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1

Mechanoluminescence of ?-irradiated alkali halide crystals  

International Nuclear Information System (INIS)

The mechanoluminescence (ML) spectra of ?-irradiated alkali halide crystals consist of a narrow band of different ranges towards the ultraviolet or violet region. The ML spectra of LiF and NaCl consist of two bands. The ML spectra obtained during the release of pressure are similar to the ML spectra obtained during the application of pressure. The ML spectra of ?-irradiated alkali halide crystals both at the release and at the application of pressure are similar to that of X-irradiated alkali halide crystals. The ML spectra are compared with the other types of luminescence spectra and it is found that the ML spectra of coloured alkali halide crystals resemble the high energy spectra and the thermoluminescence spectra to a large extent. The wavelength corresponding to the peak of the ML spectra is found to be proportional to the square of the lattice constant of the crystals. (author).

1984-01-01

2

Mechanoluminescence produced during cleavage of ?-irradiated alkali halide crystals  

International Nuclear Information System (INIS)

When g-irradiated alkali halide crystals are cleaved, then in their mechanoluminescence (ML) intensity versus time curve, two peak intensities Im1 and Im2 are observed at time tm1 and tm2 respectively. The ML intensity both beyond tm1 and tm2 decrease exponentially. It is shown that ML provides a new technique for determining the pinning time of dislocations and lifetime of the electrons in dislocation band. (author)

2001-01-01

3

Temperature dependence of positronium diffusivity in alkali halide crystals  

International Nuclear Information System (INIS)

The temperature dependence of the diffusivity of delocalized positronium atom scattered on longitudinal acoustic phonons in alkali halide crystals has been investigated theoretically. The delayed calculations including the non-elastic scattering at low temperature and the influence of the positronium scattering form-factor have been performed within the relaxation time approximation. The diffusion of self trapped positronium is analysed qualitatively. The results obtained are in good agreement with known experimental data. (author). 12 refs, 1 tab.

1997-01-01

4

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

2011-01-01

5

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

6

Apparatus for the coloration of laser-quality alkali halide crystals.  

UK PubMed Central (United Kingdom)

A heat-pipe apparatus allowing for the additive coloration of laser-quality alkali halide crystals is described. It has the following features: (1) Prepolished crystals emerge ready for direct installation in the laser; (2) F-center densities are directly proportional to the buffer gas pressure; (3) An air lock allows the same charge of alkali metal to be used many times over.

Mollenauer LF

1978-06-01

7

Cu halide nanoparticle formation by diffusion of copper in alkali halide crystals  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish Atomos de cobre han sido introducidos por difusión en cristales de NaCl, KCl y KBr a 500°C. Los cristales han sido analizados ópticamente con medidas de fotoluminiscencia y por microscopía electrónica de barrido. Los espectros de emisión y excitación, medidos a baja temperatura muestran el efecto de confinamiento de exciton, indicando la formación de nanopartículas de CuX (X=Cl, Br), lo cual ha sido confirmado por imágenes de microscopía electrónica. Este mét (more) odo es propuesto como un método alternativo para obtener nanopartículas de CuX en cristales halogenuros alcalinos. Abstract in english Copper atoms have been introduced by diffusion in NaCl, KCl and KBr crystals at 500°C. The crystals have been optically analyzed with photoluminescence measurements and by scanning electron microscopy. The emission and excitation spectra measured at low temperatures show the exciton confinement effect, indicating the formation of CuX (X=Cl, Br) nanoparticles, which has been confirmed by electron microscopy images. This is proposed as an alternative method to obtain CuX nanoparticles in alkali halides crystals.

Pérez-Rodríguez, A.; Flores-Acosta, M.; Rodríguez-Mijangos, R.; Pérez-Salas, R.

2006-04-01

8

Radiophotoluminescence of alkali-halide crystals stimulated by Bessel laser beam  

International Nuclear Information System (INIS)

A new approach to realization of optimal high-resolution reading of deep X-ray images in X-ray-sensitive materials on the base of alkali-halide crystals modified with admixtures has been suggested and investigated experimentally. A possibility to use diffraction axicons with ring aperture for forming micron bright light beams (spatially truncated Bessel beams) which can efficiently de-excite radiophotoluminescence centers lying at large depth in crystals is also presented.

2000-06-21

9

Radiophotoluminescence of alkali-halide crystals stimulated by Bessel laser beam  

CERN Document Server

A new approach to realization of optimal high-resolution reading of deep X-ray images in X-ray-sensitive materials on the base of alkali-halide crystals modified with admixtures has been suggested and investigated experimentally. A possibility to use diffraction axicons with ring aperture for forming micron bright light beams (spatially truncated Bessel beams) which can efficiently de-excite radiophotoluminescence centers lying at large depth in crystals is also presented.

Lyakh, V V; Kochubey, D I; Gyunsburg, K E; Zvezdova, N P; Kochubey, D I; Sedova, Y G; Koronkevich, V P; Poleschuk, A G; Sedukhin, A G

2000-01-01

10

Mechanoluminescence response to the plastic flow of coloured alkali halide crystals  

Energy Technology Data Exchange (ETDEWEB)

The present paper reports the luminescence induced by plastic deformation of coloured alkali halide crystals using pressure steps. When pressure is applied onto a gamma-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 I{sub m} corresponding to the peak of ML intensity versus time curve and the total ML intensity I{sub T} increase with increase in value of the applied pressure. The time t{sub m} corresponding to the ML peak slightly decreases with the applied pressure. After t{sub m}, 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 gamma-irradiated alkali halide crystals, the pinning time of dislocations, diffusion time of holes towards F-centres, the energy gap E{sub a} 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.

Chandra, B.P., E-mail: bpchandra4@yahoo.co.i [Shri Shankaracharya College of Engineering and Technology, Junwani, Bhilai (C.G.) 490020 (India); Bagri, A.K. [Department of Postgraduate Studies and Research in Physics, Rani Durgawati University, Jabalpur 482001 (India); Chandra, V.K. [Department of Electrical and Electronics Engineering, Chhatrapati Shivaji Institute of Technology, Shivaji Nagar, Kolihapuri, Durg (C.G.) 491001 (India)

2010-02-15

11

Heterogeneous reactions in the system alkali-halide crystal/air at X-ray activation  

International Nuclear Information System (INIS)

The method of electron microscopy is used to study heterogeneous synthesis of alkali metal nitrates in the system crystal (KCl, KBr, KI, NaCl, RbBr)/air at X-ray activation. Nitrate accumulation kinetics at different doses and rates (830 and 3 R s-- cm-2) of X-radiation is investigated. Peculiarities of kinetic regularities of radiation nitration of alkali-halide microcrystals are considered, and basic stages of heterogeneous process of nitrates solid-phase synthesis in the system

2010-01-01

12

Characteristics of F centers of alkali-halide crystals in ground and excited states  

International Nuclear Information System (INIS)

The molecular-statics method is used to calculate the displacements of the lattice ions nearest to the F center in alkali halide crystals with NaCl and CsCl structures (altogether twenty crystals). The calculations are made for the 1s and 2p states of the F-center electron with allowance for the angular dependence of the Coulomb potential created by the electron in the 2p state. The absorption and emission energies of the F center are calculated. The calculated energies agree qualitatively with experiment and reproduce the experimentally found tendencies of changes in these energies when passing from one crystal to another

2006-01-01

13

ESR and ESR-imaging of heavily irradiated alkali halide crystals  

International Nuclear Information System (INIS)

[en] An investigation of the formation and properties of small metal particles in electron-irradiated alkali halide-crystals by the ESR method was carried out. The behavior of ESR lines and ESR-imaging from the moment of appearance of the metallic particles is irradiated NaCl, NaCl:OH and LiF crystals is studied. The magnetic spin susceptibility and the line-width has been found to depend on dose and temperature. The ESR results are compared with a theoretical model and some conclusions made about the existence of a metal-insulator transition in irradiated crystals. (author)

1996-01-01

14

ESR and ESR-imaging of heavily irradiated alkali halide crystals  

Energy Technology Data Exchange (ETDEWEB)

An investigation of the formation and properties of small metal particles in electron-irradiated alkali halide-crystals by the ESR method was carried out. The behavior of ESR lines and ESR-imaging from the moment of appearance of the metallic particles is irradiated NaCl, NaCl:OH and LiF crystals is studied. The magnetic spin susceptibility and the line-width has been found to depend on dose and temperature. The ESR results are compared with a theoretical model and some conclusions made about the existence of a metal-insulator transition in irradiated crystals. (author).

L`Vov, S.G.; Cherkasov, F.G.; Silaev, V.A. [AN SSSR, Kazan (Russian Federation). Fiziko-Tekhnicheskij Inst.; Vitol, A.Ya. [Rizhskij Politekhnicheskij Inst., Riga (Latvia)

1996-11-01

15

Radiation-induced radio-frequency electromagnetic emission in alkali-halide crystals  

International Nuclear Information System (INIS)

The transformation and annealing of color centers (at heating from 77 to 500 K) of X-irradiated alkali-halide crystals (LiF, KBr, KCl:Tl, additively coloured KBr) along with crystal discoloration and luminescence is accompanied by radio-frequency electromagnetic emission. The photostimulated radio-frequency electromagnetic emission of crystals studied at visible and IR-light irradiation is revealed. The recombination electromagnetic emission going with transformation and colour centers annealing at photo- and thermo stimulation is provided by electron-hole recombination processes and has quantum character

2010-01-01

16

Ga+, In+ and Tl+ Impurities in Alkali Halide Crystals Distortion Trends  

CERN Document Server

A computational study of the doping of alkali halide crystals (AX: A = Na, K; X = Cl, Br) by ns2 cations (Ga+, In+ and Tl+) is presented. Active clusters of increasing size (from 33 to 177 ions) are considered in order to deal with the large scale distortions induced by the substitutional impurities. Those clusters are embedded in accurate quantum environments representing the surrounding crystalline lattice. The convergence of the distortion results with the size of the active cluster is analyced for some selected impurity systems. The most important conclusion from this study is that distortions along the (100) and (110) crystallographic directions are not independent. Once a reliable cluster model is found, distortion trends as a function of impurity, alkali cation and halide anion are identified and discussed. These trends may be useful when analycing other cation impurities in similar host lattices.

Aguado, A

2000-01-01

17

F-center and self-trapped exciton formation in strongly excited alkali halide crystals  

International Nuclear Information System (INIS)

Method of luminescent and absorption spectroscopy with time resolution was used to study the effect of density of electron pulse excitation (tp=10-8 s, P=(105-108) WXcm-2) on efficiency of ?? two-halide autolocalized exciton (TALE) and F-centers (?F) formation in CsI, CsBr, KBr, KI alkali halide crystals. It was established that for all studied systems the elevation of P power of electron beam (EB) from 105 up to 5X107 WXcm-2 resulted to sufficient decrease of production efficiency and yield of TALE luminescence. In the case when F-centers of colour are induced predominantly by pulsed irradiation in crystals, F-center yield is independent of P. If F-centers and TALE are produced in comparable amounts (CsBr crystals, T=80 K), ?? decrease with P growth is accompanied by ?F growth.

1988-01-01

18

Ion-electron and secondary electron emissions from defective alkali halide crystals  

International Nuclear Information System (INIS)

The influence of color centers (CC), produced by low energy electron irradiation, on ion- and secondary-electron emission (IEE and SEE), thermoluminescence (TL) and F1-absorption of alkali halide crystals (AHC) has been investigated. It has been shown that IEE and SEE- ? and ? coefficients, the light sum S of TL and F1-centers concentration NF1 versus electron irradiation dose change nonmonotonically due to the generation of CC in near-surface crystal layers. It has been found that at kinetic IEE the interaction of the excited electrons from the valence band with the CC electrons will be selective by means of exciton generation.

1992-01-01

19

Second-order optical nonlinearity in alkali halide crystals containing point defects  

Science.gov (United States)

Model calculation of second order susceptibilities for FA color centers in wide band gap materials are reported. The second order optical nonlinearity in crystals of alkali halide due to FA color centers evaluated theoretically. The density matrix formalism is employed and the equation of motion is solved by second order perturbation to evaluate the nonlinear optical susceptibilty for second harmonic generation as well as frequency mixing. It is found that the system shows large resonance-enhanced second order susceptibility (~10-16 mV-1) for color center concentration of ~1023 m-3. A scheme of phase matching in terms of anomalous dispersion of the centers and coherent length are discussed.

Majles Ara, Mohammad H.

2003-12-01

20

Formation of excitons nearby the defects in alkali halide crystals  

International Nuclear Information System (INIS)

Through the conducted studies by methods of pulsed spectroscopy it is shown that presence of defects, including electroneutral ones relative to the crystal lattice, essentially influences topography of distribution of electron excitations created by radiation. The lattice deformation in the area of defects is the most probable cause of the defects impact on the topography of electron excitations distribution. It is shown that there exists an oscillating potential relief, the presence whereof leads to the carriers capture and their localization in this area

1996-01-01

 
 
 
 
21

A statistical mechanical theory for the crystallization of alkali halides from aqueous solution  

Energy Technology Data Exchange (ETDEWEB)

The crystallization transitions and physical stability of model aqueous alkali halide solutions are investigated. A second-order density functional theory is developed for molecules of general symmetry, and is applied to the crystallization of anhydrous alkali halides, ice Ih, sodium chloride dihydrate, and lithium iodide trihydrate from the appropriate solutions. Thermodynamic stability theory is clarified and applied, using Kirkwood-Buff methods, to ionic solutions and a simple binary liquid mixture. The liquid correlation functions are obtained for two liquid models. In the first, ions are modeled as charged hard spheres, and the solvent as a polarizable multipolar hard sphere. The second is similar but involves a modification to the hard repulsive core of the ion-ion potential, and this is found to have a strong influence on solution properties and cyrstallization transitions. A technique involving Ewald sums is developed to aid the convergence of sums over direct lattice vectors. The resulting theory is shown to be superior for these models to a reciprocal lattice vector method. The theory for molecules such as H[sub 2]O requires a number of one-dimensional integrals to be performed numerically. The density functional theory yields minima for nearly all systems, showing the possibility of a phase transition. Model dependence is shown to be important in determining whether the equilibrium is under conditions similar to those of real systems, and whether the crystal parameters are similar to those of real solids. In applying stability concepts, it is important to distinguish between the strictest criteria of stability and the weaker criteria. This is used to clarify some misconceptions in the literature, and then give its nontrivial application to electrolytes. The results indicate that salts with only large ions, such as CsI, and those with a small ion, such as Na[sup +] or K[sup +], behave differently near the absolute stability limit.

Ursenbach, C.

1991-01-01

22

An optical criterion to obtain miscible mixed crystals in alkali halides  

Scientific Electronic Library Online (English)

Full Text Available 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 miscibles en cualquier concentración de sus componentes. Tener el resultado de estas mezclas cristalinas está relacionado al centro F a través del comportamiento observado en (more) 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 components. 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 functio (more) n 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.

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

2008-11-01

23

Luminescent unit computerization to research spectral characteristics of fine film alkali halide crystal  

International Nuclear Information System (INIS)

The fundamental optical absorption of ion crystals characterizes the creation of different free low energetic electronic excitation (the excitons and electron-hole pairs), but their straight registration is not possible because of incommensurable big absorption factor of alkali halide monocrystals. So to registration the spectrums of alkali halide monocrystal very fine layers are necessary. We have received fine films of Nal and KCl in system of KCl-Nal-KCl, KCl-KI-KCl on the base of universal vacuum post VUP-4, VUP-5 by thermal evaporation. A unique spectral unit has been created For this on the basic the SDL-2 complex. Complex consists of radiator, systems of condensers, monochromators MDR-12 and MDR-23, receivers of radiation, controller by unit. Connect and control of monochromators by means of IBM-compatible computer has been created. Kinematics schemes of monochromators provide consequent removing on output slot of monochromatic radiation in operating range of each diffraction lattice and indication its wavelength. The tumbling diffraction lattices is done the crossbar engines SHDR-711. For this special plate of control and block of reinforcement for crossbar engines in monochromators MDR-12 and MDR-23 are designed and constructed. Created controller of monochromators consists of double cascade preamplifier on transistors n-p-n type (815G) and logical scheme, constructed on summers and K555 series triggers. The preamplifier is used for reinforcement of signal to available amplifier on transistors KT837D. The logical scheme reduces the number of used categories of bidirectional port and enables unhooking the feeding to the windings of crossbar engine at conservation of previous combination of signals. The connection controller of monochromators is done through controller of port of computer with use the parallel interface. For installing computerized system of collection and data processing is provided marketed by means of modern object-oriented programming languages (Visual C++ 6.0, Visual Basic 6.0). As the result of the experiments it has been noted that the burning effect of own luminescence is in its maximum in the iodides of alkaline metals, for instance, in KI, NaI, RbI, and CsI crystals. From the point of the experimental equipment in order to registration the fundamental optical absorption of these crystals there is no necessity in such rare vacuum monochromators

2002-01-01

24

Mechanoluminescence induced by elastic deformation of coloured alkali halide crystals using pressure steps  

International Nuclear Information System (INIS)

During the elastic deformation of coloured alkali halide crystals, the bending segments of dislocations capture F-centre electrons lying in the expansion region of edge dislocations, to the states of dislocation band. After the separation from interacting F-centres, the captured electrons move together with the bending segments of dislocations and also drift along the axis of dislocations and subsequently the radiative electron-hole recombinations, owing to both the processes of captured-electron movement, give rise to the light emission. The generation rate of electrons in the dislocation band and the mechanoluminescence (ML) intensity initially increase with time, attain maximum value at a particular time, and then they decrease with time. The intensity Im corresponding to the peak of ML intensity versus time curve and the total intensity IT of ML increase with the applied pressure and also with the density of F-centres in the crystals. At low temperature, both Im and IT increase with temperature and at higher temperature they decrease with increasing temperature due to the thermal bleaching of F-centres and also due to the decrease in luminescence efficiency. Thus, both Im and IT are optimum for a particular temperature of the crystals. For longer time duration, the ML intensity decreases exponentially with time in which the decay time is equal to the lifetime of interacting F-centres. Expressions derived for the different characteristics of ML are able to explain the experimental results. It is shown that the time constant for rise of pressure, lifetime of the interacting F-centres or damping time of dislocation segments, and the activation energy can be determined from the ML measurements

2008-01-01

25

Mechanoluminescence induced by elastic deformation of coloured alkali halide crystals using pressure steps  

Energy Technology Data Exchange (ETDEWEB)

During the elastic deformation of coloured alkali halide crystals, the bending segments of dislocations capture F-centre electrons lying in the expansion region of edge dislocations, to the states of dislocation band. After the separation from interacting F-centres, the captured electrons move together with the bending segments of dislocations and also drift along the axis of dislocations and subsequently the radiative electron-hole recombinations, owing to both the processes of captured-electron movement, give rise to the light emission. The generation rate of electrons in the dislocation band and the mechanoluminescence (ML) intensity initially increase with time, attain maximum value at a particular time, and then they decrease with time. The intensity I{sub m} corresponding to the peak of ML intensity versus time curve and the total intensity I{sub T} of ML increase with the applied pressure and also with the density of F-centres in the crystals. At low temperature, both I{sub m} and I{sub T} increase with temperature and at higher temperature they decrease with increasing temperature due to the thermal bleaching of F-centres and also due to the decrease in luminescence efficiency. Thus, both I{sub m} and I{sub T} are optimum for a particular temperature of the crystals. For longer time duration, the ML intensity decreases exponentially with time in which the decay time is equal to the lifetime of interacting F-centres. Expressions derived for the different characteristics of ML are able to explain the experimental results. It is shown that the time constant for rise of pressure, lifetime of the interacting F-centres or damping time of dislocation segments, and the activation energy can be determined from the ML measurements.

Chandra, B.P. [Department of Postgraduate Studies and Research in Physics, Rani Durgavati University, Jabalpur, Madhya Pradesh 482001 (India)], E-mail: bpchandra4@yahoo.co.in

2008-07-15

26

Ab initio calculation of the lattice distortions induced by substitutional Ag- and Cu- impurities in alkali halide crystals  

International Nuclear Information System (INIS)

[en] An ab initio study of the doping of alkali halide crystals (AX: A=Li, Na, K, Rb; X = F, Cl, Br, I) by ns2 anions (Ag- and Cu-) is presented. Large active clusters with 179 ions embedded in the surrounding crystalline lattice are considered in order to describe properly the lattice relaxation induced by the introduction of substitutional impurities. In all the cases considered, the lattice distortions imply the concerted movement of several shells of neighbors. The shell displacements are smaller for the smaller anion Cu-, as expected. The study of the family of rock-salt alkali halides (excepting CsF) allows us to extract trends that might be useful at a predictive level in the study of other impurity systems. Those trends are presented and discussed in terms of simple geometric arguments

2000-08-01

27

Ab Initio Calculation of the Lattice Distortions induced by Substitutional $Ag$- and $Cu$-Impurities in Alkali Halide Crystals  

CERN Document Server

An ab initio study of the doping of alkali halide crystals (AX: A=Li, Na, K,Rb; X=F, Cl, Br, I) by ns2 anions (Ag- and Cu-) is presented. Large activeclusters with 179 ions embedded in the surrounding crystalline lattice areconsidered in order to describe properly the lattice relaxation induced by theintroduction of substitutional impurities. In all the cases considered, thelattice distortions imply the concerted movement of several shells ofneighbors. The shell displacements are smaller for the smaller anion Cu-, asexpected. The study of the family of rock-salt alkali halides (excepting CsF)allows us to extract trends that might be useful at a predictive level in thestudy of other impurity systems. Those trends are presented and discussed interms of simple geometric arguments.

Aguado, A; Alonso, J A; Aguado, Andres; Lopez, Jose M.; Alonso, Julio A.

2000-01-01

28

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

29

Mobile interstitial model and mobile electron model of mechano-induced luminescence in coloured alkali halide crystals  

International Nuclear Information System (INIS)

A theoretical study is made on the mobile interstitial and mobile electron models of mechano-induced luminescence in coloured alkali halide crystals. Equations derived indicate that the mechanoluminescence intensity should depend on several factors like strain rate, applied stress, temperature, density of F-centres and volume of crystal. The equations also involve the efficiency and decay time of mechanoluminescence. Results of mobile interstitial and mobile electron models are compared with the experimental observations, which indicated that the latter is more suitable as compared to the former. From the temperature dependence of ML, the energy gaps between the dislocation band and ground state of F-centre is calculated which are 0.08, 0.072 and 0.09 eV for KCl, KBr and NaCl crystals, respectively. The theory predicts that the decay of ML intensity is related to the process of stress relaxation in crystals. (author). 33 refs., 5 figs., 1 tab

1996-01-01

30

Measurements of spin-lattice relaxation time in mixed alkali halide crystals  

International Nuclear Information System (INIS)

Using magneto-optic techniques the ground state spin-lattice relaxation times (T1) of 'F' centers in mixed Alkali Halide cristals (KCl-KBr), was studied. A computer assisted system to optically measure short relaxation times (approx. = 1mS), was described. The technique is based on the measurement of the Magnetic Circular Dicroism (MCD) presented by F centers. The T1 magnetic field dependency at 2 K (up to 65 KGauss), was obtained as well as the MCD spectra for different relative concentration at the mixed matrices. The theory developed by Panepucci and Mollenauer for F centers spin-lattice relaxation in pure matrices was modified to explain the behaviour of T1 in mixed cristals. The Direct Process results (T approx. = 2.0 K) compared against that theory shows that the main relaxation mecanism, up to 25 KGauss, continues to be phonon modulation of the hiperfine iteraction between F electrons and surrounding nuclei. (Author).

1983-01-01

31

Ground state properties of heavy alkali halides  

CERN Document Server

We extend previous work on alkali halides by calculations for the heavy-atom species RbF, RbCl, LiBr, NaBr, KBr, RbBr, LiI, NaI, KI, and RbI. Relativistic effects are included by means of energy-consistent pseudopotentials, correlations are treated at the coupled-cluster level. A striking deficiency of the Hartree-Fock approach are lattice constants deviating by up to 7.5 % from experimental values which is reduced to a maximum error of 2.4 % by taking into account electron correlation. Besides, we provide ab-initio data for in-crystal polarizabilities and van der Waals coefficients.

Doll, K; Doll, Klaus; Stoll, Hermann

1998-01-01

32

Induction of crystal growth in alkali-halide aggregates by means of internal seeding  

Science.gov (United States)

Following our previous work, new results for seed induced nucleation and crystal growth in nano droplets are presented. A new method that allows to place the seed inside the droplet is presented. The new results show a considerable independence of the processes of nucleation and crystal growth regarding the size of the host droplet. The crystal growth model also previously reported was applied giving good predictions. It supports more insights into the growth trends for different seed placements. Based on its deviation from the ideal condition considered in the crystal growth model development, a reinterpretation for the outside seeding behavior is presented. Additionally, the present results strongly sustain a non-self-wetting behavior for ionic salts aggregates.

Rodrigues, P. C. R.; Silva Fernandes, F. M. S.

2012-06-01

33

Polarizabilities of the alkali halide dimers. II  

International Nuclear Information System (INIS)

We have measured the average electric dipole polarizabilities of twenty alkali halide dimers, using a molecular beam electric deflection method. This is a continuation of the earlier measurements of five alkali halide dimers [R. Kremens et al., J. Chem. Phys. 81, 1676 (1984)]. We compare our measurements with a simple combination of bond (via a ''spring'' model) and effective ionic polarizabilities, using literature values for the required molecular constants. Agreement between our measured and calculated values is reasonable, in most cases, considering the relative crudeness of the model.

1991-01-01

34

Structure and crowdion mechanism of H-interstitial motion in the alkali halide crystals  

International Nuclear Information System (INIS)

It is shown by the EPR method that H-centres in RbCl and RbBr crystals are orientated by axes. Presence of superhyperfine structure (SHFS) in RbBr spectra testifies to the fact that Br2- molecules interacting with two neighbouring Br- ions along the [110] are H-centres. SHFS is not disclosed for RbCl, i.e. Cl--Cl2--Cl- bonds are too weak. Formation of stale pairs of Frenkel anion defects under X-radiation at 4-20 K and selective optical exciton production in KCl, KBr, RbCl and RbBr disclosed that presence of X--X2--X- bonds is essential for low-temperature orientated H-interstitial shift from the F-centre.

1986-01-01

35

Recombination of radiation defects in alkali halide crystals at low temperature  

International Nuclear Information System (INIS)

[en] 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

36

Creation of color centers in alkali halides by pulsed irradiation  

International Nuclear Information System (INIS)

Regularities of creation and destruction of primary color centers in some alkali-halide crystals (AHC) under pulsed electron irradiation (E = 0.25 MeV, tp = 10 ns, fluence P 7.6 x 1011 el x cm-2) were investigated by the methods of optical spectroscopy with 7 ns time resolution. Values of ? yield and characteristic destruction time ? of short-lived F,H - pairs of color centers and autolocalized excitons (ALE) in 80-400 K range were determined. Correlation between processes of formation of stable and short-lived F-centers in the group of crystals of chlorides and bromides of K and Rb was established. Model of two-halide ALE decay to defects, common for AHC, was suggested. Regularities in AHC series, revealing the relationship between characteristics of defect formation (?F, ?eh, ?F, ?eh, Ep, ET) and crystal parameters (ratio of length of two-halide ALE nucleus to interanion distance) were established.

1990-01-01

37

Complexes in polyvalent metal - Alkali halide melts  

International Nuclear Information System (INIS)

[en] 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

38

Solvation at nanoscale: alkali-halides in water clusters.  

UK PubMed Central (United Kingdom)

The solvation of alkali-halides in water clusters at nanoscale is studied by photoelectron spectroscopy using synchrotron radiation. The Na 2p, K 3p, Cl 2p, Br 3d, and I 4d core level binding energies have been measured for salt-containing water clusters. The results have been compared to those of alkali halide clusters and the dilute aqueous salt solutions. It is found that the alkali halides dissolve in small water clusters as ions.

Partanen L; Mikkelä MH; Huttula M; Tchaplyguine M; Zhang C; Andersson T; Björneholm O

2013-01-01

39

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

40

Electronic excitation in bulk and nanocrystalline alkali halides.  

UK PubMed Central (United Kingdom)

The lowest energy excitations in bulk alkali halides are investigated by considering five different excited state descriptions. It is concluded that excitation transfers one outermost halide electron in the fully ionic ground state to the lowest energy vacant s orbital of one closest cation neighbour to produce the excited state termed dipolar. The excitation energies of seven salts were computed using shell model description of the lattice polarization produced by the effective dipole moment of the excited state neutral halogen-neutral metal pair. Ab initio uncorrelated short-range inter-ionic interactions computed from anion wavefunctions adapted to the in-crystal environment were augmented by short-range electron correlation contributions derived from uniform electron-gas density functional theory. Dispersive attractions including wavefunction overlap damping were introduced using reliable semi-empirical dispersion coefficients. The good agreement between the predicted excitation energies and experiment provides strong evidence that the excited state is dipolar. In alkali halide nanocrystals in which each ionic plane contains only four ions, the Madelung energies are significantly reduced compared with the bulk. This predicts that the corresponding intra-crystal excitation energies in the nanocrystals, where there are two excited states depending on whether the halide electron is transferred to a cation in the same or in the neighbouring plane, will be reduced by almost 2 eV. For such an encapsulated KI crystal, it has been shown that the greater polarization in the excited state of the bulk crystal causes these reductions to be lowered to a 1.1 eV-1.5 eV range for the case of charge transfer to a neighbouring plane. For intra-plane charge transfer the magnitude of the polarization energy is further reduced thus causing the excitation in these encapsulated materials to be only 0.2 eV less than in the bulk crystal.

Bichoutskaia E; Pyper NC

2012-11-01

 
 
 
 
41

Cohesive properties of alkali halides  

CERN Multimedia

We calculate cohesive properties of LiF, NaF, KF, LiCl, NaCl, and KCl with ab-initio quantum chemical methods. The coupled-cluster approach is used to correct the Hartree-Fock crystal results for correlations and to systematically improve cohesive energies, lattice constants and bulk moduli. After inclusion of correlations, we recover 95-98 % of the total cohesive energies. The lattice constants deviate from experiment by at most 1.1 %, bulk moduli by at most 8 %. We also find good agreement for spectroscopic properties of the corresponding diatomic molecules.

Doll, K; Doll, Klaus; Stoll, Hermann

1997-01-01

42

Study of paramagnetic radiation-induced defects in alkali halide crystals at high doses of ionizing radiation  

International Nuclear Information System (INIS)

[en] Paramagnetic radiation defects in single crystals of LiF, NaCl, NaCl-OH, KCl, KBr and some of their melts and powders have been studied after irradiation with doses 1-100 Grad by 1)3.5 MeV electrons, 2)1.5 MeV gamma rays, 3)nuclear reactor flux in the wide temperature range of 77-6a0 K. F-centres are proved to be main radiation paramagnetic defects in the mentioned monocrystals. They coagulate due to the dose and temperature of irradiation growth further producing aggregates and new alkali metal phases. For each type of the monocrystals the process of coagulation is calculated by a certain optimal combination of doses and temperatures or by annealing after irradiation. The coagulation of primary radiation defects decrease in succession:LiF, NaCl-OH, KBr, NaCl, KCl

1980-01-01

43

Hot working alkali halides for laser window applications  

International Nuclear Information System (INIS)

[en] The techniques used to hot work alkali halide crystals into laser window blanks are reviewed. From the point of view of high power laser window applications one of the materials with a high figure of merit is KCl. Thus the materials examined are KCl and alloys of KCl-KBr containing 5 mole percent KBr. The fabrication techniques include conventional and constrained press forging, isostatic press forging and hot rolling. Optical properties are paramount to the ultimate usefulness of these materials. Results on the optical properties of the hot worked material are included together with mechanical properties and microstructural data

1974-07-17

44

Thermoluminescence of alkali halides and its implications  

International Nuclear Information System (INIS)

Trapping levels present in some alkali halides namely NaCl, KCl, KBr, and KI are determined by deconvolution of the thermoluminescence (TL) curves. Unlike most of the studies undertaken over the last few decades, we have presented a comprehensive picture of the phenomenon of TL as an analytical technique capable of revealing the position of the trapping levels present in the materials. We show that for all practical purposes, TL can be described involving only the three key trapping parameters, namely, the activation energy (E), the frequency factor (s), and the order of kinetics (b) even for complex glow curves having a number of TL peaks. Finally, based on these, we logically infer the importance of TL in development and characterization of materials used in dosimetry, dating and scintillation.

2012-03-01

45

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.

2002-01-01

46

Quantum-chemical investigations of the electronic structure, mechanism of radiation defect production and recombination in alkali halide crystals  

International Nuclear Information System (INIS)

[en] The results of recent investigations of electronic and spatial structure as well as mechanism of radiation-induced production and tunneling recombination of defects in ionic crystals LiF and KCl are briefly summerized. The calculations have been performed in the framework of the semiempirical quantum- chemical method, which is the simplified version of the unrestricted Hartree-Fock-Rothaan method, and of a molecular cluster model

1981-01-01

47

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

48

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

Energy Technology Data Exchange (ETDEWEB)

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.

Haglund R.F. Jr.; Tolk, N.H.

1986-09-10

49

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

50

A new fundamental hydrogen defect in alkali halides  

International Nuclear Information System (INIS)

Atom hydrogen in neutral (H0) and negative (H-) form on substitutional and interstitial lattice sites gives rise to well characterized model defects in alkali-halides (U,U1,U2,U3 centers), which have been extensively investigated in the past. When studying the photo-decomposition of OH- defects, a new configuration of atomic charged hidrogen was discovered, which can be produced in large quantities in the crystal and is apparently not connected to any other impurity. This new hidrogen defect does not show any pronounced electronic absorption, but displays a single sharp local mode band (at 1114cm-1 in KCl) with a perfect isotope shift. The defect can be produced by various UV or X-ray techniques in crystais doped with OH-, Sh- or H- defects. A detailed study of its formation kinetics at low temperature shows that it is primarily formed by the reaction of a mobile CI2- crowdion (H-center) with hidrogen defects.

1978-01-01

51

Scintillation properties of pure alkali halides at low temperatures  

International Nuclear Information System (INIS)

Fragmentary studies in various laboratories on the scintillation behaviour of several of the alkali halides, both with and without impurity activators, indicate that in general the activated alkali halides scintillate best at room-temperature with pulse-height decreasing at lower temperatures, while the unactivated materials scintillate best at low temperatures and decrease in efficiency as the temperature increases. In our laboratory, a systematic research study on the scintillation properties of the alkali halides is underway and to date we have examined twelve pure (unactivated) alkali halides with both ?-particle and ?-ray excitation over the temperature range of 4oK to 300oK. Lil, KI, and Csl exhibit a constant scintillation pulse-height and decay-time at temperatures below 80oK. Nal exhibits a maximum in pulse-height at 60oK similar to that reported previously by VAN SCIVER et al. A second CsI sample shows both a low-temperature scintillation-component and a room-temperature component similar to that induced by overheating as in the experiments of KNOEPFEL et al. Rbl shows two regions of linearly decreasing pulse-height as temperature increases. The scintillation pulse-heights of the iodides are comparable to that observed from thallium-activated sodium iodide and the decay times are about 0.1 to 2 ?s. CsBr, KBr, and NaCl scintillate at low temperatures, but with a much lower intensity than the iodides. LiF, NaF, KCl, and RbBr exhibit no detectable scintillation over the entire temperature range studied. The temperature dependence of pulse-heights and decay-constants is the same for both ? and ?-excited emission. Analysis of the scintillation pulse-shape and the temperature-dependence gives an indication of the number of luminescence components and the mode of decay of the excited luminescence centres. (author)

1962-01-01

52

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; Deepthi Jose; Ayan Datta

2012-01-01

53

Basic mechanisms of color centres production by excitons in activated alkali halides  

International Nuclear Information System (INIS)

[en] The paper deals with some peculiarities of colour centers formation which are caused by introduction of the activator in alkali halide crystals. The crystals of KBr and KI activated with Tl+, In+, Sn++ in concentrations 1017-1018 cm-3 and irradiated with ultraviolet light are studied. Excitation spectra of photostimulated activator luminescence and thermoluminescence were measured. The kinetics of the photostimulated activator luminescence is studied. The conclusion is made that the activator does not affect the primary reaction of exciton decay with F-H pair generation, but only the secondary reactions of colour center production

1981-01-01

54

The mechanism of the electron sputtering process of alkali halides  

International Nuclear Information System (INIS)

The energy distributions of the particles leaving a polycrystalline alkali halide target under bombardment with electrons are measured. NaBr, KBr, RbBr, CsBr, NaI, KI, RbI, and CsI at target temperatures between 40 and 4000C are investigated. Among the possible ways to cause sputtering the diffusion of excitons is very improbable because no particles with energies higher than 1 eV have been found. Compared to it the experimental results are in agreement with the focussed collision replacement sequence. This mechanism is described.

1977-01-01

55

On the surface morphology of thin alkali halide photocathode films  

International Nuclear Information System (INIS)

Thin alkali halide films are currently used as transmissive UV-photocathodes and as protecting layers for visible photocathodes. The surface morphology of 20 and 75 nm thick evaporated CsI, NaI and CsBr films was investigated by means of a scanning electron microscope, to which the samples were transferred, under vacuum, with practically no contact with air. It is shown that the film continuity, in particular that of NaI, is strongly affected by short exposure to moisture. CsI, which is the less hygroscopic material among the three, exhibits the most continuous structure.

1999-12-11

56

Epitaxial growth of alkali halides on stepped metal surfaces  

International Nuclear Information System (INIS)

[en] 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

57

Structure and Bonding in Small Neutral Alkali-Halide Clusters  

CERN Document Server

The structural and bonding properties of small neutral alkali-halide clusters (AX)n, with n less than or equal to 10, A=Li, Na, K, Rb and X=F, Cl, Br, I, are studied using the ab initio Perturbed Ion (aiPI) model and a restricted structural relaxation criterion. A trend of competition between rock-salt and hexagonal ring-like isomers is found and discussed in terms of the relative ionic sizes. The main conclusion is that an approximate value of r_C/r_A=0.5 (where r_C and r_A are the cationic and anionic radii) separates the hexagonal from the rock-salt structures. The classical electrostatic part of the total energy at the equilibrium geometry is enough to explain these trends. The magic numbers in the size range studied are n= 4, 6 and 9, and these are universal since they occur for all alkali-halides and do not depend on the specific ground state geometry. Instead those numbers allow for the formation of compact clusters. Full geometrical relaxations are considered for (LiF)n (n=3-7) and (AX)_3 clusters, an...

Aguado, A; López, J M; Alonso, J A

1997-01-01

58

Intrinsic Multiple-Shot Laser-Induced Bulk Damage in Alkali Halides at 532 NM.  

Science.gov (United States)

When an alkali halide crystal is subjected to a series of laser pulses well below the established single shot damage threshold, it, nevertheless, eventually succumbs to catastrophic damage. The damage event is best described as the accumulation of laser-induced microscopic changes in the crystal lattice. For very pure crystals F centers form the predominant stable product of bandgap excitations. The role played by the accumulation of F centers in multishot laser-induced bulk damage is investigated, and model is developed which successfully describes the experimentally observed behavior for the two material studied (KBr and KI). The multishot damage model is built upon the established multiphoton absorption theory for single pulse laser-induced damage in alkali halides, and the known F center formation is suggested to play a major role in the cumulative damage process. The accumulation of F centers is accompanied by a lattice expansion and the buildup of stresses within the interaction volume of the laser beam. The model assumes that, when the defect-induced stress together with the thermal stress exceed the yield stress of the material, the crystal will fail. The model results are compared with experimental data for KBr and KI for several initial temperatures ranging from 55 K to 300 K and using 70 psec laser pulses of 22-52 GW cm^{-2} at 532 nm. It is shown that the proposed multishot damage mechanism adequately describes the observed behavior.

Casper, Richard Thomas

1990-01-01

59

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

International Nuclear Information System (INIS)

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

1994-01-01

60

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

 
 
 
 
61

Development of alkali halide-optics for high power-IR laser  

International Nuclear Information System (INIS)

[en] In this work 'Development of Alkali Halide-Optics for High Power-IR Laser' we investigated the purification of sodiumchloride-, potassiumchloride- and potassiumbromide-raw materials. We succeeded to reduce the content of impurities like Cu, Pb, V, Cr, Mn, Fe, Co and Ni in these raw materials to the lower of ppb's by a Complex-Adsorption-Method (CAM). Crystals were grown from purified substances by 'Kyropoulos' method'. Windows were cur thereof, polished and measured by FTIR-spectroscopy. Analytical data showed, that the resulting crystals were of lower quality than the raw materials. Because of this fact crystal-growing-conditions have to undergo a special improvement. Alkali halide windows from other sources on the market had been tested. (orig.)[de] Im Rahmen der Arbeiten 'Entwicklung von Salzoptiken fuer IR-Hochleistungslaser' wurde im Projektzeitraum die Aufreinigung von Natriumchlorid-, Kaliumchlorid- und Kaliumbromid-Rohstoffen naeher untersucht. Mit einem hierfuer erarbeiteten Komplex-Adsorptionsverfahren konnte eine Aufreinigung der Rohstoffe von den im IR-absorbierenden Monitorelementen - Kupfer, Blei, Vanadin, Chrom, Mangan, Eisen, Kobalt und Nickel - bis in den unteren ppb-Bereich erzielt werden. Aus den so aufgereinigten Rohstoffen wurden Probekristalle nach Kyropoulos gezogen. Daraus hergestellte Fenster wurden analytisch und spektroskopisch untersucht. Es zeigte sich, dass die Kristalle nicht von gleicher Reinheit wie die Rohstoffe sind. Eine Verbesserung der Kristallziehbedingungen ist daher erforderlich. Fuer einen Vergleich mit Kristallen eigener Herstellung wurden derzeit am Markt verfuegbare Salzoptiken untersucht und charakterisiert. (orig.)

1989-01-01

62

Fabrication of alkali halide UV photocathodes by pulsed laser deposition  

Science.gov (United States)

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.

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

2012-12-01

63

Theory of freezing of alkali halides and binary alloys  

International Nuclear Information System (INIS)

Using the basic equations of classical statistical mechanics relating the singlet densities rho1 and rho2 of a binary system to the three partial direct correlation functions csub(ij), a theory of freezing is developed. Though the theory is set up for arbitrary concentration, we focus on the freezing of the alkali halides. In particular, we show that periodic solutions of the equations for rho1 and rho2 can coexist with homogeneous solutions. The difference in free energy between periodic and homogeneous phases is built up in terms of (i) the volume difference and (ii) the Fourier components of rho1, rho2 and csub(ij). To lowest order, it is stressed that the freezing transition is determined by the charge-charge structure factor at the principal peak and by the compressibility. (author).

1981-01-01

64

Alkali halide clusters produced by fast ion impact  

International Nuclear Information System (INIS)

The most abundant geometries and relative stabilities of alkali halide clusters with a (XY)n0 configuration (e.g., LiF, NaCl, KBr) are described. Five main series were obtained: linear, cyclic, cubic, arc strips and nanotubes. The stability analysis shows that higher members are likely to be formed from the lower member of the same series and/or from two building blocks (n = 1, 2). The energy analysis (D-plot) indicates that the most compact ones (e.g., cubic and nanotubes) present higher stability when compared to the linear, cyclic and arc strip structures; moreover, relative stability between the cubic and nanotube series varies with the cluster size.

2012-02-15

65

Effect of intrinsic luminescence of alkali halide amplification by low temperature deformation  

International Nuclear Information System (INIS)

By using luminescence spectroscopy, we have established the influence of low-temperature uniaxial deformation on the configuration of a self-trapped exciton (STE) in alkali halide crystals (AHC) at the instant of radiative relaxation. In face-centered crystals, there occurs the redistribution of the luminescence intensity from the asymmetric configuration of STE to the symmetric one (III ? II ? I- types), whereas in volume-centered crystals, on the contrary, the evidence counts in favour of the asymmetric configuration of STE (I? II–types). The external deformation in the direction leads to an effective sliding of anions in the direction that coincides with the direction of the STE squeeze which classically makes for the creation, of the symmetric STE configuration in the direction, acting perpendicularly to the STE’ length results in their stretching, which in turn brings into the creation of the asymmetric STE configuration with a higher degree of the polarization.

2012-12-17

66

Silicon Halide--Alkali Metal Flames as a Source of Solar Grade Silicon. First Quarterly Report.  

Science.gov (United States)

This program is designed to test the feasibility of utilizing continuous, high temperature, diffusion flames of gaseous alkali metals and silicon halides as an economical source of high purity silicon. Thermochemical analyses of these systems indicate tha...

W. J. Miller

1977-01-01

67

Ditopic Binding of Alkali Halide Ions to Trimethylboroxine  

Directory of Open Access Journals (Sweden)

Full Text Available Trimethylboroxine (TMB) is a six-membered ring compound containing Lewis acidic boron and Lewis basic oxygenatoms that can bind halide anion and alkali metal cation, respectively. We employed Fourier transform ion cyclotron resonancespectroscopy to study the gas-phase binding of LiBrLi+ and F?(KF)2 to TMB. TMB forms association complexes with bothLiBrLi+ and F–(KF)2 at room temperature, providing direct evidence for the ditopic binding. Interestingly, the TMB·F?(KF)2anion complex is formed 33 times faster than the TMB·Li+BrLi cation complex. To gain insight into the ditopic binding of an ionpair, we examined the structures and energetics of TMB·Li+, TMB·F–, TMB·LiF (the contact ion pair), and Li+·TMB·F– (the separatedion pair) using Hartree–Fock and density functional theory. Theory suggests that F– binds more strongly to TMB than Li+and the contact ion-pair binding (TMB·LiF) is more stable than the separated ion-pair binding (Li+·TMB·F–).

Kyung Hwan Jeong; Seung Koo Shin

2010-01-01

68

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

69

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

2010-01-01

70

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

71

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

CERN Multimedia

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

72

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

CERN Multimedia

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

73

Electric-field-induced piezoelectricity of some pure and doped alkali halides  

Energy Technology Data Exchange (ETDEWEB)

We show that the measurement of electric-field-induced piezoelectricity is a sensitive method to determine third-order derivatives of the thermodynamic potential functions with respect to electric field and mechanical stress in pure and doped alkali halide crystals. The method is equivalent to a determination of the stress derivatives of the dielectric constant and to a measurement of quadratic electrostriction. Experiments are performed on LiF, KCl, KBr, KCl-KBr mixtures, and RbCl : Ag{sup +}. For the pure materials we can confirm most of the stress and electrostriction coefficients known from recent work. However, no indication is found of unusually large coefficients for KCl-KBr mixtures and for RbCl:Ag{sup +} which have been reported in the literature. (orig.)

Radgen, B.; Mlitzke, M.; Mohler, E. [Physikalisches Inst. der Univ. Frankfurt am Main, Frankfurt (Germany)

2001-02-01

74

Structure of uranyl ion luminescence spectra in pressed alkali-halide matrices  

International Nuclear Information System (INIS)

[en] The luminescent properties of the polyatomic UO22+ ions present as impurity in pressed alkali-halide matrices of KCl and KBr are studied. At 77-4.2 K the spectra of absorption, photoexcitation and radiation of such systems exhibit a vibronic structure. In this case two series of vibronic bands due to the interaction of electron transitions sup(1)?sub(u)?sup(1)?sub(g)sup(+)(sup(1)?sub(u) ? sup(1)?sub(g)sup(+)) and sup(1)?sub(u)sup(+) ? sup(1)?sub(g)sup(+)) with intramolecular impurity vibration appear in the luminescence spectra. At 4.2 K the emission vibronic bands of the sup(1)?sub(u)sup(+) ? sup(1)?sub(g)sup(+) transition are splitted to phononless lines and structural phonon wings (PW). Part of PW structure maxima are shown to be associated with an excitation of crystal vibrations of the KCl and KBr matrices

1984-01-01

75

Two types of epitaxial orientations for the growth of alkali halide on fcc metal substrates  

International Nuclear Information System (INIS)

Thin-film growth of alkali halides on (001) surfaces of fcc transition metals was studied using reflection high-energy electron diffraction. Alkali halide grew with its [100] axis rotated by 45 deg. from that of the metal substrate ([100]film//[110]substrate) for LiCl/Cu(001) and LiCl/Ni(001). On the contrary, alkali halide grew without azimuthal rotation ([100]film//[100]substrate) for LiCl/Ag(001), NaCl/Cu(001), NaCl/Ag(001), and NaCl0.6Br0.4/Ag(001). The former growth mode ([100]film//[110]substrate) occurred only with a small difference in the first-nearest neighbor (first-NN) interatomic distance between alkali halide and metal. The latter growth mode ([100]film//[100]substrate) occurred even with a large difference in the first-NN interatomic distance. The mechanism of the latter growth was explained by the preferential direction of steps on (001) surfaces of fcc metals and the migration of alkali halide molecules to the steps.

2002-10-15

76

Alkali halide phosphors as a storage material for two-dimensional X-ray imaging sensor utilizing photostimulated luminescence phenomenon  

Energy Technology Data Exchange (ETDEWEB)

The PSL phenomenon in alkali halides such as NaCl : Cu and KCl : Eu induced by excitation with X-rays were studied. The efficient PSL with a peak at about 353 [nm] and two less intense PSL peaks at about 420 [nm] and 680 [nm] were observed in X-ray irradiated NaCl : Cu phosphor crystal. The intense PSL with a peak at about 420 [nm] was also observed in X-ray irradiated KCl : Eu phosphor crystal. The emission mechanism of the PSL in both phosphor crystals, based on the recombination of electrons optically stimulated from the radiation-induced F centers with the luminescence centers such as Cu{sup 2+} ions in NaCl and Eu{sup 3+} ions in KCl, was proposed. It was found that the 353 [nm] PSL intensity in NaCl : Cu and the 420 [nm] PSL intensity in KCl : Eu linearly increased with increasing the intensity of the F-band which was created by X-ray irradiation. The alkali halide phosphor materials such as NaCl : Cu and KCl : Eu, especially KCl : Eu, thus, are the most attractive candidate as a material for two-dimensional X-ray imaging sensor utilizing PSL phenomenon, because the NaCl : Cu and the KCl : Eu phosphor crystals exhibited an efficient PSL, especially the KCl : Eu phosphor crystal also exhibited thermally stable PSL characteristics. (J.P.N).

Nanto, Hidehito; Endo, Fumitaka; Hirai, Yoshiaki; Nasu, Shouichi [Kanazawa Inst. of Tech., Nonoichi (Japan); Nakamura, Shouichi; Inabe, Katsuyuki; Takeuchi, Nozomu

1994-08-01

77

Alkali halide phosphors as a storage material for two-dimensional X-ray imaging sensor utilizing photostimulated luminescence phenomenon  

International Nuclear Information System (INIS)

The PSL phenomenon in alkali halides such as NaCl : Cu and KCl : Eu induced by excitation with X-rays were studied. The efficient PSL with a peak at about 353 [nm] and two less intense PSL peaks at about 420 [nm] and 680 [nm] were observed in X-ray irradiated NaCl : Cu phosphor crystal. The intense PSL with a peak at about 420 [nm] was also observed in X-ray irradiated KCl : Eu phosphor crystal. The emission mechanism of the PSL in both phosphor crystals, based on the recombination of electrons optically stimulated from the radiation-induced F centers with the luminescence centers such as Cu2+ ions in NaCl and Eu3+ ions in KCl, was proposed. It was found that the 353 [nm] PSL intensity in NaCl : Cu and the 420 [nm] PSL intensity in KCl : Eu linearly increased with increasing the intensity of the F-band which was created by X-ray irradiation. The alkali halide phosphor materials such as NaCl : Cu and KCl : Eu, especially KCl : Eu, thus, are the most attractive candidate as a material for two-dimensional X-ray imaging sensor utilizing PSL phenomenon, because the NaCl : Cu and the KCl : Eu phosphor crystals exhibited an efficient PSL, especially the KCl : Eu phosphor crystal also exhibited thermally stable PSL characteristics. (J.P.N).

1994-01-01

78

Interaction of soft x-ray photons with free alkali-halide molecular clusters  

International Nuclear Information System (INIS)

Alkali-halide molecular clusters were formed from the vaporized molecules in collisions with an intense beam of argon clusters. Photoionization of the alkali-halide clusters as the result of interaction with x-ray radiation has been utilized in a photoelectron spectroscopy study of cluster bonding mechanisms. The changes in the energy structure due to the transformation from molecules to the solid salt were observed both in the inner and outer shells of constituent elements (metal and halogen) and were used to deduce the geometric structure of the clusters in question.

2012-11-05

79

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

80

Silicon Halide-Alkali Metal Flames as a Source of Solar Grade Silicon. Third Quarterly Report.  

Science.gov (United States)

It is proposed to determine the feasibility of using continuous flames of alkali metals and silicon halides in a large scale process to produce solar-grade silicon at low cost. Primary emphasis is being given to the reaction of Na with SiCl sub 4 . The me...

D. B. Olson W. J. Miller

1978-01-01

 
 
 
 
81

Isotope effects of water molecules on the hydration of alkali metal and halide ions  

International Nuclear Information System (INIS)

Based on the results of hydrogen isotope fractionation in aqueous alkali halide solutions at 25degC, reported in previous papers, the hydrogen isotope effect between water molecules hydrated to a cation or an anion and bulk water molecules is estimated with the assumption that the equilibrium constant of the hydrogen isotope exchange reaction between the hydration water of sodium ion and bulk water is unity. The orders of the hydrogen isotope effects of alkali metal cations and halide anions are found to be Cs+ > K+ > Na+ > Li+, and I- > Br- > Cl- for a constant hydration number, respectively, and the hydrogen isotope effect is mainly influenced in anions rather than in cations. The oxygen isotope effect for alkali and halide ions is evaluated from the literature. The hydrogen and oxygen isotopic effects for the cations and anions show the same trend, but the magnitude of the hydrogen isotope effect for anions is significantly larger than that of the oxygen isotope effect. The free energy of transfer of alkali metal and halide ions from H2O to HDO is calculated from the hydrogen isotope effect for the individual ions. The calculated values are compared with the free energy of transfer from H2O to D2O obtained by electromotive force measurements, and are compared with the free energy of transfer from H216O to H218O calculated from the oxygen isotope effect. (author)

2001-01-01

82

Enthalpies of dissolution of alkali halides in mixtures of dimethyl sulfoxide with water or heavy water  

Energy Technology Data Exchange (ETDEWEB)

The enthalpies of dissolution of cesium fluoride, lithium and sodium chlorides, potassium bormide, sodium and cesium iodides, and tetrabutylammonium bromide were measured by means of calorimetry, and the standard enthalpies of dissolution of all alkali halides (except rubidium halides) in mixtures of dimethyl sulfoxide with water or heavy water at 298.15 K were calculated from the differences of the enthalpies of transfer. It is shown that solvation of alkali halides in the examined mixtures is more strongly affected by the nature of the anion rather than by the nature of the cation. Isotope effects on the enthalpies of solvation of the above-listed electrolytes in aqueous solutions of dimethyl sulfoxide are discussed, and the data obtained are compared with the corresponding data for tributylammonium bromide. 29 refs., 2 figs., 4 tabs.

Egorov, G.I. [Institute of Nonaqueous Solution Chemistry, Ivanovo (Russian Federation)

1995-04-20

83

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

Directory of Open Access Journals (Sweden)

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.

J. K. Pendharkar; S. K. Saxena; Yogesh Ghalsasi; M. N. Nyayate; Atul Jadhav

2012-01-01

84

A Review of Luminescent Anionic Nano System: d10 Metallocyanide Excimers and Exciplexes in Alkali Halide Hosts  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Dicyanoaurate, dicyanoargentate, and dicyanocuprate ions in solution and doped in different alkali halide hosts exhibit interesting photophysical and photochemical behavior, such as multiple emission bands, exciplex tuning, optical memory, and thermochromism. This is attributed to the formation of d...

Xiaobo Li; Howard H. Patterson

85

Structure of uranyl ion luminescence spectra in pressed alkali-halide matrices  

Energy Technology Data Exchange (ETDEWEB)

The luminescent properties of the polyatomic UO/sub 2//sup 2 +/ ions present as impurity in pressed alkali-halide matrices of KCl and KBr are studied. At 77-4.2 K the spectra of absorption, photoexcitation and radiation of such systems exhibit a vibronic structure. In this case two series of vibronic bands due to the interaction of electron transitions sup(1)..sigma..sub(u)..-->..sup(1)..sigma..sub(g)sup(+)(sup(1)..delta..sub(u) ..-->.. sup(1)..sigma..sub(g)sup(+)) and sup(1)..sigma..sub(u)sup(+) ..-->.. sup(1)..sigma..sub(g)sup(+)) with intramolecular impurity vibration appear in the luminescence spectra. At 4.2 K the emission vibronic bands of the sup(1)..sigma..sub(u)sup(+) ..-->.. sup(1)..sigma..sub(g)sup(+) transition are split to phononless lines and structural phonon wings (PW). Part of PW structure maxima are shown to be associated with an excitation of crystal vibrations of the KCl and KBr matrices.

Glinka, Yu.D.; Kushnirenko, I.Ya.; Kumeskij, V.R.

1984-03-01

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 Document Server

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

Reactions between cold methyl halide molecules and alkali-metal atoms  

CERN Multimedia

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

88

Development of processes for the production of solar grade silicon from halides and alkali metals  

Science.gov (United States)

High temperature reactions of silicon halides with alkali metals for the production of solar grade silicon in volume at low cost were studied. Experiments were performed to evaluate product separation and collection processes, measure heat release parameters for scaling purposes, determine the effects of reactants and/or products on materials of reactor construction, and make preliminary engineering and economic analyses of a scaled-up process.

Dickson, C. R.; Gould, R. K.

1980-04-01

89

A refinement of the Mollwo-Ivey rule for F-centres in alkali halides  

International Nuclear Information System (INIS)

The simple formula is a very good fit for the detailed variation of the F-center peak absorption energy, for the 16 alkali halides with NaCl structure, excluding CsF. The first term arises from incoherent photon scattering leading to electronic level transitions. The second term is a diffraction term, arising from the coherent scattering of photons from relaxed ionic aggregates around F-centers separated on the average by distances of the order of optical wavelengths

1984-01-01

90

Effects of alkali cations and halide anions on the DOPC lipid membrane.  

Science.gov (United States)

By means of molecular dynamics simulations with an all-atom force field, we investigated the affinities of alkali cations and halide anions for the dioleoylphosphatidylcholine lipid membrane in aqueous salt solutions. In addition, changes in phospholipid lateral diffusion and in headgroup mobility upon adding NaCl were observed using fluorescence spectroscopy. The simulations revealed that sodium is attracted to the headgroup region with its concentration being maximal in the vicinity of the phosphate groups. Potassium and cesium, however, do not preferentially adsorb to the membrane. Similarly, halide anions do not exhibit a strong affinity for the lipid headgroups but merely compensate for the positive charge of the sodium countercations. Nevertheless, larger halides such as bromide and iodide penetrate deeper into the headgroup region toward the boundary with the hydrophobic alkyl chain, this effect being likely underestimated within the present nonpolarizable force field. Addition of alkali halide salts modifies physical properties of the bilayer including the electronic density profiles, the electrostatic potential, and the area per lipid headgroup. PMID:19290591

Vácha, Robert; Siu, Shirley W I; Petrov, Michal; Böckmann, Rainer A; Barucha-Kraszewska, Justyna; Jurkiewicz, Piotr; Hof, Martin; Berkowitz, Max L; Jungwirth, Pavel

2009-07-01

91

Effects of alkali cations and halide anions on the DOPC lipid membrane.  

UK PubMed Central (United Kingdom)

By means of molecular dynamics simulations with an all-atom force field, we investigated the affinities of alkali cations and halide anions for the dioleoylphosphatidylcholine lipid membrane in aqueous salt solutions. In addition, changes in phospholipid lateral diffusion and in headgroup mobility upon adding NaCl were observed using fluorescence spectroscopy. The simulations revealed that sodium is attracted to the headgroup region with its concentration being maximal in the vicinity of the phosphate groups. Potassium and cesium, however, do not preferentially adsorb to the membrane. Similarly, halide anions do not exhibit a strong affinity for the lipid headgroups but merely compensate for the positive charge of the sodium countercations. Nevertheless, larger halides such as bromide and iodide penetrate deeper into the headgroup region toward the boundary with the hydrophobic alkyl chain, this effect being likely underestimated within the present nonpolarizable force field. Addition of alkali halide salts modifies physical properties of the bilayer including the electronic density profiles, the electrostatic potential, and the area per lipid headgroup.

Vácha R; Siu SW; Petrov M; Böckmann RA; Barucha-Kraszewska J; Jurkiewicz P; Hof M; Berkowitz ML; Jungwirth P

2009-07-01

92

Analysis of melting for alkali halides based on the potential energy curve  

Energy Technology Data Exchange (ETDEWEB)

We present an analysis of melting of alkali halides on the basis of lattice potential energy (PHI) versus interionic separation (r) curve. The point of inflection in the potential energy curve is identified corresponding to d{sup 2}PHI/dr{sup 2}=0. Values of interionic separations of melting points for 16 alkali halides have been calculated using the Born-Mie inverse power form and the Born-Mayer exponential forms for the potential energy functions. The parameters in the potential energy functions used are those derived from the ultrasonic data for thermoelastic properties. Values of interionic separations (r{sub m}) at melting temperature (T{sub m}) calculated in the present study are found to compare well with the corresponding values of interionic separations obtained using the Anderson formula for thermal expansivity. The expression for T{sub m}, in terms of r{sub m} and the derivative of potential energy, has been found to be satisfied with the data for alkali halides at melting.

Chauhan, R.S.; Singh, C.P

2002-12-01

93

Alkali metal/halide thermal energy storage systems performance evaluation  

Science.gov (United States)

A pseudoheat-pipe heat transfer mechanism has been demonstrated effective in terms of both total heat removal efficiency and rate, on the one hand, and system isothermal characteristics, on the other, for solar thermal energy storage systems of the kind being contemplated for spacecraft. The selection of appropriate salt and alkali metal substances for the system renders it applicable to a wide temperature range. The rapid heat transfer rate obtainable makes possible the placing of the thermal energy storage system around the solar receiver canister, and the immersing of heat transfer fluid tubes in the phase change salt to obtain an isothermal heat source.

Phillips, W. M.; Stearns, J. W.

94

Trap spectroscopy in alkali halides at synchronous measurements of exoelectron emission and luminescence by fractional glow technique. [X radiation  

Energy Technology Data Exchange (ETDEWEB)

A fractional heating technique in spectroscopy of electron traps in the conditions of synchronous registration of exoemission and luminescence is used for the first time. LiF and KCl:Tl monocrystals excited by X-rays are investigated. Based on the equality of the TSE and TSL activation energy and frequency factors, the identity of traps giving rise to the appearance of these peaks in the temperature intervals of the hole and electron trap devastation is found. The important role of the bulk charge appearing at X-ray irradiation in the TSE of dielectrics is proved experimentally. The TSE from the bulk traps in alkali halides is shown to be an emission of 'hot electrons' which is insensitive to the value of the crystal electron affinity.

Tale, I. (Latvijskij Gosudarstvennyj Univ., Riga (USSR)); Kortov, V.; Popov, V. (Ural' skij Politekhnicheskij Inst., Sverdlovsk (USSR))

1982-12-16

95

Trap spectroscopy in alkali halides at synchronous measurements of exoelectron emission and luminescence by fractional glow technique  

International Nuclear Information System (INIS)

A fractional heating technique in spectroscopy of electron traps in the conditions of synchronous registration of exoemission and luminescence is used for the first time. LiF and KCl:Tl monocrystals excited by X-rays are investigated. Basing on the equality of the TSE and TSL activation energy and frequency factors, the identity of traps giving rise to the appearance of these peaks in the temperature intervals of the hole and electron trap devastation is found. The important role of the bulk charge appearing at X-ray irradiation in the TSE of dielectrics is proved experimentally. The TSE from the bulk traps in alkali halides is shown to be an emission of 'hot electrons' which is insensitive to the value of the crystal electron affinity. (author).

1982-01-01

96

High-pressure studies of Jahn-Teller-split luminescence in alkali halides doped with In+ and Tl+  

International Nuclear Information System (INIS)

[en] Measurements of steady-state intensity and lifetime were made over a range of pressures (4-60 kbar) and temperatures (100-300 0K) for five alkali-halide crystals doped with In+ and Tl+. The emission spectrum is a doublet (or a triplet in the case of CsI:Tl), caused by a Jahn-Teller splitting of the excited state. The relative intensity distribution of the spectral peaks as a function of temperature and pressure determines the parameters for a model of two levels in ''dynamic equilibrium.'' The same model predicts lifetime changes with temperature and pressure which are in excellent agreement with the data for the In+-doped compounds. For the Tl+-doped compounds, metastable states control the lifetime, and parameters are extracted from the data for a multilevel model. Level splittings, level degeneracies, and intrinsic radiative rates are among the parameters determined in this study

1978-02-01

97

Reaction rate approach to dipolar relaxation in alkali halides: Adiabaticity versus classical, activated-tunneling, and quantal dipoles  

CERN Document Server

This paper is aimed at presenting a simple vibronic model for describing the dipolar reorientation in crystals by means of reaction rate theory. The Hamiltonian of an isolated dipole is simplified so as to render the problem solvable. Depending on the crossover splitting the dipoles may reorientate adiabatically with a high electron-transfer expectancy or exhibit low reorientation rates due to low expectancy. An important quantity to distinguish between adiabatic dipoles behaving classically and ones reorientating by means of quantum-mechanical tunneling is Christov's characteristic temperature which is found to relate to the barrier height and crossover splitting. ITC data on impurity-vacancy dipoles in Eu-doped alkali halides are reanalyzed.

Medrano, C

2007-01-01

98

Experimental studies of photon-surface interaction dynamics in the alkali halides  

International Nuclear Information System (INIS)

We describe recent measurements which have provided, in unprecedented detail, insights into the electronic mechanisms through which energy carried into a material by photon irradiation is absorbed, localized and rechanneled to produce desorption, surface modification, erosion and damage. The specific object of these studies has been desorption induced by electronic transition in alkali halide crystals, with particular emphasis on the dynamics of changes in the surface and near-surface regions. In our experiments, the irradiating ultraviolet photons are provided by a synchrotron storage ring, and the dynamical information about desorption products is obtained from optical measurements of the quantum states, yields and velocity distributions of neutral ground-state and excited-state atoms ejected from the surface of the irradiating material. These studies have shown that the dominant exit channels in photon-induced particle emission are those producing ground-state and excited-state neutral atoms. Using dynamical information about these desorbing neutral species, obtained, for example, by laser-induced fluorescence and laser Doppler spectroscopy, we are generating an increasingly comprehensive picture of the dynamics of electronic energy flow into and out of pure crystalline surfaces in these prototypical dielectrics. We are also beginning to be able to relate desorption dynamics to specific materials properties, and to discriminate between pure surface and near-surface effects in these materials. Applications of these techniques to the problem of photon-induced surface damage and to analysis of surface dynamics in dielectric materials are discussed, and the relationships between these nearly ideal model materials and the non-crystalline, covalently bonded materials more typical of real optical elements are pointed out. 19 refs., 13 figs

1986-01-01

99

Experimental studies of photon-surface interaction dynamics in the alkali halides  

Energy Technology Data Exchange (ETDEWEB)

We describe recent measurements which have provided, in unprecedented detail, insights into the electronic mechanisms through which energy carried into a material by photon irradiation is absorbed, localized and rechanneled to produce desorption, surface modification, erosion and damage. The specific object of these studies has been desorption induced by electronic transition in alkali halide crystals, with particular emphasis on the dynamics of changes in the surface and near-surface regions. In our experiments, the irradiating ultraviolet photons are provided by a synchrotron storage ring, and the dynamical information about desorption products is obtained from optical measurements of the quantum states, yields and velocity distributions of neutral ground-state and excited-state atoms ejected from the surface of the irradiating material. These studies have shown that the dominant exit channels in photon-induced particle emission are those producing ground-state and excited-state neutral atoms. Using dynamical information about these desorbing neutral species, obtained, for example, by laser-induced fluorescence and laser Doppler spectroscopy, we are generating an increasingly comprehensive picture of the dynamics of electronic energy flow into and out of pure crystalline surfaces in these prototypical dielectrics. We are also beginning to be able to relate desorption dynamics to specific materials properties, and to discriminate between pure surface and near-surface effects in these materials. Applications of these techniques to the problem of photon-induced surface damage and to analysis of surface dynamics in dielectric materials are discussed, and the relationships between these nearly ideal model materials and the non-crystalline, covalently bonded materials more typical of real optical elements are pointed out. 19 refs., 13 figs.

Haglund, R.F. Jr.; Tolk, N.H.

1986-01-01

100

Branching Transport Model of Alkali-Halide Scintillators  

CERN Document Server

We measure the time dependence of the scintillator light-emission pulses in NaI(Tl) crystals at different temperatures, after activation by gamma rays. We confirm that there are two main nonexponential components to the time decay and find that their amplitude ratio shows Arrhenius temperature dependence. We explain these nonexponential components as arising from two competing mechanisms of carrier transport to the Tl activation levels. The total light output of the NaI(Tl) detectors shows a linear temperature dependence explained by our model.

Alexandrov, B S; Littlewood, P B

2007-01-01

 
 
 
 
101

The change of the electronic structure of alkali halide films on W(110) under electron bombardment  

Energy Technology Data Exchange (ETDEWEB)

NaCl and CsI films of up to four layers were deposited onto W(110) surfaces and investigated by metastable impact electron spectroscopy (MIES), UPS and AES. The electronic structure of the films under electron bombardment was then studied by MIES/UPS. The results are compared with the corresponding ones obtained by thermal desorption spectroscopy (TDS). An interpretation of the results is attempted on the basis of existing theories for desorption induced by electronic transitions (DIET) of alkali halides. (orig.).

Dieckhoff, S.; Maus-Friedrichs, W.; Kempter, V. (Physikalisches Inst., TU Clausthal, Clausthal-Zellerfeld (Germany))

1992-03-01

102

Analysis of the thermal expansion coefficient and its temperature dependence for alkali halides  

Energy Technology Data Exchange (ETDEWEB)

A thermodynamic analysis of the Anderson parameter is found to yield useful relations for estimating the temperature dependence of interatomic separations r(T) and thermal expansion coefficient [alpha](T). The relations can be used to predict r(T) and [alpha](T) up to the melting temperatures of solids. The results obtained for sixteen alkali halides are compared with the available data reported in the literature. The values of r(T) are in close agreement with the data based on the theory of interionic potentials. The variation of the thermal expansion coefficient is discussed in the light of other investigations. (orig.)

Kumar, M. (Dept. of Physics, Inst. of Basic Sciences, Agra Univ. (India)); Upadhyay, S.P. (Dept. of Physics, Inst. of Basic Sciences, Agra Univ. (India))

1994-01-01

103

Analysis of the thermal expansion coefficient and its temperature dependence for alkali halides  

International Nuclear Information System (INIS)

A thermodynamic analysis of the Anderson parameter is found to yield useful relations for estimating the temperature dependence of interatomic separations r(T) and thermal expansion coefficient ?(T). The relations can be used to predict r(T) and ?(T) up to the melting temperatures of solids. The results obtained for sixteen alkali halides are compared with the available data reported in the literature. The values of r(T) are in close agreement with the data based on the theory of interionic potentials. The variation of the thermal expansion coefficient is discussed in the light of other investigations. (orig.).

1994-01-01

104

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

105

Off-center impurity in alkali halides: reorientation, electric polarization and pairing to F center. III. Numerical calculations  

CERN Document Server

We carried out numerical calculations by an extended-Hueckel program in order to check the analytical results reported in the preceding Part I and Part II. We typically consider alkali halide clusters composed of some tens of constituent atoms to calculate electronic energies under static conditions or versus the displacements of particular atoms. Among other things, the off-center displacement of substitutional Li+ impurity in most alkali halides is evidenced. The trigonometric profile of the rotational barriers is also confirmed for KCl.

Baldacchini, G; Grassano, U M; Scacco, A; Petrova, P; Mladenova, M; Ivanovich, M; Georgiev, M

2007-01-01

106

A comparative study of semi-empirical interionic potentials for alkali halides - II  

International Nuclear Information System (INIS)

A comprehensive study of some semi-empirical interionic potentials is carried out through the calculation of the cohesive energy, relative stability and pressure induced solid-solid phase transformations in alkali halides. The theoretical values of these properties of the alkali halides are obtained using a new set of van der Waals coefficients and zero-point energy in the expression for interionic potential. From the comparison of the present calculations with some previous sophisticated ab-initio quantum-mechanical calculations and other semi-empirical approaches, it is concluded that the present calculations in the simplest central pairwise interaction description with the new values of the van der Waals coefficients and zero-point energy are in better agreement with the experimental data than the previous calculations. It is also concluded that in some cases the better choice of the interionic potential alone in the simplest semi-empirical picture of interaction gives an agreement of the theoretical predictions with the experimental data much superior to the ab-initio quantum mechanical approaches. (author)

1985-01-01

107

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

108

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

International Nuclear Information System (INIS)

[en] 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[pt] A estrutura eletronica do centro F em halogenetos alcalinos com a estrutura do NaCl foi estudada utilizando-se o metodo Cluster-rede de Bethe. O cluster central foi tomado como sendo constituido pela vacancia, pelos cations primeiros vizinhos e pelos anions segundos vizinhos a mesma. As transicoes oticas foram calculadas e comparadas com os dados experimentais sobre o pico da banda F de absorcao. A concordancia obtida indica que este metodo pode ser usado para o estudo de propriedades deste defeito em halogenetos alcalinos

1977-01-01

109

Short-lived radiation defects in mixed silver halide crystals  

International Nuclear Information System (INIS)

The creation of raiation defects by pulsed electron beam in silver halide mixed AgBr1-xClx crystals was studied. It is shown that the radiation defects are created by a subthereshold mechanism. Irrespective of the Cl/Br cocentration ration nearly the same concentrations of radiation defects were observed under the single pulse irradiation.

1990-01-01

110

Electron transfer by the tunnel effect and its influence on the F center luminescence in alkali halides  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Concentration quenching plays an important role in luminescence phenomena, and is generally accounted for by pair interactions. In alkali halides containing F centers, whenever a member of an F center pair is optically excited at low temperature, it can return to its ground state either radiatively ...

Ecabert, M.; Schnegg, P. A.; Ruedin, Y.; Aegerter, Michel A.; Jaccard, C.

111

Mechanoluminescence in ?- irradiated potassium halide crystals induced by pressure pulse  

International Nuclear Information System (INIS)

During the application of pressure pulse in ?-irradiated potassium halide crystals, two peaks are observed in the ML intensity versus time curves. The ML intensity corresponding to the first peak is always greater than that of the second peak. The ML intensity after first peak and second peak decays exponentially with time. ML is a volumetric phenomenon, and its intensity increases with increasing size of the crystals. (author)

2005-01-01

112

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

113

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

114

Effective dielectric functions of samples obtained by evaporation of alkali halides  

International Nuclear Information System (INIS)

[en] This paper investigates the dielectric properties of inhomogeneous samples consisting of small alkali halide particles (NaCl, KBr) on gold-coated substrates. Our reflection measurements in the far infrared can be simulated as a thin layer of the power with an effective dielectric function on a perfectly reflecting substrate. Scanning electron micrographs provide useful information about sample topology. Several mixing formulas (e.g. the Maxwell-Garnett, the Bruggeman- and the Looyenga-formula) lead to effective dielectric functions neglecting the individual arrangement of the particles. The essence of our work is that, in contrast, the general ansatz of the Bergman spectral representation has to be employed in order to take into account topology effects on the dielectric function based on the so-called spectral density g adjustable to the specific situation. (orig.)

1991-01-01

115

Effective dielectric functions of samples obtained by evaporation of alkali halides  

Energy Technology Data Exchange (ETDEWEB)

This paper investigates the dielectric properties of inhomogeneous samples consisting of small alkali halide particles (NaCl, KBr) on gold-coated substrates. Our reflection measurements in the far infrared can be simulated as a thin layer of the power with an effective dielectric function on a perfectly reflecting substrate. Scanning electron micrographs provide useful information about sample topology. Several mixing formulas (e.g. the Maxwell-Garnett, the Bruggeman- and the Looyenga-formula) lead to effective dielectric functions neglecting the individual arrangement of the particles. The essence of our work is that, in contrast, the general ansatz of the Bergman spectral representation has to be employed in order to take into account topology effects on the dielectric function based on the so-called spectral density g adjustable to the specific situation. (orig.).

Sturm, J.; Grosse, P.; Theiss, W. (Technische Hochschule Aachen (Germany, F.R.). Lehrstuhl fuer Experimentalphysik 1A und 1. Physikalisches Inst.)

1991-01-01

116

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

International Nuclear Information System (INIS)

[en] 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

2009-01-01

117

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

118

Molecular Modeling and Monte Carlo Simulation of Concentrated Aqueous Alkali Halide Solutions at 25 C.  

Science.gov (United States)

A study of concentrated aqueous alkali halide solutions is made at the molecular level, through modeling and computer simulation of their structural and thermodynamic properties. It is found that the HNC approximation is the best integral equation theory to predict such properties within the framework of the primitive model (PM). The intrinsic limitations of the PM in describing ionic association and hydration effects are addressed and discussed in order to emphasize the need for explicitly including the water molecules in the treatment of aqueous electrolyte solutions by means of a civilized model (CM). As a step toward developing a CM as simple as possible, it is shown that a modified version of the SPC model of liquid water in which the Lennard-Jones interaction between intermolecular oxygen sites is replaced by a hard core interaction, is still successful enough to predict the degree of hydrogen bonding of real water. A simple civilized model (SCM) (in which the ions are treated as hard spheres interacting through Coulombic potentials and the water molecules are simulated using the simplified SPC model) is introduced in order to study the changes in the structural features of various aqueous alkali halide solutions upon varying both the concentration and the size of the ions. Both cations and anions are found to be solvated by the water molecules at expense of a breakdown in the hydrogen-bonded water network. Hydration numbers are reported for the first time for NaBr and KBr, and the first simulation -based estimates for LiBr, NaI and KI are also obtained. In several cases, values of the hydration numbers based on the SCM are found to be in excellent agreement with available experimental results obtained from x-ray diffraction measurements. Finally, it is shown that a neoprimitive model (NPM) can be developed by incorporating some of the structural features seen in the SCM into the short-range part of the PM interionic potential via a shielded square well whose width and depth's temperature coefficient can be determined from a fit of experimental data for the osmotic coefficient and heat of dilution, respectively.

Llano-Restrepo, Mario Andres

119

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

Science.gov (United States)

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 was demonstrated. Low pressure experiments were performed demonstrating the production of free silicon 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 and relatively pure silicon was produced. 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 compatability 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

120

Anomalous high-field electron injection and photoconduction in thin-film alkali halides  

International Nuclear Information System (INIS)

[en] Transient ion currents in thin-film alkali halides at ca. -4 A cm-2 at 1 ms, decay rapidly according to Iproportionalt/sup -m/ with 0-2 within 1 s, depending on voltage and temperature. For oscilloscopic presentation the initial applied voltage is 3.5--6.0 V for KI and with appropriate external resistance the increasing electronic current sweeps the potential difference across the film downward. This procedure discloses other discrete conduction regimes at 3.8 and 2.4 V. The noise amplitude attains 20% of the mean value with a random frequency estimated at approx.1 MHz. This current is attributed to field injection associated with a compact space charge at the cathode resulting from precursor defect ion drift in the disordered film. These thresholds have been confirmed by photoconductivity measurements of I versus h? in the 2--4-eV range by injection from the Al cathode. For KCl, KBr, KI, and RbI the thresholds for I versus V were verified and three injection modes were found altogether for each system

1980-01-01

 
 
 
 
121

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

122

Relationship between bond valence and bond softness of alkali halides and chalcogenides.  

UK PubMed Central (United Kingdom)

Established bond-valence parameter tables rely on the assumption that the bond-valence sum of a central atom is fully determined by interactions to atoms in its first coordination shell. In this work the influence of higher coordination shells is tested in detail for bonds between lithium and oxygen. It is demonstrated that the sum of the weak interactions with atoms of the second coordination shells significantly contributes to the valence sum and should therefore not be neglected. Since the independent refinement of the two parameters R(0) and b is hardly possible from the limited range of bond lengths occurring in the first coordination shell, the restriction of bond-valence sums to contributions from nearest neighbours implicated another far-reaching simplification: the postulation of a universally fixed value of the bond-valence parameter b which characterizes the shape of the bond-valence pseudopotential for the respective atom pair. However, recent more sophisticated applications of the bond-valence concept, e.g. to model ion-transport pathways in solid electrolytes, demand sensible estimates of the bond-valence sums for mobile ions not only at their equilibrium sites but also at interstitial sites and bottle-necks of transport pathways. Calculations of bond valences at these non-equilibrium sites require the knowledge of the actual shape of the bond-valence pseudopotential. A systematic route to a more realistic estimate of b for alkali halides and chalcogenides is developed in this work from an empirical correlation between b and the absolute softnesses of the interacting particles.

Adams S

2001-06-01

123

Relationship between bond valence and bond softness of alkali halides and chalcogenides.  

Science.gov (United States)

Established bond-valence parameter tables rely on the assumption that the bond-valence sum of a central atom is fully determined by interactions to atoms in its first coordination shell. In this work the influence of higher coordination shells is tested in detail for bonds between lithium and oxygen. It is demonstrated that the sum of the weak interactions with atoms of the second coordination shells significantly contributes to the valence sum and should therefore not be neglected. Since the independent refinement of the two parameters R(0) and b is hardly possible from the limited range of bond lengths occurring in the first coordination shell, the restriction of bond-valence sums to contributions from nearest neighbours implicated another far-reaching simplification: the postulation of a universally fixed value of the bond-valence parameter b which characterizes the shape of the bond-valence pseudopotential for the respective atom pair. However, recent more sophisticated applications of the bond-valence concept, e.g. to model ion-transport pathways in solid electrolytes, demand sensible estimates of the bond-valence sums for mobile ions not only at their equilibrium sites but also at interstitial sites and bottle-necks of transport pathways. Calculations of bond valences at these non-equilibrium sites require the knowledge of the actual shape of the bond-valence pseudopotential. A systematic route to a more realistic estimate of b for alkali halides and chalcogenides is developed in this work from an empirical correlation between b and the absolute softnesses of the interacting particles. PMID:11373385

Adams, S

2001-06-01

124

Alkali halide solutions under thermal gradients: soret coefficients and heat transfer mechanisms.  

UK PubMed Central (United Kingdom)

We report an extensive analysis of the non-equilibrium response of alkali halide aqueous solutions (Na(+)/K(+)-Cl(-)) to thermal gradients using state of the art non-equilibrium molecular dynamics simulations and thermal diffusion forced Rayleigh scattering experiments. The coupling between the thermal gradient and the resulting ionic salt mass flux is quantified through the Soret coefficient. We find the Soret coefficient is of the order of 10(-3) K(-1) for a wide range of concentrations. These relatively simple solutions feature a very rich behavior. The Soret coefficient decreases with concentration at high temperatures (higher than T ? 315 K), whereas it increases at lower temperatures. In agreement with previous experiments, we find evidence for sign inversion in the Soret coefficient of NaCl and KCl solutions. We use an atomistic non-equilibrium molecular dynamics approach to compute the Soret coefficients in a wide range of conditions and to attain further microscopic insight on the heat transport mechanism and the behavior of the Soret coefficient in aqueous solutions. The models employed in this work reproduce the magnitude of the Soret coefficient, and the general dependence of this coefficient with temperature and salt concentration. We use the computer simulations as a microscopic approach to establish a correlation between the sign and magnitude of the Soret coefficients and ionic solvation and hydrogen bond structure of the solutions. Finally, we report an analysis of heat transport in ionic solution by quantifying the solution thermal conductivity as a function of concentration. The simulations accurately reproduce the decrease of the thermal conductivity with increasing salt concentration that is observed in experiments. An explanation of this behavior is provided.

Römer F; Wang Z; Wiegand S; Bresme F

2013-07-01

125

Simple electrolyte solutions: Comparison of DRISM and molecular dynamics results for alkali halide solutions  

Science.gov (United States)

Using the dielectrically consistent reference interaction site model (DRISM) of molecular solvation, we have calculated structural and thermodynamic information of alkali-halide salts in aqueous solution, as a function of salt concentration. The impact of varying the closure relation used with DRISM is investigated using the partial series expansion of order-n (PSE-n) family of closures, which includes the commonly used hypernetted-chain equation (HNC) and Kovalenko-Hirata closures. Results are compared to explicit molecular dynamics (MD) simulations, using the same force fields, and to experiment. The mean activity coefficients of ions predicted by DRISM agree well with experimental values at concentrations below 0.5 m, especially when using the HNC closure. As individual ion activities (and the corresponding solvation free energies) are not known from experiment, only DRISM and MD results are directly compared and found to have reasonably good agreement. The activity of water directly estimated from DRISM is nearly consistent with values derived from the DRISM ion activities and the Gibbs-Duhem equation, but the changes in the computed pressure as a function of salt concentration dominate these comparisons. Good agreement with experiment is obtained if these pressure changes are ignored. Radial distribution functions of NaCl solution at three concentrations were compared between DRISM and MD simulations. DRISM shows comparable water distribution around the cation, but water structures around the anion deviate from the MD results; this may also be related to the high pressure of the system. Despite some problems, DRISM-PSE-n is an effective tool for investigating thermodynamic properties of simple electrolytes.

Joung, In Suk; Luchko, Tyler; Case, David A.

2013-01-01

126

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

127

Alkali halide solutions under thermal gradients: soret coefficients and heat transfer mechanisms.  

Science.gov (United States)

We report an extensive analysis of the non-equilibrium response of alkali halide aqueous solutions (Na(+)/K(+)-Cl(-)) to thermal gradients using state of the art non-equilibrium molecular dynamics simulations and thermal diffusion forced Rayleigh scattering experiments. The coupling between the thermal gradient and the resulting ionic salt mass flux is quantified through the Soret coefficient. We find the Soret coefficient is of the order of 10(-3) K(-1) for a wide range of concentrations. These relatively simple solutions feature a very rich behavior. The Soret coefficient decreases with concentration at high temperatures (higher than T ? 315 K), whereas it increases at lower temperatures. In agreement with previous experiments, we find evidence for sign inversion in the Soret coefficient of NaCl and KCl solutions. We use an atomistic non-equilibrium molecular dynamics approach to compute the Soret coefficients in a wide range of conditions and to attain further microscopic insight on the heat transport mechanism and the behavior of the Soret coefficient in aqueous solutions. The models employed in this work reproduce the magnitude of the Soret coefficient, and the general dependence of this coefficient with temperature and salt concentration. We use the computer simulations as a microscopic approach to establish a correlation between the sign and magnitude of the Soret coefficients and ionic solvation and hydrogen bond structure of the solutions. Finally, we report an analysis of heat transport in ionic solution by quantifying the solution thermal conductivity as a function of concentration. The simulations accurately reproduce the decrease of the thermal conductivity with increasing salt concentration that is observed in experiments. An explanation of this behavior is provided. PMID:23758489

Römer, Frank; Wang, Zilin; Wiegand, Simone; Bresme, Fernando

2013-06-26

128

Photography: enhancing sensitivity by silver-halide crystal doping  

International Nuclear Information System (INIS)

[en] 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 PHIeff of photoinduced silver cluster formation in silver halide microcrystals is usually much lower than the photoionization theoretical limit PHItheor=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 HCO2- as a specific hole scavenger. First, the dopant scavenges the photoinduced hole, thus enhancing the electron escape from the pair recombination. Second, the CO2·- radical so formed transfers an electron to another silver cation, so that the PHIeff limit may be of 2Ag0 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

2002-09-05

129

Development of processes for the production of solar grade silicon from halides and alkali metals, phase 1 and phase 2  

Science.gov (United States)

High temperature reactions of silicon halides with alkali metals for the production of solar grade silicon are described. Product separation and collection processes were evaluated, measure heat release parameters for scaling purposes and effects of reactants and/or products on materials of reactor construction were determined, and preliminary engineering and economic analysis of a scaled up process were made. The feasibility of the basic process to make and collect silicon was demonstrated. The jet impaction/separation process was demonstrated to be a purification process. The rate at which gas phase species from silicon particle precursors, the time required for silane decomposition to produce particles, and the competing rate of growth of silicon seed particles injected into a decomposing silane environment were determined. The extent of silane decomposition as a function of residence time, temperature, and pressure was measured by infrared absorption spectroscopy. A simplistic model is presented to explain the growth of silicon in a decomposing silane enviroment.

Dickson, C. R.; Gould, R. K.; Felder, W.

1981-03-01

130

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

131

A Review of Luminescent Anionic Nano System: d10 Metallocyanide Excimers and Exciplexes in Alkali Halide Hosts  

Directory of Open Access Journals (Sweden)

Full Text Available Dicyanoaurate, dicyanoargentate, and dicyanocuprate ions in solution and doped in different alkali halide hosts exhibit interesting photophysical and photochemical behavior, such as multiple emission bands, exciplex tuning, optical memory, and thermochromism. This is attributed to the formation of different sizes of nanoclusters in solution and in doped hosts. A series of spectroscopic methods (luminescence, UV-reflectance, IR, and Raman) as well as theoretical calculations have confirmed the existence of excimers and exciplexes. This leads to the tunability of these nano systems over a wide wavelength interval. The population of these nanoclusters varies with temperature and external laser irradiation, which explains the thermochromism and optical memory. DFT calculations indicate an MLCT transition for each nanocluster and the emission energy decreases with increasing cluster size. This is in agreement with the relatively long life-time for the emission peaks and the multiple emission peaks dependence upon cluster concentration.

Xiaobo Li; Howard H. Patterson

2013-01-01

132

Two-electron F' centers in alkali halides: a saddle point approach. I. General and semicontinuum analyses  

CERN Document Server

The F' center in an alkali halide forms when an anion vacancy traps two electrons which is the prerequisite of a diatomic molecule. Indeed, the center may displace left or right along in a (110) plane, due to its coupling to the B_{1u} vibrational mode of polarization respectively. On jumping from the initial position to the final position the F' center passes through a saddle point which configuration is molecule-like being conformed by two neighboring semi-vacancies along . Each semi-vacancy traps one electron to change its effective charge from +1/2 to -1/2 formin a semi-F' center. We ouline the basic theory so as to perform calculations on the F' eigenenergies in the two configurations to see which one of them is more favorable.

Georgiev, M

2006-01-01

133

Cu halide nanoparticle formation by diffusion of copper in alkali halide crystals  

Directory of Open Access Journals (Sweden)

Full Text Available Atomos de cobre han sido introducidos por difusión en cristales de NaCl, KCl y KBr a 500±C. Los cristales han sido analizados óptimamente con medidas de fotoluminiscencia y por microscopía electrónica de barrido. Los espectros de emisión y excitación, medidos a baja temperatura muestran el efecto de confinamiento de exciton, indicando la formación de nanopartículas de CuX (X=Cl, Br), lo cual ha sido confirmado por imágenes de microscopía electrónica. Este método es propuesto como un método alternativo para obtener nanopartículas de CuX en cristales halogenuros alcalinos.

A. Pérez-Rodríguez; M. Flores-Acosta; R. Rodríguez-Mijangos; R. Pérez-Salas

2006-01-01

134

Effect of replacing calcium oxide with calcium halide on crystallization and some physical properties of calcium vanadium phosphate glass ceramics  

International Nuclear Information System (INIS)

[en] The effect of halide ions on density, electrical, magnetic and crystallization kinetics for (20X-50P2O5-30V2O5) mole% has been investigated, where X=CaO, CaF2, CaCl2 and CaBr2. Halide ions reduce the glass transition temperature, crystallization temperature and activation energy of crystallization. Density, electrical conductivity and magnetic susceptibility increase while molar volume, glass thermal stability and interatomic distance between transition metal ions decrease as the halide ions replace the oxygen ions in these glasses. -- Research Highlights: ? Replacing oxygen ions by halide ions decreases glass transition temperature and thermal stability. ? Replacing oxygen ions by halide ions increases electrical conductivity and decreases activation energy. ? Replacing oxygen ions by halide ions enhances the tendency of glass ceramic and decreases the crystallization activation energy.

2011-02-01

135

Electrohydrodynamic emission of positive and negative ions from alkali-metal halide melts  

International Nuclear Information System (INIS)

The characteristics of electrohydrodynamic (EHD) emission of positive and negative ions from melts of alkali-metal metals are presented. The angular current density is 3-4 ?A/sr with emission currents of 0.1-0.5 ?A. The salt EHD sources which have been developed yield stable currents of K+, Rb+, Cs+, F-, Cl-, and I- ions for several tens of hours. 10 refs., 4 figs., 1 tab.

1992-01-01

136

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

Directory of Open Access Journals (Sweden)

Full Text Available 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. 350 K are accessible. Elemental analysis, ion chromatography and site occupancy refinements from single-crystal X-ray diffraction agree with respect to the stoichiometric composition of the samples.

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

2011-01-01

137

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 Document Server

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

138

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

Science.gov (United States)

Intercomparisons between flow stress, microhardness, and rosette size measurements for purified KCl single crystals, KCl:Ca, KCl:Sr, and KCl(x)Br(l-x) mixed single crystals are made. A good correlation between the flow stress and inverse of the length of ...

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

1972-01-01

139

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 6500C 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.

1978-01-01

140

Crystallization of iron phosphate glass containing mixed alkali oxides  

International Nuclear Information System (INIS)

[en] 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

2010-01-01

 
 
 
 
141

MEASUREMENTS OF STORED ENERGY RELEASE OF X-IRRADIATED ALKALI HALIDES  

Digital Repository Infrastructure Vision for European Research (DRIVER)

KBr crystals were irradiated at about 10 K with 100 kV X-rays. During a linear rise of temperature the energy release due to the recombination of defects was determined. With the aid of optical absorption measurements the peaks could be attributed to the annealing of various configurations of two di...

Schrey, P.; Balzer, R.

142

Molecular simulation of aqueous electrolyte solubility. 3. Alkali-halide salts and their mixtures in water and in hydrochloric acid.  

UK PubMed Central (United Kingdom)

We extend the osmotic ensemble Monte Carlo (OEMC) molecular simulation method (Mou?ka et al. J. Phys Chem. B 2011, 115, 7849-7861) for directly calculating the aqueous solubility of electrolytes and for calculating their chemical potentials as functions of concentration to cases involving electrolyte hydrates and mixed electrolytes, including invariant points involving simultaneous precipitation of several solutes. The method utilizes a particular semigrand canonical ensemble, which performs simulations of the solution at a fixed number of solvent molecules, pressure, temperature, and specified overall electrolyte chemical potential. It avoids calculations for the solid phase, incorporating available solid chemical potential data from thermochemical tables, which are based on well-defined reference states, or from other sources. We apply the method to a range of alkali halides in water and to selected examples involving LiCl monohydrate, mixed electrolyte solutions involving water and hydrochloric acid, and invariant points in these solvents. The method uses several existing force-field models from the literature, and the results are compared with experiment. The calculated results agree qualitatively well with the experimental trends and are of reasonable accuracy. The accuracy of the calculated solubility is highly dependent on the solid chemical potential value and also on the force-field model used. Our results indicate that pairwise additive effective force-field models developed for the solution phase are unlikely to also be good models for the corresponding crystalline solid. We find that, in our OEMC simulations, each ionic force-field model is characterized by a limiting value of the total solution chemical potential and a corresponding aqueous concentration. For higher values of the imposed chemical potential, the solid phase in the simulation grows in size without limit.

Mou?ka F; Lísal M; Smith WR

2012-05-01

143

Measurements of stored energy release of X-irradiated alkali halides  

International Nuclear Information System (INIS)

KBr crystals were irradiated at about 10 K with 100 KV X-rays. During a linear rise of temperature the energy release due to the recombination of defects was determined. With the aid of optical absorption measurements the peaks could be attributed to the annealing of various configurations of two different Frenkel pairs, namely vacancy and interstitial ion, and F-center and interstitial atom. The stored energies per Frenkel pair are determined to be Esub(?+I) = (4.0 +- 0.8) eV and Esub(F+H) = (2.7 +- 0.6) eV respectively. (orig.).

1976-08-30

144

Measurements of stored energy release of X-irradiated alkali halides  

International Nuclear Information System (INIS)

KBr crystals were irradiated at about 10K with 100kV X-rays. During a linear rise of temperature the energy release due to the recombination of defects was determined. With the aid of optical absorption measurements the peaks could be attributed to the annealing of various configurations of two different Frenkel pairs, namely vacancy and interstitial ion, and F-center and interstitial atom. The stored energies per Frenkel pair are determined to be Esub(?+I)=(4.0+-0.8)eV and Esub(F+H)=(2.7+-0.6)eV respectively

1976-09-03

145

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

146

Dipole-driven self-organization of zwitterionic molecules on alkali halide surfaces  

Directory of Open Access Journals (Sweden)

Full Text Available We investigated the adsorption of 4-methoxy-4?-(3-sulfonatopropyl)stilbazolium (MSPS) on different ionic (001) crystal surfaces by means of noncontact atomic force microscopy. MSPS is a zwitterionic molecule with a strong electric dipole moment. When deposited onto the substrates at room temperature, MSPS diffuses to step edges and defect sites and forms disordered assemblies of molecules. Subsequent annealing induces two different processes: First, at high coverage, the molecules assemble into a well-organized quadratic lattice, which is perfectly aligned with the directions of the substrate surface (i.e., rows of equal charges) and which produces a Moiré pattern due to coincidences with the substrate lattice constant. Second, at low coverage, we observe step edges decorated with MSPS molecules that run along the direction. These polar steps most probably minimize the surface energy as they counterbalance the molecular dipole by presenting oppositely charged ions on the rearranged step edge.

Laurent Nony; Franck Bocquet; Franck Para; Frédéric Chérioux; Eric Duverger; Frank Palmino; Vincent Luzet; Christian Loppacher

2012-01-01

147

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

Energy Technology Data Exchange (ETDEWEB)

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 lambda/sub 1/, 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.

Burckhardt, W. (Friedrich-Schiller-Universitaet, Jena (German Democratic Republic). Sektion Chemie); Bussemer, P.; Dietrich, U. (Friedrich-Schiller-Universitaet, Jena (German Democratic Republic). Sektion Physik)

1984-09-16

148

Creation and destruction of X-3 centres in alkali halides by X-radiation  

International Nuclear Information System (INIS)

[en] The production (etasub(X3-)) and destruction efficiencies of X3-centres in NaCl, KCl, KBr, and KI by X-radiation versus the irradiation temperature (in the range of 80 to 320 K) are investigated by optical absorption and thermoluminescence methods. Both, the increase (80 to 150 K) and decrease (200 to 250 K) of etasub(X3-) in KBr and KI at the adsorbed dose of 1019 to 1021 eV cm-3 are shown to be in correlation with the F-centre creation efficiency (etasub(F)). In chlorides etasub(F) does not decrease with etasub(X3-) and these crystals are characterized by a high defect creation efficiency at approximately room temperatures. It is supposed that the creation of large halogen aggregates is much more efficient in chlorides than in bromides and iodides. (author)

1980-07-01

149

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

150

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

Scientific Electronic Library Online (English)

Full Text Available 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 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+ (more) 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 (more) . 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.

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

2011-04-01

151

Crystallization kinetics of alkali feldspars in cooling and decompression-induced crystallization experiments in trachytic melt  

Science.gov (United States)

Cooling and decompression experiments have been carried out on trachytic melts in order to investigate crystallization kinetics of alkali feldspar, the effect of the degree of undercooling ( ?T = T liquidus - T experimental) and time on nucleation and crystal growth process. This experimental work gives us new data about crystallization kinetics of trachytic melts, and it that will be useful to better understand the natural system of Campi Flegrei volcanoes. Experiments have been conducted using cold seal pressure vessel apparatus, at pressure between 30 and 200 MPa, temperature between 750 and 855 °C, time between 7,200 and 57,600 s and redox condition close to the NNO +0.8 buffer. These conditions are ideal to reproducing pre- and syn-eruptive conditions of the Campi Flegrei volcanoes, where the "conditions" pertain to the complete range of pressures, temperatures and time at which the experiments were performed. Alkali feldspar is the main phase present in this trachyte, and its abundance can strongly vary with small changes in pressure, temperature and water content in the melt, implying appreciable variations in the textures and in the crystallization kinetics. The obtained results show that crystallization kinetics are strictly related to ?T, time, final pressure, superheating (- ?T) and water content in the melt. ?T is the driving force of the crystallization, and it has a strong influence on nucleation and growth processes. In fact, the growth process dominates crystallization at small ?T, whereas the nucleation dominates crystallization at large ?T. Time also is an important variable during crystallization process, because long experiment durations involve more nucleation events of alkali feldspar than short experiment durations. This is an important aspect to understand magma evolution in the magma chamber and in the conduit, which in turn has strong effects on magma rheology.

Arzilli, Fabio; Carroll, Michael R.

2013-10-01

152

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.

Baker, J.; Lindgård, Per-Anker

1999-01-01

153

Crystallization conditions and crystal habits of potassium halides in industrial crystallizers; Kogyo shoseki sochi ni okeru harogenka karium no shoseki joken to shoheki  

Energy Technology Data Exchange (ETDEWEB)

The crystallization of potassium halides has been carried out using cone-type fluidizing and mixing crystallizers operated as industrial crystallizers. Operational data obtained over ten years were also analyzed. As a result, it became clear that there were limiting values in the degree of supersaturation for obtaining single crystals of good shape. The addition of habit modifiers resulted in an increase in the limiting degree of supersaturation and in the depression of agglomeration. The change of limiting degree of supersaturation and notable changes in the crystal habit also occurred upon pH control. 6 refs., 10 figs., 1 tab.

Miki, H.; Aoyama, Y. [Crystal Engineering Corp., Osaka (Japan)

1995-05-10

154

Development of processes for the production of solar grade silicon from halides and alkali metals, Phase 1 and Phase 2. Final report, October 1979 - February 1981  

Energy Technology Data Exchange (ETDEWEB)

High temperature reactions of silicon halides with alkali metals for the production of solar grade silicon are described. Product separation and collection processes were evaluated, measure heat release parameters for scaling purposes and effects of reactants and/or products on materials of reactor construction were determined, and preliminary engineering and economic analysis of a scaled up process were made. The feasibility of the basic process to make and collect silicon was demonstrated. The jet impaction/separation process was demonstrated to be a purification process. The rate at which gas phase species from silicon particle precursors, the time required for silane decomposition to produce particles, and the competing rate of growth of silicon seed particles injected into a decomposing silane environment were determined. The extent of silane decomposition as a function of residence time, temperature, and pressure was measured by infrared absorption spectroscopy. A simplistic model is presented to explain the growth of silicon in a decomposing silane enviroment.

Dickson, C.R.; Gould, R.K.; Felder, W.

1981-03-01

155

Development of processes for the production of solar grade silicon from halides and alkali metals. Second quarterly report, 1 January-31 March 1980  

Energy Technology Data Exchange (ETDEWEB)

This program is directed toward the development of processes involving high temperature reactions of silicon halides with alkali metals for the production of solar grade silicon in volume at low cost. Experiments are being performed to evaluate product separation and collection processes, measure heat release parameters for scaling purposes, determine the effects of reactants and/or products on materials of reactor construction, and make preliminary engineering and economic analyses of a scaled-up process. Samples of the silicon product will be delivered to JPL for evaluation of solar cell performance. During this reporting period, the program efforts were directed toward the measurement of reagent flow rates and silicon collection efficiencies, the construction of a new sodium heat pipe to permit one to two hour runs, and the completion of the economic and engineering analyses of the AeroChem process to make solar grade silicon. Progress is reported.

Dickson, C.R.; Gould, R.K.

1980-04-01

156

Lithium-selective phosphine oxide-based ditopic receptors show enhanced halide binding upon alkali metal ion coordination.  

UK PubMed Central (United Kingdom)

Previous work on a ditopic receptor based on a tripodal phosphine oxide core demonstrated preferential enhancement of bromide binding over chloride or iodide in the presence of lithium cation. Current studies on an elongated receptor provide evidence that preferential bromide binding enhancement in the presence of lithium cation is common to this receptor class in general, and that lengthening of the receptor results in an overall increase in halide association. Furthermore, the extended receptor shows a strong preference for Li(+) binding in solution.

Gavette JV; Lara J; Reling LL; Haley MM; Johnson DW

2013-01-01

157

Energetic aspects of water radiolysis on surface of alkali-halogen crystals  

International Nuclear Information System (INIS)

It is established that radiolysis rate of water adsorbed with alkali-halogen crystals depends on the nature of salt, adsorbate concentration and crystal sizes. It is shown that water decomposition on the surface of potassium and rubidium iodides results from the interaction with components of electron-hole pairs. Assumption of diffusive sink of thermalized electrons and holes to the surface from crystal volume of 0.1-1 mm depth was suggested.

1987-01-01

158

Single mode mid-infrared silver halide asymmetric flat waveguide obtained from crystal extrusion.  

UK PubMed Central (United Kingdom)

A flat waveguide for the middle infrared was made by co-extrusion of two silver halide crystals of different chemical compositions. The transmission of the waveguide and its modal behavior was studied using a Fourier Transform Spectrometer and a dedicated optical bench. Analyzing this spectrum, we were able to obtain the cut-off wavelength of the waveguide. We observed a single mode behavior for wavelengths longer than 8.83mum, in good agreement with the theoretically expected values. This novel procedure is ideal for tailoring the properties of the waveguide for specific applications, in particular the spectral range where it exhibits a single-mode behavior. It can thus be applied to achieve modal filtering for mid-IR astronomical interferometers (e.g. beam combiners, nullers, etc.).

Grille R; Martin G; Labadie L; Arezki B; Kern P; Lewi T; Tsun A; Katzir A

2009-07-01

159

Development of processes for the production of solar grade silicon from halides and alkali metals. Third quarterly report, April 1-June 30, 1980  

Energy Technology Data Exchange (ETDEWEB)

This program is directed toward the development of processes involving high temperature reactions of silicon halides with alkali metals for the production of solar grade silicon in volume at low cost. Experiments are performed to evaluate product separation and collection processes, measure heat release parameters for scaling purposes, determine the effects of reactants and/or products on materials of reactor construction, and make preliminary engineering and economic analyses of a scaled-up process. During this report period work concentrated on preparing samples of silicon for purity analyses. The results of six such analyses are given. In general, they indicate that the process is capable of producing very pure silicon. A number of impurity elements appear in 0.1 to 10 ppMa concentrations in one or another of the samples in unpredictable patterns. This would be expected for the one hour runs performed since atmospheric dust has easy access to collection surfaces during assembly and laboratory conditions do not allow clean assembly procedures to be followed. Particularly encouraging is the observation that sodium levels are below 10 ppMa in most runs.

Gould, R.K.

1980-09-01

160

Development of processes for the production of solar grade silicon from halides and alkali metals. First quarterly report, October 3-December 31, 1979  

Energy Technology Data Exchange (ETDEWEB)

This program is directed toward the development of processes involving high temperature reactions of silicon halides with alkali metals for the production of solar grade silicon in volume at low cost. Experiments are being performed to evaluate product separation and collection processes, measure heat release parameters for scaling purposes, determine the effects of reactants and/or products on materials of reactor construction, and make preliminary engineering and economic analyses of a scaled-up process. Samples of the silicon product will be delivered to JPL for evaluation of solar cell performance. During this reporting period the silicon reactor test apparatus reached operational capabilities after a shutdown for two months. Several design improvements were made while returning it to an operational stage. During the initial series of experiments complete product separation of the silicon from the salt was achieved and small samples (approx. = 3 to 40 g) of fused silicon were collected. The test apparatus is now being operated on a routine basis for periods of about twenty minutes. Finally, the initial work began on the engineering and economic analysis for scale-up of the silicon production process.

Dickson, C.R.; Gould, R.K.

1980-02-01

 
 
 
 
161

Neutron inelastic scattering investigation of phonons in alkali-halides and a neutron small-angle scattering study of voids in creep-deformed steel  

International Nuclear Information System (INIS)

[en] Studies on lattice dynamics in alkali-halides have been performed on RbBr and NaCl using inelastic scattering of thermal neutrons. Anharmonic properties of RbBr have been examined by measuring phonon peaks at the three temperatures 80, 290 and 370 K. In NaCl a three dimensional phonon dispersion map has been obtained. 72 phonon frequencies in off-symmetry directions have been determined. In creep-deformed alloy 800 the void radius distribution was obtained using neutron small-angle scattering. Six samples with different creep-times were studied. As these samples also contain carbides and ?'-precipitates the measured intensity is in principle due to scattering from three kinds of particles. Transmission electron microscopy measurements show that the scattering by the carbides is negligible, however. The relative radius distribution of ?'-particles, calculated for each sample individually, has an average radius of approximately 25 A. Because of experimental difficulties the void radius distribution could be determined only for samples with 5 and 10% creep. The voids appear to have a broad distribution around 300 A and the volume fraction of voids shows an increase of 7% between these two samples. (Auth.)

1981-01-01

162

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

International Nuclear Information System (INIS)

[en] 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

1991-11-15

163

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

164

Vibration spectra and local symmetry of impurity tetrahedral anions ReO4- in halide-cesium crystals  

International Nuclear Information System (INIS)

[en] The RS and IR absorption spectra of impurity tetrahedralmolecular anions(MA) ReO4- in halide-cesium crystals are investigated. It is established that in such crystals there variants of implantation of MA ReO4- into a lattice of crystals are possible. In this case for the knotty variant of inplantation the formation of complexes of MA ReO4-with cations of Me+ and Me2+ metals with the different local symmetry of MA is revealed

1992-01-01

165

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 d...

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

166

Development of processes for the production of solar-grade silicon from halides and alkali metals. Final report, October 1979-February 1981  

Energy Technology Data Exchange (ETDEWEB)

Processes were developed involving high temperature reactions of silicon halides with alkali metals for the production of solar grade silicon in volume at low cost. Experiments were performed to evaluate product separation and collection processes, measure heat release parameters for scaling purposes, determine the effects of reactants and/or products on materials of reactor construction, and make preliminary engineering and economic analyses of a scaled-up process. The process was found to have a low manufacturing cost and the lowest plant cost of all the present JPL sponsored processes, and produces the silicon product at the low price of $10/kg in 1980 dollars. The kinetics and mechanism of the formation and growth of silicon particles from the decomposition of silane at high temperatures is characterized. The experiments were aimed at determining the rates at which gas-phase species form silicon particle precursors, the time required for silane decomposition to produce particles, and the competing rate of growth of silicon seed particles injected into a decomposing silane environment. A high-temperature fast-flow reactor was modified to study the decomposition of silane and the subsequent growth of particles. Optical diagnostics consisting of absorption and Mie scattering of the light at 90/sup 0/ from He-Ne or Ar/sup +/ lasers were used to determine the appearance growth rates and absolute sizes of the particles. The extent of silane decomposition as a function of residence time, temperature, and pressure was measured by infrared absorption spectroscopy. A simplistic model is presented to explain the growth of silicon in a decomposing silane environment. (LEW)

Dickson, C.R.; Gould, R.K.; Felder, W.

1981-03-01

167

Quantum mechanical study of the lattice distortions induced by aliovalent Pb{sup 2+} impurities in alkali halides  

Energy Technology Data Exchange (ETDEWEB)

An embedded cluster analysis of the lattice distortions induced by a Pb{sup 2+} substitutional impurity in NaI, RbI and CsF crystals is presented. Active clusters containing more than 100 atoms and embedded in a quantum representation of the crystalline environment are used. Charge compensation is achieved by introducing a cation vacancy in the host lattice. Both nearest-neighbor (NN) and next-nearest-neighbor (NNN) vacancy positions are explicitly considered, as well as the case where vacancy and impurity are well separated from each other. Only in the first two cases, the impurity adopts an off-center equilibrium position. Distortion trends as a function of the host lattice are identified and discussed. These trends are then employed to advance the expected distortions in similar crystals. The examples of Pb{sup 2+}-doped RbF and KBr are found to behave according to the expectations. Finally, the relative stability of the NN and NNN configurations is discussed. (orig.)

Aguado, A. [Oxford Univ. (United Kingdom). Physical and Theoretical Chemistry Lab.

2002-02-01

168

Synthesis and single-crystal structure determination of the zinc nitride halides Zn2NX (X=Cl, Br, I)  

Science.gov (United States)

A series of zinc nitride halides, Zn2NX (X=Cl, Br, I), has been synthesized from solid-liquid reactions of zinc nitride with the respective zinc halides under vacuum, and their crystal structures were determined using single-crystal and powder X-ray diffraction. While Zn2NCl and Zn2NBr crystallize in the acentric orthorhombic space group Pna21, Zn2NI adopts the centrosymmetric space group Pnma; Zn2NCl and Zn2NBr can be considered to belong to the anti-?-NaFeO2 type, and Zn2NI is closely related. Each N3- is tetrahedrally coordinated by zinc atoms, and the X- anions are located in the vacancies of the framework formed by corner-sharing [NZn4] tetrahedra. According to TGA/DTA analyses, the Zn2NX compounds exhibit good thermal stability. The electronic structure has been analyzed by employing density-functional theory and the HSE06 hybrid functional.

Liu, Xiaohui; Wessel, Claudia; Pan, Fangfang; Dronskowski, Richard

2013-07-01

169

Growth and properties of large single crystals of YBa sub 2 Cu sub 3 O sub 7-. delta  

Energy Technology Data Exchange (ETDEWEB)

The use of a molten eutectic flux based on mixed alkali halides has allowed us to grow single crystals of YBCO with thicknesses of up to 4mm and total volumes approaching 0.3 cm{sup 3}. The crystals are superconducting as grown but are improved by oxygen annealing. Both neutron scattering and optical microscopy confirm the single crystal nature. (orig.).

Bosi, S.; Hunter, B.; Town, S.; Puzzer, T.; Nouruzi-Khorasani, A.; Cochrane, J.; Bailey, A.; Russell, G.J.; Taylor, K.N.R. (Advanced Electronic Materials Group, Univ. of NSW, Kensington (Australia))

1989-12-01

170

Coordination trends in alkali metal crown ether uranyl halide complexes: the series [A(crown)]2[UO(2)X(4)] where A=Li, Na, K and X=Cl, Br.  

Science.gov (United States)

UO(2)(C(2)H(3)O(2))(2).2H(2)O reacts with AX or A(C(2)H(3)O(2) or ClO(4)) (where A = Li, Na, K; X = Cl, Br) and crown ethers in HCl or HBr aqueous solutions to give the sandwich-type compounds [K(18-crown-6)](2)[UO(2)Cl(4)] (1), [K(18-crown-6)](2)[UO(2)Br(4)] (2), [Na(15-crown-5)](2)[UO(2)Cl(4)] (3), [Na(15-crown-5)](2)[UO(2)Br(4)] (4), [Li(12-crown-4)](2)[UO(2)Cl(4)] (5), and [Li(12-crown-4)](2)[UO(2)Br(4)] (6). The compounds have been characterized by single-crystal X-ray diffraction, powder diffraction, elemental analysis, IR, and Raman spectroscopy. The [UO(2)X(4)](2-) ions coordinate to two [A(crown)](+) cations through the four halides only (2), through two halides only (3), through the two uranyl oxygens and two halides (3, 4), or through the two uranyl oxygen atoms only (5, 6). Raman spectra reveal nu(U-O) values that correlate with expected trends. The structural trends are discussed within the context of classical principles of hard-soft acid-base theory. PMID:11421684

Danis, J A; Lin, M R; Scott, B L; Eichhorn, B W; Runde, W H

2001-07-01

171

Coordination trends in alkali metal crown ether uranyl halide complexes: the series [A(crown)]2[UO(2)X(4)] where A=Li, Na, K and X=Cl, Br.  

UK PubMed Central (United Kingdom)

UO(2)(C(2)H(3)O(2))(2).2H(2)O reacts with AX or A(C(2)H(3)O(2) or ClO(4)) (where A = Li, Na, K; X = Cl, Br) and crown ethers in HCl or HBr aqueous solutions to give the sandwich-type compounds [K(18-crown-6)](2)[UO(2)Cl(4)] (1), [K(18-crown-6)](2)[UO(2)Br(4)] (2), [Na(15-crown-5)](2)[UO(2)Cl(4)] (3), [Na(15-crown-5)](2)[UO(2)Br(4)] (4), [Li(12-crown-4)](2)[UO(2)Cl(4)] (5), and [Li(12-crown-4)](2)[UO(2)Br(4)] (6). The compounds have been characterized by single-crystal X-ray diffraction, powder diffraction, elemental analysis, IR, and Raman spectroscopy. The [UO(2)X(4)](2-) ions coordinate to two [A(crown)](+) cations through the four halides only (2), through two halides only (3), through the two uranyl oxygens and two halides (3, 4), or through the two uranyl oxygen atoms only (5, 6). Raman spectra reveal nu(U-O) values that correlate with expected trends. The structural trends are discussed within the context of classical principles of hard-soft acid-base theory.

Danis JA; Lin MR; Scott BL; Eichhorn BW; Runde WH

2001-07-01

172

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

173

Preparation, phase equilibria, and crystal chemistry of La, Pr, Nd, Sm, Eu, and Gd hydroxide halides  

International Nuclear Information System (INIS)

The phase equilibria of the hydroxide halides of La, Pr, Nd, Sm, Eu, and Gd in hydrothermal media have been investigated. The hydroxide chlorides, bromides, and iodides of La, Pr, and Nd were prepared in the temperature and pressure range 5500 to 6000 and 1333 to 1530 atm. Equilibria of the hydroxide halides of Sm, Eu, and Gd show a temperature dependence; chlorides and bromides were prepared at 550 to 7500 and 1667 atm, and 350 to 5500 and 1333 to 1533 atm, respectively. The hydroxide iodides of Sm, Eu, and Gd were obtained at 5500 and 1400 to 1933 atm. The crystalline products, which have been characterized by analytical and X-ray methods, are unaffected by pressure. Several different phases have been identified in the lanthanide (Ln) systems. For Ln = La, Pr, and Nd, the products include Ln(OH)3, Ln7(OH)18X3, and Ln(OH)2Y (X = lattice l-, Br-, I-; Y = Cl-, Br-). For Ln = Sm, Eu, and Gd, a wider variety of phases are encountered, some of which are unidentified. The identified products include Ln(OH)3, Ln7(OH)18X3, Ln3O(OH)5Br2, Ln3(OH)8I (Ln = Sm, Eu, Gd), and Ln(OH)2Y (Ln = Eu, Gd; Y = Cl-, Br-). All observed Ln(OH)2Y phases have the Y(OH)2Cl-type structure. The Ln(OH)2Br phases have not been previously characterized. Diffraction data for the Ln7(OH)18X3 phases show a new hexagonal structure type with a pronounced UCl3-type substructure. The quaternary Ln3O(OH)5Br2 phases have an orthorhombic structure similar to that of Y3O(OH)5Cl2. Thermal decomposition processes of all the identified phases have been characterized. The structure of La7(OH)18I3 is a substitution derivative of the UCl3-type structure. The Gd3O(OH)5Br2 structure (Pmmn) is similar to that previously reported for Y3O(OH)5Cl2

174

Rare-Earth Tri-Halide Methanol-Adduct Single-Crystal Scintillators for Gamma Ray and Neutron Detection - 8/17/09  

Energy Technology Data Exchange (ETDEWEB)

Cerium activated rare-earth tri- halides represent a well-known family of high performance inorganic rare-earth scintillators - including the high-light-yield, high-energy-resolution scintillator, cerium-doped lanthanum tribromide. These hygroscopic inorganic rare-earth halides are currently grown as single crystals from the melt - either by the Bridgman or Czochralski techniques slow and expensive processes that are frequently characterized by severe cracking of the material due to anisotropic thermal stresses and cleavage effects. We have recently discovered a new family of cerium-activated rare-earth metal organic scintillators consisting of tri-halide methanol adducts of cerium and lanthanum namely CeCl3(CH3OH)4 and LaBr3(CH3OH)4:Ce. These methanol-adduct scintillator materials can be grown near room temperature from a methanol solution, and their high solubility is consistent with the application of the rapid solution growth methods that are currently used to grow very large single crystals of potassium dihydrogen phosphate. The structures of these new rare-earth metal-organic scintillating compounds were determined by single crystal x-ray refinements, and their scintillation response to both gamma rays and neutrons, as presented here, was characterized using different excitation sources. Tri-halide methanol-adduct crystals activated with trivalent cerium apparently represent the initial example of a solution-grown rare-earth metal-organic molecular scintillator that is applicable to gamma ray, x-ray, and fast neutron detection.

Boatner, Lynn A [ORNL; Wisniewski, D. [Institute of Physics, Nicolaus Copernicus University, Toru?, Poland; Neal, John S [ORNL; Bell, Zane W [ORNL; Ramey, Joanne Oxendine [ORNL; Kolopus, James A [ORNL; Chakoumakos, Bryan C [ORNL; Custelcean, Radu [ORNL; Wisniewska, Monika [Environmental College, Bydgoszcz, Poland; Peña, K. E. [Oak Ridge National Laboratory (ORNL)

2009-01-01

175

Secondary processes in the environmental alteration of insulating crystals  

International Nuclear Information System (INIS)

The secondary defect formation processes in ionic crystals arising in response to different environmental perturbations, including irradiation are reviewed. Defect condensation is considered in the case of incorporation of excess alkali (halogen) in alkali halides, excess oxygen in alkaline earth oxides, as well as appearing porosity in transition metal oxides. Oxygen vacancy ordering in reduced molybdenum trioxide and complexing in wustite, Fesub(1-x)O, is described, as well as planar defect arrays. In conclusion, the loss of structural correlation is discussed

1981-05-23

176

Spectral-luminescence properties of the halide-cesium crystals with the impurity of the tetrahedral molecular anions  

International Nuclear Information System (INIS)

[en] Absorption, excitation (PLE) and emission (PL) spectra as well as infrared absorption spectra and Raman spectra of the tetrahedral molecular anions (MA) CrO42-. MoO42-, ReO4- in the halide-cesium crystals (CsHal) CsCl, CsBr, CsI have been studied in the temperature range of 4.2 K to 300 K. Impure MA in crystals CsHal is characterized by complicated structure of the infrared absorption and Raman spectra. The structure of the spectra is due to the splitting of the degenerate vibration ?2(E), ?3(F2), ?4(F2) of the impure MA as a result of the decreasing of their local symmetry from Td to C3v, C2v or Cs because of the formation of the complexes of the several types. Such molecular complexes are formed with anion or cation vacancies or with metal cations Me+(Na+, K+, Rb+, Tl+) and Me2+(Mg2+, Ca2+, Sr2+, Ba2+) which have been doped to the crystals for the charge compensation of the impure MA. Observed structure of the vibrational spectra has been identified by the calculation of the MA vibration, decreased the local symmetry in the formed complexes and by the computer optimisation of the theoretical and observed data of the vibrational frequency of MA in crystals. Luminescence of the crystals CsHal with the impure MA CrO42-, MoO4-, ReO4- can be observed only at low temperature. Impure complexes with different structure and symmetry which are formed by the same tetrahedral MA are characterized by different value of the electron-phonon interaction that may be seen in the structure of the absorption, PL and PLE spectra or in the character of the temperature dependence of the emission quantum yield. The parameters of spin orbit and spin lattice interactions in the impure complexes has been received. (author)

1989-01-01

177

Structural morphology of analbite: the influence of the substitution of K by Na on the crystal morphology of alkali feldspars  

Energy Technology Data Exchange (ETDEWEB)

The habit of the theoretical growth form of monoclinic high sanidine (KAlSi[sub 3]O[sub 8]) calculated from the attachment energies in an electrostatic point charge model is most similar to that of the alpine vein potassium feldspar called adularia. The effect on the crystal growth of alkali feldspar due to the substitution of K by Na has been investigated by the calculation of the attachment energies of analbite (NaAlSi[sub 3]O[sub 8]), which is triclinic with a disordered Si/Al distribution. The theoretical growth form of analbite consists of [l brace]110[r brace], [l brace]1anti 10[r brace], [l brace]001[r brace], [l brace]010[r brace] and, as additional minor forms, [l brace]021[r brace] and [l brace]0anti 21[r brace]. Hence other habits than the Adularia type cannot be explained by the crystal structure of disordered alkali feldspars. Either ordering of Si and Al during the growth or external factors, such as impurities or supersaturation, must be examined as possible habit modifiers. They must be responsible for the platy Finisterre, the elongated Baveno or the thick prismatic Carlsbad habit of many alkali feldspar crystals.

Woensdregt, C.F. (Inst. of Earth Sciences, Utrecht Univ. (Netherlands))

1992-01-01

178

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.

2007-01-01

179

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

CERN Multimedia

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

180

Oxidation of hydrogen halides to elemental halogens  

Energy Technology Data Exchange (ETDEWEB)

A process for oxidizing hydrogen halides having substantially no sulfur impurities by means of a catalytically active molten salt is disclosed. A mixture of the subject hydrogen halide and an oxygen bearing gas is contacted with a molten salt containing an oxidizing catalyst and alkali metal normal sulfates and pyrosulfates to produce an effluent gas stream rich in the elemental halogen and substantially free of sulfur oxide gases.

Rohrmann, Charles A. (Kennewick, WA); Fullam, Harold T. (Richland, WA)

1985-01-01

 
 
 
 
181

Metal--metal bonding in reduced scandium halides. Synthesis and crystal structure of scandium monochloride  

International Nuclear Information System (INIS)

The synthesis of a number of reduced scandium chlorides is achieved by reaction of excess metal with ScCl3 in sealed Ta tubing above 8770C for periods of weeks to months. Extreme conditions are necessary because of both the kinetic problems of forming extended metal--metal bonded structures and the fact that ScCl1.5 effectively blocks further reaction on metal surfaces below this temperature. Single-crystal x-ray diffraction data showed that a gray-black laminar phase was ScCl with a sheet structure consisting of close-packed homoatomic layers sequenced Cl--Sc--Sc--Cl along [001] (R3m, trigonal cell; a = 3.473 (2) A, c = 26.71 (4) A, Z = 6; R = 0.088, R/sub w/ = 0.101 for 79 independent reflections taken with Mo K? radiation). The phase is thus polytopic (ignoring the difference in metal atom) with ZrCl and isostructural with ZrBr even though there are only two-thirds as many electrons for bonding the double-metal sheets of scandium. The general occurrence of metal-metal bonding in clusters, ribbons, and sheets in transition metal groups 3--5 is considered

1977-01-01

182

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)

1965-06-04

183

Recognition of alkali metal halide contact ion pairs by uranyl-salophen receptors bearing aromatic sidearms. The role of cation-pi interactions.  

UK PubMed Central (United Kingdom)

Hard anions have long been known to bind strongly to the uranium of uranyl-salophen complexes. Upon functionalization of the salophen framework with one or two benzyloxy substituents, efficient ditopic receptors for alkali metal ions are obtained. The solid-state structures of complexes formed by the two-armed receptor 1 with CsF and with the chlorides of K+, Rb+, and Cs+ reported here reveal the existence of dimeric supramolecular assemblies in which two receptor units assemble into capsules fully enclosing (MX)2 ion quartets. In addition to the strong coordinative binding of the anion to the uranyl center and to electrostatic cation-anion interactions, stabilizing interactions arise from coordination of each cation to six oxygens, three from each receptor, and most importantly, to two aromatic sidearms belonging to different receptors. There are marked differences in organization at the supramolecular level in the CsCl complex of the one-armed receptor 3, in that four uranyl-salophen units instead of two are assembled in a capsule-like arrangement housing a (CsCl)2 ion quartet. However, both receptors achieve the common goal of having each metal cation in close contact with carbon atoms of two aromatic rings. 1H NMR data provide strong evidence that cation-pi(arene) interactions with the sidearms participate in binding also in solution.

Cametti M; Nissinen M; Dalla Cort A; Mandolini L; Rissanen K

2005-03-01

184

Recognition of alkali metal halide contact ion pairs by uranyl-salophen receptors bearing aromatic sidearms. The role of cation-pi interactions.  

Science.gov (United States)

Hard anions have long been known to bind strongly to the uranium of uranyl-salophen complexes. Upon functionalization of the salophen framework with one or two benzyloxy substituents, efficient ditopic receptors for alkali metal ions are obtained. The solid-state structures of complexes formed by the two-armed receptor 1 with CsF and with the chlorides of K+, Rb+, and Cs+ reported here reveal the existence of dimeric supramolecular assemblies in which two receptor units assemble into capsules fully enclosing (MX)2 ion quartets. In addition to the strong coordinative binding of the anion to the uranyl center and to electrostatic cation-anion interactions, stabilizing interactions arise from coordination of each cation to six oxygens, three from each receptor, and most importantly, to two aromatic sidearms belonging to different receptors. There are marked differences in organization at the supramolecular level in the CsCl complex of the one-armed receptor 3, in that four uranyl-salophen units instead of two are assembled in a capsule-like arrangement housing a (CsCl)2 ion quartet. However, both receptors achieve the common goal of having each metal cation in close contact with carbon atoms of two aromatic rings. 1H NMR data provide strong evidence that cation-pi(arene) interactions with the sidearms participate in binding also in solution. PMID:15771518

Cametti, Massimo; Nissinen, Maija; Dalla Cort, Antonella; Mandolini, Luigi; Rissanen, Kari

2005-03-23

185

Growth and properties of large single crystals of YBa2Cu3O7-?  

International Nuclear Information System (INIS)

[en] The use of a molten eutectic flux based on mixed alkali halides has allowed the authors to grow single crystals of YBCO with thicknesses of up to 4 mm and total volumes approaching 0.3 cm3. The crystals are found to be superconducting as grown but are improved by oxygen annealing. Both neutron scattering and optical microscopy confirm the single crystal nature

1989-01-01

186

Crystal growth and evaluation of scintillation properties of Eu and alkali-metal co-doped LiSrAlF6 single crystals for thermal neutron detector  

International Nuclear Information System (INIS)

In recent work, Na co-doping have found to improve the light output of Eu doped LiCaAlF6 (Eu:LiCAF) for thermal neutron scintillator. We grew Eu 2% and alkali metal 1% co-doped LiSAF crystals by Micro-Pulling down method to understand the effect of alkali metal co-doping on scintillation properties and mechanism compared with LiCAF. In photo- and ?-ray induced radio-luminescence spectra of the all grown crystals, the emissions from d-f transition of Eu2+ were observed. Without relation to excitation source, decay times of co-doped LiSAF were longer than Eu only doped one. The light yield of Na, K and Cs co-doped LiSAF under 252Cf neutron excitation were improved. Especially, K co-doped Eu:LiSAF reached 33200 ph/n, which outperformed Eu only doped one by approximately 20% (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2012-01-01

187

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.

188

Thermoluminescence of gamma irradiated barium doped KCl : KBr mixed crystals  

International Nuclear Information System (INIS)

The thermoluminescence (TL) of alkali halides under various parameter have been studied. The divalent impurity ions can strongly affect the mechanical properties of alkali halide crystals. Mixed crystals of ? irradiated barium doped KCl:KBr have been characterized by measuring the thermoluminescence. Two peaks are observed in the TL intensity with increasing composition of KBr in KCl, the TL intensity increases and attains a saturation value for a particular composition of KBr and KCl. It is due to the increase in the number of luminescence centres and concentration quenching with increasing composition of KCl and KBr, because the mixed crystals of critical composition contain higher number of vacancies which produces larger number of colour centres. (author)

2005-01-01

189

The fast light of CsI(Na) crystals  

CERN Document Server

The responds of different common alkali halide crystals to alpha-rays and gamma-rays are tested in our research. It is found that only CsI(Na) crystals have significantly different waveforms between alpha and gamma scintillations, while others have not this phenomena. It is suggested that the fast light of CsI(Na) crystals arises from the recombination of free electrons with self-trapped holes of the host crystal CsI. Self-absorption limits the emission of fast light of CsI(Tl) and NaI(Tl) crystals.

Sun, Xilei; Hu, Tao; Zhou, Li; Cao, Jun; Wang, Yifang; Zhan, Liang; Yu, Boxiang; Cai, Xiao; Fang, Jian; Xie, Yuguang; An, Zhenghua; Wang, Zhigang; Xue, Zhen; Zhang, Aiwu; Lu, Qiwen; Ning, Feipeng; Ge, Yongshuai; Liu, Yingbiao

2011-01-01

190

Growth of KCl1–xBrx Mixed Crystals with Different Composition Percent and Study of KBr Concentration Effect on Optical Characteristics of Mixed Crystals  

Directory of Open Access Journals (Sweden)

Full Text Available In the present research, mixed crystals KCl1–xBrx (x = 0.1, 0.3, 0.5, 0.7 & 0.9) were grown by Czochralski method. Then some analysis such as chemical etching, XRD, and absorbing spectrum were established on the irradiated crystals by ?-ray. The results of this research show that configuration of defects in mixed crystals in contrast with pure crystals is different. Somehow that type and percentage of cumulative composition cause to changing in lattice parameter and lattice defect density in alkali halide crystals and finally change optical properties of crystal.

Feridoun Samavat; Ebrahim Haji-Ali; Sajad Shahmaleki; Somayeh Solgi

2012-01-01

191

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 – 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

192

Physics of halide scintillators  

International Nuclear Information System (INIS)

[en] The paper reviews the results obtained within the last 5-6 years in the field of the physics of some halide crystals which have led to a better understanding of their characteristics. The luminescence and scintillation characteristics of caesium iodides, widely used in the existing detectors, as well as the properties of some other selected materials are discussed in view of their possible applications. For all the systems concerned, the emission important for their practical applications arises from the radiative decay of excitons of various types. The following features are considered in more detail: (1) the excited states structure, the mechanism of excitation of the localized exciton emission in the impurity-induced absorption bands, the processes of defects creation, and the scintillation mechanism in CsI:Tl and CsI:Na scintillators; (2) the luminescence of on-centre excitons in CsI and RbI crystals; (3) the luminescence of free cation excitons in the CsPbX3-type aggregates thermally created in CsX:Pb single crystals (X=Cl, Br); (4) the model of the excited states responsible for the cation exciton luminescence of lead halides

2001-01-01

193

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.)

1992-01-01

194

Dislocations in SmS single crystals  

International Nuclear Information System (INIS)

Single crystals of SmS with NaCl structure are grown by zone melting in a sealed molybdenum tube. Dislocations introduced during cleaving the crystal are investigated by transmission electron microscopy. The dislocations have Burgers vector of 1/2 and their glide plane is (11-bar0), i.e. the slip system is (11-bar0) as in alkali-halide NaCl-type crystals. The slip seems to be governed by the Peierls mechanism for the screw dislocation. (author)

1985-09-16

195

Quaternary system of cesium halides  

International Nuclear Information System (INIS)

[en] The state diagram of the quaternary system consisting of fluorides, chlorides, bromides, and iodides of cesium has been studied by visual-polythermal, partially X-ray phase and thermographical analyses. The crystallization volume of the quaternary system involves the crystallization volume of cesium fluoride and the crystallization volume of the ternary solid solutions of the rest cesium halides. A quaternary nonvariant point corresponding to melting point 360 deg C appears on the crystallization surface which separates the cesium fluoride volume from the volume of the ternary solid solutions

1977-01-01

196

Formation of tungsten monocarbide from a molten tungstate-halide phase by gas sparging  

Energy Technology Data Exchange (ETDEWEB)

Tungsten monocarbide is prepared by sparging a molten composition comprising an alkali metal halide and an oxygen compound of tungsten with a gas comprising a gaseous hydrocarbon, particularly methane.

Gomes, J.M.; Baglin, E.G.; Raddatz, A.E.

1984-12-18

197

Structural and electronic properties of luminescent copper(I) halide complexes of bis[2-(diphenylphosphano)phenyl] ether (DPEphos). Crystal structure of [CuCl(DPEphos)(dmpymtH].  

UK PubMed Central (United Kingdom)

Heteroleptic copper(I) halide complexes containing the bis[2-(diphenylphosphano)phenyl]ether (DPEphos) ligand and the heterocyclic thioamides pyridine-2(1H)-thione (py2SH), pyrimidine-2(1H)-thione (pymtH) or 4,6-dimethylpyrimidine-2(1H)-thione (dmpymtH) have been synthesized and characterized by (1)H-NMR, IR spectroscopy, elemental analyses and melting point determinations. The complexes can be readily obtained by the addition of the thione ligand to a CuX-diphosphane adduct in dichloromethane-ethanol solution. The molecular structure of [CuCl(DPEphos)(dmpymtH)] complex has been established by single-crystal X-ray diffraction. The structure features a tetrahedral copper(I) center with two phosphorus atoms from the chelating diphos ligand, one halogen atom and the exocyclic sulfur atom of the heterocyclic thioamide unit. The complexes are strongly emissive in the solid state at ambient temperature. DFT and TD-DFT calculations were employed to study the structural, electronic and photophysical properties of the novel complexes. Electronic absorption spectra show two broad bands in the regions 275-290 and 380-398 nm of mixed MLCT/IL character. Intense blue-green emission is observed in the region 500-558 nm for complexes having py2SH or dmpymtH thione ligands. The emitting first triplet excited state, T(1) is mainly localized on the thione ligand.

Aslanidis P; Cox PJ; Tsipis AC

2010-11-01

198

Structural and electronic properties of luminescent copper(I) halide complexes of bis[2-(diphenylphosphano)phenyl] ether (DPEphos). Crystal structure of [CuCl(DPEphos)(dmpymtH].  

Science.gov (United States)

Heteroleptic copper(I) halide complexes containing the bis[2-(diphenylphosphano)phenyl]ether (DPEphos) ligand and the heterocyclic thioamides pyridine-2(1H)-thione (py2SH), pyrimidine-2(1H)-thione (pymtH) or 4,6-dimethylpyrimidine-2(1H)-thione (dmpymtH) have been synthesized and characterized by (1)H-NMR, IR spectroscopy, elemental analyses and melting point determinations. The complexes can be readily obtained by the addition of the thione ligand to a CuX-diphosphane adduct in dichloromethane-ethanol solution. The molecular structure of [CuCl(DPEphos)(dmpymtH)] complex has been established by single-crystal X-ray diffraction. The structure features a tetrahedral copper(I) center with two phosphorus atoms from the chelating diphos ligand, one halogen atom and the exocyclic sulfur atom of the heterocyclic thioamide unit. The complexes are strongly emissive in the solid state at ambient temperature. DFT and TD-DFT calculations were employed to study the structural, electronic and photophysical properties of the novel complexes. Electronic absorption spectra show two broad bands in the regions 275-290 and 380-398 nm of mixed MLCT/IL character. Intense blue-green emission is observed in the region 500-558 nm for complexes having py2SH or dmpymtH thione ligands. The emitting first triplet excited state, T(1) is mainly localized on the thione ligand. PMID:20922239

Aslanidis, P; Cox, P J; Tsipis, A C

2010-10-04

199

Crystal Structures of Polymerized Fullerides AC60, A=K, Rb, Cs and Alkali-mediated Interactions  

CERN Multimedia

Starting from a model of rigid interacting C60 polymer chains on an orthorhombic lattice, we study the mutual orientation of the chains and the stability of the crystalline structures Pmnn and I2/m. We take into account i) van der Waals interactions and electric quadrupole interactions between C60 monomers on different chains as well as ii) interactions of the monomers with the surrounding alkali atoms. The direct interactions i) always lead to an antiferrorotational structure Pmnn with alternate orientation of the C60 chains in planes (001). The interactions ii) with the alkalis consist of two parts: translation-rotation (TR) coupling where the orientations of the chains interact with displacements of the alkalis, and quadrupolar electronic polarizability (ep) coupling, where the electric quadrupoles on the C60 monomers interact with induced quadrupoles due to excited electronic d states of the alkalis. Both interactions ii) lead to an effective orientation-orientation interaction between the C60 chains and ...

Verberck, B; Nikolaev, A V

2002-01-01

200

Total organic halide measurements  

Energy Technology Data Exchange (ETDEWEB)

Currently, the most popular method of analyzing total dissolved halide in water involves carbon adsorption, oxidative combustion, and measurement of the hydrogen halide by microcoulometry. Total dissolved organic halide can be used as an indicator of water quality, providing a direct measure of disinfection by-product formation and, in some circumstances, a surrogate measure of individual organic pollutants. An important application of organic halide measurements is in unit process design, control, and monitoring. Each potential application, however, must be carefully assessed to determine the usefulness of organic halide measurements.

Dressman, R.C.; Stevens, A.A.

1988-11-01

 
 
 
 
201

Application of radioisotopes to studies of crystal imperfections  

International Nuclear Information System (INIS)

Radioisotopes have been used in two important ways in studying imperfections in alkali halide crystals. The zone refining of the compounds has been monitored by addition of tracers, and segregation coefficients have been determined from such measurements. The other application has been to insert small concentrations of impurity ions into alkali halides in order to study the phonon scattering by such impurities or by the vacancies they introduce; these measurements are carried out at very low temperatures where the phonon mean free path is limited by lattice imperfections. The most commonly used radioisotope in this work has been Ca45. This work is reviewed and some current and possible future applications of radioisotopes in this field are mentioned. (author)

1962-01-01

202

Local fields in ionic crystals  

International Nuclear Information System (INIS)

Local fields arising from the electronic distortion in perfect ionic crystals are described in terms of multipolar excitations. Field factors for the alkali halides and chalcogenide ions are found to differ significantly from the Lorentz value of 4?/3, the correction size following an exponential dependence on the difference in ionic radii. Local fields are only slightly modified by these corrections however, and together with the Clausius-Mossotti relation may be regarded as accurate to within 2% if the Lorentz value is adopted. (author).

1981-01-01

203

Density and molar volume of molten mixtures of potassium rubidium and cesium with their halides  

International Nuclear Information System (INIS)

Density of KI-K, RbCl-Rb and CsCl-Cs melts countaining from 5 to 95 at% of alkali metal is measured by means of hydrostatic weighting. The molar volumes of metal-salt melts are calculated. The results obtained are compared to data for other alkali metal solutions in their molten halides.

1993-01-01

204

Structural Criteria for the Design of Anion Receptors: The Interaction of Halides with Electron-Deficient Arenes  

Energy Technology Data Exchange (ETDEWEB)

This paper refines the nature of the interactions between electron-deficient arenes and halide anions. Conclusions are based on (1) new crystal structures containing alkali halide salts with 1,2,4,5-tetracyanobenzene (TCB) and 18-crown-6, (2) evaluation of crystal structures found in the Cambridge Structural Database, and (3) MP2/aug-cc-pVDZ calculations of F?, Cl?, and Br? complexes with TCB, 1,3,5-tricyanobenzene, triazine, and hexafluorobenzene. When the halide lies above the plane of the ? system, the results establish that three distinctly different types of complexes are possible: strongly covalent ? complexes, weakly covalent donor ?-acceptor complexes, and electrostatic anion-? complexes. When aryl C?H groups are present, a fourth type of interaction leads to C?H???X? hydrogen bonding. Characterization of the different geometries encountered with the four possible binding motifs provides criteria needed to design host architectures containing electron-deficient arenes. This research was performed in part using the Molecular Science Computing Facility (MSCF) in the William R. Wiley Environmental Molecular Sciences laboratory, a national scientific user facility sponsored by the U.S. Department of Energy?s Office of Biological and Environmental Research located at the Pacific Northwest National Laboratory. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

Berryman, Orion B.; Bryantsev, Vyacheslav; Stay, David P.; Johnson, Darren W.; Hay, Benjamin P.

2007-01-10

205

????????????????? ???????? Effect of the Ratio of SiO2 and Al2O3 on the Viscosity and Crystallization of Non-Alkali Aluminoborosilicate Glasses at High Temperature  

Directory of Open Access Journals (Sweden)

Full Text Available ????????????????????????????????????????????????????????????????????????????????????????????????Effect of the ratio of SiO2 and Al2O3 on the viscosity and crystallization of non-alkali aluminoborosilicate glasses at high temperature was investigated. The results showed that the viscosity, the fiber-drawing temperature and the activation energy for vicious flow were increased, the liquidus temperature was decreased and the difference between the fiber-drawing temperature & the liquidus temperature was increased with the ratio of SiO2 and Al2O3 increased.

???; ???; ???; ??; ???

2013-01-01

206

Single electron states and energies of valence electrons in ionic crystals  

International Nuclear Information System (INIS)

The peculiarities of 4f-5d excitation spectra in rare earth monochalcogenides and their connection with the peculiarities of electrical properties of these materials, the origin of nepheloxetic effect in ionic compounds, the binding energies of valence electrons in alkali metal halides have been considered. It is shown, that the initial basis of neutral atom single electron functions is more convenient for the calculation of varions ionic crystal characteristics as compared to the basis of the corresponding ionic functions.

1985-01-01

207

Luminescent quantum efficiency of Eu{sup 2+} ions in mixed KCl{sub 1-x}Br{sub x} crystals  

Energy Technology Data Exchange (ETDEWEB)

In this work, the luminescent quantum efficiency of Eu{sup 2+} ions in mixed KCl{sub 1-x}Br{sub x} crystals is determined by using simultaneous and multiwavelength measurement of photoacoustic and luminescent signals after pulsed laser excitation. This method, which was first demonstrated in Eu{sup 2+} doped alkali halides (NaCl, KCl, KBr and KI) is now extended to mixed crystals. It is found that the quantum efficiency is reduced for mixed KCl{sub 1-x}Br{sub x} crystals from {phi}{approx}100%, in pure alkali halides (KCl and KBr), to a value {phi}{approx}60% for x{approx}0.6. (author)

Munoz, J.A.; Paolo, R. di; Tocho, J.O.; Cusso, F. [Departamento Fisica de Materiales, C-IV, Universidad Autonoma de Madrid, 28049 Madrid (Spain); Castaneda, B. [Departamento de Investigacion en Fisica, Universidad de Sonora, PO Box 1626, Hermosillo, Sonora 83000 (Mexico); Perez-Salas, R.; Aceves, R.; Barboza-Flores, M. [Centro de Investigacion en Fisica, Universidad de Sonora, PO Box 5-088, Hermosillo, Sonora 83190 (Mexico)

1998-05-11

208

Studies on the melts of alkali metal acetates.  

UK PubMed Central (United Kingdom)

The density, viscosity, and electrical conductivity of alkali metal acetates were measured over the temperature interval between melting and decomposition. The apparent activation energies of the equivalent conductivities and viscosities were calculated. It has been concluded from the results that alkali metal acetates, similarly to alkali metal benzenesulphonates studied earlier, exhibit properties quite unlike those of alkali metal halides. In the dependence of equivalent conductivity on the nature of the cation, the anomalous behaviour of lithium salts appears to be due to association prevailing in the melt phase.

Halmos Z; Meisel T; Seybold K; Erdey L

1970-12-01

209

Studies on the melts of alkali metal acetates.  

Science.gov (United States)

The density, viscosity, and electrical conductivity of alkali metal acetates were measured over the temperature interval between melting and decomposition. The apparent activation energies of the equivalent conductivities and viscosities were calculated. It has been concluded from the results that alkali metal acetates, similarly to alkali metal benzenesulphonates studied earlier, exhibit properties quite unlike those of alkali metal halides. In the dependence of equivalent conductivity on the nature of the cation, the anomalous behaviour of lithium salts appears to be due to association prevailing in the melt phase. PMID:18960850

Halmos, Z; Meisel, T; Seybold, K; Erdey, L

1970-12-01

210

Recombination luminescence and energy transfer in ionic crystals at XUV excitation by synchrotron radiation  

Energy Technology Data Exchange (ETDEWEB)

The relative quantum yield spectra of recombination luminescence for MgO, ..cap alpha..-Al/sub 2/O/sub 3/, SiO/sub 2/, and several alkali halide crystals are measured by synchrotron radiation in the photon energy interval 50 to 250 eV. The main feature of the spectra of oxides is a suppression of the volume luminescence due to surface losses of electrons and holes. For alkali halides surface as well as volume recombination luminescence take place. The more intensive the surface luminescence is the larger the absorption coefficient for exciting photons. The quantum yield spectra may be interpreted quantitatively on the basis of the hot carrier diffusion theory, the diffusion lengths being 2200 A for MgO, 1500 A for ..cap alpha..-Al/sub 2/O/sub 3/, and 300 A for SiO/sub 2/.

Elango, M.; Pruulmann, J.; Zhurakovskii, A.P. (AN Ehstonskoj SSR, Tartu. Inst. Fiziki)

1983-02-01

211

Recombination luminescence and energy transfer in ionic crystals at XUV excitation by synchrotron radiation  

International Nuclear Information System (INIS)

[en] The relative quantum yield spectra of recombination luminescence for MgO, ?-Al2O3, SiO2, and several alkali halide crystals are measured by synchrotron radiation in the photon energy interval 50 to 250 eV. The main feature of the spectra of oxides is a suppression of the volume luminescence due to surface losses of electrons and holes. For alkali halides surface as well as volume recombination luminescence take place. The more intensive the surface luminescence is the larger the absorption coefficient for exciting photons. The quantum yield spectra may be interpreted quantitatively on the basis of the hot carrier diffusion theory, the diffusion lengths being 2200 A for MgO, 1500 A for ?-Al2O3, and 300 A for SiO2. (author)

1983-02-01

212

On certain features of crystal structure and properties of alkali metal 6,8-dinitro- and 6,8,10-trinitro-1,4-dioxaspiro[4.5]deca-6,9-dienides  

International Nuclear Information System (INIS)

[en] Specific features of crystal structure of alkali metals (M = Li, Na, K, Rb, Cs) spirocyclic complexes in the title have been studied by the methods of microscopy and crystallography. Methods of thermal decomposition of the complexes in the air, depending on cation nature, have been ascertained. 6 refs.; 4 figs.; 4 tabs

1994-01-01

213

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

Energy Technology Data Exchange (ETDEWEB)

The most essential contribution in the investigation of CeF{sub 3} 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 {gamma}-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.

Gusev, Y.I.; Melchakov, E.N.; Mironov, I.A.; Panteleev, L.A.; Reiterov, V.M.; Rodnyi, P.A.; Seliverstov, D.M.; Shchetkowsky, A.I.; Yazikov, D.M.; Zakharov, N.G.

1994-12-31

214

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

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.  

UK PubMed Central (United Kingdom)

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.

Lal M; Dutt D; Tyagi CH

2012-04-01

216

Depolarizers for lithium halide batteries  

Energy Technology Data Exchange (ETDEWEB)

The present invention relates to a depolarizer for use in a lithium halide battery which comprises a halogen and a charge transfer complex consisting of the halogen and an organic component of (A) quaternary amine halide selected from the group consisting of (I) polyvinylalkylpyridinium halide or polyvinylalkylquinolinium halide and (II) poly (N,n'-dialkyl 1,2 bis (4-pyridinium halide)) ethylene or poly (N-alkyl 1,2 bis (4pyridinium halide) ethylene) and (B) phenyl methane dyes wherein said halogen is present in an amount of from about 3 to 50 parts by weight for each part of organic component.

Harney, M.J.

1981-06-30

217

Mass spectrometric study of ionic sublimation from a KI single crystal  

International Nuclear Information System (INIS)

Ionic sublimation from a KI single crystal was studied using the mass spectrometry method in the range of temperatures from 670 to 900 K. Emission of positive K+, K2+, K2I+, K3I2+ and negative I-, K2I- ions was recorded. Analysis of mass spectra and temperature dependences of ionic current of K+, K2+, K2I+ was conducted in the framework of surface discharge model for alkali metal halides. It was shown that the character of ionic sublimation of potassium iodide corresponds to a double electric layer in crystal-vacuum interface with positive excessive charge on the surface

2003-01-01

218

Detection of alkali metal ions in DNA crystals using state-of-the-art X-ray diffraction experiments  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The observation of light metal ions in nucleic acids crystals is generally a fortuitous event. Sodium ions in particular are notoriously difficult to detect because their X-ray scattering contributions are virtually identical to those of water and Na+…O distances are only slightly shorter than s...

Tereshko, Valentina; Wilds, Christopher J.; Minasov, George; Prakash, Thaza P.; Maier, Martin A.; Howard, Andrew

219

Process for oxidation of hydrogen halides to elemental halogens  

Energy Technology Data Exchange (ETDEWEB)

An improved process for generating an elemental halogen selected from chlorine, bromine or iodine, from a corresponding hydrogen halide by absorbing a molten salt mixture, which includes sulfur, alkali metals and oxygen with a sulfur to metal molar ratio between 0.9 and 1.1 and includes a dissolved oxygen compound capable of reacting with hydrogen halide to produce elemental halogen, into a porous, relatively inert substrate to produce a substrate-supported salt mixture. Thereafter, the substrate-supported salt mixture is contacted (stage 1) with a hydrogen halide while maintaining the substrate-supported salt mixture during the contacting at an elevated temperature sufficient to sustain a reaction between the oxygen compound and the hydrogen halide to produce a gaseous elemental halogen product. This is followed by purging the substrate-supported salt mixture with steam (stage 2) thereby recovering any unreacted hydrogen halide and additional elemental halogen for recycle to stage 1. The dissolved oxygen compound is regenerated in a high temperature (stage 3) and an optical intermediate temperature stage (stage 4) by contacting the substrate-supported salt mixture with a gas containing oxygen whereby the dissolved oxygen compound in the substrate-supported salt mixture is regenerated by being oxidized to a higher valence state.

Lyke, Stephen E. (Middleton, WI)

1992-01-01

220

Fractional crystallization of an alkali basalt magma: the Chaine des Puys volcanic series (French Massif Central). II. Geochemistry  

Energy Technology Data Exchange (ETDEWEB)

The behavior of hygromagmaphile elements (U, Th, Ta, La), and determination of mineral partition coefficients (feldspars, olivines, clinopyroxenes, amphibole, mica, titanomagnetite) are used for interpretation of trace elements analyses on samples of the Chaine des Puys (Massif Central, France). Existence and unicity of the series generated by a fractional crystallization process are proved. We follow qualitatively the mineralogical evolution and we determine quantitatively some of the essential physical parameters: temperature, f/sub O/sub 2//, degree of differentiation (f) for any sample, proportions of each mineralogical phase which crystallizes and chemical composition of initial melt. The properties of this primary melt prove a direct mantellic origin, without initial contamination, which takes place in a geodynamic area of distention tectonic. 15 figures, 10 tables.

Villemant, B.; Joron, J.L.; Jaffrezic, H.; Treuil, M.; Maury, R.; Brousse, R.

1980-01-01

 
 
 
 
221

The 2.0 angstroms crystal structure of a pocilloporin at pH 3.5: the structural basis for the linkage between color transition and halide binding.  

Science.gov (United States)

The pocilloporin Rtms5 and an engineered variant Rtms5H146S undergo distinct color transitions (from blue to red to yellow to colorless) in a pH-dependent manner. pK(a) values of 4.1 and 3.2 were determined for the blue (absorption lambda(max), 590 nm) to yellow (absorption lambda(max), approximately 453 nm) transitions of Rtms5 and Rtms5H146. The pK(a) for the blue-yellow transition of Rtms5H146S increased by 1.4 U in the presence of 0.1 M KI, whereas the pK(a) for the same transition of Rtms5 was relatively insensitive to added halides. To understand the structural basis for these observations, we have determined to 2.0 angstroms resolution the crystal structure of a yellow form of Rtms5H146S at pH 3.5 in the presence of iodide. Iodide was found occupying a pocket in the structure with a pH of 3.5, forming van der Waals contacts with the tyrosyl moiety of the chromophore. Elsewhere, it was determined that this pocket is occupied by a water molecule in the Rtms5H146S structure (pH 8.0) and by the side chain of histidine 146 in the wild-type Rtms5 structure. Collectively, our data provide an explanation for the observed linkage between color transitions for Rtms5H146S and binding to halides. PMID:16613486

Wilmann, Pascal G; Battad, Jion; Beddoe, Travis; Olsen, Seth; Smith, Sean C; Dove, Sophie; Devenish, Rodney J; Rossjohn, Jamie; Prescott, Mark

222

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

223

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

International Nuclear Information System (INIS)

[en] 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

224

Luminescent defects created in alkali iodides by plastic deformation at 4.2 K  

International Nuclear Information System (INIS)

[en] Several new types of luminescent defects have been found to appear in KI, RbI and CsI crystals deformed plastically at 4.2 K. The spectral characteristics of their luminescence have been studied at 4.2 K and compared with those reported earlier for the self-trapped excitons as well as for the localized excitons created in alkali halide crystals by plastic deformation at 295 K. The amount and the origin of the defects have been found to depend on the stress magnitude, deformation temperature and crystal plasticity. The emission bands observed have been ascribed to the excitons localized near various crystal structure defects and divided into three groups according to the crystal lattice relaxation. An analysis method has been proposed for the determination of the defect structure on the basis of the characteristics of the corresponding exciton luminescence, and the origin and the structure of the defects produced by the deformation at 4.2 K have been discussed. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

1999-01-04

225

Luminescent defects created in alkali iodides by plastic deformation at 4.2 K  

Energy Technology Data Exchange (ETDEWEB)

Several new types of luminescent defects have been found to appear in KI, RbI and CsI crystals deformed plastically at 4.2 K. The spectral characteristics of their luminescence have been studied at 4.2 K and compared with those reported earlier for the self-trapped excitons as well as for the localized excitons created in alkali halide crystals by plastic deformation at 295 K. The amount and the origin of the defects have been found to depend on the stress magnitude, deformation temperature and crystal plasticity. The emission bands observed have been ascribed to the excitons localized near various crystal structure defects and divided into three groups according to the crystal lattice relaxation. An analysis method has been proposed for the determination of the defect structure on the basis of the characteristics of the corresponding exciton luminescence, and the origin and the structure of the defects produced by the deformation at 4.2 K have been discussed. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

Babin, V.; Elango, A.; Kalder, K.; Maaroos, A.; Vasil' chenko, E.; Zazubovich, S. [Institute of Physics, University of Tartu, Riia 142, EE2400 Tartu (Estonia); Shunkeev, K. [Aktybinsk University, Aktybinsk (Kazakhstan)

1999-01-04

226

High Biomass Specific Methyl Halide Production Rates of Selected Coastal Marsh Plants and its Relationship to Halide Content  

Science.gov (United States)

Salt tolerant coastal marsh plants (halophytes) have previously been shown to be globally significant producers of methyl chloride (MeCl) and methyl bromide (MeBr). While halophytes are known for their high salt content, there are few reports of their halide content. Our studies have attempted to quantify biomass specific methyl halide (MeX) production from these plants and relate it to tissue halide levels. MeCl, MeBr and MeI production rates and tissue chloride, bromide and iodide concentrations from selected coastal marsh plants were measured for nearly a year. Certain halophyte species (i.e. Batis and Frankenia) have very high summer biomass specific production rates for MeX (e.g. Frankenia: 1 ug MeCl /gfwt/hr; 80 ng MeBr/gfwt/hr; 8 ng MeI/gfwt/hr). These rates of MeCl and MeBr production are much higher than those from other coastal marsh plants or seaweeds. Plant halide levels remain high throughout the year, while MeX production peaks at a high level in mid summer falling to low winter rates. This implies a linkage to plant growth. Higher levels of chloride and bromide were seen in the fleshy marsh plants such as Batis (saltwort, approximately 20 percent dry wt chloride, 0.4 percent dry wt bromide) and Salicornia (pickleweed) than in the others such as Frankenia (alkali heath) approx 7 percent dry wt chloride, 0.1 percent dry wt bromide) or Spartina (cordgrass). No such trend was seen for iodide, which ranged from 4 - 10 ppm. Calculations show the daily halide losses from MeX production are far less than the variability in tissue halide content. MeX production removes a small fraction of the total tissue halide from these plants suggesting that MeX production is not a mechanism used by these species to control internal halide levels. Saltwort cell-free extracts incubated with bromide or iodide in the presence of S-adenosyl-L-methionine (SAM) produced the corresponding MeX. MeBr production was inhibited by caffeic acid the substrate of lignin-specific O-methyl transferase. MeX production may be a result of non-specific methylation of halides by SAM utilizing methyl transferases used in other biosynthetic pathways.

Manley, S. L.; Wang, N.; Cicerone, R. J.

2002-12-01

227

Dynamics of early stage defect production in irradiated alkali halides  

International Nuclear Information System (INIS)

The growth of F, HD and V2m centres in X-irradiated KCl (0.01 mol% SrCl2) 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 HD centres, which decreases with increasing temperature of irradiation and partially recovers on re-irradiation at a lower temperature. The growth of F and V2m 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-?it) 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.)).

2050-01-00

228

ENDOR measurements of S- centres in alkali halides  

International Nuclear Information System (INIS)

The characteristic feature of the S- centres is the p-hole, which corresponds to the lack of one electron to the Ar configuration. Because of this simple structure these centres can be regarded as model systems for the study of defect electrons and for their theoretical treatment. The validity of calculations from first principles made for one-electron systems can be tested for defect-electron systems too. The distribution of the unpaired electron over several shells of neighbour ions was determined by ENDOR measurements in KCl. Experimental data are presented and compared with theoretical calculations. (orig.).

1976-08-30

229

Neutron scattering experiments of the ionic crystal deformed plastically with uniaxial compression under high temperature  

Energy Technology Data Exchange (ETDEWEB)

As an aim of huge growth of alkali halide (AH) single crystal, a mosaic structure of small size AH single crystal deformed plastically with uniaxial compression under high temperature was evaluated due to its neutron irradiation experiment. Using TAS-2 installed at JRR-3M guide hole of Japan Atomic Energy Research Institute, locking curve at a representative face factor of the specimen was measured to observe the mosaic structure accompanied with expansion of the crystal due to compression. As a result, though the specimen before compression could be supposed to be divided to some parts already, the locking curve under 10 sec. of compression time showed already some fracture to divisions to suppose finer degradation of the crystal, and division of the locking curve at 600 sec. of compression time could be observed onto its 220 face. And, every compressed specimens showed some changes of crystallization method from standard sample. (G.K.)

Tsuchiya, Yoshinori; Minakawa, Nobuaki; Aizawa, Kazuya; Ozawa, Kunio [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

1996-04-01

230

Morphology variation in growth process of InN pillar crystal films on Si (1 0 0) substrate by halide chemical vapor deposition under atmospheric pressure  

International Nuclear Information System (INIS)

The morphology variation in growth process of InN films on Si (1 0 0) substrate by means of AP-HCVD investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray pole-figure. These results imply that the InN pillar crystal is grown perpendicular to Si (1 0 0) substrate with increasing growth time.

2008-04-15

231

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)

2008-01-01

232

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

233

Sulfides, sulfohalides and halides  

International Nuclear Information System (INIS)

[en] Experimental material on hydrothermal synthesis of simple and complex chalcogenides Asub(x)Bsub(y) (A=Cd, In, Cu, Zn, Hg, Pb, As, Sb, Bi, Ag; B=S, Se, Te), chalcohalogenides Asub(x)Bsub(y)Csub(z) (A=Sb, Bi, Hg, Pb, Cu, Au; B=S, Se, Te; C=Cl, Br, I), halides ACsub(x) (A=Sb, Bi, Cu; C=Br, I), K(TR)Fsub(x) (TR - rare earths) has been generalized. Physicochemical conditions of synthesis in multicomponent systems are investigated, morphogenetic peculiarities and their characteristic properties are described

1984-01-01

234

Halide laser glasses  

International Nuclear Information System (INIS)

Energy storage and energy extraction are of prime importance for efficient laser action and are affected by the line strengths and linewidths of optical transitions, excited-state lifetimes, nonradiative decay processes, spectroscopic inhomogeneities, nonlinear refractive index, and damage threshold. These properties are all host dependent. To illustrate this, the spectroscopic properties of Nd3+ have been measured in numerous oxide, oxyhalide, and halide glasses. A table summarizes the reported ranges of stimulated emission cross sections, peak wavelengths, linewidths, and radiative lifetimes associated with the 4F/sub 3/2/ ? 4I/sub 11/2/ lasing transition.

1982-03-01

235

Halide laser glasses  

Energy Technology Data Exchange (ETDEWEB)

Energy storage and energy extraction are of prime importance for efficient laser action and are affected by the line strengths and linewidths of optical transitions, excited-state lifetimes, nonradiative decay processes, spectroscopic inhomogeneities, nonlinear refractive index, and damage threshold. These properties are all host dependent. To illustrate this, the spectroscopic properties of Nd/sup 3 +/ have been measured in numerous oxide, oxyhalide, and halide glasses. A table summarizes the reported ranges of stimulated emission cross sections, peak wavelengths, linewidths, and radiative lifetimes associated with the /sup 4/F/sub 3/2/ ..-->.. /sup 4/I/sub 11/2/ lasing transition.

Weber, M.J.

1982-01-14

236

Intrinsic luminescence of alkali silicate glasses  

Energy Technology Data Exchange (ETDEWEB)

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.

Arbuzov, V.I.; Grabovskis, V.Y.; Tolstoi, M.N.; Vitol, I.K.

1986-09-01

237

Intrinsic luminescence of alkali silicate glasses  

International Nuclear Information System (INIS)

[en] 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

1986-01-01

238

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

239

Photoionization in alkali lasers.  

UK PubMed Central (United Kingdom)

We have calculated photoionization rates in alkali lasers. The photoionization of alkali atoms in the gain medium of alkali lasers can significantly degrade the laser performance by reducing the neutral alkali density and with it the gain. For a ten atmosphere Rb laser and a Cs exciplex laser, the photoionization induced alkali atom loss rates are greater than 10(5) sec(-1). These high loss rates will quickly deplete the neutral alkali density, reducing gain, and may require fast, possibly, supersonic flow rates to sufficiently replenish the neutral medium for CW operation.

Knize RJ; Zhdanov BV; Shaffer MK

2011-04-01

240

Alkali metal nitrate purification  

Energy Technology Data Exchange (ETDEWEB)

A process is disclosed for removing contaminants from impure alkali metal nitrates containing them. The process comprises heating the impure alkali metal nitrates in solution form or molten form at a temperature and for a time sufficient to effect precipitation of solid impurities and separating the solid impurities from the resulting purified alkali metal nitrates. The resulting purified alkali metal nitrates in solution form may be heated to evaporate water therefrom to produce purified molten alkali metal nitrates suitable for use as a heat transfer medium. If desired, the purified molten form may be granulated and cooled to form discrete solid particles of purified alkali metal nitrates.

Fiorucci, Louis C. (Hamden, CT); Morgan, Michael J. (Guilford, CT)

1986-02-04

 
 
 
 
241

Solution enthalpy of alkali halogenides in D2O  

International Nuclear Information System (INIS)

[en] The enthalpy of solution of NaF, HCl, KI, RbBr, and CsCl in heavy water and the enthalpy of dilution of KCl and KI solutions in D2O were measured calorimetrically. The enthalpies of solution of 20 alkali halides in D2O in the low-concentration range up to infinite dilution were found by the method of differences in transfer enthalpies

1978-01-01

242

Formation of tungsten monocarbide from a molten tungstate-halide phase by gas sparging  

Energy Technology Data Exchange (ETDEWEB)

A process for preparation of tungsten monocarbide is described comprising: (a) providing a molten composition comprising an alkali metal halide and an oxygen compound of tungsten; (b) sparging the composition with a gas comprising a gaseous hydrocarbon which is selected from the group consisting of natural gas, methane, ethane, acetylene, propane, butane, mixtures thereof, and admixtures of these gases with H/sub 2/ or CO, at a temperature of about 900/sup 0/ to 1100/sup 0/C for a sufficient time for the tungsten compound to be substantially converted to tungsten carbide; and (c) decanting the molten halide from the tungsten carbide product.

Gomes, J.M.; Raddatz, A.E.; Baglin, E.G.

1988-02-23

243

On the reaction of tellurium with tungsten halides: synthesis and crystal structure of Te7WOCl5, a compound with a polymer tellurium cation  

International Nuclear Information System (INIS)

The reaction of tellurium with WOCl4 in the presence of a large excess of WCl6 in a sealed evacuated glass ampoule at 150degC yields beside the main product Te8(WCl6)2 a small amount of Te7WOCl5. The crystal structure determination (orthorhombic space group Pcca, lattice parameters at 173 K: a = 2596.5(9) pm, b = 810.0(3) pm, c = 775.7(2) pm) shows that Te7WOCl5 is built of one-dimensional band shaped polymeric tellurium cations, one-dimensional associated pyramidal WOCl4anions and of isolated Cl- anions. Te7WOCl5 can thus be formulated as [Te72+]n [WOCl4-]n (Cl-). The structure is closely related but not isotypic to the bromine containing analogue Te7WOBr5. The difference between the two structures lies in different directions of the polar [WOX4-]n chains (X = Cl, Br). The strongly elongated thermal ellipsoid of one tellurium atom is shown to be caused by thermal vibration by determining the crystal structure of Te7WOCl5 at three different temperatures (223, 173 and 123 K). All displacement parameters of all atoms can be extrapolated to zero for 0 K. (orig.).

1993-01-01

244

Milk-alkali syndrome  

Science.gov (United States)

Milk-alkali syndrome is an acquired condition in which there are high levels of calcium ( hypercalcemia ) and ... Milk-alkali syndrome is caused by drinking too much milk (which is high in calcium) and taking ...

245

Raman spectra of ionic liquids: A simulation study of LaCl3 and its mixtures with alkali chlorides  

Science.gov (United States)

Theoretical Raman spectra of the elpasolite-structured crystal Cs2NaLaCl6 and of molten mixtures of LaCl6 with NaCl and CsCl have been obtained from computer simulations in order to examine how the Raman spectra reflect the coordination structure around the La3+ ions. This system is a model for many other trivalent metal halides and for examining how the network structure of the pure melts is broken down by the addition of alkali halides with different structure-breaking powers. The results suggest a way of reconciling the conclusions of Raman studies about the structures of the melts with those of neutron and x-ray-diffraction studies, which have already been examined with the same simulation methods. The Raman spectra, both polarized and depolarized, are calculated from a model for the dependence of the polarizability of the system on the ionic coordinates which was inspired by electronic structure calculations of the polarizabilities of ions in a condensed phase environment. Some results on the lifetimes of the coordination complexes responsible for the appearance of the discrete Raman bands are discussed.

Glover, William J.; Madden, Paul A.

2004-10-01

246

Calculation of the band gap energy of ionic crystals  

Energy Technology Data Exchange (ETDEWEB)

The band gap of alkali halides, alkaline-earth oxides, Al{sub 2}O{sub 3} and SiO{sub 2} crystals has been calculated using the perturbed-ion model supplemented with some assumptions for the treatment of excited states. The gap is calculated in several ways: as a difference between one-electron energy eigenvalues and as a difference between the total energies of appropriate electronic states of the crystal, both at the HF level and with inclusion of Coulomb correlation effects. The results compare well with experimental band gap energies and with other theoretical calculations, suggesting that the picture of bonding and excitation given by the model can be useful in ionic materials. (Author)

Aguado, A.; Lopez, J.M.; Alonso, J.A. [Departamento de Fisica Teorica, Facultad de Ciencias, Universidad de Valladolid, 47011, Valladolid (Spain); Ayuela, A. [Institut fur Theoretische Physik, Technische Universitat Dresden, 01062 Dresden (Germany); Rivas S, J.F. [Instituto de Fisica, Universidad Autonoma de Puebla, 72750 Puebla (Mexico); Berrondo, M. [Brigham Young University, Provo, UT84602 (United States)

1998-12-31

247

Calculation of the Band Gap Energy of Ionic Crystals  

CERN Multimedia

The band gap of alkali halides, alkaline-earth oxides, Al2O3 and SiO2 crystals has been calculated using the Perturbed-Ion model supplemented with some assumptions for the treatment of excited states. The gap is calculated in several ways: as a difference between one-electron energy eigenvalues and as a difference between the total energies of appropriate electronic states of the crystal, both at the HF level and with inclusion of Coulomb correlation effects. The results compare well with experimental band gap energies and with other theoretical calculations, suggesting that the picture of bonding and excitation given by the model can be useful in ionic materials.

Aguado, A; López, J M; Rivas-Silva, J F; Berrondo, M; Alonso, J A

1998-01-01

248

Calculation of the band gap energy of ionic crystals  

International Nuclear Information System (INIS)

[en] The band gap of alkali halides, alkaline-earth oxides, Al2O3 and SiO2 crystals has been calculated using the perturbed-ion model supplemented with some assumptions for the treatment of excited states. The gap is calculated in several ways: as a difference between one-electron energy eigenvalues and as a difference between the total energies of appropriate electronic states of the crystal, both at the HF level and with inclusion of Coulomb correlation effects. The results compare well with experimental band gap energies and with other theoretical calculations, suggesting that the picture of bonding and excitation given by the model can be useful in ionic materials. (Author)

1998-01-01

249

Effect of uniaxial stress on luminescence of X- and VUV- irradiated NaCl and NaBr crystals  

Energy Technology Data Exchange (ETDEWEB)

The effect of uniaxial stress applied at 80 K along the <1 1 0> crystal axis on the self-trapped exciton (STE) and impurity-induced luminescence has been studied for NaCl and NaBr crystals under X-ray and VUV-light excitation. It has been shown that the intensities of both the {pi} and the {sigma} STE luminescence bands increased in X-rayed NaCl more than 10 times under the applied uniaxial stress, whereas only a small stress-induced increase of the intrinsic luminescence has been observed in NaBr crystal. TSL measurements have shown that the creation of fundamental radiation defects (F-H pairs) is strongly suppressed in stressed NaCl. It is concluded that the influence of the uniaxial stress is less pronounced in alkali halides with the on-centre final configuration of the STE (NaBr) whereas the stress-induced effects may be very large in alkali halides in which the relaxation of the electronic excitations occurs by means of the off-centre relaxation (NaCl, KI and RbI). In the latter case, a strong stress-induced effect is mainly connected with an increase in the energy barrier between the minima of two different STE configurations, a radiative off-centre one and the one forming the radiation defects (F-H pairs)

Elango, A. E-mail: svet@fi.tartu.ee; Sagimbaeva, Sh.; Sarmukhanov, E.; Savikhina, T.; Shunkeev, K

2001-10-01

250

Effect of uniaxial stress on luminescence of X- and VUV- irradiated NaCl and NaBr crystals  

International Nuclear Information System (INIS)

[en] The effect of uniaxial stress applied at 80 K along the crystal axis on the self-trapped exciton (STE) and impurity-induced luminescence has been studied for NaCl and NaBr crystals under X-ray and VUV-light excitation. It has been shown that the intensities of both the ? and the ? STE luminescence bands increased in X-rayed NaCl more than 10 times under the applied uniaxial stress, whereas only a small stress-induced increase of the intrinsic luminescence has been observed in NaBr crystal. TSL measurements have shown that the creation of fundamental radiation defects (F-H pairs) is strongly suppressed in stressed NaCl. It is concluded that the influence of the uniaxial stress is less pronounced in alkali halides with the on-centre final configuration of the STE (NaBr) whereas the stress-induced effects may be very large in alkali halides in which the relaxation of the electronic excitations occurs by means of the off-centre relaxation (NaCl, KI and RbI). In the latter case, a strong stress-induced effect is mainly connected with an increase in the energy barrier between the minima of two different STE configurations, a radiative off-centre one and the one forming the radiation defects (F-H pairs)

2001-01-01

251

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

252

Transformation of the luminescent centres in KCl-In crystals under synchrotron radiation  

CERN Multimedia

In view of the opportunity to use alkali-halide crystals with indium impurity for the registration of ionising radiation we have studied the influence of a method of impurity doping and mechanical treatment of a crystal on its sensitivity to X-ray. It is shown that the doping of a crystal with In sup 3 sup + reduces the sensitivity of medium. Optical and X-ray spectral experiments have allowed us to conclude that this phenomenon is caused by a change in the impurity centre structure. It is proved experimentally that mechanical crushing results in the transformation of the luminescent centres. This does not allow the effective conversion of the centres under synchrotron radiation.

Gyunsburg, K E; Kochubey, D I; Sedova, Y G

2000-01-01

253

Multiphased mixed crystals: Interconnection of the conductivity activation energy with bulk properties  

International Nuclear Information System (INIS)

Using the miscible alkali halides, viz. N?Br and KCl, multiphased binary and ternary mixed crystals have recently been grown. Such crystals are important because of their potential applications, for example, for the construction of laser optical windows. The temperature dependence of their conductivity and the corresponding activation energy E have also been recently reported for various compositions. Here, we show that, upon combining experimental data alone, an interesting correlation emerges, which indicates that the energy E varies linearly with B?, where B stands for the measured bulk modulus of the multiphased mixed crystals and ? denotes the mean volume per atom. This conforms with an early model that interconnects the Gibbs energy for the formation and migration of defects in solids with bulk properties.

2008-10-01

254

Multiphased mixed crystals: Interconnection of the conductivity activation energy with bulk properties  

Energy Technology Data Exchange (ETDEWEB)

Using the miscible alkali halides, viz. N{alpha}Br and KCl, multiphased binary and ternary mixed crystals have recently been grown. Such crystals are important because of their potential applications, for example, for the construction of laser optical windows. The temperature dependence of their conductivity and the corresponding activation energy E have also been recently reported for various compositions. Here, we show that, upon combining experimental data alone, an interesting correlation emerges, which indicates that the energy E varies linearly with B{omega}, where B stands for the measured bulk modulus of the multiphased mixed crystals and {omega} denotes the mean volume per atom. This conforms with an early model that interconnects the Gibbs energy for the formation and migration of defects in solids with bulk properties.

Katsika-Tsigourakou, Vassiliki [Department of Solid State Physics, Faculty of Physics, University of Athens, Panepistimiopolis, 15784 Zografos (Greece)], E-mail: vkatsik@phys.uoa.gr; Vassilikou-Dova, Aglaia [Department of Solid State Physics, Faculty of Physics, University of Athens, Panepistimiopolis, 15784 Zografos (Greece)

2008-10-01

255

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

Energy Technology Data Exchange (ETDEWEB)

Two new organic-inorganic compounds based on polyoxometalates, metal halide clusters and organic ligands: [BW{sub 12}O{sub 40}]{sub 2}[Cu{sub 2}(Phen){sub 4}Cl](H{sub 2}4, 4 Prime -bpy){sub 4}{center_dot}H{sub 3}O{center_dot}5H{sub 2}O (1) and [HPW{sub 12}O{sub 40}][Cd{sub 2}(Phen){sub 4}Cl{sub 2}](4, 4 Prime -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 [BW{sub 12}O{sub 40}]{sup 5-}, metal halide clusters [Cu{sub 2}(Phen){sub 4}Cl]{sup +}and 4, 4 Prime -bpy ligands, while compound 2 is constructed from [PW{sub 12}O{sub 40}]{sup 3-}, metal halide cluster [Cd{sub 2}(Phen){sub 4}Cl{sub 2}]{sup 2+} and 4, 4 Prime -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: Black-Right-Pointing-Pointer First examples of hybrids based on polyoxometalates, metal halide clusters and organic ligands. Black-Right-Pointing-Pointer Two different kinds of metal halide clusters. Black-Right-Pointing-Pointer Supramolecular structures based on polyoxometalates, metal halide clusters and organic ligands. Black-Right-Pointing-Pointer Hybridization of three different of building blocks.

Wang Lamei; Fan Yong; Wang Yan; Xiao Lina; Hu Yangyang; Peng Yu; Wang Tiegang; Gao Zhongmin; Zheng Dafang [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Department of Chemistry, Jilin University, Changchun 130023 (China); Cui Xiaobing, E-mail: cuixb@mail.jlu.edu.cn [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Department of Chemistry, Jilin University, Changchun 130023 (China); Xu Jiqing, E-mail: xjq@mail.jlu.edu.cn [College of Chemistry and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Department of Chemistry, Jilin University, Changchun 130023 (China)

2012-07-15

256

Remarkable effect of alkali metal on polymerization of cyclic esters catalyzed by samarium-alkali metal multinuclear alkoxide clusters.  

UK PubMed Central (United Kingdom)

The remarkable effect of alkali metal on catalytic reactivity of samarium-alkali metal multinuclear alkoxide clusters is systematically studied. Three samarium-alkali metal multinuclear alkoxide clusters are synthesized in high yield by the reaction of anhydrous SmCl(3) with different molar ratios of alkali metal alkoxide and MOH (M = Na or K) in tetrahydrofuran (THF). These clusters were fully characterized by elemental analysis, IR, (1)H NMR and single-crystal structural analysis. These clusters exhibited good catalytic activity for the ring-opening polymerization of ?-caprolactone (?-CL), L-lactide (L-LA) and trimethylene carbonate (TMC). It is interesting to note that the catalytic activity is much influenced by the alkali metals of the clusters. For the polymerization of these cyclic esters, the catalytic activities all increase with the increase of the molar ratio of alkali metal to samarium metal.

Sheng H; Shi J; Feng Y; Wang H; Jiao Y; Sheng H; Zhang Y; Shen Q

2012-08-01

257

Remarkable effect of alkali metal on polymerization of cyclic esters catalyzed by samarium-alkali metal multinuclear alkoxide clusters.  

Science.gov (United States)

The remarkable effect of alkali metal on catalytic reactivity of samarium-alkali metal multinuclear alkoxide clusters is systematically studied. Three samarium-alkali metal multinuclear alkoxide clusters are synthesized in high yield by the reaction of anhydrous SmCl(3) with different molar ratios of alkali metal alkoxide and MOH (M = Na or K) in tetrahydrofuran (THF). These clusters were fully characterized by elemental analysis, IR, (1)H NMR and single-crystal structural analysis. These clusters exhibited good catalytic activity for the ring-opening polymerization of ?-caprolactone (?-CL), L-lactide (L-LA) and trimethylene carbonate (TMC). It is interesting to note that the catalytic activity is much influenced by the alkali metals of the clusters. For the polymerization of these cyclic esters, the catalytic activities all increase with the increase of the molar ratio of alkali metal to samarium metal. PMID:22733088

Sheng, Hongting; Shi, Jianhua; Feng, Yan; Wang, Hui; Jiao, Yonghua; Sheng, Hanjing; Zhang, Yong; Shen, Qi

2012-06-25

258

Structural motifs in secondary ammonium halides : ring-stacking and ring-laddering in the organic solid state  

DEFF Research Database (Denmark)

The ring-stacking and ring-laddering concepts of structural inorganic chemistry may be applied to rationalize motifs observed for secondary ammonium halides R(2)NH(2)X (X = Cl, Br) in the organic solid state. General examination of the directional preferences of N(+)...X(-) contacts in 166 crystal structures confirms that the shortest contacts (3.0-3.2 and 3.2-3.4 A, X = Cl, Br) are N(+)-H...X(-) hydrogen bonds lying approximately along the directions of the N(+)-H bond vectors. The next shortest N(+)...X(-) contacts display two preferred directions of approach: i) contacts in the distance range 3.2-3.5 (X = Cl) and 3.2-3.9 A (X = Br) lie close to the H-N(+)-H plane, along the direction of the bisector of the H-N(+)-H angle; ii) contacts in the distance range 4.0-4.2 (X = Cl) and 4.0-4.4 A (X = Br) lie close to the H-N(+)-H plane, along the direction of an axis extending to the rear of one of the N(+)-H bonds. Both directions of approach lead frequently to association of R(2)NH(2) (+)X(-) ion pairs into laddered motifs. Stacking association is also observed, giving rise in one case to discrete cubanes and in several other cases to extended stacked-cube arrangements. In each case, the distribution of N(+)...X(-) contacts reflects a balance between the directional properties of the N(+)-H...X(-) hydrogen bonds and (primarily steric) interactions between the R groups of the organic moieties. The ladder and stack motifs of the organic ammonium halides are in many cases directly comparable to those in alkali metal amides, [R(2)NM](n), and information derived from the extensive organic sample provides insight into the motifs adopted by the inorganic complexes.

Bond, Andrew D

2004-01-01

259

New ET cation radical salts with lead halide anions  

Energy Technology Data Exchange (ETDEWEB)

We report here the synthesis of ET salts with lead halide anions of ET{sub 2}Pb{sub 3}Br{sub 8} (I), ET{sub 6}Pb{sub 3}Br{sub 9}.PhCl.(CH{sub 3}){sub 2}CO (II) and (ET)PbI{sub 3} (III) composition. Crystal structure, ESR and electrical properties of the compound II are described, in which [PbBr{sub 3}]{sub n} polyanionic chains are found. (orig.)

Zhilyaeva, E.I. [Inst. of Chemical Physics, Russian Academy of Sciences, Chernogolovka (Russian Federation); Lyubovskaya, R.N. [Inst. of Chemical Physics, Russian Academy of Sciences, Chernogolovka (Russian Federation); Gritsenko, V.V. [Inst. of Chemical Physics, Russian Academy of Sciences, Chernogolovka (Russian Federation); Dyachenko, O.A. [Inst. of Chemical Physics, Russian Academy of Sciences, Chernogolovka (Russian Federation); Yudanova, E.I. [Inst. of Chemical Physics, Russian Academy of Sciences, Chernogolovka (Russian Federation); Lyubovskii, R.B. [Inst. of Chemical Physics, Russian Academy of Sciences, Chernogolovka (Russian Federation)

1995-03-15

260

Exchange experiments of C60 and halides on a Au(1 1 1) surface  

Science.gov (United States)

The influence of halides (I?, Br?, Cl?) on the stability of C60 adlayers on Au(1 1 1) was studied by scanning tunneling microscopy (STM) in air at room temperature. The C60 layers on gold were immersed into alkali halides solutions of several concentrations for different time intervals. The results show that C60 can be removed from the gold surface by iodide when the halide concentration is high and time of immersion is long. A rotated hexagonal structure of iodide is formed on some surface areas although with distortion. Bromide and chloride do not remove C60 completely from the gold surface. Nevertheless, they are able to penetrate the C60 layer. The result is that bromide and chloride adsorb on top of the gold and C60 sits on the halide adlayer. This condition enables the growth of well organized domains of C60. It is possible to identify the formation of multilayers of the fullerene on some areas. Intramolecular resolution for C60 was attained in the STM images when the halides were present on the surface.

Pinheiro, Lucidalva dos Santos; Filho, Josué Mendes

2013-09-01

 
 
 
 
261

Structure and optical properties of high light output halide scintillators  

Science.gov (United States)

Structural and optical properties of several high light output halide scintillators and closely related materials are presented based on first-principles calculations. The optical properties are based on the Engel-Vosko generalized gradient approximation and the recently developed density functional of Tran and Blaha. The materials investigated are BaBr2 , BaIBr, BaCl2 , BaF2 , BaI2 , BiI3 , CaI2 , Cs2LiYCl6 , CsBa2Br5 , CsBa2I5 , K2LaBr5 , K2LaCl5 , K2LaI5 , LaBr3 , LaCl3 , SrBr2 , and YI3 . For comparison results are presented for the oxide CdWO4 . We find that the Tran Blaha functional gives greatly improved band gaps and optical properties in this class of materials. Furthermore, we find that unlike CdWO4 , most of these halides are highly isotropic from an optical point of view even though in many cases the crystal structures and other properties are not. This general result is rationalized in terms of halide chemistry. Implications for the development of ceramic halide scintillators are discussed.

Singh, David J.

2010-10-01

262

High duty factor rare gas halide laser  

Energy Technology Data Exchange (ETDEWEB)

This patent describes a high duty factor rare gas halide laser is described comprising: (a) a rare gas halide gas mixture composed of at least one rare gas and one halide compound; (b) a hollow discharge tube of dielectric material containing the laser gas mixture; (c) means for exciting the laser gas mixture by high frequency electrodeless discharge; and (d) means for producing rapid recombination throughout the discharge tube of the halide compound after disassociation, comprising inner wall surfaces of the hollow discharge tube that are chemically inert to atomic and molecular species derived from the halide compound.

Christensen, C.P. Jr.; Moutoulas, C.

1989-01-03

263

Anharmonic properties of rubidium halides  

International Nuclear Information System (INIS)

The anharmonic properties of rubidium halides are investigated using a three-body interaction (TBI) potential. This includes the prediction of second-, third- and fourth-order elastic constants, the pressure dependence of second- and third-order elastic constants. The agreement between experimental and theoretical results is, generally, good. The inclusion of anharmonic terms in the potential might lead to further improvements. (author).

1988-01-01

264

Metallic halides of the lanthanides  

International Nuclear Information System (INIS)

A short survey of the now known metallic halides of the lanthanides is given. These have the formula types MX2, M'MX3 and M2X5. Metallic behaviour arises from the 4fn-15d1 valence state of the lanthanide element (M). 16 refs.

1991-01-01

265

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.

2012-01-01

266

The nature of halogen...halide synthons: theoretical and crystallographic studies.  

Science.gov (United States)

Two types of halogen...halide synthons are investigated on the basis of theoretical and crystallographic studies; the simple halogen...halide synthons and the charge assisted halogen...halide synthons. The former interactions were investigated theoretically (ab initio) by studying the energy of interaction of a halide anion with a halocarbon species as a function of Y...X- separation distance and the C-Y...X- angle in a series of complexes (R-Y...X-, R=methyl, phenyl, acetyl or pyridyl; Y=F, Cl, Br, or I; X-=F-, Cl-, Br-, or I-). The theoretical study of the latter interaction type was investigated in only one system, the [(4BP)Cl]2 dimer, (4BP=4-bromopyrdinium cation). Crystal structure determinations, to complement the latter theoretical calculations, were performed on 13 n-chloropyridinium and n-bromopyridinium halide salts (n=2-4). The theoretical and crystallographic studies indicate that these interactions are controlled by electrostatics and are characterized by linear C-Y...X- angles and separation distances less than the sum of van der Waals radius (rvdW) of the halogen atom and the ionic radii of the halide anion. The strength of these contacts from calculations varies from weak or absent, e.g., H3C-Cl...I-, to very strong, e.g., HCC-I...F- (energy of interaction ca. -153 kJ/mol). The strengths of these contacts are influenced by four factors: (a) the type of the halide anion; (b) the type of the halogen atom; (c) the hybridization of the ipso carbon; (d) the nature of the functional groups. The calculations also show that charge assisted halogen...halide synthons have a comparable strength to simple halogen...halide synthons. The nature of these contacts is explained on the basis of an electrostatic model. PMID:17388325

Awwadi, Firas F; Willett, Roger D; Peterson, Kirk A; Twamley, Brendan

2007-03-08

267

PRODUCTION OF ALKALI BICARBONATE AND ALKALI HYDROXIDE FROM ALKALI CARBONATE IN AN ELECTROLYTIC CELL  

UK PubMed Central (United Kingdom)

Alkali bicarbonate is synthesized in an electrolytic cell (100) from alkali carbonate. The electrolytic cell (100) includes an alkali ion conductive membrane (110) positioned between an anolyte compartment (112) configured with an anode (116) and a catholyte compartment (114) configured with a cathode (118). The alkali conductive membrane (110) selectively transports alkali ions (120) and prevents the transport of anions produced in the catholyte compartment. An aqueous alkali carbonate solution is introduced into the anolyte compartment (112) and electrolyzed at the anode (116) to produce carbon dioxide and/or hydrogen ions which react with alkali carbonate to produce alkali bicarbonate. The alkali bicarbonate is recovered by filtration or other separation techniques. When the catholyte solution includes water, pure alkali hydroxide is produced. When the catholyte solution includes methanol, pure alkali methoxide is produced.

PENDLETON JUSTIN; JOSHI ASHOK; BHAVARAJU SAI

268

Palladium-catalyzed coupling of aryl halides with alkynes  

UK PubMed Central (United Kingdom)

A method is provided to couple an aryl halide to an alkyne comprising reacting a compound of the formula ArX, wherein Ar is a substituted or unsubstituted aryl group and X is I or Br, with a compound of the formula HC[identical to]C-R1 wherein R1 is a substituted or unsubstituted organic group, in the presence of an effective amount of a phosphine-free, oxime-free palladium catalyst (C1-C4)alkyl N+(-OAc) or an alkali metal carbonate, to yield a compound of the formula Ar-C[identical to]C-R1, wherein the reaction is carried out in the absence of an organic amine or copper(I).

URGAONKAR SAMEER; VERKADE JOHN G

269

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 (MX6)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

270

Fluorescence Properties of Colour Centres Produced by Ultrashort Laser Irradiation in LiF Crystals  

Energy Technology Data Exchange (ETDEWEB)

LiF is a nonhygroscopic alkali halide crystal which possesses good optical and physical properties, and can host different species of colour centres at room temperature. Colour centres in LiF present broad absorption and emission bands in the near UV, visible and near IR regions of the spectrum. In this paper we study spectroscopic properties of colour centres produced in LiF by ultrashort laser pulses. The absorption and emission properties of these materials were measured showing that during the irradiation F, F{sub 2}, F{sub 2}{sup +}, F{sub 3}{sup +} and F{sub 2}{sup -} colour centres were created in the crystals. A colour centres formation dose-like curve as a function of the ultrashort pulse energy was determined using fluorescence spectroscopy.

Samad, R E; Courrol, L C; Gomes, L; Ranieri, I M; Baldochi, S L; De Freitas, A Z; Vieira, N D Jr, E-mail: resamad@gmail.co

2010-11-01

271

A review on the photochemistry of OH- and H- defects in KCL crystals  

International Nuclear Information System (INIS)

A comprehensive investigation of the photodissociation of substitutional OH- defects in KCl over a wide range of temperature, was reviewed including the study of the primary and secondary reaction products of this photodissociation. It was found that at LNT, the stability of the U2 center(OH- primary photoproduct) against optical bleaching is considerably higher than at LHeT. The same effect was observed in OH- itself at RT. These low efficiency photodecomposition processes indicate efficient beck processes that apparently recombine the photoproducts regenerating the original centers. The used KCl host material stands as a representative for the large family of cubic alkali halide crystals, while the OH- ion represents other diatomic molecules of the type XH- (like SH-), with supposedly simmilar properties. The observed phenomena and processes in KCI:OH- may therefore be regarded as a model case for a large group of (crystal + defect)-systems.

1978-01-01

272

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

273

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

274

Alkali treatment of coal  

Energy Technology Data Exchange (ETDEWEB)

Alkali fusion was examined for 3 Japanese coals without any solvents (320-440C) and the alkali-treated coals were extracted with solvents (benzene, methanol and pyridine). Extract yields, especially the yield of pyridine extract, were greatly affected by the reaction temperature and time, and the best yield (about 85%) was achieved under mild conditions (320-350 C for 1h). The characteristics and the decomposition process of this procedure are discussed in comparison with other methods.

Asahara, T.; Kito, T.; Kato, Y.; Yamaye, M.; Yoshinaga, K.; Tsukita, N.

1983-09-01

275

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

CERN Document Server

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

276

Self-Correction of Lanthanum-Cerium Halide Gamma Spectra (pre-print)  

Energy Technology Data Exchange (ETDEWEB)

Lanthanum-cerium halide detectors generally exhibit superior energy resolutions for gamma radiation detection compared with conventional sodium iodide detectors. However, they are also subject to self-activities due to lanthanum-138 decay and contamination due to beta decay in the low-energy region and alpha decay in the high-energy region. The detector’s self-activity and crystal contamination jointly contribute a significant amount of uncertainties to the gamma spectral measurement and affect the precision of the nuclide identification process. This paper demonstrates a self-correction procedure for self-activity and contamination reduction from spectra collected by lanthanum-cerium halide detectors. It can be implemented as an automatic self-correction module for the future gamma radiation detector made of lanthanum-cerium halide crystals.

Ding Yuan, Paul Guss, and Sanjoy Mukhopadhyay

2009-04-01

277

Self-Correction of Lanthanum-Cerium Halide Gamma Spectra (pre-print)  

International Nuclear Information System (INIS)

[en] Lanthanum-cerium halide detectors generally exhibit superior energy resolutions for gamma radiation detection compared with conventional sodium iodide detectors. However, they are also subject to self-activities due to lanthanum-138 decay and contamination due to beta decay in the low-energy region and alpha decay in the high-energy region. The detector's self-activity and crystal contamination jointly contribute a significant amount of uncertainties to the gamma spectral measurement and affect the precision of the nuclide identification process. This paper demonstrates a self-correction procedure for self-activity and contamination reduction from spectra collected by lanthanum-cerium halide detectors. It can be implemented as an automatic self-correction module for the future gamma radiation detector made of lanthanum-cerium halide crystals.

2009-01-01

278

Alkali and Halogen Chemistry in Volcanic Gases on Io  

CERN Document Server

We use chemical equilibrium calculations to model the speciation of alkalis and halogens in volcanic gases emitted on Io. The calculations cover wide temperature (500-2000 K) and pressure (10^-6 to 10^+1 bars) ranges, which overlap the nominal conditions at Pele (T = 1760 K, P = 0.01 bars). About 230 compounds of 11 elements (O, S, Li, Na, K, Rb, Cs, F, Cl, Br, I) are considered. We predict the major alkali and halogen species in a Pele-like volcanic gas and the major alklai and halogen condensates. We also model disequilibrium chemistry of the alkalis and halogens in the volcanic plume. Based on this work and our prior modeling for Na, K, and Cl in a volcanic plume, we predict the major loss processes for the alkali halide gases are photolysis and/or condensation onto grains. On the basis of elemental abundances and photochemical lifetimes, we recommend searching for gaseous KCl, NaF, LiF, LiCl, RbF, RbCl, CsF, and CsCl around volcanic vents during eruptions. Based on abundance considerations and observation...

Schaefer, L

2004-01-01

279

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

280

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.)

1981-01-01

 
 
 
 
281

Chlor-Alkali Technology.  

Science.gov (United States)

Chlor-alkali technology is one of the largest electrochemical industries in the world, the main products being chlorine and caustic soda (sodium hydroxide) generated simultaneously by the electrolysis of sodium chloride. This technology is reviewed in terms of electrochemical principles and manufacturing processes involved. (Author/JN)

Venkatesh, S.; Tilak, B. V.

1983-01-01

282

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

CERN Multimedia

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 crystals (AHC), we confirmed the earlier proposed model of TL in AHCs. It is assumed that, in addition to the nonradiative H-F recombination, there exists the two-stage recombination of H-centers at anion vacancies resulting in the radiative recombination of a hole at an F-center. The energy of a quantum in the oscillatory rule corresponds to a local vibrational mode of an X2 halide molecule.

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

2010-01-01

283

Hydrothermal alkali metal recovery process  

Energy Technology Data Exchange (ETDEWEB)

In a coal gasification operation or similar conversion process carried out in the presence of an alkali metal-containing catalyst wherein solid particles containing alkali metal residues are produced, alkali metal constituents are recovered from the particles by treating them with a calcium or magnesium-containing compound in the presence of water at a temperature between about 250/sup 0/F and about 700/sup 0/F and in the presence of an added base to establish a pH during the treatment step that is higher than would otherwise be possible without the addition of the base. During the treating process the relatively high pH facilitates the conversion of water-insoluble alkali metal compounds in the alkali metal residues into water-soluble alkali metal constituents. The resultant aqueous solution containing watersoluble alkali metal constituents is then separated from the residue solids, which consist of the treated particles and any insoluble materials formed during the treatment step, and recycled to the gasification process where the alkali metal constituents serve as at least a portion of the alkali metal constituents which comprise the alkali metal-containing catalyst. Preferably, the base that is added during the treatment step is an alkali metal hydroxide obtained by water washing the residue solids produced during the treatment step.

Clavenna, L.R.; Eakman, J.M.; Kalina, T.; Wolfs, D.Y.

1980-08-26

284

Hydrothermal alkali metal recovery process  

Energy Technology Data Exchange (ETDEWEB)

In a coal gasification operation or similar conversion process carried out in the presence of an alkali metal-containing catalyst wherein solid particles containing alkali metal residues are produced, alkali metal constituents are recovered from the particles by treating them with a calcium or magnesium-containing compound in the presence of water at a temperature between about 250.degree. F. and about 700.degree. F. and in the presence of an added base to establish a pH during the treatment step that is higher than would otherwise be possible without the addition of the base. During the treating process the relatively high pH facilitates the conversion of water-insoluble alkali metal compounds in the alkali metal residues into water-soluble alkali metal constituents. The resultant aqueous solution containing water-soluble alkali metal constituents is then separated from the residue solids, which consist of the treated particles and any insoluble materials formed during the treatment step, and recycled to the gasification process where the alkali metal constituents serve as at least a portion of the alkali metal constituents which comprise the alkali metal-containing catalyst. Preferably, the base that is added during the treatment step is an alkali metal hydroxide obtained by water washing the residue solids produced during the treatment step.

Wolfs, Denise Y. (Houston, TX); Clavenna, Le Roy R. (Baytown, TX); Eakman, James M. (Houston, TX); Kalina, Theodore (Morris Plains, NJ)

1980-01-01

285

Halide glasses and their optical properties  

Energy Technology Data Exchange (ETDEWEB)

The different families of halide glasses are considered by reference to the glass-forming ability of divalent, trivalent and quadrivalent halides. The passive optical behavior, such as that in the IR transmission range, the low-loss potentially and scattering problems, is discussed as well as the active function of halide glasses considered as new matrices for rare-earth or transition-metal spectroscopy. Some other properties such as electrical or magnetic ones and those associated with purification, devitrification, chemical durability will be discussed. (orig.).

Lucas, J.; Adam, J.L. (Rennes-1 Univ., 35 (France). Lab. de Chimie Minerale)

1989-12-01

286

Mechanism and Selectivity in Nickel-Catalyzed Cross- Electrophile Coupling of Aryl Halides with Alkyl Halides.  

UK PubMed Central (United Kingdom)

The direct cross-coupling of two different electro- philes, such as an aryl halide with an alkyl halide, offers many ad- vantages over conventional cross-coupling methods that require a carbon nucleophile. Despite its promise as a versatile synthetic strategy, a limited understanding of the mechanism and origin of cross selectivity has hindered progress towards reaction develop- ment and design. Herein, we shed light on the mechanism for the nickel-catalyzed cross-electrophile coupling of aryl halides with alkyl halides and demonstrate that the selectivity arises from an unusual catalytic cycle that combines both polar and radical steps to form the new C-C bond.

Biswas S; Weix DJ

2013-08-01

287

Alkalis in alternative biofuels  

Energy Technology Data Exchange (ETDEWEB)

The alkali content and behavior of inorganic material of annually produced biofuels severely limits their use for generating electrical power in conventional furnaces. A recent eighteen-month investigation of the chemistry and firing characteristics of 26 different biofuels has been conducted. Firing conditions were simulated in the laboratory for eleven biofuels. This paper describes some results from the investigation including fuel properties, deposits, deposition mechanisms, and implications for biomass boiler design, fuel sampling and characterizations. Urban wood fuel, agricultural residues, energy crops, and other potential alternate fuels are included in the study. Conventional methods for establishing fuel alkali content and determining ash sticky temperatures were deceptive. The crux of the problem was found to be the high concentration of potassium in biofuels and its reactions with other fuel constituents which lower the ``sticky temperature`` of the ash to the 650 C to 760 C (1,200 F-1,400 F).

Miles, T.R. [Miles (T.R.), Portland, OR (United States); Miles, T.R. Jr. [Miles (T.R. Jr.), Portland, OR (United States); Bryers, R.W. [Foster Wheeler Dev. Corp., Livingston, NJ (United States); Baxter, L.L. [Sandia National Labs., Livermore, CA (United States). Combustion Research Facility; Jenkins, B.M. [Univ. of California, Davis, CA (United States). Biological and Agricultural Engineering; Oden, L.L. [Bureau of Mines, Albany, OR (United States). Dept. of the Interior

1994-12-31

288

Heidelberg polarized alkali source  

International Nuclear Information System (INIS)

A new atomic beam type polarized alkali ion source has been installed at Heidelberg. In order to improve the beam polarization considerably optical pumping is applied in combination with an adiabatic medium field transition which results in beams in single hyperfine sublevels. The m state population is determined by laser-induced fluorescence spectroscopy. Highly polarized beams (P/sub s/ > 0.9, s = z, zz) with intensities of 30 to 130 ?A can be extracted for Li+ and Na+, respectively.

1984-01-01

289

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.

1987-01-01

290

Reactions of diiminopyridine ligands with chalcogen halides.  

UK PubMed Central (United Kingdom)

The reactions of the chalcogen halides (Ch = S, Se, Te) with a series of diiminopyridine (DIMPY) ligands were explored. It was determined through these studies that varying both the substitution on the ?-carbon and the chalcogen halide reagent afforded different products. If methyl groups were present on the ?-carbon, reactivity was observed through the eneamine tautomer to yield N,N',C-bound neutral chalcogen complexes. In the cases where H and C(6)H(5) groups were in the same position, N,N',N?-chelated chalcogen cations or dications were produced. Many of the reactions resulted in complex mixtures postulated to occur by the release of halogen decomposing the product or, for reactions with the CH(3) substituted ligand, uncontrollable reactivity with the eneamine tautomer. This is the first report of reactions of sulfur and selenium halides with the ubiquitous diiminopyridine ligands and only the second example for a tellurium halide.

Martin CD; Ragogna PJ

2012-03-01

291

Interaction of boron halides with carbon preparations  

International Nuclear Information System (INIS)

Interaction of boron trichloride and tribromide with hydroxyfunctional groups of diamond and technical carbon surface under the pressure of halide vapours in the range 0.33-3.52 kPa and in the temperature range 32-200 deg C has been investigated. It is shown that interaction under the conditions takes place irreversibly. The rate of boron halide adsorption is described by kinetic equation for homogeneous surface. Activation energies of chemisorption and rate constants are found.

1987-01-01

292

Optically pumped divalent metal halide lasers  

Energy Technology Data Exchange (ETDEWEB)

A laser system, emitting energy in or near the visible region of the spectrum, is described comprising: (a) enclosure means; (b) a molecular divalent metal halide and an inert buffer gas, present within the enclosure means; (c) a heat source, for vaporization of the molecular divalent metal halide, capable of maintaining the enclosure means at a temperature within the range from about 50/sup 0/ to about 550/sup 0/C; (d) a source of dissociative energy, located in proximity to the enclosure means and in communication therewith, for effecting dissociation of the vaporized molecular divalent metal halide into diatomic metal halide fragments thereof present in a ground electronic energy state; (e) optical pumping means, located in proximity to the enclosure means and in communication therewith; whereby the diatomic metal halide fragments are raised from the ground electron energy state to one or more vibrational energy levels of a low-lying electronic excited state; and (f) an optical cavity, disposed about the enclosure means, aligned to obtain lasing from optical transition in which the diatomic metal halide fragments return to their ground electronic energy state.

Eden, J.G.; Greene, D.P.; Kileen, K.P.

1988-04-05

293

Electrochemically promoted carbon-halide bond cleavage in 4-nitrobenzyl halides  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This manuscript reports the study of the carbon-halide bond cleavage in 4-nitrobenzyl halides, taking special attention to the iodide and fluoride derivatives. The electrochemical reduction mechanism has been disclosed for both compounds by terms of cyclic voltammetry and controlled potential ele...

Cabán Huertas, Zahilia

294

The influence of Halide and pseudo-Halide antioxidants in Fenton-like reaction systems  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An application of the N,N’-(5-nitro-1,3-phenylene)bisglutaramide (NPG) hydroxylation assay for spectrophotometric determination of the rate of oxidising species generation in Fenton-like systems in the presence of halide and pseudo-halide antioxidants was evaluated. Using ion chromatography it was d...

Maleši?, J.; Kolar, J.; Strli?, M.; Polanc, S.

295

Calcium phosphate cements with strontium halides as radiopacifiers.  

UK PubMed Central (United Kingdom)

High radiopacity is required to monitor the delivery and positioning of injectable implants. Inorganic nonsoluble radiopacifiers are typically used in nondegradable bone cements; however, their usefulness in resorbable cements is limited due to their low solubility. Strontium halides, except strontium fluoride, are ionic water-soluble compounds that possess potential as radiopacifiers. In this study, we compare the radiopacity, mechanical properties, composition, and cytotoxicity of radiopaque brushite cements prepared with strontium fluoride (SrF2 ), strontium chloride (SrCl2 ·6H2 O), strontium bromide (SrBr2 ), or strontium iodide (SrI2 ). Brushite cements containing 10 wt % SrCl2 ·6H2 O, SrBr2 , or SrI2 exhibited equal to or higher radiopacity than commercial radiopaque cements. Furthermore, the brushite crystal lattice in cements that contained the ionic radiopacifiers was larger than in unmodified cements and in cements that contained SrF2 , indicating strontium substitution. Despite the fact that the strontium halides increased the solubility of the cements and affected their mechanical properties, calcium phosphate cements containing SrCl2 ·6H2 O, SrBr2 , and SrI2 showed no significant differences in Saos-2 cell viability and proliferation with respect to the control. Strontium halides: SrCl2 ·6H2 O, SrBr2 , and SrI2 may be potential candidates as radiopacifiers in resorbable biomaterials although their in vivo biocompatibility, when incorporated into injectable implants, is yet to be assessed. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2013.

López A; Montazerolghaem M; Engqvist H; Ott MK; Persson C

2013-08-01

296

Chlor-alkali electrolysis  

International Nuclear Information System (INIS)

[en] 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

297

Purification of alkali metal nitrates  

Energy Technology Data Exchange (ETDEWEB)

A process is disclosed for removing heavy metal contaminants from impure alkali metal nitrates containing them. The process comprises mixing the impure nitrates with sufficient water to form a concentrated aqueous solution of the impure nitrates, adjusting the pH of the resulting solution to within the range of between about 2 and about 7, adding sufficient reducing agent to react with heavy metal contaminants within said solution, adjusting the pH of the solution containing reducing agent to effect precipitation of heavy metal impurities and separating the solid impurities from the resulting purified aqueous solution of alkali metal nitrates. The resulting purified solution of alkali metal nitrates may be heated to evaporate water therefrom to produce purified molten alkali metal nitrate suitable for use as a heat transfer medium. If desired, the purified molten form may be granulated and cooled to form discrete solid particles of alkali metal nitrates.

Fiorucci, Louis C. (Hamden, CT); Gregory, Kevin M. (Woodridge, IL)

1985-05-14

298

Chemistry of gaseous lower-valent actinide halides  

Energy Technology Data Exchange (ETDEWEB)

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

Hildenbrand, D.L.

1983-05-24

299

Crystal Electrostatic Energy  

CERN Document Server

It has been shown that to calculate the parameters of the electrostatic field of the ion crystal lattice it sufficient to take into account ions located at a distance of 1-2 lattice spacings. More distant ions make insignificant contribution. As a result, the electrostatic energy of the ion lattice in the alkaline halide crystal produced by both positive and negative ions is in good agreement with experiment when the melting temperature and the shear modulus are calculated. For fcc and bcc metals the ion lattice electrostatic energy is not sufficient to obtain the observed values of these parameters. It is possible to resolve the contradiction if one assumes that the electron density is strongly localized and has a crystal structure described by the lattice delta - function. As a result, positive charges alternate with negative ones as in the alkaline halide crystal. Such delta-like localization of the electron density is known as a model of nearly free electrons.

Ivanchin, Alexander

2010-01-01

300

Structural phase transitions in alkali graphite intercalation compounds  

Energy Technology Data Exchange (ETDEWEB)

The structural properties of stage 2 and stage 3 alkali GlC's, prepared from single-crystal graphite, were extensively studied using x-ray scattering techniques. A unified picture for the ordering transitions and low-temperature in-plane structures is presented. The ordering transition is found to be similar in all cases. Alkali in-plane ordering always precedes the c-axis ordering and subsequent formation of an (hcp) structure. All low-temperature ordered in-plane structures belong to a discrete set of long-range commensurate domain structures. A unique in-plane polymorphic transition (T/sub c/ = 95K) in stage 2 potassium can be understood in terms of this model. Two new structural transitions are investigated. The first transition is a continuous inhibition of c-axis order at temperatures below 150K. This disordering transition was observed in stage 2 and stage 3 cesium and stage 2 rubidium samples. The second transition is an unusual polymorphic transformation from an hcp structure to an fcc structure (T/sub c/ approx. 160K) in stage 2 cesium. The question of alkali registry is resolved. At low temperatures, the variations in peak intensity result from ordered domains and displacements of alkali atoms away from carbon centers at the walls. At high temperatures, above the ordering transition, stage n greater than or equal to 2 alkali GlC's are found to be intermediate between a lattice liquid and a 2-D fluid.

Winokur, M.J.

1985-01-01

 
 
 
 
301

Method of producing halide-free metal and hydroxides  

Energy Technology Data Exchange (ETDEWEB)

A method for producing a halide-free oxide or hydroxide of a subject element from the corresponding subject element halide, is described comprising: in a first reaction step, providing a liquid medium comprising a water-free alcohol and contacting the alcoholic medium with the subject element halide and further contacting the alcohol and the subject element halide with a replacement species that reacts with halides, physically separating the medium containing the alkoxide from the precipitate salt, and in a second reaction step, hydrolyzing the subject element alkoxide with 18 mega ohm purity water to produce the corresponding subject element oxide or subject element hydroxide.

Melas, A.A.

1988-05-03

302

Crystal Structure and Magnetic Behavior of [(C(2)H(5))(4)N](2)Cu(5)Cl(12). A Novel Two-Dimensional Copper(II) Halide Network Derived from the CuCl(2) Structure.  

Science.gov (United States)

A new chlorocuprate(II), [(C(2)H(5))(4)N](2)Cu(5)Cl(12), was prepared by reaction of CuCl(2).2H(2)O and (C(2)H(5))(4)NCl in 1,1,2-trichloroethane-ethanol followed by water-ethanol evaporation. The crystal structure, solved by single-crystal X-ray diffraction at room temperature, was found to be triclinic, space group P&onemacr;, with cell parameters a = 8.9123(9) Å, b = 11.0690(8) Å, c = 11.2211(9) Å, alpha = 118.766(6) degrees beta = 109.041(8) degrees, gamma = 97.465(7) degrees, and Z = 1, and consists of a two-dimensional network of [(Cu(5)Cl(12))(2)(-)](infinity) parallel to the a, b plane, alternating with layers of the organic cations along c. The anionic sheets are built up by aggregation of infinite zigzag chains of alternating tetranuclear and mononuclear subsequences. This structure can be related to the anhydrous CuCl(2) structure by systematic removal of (Cu(2)Cl(6))(2+) fragments. The magnetic susceptibility of this compound can be described by a simple model, suggested by the structural data, that considers independent contributions of linear tetramers, with antiferromagnetically coupled pairs of copper atoms (J(1)/k = -64(2) K), and almost magnetically isolated Cu(II) centers, that obey a Curie-Weiss law with a &THETAV; = -2.7(8) K. PMID:11666180

Ayllón, José A.; Santos, Isabel C.; Henriques, Rui T.; Almeida, Manuel; Alcácer, Luís; Duarte, Maria T.

1996-01-01

303

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

304

Tetraethylene glycol adducts of alkaline earth halides  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Reaction of commercially available tetraethylene glycol with different alkaline earth metal halides affords tetraethylene glycol complexes with different coordination numbers at the metal ion and structural features; depending on the ionic radius of the metal ion, one or two ligand molecules will be...

Gschwind, Fabienne; Fromm, Katharina M.

305

Reactivity of halide and pseudohalide ligands  

International Nuclear Information System (INIS)

Reactivity of halide and pseudohalide (cyanide, azide, thiocyanate, cyanate) ligands tending to form bridge bonds in transition metal (Re, Mo, W) complexes is considered. Complexes where transition metal salts are ligands of other, complex-forming ion, are described. Transformation of innerspheric pseudohalide ligands is an important way of directed synthesis of these metal coordination compounds.

1987-01-01

306

Holographic interconnectors in silver halide sensitized gelatin  

Digital Repository Infrastructure Vision for European Research (DRIVER)

When making interconnection holographic systems, it is important to obtain high diffraction efficiency and low noise levels. Silver halide sensitized gelatins have been shown to be an excellent material to use in transmission holographic systems because these two objetives can be met. Using a copyin...

Fuentes Rosillo, Rosa; Pascual Villalobos, Inmaculada; Beléndez Vázquez, Augusto; Fimia Gil, Antonio; Egozcue Rubí, Juan José

307

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

CERN Multimedia

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

A Cluster-Bethe lattice treatment for the U2-center in alkali-halides  

International Nuclear Information System (INIS)

A Cluster-Bethe lattice calculation for the electronic density of states of a U2 center in the rock-salt structure is presented for a simple one-orbital Hamiltonian. The parameters involved in the Hamiltonian are given values based on qualitative arguments for Na, K, Rb chlorides and bromides and the proton contact term is calculated for these sets of parameters, in fair agreement with experimental data

1976-01-01

309

Long-lived submicrometric bubbles in very diluted alkali halide water solutions.  

UK PubMed Central (United Kingdom)

Solutions of LiCl and of NaCl in ultrapure water were studied through Rayleigh/Brillouin scattering as a function of the concentration (molarity, M) of dissolved salt from 0.2 M to extremely low concentration (2 × 10(-17) M). The Landau-Placzek ratio, R/B, of the Rayleigh scattering intensity over the total Brillouin was measured thanks to the dynamically controlled stability of the used Fabry-Perot interferometer. It was observed that the R/B ratio follows two stages as a function of increasing dilution rate: after a strong decrease between 0.2 M and 2 × 10(-5) M, it increases to reach a maximum between 10(-9) M and 10(-16) M. The first stage corresponds to the decrease of the Rayleigh scattering by the ion concentration fluctuations with the decrease of salt concentration. The second stage, at lower concentrations, is consistent with the increase of the Rayleigh scattering by long-lived sub-microscopic bubbles with the decrease of ion concentration. The origin of these sub-microscopic bubbles is the shaking of the solutions, which was carried out after each centesimal dilution. The very long lifetime of the sub-microscopic bubbles and the effects of aging originate in the electric charge of bubbles. The increase of R/B with the decrease of the low salt concentration corresponds to the increase of the sub-microscopic bubble size with the decrease of concentration, which is imposed by the bubble stability due to the covering of the surface bubble by negative ions.

Duval E; Adichtchev S; Sirotkin S; Mermet A

2012-03-01

310

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.

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

2011-01-01

311

Raman scattering and quantum confinement in heavily electron-irradiated alkali halides  

International Nuclear Information System (INIS)

In this paper we will study the properties of several unusual Raman scattering peaks in heavily irradiated NaCl with vast amounts of colloidal sodium and chlorine precipitates. It appears that the laser excitation light interacts with both the electronic and vibration systems of the Na colloids, which gives rise to new Raman scattering peaks, which can be associated with electronic and vibrational excitations confined in extremely thin (about 6 nm) quantum wires. (author)

2002-10-07

312

Preparation and use of electrodes in the electrolysis of alkali halides  

Energy Technology Data Exchange (ETDEWEB)

A process is described for electrolysis of aqueous solutions of sodium chloride in an electrolytic cell comprising an anolyte compartment and catholyte compartment separated by a diaphragm to produce an aqueous solution of sodium hydroxide in the catholyte compartment, and chlorine in the anolyte compartment. The cathode of the process is a low hydrogen overvoltage cathode made by applying to an electroconductive substrate a coating solution of nickel oxide and ruthenium oxide precursor compounds and an etchant capable of etching the surface of the substrate and/or any previously applied coating. Heating is done to remove volatiles from the so-coated substrate to cause the metal values of the precursor compounds and those etched from the substrate or previously applied coating. Further, heating is performed in the presence of oxygen, air or an oxidizing agent, to a temperature sufficient to oxidize the metal values, thereby obtaining on the substrate an electrocatalytically-active heaterogeneous metal oxide structure comprising RuO/sub 2/ and NiO.

Beaver, R.N.; Byrd, C.E.; Alexander, L.E.

1986-02-25

313

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

Energy Technology Data Exchange (ETDEWEB)

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.

Loubriel, G.M.; Green, T.A.; Tok, N.H.; Haglund R.F. Jr.

1987-09-01

314

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

315

Alkali metal cluster theory  

International Nuclear Information System (INIS)

[en] The tight-binding Hubbard model has been applied to alkali metal clusters with Hartree-Fock self-consistent methods and perturbation methods for the numerical calculations. The relaxation has been studied between the equilibrium structures and the range of the hopping matrix elements in the Hubbard Hamiltonian. The structures are not sensitive to the interaction range but are determined by the number of valence electrons each atom has. Inertia tensors are used to analyze the symmetries of the clusters. The principal axes of the clusters are determined to be the axes of rotational symmetries of clusters if the clusters have any. The eigenvalues of inertia tensors are compared between this model and the ellipsoidal jellium model. The agreement is good for large clusters. At a finite temperature, the thermal motion fluctuates the structures. A fluctuation function has been defined with the distance matrix of a cluster. The fluctuation has been studied with the Monte Carlo simulation method. Energy levels of clusters are calculated from the Hubbard model. Ionization potentials and magic numbers are also obtained from these energy levels. The results confirm that the Hubbard model is a good approximation for a small cluster. The excitation energy is presented by the difference between the original level and excited level, and the electron-hole interactions. The author also studied cooling of clusters between the nozzle and detector in molecular beam apparatus with three cooling mechanisms, adiabatic expansion, photon emission and cluster decay. The adiabatic expansion and the photon emission do not affect mass abundances of clusters. The studies show that cluster decay cooling produces a shift in the mass spectra. The shift is dependent on the temperature of the beam and increases as the temperature increases

1990-01-01

316

Alkali metal cluster theory  

Energy Technology Data Exchange (ETDEWEB)

The tight-binding Hubbard model has been applied to alkali metal clusters with Hartree-Fock self-consistent methods and perturbation methods for the numerical calculations. The relaxation has been studied between the equilibrium structures and the range of the hopping matrix elements in the Hubbard Hamiltonian. The structures are not sensitive to the interaction range but are determined by the number of valence electrons each atom has. Inertia tensors are used to analyze the symmetries of the clusters. The principal axes of the clusters are determined to be the axes of rotational symmetries of clusters if the clusters have any. The eigenvalues of inertia tensors are compared between this model and the ellipsoidal jellium model. The agreement is good for large clusters. At a finite temperature, the thermal motion fluctuates the structures. A fluctuation function has been defined with the distance matrix of a cluster. The fluctuation has been studied with the Monte Carlo simulation method. Energy levels of clusters are calculated from the Hubbard model. Ionization potentials and magic numbers are also obtained from these energy levels. The results confirm that the Hubbard model is a good approximation for a small cluster. The excitation energy is presented by the difference between the original level and excited level, and the electron-hole interactions. The author also studied cooling of clusters between the nozzle and detector in molecular beam apparatus with three cooling mechanisms, adiabatic expansion, photon emission and cluster decay. The adiabatic expansion and the photon emission do not affect mass abundances of clusters. The studies show that cluster decay cooling produces a shift in the mass spectra. The shift is dependent on the temperature of the beam and increases as the temperature increases.

Chen, J.

1990-01-01

317

Alkali metal and ammonium fluoro(trifluoroacetato)metallates M'[ M''3(?3-F)(CF3COO)6(CF3COOH)3], where M' = Li, Na, K, NH4, Rb, or Cs and M'' = Ni or Co. Synthesis and crystal structures  

Science.gov (United States)

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[Ni3(?3-F)(CF3COO)6(CF3COOH)3](CF3COOH)3 ( I), M'[Ni3(?3-F)(CF3COO)6(CF3COOH)3] ( M' = Na ( II), NH4 ( IV), Rb ( V), and Cs ( VI)), NH4[Co3(?3-F) (CF3COO)6(CF3COOH)3] ( III), and Cs[Ni3(?3-F)(CF3COO)6(CF3COOH)3](CF3COOH)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 3?(?3-F)(CF3COO)6(CF3COOH)3]- ( M? = 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?3 F] triangle. The oxygen atoms of the axial CF3COOH molecules complete the coordination environment of M? atoms to an octahedron.

Tereshchenko, D. S.; Morozov, I. V.; Boltalin, A. I.; Karpova, E. V.; Glazunova, T. Yu.; Troyanov, S. I.

2013-01-01

318

Tellurite glass as a waste form for mixed alkali–chloride waste streams: Candidate materials selection and initial testing  

International Nuclear Information System (INIS)

Highlights: ? We provide the first standardized chemical durability test on tellurite glasses. ? The glasses we studied showed a wide variety of chemical durability. ? The best-performing glass showed good halide retention following melting and durability testing. ? These glasses have very high densities resulting in high volumetric waste loading ability. - Abstract: Tellurite glasses have historically been shown to host large concentrations of halides. They are here considered for the first time as a waste form for immobilizing chloride wastes, such as may be generated in the proposed molten alkali salt electrochemical separations step in nuclear fuel reprocessing. Key properties of several tellurite glasses are determined to assess acceptability as a chloride waste form. TeO2 glasses with other oxides (PbO, Al2O3 + B2O3, WO3, P2O5, or ZnO) were fabricated with and without 10 mass% of a simulated (non-radioactive) mixed alkali, alkaline-earth, and rare earth chloride waste. Measured chemical durability is compared for the glasses, as determined by the product consistency test (PCT), a common standardized chemical durability test often used to validate borosilicate glass waste forms. The glass with the most promise as a waste form is the TeO2–PbO system, as it offers good halide retention, a low sodium release (by PCT) comparable with high-level waste silicate glass waste forms, and a high storage density.

2012-01-01

319

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. In this project we are searching for improved mixed materials with optimal desorption temperature and kinetics. We apply 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, 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, giving in total almost two million combinations.

Jensen, Peter Bjerre; Lysgaard, Steen

320

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

 
 
 
 
321

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

322

EVALUATION OF METHODS FOR THE DETERMINATION OF TOTAL ORGANIC HALIDE IN WATER AND WASTE  

Science.gov (United States)

Various methods for the determination of total organic halides (TOX) in groundwater and in waste oil samples have been evaluated. Of three inorganic halide species generation approaches and three inorganic halide determinative techniques evaluated for groundwater analyses, one co...

323

Synthesis of Cyclic Aza-Ether Compounds and Studies of Their Use as Anion Receptors in Non-Aqueous Lithium Halide Salt Solutions  

Energy Technology Data Exchange (ETDEWEB)

A series of new anion receptors, based on cyclic aza-ether compounds, have been synthesized. In all of these cyclic aza-ether compounds, the electron-withdrawing group CF{sub 3}SO{sub 2} was attached to each of the nitrogen atoms. When used as additives, all of them can significantly increase the ionic conductivity of lithium halide salts in THF solutions. This is due to the complexation between these compounds and halide anions. Ionic conductivity studies show that the complexation behavior is related to both the ring structure of the cyclic compounds and the characteristics of the halide anions. X-ray diffraction data show that the diffraction patterns of the complex crystals are different from the pure cyclic aza-ether compounds. New Bragg peaks representing a large d-spacing ({approx}15 {angstrom}) are observed for the complex crystals which provides a clear evidence for complexation.

Lee, H. S.; Sun, X.; Yang, X. Q.; McBreen, J.; Callahan, J. H.; Choi, L. S.

1999-11-01

324

Regenerable activated bauxite adsorbent alkali monitor probe.  

Science.gov (United States)

This invention relates to a regenerable activated bauxite adsorber alkali monitor probe for field applications to provide reliable measurement of alkali-vapor 5 concentration in combustion gas with special emphasis on pressurized fluidized-bed combustion ...

S. H. D. Lee

1991-01-01

325

Mechanical filter for alkali atoms  

CERN Multimedia

A device for separating gases of different mass is discussed. Such a device could be used in a laser-driven spin exchange source of polarized hydrogen atoms to reduce the contamination of alkali atoms. A Monte Carlo simulation has shown that the suggested apparatus based on a commercial turbo pump could reduce by a factor of 10-15 the concentration of the alkali-metal atoms in the hydrogen flow from a laser driven polarized source. This would greatly enhance the effective polarization in hydrogen targets.

Toporkov, D K

2000-01-01

326

Characterization of a novel alkali metal and transition metal plasma source  

International Nuclear Information System (INIS)

[en] 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

1989-01-01

327

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

328

On the temperature and pressure dependence of the defect formation volume in ionic crystals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The Schottky formation volume in alkali halides not only exceeds the molecular volume but also depends on temperature and pressure. The coefficient ? v for the thermal expansion of the defect-volume has been found in terms of the bulk expansivity ? and the temperature dependence of the pressure deri...

Varotsos, P.A.

329

The calcium-alkali syndrome.  

Science.gov (United States)

The milk-alkali syndrome was a common cause of hypercalcemia, metabolic alkalosis, and renal failure in the early 20th century. It was caused by the ingestion of large quantities of milk and absorbable alkali to treat peptic ulcer disease. The syndrome virtually vanished after introduction of histamine-2 blockers and proton pump inhibitors. More recently, a similar condition called the calcium-alkali syndrome has emerged as a common cause of hypercalcemia and alkalosis. It is usually caused by the ingestion of large amounts of calcium carbonate salts to prevent or treat osteoporosis and dyspepsia. We describe a 78-year-old woman who presented with weakness, malaise, and confusion. She was found to have hypercalcemia, acute renal failure, and metabolic alkalosis. Upon further questioning, she reported use of large amounts of calcium carbonate tablets to treat recent heartburn symptoms. Calcium supplements were discontinued, and she was treated with intravenous normal saline. After 5 days, the calcium and bicarbonate levels normalized and renal function returned to baseline. In this article, we review the pathogenesis of the calcium-alkali syndrome as well as the differences between the traditional and modern syndromes. PMID:23543983

Arroyo, Mariangeli; Fenves, Andrew Z; Emmett, Michael

2013-04-01

330

ICCG-10: The 10th International Conference on Crystal Growth  

Science.gov (United States)

The conference was held as scheduled. Papers presented at the conference included those on fundamentals of nucleation and growth, crystal growth mechanisms, convection and segregation, morphological stability, dendrites and pattern formation, nonlinear optic crystals, oxide crystal growth, II-VI materials, laser materials, miscellaneous chaleogenides, silicon/germanium, wide bandgap materials, halides, superconductors, refractory compounds, biomaterials, and gel growth.

Witt, August F.

1992-10-01

331

Synthesis of cyclic aza-ether compounds and studies of their use as anion receptors in nonaqueous lithium halide salts solution  

Energy Technology Data Exchange (ETDEWEB)

A series of new anion receptors, based on cyclic aza-ether compounds, have been synthesized. The synthesis and characterization of these compounds are described. In all these cyclic aza-ether compounds, the electron-withdrawing group CF{sub 3}SO{sub 2} was attached to each of the nitrogen atoms. Each member of this class of compounds contains a different number of nitrogen atoms. When used as additives, all of them can significantly increase the ionic conductivity of lithium halide salts in tetrahydrofuran solutions due to the ion-pair dissociation effect. This ion-pair dissociation effect is a results of complexation between these compounds and the halide anions. Ionic conductivity studies show that the complexation behavior is related to both the ring structure of the cyclic compounds and the characteristics of the halide anions. X-ray diffraction data show that the diffraction patterns of the complex crystals grown from cosolution of the cyclic aza-ether compound and lithium halide salts are completely different than those from the pure cyclic aza-ether compounds. New Bragg peaks representing a large d-spacing ({approximately}15 {angstrom}) are observed for the complex crystals. This is clear evidence of the complexation between the cyclic aza-ether compound and halide anions.

Lee, H.S.; Sun, X.; Yang, X.Q.; McBreen, J.; Callahan, J.H.; Choi, L.S.

2000-01-01

332

Lanthanum halide scintillators for time-of-flight 3-D pet  

Energy Technology Data Exchange (ETDEWEB)

A Lanthanum Halide scintillator (for example LaCl.sub.3 and LaBr.sub.3) with fast decay time and good timing resolution, as well as high light output and good energy resolution, is used in the design of a PET scanner. The PET scanner includes a cavity for accepting a patient and a plurality of PET detector modules arranged in an approximately cylindrical configuration about the cavity. Each PET detector includes a Lanthanum Halide scintillator having a plurality of Lanthanum Halide crystals, a light guide, and a plurality of photomultiplier tubes arranged respectively peripherally around the cavity. The good timing resolution enables a time-of-flight (TOF) PET scanner to be developed that exhibits a reduction in noise propagation during image reconstruction and a gain in the signal-to-noise ratio. Such a PET scanner includes a time stamp circuit that records the time of receipt of gamma rays by respective PET detectors and provides timing data outputs that are provided to a processor that, in turn, calculates time-of-flight (TOF) of gamma rays through a patient in the cavity and uses the TOF of gamma rays in the reconstruction of images of the patient.

Karp, Joel S. (Glenside, PA); Surti, Suleman (Philadelphia, PA)

2008-06-03

333

Growth and characterization of polycrystalline lanthanide halide scintillators  

Science.gov (United States)

We are exploring a novel time- and cost-efficient approach to produce robust, large-volume polycrystalline lanthanide halide scintillators using a hot wall evaporation (HWE) technique. To date, we have fabricated LaBr3:Ce and LaCl3:Ce films (slabs) measuring up to 7 cm in diameter and 7+ mm in thickness (20–25 cm3 in volume) on quartz substrates. These polycrystalline scintillators exhibit very bright emissions approaching those exhibited by their melt-grown crystal counterparts. Scanning electron micrographs (SEMs) and X-ray diffraction analysis confirm polycrystalline growth with columnar structures, both of which help in light piping, thereby contributing to the observed high light yields. The new scintillators also exhibit good energy resolution for ?-rays over the tested range of 60 keV (241Am) to 662 keV (137Cs), although they have not yet reached that of the corresponding crystals. The measured response linearity over the same energy range is comparable for both our HWE synthesized films and melt-grown commercially-available reference crystals. Similar consistency in response is also observed in terms of their decay time and afterglow behaviors. The data collected so far demonstrate that our HWE technique permits the rapid creation of scintillators with desired structural and compositional characteristics, without the introduction of appreciable defects, and yields material performance equivalent to or approaching that of crystals. Consequently, the deposition parameters may be manipulated to tailor the physical and scintillation performance of the resulting structures, while achieving a cost per unit volume that is substantially lower than that of crystals. In turn, this promises to allow the use of these novel scintillation materials in such applications as SPECT, PET, room-temperature radioisotope identification and homeland security, where large volumes of materials in a wide variety of shapes and sizes are needed. This paper describes our growth and testing of polycrystalline LaBr3:Ce scintillators and provides comparative characterizations of their performance with crystals.

Nagarkar, V. V.; Miller, S. R.; Gelfandbein, V.; Shirwadkar, U.; Gaysinskiy, V.

2011-10-01

334

Investigation of doped cuprous halides for photovoltaic and display applications  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The thesis mainly focuses on the growth and optoelectronic characterisation of the doped cuprous halides (CuX) with high UV/blue emission properties and the light harvesting in the CuBr/Si based heterojunction photovoltaic (PV) cells. Since cuprous halides are short wavelength emitters with high exc...

Vijayaraghavan, Rajani K.

335

Silver-halide sensitized holograms and their applications  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Silver-halide sensitized gelatin (SHSG) has the sensitometric and spectral response of silver halide emulsions and the holographic characteristics of dichromated gelatin, and therefore when properly processed it has little scattering and absorption. SHSG is one of the most promising techniques today...

Fimia Gil, Antonio; Pascual Villalobos, Inmaculada; Vázquez Ferri, Carmen; Beléndez Vázquez, Augusto

336

Regioselective Heck reaction of aliphatic olefins and aryl halides.  

UK PubMed Central (United Kingdom)

A regioselective Heck reaction of aliphatic olefins and aryl bromides is realized at internal carbons of olefins. Methanol solvent promoted halide ionization from neutral arylpalladium halide complexes via hydrogen bonding, so as to create cationic aryl-Pd species for regioselective olefin insertion.

Qin L; Hirao H; Zhou JS

2013-09-01

337

The coacervation of aqueous solutions of tetraalkylammonium halides  

International Nuclear Information System (INIS)

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 resulting from hydrophobic hydration has been assessed. The analogy between these systems and anionic ion exchange resins has been shown especially for Uranium VI extraction

1979-01-01

338

EXAFS measurement of molten cuprous halides  

International Nuclear Information System (INIS)

EXAFS measurement of molten CuCl and CuBr has been carried out near the melting temperatures in order to study the partial structure. EXAFS oscillation was clearly observed and the structural parameters for the nearest neighboring Cu-halogen pairs were obtained from standard curve fit analyses. The obtained Cu-halogen distance is, however, about 0.1A shorter than the distance obtained from neutron diffraction measurement with isotopic substitution. The result may suggest cluster formation such as a CuX trimer (X=Cl, Br) in molten cuprous halides. (author).

1993-01-01

339

Metal-rich gadolinium hydride halides  

International Nuclear Information System (INIS)

[en] Preparation, structures, and thermal behaviour of gadolinium hydride halides GdXH/sub n/ (X = Cl, Br, I; 0.7 2, and GdX3 in sealed Ta ampoules to 900 0C and 950 0C. The arrangement of the heavy atoms corresponds to the 3 slab (X-Gd-Gd-X) structures of ZrCl and ZrBr. Besides these, a new stacking variant containing only 2 slabs in the identity period (2s-GdBrH/sub 0.69/ and 2s-GdIH/sub 0.80/; nomenclature of niobium dichalcogenides) is found. (author)

1985-01-01

340

Violet laser emission in copper halides  

Science.gov (United States)

With two-photon excitation into the longitudinal exciton or into the excitonic continuum copper halides show laser emission at wavelengths of 413.3 nm (CuI), 422.5 nm (CuBr), and 391.9 nm (CuCl). The linewidth of the emission is very narrow in CuI and CuBr (below 0.004 nm) and much broader in CuCl (0.4 nm). The laser transition occurs between the bottleneck of the exciton polariton and the longitudinal optical phonon.

Reimann, K.; Ruebenacke, St.

1994-10-01

 
 
 
 
341

Energy levels and predissociation in mercuric halides  

International Nuclear Information System (INIS)

Electron energy-loss spectra were obtained over an extended energy-loss range (approximately 5 to 15 eV) for incident electron energies of 200 eV and scattering angles of 20 in the mercuric halides HgBr2 and HgCl2. Under these conditions of impact energy and scattering angle, the energy-loss spectra correspond closely to optical absorption spectra, though the energy-loss spectra extend to much higher energies than previous photoabsorption spectra, and reveal many more excited states of these molecules than had previously been observed. This preliminary report gives raw spectra and tentative identifications of the principal features of these spectra.

1981-01-01

342

Effect of uniaxial stress on luminescence of undoped and thallium-doped KI and RbI crystals  

Energy Technology Data Exchange (ETDEWEB)

The effect of uniaxial stress applied at various temperatures along the (100) crystal axis on the self-trapped exciton (STE) and impurity-induced luminescence has been studied for pure and Tl{sup +}, Na{sup +}-containing KI and RbI crystals under excitation in the exciton and band-to-band absorption region as well as under x-ray excitation. An increase of the intrinsic/extrinsic emission intensity ratios has been observed and explained by the stress-induced (i) enhancement of the self-trapping efficiency of electronic excitations and the decrease of their migration length and (ii) suppression of the nonradiative decay of excitons into stable radiation defects. A strong influence of the uniaxial stress on the structure of the STE adiabatic potential energy surface has been detected in RbI which is evident in the stress-induced increase of the E{sub x}/{pi} and, particularly, of the {sigma}/E{sub x} emission intensity ratios. This effect has been connected with the increase in the energy barriers between various STE configurations in the compressed crystal lattice. The dependence of the on-centre STE emission intensity in alkali halides on the distance between the nearest lattice anions and on their size has been discussed. (author)

Babin, V. [Institute of Physics, University of Tartu, Riia Street 142, 51014 Tartu (Estonia); Tartu University, Taehe Street 4, EE2400 Tartu (Estonia); Bekeshev, A.; Shunkeev, K. [Aktybinsk University, Aktybinsk (Kazakhstan); Elango, A.; Kalder, K.; Maaroos, A.; Vasil' chenko, E.; Zazubovich, S. [Institute of Physics, University of Tartu, Riia Street 142, 51014 Tartu (Estonia)

1999-03-15

343

Effect of uniaxial stress on luminescence of undoped and thallium-doped KI and RbI crystals  

International Nuclear Information System (INIS)

[en] The effect of uniaxial stress applied at various temperatures along the (100) crystal axis on the self-trapped exciton (STE) and impurity-induced luminescence has been studied for pure and Tl+, Na+-containing KI and RbI crystals under excitation in the exciton and band-to-band absorption region as well as under x-ray excitation. An increase of the intrinsic/extrinsic emission intensity ratios has been observed and explained by the stress-induced (i) enhancement of the self-trapping efficiency of electronic excitations and the decrease of their migration length and (ii) suppression of the nonradiative decay of excitons into stable radiation defects. A strong influence of the uniaxial stress on the structure of the STE adiabatic potential energy surface has been detected in RbI which is evident in the stress-induced increase of the Ex/? and, particularly, of the ?/Ex emission intensity ratios. This effect has been connected with the increase in the energy barriers between various STE configurations in the compressed crystal lattice. The dependence of the on-centre STE emission intensity in alkali halides on the distance between the nearest lattice anions and on their size has been discussed. (author)

1999-03-15

344

Medium low alkali biochemical catalyst  

UK PubMed Central (United Kingdom)

The invention relates to a medium and low alkali biochemical catalyst which is composed of inorganic alkaline, lipase, anthraquinone, osmotic agent and surface active agent, wherein, the mass percentage of all the components is as follows: inorganic alkaline 35 percent to 45 percent, lipase 10 percent to 15 percent, anthraquinone 15 percent to 20 percent, osmotic agent 10 percent to 15 percent and surface active agent 10 percent to 15 percent. The catalyst is applicable in the dipping and fiber processing of cornstock, cotton stalk, willow timber, reed, Anaphalis yedoensis, straw, pernyi and other plant fiber under normal temperature and normal pressure. The sources of the raw materials are wide and the scope of application is wide. The catalyst can improve the speed of delignify and the fiber yield, and reduce the residual alkali value.

XIANGFENG GONG

345

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

346

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

347

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

348

Isolation and molecular structures of novel organotellurium(IV) halides, oxyhalide and mixed halide.  

UK PubMed Central (United Kingdom)

The formation of chiral (R)-[2-(4-ethyl-2-oxazolinyl)phenyl]tellurium(IV) trihalides (trichloride (5), tribromide (6) and triiodide (7)) and (R)-[2-(4-ethyl-2-oxazolinyl)phenyl]tellurium(II) bromide (8) is described. The molecular structure of the first chiral organotellurium(IV) triiodide (7) is discussed. The most interesting feature of the structure of 5 is the observation of the shortest intramolecular TeN distance for any organotellurium(IV) trichloride. Compounds 5 and 6 do not undergo electrophilic addition reaction with olefins. Attempted addition reaction of 6 with olefin in methanol leads to the isolation of the rare partially hydrolysed tellurium(IV) halide, methyl-2-(dibromooxotellurium)benzoate (9). Novel stable mixed halide 12 was isolated from the bromination of 11. DFT calculations indicate that both the isomers 12a and 12b have similar stability.

Rakesh P; Singh HB; Butcher RJ

2012-09-01

349

Regenerable activated bauxite adsorbent alkali monitor probe  

Energy Technology Data Exchange (ETDEWEB)

A regenerable activated bauxite adsorber alkali monitor probe for field applications to provide reliable measurement of alkali-vapor concentration in combustion gas with special emphasis on pressurized fluidized-bed combustion (PFBC) off-gas. More particularly, the invention relates to the development of a easily regenerable bauxite adsorbent for use in a method to accurately determine the alkali-vapor content of PFBC exhaust gases.

Lee, Sheldon H. D. (Willowbrook, IL)

1992-01-01

350

Regenerable activated bauxite adsorbent alkali monitor probe  

Energy Technology Data Exchange (ETDEWEB)

A regenerable activated bauxite adsorber alkali monitor probe for field applications to provide reliable measurement of alkali-vapor concentration in combustion gas with special emphasis on pressurized fluidized-bed combustion (PFBC) off-gas. More particularly, the invention relates to the development of a easily regenerable bauxite adsorbent for use in a method to accurately determine the alkali-vapor content of PFBC exhaust gases. 6 figs.

Lee, S.H.D.

1992-12-22

351

Regenerable activated bauxite adsorbent alkali monitor probe  

Energy Technology Data Exchange (ETDEWEB)

This invention relates to a regenerable activated bauxite adsorber alkali monitor probe for field applications to provide reliable measurement of alkali-vapor 5 concentration in combustion gas with special emphasis on pressurized fluidized-bed combustion (PFBC) off-gas. More particularly, the invention relates to the development of a easily regenerable bauxite adsorbent for use in a method to accurately determine the alkali-vapor content of PFBC 10 exhaust gases.

Lee, S.H.D.

1991-01-22

352

Influence of alkali on the coke properties  

Energy Technology Data Exchange (ETDEWEB)

The influence of alkalis on coke properties was investigated by examination of the Kokura No. 2 blast furnace, Sumitomo Metal Industries, after water quenching. The rate of solution loss reaction was found to be dependent upon the content of adsorbed alkali in coke ash. Gasification of coke with alkalis degraded the coke properties and made gas permeability worse. The control of the gasification of coke by the solution loss reaction is an effective way to prevent the degradation of coke.

Hatano, M.; Miyazaki, T.; Iwanaga, Y.

1980-09-01

353

Palladium-catalyzed amination of aryl halides on solid support.  

UK PubMed Central (United Kingdom)

[reaction: see text] The first examples of the Pd(0)-catalyzed amination of aryl halides using Rink-resins as nitrogen source are described. Pd(2)dba(3)/BINAP/NaO-t-Bu was found to be the most efficient catalyst/base system, while a solvent mixture of dioxane and tert-butyl alcohol was shown to enhance the selectivity toward the desired monoarylation. Moderate to good yields and excellent purities of the amination products were found with electron-poor aryl halides, while electon-rich aryl halides failed to react under these conditions.

Weigand K; Pelka S

2002-12-01

354

Palladium-catalyzed amination of aryl halides on solid support.  

Science.gov (United States)

[reaction: see text] The first examples of the Pd(0)-catalyzed amination of aryl halides using Rink-resins as nitrogen source are described. Pd(2)dba(3)/BINAP/NaO-t-Bu was found to be the most efficient catalyst/base system, while a solvent mixture of dioxane and tert-butyl alcohol was shown to enhance the selectivity toward the desired monoarylation. Moderate to good yields and excellent purities of the amination products were found with electron-poor aryl halides, while electon-rich aryl halides failed to react under these conditions. PMID:12489962

Weigand, Klaus; Pelka, Sylvie

2002-12-26

355

Iridium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides  

Directory of Open Access Journals (Sweden)

Full Text Available Iridium-catalyzed intramolecular [4 + 2] cycloadditions of diene-tethered alkynyl halides were investigated by using [IrCl(cod)]2 as catalyst, and dppe was found to be the most suitable phosphine ligand for the reaction. No oxidative insertion of the iridium into the carbon–halide bond was observed, and the reactions proceeded to provide the halogenated cycloadducts in good yield (75–94%). These results are the first examples of cycloadditions of alkynyl halides using an iridium catalyst.

Andrew Tigchelaar; William Tam

2012-01-01

356

Study of the anharmonicity properties of copper halides  

International Nuclear Information System (INIS)

The anharmonic properties of copper halides have been investigated by means of a three-body interaction potential extended to include the van der Waals effects. For this purpose, the third-order elastic constants and the pressure derivatives of second-order elastic constants have been computed after deriving their correct expressions from the present potential following the lines of Sharma and Verma. Our results have, generally, followed a systematic trend and given a satisfactory prediction of the available experimental data on the anharmonic properties of copper halides. This potential has as scope of its application to describe the dynamical and dielectric properties of these halides.

1987-01-01

357

Straightforward synthesis of thiazoline-incorporated chalconoids from phenacyl halides.  

UK PubMed Central (United Kingdom)

A series of thiazoline-incorporated chalconoids, designed based on natural product scaffold, were efficiently synthesized via the reaction of 3-methyl-4-arylthiazole-2(3H)-thiones and appropriate phenacyl halides, and subsequent desulfurization. The starting 3-methyl-4- arylthiazole-2(3H)-thiones were also prepared from phenacyl halides. The structural aspects and (Z)-geometry of compounds were confirmed by IR and (1)H NMR spectral data. This chemistry provides a new library of compounds basically originated from phenacyl halides as building blocks, with potential activity for biomedical screening.

Ayati A; Emami S

2013-02-01

358

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; A.NARENDER REDDY; U.VENKATA TILAK; M.RAGHAVENDRA

2013-01-01

359

Colloquium: The unexpected properties of alkali metal iron selenide superconductors  

Science.gov (United States)

The iron-based superconductors that contain FeAs layers as the fundamental building block in the crystal structures have been rationalized in the past using ideas based on the Fermi surface nesting of hole and electron pockets when in the presence of weak Hubbard U interactions. This approach seemed appropriate considering the small values of the magnetic moments in the parent compounds and the clear evidence based on photoemission experiments of the required electron and hole pockets. However, recent results in the context of alkali metal iron selenides, with generic chemical composition AxFe2-ySe2 (A=alkali metal element), have challenged those previous ideas since at particular compositions y the low-temperature ground states are insulating and display antiferromagnetic order with large iron magnetic moments. Moreover, angle-resolved photoemission studies have revealed the absence of hole pockets at the Fermi level in these materials. The present status of this exciting area of research, with the potential to alter conceptually our understanding of the iron-based superconductors, is here reviewed, covering both experimental and theoretical investigations. Other recent related developments are also briefly reviewed, such as the study of selenide two-leg ladders and the discovery of superconductivity in a single layer of FeSe. The conceptual issues considered established for the alkali metal iron selenides, as well as several issues that still require further work, are discussed.

Dagotto, Elbio

2013-04-01

360

Topological insulator phase in halide perovskite structures  

Science.gov (United States)

Topological insulators are a novel quantum state of matter that reveals their properties and shows exotic phenomena when combined with other phases. Hence, priority has been given to making a good quality topological insulator interface with other compounds. From the applications point of view, the topological insulator phase in perovskite structures could be important to provide the various heterostructure interfaces with multifunctional properties. Here, by performing a tight-binding analysis and first-principles calculations, we predict that cubic-based CsPbI3 and CsSnI3 perovskite compounds under reasonable hydrostatic pressure are feasible candidates for three-dimensional topological insulators. Combined with cubic symmetry, the spin and total angular momentum doublets forming the valence and conduction bands result in a prototype of a continuum model, representing three-dimensional isotropic Dirac fermions, and govern the topological phase transition in halide perovskite materials.

Jin, Hosub; Im, Jino; Freeman, Arthur J.

2012-09-01

 
 
 
 
361

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

362

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.

Pti?ek Siro?i?, A.; Kratofil Krehula, LJ; Katan?i?, Z.; Reš?ek, A.; Hrnjak Murgi?, Z.; Jelen?i?, J.

2011-01-01

363

Interactions of alkali cations with glutamate transporters  

Science.gov (United States)

The transport of glutamate is coupled to the co-transport of three Na+ ions and the countertransport of one K+ ion. In addition to this carrier-type exchange behaviour, glutamate transporters also behave as chloride channels. The chloride channel activity is strongly influenced by the cations that are involved in coupled flux, making glutamate transporters representative of the ambiguous interface between carriers and channels. In this paper, we review the interaction of alkali cations with glutamate transporters in terms of these diverse functions. We also present a model derived from electrostatic mapping of the predicted cation-binding sites in the X-ray crystal structure of the Pyrococcus horikoshii transporter GltPh and in its human glutamate transporter homologue EAAT3. Two predicted Na+-binding sites were found to overlap precisely with the Tl+ densities observed in the aspartate-bound complex. A novel third site predicted to favourably bind Na+ (but not Tl+) is formed by interaction with the substrate and the occluding HP2 loop. A fourth predicted site in the apo state exhibits selectivity for K+ over both Na+ and Tl+. Notably, this K+ site partially overlaps the glutamate-binding site, and their binding is mutually exclusive. These results are consistent with kinetic and structural data and suggest a plausible mechanism for the flux coupling of glutamate with Na+ and K+ ions.

Holley, David C.; Kavanaugh, Michael P.

2008-01-01

364

Self-trapped excitons in pure and Na- and Tl-doped caesium halides and the recombination luminescence  

International Nuclear Information System (INIS)

[en] On the basis of a method used earlier to predict the off-centre relaxed triplet self-trapped excitons in alkali halides, similar systems in caesium halides are studied. This work confirms the expected off-centre relaxation along the [100] cubic axes with increasing magnitude in the order CsI, CsBr and CsCl. The calculated emission energies are in reasonable agreement with observed values. The well-known 2.95 eV emission band of CsI:Na has been studied as a tunnelling recombination between a close pair consisting of a VK centre and a Na atom. For a number of close-pair geometries the emission energies are close to 3 eV. The strong emission bands of CsI:Tl at 2.25 eV and 2.55 eV have been interpreted as arising from tunnelling recombination of close pairs each consisting of a Tl0 and a VK centre. The calculated emission energies and polarizations are discussed in conjunction with the experimental data. (author)

1999-07-19

365

Halide and proton binding kinetics of yellow fluorescent protein variants.  

UK PubMed Central (United Kingdom)

A T203Y substitution in green fluorescent protein causes a red shift in emission to yield a class of mutants known as yellow fluorescent protein (YFP). Many of these YFP mutants bind halides with affinities in the millimolar range, which often results in the chromophore pK values being shifted into the physiological range. While such sensitivities may be exploited for halide and pH sensors, it is desirable to reduce such environmental sensitivities in other studies, such as in Förster resonance energy transfer probes to measure conformational changes within fusion proteins. Venus and Citrine are two such variants that have been developed with much reduced halide sensitivities. Here we compare the kinetics of halide binding, and the coupled protonation reaction, for several YFP variants and detect slow kinetics (dissociation rate constants in the range of 0.1-1 s(-1)), indicative of binding to an internal site, in all cases. The effective halide affinity for Venus and Citrine is much reduced compared with that of the original YFP 10C construct, primarily through a reduced association rate constant. Nuclear magnetic resonance studies of YFP 10C confirm halide binding occurs on a slow time scale (<4 s(-1)) and that perturbations in the chemical shift occur throughout the sequence and structure.

Seward HE; Basran J; Denton R; Pfuhl M; Muskett FW; Bagshaw CR

2013-04-01

366

Pfa and the alkali-silica reaction  

Energy Technology Data Exchange (ETDEWEB)

To prevent alkali-silica reaction in concretes made with Portland cement, pulverized fuel ash (pfa) can be added. The pfa acts as a source of synthetic pozzolana. A test programme is described that was designed to study the effectiveness of pfa to reduce the expansion of high-alkali Portland cements.

Buttler, F.G.; Newman, J.B.; Owens, P.

1980-11-01

367

Microscopic Surface Structure of Liquid Alkali Metals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report an x-ray scattering study of the microscopic structure of the surface of a liquid alkali metal. The bulk liquid structure factor of the eutectic K67Na33 alloy is characteristic of an ideal mixture, and so shares the properties of an elemental liquid alkali metal. Analysis of off-specular d...

Tostmann, E.; DiMasi, E.; Pershan, Peter S.; Ocko, B. M.; Shpyrko, O. G.; Deutsch, M.

368

Beam-exposure dependence and mechanisms of photon-stimulated desorption from alkali fluorides  

International Nuclear Information System (INIS)

Photon-stimulated desorption experiments were performed on the (001) face of LiF for photon energies near the F(2s) and Li(1s) edges (from 37 to 72 eV). There are structures in the F+ yield above the F(2s) edge which are absent in the Li+ spectrum, differences in detail in the Li+ and F+ 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.

1984-01-01

369

Cluster harvesting by successive reduction of a metal halide with a nonconventional reduction agent: a benefit for the exploration of metal-rich halide systems.  

UK PubMed Central (United Kingdom)

The preparation of thermally labile compounds is a great temptation in chemistry which requires a careful selection of reaction media and reaction conditions. With a new scanning technique denoted here as Cluster Harvesting, a whole series of metal halide compounds is detected by differential thermal analysis (DTA) in fused silica tubes and structurally characterized by X-ray powder diffraction. Experiments of the reduction of tungsten hexahalides with elemental antimony and iron are presented. A cascade of six compounds is identified during the reduction with antimony, and five compounds or phases are monitored following the reduction with iron. The crystal structure of Fe2W2Cl10 is reported, and two other phases in the Fe-W-Cl system are discussed.

Ströbele M; Mos A; Meyer HJ

2013-06-01

370

The 10th International Conference on Crystal Growth (ICCG-10)  

Science.gov (United States)

Poster topics include: fundamentals of nucleation and growth; crystal growth mechanisms; convection and segregation; morphological stability; dendrites and pattern formation; non-linear optic crystals; oxide crystal growth; II-VI materials; laser materials (oxides and fluorides); miscellaneous chalcogenides, silicon/germanium; III-V bulk growth, wide bandgap materials (SIC, diamond, nitrides); special techniques; halides; superconductors; special topics; refractory compounds; aqueous solution growth; biomaterials, industrial crystallization; and gel growth.

1992-08-01

371

Crystal structure of a new adduct between telluric acid and alkali cyclo-triphophates: Te(OH)6.Na3P3O9.K3P3O9  

International Nuclear Information System (INIS)

Mr=889.74, monoclinic, C2/c, a=18.42(1), b=10.644(5), c=12.348(8) A, ?=119.76(5)0, V=2102(2) A3, Z=4, Dx=2.811 Mg m-3, ?(Ag K?)=0.5608 A, ?=1.38 mm-1, F(000)=1720, T=298 K, R=0.017 for 2553 independent reflexions. The crystal structure is built up of planes (z?0.0 and 0.5) of a hexagonal network of P3O9 groups centred by Te(OH)6 groups, alternating with planes (z?0.25 and 0.75) of the associated cations. (orig.).

1987-01-01

372

Review of alkali laser research and development  

Science.gov (United States)

In this review we present an analysis of optically pumped alkali laser research and development from the first proposal in 1958 by Schawlow and Townes to the current state. In spite of the long history, real interest in alkali vapor lasers has appeared in the past decade, after the demonstration of really efficient lasing in Rb and Cs vapors in 2003 and the first successful power scaling experiments. This interest was stimulated by the possibility of using efficient diode lasers for optical pumping of the alkali lasers and by the fact that these lasers can produce a high quality and high power output beam from a single aperture. We present a review of the most important achievements in high power alkali laser research and development, discuss some problems existing in this field, and provide future perspectives in diode pumped alkali laser development.

Zhdanov, Boris V.; Knize, Randy J.

2013-02-01

373

Characterization and crystal structure of cadmium(II) halide complexes with amino acids and their derivatives: VII. Crystal structures of aquadibromo(3-aminopropanoic acid)cadmium(II), dichloro(4-aminobutanoic acid)cadmium(II), diaquabis(aminohexanoic acid)cadmium(II) tetrachlorocadmium(II), and dibromo(azetidine-3-carboxylic acid)cadmium(II).  

UK PubMed Central (United Kingdom)

Seven cadmium complexes: [CdX2(Hapro)(H2O)n] (X: Cl(1), Br(2)), [CdX2(Hgaba)] (X: Cl(3), Br(4)), [Cd(Hahex)2(H2O)2][CdCl4] (5), and [CdX2(Haze-3)](H2O)n (X: Cl(6), Br(7)) have been prepared and investigated by means of IR and FT Raman spectra. The crystal and molecular structures of 2, 3, 5 and 7 were determined by a single-crystal X-ray diffraction method. In complex 2, the cadmium atom is in a distorted octahedral geometry, ligated by two carboxyl oxygen atoms of Hapro, a water molecule, and three bromine atoms; one is terminal and each of the other two is bridging two cadmium atoms to make a polymer. The structure of 3 consists of one-dimensional polymers bridged by two chlorine atoms and a carboxyl group. The carboxyl oxygen atoms of Hgaba coordinate forkedly to two cadmium atoms. The cadmium atom of [Cd(Hahex)2(H2O)2]2+ in complex 5 is in a distorted octahedral geometry, ligated by four carboxyl oxygen atoms of two molecules of Hahex and by two water molecules. [Cd(Hahex)2(H2O)2]2+ exists between two layers which are formed of infinite [CdCl4]2- chains. The carboxyl oxygen atoms of Hahex coordinate to the same cadmium atom. In complex 7, the cadmium atom is ligated by two carboxyl oxygen atoms and four bridging bromine atoms to make a polymer.

Kuriyama S; Inomata Y; Arai Y; Howell FS

2006-08-01

374

Characterization and crystal structure of cadmium(II) halide complexes with amino acids and their derivatives: VII. Crystal structures of aquadibromo(3-aminopropanoic acid)cadmium(II), dichloro(4-aminobutanoic acid)cadmium(II), diaquabis(aminohexanoic acid)cadmium(II) tetrachlorocadmium(II), and dibromo(azetidine-3-carboxylic acid)cadmium(II).  

Science.gov (United States)

Seven cadmium complexes: [CdX2(Hapro)(H2O)n] (X: Cl(1), Br(2)), [CdX2(Hgaba)] (X: Cl(3), Br(4)), [Cd(Hahex)2(H2O)2][CdCl4] (5), and [CdX2(Haze-3)](H2O)n (X: Cl(6), Br(7)) have been prepared and investigated by means of IR and FT Raman spectra. The crystal and molecular structures of 2, 3, 5 and 7 were determined by a single-crystal X-ray diffraction method. In complex 2, the cadmium atom is in a distorted octahedral geometry, ligated by two carboxyl oxygen atoms of Hapro, a water molecule, and three bromine atoms; one is terminal and each of the other two is bridging two cadmium atoms to make a polymer. The structure of 3 consists of one-dimensional polymers bridged by two chlorine atoms and a carboxyl group. The carboxyl oxygen atoms of Hgaba coordinate forkedly to two cadmium atoms. The cadmium atom of [Cd(Hahex)2(H2O)2]2+ in complex 5 is in a distorted octahedral geometry, ligated by four carboxyl oxygen atoms of two molecules of Hahex and by two water molecules. [Cd(Hahex)2(H2O)2]2+ exists between two layers which are formed of infinite [CdCl4]2- chains. The carboxyl oxygen atoms of Hahex coordinate to the same cadmium atom. In complex 7, the cadmium atom is ligated by two carboxyl oxygen atoms and four bridging bromine atoms to make a polymer. PMID:16684568

Kuriyama, Shigeaki; Inomata, Yoshie; Arai, Yumiko; Howell, Frank Scott

2006-03-27

375

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

International Nuclear Information System (INIS)

[en] 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

376

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

Energy Technology Data Exchange (ETDEWEB)

The conception of high level radwaste immobilization from M{sup 1}-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 ({gamma}, up to 5{center_dot}10{sup 8} 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)

Orlova, A.I.; Petkov, V.I.; Egorkova, O.V.; Kurazhkovskaya, V.S.; Kemenov, D.V. [Nizhny Novgorod State Univ. Chemical Dept., Nizhny Novgorod (Russian Federation); Skiba, O.V.

1997-12-31

377

Interaction of osmium tetroxide with chalcogen halides and chalcogen halide complexes of osmium  

International Nuclear Information System (INIS)

Chalcogen halide coordination and simple osmium complexes of OsCl4(ECl4)2 composition, where E=S, Se, Te; OsS2O2Cl3; OsS4Cl3; OsS4Cl2; OsS2Br4; OsBr4(SeBr4)2 are prepared in nonaqueous chlorotropic media. Magnetic properties of the compounds, electron and oscillating IR spectra are investigated. The conclusion on complex composition is made based on recent data.

1988-01-01

378

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

International Nuclear Information System (INIS)

[en] 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.

2009-01-01

379

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

Energy Technology Data Exchange (ETDEWEB)

Electron paramagnetic resonance (EPR) spectra of Mn(II) ions in cadmium phosphate glasses are presented with mixed alkali variation as xLi{sub 2}O + (20 - x) Na{sub 2}O + 20 CdO + 59.5 P{sub 2}O{sub 5} + 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{center_dot}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.

Giridhar, G; Rangacharyulu, M; Ravikumar, R V S S N [Department of Physics, Acharya Nagarjuna University, Nagarjuna Nagar-522 510 (India); Rao, P Sambasiva, E-mail: rvssn@yahoo.co.in [Department of Chemistry, Pondicherry University, Pondicherry - 605 014 (India)

2009-07-15

380

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

 
 
 
 
381

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

382

Measurement of alkali in PFBC exhaust  

Energy Technology Data Exchange (ETDEWEB)

This project supports the DOE/METC Fossil Energy Program for the development of Pressurized fluidized bed combustion (PFBC) technology. Based on the analytical activated-bauxite sorber-bed technique, we are developing the RABSAM as an alternative to the on-line alkali analyzer for field application. RABSAM is a sampling probe containing a regenerable activated-bauxite adsorbent (RABA). It can be inserted directly into the PFBC exhaust duct and requires no high temperature/high pressure (HTHP) sampling line. Alkali vapors are captured by the adsorbent purely through physical adsorption. The adsorbent is regenerated by a simple water-reaching process, which also recovers the adsorbed alkalis. The alkali analysis of the leachate by atomic absorption (AA) provides a basis for calculating the time-averaged alkali-vapor concentration in the PFBC exhaust. If the RABA is to use commercial-grade activated bauxite, the clay impurities in activated bauxite can react with alkali vapors and, therefore, need to be either removed or deactivated. In earlier work, a 6[und M]-LiCl-solution impregnation technique was shown to deactivate these impurities in fresh activated bauxite. During this year, RABA prepared by this technique was tested in a pressurized alkali-vapor sorption test unit to determine its NaCl-vapor capture efficiency and the regenerability of the sorbent by water extraction. Results of this study are presented and discussed in the following.

Schmalzer, D.K.; Steindler, M.J.; Lee, S.H.D.; Swift, W.M.

1992-01-01

383

Measurement of alkali in PFBC exhaust  

Energy Technology Data Exchange (ETDEWEB)

This project supports the DOE/METC Fossil Energy Program for the development of PFBC technology. Based on the analytical activated-bauxite sorber-bed technique, we are developing the RABSAM as an altemative to the on-line alkali analyzer for field application. As shown in Fig. 1, the RABSAM is a sampling probe containing a regenerable activated-bauxite adsorbent (RABA). It can be inserted directly into the PFBC exhaust duct and requires no HTHP sampling line. Alkali vapors are captured by the adsorbent purely through physical adsorption. The adsorbent is regenerated by a simple water-leaching process, which also recovers the adsorbed alkalis. The alkali analysis of the leachate by atomic absorption (AA) provides a basis for calculating the time-averaged alkali-vapor concentration in the PFBC exhaust. If the RABA is to use commercial grade activated bauxite, the clay impurities in activated bauxite can react with alkali vapors and, therefore, need to be either removed or deactivated. In earlier work, a 6M-LiCl-solution impregnation technique was shown to deactivate these impurities in fresh activated bauxite [8]. During this year, RABA prepared by this technique was tested in a pressurized alkali-vapor sorption test unit to determine its NaCl-vapor capture efficiency and the regenerability of the sorbent by water extraction. Results of this study are presented and discussed.

Lee, S.H.D.; Swift, W.M.

1992-11-01

384

Measurement of alkali in PFBC exhaust  

Energy Technology Data Exchange (ETDEWEB)

This project supports the DOE/METC Fossil Energy Program for the development of PFBC technology. Based on the analytical activated-bauxite sorber-bed technique, we are developing the RABSAM as an altemative to the on-line alkali analyzer for field application. As shown in Fig. 1, the RABSAM is a sampling probe containing a regenerable activated-bauxite adsorbent (RABA). It can be inserted directly into the PFBC exhaust duct and requires no HTHP sampling line. Alkali vapors are captured by the adsorbent purely through physical adsorption. The adsorbent is regenerated by a simple water-leaching process, which also recovers the adsorbed alkalis. The alkali analysis of the leachate by atomic absorption (AA) provides a basis for calculating the time-averaged alkali-vapor concentration in the PFBC exhaust. If the RABA is to use commercial grade activated bauxite, the clay impurities in activated bauxite can react with alkali vapors and, therefore, need to be either removed or deactivated. In earlier work, a 6M-LiCl-solution impregnation technique was shown to deactivate these impurities in fresh activated bauxite [8]. During this year, RABA prepared by this technique was tested in a pressurized alkali-vapor sorption test unit to determine its NaCl-vapor capture efficiency and the regenerability of the sorbent by water extraction. Results of this study are presented and discussed.

Lee, S.H.D.; Swift, W.M.

1992-01-01

385

Measurement of alkali in PFBC exhaust  

Energy Technology Data Exchange (ETDEWEB)

This project supports the DOE/METC Fossil Energy Program for the development of Pressurized fluidized bed combustion (PFBC) technology. Based on the analytical activated-bauxite sorber-bed technique, we are developing the RABSAM as an alternative to the on-line alkali analyzer for field application. RABSAM is a sampling probe containing a regenerable activated-bauxite adsorbent (RABA). It can be inserted directly into the PFBC exhaust duct and requires no high temperature/high pressure (HTHP) sampling line. Alkali vapors are captured by the adsorbent purely through physical adsorption. The adsorbent is regenerated by a simple water-reaching process, which also recovers the adsorbed alkalis. The alkali analysis of the leachate by atomic absorption (AA) provides a basis for calculating the time-averaged alkali-vapor concentration in the PFBC exhaust. If the RABA is to use commercial-grade activated bauxite, the clay impurities in activated bauxite can react with alkali vapors and, therefore, need to be either removed or deactivated. In earlier work, a 6{und M}-LiCl-solution impregnation technique was shown to deactivate these impurities in fresh activated bauxite. During this year, RABA prepared by this technique was tested in a pressurized alkali-vapor sorption test unit to determine its NaCl-vapor capture efficiency and the regenerability of the sorbent by water extraction. Results of this study are presented and discussed in the following.

Schmalzer, D.K.; Steindler, M.J.; Lee, S.H.D.; Swift, W.M.

1992-12-01

386

Water in the Hydration Shell of Halide Ions Has Significantly Reduced Fermi Resonance and Moderately Enhanced Raman Cross Section in the OH Stretch Regions.  

Science.gov (United States)

Water in the presence of electrolytes plays an important role in biological and industrial processes. The properties of water, such as the intermolecular coupling, Fermi resonance (FR), hydrogen-bonding, and Raman cross section were investigated by measuring the Raman spectra in the OD and OH stretch regions in presence of alkali halides (NaX; X = F, Cl, Br, I). It is observed that the changes in spectral characteristics by the addition of NaX in D2O are similar to those obtained by the addition of H2O in D2O. The spectral width decreases significantly by the addition of NaX in D2O (H2O) than that in the isotopically diluted water. Quantitative estimation, on the basis of integrated Raman intensity, revealed that the relative Raman cross section, ?H/?b (?H and ?b are the average Raman cross section of water in the first hydration shell of X(-) and in bulk, respectively), in D2O and H2O is higher than those in the respective isotopically diluted water. These results suggest that water in the hydration shell has reduced FR and intermolecular coupling compared to those in bulk. In the isotopically diluted water, the relative Raman cross section increases with increase in size of the halide ions (?H/?b = 0.6, 1.1, 1.5, and 1.9 for F(-), Cl(-), Br(-), and I(-), respectively), which is assignable to the enhancement of Raman cross section by charge transfer from halide ions to the hydrating water. Nevertheless, the experimentally determined ?H/?b is lower than the calculated values obtained on the basis of the energy of the charge transfer state of water. The weak enhancement of ?H/?b signifies that the charge transfer transition in the hydration shell of halide ions causes little change in the OD (OH) bond lengths of hydrating water. PMID:23895453

Ahmed, Mohammed; Singh, Ajay K; Mondal, Jahur A; Sarkar, Sisir K

2013-08-12

387

Water in the Hydration Shell of Halide Ions Has Significantly Reduced Fermi Resonance and Moderately Enhanced Raman Cross Section in the OH Stretch Regions.  

UK PubMed Central (United Kingdom)

Water in the presence of electrolytes plays an important role in biological and industrial processes. The properties of water, such as the intermolecular coupling, Fermi resonance (FR), hydrogen-bonding, and Raman cross section were investigated by measuring the Raman spectra in the OD and OH stretch regions in presence of alkali halides (NaX; X = F, Cl, Br, I). It is observed that the changes in spectral characteristics by the addition of NaX in D2O are similar to those obtained by the addition of H2O in D2O. The spectral width decreases significantly by the addition of NaX in D2O (H2O) than that in the isotopically diluted water. Quantitative estimation, on the basis of integrated Raman intensity, revealed that the relative Raman cross section, ?H/?b (?H and ?b are the average Raman cross section of water in the first hydration shell of X(-) and in bulk, respectively), in D2O and H2O is higher than those in the respective isotopically diluted water. These results suggest that water in the hydration shell has reduced FR and intermolecular coupling compared to those in bulk. In the isotopically diluted water, the relative Raman cross section increases with increase in size of the halide ions (?H/?b = 0.6, 1.1, 1.5, and 1.9 for F(-), Cl(-), Br(-), and I(-), respectively), which is assignable to the enhancement of Raman cross section by charge transfer from halide ions to the hydrating water. Nevertheless, the experimentally determined ?H/?b is lower than the calculated values obtained on the basis of the energy of the charge transfer state of water. The weak enhancement of ?H/?b signifies that the charge transfer transition in the hydration shell of halide ions causes little change in the OD (OH) bond lengths of hydrating water.

Ahmed M; Singh AK; Mondal JA; Sarkar SK

2013-08-01

388

Reactions of ultracold alkali metal dimers  

CERN Multimedia

We investigate the energetics of reactions involving pairs of alkali metal dimers. Atom exchange reactions to form homonuclear dimers are energetically allowed for some but not all of the heteronuclear dimers. We carry out high-level electronic structure calculations on the potential energy surfaces of all the heteronuclear alkali metal trimers and show that trimer formation reactions are always energetically forbidden for low-lying singlet states of the dimers. The results have important implications for the stability of quantum gases of alkali metal dimers.

Zuchowski, Piotr S

2010-01-01

389

The surface charge of KCl as influenced by crystal lattice defects  

Energy Technology Data Exchange (ETDEWEB)

Recently, nonequilibrium electrokinetic measurements using laser-Doppler electrophoresis were reported for alkali halides and the sign of their surface charge was thus determined. These results are generally as expected from simplified lattice ion hydration theory with KCl, under normal circumstances, being the most significant exception. In this regard, lattice defects (F centers and oxygen imperfections) have been found to influence the surface charge of KCl and its electrophoretic mobility. In particular, the presence of oxygen defect states in the crystal lattice has been found to be responsible for KCl's unexpected behavior. The concentration of oxygen defect states in KCl, as characterized by UV/Vis absorption, was varied in order to study their influence on the electrokinetic behavior and subsequently on the flotation response of KCl. At low oxygen contents (<60 ppm) KCl is positively charged as expected from lattice ion hydration theory. However, typically, KCl contains substantial oxygen (>300 ppm), sufficient to impart a negative surface charge and this accounts for the selective flotation of KCl from NaCl by heterocoagulation with oppositely charged alkyl amine hydrochloride collector colloids.

Yalamanchili, M.R.; Miller, J.D. (Univ. of Utah, Salt Lake City, UT (United States). Dept. of Metallurgical Engineering)

1994-03-01

390

Zintl cluster chemistry in the alkali-metal-gallium systems  

Energy Technology Data Exchange (ETDEWEB)

Previous research into the alkali-metal-gallium systems has revealed a large variety of networked gallium deltahedra. The clusters are analogues to borane clusters and follow the same electronic requirements of 2n+2 skeletal electrons for closo-deltahedra. This work has focused on compounds that do not follow the typical electron counting rules. The first isolated gallium cluster was found in Cs{sub 8}Ga{sub 11}. The geometry of the Ga{sub 11}{sup 7{minus}} unit is not deltahedral but can be described as a penta-capped trigonal prism. The reduction of the charge from a closo-Ga{sub 11}{sup 13{minus}} to Ga{sub 11}{sup 7{minus}} is believed to be the driving force of the distortion. The compound is paramagnetic because of an extra electron but incorporation of a halide atom into the structure captures the unpaired electron and forms a diamagnetic compound. A second isolated cluster has been found in Na{sub 10}Ga{sub 10}Ni where the tetra-capped trigonal prismatic gallium is centered by nickel. Stabilization of the cluster occurs through Ni-Ga bonding. A simple two-dimensional network occurs in the binary K{sub 2}Ga{sub 3} Octahedra are connected through four waist atoms to form a layered structure with the potassium atoms sitting between the layers. Na{sub 30.5}Ga{sub 60{minus}x}Ag{sub x} is nonstoichiometric and needs only a small amount of silver to form (x {approximately} 2--6). The structure is composed of three different clusters which are interconnected to form a three-dimensional structure. The RbGa{sub 3{minus}x}Au{sub x} system is also nonstoichiometric with a three-dimensional structure composed of Ga{sub 8} dodecahedra and four-bonded gallium atoms. Unlike Na{sub 30.5}Ga{sub 60{minus}x}Ag{sub x}, the RbGa{sub 3} binary is also stable. The binary is formally a Zintl phase but the ternary is not. Some chemistry in the alkali-metal-indium system also has been explored. A new potassium-indium binary is discussed but the structure has not been completely characterized.

Henning, R.

1998-03-27

391

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.

Xuebing Zhao; Evert van der Heide; Ting Zhang; Dehua Liu

2010-01-01

392

Hemibonding of hydroxyl radical and halide anion in aqueous solution.  

UK PubMed Central (United Kingdom)

Molecular geometries and properties of the possible reaction products between the hydroxyl radical and the halide anions in aqueous solution were investigated. The formation of two-center three-electron bonding (hemibonding) between the hydroxyl radical and halide anions (Cl, Br, I) was examined by density functional theory (DFT) calculation with a range-separated hybrid (RSH) exchange-correlation functional. The long-range corrected hybrid functional (LC-?PBE), which have given quantitatively satisfactory results for odd electron systems and excited states, was examined by test calculations for dihalogen radical anions (X(2)(-); X = Cl, Br, I) and hydroxyl radical-water clusters. Equilibrium geometries with hemibonding between the hydroxyl radical and halide anions were located by including four hydrogen-bonded water molecules. Excitation energies and oscillator strengths of ?-?* transitions calculated by the time-dependent DFT method showed good agreement with observed values. Calculated values of the free energy of reaction on the formation of hydroxyl halide radical anion from the hydroxyl radical and halide anion were endothermic for chloride but exothermic for bromide and iodide, which is consistent with experimental values of equilibrium constants.

Yamaguchi M

2011-12-01

393

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

394

Kozulite, an Mn-rich alkali amphibole.  

UK PubMed Central (United Kingdom)

The crystal structure of kôzulite, an Mn-rich alkali amphibole with the ideal formula NaNa(2)[Mn(4) (2+)(Fe(3+),Al)]Si(8)O(22)(OH)(2), tris-odium tetra-manganese iron/aluminium octa-silicate dihydroxide, was refined from a natural specimen with composition (K(0.20)Na(0.80))(Na(1.60)Ca(0.18)Mn(2+) (0.22))(Mn(2+) (2.14)Mn(3+) (0.25)Mg(2.20)Fe(3+) (0.27)Al(0.14))(Si(7.92)Al(0.06)Ti(0.02))O(22)[(OH)(1.86)F(0.14)]. The site occupancies determined from the refinements are M1 = 0.453?(1) Mn + 0.547?(1) Mg, M2 = 0.766?(1) Mn + 0.234?(1) Mg, and M3 = 0.257?(1) Mn + 0.743?(1) Mg, where Mn and Mg represent (Mn+Fe) and (Mg+Al), respectively. The average M-O bond lengths are 2.064?(1), 2.139?(1), and 2.060?(1)?Å for the M1, M2, and M3 sites, respectively, indicating the preference of large Mn(2+) for the M2 site. Four partially occupied amphibole A sites were revealed from the refinement, with A(m) = 0.101?(4)?K, A(m)' = 0.187?(14) Na, A(2) = 0.073?(6) Na, and A(1) = 0.056?(18) Na, in accord with the result derived from microprobe analysis (0.20?K + 0.80 Na), considering experimental uncertainties.

Barkley MC; Yang H; Downs RT

2010-01-01

395

76 FR 18127 - Energy Conservation Standards for Metal Halide Lamp Fixtures: Public Meeting and Availability of...  

Science.gov (United States)

...EERE-2009-BT-STD-0018] RIN 1904-AC00 Energy Conservation Standards for Metal Halide...for purposes of establishing energy conservation standards for metal halide...equipment; and potential energy conservation standard levels derived...

2011-04-01

396

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

397

Application of lanthanum halide scintillators and low-resolution dense plastics for modern MC&A needs.  

Energy Technology Data Exchange (ETDEWEB)

Recent developments in lanthanum halide scintillators and low-resolution dense plastics give breadth to gamma-ray methods of nuclear material detection suitable for modern MC and A needs. Demanding goals for modernization of MC and A cover both portable and continuous on-line measurement applications that are quantitative for inventory/verification, and that serve those quantitative measurement needs plant-wide. Improved performance (sensitivity and reoslution) is important for portable applications in which a single detector must measure many types of materials. Budget is a major issue for continuous inventory measurements with hundreds or even thousands of detectors placed throughout a facility. Experimentally proven resolution of under 4% for 662 keV {sup 137}Cs gamma rays measured with large cerium-doped LaCl{sub 3} (lanthanum chloride) crystals set a new performance standard for versatile, efficient portable applications comparable in price to NaI(Tl), which has been dominant for decades. While the relatively high cost of crystals remains an obstacle for the application of very large numbers of lanthanum halide scintillators as distributed networked detectors, scintillators made from high-density plastic offer a different type of solution for these gamma-ray measurements. Compared to lanthanum halide crystals they are inexpensive and can be larger in size. Despite lower resolution than NaI(Tl), a quantitative interpretation of the photopeak response of the low-cost dense plastic detectors can be tailored to the unique mechanical and spectral properties of different materials at each of hundreds of fixed on-line locations in a plant. This paper describes the properties and presents experimental results for the two new spectrometer types that, together, bracket NaI(Tl) detectors in both performance and cost, fulfilling modern demands for portable and continuous on-line accountability of uranium and plutonium.

Chung, K. (Kiwhan); Belian, A. P. (Anthony P.); McKigney E. A. (Edward A.); Russo, P. A. (Phyllis A.)

2004-01-01

398

Slow relaxation, confinement, and solitons  

CERN Document Server

Millisecond crystal relaxation has been used to explain anomalous decay in doped alkali halides. We attribute this slowness to Fermi-Pasta-Ulam solitons. Our model exhibits confinement of mechanical energy released by excitation. Extending the model to long times is justified by its relation to solitons, excitations previously proposed to occur in alkali halides. Soliton damping and observation are also discussed.

Schulman, L S; Scardicchio, A; Facchi, P; Nikl, M; Polák, K; Gaveau, B

2002-01-01

399

Methyl halide emissions from greenhouse-grown mangroves  

Science.gov (United States)

Two mangrove species, Avicennia germinans and Rhizophora mangle, were greenhouse grown for nearly 1.5 years from saplings. A single individual of each species was monitored for the emission of methyl halides from aerial tissue. During the first 240 days, salinity was incrementally increased with the addition of seawater, and was maintained between 18 and 28‰ for the duration of the study. Exponential growth occurred after 180 days. Methyl halide emissions normalized to leaf area were measured throughout the study and varied dramatically. Emission rates normalized to land area (mg m-2 y-1), assuming a LAI = 5, yielded 82 and 29 for CH3Cl, 10 and 1.6 for CH3Br, and 26 and 11 for CH3I, for A. germinans and R. mangle, respectively. From these preliminary determinations, only CH3I emissions emerge as being of possible global atmospheric significance. This study emphasizes the need for field studies of methyl halide emissions from mangrove forests.

Manley, Steven L.; Wang, Nun-Yii; Walser, Maggie L.; Cicerone, Ralph J.

2007-01-01

400

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

1986-01-01

 
 
 
 
401

Solvated Positron Chemistry. Competitive Positron Reactions with Halide Ions in Water  

DEFF Research Database (Denmark)

It is shown by means of the angular correlation technique that the binding of positrons to halides is strongly influenced by solvation effects. For aqueous solutions we find increasing values for the binding energies between the halide and the positron with increasing mass of the halide. This is contrary to the calculations of Cade and Farazdel for the vacuum case

Christensen, Palle; Pedersen, Niels JØrgen

1979-01-01

402

Copper(I)-catalyzed boryl substitution of unactivated alkyl halides.  

UK PubMed Central (United Kingdom)

Borylation of alkyl halides with diboron proceeded in the presence of a copper(I)/Xantphos catalyst and a stoichiometric amount of K(O-t-Bu) base. The boryl substitution proceeded with normal and secondary alkyl chlorides, bromides, and iodides, but alkyl sulfonates did not react. Menthyl halides afforded the corresponding borylation product with excellent diastereoselectivity, whereas (R)-2-bromo-5-phenylpentane gave a racemic product. Reaction with cyclopropylmethyl bromide resulted in ring-opening products, suggesting the reaction involves a radical pathway.

Ito H; Kubota K

2012-02-01

403

Copper(I)-catalyzed boryl substitution of unactivated alkyl halides.  

Science.gov (United States)

Borylation of alkyl halides with diboron proceeded in the presence of a copper(I)/Xantphos catalyst and a stoichiometric amount of K(O-t-Bu) base. The boryl substitution proceeded with normal and secondary alkyl chlorides, bromides, and iodides, but alkyl sulfonates did not react. Menthyl halides afforded the corresponding borylation product with excellent diastereoselectivity, whereas (R)-2-bromo-5-phenylpentane gave a racemic product. Reaction with cyclopropylmethyl bromide resulted in ring-opening products, suggesting the reaction involves a radical pathway. PMID:22260229

Ito, Hajime; Kubota, Koji

2012-01-19

404

Reactivity of halide and pseudohalide ligands in transition metal complexes  

Energy Technology Data Exchange (ETDEWEB)

The review generalizes experimental material on reactions of coordinated halide ligands, as well as cyanide, azide, thiocyanate and cyanate ligands in transition metal (Mo, W, Ru, etc.) complexes. It is shown that transformation of the intrasphere pseudohalide ligands is a very important method of directed synthesis of coordination compounds. The tendency of halide and pseudohalide ions to the formation of low-soluble salts or strong complexes can be widely used in preparation coordination chemistry for the ''forced'' introduction of solvent molecules into the complexes.

Kukushkin, Yu.N.; Kukushkin, V.Yu. (Leningradskij Tekhnologicheskij Inst. (USSR))

1984-01-01

405

Reactivity of halide and pseudohalide ligands in transition metal complexes  

International Nuclear Information System (INIS)

The review generalizes experimental material on reactions of coordinated halide ligands, as well as cyanide, azide, thiocyanate and cyanate ligands in transition metal (Mo, W, Ru, etc.) complexes. It is shown that transformation of the intrasphere pseudohalide ligands is a very important method of directed synthesis of coordination compounds. The tendency of halide and pseudohalide ions to the formation of low-soluble salts or strong complexes can be widely used in preparation coordination chemistry for the ''forced'' introduction of solvent molecules into the complexes.

1984-01-01

406

Importance of dispersion in density functional calculations of cesium chloride and its related halides  

Science.gov (United States)

The ionic compound cesium chloride adopts a cubic crystal structure bearing the same name. However, ab initio electronic structure calculations based on density functional theory methods using generalized gradient approximation functionals do not predict that cesium chloride adopts this phase. In this paper we apply semiempirical methods (density functional theory plus a pairwise dispersion correction) to account for missing van der Waals interactions within cesium chloride. The C6 and R0 dispersion parameters for cesium are established within Grimme's DFT+D2 formalism. Inclusion of the dispersion corrections is found not only to improve the quality of structures in comparison to experiment for all cesium halides, but also leads to the correct prediction of the ground-state phase under ambient conditions.

Zhang, F.; Gale, J. D.; Uberuaga, B. P.; Stanek, C. R.; Marks, N. A.

2013-08-01

407

Mid-infrared diffused planar waveguides made of silver halide chloro-bromide.  

UK PubMed Central (United Kingdom)

We have developed waveguides for the mid-IR spectrum using silver halide crystals. Diffused planar waveguides constructed from silver chlorobromide (AgClBr) with different diffusion thicknesses were designed and characterized. The waveguides were based on our changing the refractive index of the guiding layer by a diffusion of Br- ions into crystalline AgCl substrates. The waveguides were analyzed and investigated with a 10.6-microm CO2 laser, and the optically measured thicknesses of the waveguides were found to vary between 65 and 600 microm. The propagation losses were in the range of 4-16 dB/cm, and the maximal entrance angle was 62 degrees. The output beam distribution was measured and was in good correlation with a numerical analysis simulation based on a ray-tracing model, by use of the eikonal equation.

Dekel B; Katzir A

2002-06-01

408

Holographic diffuser by use of a silver halide sensitized gelatin process.  

UK PubMed Central (United Kingdom)

Diffusers play an important role in liquid crystal display (LCD) application as a beam-shaping device, a brightness homogenizer, a light-Scattering device, and an imaging screen. The transmittance and diffusing angle of the diffusers are the critical aspects for the applications to the LCD. The holographic diffusers by use of various processing methods have been investigated. The diffusing characteristics of different diffusing materials and processing methods have been evaluated and compared. The microstructures of holographic diffuse have been investigated by use of using scanning electron microscopy. The holographic diffusers by use of the silver halide sensitized gelatin (SHSG) method have the structural merits for the improvement of the quality of diffusers. The features of holographic diffuser were exceptional in terms of transmittance and diffusing angle. The replication method by use of the SHSG process can be directly used for the manufacturing of diffusers for the display application.

Kim SI; Choi YS; Ham YN; Park CY; Kim JM

2003-05-01

409

C3A polymorphs related to industrial clinker alkalies content  

International Nuclear Information System (INIS)

The C3A crystalline structure in Portland clinkers is basically determined by the incorporation of alkali-oxides and is also function of the cooling rate, both actions have a combined effect on the changes in reactivity of clinkers. Industrial clinkers have been found to contain cubic or orthorhombic forms of aluminate, alone or in combination; the monoclinic modification has not been observed. The aim of this research is to evaluate the different polymorphs of C3A present on industrial clinkers produced with different amounts of sodium and potassium oxide in the raw mix. The optical microscopy was useful to distinguish the different kinds of C3A based on their crystal features. The SEM (scanning electron microscopy)-EDS analysis was used on the chemical characterization of the C3A. An accurate quantification of the phases, including proportions of C3A polymorphs, could be achieved using X-ray diffraction with Rietveld refinement. The quantification was confirmed by chemical selective dissolution applied in samples for which the refinement indicated almost only one type of C3A polymorph. Finally, correlations between alkalies contents, Na2O and CaO for white cement clinker and K2O and CaO for grey clinker suggest partial substitution of CaO and incorporation of Na2O or K2O in the vacant site of the cubic C3A leading to the formation of the orthorhombic phase.

2004-01-01

410

The effects of halide anions on the dielectric response of potassium halide solutions in visible, UV and far UV region.  

UK PubMed Central (United Kingdom)

Based on the experimentally measured dispersion of refractive indices, we studied the effects of halide anions on the dielectric response of potassium halide solutions in the visible, UV and far UV regions. It was shown that a specific ion effect according to the Hofmeister series is clearly demonstrated for the visible range of spectra. For the near-, mid-, and far UV ranges of spectra, the specific ion effect essentially depends on solution concentration and temperature. The influence of ions on the behavior of dynamic dielectric permittivity of a solution is discussed on the basis of ion/water and ion/ion electrostatic and electrodynamic interactions and hydration shell structure.

Shagieva FM; Boinovich LB

2013-06-01

411

Changes in the nature of chemical bonding under compression of crystals  

International Nuclear Information System (INIS)

A method is developed for the determination of effective charges of atoms in binary crystalline substances under pressure from experimentally found values of volumes, compressibilities, and thermochemical characteristics. Using this method, changes in electronegativities and charges of atoms in binary crystalline alkali metal halides, alkaline earth metal and cadmium chalcogenides, boron, indium, lanthanum, thorium, and uranium pnictides are calculated with pressure up to 10 GPa. The data obtained are in good correlation with the known spectroscopic studies of the nature of chemical bonding

2005-01-01

412

Alkali metal and alkali metal hydroxide intercalates of the layered transition metal disulfides  

International Nuclear Information System (INIS)

[en] The intercalation reaction of some layered transition metal disulfides with alkali metals, alkali metal hydroxides, and tetraalkylammonium hydroxides were investigated. The alkali metal intercalates were prepared in the respective metal-hexamethylphosphoric triamide solutions in vaccuo, and the hydroxide intercalates in aqueous hydroxide solutions. According to the intercalation reaction, the c-lattice parameter was increased, and the increase indicated the expansion of the interlayer distance. In the case of alkali metal intercalates, the expansion of the interlayer distance increased continuously, corresponding to the atomic radius of the alkali metal. On the other hand, the hydroxide intercalates showed discrete expansion corresponding to the effective ionic radius of the intercalated cation. All intercalates of TaS2 amd NbS2 were superconductors. The expansion of the interlayer distance tended to increase the superconducting transition temperature in the intercalates of TaS2 and vice versa in those of NbS2. (orig.)

1981-01-01

413

Adsorption of NOx on {gamma}-alumina treated with alkali carbonates and alkali hydroxides  

Energy Technology Data Exchange (ETDEWEB)

The effectiveness of alkali carbonate-treated and alkali hydroxide-treated {gamma}-alumina for the adsorption of NO{sub 2} and NO has been examined in this study. All of the alkali-treated aluminas perform better than bare aluminas, and the performance of the alkali-treated aluminas improves with increasing mass (atomic radii) of the alkali. The most efficient material examined is 33% CsOH-treated {gamma}-alumina. As NO{sub 2} is adsorbed, NO is produced in a 3:1 ratio. Surface acidity does not affect the adsorption of these species. The adsorbed N-containing species are strongly bound at the sorbent surface with a decomposition temperature over 600 C. Thermal desorption of these species provides an effective means of regenerating these materials.

Lee, M.R.; Wolan, J.T.; Hoflund, G.B.

1999-10-01

414

Reflection holographic optical elements in silver-halide sensitized gelatin  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Silver halide sensitized gelatin has proved to be an alternative to dichromated gelatin as a recording material in the production of transmission holographic optical elements (HOEs). In this paper, we will discuss the possible applications of this process to the production of reflection HOEs.

Pascual Villalobos, Inmaculada; Beléndez Vázquez, Augusto; Fimia Gil, Antonio

415

Alternative route to metal halide free ionic liquids  

International Nuclear Information System (INIS)

[en] An alternative synthetic route to metal halide free ionic liquids using trialkyloxonium salt is proposed. Utility of this synthetic route has been demonstrated by preparing 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid through the reaction between 1-methylimidazole and triethyloxonium tetra-fluoroborate in anhydrous ether. (author)

2008-01-01

416

Electron diffraction study of molecular structure of uranium halides  

International Nuclear Information System (INIS)

Using the high-temperature gas electron diffraction method, uranium tetrahalides UX4 (X=F-I), and uranium trichloride and triiodide are studied. Some methodical peculiarities are discussed and the results of studies of the structure of uranium halides are discussed. The frequencies of vibration spectrum and strength constants are estimated. 25 refs.; 2 figs.; 2 tabs

1990-01-01

417

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

418

Assessing Global Terrestrial Sources of Methyl Halides - Ozone Regulating Gases  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Methyl bromide (CH3Br) and methyl chloride (CH3Cl) play significant roles in the depletion of the stratospheric ozone layer. The vast portion of methyl halide sources and sinks sources and sinks are natural in origin. The sources are poorly constrained, leading to unbalanced budgets. Budget closure ...

Gancarczyk, Maciej

419

Copper-catalyzed nucleophilic trifluoromethylation of propargylic halides.  

UK PubMed Central (United Kingdom)

Reactions of propargylic halides with trifluoromethyltrimethylsilane in the presence of a catalytic amount of copper(i) thiophene-2-carboxylate (CuTC) have been found to give the corresponding trifluoromethylated products in good to high yields with a high selectivity.

Miyake Y; Ota S; Shibata M; Nakajima K; Nishibayashi Y

2013-08-01

420

Palladium-Catalyzed Catellani Aminocyclopropanation Reactions with Vinyl Halides.  

UK PubMed Central (United Kingdom)

Palladium is shown to catalyze an intramolecular aminocyclopropanation of norbornenes with aliphatic vinyl halides in good yields. The reaction tolerates a variety of amine substituents and gives good results with a variety of carbocyclic and oxabicyclic [2.2.1] alkene acceptors. Notably, stabilized enolate nucleophiles were also employed in cyclopropanation reactions.

Khanna A; Premachandra ID; Sung PD; Van Vranken DL

2013-06-01

 
 
 
 
421

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

422

Reflection holographic optical elements in silver-halide-sensitized gelatin  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Silver halide sensitized gelatin has proven to be an alternative to dichromated gelatin as a recording material in the production of transmission holographic optical elements (HOEs). In this paper we discuss the possible applications of this process to the production of reflection HOEs as well as th...

Pascual Villalobos, Inmaculada; Beléndez Vázquez, Augusto; Fimia Gil, Antonio

423

Mercury halide lasers utilizing electrodes coated with a getter  

Energy Technology Data Exchange (ETDEWEB)

A laser utilizing mercury halides as the lasing medium is disclosed. Electrodes selectively coated with a mercury gettering material are utilized to establish a glow discharge in the lasing medium. Proper ratio of mercury to bromine is maintained in the lasing medium to ensure long life operation.

Liu, C.S.; Hirayama, C.

1984-05-29

424

Kinetics of halide ion exchange on nickel hydroxide  

International Nuclear Information System (INIS)

Kinetics of halide ion (Cl-, Br-, I-) and hydroxide ions exchange on granulated nickel(II) hydroxide was investigated. It is shown that the process is limited by diffusion in the granule porous space. Effective diffusion coefficients were identified, their values correlating with theoretically calculated coefficients of self-diffusion for the given system

2004-01-01