobenzene (6) with 1. The first crystal structure of a bis(ferrocenylvinyl)benzene chromophore (5) is reported.

Ko?nig, Burkhard; Zieg, H.; Bubenitschek, P.; Jones, P. G.

1994-01-01

336

Alkali metal and rare earth element evolution of rock-forming minerals from the Gatumba area pegmatites (Rwanda): Quantitative assessment of crystal-melt fractionation in the regional zonation of pegmatite groups  

Science.gov (United States)

This study presents a general model for the evaluation of Rayleigh fractional crystallisation as the principal differentiation mechanism in the formation of regionally zoned common and rare-element pegmatites. The magmatic evolution of these systems from a granitic source is reconstructed by means of alkali element and rare earth element (REE) analyses of rock-forming minerals (feldspars, micas and tourmaline), which represent a whole sequence of regional pegmatite zonation. The Gatumba pegmatite field (Rwanda, Central Africa) is chosen as case study area because of its well-developed regional zonation sequence. The pegmatites are spatially and temporally related to peraluminous G4-granites (986 ± 10 Ma). The regional zonation is developed around a G4-granite and the proximal pegmatites grade outwardly into biotite, two-mica and muscovite pegmatites. Rare-element (Nb-Ta-Sn) pegmatites occur most distal from the granite.

Hulsbosch, Niels; Hertogen, Jan; Dewaele, Stijn; André, Luc; Muchez, Philippe

2014-05-01

337

Effect of temperature on non-destructive wave propagation in potassium halides  

Energy Technology Data Exchange (ETDEWEB)

Temperature dependence of ultrasonic attenuation is investigated for potassium halides in the temperature range 100-400 K. These calculations are done for KCl, KBr and KI for longitudinal and shear waves along the Left-Pointing-Angle-Bracket 1 1 1 Right-Pointing-Angle-Bracket direction. The non-linearity coupling parameters and thermal relaxation time have also been obtained for these crystals. In the present investigation, it has been found that phonon-phonon interaction is the dominant cause for ultrasonic attenuation.

Raju, Krishna Murti, E-mail: rajukm@yahoo.com [Department of Physics, Bipin Bihari P.G. College, Jhansi, Uttar Pradesh 284001 (India)

2012-09-01

338

Hydroxy- and Mercaptopyridine Pincer Platinum and Palladium Complexes Generated by Silver-Free Halide Abstraction  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A silver-free route has been employed for the synthesis of a number of Pd and Pt complexes supported by an NCN “pincer” ligand (NCN ) [2,6-(Me2NCH2)2C6H3]-) via halide abstraction. This was achieved by the use of o-, m-, and p-hydroxypyridines or o- and p-mercaptopyridines in basic ethanol solutions. The acidic OH or SH protons are removed to generate the formally anionic ligands. X-ray crystal structure determination of these complexes shows that the bonding of the substitute...

Chuchuryukin, A. V.; Chase, P. A.; Mills, A. M.; Lutz, M.; Spek, A. L.; Klink, G. P. M.; Koten, G.

2006-01-01

339

ACCUMULATION OF ALKALIS IN THE RECYCLING FILTRATE OF THE PHOSPHOGYPSUM PULPS  

Directory of Open Access Journals (Sweden)

Full Text Available Sodium and potassium combinations existing in phosphogypsum are highly soluble and remain in the filtrate, their amount increasing with each recycle. It has been determined that the amount of alkalis in the recycling filtrate depends on an amount of alkalis in uncleaned phosphogypsum, a number of recycles in the filtrate, the technology of the phosphogypsum pulp preparation and an amount of soluble phosphates. New phosphate formations composed in an acid medium (pH = 4.5-5 are well crystalized crystals. They do not alter the filtrability of the phosphogypsum pulp. The new combinations formed in an alkaline medium (pH = 7-11 are colloidal. They settle down on the surface of the hard particles and make the filtration of the phosphogypsum pulp complicated. The filtrated phosphogypsum is more humid which causes the growth of the amount of alkalis carried out together with moisture and thus the lower alkali concentration is observed in the recycling filtrate. In the discussed case, the larger amount of soluble phosphates of uncleaned phosphogypsum is formed the larger amount of the colloidal particles in the neutralized phosphogypsum pulp which results in complicated filtration. In all the cases, the alkali concentration in the recycling filtrate approaches the maximum degree which would take place if alkalis existing in uncleaned phosphogypsum were thawed in humidity of cleaned phosphogypsum.

ANTANAS KAZILIUNAS

2011-12-01

340

Exciton emissions in alkali cyanides  

International Nuclear Information System (INIS)

The emissions of Alkali Cyanides X irradiated at low temperature were measured. In addition to the molecular (Frenkel Type) exciton emissions, another emitting centre was found and tentatively assigned to a charge transfer self trapped exciton. The nature of the molecular exciton emitting state is discussed. (Author)

1979-01-01

 
 
 
 
341

Radiolysis of non-stoichiometric ZnSe(Te,O) crystals under high dose gamma-irradiation  

International Nuclear Information System (INIS)

Full text: The radiolysis is the main mechanism of radiation induced defect production in wide gap alkali halide crystals used as scintillators, for example CsI(Tl), which limits their application up to I Mrad. The paper presents the results of studying the product of radiolysis and gamma-ray induced luminescence (GL) depending on a dose of gamma-irradiation of new scintillating ZnSe crystals containing Te impurity from 0.01 to 0.6 mass % and subjected to oxidizing or reducing thermal treatment. The X-ray analysis showed a super-stoichiometric content of zinc in the crystals, consequently, the number of intrinsic defects was estimated ?1020 cm-3. Spectra of gamma-induced luminescence (GL) at 300 K contain a wide band at 630-680 nm and the edge of optical absorption is at 480-492.6 nm depending on impurity. The spectra are stable at the dose of 1 Mrad. After continuous gamma-irradiation at 300 K to the high dose of I09 R the intensity of the GL band decreases significantly and additional bands appear al 650-720 nm. The edge of optical absorption did not change, however the optical density at 630-720 nm increased from 0.15-0.2 to 0.17-0.23 depending on impurity. It is indicative of defect transformation under the irradiation. However the light output of GL did not change. The radiolysis product was washed out the sample surface and analyzed by X-ray fluorescent method. The subsurface layer about 5 nm thick was found to destruct because of radiolysis. The stoichiometry ratio of the remained bulk of the irradiated samples did not change. The radiolysis mechanism via Auger decay is considered theoretically, in which shock waves generated under ionization produce much damage near the surface and at edges. Thus, ZnSe (Te,O) is much harder to the irradiation than alkali halide scintillators. Depending on the ratio of luminescent and quenching centers and kinetics of radiative and non-radiative relaxation from excited states in scintillating ZnSe(Te,O) crystals, either high radiation hardness or damage from radiolysis is expected

2001-01-01

342

Effect of lithium-sodium mixed-alkali on phase transformation kinetics in Er3+/Yb3+ co-doped aluminophosphate glasses  

International Nuclear Information System (INIS)

Er3+ doped aluminophosphate glasses with various Na2O/Li2O ratios were prepared at 1250 deg. C using a silica crucible to study mixed alkali effect (MAE). The effect of relative alkali content on glass transition temperature, crystallization temperature and thermal stability were investigated using differential scanning calorimetry (DSC). In addition, apparent activation energies for crystallization, E c, were determined employing the Kissinger equation. The effect of Al2O3 content on the magnitude of MAE was also discussed. No mixed-alkali effect is observed on crystallization temperature

2006-04-15

343

Metal halides in liquid and gaseous states  

International Nuclear Information System (INIS)

The structure of alkali, alkaline earth, rare earth, transition metal, actinides, Be, Cd, In halogenides in gaseous and liquid states is considered. The following configurations: linear - CdX2; tetrahedral-tetrahalogenides of the 4-group elements; trigonal-bipyramidal - Nb, Ta pentahalogenide; octahedral - MoF6, WCL6, TeF6, are established for MXn molecules. The structure data (the angles between bonds and interatomic distances) on halogenide molecules in the gaseous state are presented

1987-01-01

344

Transient photocurrent measurements in alkali chalcogenide ternary compound semiconductors  

International Nuclear Information System (INIS)

The charge transport properties of two alkali metal chalcogenide, semiconductor ternary compounds Cs2Cd3Te4 and Cs2Hg6S7, having potential as efficient high-energy radiation detectors, were investigated. A key property that determines the detector performance is the minority carrier lifetime, which was determined by measurement of photocurrent transients using pulsed laser excitation. The alkali metal chalcogenide semiconductor crystals were grown by a modified Bridgman method. The Cs2Cd3Te4 compound has a minority lifetime of 2.45 µs at 295 K, which is comparable to that of cadmium zinc telluride (CZT). The Cs2Hg6S7 showed charge trapping with decay times of 120 µs. The excellent charge transport properties of Cs2Cd3Te4 indicate that this ternary compound semiconductor should be well suited for gamma radiation detector devices that operate at room temperature. (paper)

2013-01-01

345

Process and composition for drying of gaseous hydrogen halides  

Energy Technology Data Exchange (ETDEWEB)

This patent describes a scavenger, having utility for drying a gaseous hydrogen halide of the formula HX, wherein X is selected from the group consisting of bromine, chlorine, fluorine, and iodine, to remove water impurity therefrom and produce an essentially completely water-free gaseous hydrogen halide effluent characterized by residual water concentration of below 0.1 part per million by volume (ppm), the scavenger comprising: a support; and associated with the support an active scavenging moiety selected from one or more members of the group consisting of: metal halide compounds dispersed in the support, of the formula MX{sub y}; metal halide pendant functional groups, of the formula {minus}MX{sub y{minus}1}, covalently bonded to the support. This patent describes an apparatus for drying a gaseous hydrogen halide of the formula HX, wherein X is selected from the group consisting of bromine, chlorine, fluorine, and iodine, to remove water impurity therefrom, comprising: a vessel containing a bed of a scavenger according to the above claim; means for introducing the water impurity-containing gaseous hydrogen halide to the vessel for passage through the bed therein; and means for discharging water impurity-depleted gaseous hydrogen halide from the vessel.

Tom, G.M.; Brown, D.W.

1989-08-01

346

Nickel-Catalyzed Borylation of Halides and Pseudo-Halides with Tetrahydroxydiboron [B2(OH)4  

Science.gov (United States)

Arylboronic acids are gaining increased importance as reagents and target structures in a variety of useful applications. Recently, the palladium-catalyzed synthesis of arylboronic acids employing the atom economical tetrahydroxydiboron (BBA) reagent has been reported. The high cost associated with palladium, combined with several limitations of both palladium and copper-catalyzed processes, prompted us to develop an alternative method. Thus, the nickel-catalyzed borylation of aryl and heteroaryl halides and pseudo-halides using tetrahydroxydiboron (BBA) has been formulated. The reaction proved to be widely functional group tolerant and applicable to a number of heterocyclic systems. To the best of our knowledge, the examples presented here represent the only effective Ni-catalyzed Miyaura borylations conducted at room temperature.

Molander, Gary A.; Cavalcanti, Livia N.; Garcia-Garcia, Carolina

2013-01-01

347

Barium halide nanocrystals in fluorozirconate based glass ceramics for scintillation application  

Energy Technology Data Exchange (ETDEWEB)

Europium (Eu)-activated barium halide nanocrystals in fluorozirconate based glass ceramics represent a promising class of Xray scintillators. The scintillation in these glass ceramics is mainly caused by the emission of divalent Eu incorporated in hexagonal BaCl{sub 2} nanocrystals which are formed in the glass matrix upon appropriate annealing. Experiments with cerium (Ce)-activated fluorozironate glass ceramics showed that Ce is an interesting alternative. In order to get a better understanding of the scintillation mechanism in Eu- or Ce-activated barium halide nanocrystals, an investigation of the processes in the corresponding bulk material is essential. The objective of this thesis is the investigation of undoped, Eu-, and Ce-doped barium halides by X-ray excited luminescence (XL), pulse height, and scintillation decay spectra. That will help to figure out which of these crystals has the most promising scintillation properties and would be the best nanoparticles for the glass ceramics. Furthermore, alternative dopants like samarium (Sm) and manganese (Mn) were also investigated. Besides the above-mentioned optical investigation electron paramagnetic resonance (EPR) and Moessbauer measurements were carried out in order to complete the picture of Eu-doped barium halides. The EPR data of Eu-doped BaI{sub 2} is anticipated to yield more information about the crystal field and crystal structure that will help to understand the charge carrier process during the scintillation process. The main focus of the Moessbauer investigations was set on the Eu-doped fluorochlorozirconate glass ceramics. The results of this investigation should help to improve the glass ceramics. The Eu{sup 2+}/Eu{sup 3+} ratio in the glass ceramics should be determined and optimize favor of the Eu{sup 2+}. We also want to distinguish between Eu{sup 2+} in the glass matrix and Eu{sup 2+} in the nanocrystals. For a better understanding of Moessbauer spectroscopy on Eu also measurements on Eu in a CaF{sub 2} host lattice were carried out. (orig.)

Selling, J.

2007-07-01

348

Elastic properties of cubic crystals: Every's versus Blackman's diagram  

Energy Technology Data Exchange (ETDEWEB)

Blackman's diagram of two dimensionless ratios of elastic constants is frequently used to correlate elastic properties of cubic crystals with interatomic bondings. Every's diagram of a different set of two dimensionless variables was used by us for classification of various properties of such crystals. We compare these two ways of characterization of elastic properties of cubic materials and consider the description of various groups of materials, e.g. simple metals, oxides, and alkali halides. With exception of intermediate valent compounds, the correlation coefficients for Every's diagrams of various groups of materials are greater than for Blackaman's diagrams, revealing the existence of a linear relationship between two dimensionless Every's variables. Alignment of elements and compounds along lines of constant Poisson's ratio v((100), m), (m arbitrary perpendicular to (100)) is observed. Division of the stability region in Blackman's diagram into region of complete auxetics, auxetics and non-auxetics is introduced. Correlations of a scaling and an acoustic anisotropy parameter are considered.

Paszkiewicz, T; Wolski, S [Faculty of Mathematics and Applied Physics, Rzeszow University of Technology, ul. W. Pola 1, PL-35-959 Rzeszow (Poland)], E-mail: tapasz@prz.edu.pl, E-mail: wolan@prz.edu.pl

2008-03-01

349

Theoretical study on RbCl crystal with M\\"{o}bius inverse potentials  

CERN Document Server

The alkali halides have been studied very frequently for their simple structures and interesting properties, for example, the high-pressure induced transition$^1$. There are several successful models that can be employed. The most famous model of them is the Tosi-Fumi interionic potential$^2$ which is an empirical potential derived from the experimental data. Whereas, here we developed a new potential model based on the M\\"{o}bius lattice inversion method$^{3,4}$, which can be derived directly from the cohesive energy curve without any experimental data and is more effective than the ab initial calculation. With the M\\"{o}bius interionic potentials, we calculated the structural and elastic properties of RbCl crystal. The results are in good agreement with experiments. We also studied the high-pressure induced B1-B2 transition of RbCl crystal and estimated approximately the transition-point which is about 1.09GPa. Further more, we used this potential model to simulate the RbCl melting with molecular dynamics. ...

Shen, Y; Chen, N; Shen, Yue; Zhang, Shuo; Chen, Nan-xian

2003-01-01

350

Moessbauer spectroscopy study of 57Fe implanted in simple ionic crystals  

International Nuclear Information System (INIS)

Conversion electron Moessbauer spectroscopy is used to study the hyperfine interactions of 57Fe nuclei implanted in a series of alkali halides crystals: LiF, LiI, NaF, NaCl, KF, KCl, KBr, KI and RbCl. Iron ions Fe+ were implanted at an energy of 70 keV and a dose of 1016/cm2. Implantations and measurements of Moessbauer spectra were performed at room temperature. The Moessbauer spectra obtained present either well-resolved symmetric quadrupole doublets in LiI, NaCl, KBr, KI and RbCl or unresolved broad structures in NaF and KF. In all implanted crystals iron was found mostly in Fe3+ state, with the exception of LiF and KCl in which a significant fraction of Fe2+ was also detected. In order to explain the electric field gradients at iron nuclei it was assumed that Fe3+ ions are located at cationic sites and are associated with two vacancies (linear and planar V--Fe3+-V- complexes). Extensive calculations of the electric field gradients were carried out including dipolar polarizability of anions. A fairly good agreement between experimental and theoretical quadrupole splittings has been achieved. (orig.)

1981-05-01

351

Alkali metal and ammonium fluoro(trifluoroacetato)metallates M Prime [M Prime Prime {sub 3}({mu}{sub 3}-F)(CF{sub 3}COO){sub 6}(CF{sub 3}COOH){sub 3}], where M Prime = Li, Na, K, NH{sub 4}, Rb, or Cs and M Prime Prime = Ni or Co. Synthesis and crystal structures  

Energy Technology Data Exchange (ETDEWEB)

A series of fluoro(trifluoroacetato)metallates were synthesized by crystallization from solutions in trifluoroacetic acid containing nickel(II) or cobalt(II) nitrate hydrates and alkali metal or ammonium fluorides: Li[Ni{sub 3}({mu}{sub 3}-F)(CF{sub 3}COO){sub 6}(CF{sub 3}COOH){sub 3}](CF{sub 3}COOH){sub 3} (I), M Prime [Ni{sub 3}({mu}{sub 3}-F)(CF{sub 3}COO){sub 6}(CF{sub 3}COOH){sub 3}] (M Prime = Na (II), NH{sub 4} (IV), Rb (V), and Cs (VI)), NH{sub 4}[Co{sub 3}({mu}{sub 3}-F) (CF{sub 3}COO){sub 6}(CF{sub 3}COOH){sub 3}] (III), and Cs[Ni{sub 3}({mu}{sub 3}-F)(CF{sub 3}COO){sub 6}(CF{sub 3}COOH){sub 3}](CF{sub 3}COOH){sub 0.5} (VII). The crystal structures of these compounds were determined by single-crystal X-ray diffraction. All structures contain triangular trinuclear complex anions [M{sub 3} Double-Prime ({mu}{sub 3}-F)(CF{sub 3}COO){sub 6}(CF{sub 3}COOH){sub 3}]{sup -} (M Double-Prime = Ni, Co) structurally similar to trinuclear 3d metal oxo carboxylate complexes. The three-coordinated F atom is located at the center of the triangle formed by Ni(II) or Co(II) atoms. The metal atoms are linked in pairs by six bridging trifluoroacetate groups located above and below the plane of the [M Double-Prime {sub 3} F] triangle. The oxygen atoms of the axial CF{sub 3}COOH molecules complete the coordination environment of M Double-Prime atoms to an octahedron.

Tereshchenko, D. S.; Morozov, I. V., E-mail: miv448@mail.ru; Boltalin, A. I.; Karpova, E. V.; Glazunova, T. Yu.; Troyanov, S. I. [Moscow State University, Department of Chemistry (Russian Federation)

2013-01-15

352

Study of Ammonium Halides by Neutron Spectrometry  

International Nuclear Information System (INIS)

The scattering of slow neutrons from the ammonium halides NH4Cl, ND4Cl, and NH4Br has been studied at several temperatures with a view to elucidate the nature of the specific heat anomaly associated with these substances. According to Pauling the anomaly is due to the onset of free rotation of the ammonium ion, whereas according to Frenkel the anomaly is due to an order-disorder process. The present measurements rule out the possibility of free rotation thus confirming the Frenkel hypothesis. Values of the torsional frequencies and barrier heights for rotation have been derived and the relation of neutron scattering data to infra-red absorption. Raman scattering and NMR results are discussed. (author)

1963-01-01

353

New alkali metal diphosphates how materials to preserve the security of the environment: CsNaCu(P2O7), Rb2Cu(P2O7) and CsNaCo(P2O7) synthesis and crystal structure determination  

Science.gov (United States)

In this work we describe preliminary results of the synthesis and of a crystal-chemical study of synthetic phosphates with transition metals. Due to the increasing requirements for environmental safety specialists from various industries, we are searching for sustainable forms of immobilization of hazardous waste during storage. We are also developing a component-based waste for new materials. In our continued exploratory synthesis of compounds containing transition-metals, we were able to produce the new diphosphate phases CsNaCu(P2O7), Rb2Cu(P2O7) and CsNaCo(P2O7). A crystal chemical study has allowed us to identify new phosphates. Crystals of CsNaCu(P2O7) (Phase 1) is orthorhombic, crystallizes in space group Pmn21, with a = 5.147(8), b = 15.126(2), c = 9.717(2) Å, V = 756.20 Å3, R1 = 0.066 and Rb2Cu(P2O7) (Phase 2) is orthorhombic as well, crystallizes in space group Pmcn, with a = 5.183(8), b = 10.096(1), c = 15.146(3) Å, V = 793.55 Å3, R1 = 0.063, they have been obtained by high-temperature reaction of RbNO3, CsNO3, Cu(NO3)2, NaOH and (NH4)4P2O7. Synthetic crystals of the phosphate of copper and rubidium were studied in detail by us on the structures of Rb2Cu(P2O7) and Rb2Cu3(P2O7)2 - new alkali metal copper diphosphates (CHERNYATIEVA et al., 2008). Here we report the synthesis, the structure and the properties of the title compounds and we compare these phases with the previously discovered K2CuP2O7 (ELMAADI et al., 1995) and CsNaMnP2O7 (HUANG et al., 1998). These structures crystallize in other space groups, although their structures are also based on 2-D layers, formed by P2O7 groups combined with polyhedra of the transition metals (CHERNYATIEVA et al., 2012). A crystal chemical study has allowed us to identify even new diphosphates CsNaCu(P2O7) (Phase 3). Crystals of CsNaCoP2O7 is monoclinic, space group P 21/n, with a = 7,424(2), b = 7,648(1), c = 12,931(3)Å, ? = 90,71(2)° , V = 734.2(3) Å3 and R1 = 0.060. The structure is based framework of Co tetrahedra and P2O7 groups. The structure of the [Co(P2O7)]2-framework in more detail. The phosphate groups and tetrahedra coordinate cobalt ions form topology. This is a unique 4-coordination topology, where Co and P2O7 groups in the structure are topologically equivalent. References CHERNYATIEVA, A. P., KRIVOVICHEV, S. V., SPIRIDONOVA, D. V. (2008): International conference «Inorganic Materials» Dresden (2008) P3 - 143. CHERNYATIEVA, A. P, SPIRIDONOVA, D. V., KRIVOVICHEV, S. V. The crystal structures of two new synthetic compounds CsNaCu(P2O7) and Rb2Cu(P2O7), Acta Mineralogica-Petrographica (2012) Vol.7, p.25 EL MAADI, A., BOUKHARI, A., HOLT, E.M. (1995) Journal of Alloys Compounds, 223: 13-17. HUANG, Q., HWU, S. J., MO, X. H. (2001): Angewandte Chemie - International Edition, 40: 1690-1693.

Chernyatieva, Anastasiya; Filatova, Alyona; Spiridonova, Dariya; Krivovichev, Sergey

2013-04-01

354

High average brightness rare-gas halide laser technology  

Energy Technology Data Exchange (ETDEWEB)

The authors describe several high repetition rate (100-1000Hz) discharge pumped rare-gas halide laser systems having near diffraction-limited divergence, resulting in unusually high average brightness.

Moody, S.E.; Mullaney, G.J.; Grossman, W.; Cassady, P.E.; Byron, S.

1982-01-01

355

Measurement of cadmium vapor pressure in the metal halide arc  

International Nuclear Information System (INIS)

Spectral diagnostics of operating arcs are used to determine the core densities of cadmium as an additive in high pressure mercury and metal halide (NaI, ScI_3, ThI_4) arcs. Based on the cold spot temperatures of the arc tube (700"0C to 800"0C), the total charge of cadmium would be expected to be vaporized, which the data substantiate when only mercury and cadmium are present; however, the presence of the metal halides suppresses the cadmium vapor pressure significantly. Absorbance measurements in closed cells containing various amounts of cadmium and metal halides point to a chemical interaction between cadmium and the metal halides which affects the cadmium vapor pressure

1984-01-01

356

Optimized spatial frequency response in silver halide sensitized gelatin  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Silver halide sensitized gelatin processing is optimized to increase the spatial frequency response in Agfa-Gevaert 8E75 HD emulsion; therefore a diffraction efficiency of 55% in reflection gratings of 5000 lines/mm is achieved.

Fimia Gil, Antonio; Pascual Villalobos, Inmaculada; Bele?ndez Va?zquez, Augusto

1991-01-01

357

The chemistry of the liquid alkali metals  

International Nuclear Information System (INIS)

The subject is covered in chapters, entitled: some basic physical and chemical properties of Li, Na, K, Rb and Cs; manipulation of the liquids; chemistry of purification methods; species formed by dissolved elements; solubilities and analytical methods; alkali metal mixtures; solvation in liquid metals; application of electrical resistivity measurements; dissociation of hydroxide and amide groups in liquid alkali metal media; reactions between liquid alkali metals and water; reactions of nitrogen with lithium and the group II metals in liquid sodium; formation, dissociation and stability of heteronuclear polyatomic anions; reactions of the liquid alkali metals and their alloys with simple aliphatic hydrocarbons; reactions with some halogen compounds; hydrogen, oxygen and carbon meters; surface chemistry and wetting; corrosion of transition metals by the liquid alkali metals; modern applications of the liquid alkali metals. (U.K.)

1984-01-01

358

Temperature programmed desorption (TDP) of CO from alkali doped EUROPT-1 (6.3 % Pt/SiO/sub 2/)  

International Nuclear Information System (INIS)

The temperature programmed desorption technique was applied to investigate the changed characteristics of Pt/SiO/sub 2/ (EUROPT-1) upon alkali doping, CO desorption peak maxima sifted towards higher temperature as the concentration of alkali increased. This indicated strengthening of catalyst-CO bonding. these results are similar to those previously observed in the case of thermal desorption of CO from potassium covered Pt(III) single crystal. (author)

1996-09-01

359

Liquid alkali metals and alkali-based alloys as electron-ion plasmas  

International Nuclear Information System (INIS)

The article reviews the theory of thermodynamic and structural properties of liquid alkali metals and alkali-based alloys, within the framework of linear screening theory for the electron-ion interactions. (author)

1981-01-01

360

Synthesis of methyl halides from biomass using engineered microbes.  

Science.gov (United States)

Methyl halides are used as agricultural fumigants and are precursor molecules that can be catalytically converted to chemicals and fuels. Plants and microorganisms naturally produce methyl halides, but these organisms produce very low yields or are not amenable to industrial production. A single methyl halide transferase (MHT) enzyme transfers the methyl group from the ubiquitous metabolite S-adenoyl methionine (SAM) to a halide ion. Using a synthetic metagenomic approach, we chemically synthesized all 89 putative MHT genes from plants, fungi, bacteria, and unidentified organisms present in the NCBI sequence database. The set was screened in Escherichia coli to identify the rates of CH(3)Cl, CH(3)Br, and CH(3)I production, with 56% of the library active on chloride, 85% on bromide, and 69% on iodide. Expression of the highest activity MHT and subsequent engineering in Saccharomyces cerevisiae results in productivity of 190 mg/L-h from glucose and sucrose. Using a symbiotic co-culture of the engineered yeast and the cellulolytic bacterium Actinotalea fermentans, we are able to achieve methyl halide production from unprocessed switchgrass (Panicum virgatum), corn stover, sugar cane bagasse, and poplar (Populus sp.). These results demonstrate the potential of producing methyl halides from non-food agricultural resources. PMID:19378995

Bayer, Travis S; Widmaier, Daniel M; Temme, Karsten; Mirsky, Ethan A; Santi, Daniel V; Voigt, Christopher A

2009-05-13

 
 
 
 
361

Novel ?- and X-ray scintillator research: on the emission wavelength, light yield and time response of Ce3+ doped halide scintillators  

International Nuclear Information System (INIS)

This work reviews the scintillation properties of many Ce3+ doped halide compounds studied during the past two decades with the aim to find new relationships between scintillation performance and materials properties. Three major types of compounds are reviewed; lanthanide trihalides LnX3, (pseudo)-elpasolites M2ALnX6 and ternary halides Am Lnn Xo where M and A are alkali cations, Ln is a rare earth cation and X is a halide anion. We will address the relationship of the emission wavelength of Ce3+ and its Stokes shift with the structure, type of anions, coordination number, band gap etc. A comparison between the observed absolute scintillation yield with the fundamental limits will be made. Scintillation losses due to thermal ionization processes and the relationship between Stokes shift, self absorption, and decay time lengthening are treated. Various trends will be identified that may guide us in the continuing quest for better scintillators. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2009-01-01

362

Performance of Alkali Activated Slag with Various Alkali Activators  

Directory of Open Access Journals (Sweden)

Full Text Available The need to meet a sustainable development is now an important challenge to the cement industry. The production of OPC is responsible for about 7% of the world?s CO2 emission, a major contributor to the green house effect which is implicated in global warming and climatic changes, lead to the search for more environmentally viable alternative to cement. One of those alternative material is alkali activated slag (AAS where ground granulated blast furnace slag is used not as partial replacement to cement but also as a sole binder in the production of concrete. The overall aim of the study was to investigate the potential of alkali activated slag as a sole binder in producing concrete.The performance of alkali-activated slag concrete with sodium silicate, sodium hydroxide, sodium carbonate as activator are used at 4% Na2O(by weight of slag and 4% of hydrated lime by total weight of solid binder content if used as a retarder. The scope of the work covered four mixes: - Normal OPC mix and three alkali activated slag mixesof the same binder content and the same water binder ratio. The fresh concrete properties studied were setting time and workability and the Engineering properties studied are compressive strength was measured in 1,7,28 days, split tensile strength was measured in 7,28 days and flexure, punching shear strength was compared in 12 days only. The AAS concrete with different activators investigated was found to achieve good workability comparable with that of OPC. Sodium silicate, sodium hydroxide activated slag mixes sets very quickly. AAS concrete is much more sensitive to curing where if there is no addition of retarder (hydrated lime to the mix. Among AAS mix sodium silicate was the best; sodium carbonate was the second; and sodium hydroxide was third in terms of compressive, split tensile strengths and in terms of flexure strength and punching shear strength sodium hydroxide was best; sodium carbonate was second; sodium silicate (water glass was third.

D.V.S.P.RAJESH

2013-02-01

363

Characterization of Waste Poly(Ethylene-Terephthalate after Alkali Treatment  

Directory of Open Access Journals (Sweden)

Full Text Available Poly(ethylene terephthalate, PET, recycling represents one of the most successful and widespread examples of polymer recycling. This material is fully recyclable and may be used for manufacturing new products in many industrial areas. Nevertheless, the excellent properties of PET needed for its many applications are also responsible for the difficult degradation of PET and an accumulation of polymer waste, which in turn creates serious environmental problems connected to littering and illegal landfilling or incineration. The main goal of this study was to examine the effect of alkali pretreatment on the properties of PET flakes. PET flakes were washed at twotemperatures, 70 °C and 75 °C and in various time intervals of 15, 18, 21, 25, and 30 min. All samples were characterized by FTIR spectroscopy, differential scanning calorimetry and by contact angle measurements. The results showed that during the alkali treatment the partial depolymerization of PET was obtained, which resulted in the formation of various types of oligomers with hydroxyl and carboxyl end groups, which were the result of loss of high molecular structure. Decrease of intensity of characteristic vibrational bands (CO at 1717, COO at 1265 and CH2 at 722 cm-1 with extended time was observed (Figs. 1 and 2. Further on, the formation of hydroxyl groups at ? = 3428 cm-1 was also observed as a result of PET depolimerization during the alkali treatment, which behaviour was better visible for samples washed at 75 °C and with extended washing time (Fig 2b. During the DSC thermal analysis, multiple melting peaks were observed in some studied samples which could be linked to partial melting and re-crystallization of PET or to the occurrence of new polymer fractions of lower molecular mass (Figs. 3 and 4. It is evident that the contact angle of PET samples (Fig. 5 decreases in comparison to the PET 0, which points to the changes on the PET surface during the alkali treatment. Decrease in contact angle (which is measured with water indicates an increase in surface hydrophilicity and increase in the number of present polar -OH and -COOH groups formed during the partial degradation. Also, the values of total surface energies and their polar and dispersive components indicate that during the alkali treatment the surface characteristics of PET flakes were slightly changed due to depolymerization (Table 3. Generally, it can be concluded that partial depolymerization of PET flakes occurs during the alkali treatment but the material retains its good properties and it is appropriate for the further recycling process.

Reš?ek, A.

2011-07-01

364

40 CFR 721.8900 - Substituted halogenated pyridinol, alkali salt.  

Science.gov (United States)

... Substituted halogenated pyridinol, alkali salt. 721.8900 Section 721.8900... Substituted halogenated pyridinol, alkali salt. (a) Chemical substances and...as substituted halogenated pyridinols, alkali salts (PMNs P-88-1271 and...

2010-07-01

365

40 CFR 721.1878 - Alkali metal alkyl borohydride (generic).  

Science.gov (United States)

...2009-07-01 2009-07-01 false Alkali metal alkyl borohydride (generic...Specific Chemical Substances § 721.1878 Alkali metal alkyl borohydride (generic...chemical substance identified generically as alkali metal alkyl borohydride (PMN...

2009-07-01

366

40 CFR 721.5278 - Substituted naphthalenesulfonic acid, alkali salt.  

Science.gov (United States)

...Substituted naphthalenesulfonic acid, alkali salt. 721.5278 Section 721.5278...Substituted naphthalenesulfonic acid, alkali salt. (a) Chemical substance and...substituted naphthalenesulfonic acid, alkali salt (PMN P-95-85) is...

2009-07-01

367

Carbon and proton shielding tensors in methyl halides.  

Science.gov (United States)

The series of methyl halides, CH(3)X (X = F, Cl, Br, and I), is prototypic for demonstrating the s.c. normal halogen dependence of light-atom nuclear magnetic resonance shielding constants in the presence of halogen atoms of varying electronegativity. We report a systematic experimental and first-principles theoretical study of the (13)C and (1)H shielding tensors in this series. The experimental shielding constants were obtained from gas-phase NMR experiments and the anisotropies were determined using liquid crystal NMR spectroscopy. After taking into account rovibrational effects and solute-solvent interactions, this provided the currently best experimental estimates for the full shielding tensors. Quantum chemical calculations were carried out at ab initio and density functional theory levels, involving relativistic corrections taken into account at the leading-order Breit-Pauli perturbation level. Anharmonic and harmonic vibrational corrections were performed. The main trends of the shielding constants and anisotropies of the nearby light (13)C and (1)H nuclei as functions of the halogen mass, were confirmed to be mainly due to relativistic spin-orbit effects. For carbon, also the scalar relativistic effects are important for quantitative results. Thermal averaging at 300 K decreases the magnitude of all the parameters but exhibits partial cancellation between the nonrelativistic and smaller relativistic rovibrational averages. For the shielding anisotropy, the relativistic terms add to the negative rovibrational effect. Overall, the current experimental and theoretical results are in excellent agreement for all the shielding parameters, setting a standard for further investigations of normal halogen dependence. PMID:20200746

Kantola, Anu M; Lantto, Perttu; Vaara, Juha; Jokisaari, Jukka

2010-03-20

368

An EPR investigation of Ag sup 0 and Ag sup 2+ in irradiated single crystal of potassium fluoride doped with silver fluoride  

Energy Technology Data Exchange (ETDEWEB)

The electron paramagnetic resonance absorption spectra of a singly ionized diatomic fluoride molecule-ion F{sub 2}{sup {minus}}, atomic silver Ag{sup 0}, and divalent silver Ag{sup 2+} contained in single crystals of potassium fluoride were re-examined at X-band wavelengths. The F{sub 2}{sup {minus}} and Ag{sup 0} centers are produced simultaneously by {gamma}-irradiation at liquid nitrogen temperature. The divalent silver Ag{sup 2+} centers are formed by subsequently warming the irradiated samples to room temperature for a few hours and then cooling to 77 K. All field-strength positions of resonance-absorption lines observed at low temperatures were satisfactorily predicted by computer simulation. The high degree of resolution exhibited by the spectra is due in part to the large nuclear magnetic moment of fluorine and in part to the fact that spectral lines in KF are narrow compared to those of similar systems in other alkali halide crystals. For atomic silver, the hexafluoride cluster is cubic. By contrast, the divalent silver center is tetragonally distorted along a crystal cube edge as a consequence of the Jahn-Teller effect.

Yu Cheng.

1991-01-01

369

Elaboration of phosphate ceramics as a safe form for halide salt waste immobilization of 'dry' fuel reprocessing  

International Nuclear Information System (INIS)

The conception of high level radwaste immobilization from M1-containing molten salts and their solid forms into NZP-like structure phosphate ceramics are considered. The crystal-chemical principle on radionuclide incorporation into this structure is described. The prepared NZP ceramics was tested and it was shown that they had stability to action of such factors as temperature (up to 1200-1600degC), pressure (up to 500 MPa), radiation (?, up to 5·108 Gy), water solutions (up to 400degC, 60 MPa). Their structure is able to contain alkali elements up to 30-40%. Such monophase phosphate compositions may be formed at process of alkali chloride wastes solidification. The reactions of alkali chlorides, radionuclides, with phosphates are taken up here. (author)

1997-01-01

370

Purification and characterization of an extracellular, thermo-alkali-stable, metal tolerant laccase from Bacillus tequilensis SN4.  

Science.gov (United States)

A novel extracellular thermo-alkali-stable laccase from Bacillus tequilensis SN4 (SN4LAC) was purified to homogeneity. The laccase was a monomeric protein of molecular weight 32 KDa. UV-visible spectrum and peptide mass fingerprinting results showed that SN4LAC is a multicopper oxidase. Laccase was active in broad range of phenolic and non-phenolic substrates. Catalytic efficiency (kcat/Km) showed that 2, 6-dimethoxyphenol was most efficiently oxidized by the enzyme. The enzyme was inhibited by conventional inhibitors of laccase like sodium azide, cysteine, dithiothreitol and ?-mercaptoethanol. SN4LAC was found to be highly thermostable, having temperature optimum at 85°C and could retain more than 80% activity at 70°C for 24 h. The optimum pH of activity for 2, 6-dimethoxyphenol, 2, 2'-azino bis[3-ethylbenzthiazoline-6-sulfonate], syringaldazine and guaiacol was 8.0, 5.5, 6.5 and 8.0 respectively. Enzyme was alkali-stable as it retained more than 75% activity at pH 9.0 for 24 h. Activity of the enzyme was significantly enhanced by Cu2+, Co2+, SDS and CTAB, while it was stable in the presence of halides, most of the other metal ions and surfactants. The extracellular nature and stability of SN4LAC in extreme conditions such as high temperature, pH, heavy metals, halides and detergents makes it a highly suitable candidate for biotechnological and industrial applications. PMID:24871763

Sondhi, Sonica; Sharma, Prince; Saini, Shilpa; Puri, Neena; Gupta, Naveen

2014-01-01

371

Purification and Characterization of an Extracellular, Thermo-Alkali-Stable, Metal Tolerant Laccase from Bacillus tequilensis SN4  

Science.gov (United States)

A novel extracellular thermo-alkali-stable laccase from Bacillus tequilensis SN4 (SN4LAC) was purified to homogeneity. The laccase was a monomeric protein of molecular weight 32 KDa. UV-visible spectrum and peptide mass fingerprinting results showed that SN4LAC is a multicopper oxidase. Laccase was active in broad range of phenolic and non-phenolic substrates. Catalytic efficiency (kcat/Km) showed that 2, 6-dimethoxyphenol was most efficiently oxidized by the enzyme. The enzyme was inhibited by conventional inhibitors of laccase like sodium azide, cysteine, dithiothreitol and ?-mercaptoethanol. SN4LAC was found to be highly thermostable, having temperature optimum at 85°C and could retain more than 80% activity at 70°C for 24 h. The optimum pH of activity for 2, 6-dimethoxyphenol, 2, 2?-azino bis[3-ethylbenzthiazoline-6-sulfonate], syringaldazine and guaiacol was 8.0, 5.5, 6.5 and 8.0 respectively. Enzyme was alkali-stable as it retained more than 75% activity at pH 9.0 for 24 h. Activity of the enzyme was significantly enhanced by Cu2+, Co2+, SDS and CTAB, while it was stable in the presence of halides, most of the other metal ions and surfactants. The extracellular nature and stability of SN4LAC in extreme conditions such as high temperature, pH, heavy metals, halides and detergents makes it a highly suitable candidate for biotechnological and industrial applications.

Sondhi, Sonica; Sharma, Prince; Saini, Shilpa; Puri, Neena; Gupta, Naveen

2014-01-01

372

BEAM EXPOSURE DEPENDENCE AND MECHANISMS OF PHOTON-STIMULATED DESORPTION FROM ALKALI FLUORIDES  

Energy Technology Data Exchange (ETDEWEB)

Photon-stimulated desorption experiments were performed on the (001) face of LiF for photon energies near the F(2s) and Li(ls) edges (from 37 to 72 eV). There are structures in the F{sup +} yield above the F(2s) edge which are absent in the Li{sup +} spectrum, differences in detail in the Li{sup +} and F{sup +} yields near the Li(1s) edge, and considerable broadening of the desorption yields as compared to the bulk photoabsorption spectrum. The first observation of a strong x-ray, and visible, beam exposure dependence of ion yields from LiF and NaF is also presented. These results are discussed in terms of electronic and defect properties of alkali halides.

Parks, C.C.; Shirley, D.A.; Loubriel, G.

1983-11-01

373

Limestone double alkali design and economics  

Energy Technology Data Exchange (ETDEWEB)

This paper outlines the process design and cost factors associated with FMC's Limestone Double Alkali System. The system combines the proven advantages in the area of high dioxide removal, low maintenance, and low operating costs of lime double alkali with the advances in process technology necessary to utilize low cost limestone as the regeneration reagent.

Camponeschi, B.S.

1982-12-01

374

Temperature Dependence of Local Structure Around Rb+ and Cs+ Ions in Alkali Doped Fullerenes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Rb and Cs K-edge EXAFS spectra have been measured in the temperature range from 10 to 290 K, in order to investigate the temperature dependence of local structure around Rb+ and Cs+ ions in various alkali doped fullerenes. It has been found that the alkali metal ions in Rb3C60, K2RbC60 and Na2CsC60 occupy the center of the tetrahedral and octahedral sites of C60 crystals. The metal ion in the octahedral site exhibits a large fluctuation in comparison with that in the tetrahedral site. The inc...

1997-01-01

375

Lead halide perovskites and other metal halide complexes as inorganic capping ligands for colloidal nanocrystals.  

Science.gov (United States)

Lead halide perovskites (CH3NH3PbX3, where X = I, Br) and other metal halide complexes (MX(n), where M = Pb, Cd, In, Zn, Fe, Bi, Sb) have been studied as inorganic capping ligands for colloidal nanocrystals. We present the methodology for the surface functionalization via ligand-exchange reactions and the effect on the optical properties of IV-VI, II-VI, and III-V semiconductor nanocrystals. In particular, we show that the Lewis acid-base properties of the solvents, in addition to the solvent dielectric constant, must be properly adjusted for successful ligand exchange and colloidal stability. High luminescence quantum efficiencies of 20-30% for near-infrared emitting CH3NH3PbI3-functionalized PbS nanocrystals and 50-65% for red-emitting CH3NH3CdBr3- and (NH4)2ZnCl4-capped CdSe/CdS nanocrystals point to highly efficient electronic passivation of the nanocrystal surface. PMID:24746226

Dirin, Dmitry N; Dreyfuss, Sébastien; Bodnarchuk, Maryna I; Nedelcu, Georgian; Papagiorgis, Paris; Itskos, Grigorios; Kovalenko, Maksym V

2014-05-01

376

Optical properties of halide and oxide compounds including the excitonic effects  

Science.gov (United States)

We have studied the optical properties of alkali halide and alkaline-earth oxide compounds including the excitonic effects by using the newly developed bootstrap kernel approximation for the exchange-correlation kernel of the Time-Dependent Density Functional Theory (TD-DFT) implemented in Full-Potential Linearized Augmented Plane Wave (FP-LAPW) method in the elk code. The bootstrap calculations are computationally less expensive and give results the same quality as the Bethe-Salpeter equation. We found improved results when compared to normal Density Functional Theory calculations, and observed results are comparable with the experiments. The lower energy peak of imaginary part of dielectric spectra shifts to lower energy regions as we move from MgO to BaO indicating the decrease in the band gap of these compounds from MgO to BaO. In all the studied compounds, the lower energy peak of the imaginary part of dielectric function is due to the transition from halogen p or oxide p states to metal derived s/d states.

Shwetha, G.; Kanchana, V.

2014-04-01

377

Design and construction of a copper-halide laser  

International Nuclear Information System (INIS)

The considerations necessary for the design and construction of an inexpensive, reliable copper halide laser are presented. A broad range of parameters which govern the output of the double-pulse copper-halide laser was studied. The laser has an optimum operating temperature which is different for each halide uCl, CuBr, CuI), but corresponds to a halide vapor pressure of about 0.1 torr for all three halides. At low repetition rates the highest laser output is achieved with helium as buffer gas. The laser output increases linearly with laser tube cross-section. As the tube diameter is increased, the dissociation energy must be increased, but not the excitation energy. A thyratron bias circuit has been developed which permits both dissociation and excitation pulses to be obtained from the same capacitor (with a small delay) without thyratron latch. Use of the single thyratron reduces the laser cost considerably. A laser tube with an operating life of many hundreds of hours has been designed. The description of a laser with an output of 0.5 mJ per pulse at repetition rates of up to 120 pulses per second is given. The design and construction of various components of this laser are given in detail. (authors)

1979-01-01

378

Alteration of alkali reactive aggregates autoclaved in different alkali solutions and application to alkali-aggregate reaction in concrete  

International Nuclear Information System (INIS)

Surface alteration of typical aggregates with alkali-silica reactivity and alkali-carbonate reactivity, i.e. Spratt limestone (SL) and Pittsburg dolomitic limestone (PL), were studied by XRD and SEM/EDS after autoclaving in KOH, NaOH and LiOH solutions at 150 deg. C for 150 h. The results indicate that: (1) NaOH shows the strongest attack on both ASR and ACR aggregates, the weakest attack is with LiOH. For both aggregates autoclaved in different alkali media, the crystalline degree, morphology and distribution of products are quite different. More crystalline products are formed on rock surfaces in KOH than that in NaOH solution, while almost no amorphous product is formed in LiOH solution; (2) in addition to dedolomitization of PL in KOH, NaOH and LiOH solutions, cryptocrystalline quartz in PL involves in reaction with alkaline solution and forms typical alkali-silica product in NaOH and KOH solutions, but forms lithium silicate (Li2SiO3) in LiOH solution; (3) in addition to massive alkali-silica product formed in SL autoclaved in different alkaline solutions, a small amount of dolomite existing in SL may simultaneously dedolomitize and possibly contribute to expansion; (4) it is promising to use the duplex effect of LiOH on ASR and ACR to distinguish the alkali-silica reactivity and alkali-carbonate reactivity of aggregate when both ASR and ACR might coexist

2006-06-01

379

Chemistry of gaseous lower valent actinide halides. Final technical report, August 1979-August 1985  

International Nuclear Information System (INIS)

The objective of this program was to provide accurate thermochemical information for key actinide-halide and oxyhalide systems, starting with uranium halides, so that the basic factors underlying the chemical bonding and chemical reactivity in these systems can be elucidated in a systematic way. Our principal focus was on the gaseous halides, mainly the lower valent halides, because these molecular species largely will define the high temperature chemistry in the nuclear applications of interest. 6 refs., 2 tabs

1986-01-01

380

Effect of alkali addition on DC conductivity & thermal properties of vanadium-bismo-borate glasses  

Science.gov (United States)

The DC Conductivity and Differential Thermal Analysis of glasses with composition (30-x)Li2O?xV2O5?20Bi2O3?50B2O3(x=15, 10, 5) has been carried out in order to study the effect of replacing the Transition Metal Oxide (TMO) with alkali oxide. A significant increase in the DC conductivity has been observed with increase in alkali content. Again the thermal measurements have shown the decrease in both glass transition temperature (Tg) and crystallization temperature (Tx). The Glass Stability (GS) and Glass Forming Ability (GFA) have also been calculated and these also were found to decrease with increase in alkali oxide content at the cost of TMO.

Khasa, S.; Dahiya, M. S.; Agarwal, A.

2014-04-01

 
 
 
 
381

EPR and optical absorption studies on manganese ion doped in mixed alkali cadmium phosphate glasses  

International Nuclear Information System (INIS)

Electron paramagnetic resonance (EPR) spectra of Mn(II) ions in cadmium phosphate glasses are presented with mixed alkali variation as xLi2O + (20 - x) Na2O + 20 CdO + 59.5 P2O5 + 0.5 MnO glass system with 5 ? x ? 15 mol%. The EPR spectra of Mn(II) ions doped samples exhibit a sextet centered at g = 2·0. The optical absorption spectrum at room temperature shows three bands for Mn(II) ions in octahedral symmetry. The crystal field (Dq) and Racah parameters (B and C) are evaluated. From EPR and optical spectral studies reveals the nature of the bonding is dominantly ionic and its site symmetry is octahedral. At equal composition of alkali content, i.e. for x = 10 the glass system shows the mixed alkali effect.

2009-07-01

382

Effect of the alkali metal activator on the properties of fly ash-based geopolymers  

Energy Technology Data Exchange (ETDEWEB)

The alkali and alkali earth metal cations present during the formation of most known aluminosilicate structures have a very significant effect on both the physical and chemical properties of the final product. Geopolymers are no exception, although this effect has not been thoroughly quantified and in the case of waste-based geopolymers it has not received any significant attention. The present study investigates the effect of mainly Na{sup +} and K{sup +} on the physical and chemical properties of fly ash-based geopolymeric binders both before and after setting has occurred. A variety of tests were conducted, including rheological measurements, various leaching tests, compressive strength testing, specific surface area determinations, and infrared spectroscopy (IR). It is concluded that the alkali metal cation controls and affects almost all stages of geopolymerization, from the ordering of ions and soluble species during the dissolution process to playing a structure-directing role during gel hardening and eventual crystal formation.

Jaarsveld, J.G.S. van; Deventer, J.S.J. van

1999-10-01

383

Radiolytic decomposition of binary mixtures of potassium nitrate and halides  

International Nuclear Information System (INIS)

The radiolytic decomposition of pure KNO3 and its binary mixtures with KCl, KBr, and KI in 25, 50 and 75% compositions have been studied in a wide dose range up to 100 Mrads. At low doses NO2- concentration increases rapidly and linearly but at higher doses the rate of decomposition becomes slower presumably due to the backward reaction involving recombination reaction. G(NO2-) values of all the mixtures at all compositions are lower than for pure KNO3 and otherwise decrease in the order KI > KBr > KCl. G(NO2-) of the binary mixtures decreases with the increasing amount of halides. G(NO2-) values are also found to be affected by the electronegativity, polarizability and ionic size of the halide ion. A part of the energy seems to be shared by the halide resulting in the formation of color centre which may release energy upon dissolution

1986-09-07

384

“On water” sp3–sp2 cross-couplings between benzylic and alkenyl halides  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Organic-solvent-free cross-couplings between benzylic and alkenyl halides have been developed. Various alkenyl halides can be effciently benzylated by combining the precursor halides in the presence of Zn dust and a Pd catalyst at room temperature, in water as the only medium.

Krasovskaya, Valeria; Krasovskiy, Arkady; Bhattacharjya, Anish; Lipshutz, Bruce H.

2011-01-01

385

Oxygen mobility in alkali feldspars  

International Nuclear Information System (INIS)

The oxygen mobility is shown from oxygen atoms exchange between potassic and sodic feldspars and 18 oxygen enriched water. Exchanges are carried out in autoclaves between 400 and 800 deg. C under a water pressure between 300 and 800 bars. The oxygen is extracted from silicate by a ClF3 attack. Two distinct mechanisms may be found. The first one is auto-diffusion; for adularia we have: D = 9.10-7 exp(-32000/RT) (cm2.s-1), for albite: D 4.5.10-5 exp(-37000/RT) (cm2.s-1). The second one, more rapid, is associated with alkali atoms exchanges. These results are applied to the order-disorder problem in feldspars and to the oxygen geochemistry. (author)

1968-01-01

386

Determination of the degree of dissociation of alkali cations in binary silicate melts in accordance with cryoscopy and electrical conductivity data  

Energy Technology Data Exchange (ETDEWEB)

This paper performs cryoscopic measurements of the decrease in the solidification temperature of solutions of silicates of alkali metals in halides. On the basis of these the values of the degree of dissociations of the cation-anion silicate complexes have been calculated. A method is proposed for evaluating the proportion of cations participating in the current transport in Me/sub 2/O-SiO/sub 2/ melts by calculating the degree of dissociation of the polymeric complexes according to the data on electrical conductivity. It is shown that there is satisfactory agreement between the results obtained using both methods.

Bobylev, I.B.; Anfilogov, V.N.; Zyuzeva, N.A.

1986-09-01

387

DELIGNIFICATION OF SUGARCANE BAGASSE WITH ALKALI AND PERACETIC ACID AND CHARACTERIZATION OF THE PULP  

Directory of Open Access Journals (Sweden)

Full Text Available Sugarcane bagasse was delignified with alkali and peracetic acid in a two-stage process to obtain pulps with high yield and low kappa number. The experimental results indicated that alkali pretreatment prior to peracetic acid (PAA delignification could significantly reduce PAA loading by partially removing lignin and swelling the fibers. An optimum condition for the two-stage delignification was obtained for pulping of sugarcane bagasse. The pulps were further characterized by chemical composition analysis, strength property tests, Fourier Transform Infrared Spectroscopy (FTIR, X-Ray Diffraction (XRD, and Thermal Gravimetric Analysis (TGA. It was found that the alkali-PAA process could be conducted under milder conditions with resulting higher pulping selectivity, higher degree of polymerization (DP, and superior mechanical properties of pulps, compared to the kraft pulping process. Both kraft pulps and alkali-PAA pulp had similar FTIR spectra, XRD spectra, and TGA (DTG curves. However, further analysis indicated that the alkali-PAA pulp had higher infrared crystallization index and cellulose crystallinity.

Ting Zhang

2010-06-01

388

Diode pumped alkali vapor fiber laser  

Energy Technology Data Exchange (ETDEWEB)

A method and apparatus is provided for producing near-diffraction-limited laser light, or amplifying near-diffraction-limited light, in diode pumped alkali vapor photonic-band-gap fiber lasers or amplifiers. Laser light is both substantially generated and propagated in an alkali gas instead of a solid, allowing the nonlinear and damage limitations of conventional solid core fibers to be circumvented. Alkali vapor is introduced into the center hole of a photonic-band-gap fiber, which can then be pumped with light from a pump laser and operated as an oscillator with a seed beam, or can be configured as an amplifier.

Payne, Stephen A. (Castro Valley, CA); Beach, Raymond J. (Livermore, CA); Dawson, Jay W. (Livermore, CA); Krupke, William F. (Pleasanton, CA)

2007-10-23

389

Diode pumped alkali vapor fiber laser  

Energy Technology Data Exchange (ETDEWEB)

A method and apparatus is provided for producing near-diffraction-limited laser light, or amplifying near-diffraction-limited light, in diode pumped alkali vapor photonic-band-gap fiber lasers or amplifiers. Laser light is both substantially generated and propagated in an alkali gas instead of a solid, allowing the nonlinear and damage limitations of conventional solid core fibers to be circumvented. Alkali vapor is introduced into the center hole of a photonic-band-gap fiber, which can then be pumped with light from a pump laser and operated as an oscillator with a seed beam, or can be configured as an amplifier.

Payne, Stephen A. (Castro Valley, CA); Beach, Raymond J. (Livermore, CA); Dawson, Jay W. (Livermore, CA); Krupke, William F. (Pleasanton, CA)

2006-07-26

390

Molecular beam photodissociation of the alkali iodides using 347.1 nm light  

International Nuclear Information System (INIS)

Several recent studies using absorption and emission spectroscopy and scattering of atomic beams have given information on the number, position, and symmetry of the low lying excited states of the alkali iodides which correlate to the separated ground state atoms. Most of the work has supported conclusions drawn from earlier spectroscopic measurements that Hund's case (c) coupling obtains resulting in five states with ? = 0+, 0-, 1, 1 and 2. Results from the scattering of spin polarized potassium off iodine atoms, however, was interpreted using a j-j coupling scheme to give only two states with ? = 1 and 2. Of additional interest is the importance of the adiabatic noncrossing rule for the 0+ state which has the same symmetry as the ground state. The authors have extended earlier work on the molecular beam photodissociation studies on KI to the NaI, RbI, and CsI systems. A molecular beam of the alkali halide is crossed with a pulsed, polarized light beam of energy 3.57 eV. (Auth.)

1977-04-22

391

Density of mixed alkali borate glasses: A structural analysis  

International Nuclear Information System (INIS)

Density of mixed alkali borate glasses has been correlated with the glass structure. It is assumed that in such glasses each alkali oxide associates with a proportional quantity of B2O3. The number of BO3 and BO4 units related to each type of alkali oxide depends on the total concentration of alkali oxide. It is concluded that in mixed alkali borate glasses the volumes of structural units related to an alkali ion are the same as in the corresponding binary alkali borate glass. This reveals that each type of alkali oxide forms its own borate matrix and behaves as if not affected with the presence of the other alkali oxide. Similar conclusions are valid for borate glasses with three types of alkali oxide

2005-05-15

392

Density of mixed alkali borate glasses: A structural analysis  

Energy Technology Data Exchange (ETDEWEB)

Density of mixed alkali borate glasses has been correlated with the glass structure. It is assumed that in such glasses each alkali oxide associates with a proportional quantity of B{sub 2}O{sub 3}. The number of BO{sub 3} and BO{sub 4} units related to each type of alkali oxide depends on the total concentration of alkali oxide. It is concluded that in mixed alkali borate glasses the volumes of structural units related to an alkali ion are the same as in the corresponding binary alkali borate glass. This reveals that each type of alkali oxide forms its own borate matrix and behaves as if not affected with the presence of the other alkali oxide. Similar conclusions are valid for borate glasses with three types of alkali oxide.

Doweidar, H. [Glass Research Group, Physics Department, Faculty of Science, Mansoura University, P.O. Box 83, Mansoura 35516 (Egypt)]. E-mail: hdoweidar@mans.edu.eg; El-Damrawi, G.M. [Glass Research Group, Physics Department, Faculty of Science, Mansoura University, P.O. Box 83, Mansoura 35516 (Egypt); Moustafa, Y.M. [Glass Research Group, Physics Department, Faculty of Science, Mansoura University, P.O. Box 83, Mansoura 35516 (Egypt); Ramadan, R.M. [Glass Research Group, Physics Department, Faculty of Science, Mansoura University, P.O. Box 83, Mansoura 35516 (Egypt)

2005-05-15

393

Excitons versus free charges in organo-lead tri-halide perovskites  

Science.gov (United States)

Excitonic solar cells, within which bound electron-hole pairs have a central role in energy harvesting, have represented a hot field of research over the last two decades due to the compelling prospect of low-cost solar energy. However, in such cells, exciton dissociation and charge collection occur with significant losses in energy, essentially due to poor charge screening. Organic–inorganic perovskites show promise for overcoming such limitations. Here, we use optical spectroscopy to estimate the exciton binding energy in the mixed-halide crystal to be in the range of 50?meV. We show that such a value is consistent with almost full ionization of the exciton population under photovoltaic cell operating conditions. However, increasing the total photoexcitation density, excitonic species become dominant, widening the perspective of this material for a host of optoelectronic applications.

D’Innocenzo, Valerio; Grancini, Giulia; Alcocer, Marcelo J. P.; Kandada, Ajay Ram Srimath; Stranks, Samuel D.; Lee, Michael M.; Lanzani, Guglielmo; Snaith, Henry J.; Petrozza, Annamaria

2014-04-01

394

Raman and mid-infrared spectroscopic study of geometrically frustrated hydroxyl cobalt halides at room temperature  

International Nuclear Information System (INIS)

Mid-infrared absorption and Raman spectra of the geometrically frustrated material series, hydroxyl cobalt halides ß-Co2(OH)3Cl and ß-Co2(OH)3Br, are first, to the best of our knowledge, measured at room temperature, to study the corresponding relationship between their vibrational spectral properties and crystal microstructures. Through the comparative analysis of the four spectra we have categorically assigned the OH-related vibration modes of hydroxyl groups in the trimeric hydrogen bond environment (Co3 ?OH)3 ... Cl/Br, and tentatively suggested vibration modes of O-Co-O, Co-O and Cl/Br-Co-Cl/Br units. These results can also become the basis for analysing their low-temperature spectral properties, which can help to understand the underlying physics of their exotic geometric frustration phenomena around phase transition temperatures. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

2011-07-01

395

Phonon Dispersion Relations in Alkali Metals  

International Nuclear Information System (INIS)

It has been shown in this paper that the phonon dispersion curves of sodium in the [100], [110] and [111] symmetry directions can be explained well on the basis of a simple model, where one has to consider only central force constants between nearest and next nearest neighbours. The tangential force constant between the nearest neighbours is very much smaller as compared to the radial force constant, while for the next nearest neighbours the radial and tangential force constants are comparable. The calculation is carried out on the basis of the model suggested by de Launay, where it is shown that the conduction electrons exert a volume force for longitudinal modes. The stiffness constant of the electron gas is its bulk modulus which in de Launay's model is equal to the Cauchy discrepancy (C12-C14) for the cubic crystals. The three force constants ?1, ?2 and ?1' can be determined from the measured elastic constants and the secular equation can be solved to give the dispersion curves. The dispersion curves have also been obtained using the calculated values of the bulk modulus of the electron gas after considering not only the exchange and correlation energies but also the Fermi kinetic energy. These also agree fairly well with experiment. The measured elastic constants as well as calculated bulk modulus of the electron gas indicate that the Cauchy relation C12 = C44 holds good approximately in alkali metals. This result is rather surprising as it requires that the interaction between the atoms be central in nature in spite of the metallic binding. A justification for this has been given by Cochran. A model with four force constants is being worked out. They can be determined from the three elastic constants and calculated bulk modulus of the electron gas. (author)

1965-04-01

396

First-order correction for bond energy applied to polar molecules: Alkali halides, alkali cyanides, LiCH{sub 3}, and CH{sub 3}F  

Energy Technology Data Exchange (ETDEWEB)

The ionic bond in molecules containing an electropositive moiety and an electronegative moiety originates from a coupling between the ionic and the covalent contributions. Some representative cases in the example of LiF, LiCl, NaF, NaCl, KF, KCl, LiCH{sub 3}, CH{sub 3}F, LiCN, NaCN and KCN are calculated by ab initio and density functional methods. The resulting bond energy can be improved a posteriori by a recently proposed first-order method using the dipole moment or the effective charge. For the ab initio calculations, this method brings about a systematic improvement of the bond energy with respect to the experimental value. While the density functional method gives qualitatively mixed results, application of this first-order method generally improves the bond energy.

Lee, Dong-ki [Department of Chemistry and School of Molecular sciences (BK21), Korea Advanced Institute of Science and Technology, 305-701 Daejeon (Korea, Republic of); Lee, Yoon Sup [Department of Chemistry and School of Molecular sciences (BK21), Korea Advanced Institute of Science and Technology, 305-701 Daejeon (Korea, Republic of)], E-mail: YoonSupLee@kaist.ac.kr; Hagebaum-Reignier, D. [Chimie Theorique, Case 521 (CNRS, UMR 6517), Campus de Saint-Jerome, Universite de Provence, 13397 Marseille Cedex 20 (France); Jeung, Gwang-Hi [Chimie Theorique, Case 521 (CNRS, UMR 6517), Campus de Saint-Jerome, Universite de Provence, 13397 Marseille Cedex 20 (France)], E-mail: jeung@up.univ-mrs.fr

2006-09-11

397

Crystal chemistry of ceramic/metal systems. Final report, 29 September 1992-13 December 1996  

Energy Technology Data Exchange (ETDEWEB)

During the course of the project, several models for thermal expansion were developed extending earlier work of Reeber. The product of thermal expansion, bulk modulus, and volume has been shown to approach a constant at high temperatures for alkali halides, rare earth oxides, FCC metals, and ZnS. Models have been applied to investigate high temperature thermal expansion of alkali halides, rare earth oxides, group IV elements, FCC metals, BCC metals, SiC, III-V and II-VI compounds. Analytical expressions have been provided that represent the thermal expansion of these materials from near 0 K to the melting point. Models have also been extended to high pressure thermal expansion of MgO, NaCl, Group IV elements, and W. The bulk modulus and self-diffusion for W and Ta have been predicted to their melting points.

Reeber, R.R.

1997-01-16

398

Improved alkali-metal/silicate binders  

Science.gov (United States)

Family of inorganic binders utilizes potassium or sodium oxide/silicate dispersion and employs high mole ratio of silicon dioxide to alkali-metal binder. Binders are stable, inexpensive, extremely water resistant, and easy to apply.

Schutt, J.

1978-01-01

399

Calcium silicate hydrate: Crystallisation and alkali sorption  

International Nuclear Information System (INIS)

Homogeneous single C-S-H gels has been prepared for the investigation of alkali binding potential and crystallisation. A distribution coefficient, Rd, was introduced to express the partition of alkali between solid and aqueous phases at 25 deg. C. Rd is independent of alkali hydroxide concentration and depends only on Ca:Si ratio over wide ranges of alkali concentration. The trend of numerical values of Rd indicates that alkali bonding into the solid improves as its Ca:Si ratio decreases. Reversibility is demonstrated, indicating a possibility of constant Rd value of the material. Al has been introduced to form C-A-S-H gels and their alkali sorption properties also determined. Al substituted into C-S-H markedly increases Rd, indicating enhancement of alkali binding. However, the dependence of Rd on alkali concentration is non-ideal with composition. A two-site model for bonding is presented. Crystallisation both under saturated steam and 1 bar vapour pressure has been investigated. It has been shown that heat treatment by saturated steam causes crystallisation of gels. The principal minerals obtained were (i) C-S-H gel and Ca(OH)2 at -55 deg. C, (ii) 1.1 nm tobermorite, jennite and afwillite at 85 -130 deg. C, and (iii) xonotlite, foshagite and hillebrandite at 150-180 deg. C. Properties of crystalline C-S-H were also reported for reversible phase transformation, pH conditioning ability, seeding effect and solubility. At 1 bar pressure, crystallisation is slower than in saturated steam due to lower water activity. Tobermorite-like nanodomains develop during reaction at low Ca/Si ratios. In some Ca-rich compositions, Ca(OH)2 is exsolved and occurs as nano-sized crystallites. (author)

2000-01-01

400

Thermodynamic properties of alkali metal arsenates  

International Nuclear Information System (INIS)

Experimental determination of standard formation heat, phase transformation heat using DTA, calorimetry methods and estimates of standard formation heat, entropy and heat capacity of alkali metal arsenates using phase diagrams of the MeAsO_3-Me_3AsO_4 (Me-Na, K, Rb, Cs) systems are considered. Some regularities in changing thermodynamic properties of the compounds depending on atomic number ionic radii of alkali metal, molecular mass of arsenates have been found

1985-01-01

 
 
 
 
401

Method for calcining nuclear waste solutions containing zirconium and halides  

International Nuclear Information System (INIS)

A reduction in the quantity of gelatinous solids which are formed in aqueous zirconium-fluoride nuclear reprocessing waste solutions by calcium nitrate added to suppress halide volatility during calcination of the solution while further suppressing chloride volatility is achieved by increasing the aluminum to fluoride mole ratio in the waste solution prior to adding the calcium nitrate

1979-01-01

402

Dielectric measurements of adsorbed krypton on lamellar halides  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present simultaneous measurements of adsorption isotherms and dielectric isotherms for krypton on lamellar halides. The comparison between the two isotherms shows that dielectric method is well adapted to characterize the multilayer formation. The evolution of dielectric properties from a two-dimensional system towards the bulk is also obtained.

Laheurte, J. P.; Noiray, J. C.; Obadia, M.; Romagnan, J. P.

1981-01-01

403

Semiempirical and DFT Investigations of the Dissociation of Alkyl Halides  

Science.gov (United States)

Enthalpy changes corresponding to the gas phase heats of dissociation of 12 organic halides were calculated using two semiempirical methods, the Hartree-Fock method, and two DFT methods. These calculated values were compared to experimental values where possible. All five methods agreed generally with the expected empirically known trends in the…

Waas, Jack R.

2006-01-01

404

Alkali metal crystalline polymer electrolytes  

Science.gov (United States)

Polymer electrolytes have been studied extensively because uniquely they combine ionic conductivity with solid yet flexible mechanical properties, rendering them important for all-solid-state devices including batteries, electrochromic displays and smart windows. For some 30 years, ionic conductivity in polymers was considered to occur only in the amorphous state above Tg. Crystalline polymers were believed to be insulators. This changed with the discovery of Li+ conductivity in crystalline poly(ethylene oxide)6:LiAsF6 (refs 4, 5). However, new crystalline polymer electrolytes have proved elusive, questioning whether the 6:1 complex has particular structural features making it a unique exception to the rule that only amorphous polymers conduct. Here, we demonstrate that ionic conductivity in crystalline polymers is not unique to the 6:1 complex by reporting several new crystalline polymer electrolytes containing different alkali metal salts (Na+, K+ and Rb+), including the best conductor poly(ethylene oxide)8:NaAsF6 discovered so far, with a conductivity 1.5 orders of magnitude higher than poly(ethylene oxide)6:LiAsF6. These are the first crystalline polymer electrolytes with a different composition and structures to that of the 6:1 Li+ complex.

Zhang, Chuhong; Gamble, Stephen; Ainsworth, David; Slawin, Alexandra M. Z.; Andreev, Yuri G.; Bruce, Peter G.

2009-07-01

405

Substitution mechanism of alkali metals for strontium in strontium hydroxyapatite  

International Nuclear Information System (INIS)

Strontium hydroxyapatites substituted by alkali metals are synthesized by double decomposition method in basic medium. Structures of Sr9.50Na0.30(PO4)6(OH)1.30 (SrNaHAp) and Sr9.81K0.12(PO4)6(OH)1.74 (SrKHAp) are determined by X-ray powder diffraction. Both compounds are isotypic and crystallize in hexagonal system (space group P63/m) with the following cells: a=9.751(3) A and c=7.279(3) A for SrNaHAp and a=9.755(4) A and c=7.284(3) A for SrKHAp. Results are compared to those of Sr10(PO4)6(OH)2. According to the site occupancy factors, in SrNaHAp sodium is localized in site (I) and in SrKHAp potassium in site (II). Both structures contain vacancies in hydroxyl and metal sites. The mechanism of alkali metals substitution for strontium proposed explains the vacancies formation

2003-01-25

406

Acquisition of alkali-soluble fluoride by enamel through treatment with NaF-containing toothpastes in vitro.  

Science.gov (United States)

The first aim of the present study was to examine if alkali-soluble fluoride (calcium fluoride-like material and adsorbed fluoride) forms when a NaF-containing toothpaste is applied on human enamel surface in vitro. The centrifuged supernatants of toothpastes dissolved in distilled water were used and four different commercial NaF-containing toothpastes were tested. The second aim was to investigate if pyrophosphate would interfere with the deposition of alkali soluble fluoride. The formation of alkali-soluble fluoride was determined by chemical analysis and visualized by scanning electron microscopy (SEM). It was ascertained that all tested toothpastes contained free fluoride according to the manufacturers' specifications. It was shown that they promoted deposition of alkali soluble fluoride on the enamel surface. The amount of deposited material increased with the time of exposure. The clinical effect of a NaF-containing toothpaste may thus well depend on an initial formation of alkali-soluble fluoride. Fluoride from this reservoir may adsorb onto the enamel crystals and inhibit further demineralization or increase the rate of remineralization during cariogenic challenges. It was also demonstrated that pyrophosphate did not interfere with the deposition of alkali soluble fluoride. PMID:1315451

Cruz, R; Ogaard, B; Rölla, G

1992-04-01

407

Solubility of alkali and alkaline earth metal sulfates in anhydrous hydrogen peroxide  

International Nuclear Information System (INIS)

Solubility of alkali and alkaline earth metals sulfates is determined by isothermal method in anhydrous hydrogen method. Sodium sulfated of anhydrous hydrogen peroxide are crystallized in form of Na_2SO_4x2H_2O_2 solvates. Presence of peroxosolvates in the rest of solvates was not determined. Solubility of fluorides and perchlorates in hydrogen peroxide was also considered. 9 refs., 1 fig

1995-03-01

408

Spectroscopic effects of disorder and vibrational localization in mixed-halide metal-halide chain solids  

Energy Technology Data Exchange (ETDEWEB)

Resonance Raman techniques, together with lattice-dynamics and Peierls-Hubbard modelling, are used to explore the electronic and vibrational dynamics of the quasi-one-dimensional metal-halogen chain solids [Pt(en){sub 2}][R(en){sub 2}X{sub 2}](ClO{sub 4}){sub 4}, (en = C{sub 2}H{sub 8}N{sub 2} and X=Cl, Br), abbreviated ``PLX.`` The mixed-halide materials PtCl{sub 1-x}Br{sub x} and PtCl{sub 1-x}I{sub x} consist of long mixed chains with heterojunctions between segments of the two constituent materials. Thus, in addition to providing mesoscale modulation of the chain electronic states, they serve as prototypes for elucidating the properties to be expected for macroscopic heterojunctions of these highly nonlinear materials. Once a detailed understanding of the various local vibrational modes occurring in these disordered solids is developed, the electronic structure of the chain segments and junctions can be probed by tuning the Raman excitation through their various electronic resonances.

Love, S.P.; Scott, B.; Worl, L.A.; Huckett, S.C.; Saxena, A.; Huang, X.Z.; Bishop, A.R.; Swanson, B.I.

1993-02-01

409

Lanthanum halide scintillators: Properties and applications  

International Nuclear Information System (INIS)

BrilLanCe[reg]-350 and BrilLanCe[reg]-380, Saint-Gobain Crystals' trade-names for LaCl3:Ce and LaBr3:Ce are being brought to market under exclusive license to Delft and Bern Universities. We are reporting the properties of crystals produced with commercially viable processes and find they match others' observations. These scintillators are bright (60,000 photons/MeV for LaBr3:Ce) and have very linear response, a combination that leads to very good energy resolution (3:Ce). The materials also have fast scintillation decay times (3:Ce). These excellent properties are retained at high temperature with only moderate light loss (138 and Ac227, the latter having been substantially reduced in recent processing. BrilLanCe[reg]-350 is now available in detectors up to 51 mm diameter while 38 mm diameter is available for BrilLanCe[reg]-380. Larger sizes are expected

2006-07-15

410

Lanthanum halide scintillators: Properties and applications  

Energy Technology Data Exchange (ETDEWEB)

BrilLanCe[reg]-350 and BrilLanCe[reg]-380, Saint-Gobain Crystals' trade-names for LaCl{sub 3}:Ce and LaBr{sub 3}:Ce are being brought to market under exclusive license to Delft and Bern Universities. We are reporting the properties of crystals produced with commercially viable processes and find they match others' observations. These scintillators are bright (60,000 photons/MeV for LaBr{sub 3}:Ce) and have very linear response, a combination that leads to very good energy resolution (<3% at 662 keV and about 6% at 122 keV for LaBr{sub 3}:Ce). The materials also have fast scintillation decay times (<30 ns) which supports counting applications at very high rate. These fast light output properties also lead to very fast timing (<300 ps coincidence resolving time on 30 mm long pieces of LaBr{sub 3}:Ce). These excellent properties are retained at high temperature with only moderate light loss (<10%) at 175 deg. C in both materials. The detectors carry natural background in La{sup 138} and Ac{sup 227}, the latter having been substantially reduced in recent processing. BrilLanCe[reg]-350 is now available in detectors up to 51 mm diameter while 38 mm diameter is available for BrilLanCe[reg]-380. Larger sizes are expected.

Iltis, Alain [Saint-Gobain Crystals, 104 Route de Larchant, 77140 St Pierre les Nemours (France)]. E-mail: Alain.Al.Iltis@saint-gobain.com; Mayhugh, M.R. [Saint-Gobain Crystals, 12345 Kinsman Road, Newbury, OH 44122 (United States); Menge, P. [Saint-Gobain Crystals, 12345 Kinsman Road, Newbury, OH 44122 (United States); Rozsa, C.M. [Saint-Gobain Crystals, 12345 Kinsman Road, Newbury, OH 44122 (United States); Selles, O. [ENSCP, laboratoire de chimie appliquee de l' etat solide, 10 rue Pierre and Marie Curie, 75005 Paris (France); Solovyev, V. [Saint-Gobain Crystals, 12345 Kinsman Road, Newbury, OH 44122 (United States)

2006-07-15

411

Viscosity behavior and mixed alkali effect of alkali aluminosilicate glass melts  

Energy Technology Data Exchange (ETDEWEB)

The viscosities of (25-x)Na2O{center_dot}xK2O{center_dot}yAl2O3centre dot(27-y)SiO2 glasses between 1400-1000degC and their transformation temperatures (Tg) were determined. In the case of mixed alkali glass melts with Al2O3/R2O=0 (R2O=Na2O+K2O), a viscosity minimum, so-called mixed alkali effect has been found against K2O/R2O. However, mixed alkali aluminosilicate glass melts show no minimum but a linearity. This indicates that the mixed alkali effect in viscosity becomes weaker or disappears with decreasing nonbridging oxygen content. On the other hand, although viscosity minima have been found at Tg curves, this mixed alkali effect in Tg showed an independence of Al2O3 content. The results of this experiment were compared with the previous work on the resistivity measurement in mixed alkali aluminosilicate melts and it has been concluded that the models for the mixed alkali effect in both properties (viscosity and electrical conductivity) have to be considered separately. 29 refs., 8 figs.

Kim, K.; Lee, H. [Kunsan National University, Chunbuk (Korea, Republic of)

1997-10-01

412

Alkali-bonded composites for thermal and acoustic insulation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Geopolymers are alkali bonded ceramics that thank to their fully inolrganic nature have high temperature resistance depending on their compositions. An overview of the research of ISTEC on Alkali-bonded composites for thermal and acoustic insulation have been presented

Medri, Valentina

2012-01-01

413

Sampling And Measuring Alkali Salts In Industrial Gasification Plants  

Energy Technology Data Exchange (ETDEWEB)

A new alkali sampling technique was used for measuring sodium and potassium salts in gases from two different industrial biomass gasifiers. The method allows sampling tars and alkali salts in the same solution. (author)

Kowalski, T.; Schuler, A.J.; Ludwig, Chr.; Schneebeli, J.; Biollaz, S.

2005-03-01

414

Experimental determination of partition coefficients for Rb, Sr, and Ba between alkali feldspar and silicate liquid  

International Nuclear Information System (INIS)

Partitioning of Rb, Sr and Ba between alkali feldspar and a synthetic granitic melt has been determined at 8 kb and 720 to 7800C for a single quaternary granite composition. The results suggest that Henry's Law is obeyed by Rb up to approximately 0.8 wt.%Rb2O in both the liquid and in the alkali feldspar. The measured D values for Rb range from 0.77 to 1.1 For Ba, Henry's Law is obeyed up to approximately 0.6 wt.% BaO in the liquid and approximately 5 wt.% BaO in the alkali feldspar. D values for Ba range from 6.4 to 14. For Sr there is only a crude relationship between concentration in the liquid and concentration in the alkali feldspar at concentrations greater than approximately 0.6wt.%SrO in the liquid and approximately 0.4 wt.% SrO in the alkali feldspar. D values for Sr range from 1.2 to 5.0. Partitioning of Sr is apparently sensitive to the concentration of Ba in the system and this partly explains the failure of Sr to obey Henry's Law. Linear least-squares fits to the partitioning data as a function of temperature suggest inverse correlation between temperature and D values. Rb shows only a slight temperature effect whereas Ba and Sr appear to be rather strongly affected by temperature, but the temperature range examined here is small compared to the scatter in the data making these trends relatively uncertain. Other factors that appear to affect partitioning, especially of Sr, are growth rate, development of sector zoning, and Or content of the alkali feldspar. These factors severely limit the use of partitioning of these elements in alkali feldspar as geothermometers. The technique for measuring growth rates utilized here combined with measurement of trace element depletion in diffusion boundary layers adjacent to the alkali feldspar crystals makes it possible to estimate diffusivities for Ba and Sr. These estimates suggest a difference of 2 orders of magnitude between diffusivities for Ba and Sr in a vapor-saturated melt and those measured for a dry obsidian glass. (author)

1978-06-01

415

Selection of non-adsorbing alkali components  

Energy Technology Data Exchange (ETDEWEB)

This project consists of three phases of laboratory experimental study. In phase I (screening), eight candidate materials, 304SS (serves as a base material for comparison), Hastelloy C-276, Hastelloy X, Haynes No. 188, Allonized 304SS, Pt-coated 304SS, and ceramic-coated 304SS, will be subjected to atmospheric TGA study under the simulated PFBC (oxidizing) environment with and without alkali vapor doping. Each candidate material will be evaluated for its resistance toward alkali-vapor capture. In addition, a post-test metallographic characterization of the sample will be performed to obtain a better understanding of the alkali capture mechanism and material behavior. The material(s) with little or no alkali-vapor adsorption will be selected as the promising material(s) for the Phase II study. In Phase II, the promising material(s) will be further tested in the TGA under elevated pressure to simulate the PFBC environment (in terms of temperature, pressure, and gas composition). The effect of pressure on the extent of alkali-vapor adsorption will be evaluated, and the test samples will be metallographically characterized. The most promising candidate material(s) will be identified and recommended for further tesfing in the actual PFBC environment. In Phase III, four materials will be selected from the eight candidate materials screened in the PFBC environment and will be evaluated for their alkali-vapor capture by atmospheric TGA under the coal gasification fuel gas (reducing) environment. The tested samples will also be metallographically characterized. The most promising material(s) will be identified and recommended for further testing in the actual coal gasification environment.

Lee, S.H.D.; Natesan, K.; Swift, W.M.

1992-01-01

416

Selection of non-adsorbing alkali components  

Energy Technology Data Exchange (ETDEWEB)

This project consists of three phases of laboratory experimental study. In phase I (screening), eight candidate materials, 304SS (serves as a base material for comparison), Hastelloy C-276, Hastelloy X, Haynes No. 188, Allonized 304SS, Pt-coated 304SS, and ceramic-coated 304SS, will be subjected to atmospheric TGA study under the simulated PFBC (oxidizing) environment with and without alkali vapor doping. Each candidate material will be evaluated for its resistance toward alkali-vapor capture. In addition, a post-test metallographic characterization of the sample will be performed to obtain a better understanding of the alkali capture mechanism and material behavior. The material(s) with little or no alkali-vapor adsorption will be selected as the promising material(s) for the Phase II study. In Phase II, the promising material(s) will be further tested in the TGA under elevated pressure to simulate the PFBC environment (in terms of temperature, pressure, and gas composition). The effect of pressure on the extent of alkali-vapor adsorption will be evaluated, and the test samples will be metallographically characterized. The most promising candidate material(s) will be identified and recommended for further tesfing in the actual PFBC environment. In Phase III, four materials will be selected from the eight candidate materials screened in the PFBC environment and will be evaluated for their alkali-vapor capture by atmospheric TGA under the coal gasification fuel gas (reducing) environment. The tested samples will also be metallographically characterized. The most promising material(s) will be identified and recommended for further testing in the actual coal gasification environment.

Lee, S.H.D.; Natesan, K.; Swift, W.M.

1992-11-01

417

Palladium- (and nickel-) catalyzed vinylation of aryl halides  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Functionalized styrenes are extremely useful building blocks for organic synthesis and for functional polymers. One of the most general syntheses of styrenes involves the combination of an aryl halide with a vinyl organometallic reagent under catalysis by palladium or nickel complexes. This Feature Article provides the first comprehensive summary of the vinylation methods currently available along with a critical comparison of the efficiency, cost and scope of the methods.

Denmark, Scott E.; Butler, Christopher R.

2009-01-01

418

Influence of the Print Run on Silver Halide Printing Plates  

Directory of Open Access Journals (Sweden)

Full Text Available The most common printing technique today is lithography. The difference between printing and nonprinting areason a printing plate is accomplished by opposite physical and chemical properties of those areas (MacPhee, 1998.The printing areas are made of photoactive layer that attracts oil and chemical substances with oil solvent – printinginks. The nonprinting areas are made of aluminium-oxide which attracts water based substances – the fountainsolution.There are many of various types of photoactive layer which are used for production of offset printing plates, amongothers is silver halide layer. The usage of the silver halide technology in the graphic reproduction is not a novelty.The filmmaking phase is based on the usage of the silver halide as the photographically active ingredient, for instance,AgBr (silver bromide. The new, digital plate making technology (Computer to Plate, CtP eliminates thefilmmaking phase and therefore enables control of the printing plate’s exposure made by computer. CtP technologyeliminates the filmmaking phase, but it also results with the reduction of needed material quantities and requiredtime for the production (Limburg, 1994; Seydel, 1996.In this paper the basis of the graphic reproduction by using the silver halide digital printing plates was described.The changes of the AgX copying l