KBr System Research Articles

Nanocrystalline solid slabs of pure and CdS added KCl–KBr for energy storage application: Preparation and properties

The present study illustrates, for the first time, the possibility of preparing nanocrystalline solid slabs of pure and CdS (5 wt%) added KCl1−xBrx(with x = 0.0, 0.25, 0.5, 0.75 and 1.0) with good quality by using a melt quenching process. The ten samples prepared have been found to exhibit the halite crystal structure with reduced crystal grain size (average crystallite sizes observed in the range 43 to 97 nm), homogeneous morphology (cuboid shape) and phase purity. Optical measurements (absorption/reflectance and photoluminescence) show a significant difference between the melt quenched samples, precursors and ball milled samples (prepared for comparison); CdS addition leads to an extra photoluminescent peak at around 280 nm. The melt quenched samples exhibit much higher dielectric constants (indicating that they can be used as efficient energy storage materials) than the bulk (single/ poly) crystalline KCl–KBr (simple and mixed) systems, which could be due to their lower crystal grain/ crystallite sizes; for example, the ɛr value observed for the CdS added KCl0.5Br0.5 (with an applied AC field frequency of 1 kHz) increases from 2075 at 30 °C to 6188 at 190 °C, which is very interesting.

Applications of Selectfluor for the Oxidation of Sulfides, Urazoles and Alcohols Under the Solvent-free Conditions

Aims: Using Selectorfluor® for the oxidation of urazoles and sulfides as well as the oxidation of alcohols under mild conditions. Background: [1-Chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane-bis(tetrafluoroborate)] so-called Selectorfluor®, is a reagent/catalyst that is donor of the electrophilic fluorine atom. Selectorfluor ® is a colorless salt which was first introduced in 1992. This year, Banks et al. prepared a salt from the reaction of dichloromethane with dabco and sodium tetrafluoroborate, and then reacted it with fluorine gas to prepare the Selectorfluor®. Objective: Unlike the highly hazardous F2, the Selectorfluor® is a stable, non-hygroscopic, easy to handle and commercially available reagent that has many applications in organic reactions. Methods: Substrate [alcohols, urazoles or sulfides (1 mmol)] was added to the mixture of Selectorfluor ® (0.708 g, 2 mmol), KBr (0.236 g, 2 mmol), and 0.2 g wet SiO2 (50%). The mixture was ground with a mortar and pestle for 10-15 minutes. Then, the product was extracted with CH2Cl2 (2×10 mL). The solution was dried with anhydrous sodium sulfate and filtered again. Simple distillation of the CH2Cl2 gave the crude product. Aldehyde/ketones and sulfoxides were purified by short column chromatography on silica gel with EtOAc/n-hexane (1:3 to 1:5). Urazoles were purified by the sublimation method. Results: Some advantages of these oxidation reactions using the Selectorfluor®/KBr system are: a) both reagent and catalyst are safe and easy to handle; b) the procedure is solvent-free; c) the reaction is carried out at room temperature; d) yields are good to excellent; e) work-up is convenient since the reagent/catalyst residue is ionic and insoluble in the organic solvents. Conclusion: Selectorfluor® is a safe and stable reagent that is easy to work with, although it is slow and lazy in reaction, and it cannot react well at room temperature. The literature survey shows that the best conditions for a reaction are acetonitrile reflux and that the solvent-free is not very desirable conditions.

Viscometric and Densimetric Study of Water–PEG–KBr Systems

The dynamic viscosity and density of a water–PEG–KBr system are measured in the ranges of 293.15–323.15 K and 0–0.001 mol parts. Polyethylene glycol samples with average molecular weights of 1000, 1500, 3000, 4000, and 6000 g/mol are used. The concentration of KBr is 0.01 mol parts. The activation parameters of viscous flow (Gibbs energy, enthalpy, and entropy) and the partial molar volume of PEG in a solution are calculated using experimental data in the specified range of temperatures and concentrations. It is shown that the activation parameters of viscous flow grow along with concentration and molar weight. It is found that the partial molar volume of PEG in a solution falls as the concentration rises, and the partial molar volume per monomer does not change, depending on the average molecular weight of PEG. A simple way of determining the hydration number of a polymer molecule is described, based on which the hydration number of a PEG macromolecule in a solution is calculated. It is found that the hydration number of a PEG macromolecule falls as the temperature rises and grows along with the molecular weight.

Analysis of GRACE range-rate residuals with focus on KBR instrument system noise

We investigate the post-fit range-rate residuals after the gravity field parameter estimation from the inter-satellite ranging data of the gravity recovery and climate experiment (grace) satellite mission. Of particular interest is the high-frequency spectrum (f> 20 mhz) which is dominated by the microwave ranging system noise. Such analysis is carried out to understand the yet unsolved discrepancy between the predicted baseline errors and the observed ones. The analysis consists of two parts. First, we present the effects in the signal-to-noise ratio (snrs) of the k-band ranging system. The snrs are also affected by the moon intrusions into the star cameras’ field of view and magnetic torquer rod currents in addition to the effects presented by Harvey et al. (2016). Second, we analyze the range-rate residuals to study the effects of the kbr system noise. The range-rate residuals are dominated by the non-stationary errors in the high-frequency observations. These high-frequency errors in the range-rate residuals are found to be dependent on the temperature and effects of sun intrusion into the star cameras’ field of view reflected in the snrs of the k-band phase observations.

Convenient high-pressure syntheses of [PtX3(C2H4)]− (X = Cl, Br) salts with a variety of organic cations from PtX2

Reaction between PtX2 (X = Cl or Br) with an equimolar amount of the appropriate [Cat]+X− in toluene in an autoclave under 25 bars of C2H4 yields the corresponding [Cat][PtX3(C2H4)] in moderate to excellent isolated yields and high purity (X = Cl, Cat = nBu4P; X = Br, Cat = nBu4P, Ph4P, nBu4N). The same reaction does not yield any olefin complex if X = I and no reaction also occurs for the PtBr2 + KBr system in water, THF, acetone or toluene.

Controllable Synthesis and Acetylene Hydrogenation Performance of Supported Pd Nanowire and Cuboctahedron Catalysts

Supported Pd nanowire and cuboctahedron catalysts have been synthesized in an ethylene glycol–poly(vinylpyrrolidone)–KBr system using a precipitation–reduction method. KBr plays a critical role in controlling the morphology of Pd: with a variety of relatively low KBr concentrations, Pd nanowires with different lengths were obtained, but after adding sufficient KBr, shape evolution from nanowires to cuboctahedrons was observed. HRTEM images showed that the twisted Pd nanowires were actually composed of primary cuboctahedrons. Furthermore, lattice distortion was observed at interfacial regions, and the number of crystal boundaries increased with increasing length of the nanowires. The catalytic performance of the Pd materials was investigated in the selective hydrogenation of acetylene. The activities of the Pd nanowire catalysts were significantly higher than those of the cuboctahedron catalyst and gradually increased with the increasing number of crystal boundaries, indicating that the defect sites at crystal boundaries are more active owing to the exposure of larger numbers of Pd atoms. However, higher activity resulted in excessive hydrogenation and a decrease in ethylene selectivity. Therefore, the Pd cuboctahedron catalyst possessed higher selectivity. The relationship between crystal boundaries and catalytic performance was quantified, and the catalytic activity was found to increase linearly with an increasing number of crystal boundaries, whereas the trend in the selectivity was the reverse.

Comment on ‘Temperature dependence of the energy dissipation in dynamic forcemicroscopy’

A recent article in this journal by Roll et al (2008 Nanotechnology 19 045703) presentsexperimental results of the temperature dependence of dissipation in dynamic forcemicroscopy which they use to elucidate the mechanisms of such a dissipation signal in thePTCDA on KBr system. We argue here that dissipation results are often highly dependentupon the tip structure, and urge caution in the interpretation of single sets of experimentaldata.

The first report on the catalytic oxidation of urazoles to their corresponding triazolinediones via in situ catalytic generation of Br + using periodic acid or oxone ®/KBr system

A combination of periodic acid or oxone ® and a catalytic amount of KBr in the presence of few drops of water, were used for the catalytic oxidation of urazoles and bis-urazoles to their corresponding triazolinediones under mild and heterogeneous conditions with moderate to excellent yields.

Raman Spectroscopic Study of Molten PbBr2—NaBr and PbBr2—KBr Mixtures.

Abstract Raman spectra of molten PbBr2–NaBr and PbBr2–KBr systems showed the strongly polarized bands at about 150 cm−1. These Raman bands were identified as the totally symmetric stretching vibration modes of tetrahedral species PbBr42− by consulting with the result of neutron diffraction. The shape of Raman spectra did not change drastically with increasing concentration of alkali bromide or a rise of temperature. These results suggest that there existed PbBr42− complex ions in the mixture melts, which might not form further clustering or networking.

Raman spectroscopic study of molten PbBr 2–NaBr and PbBr 2–KBr mixtures

Raman spectra of molten PbBr 2–NaBr and PbBr 2–KBr systems showed the strongly polarized bands at about 150 cm −1. These Raman bands were identified as the totally symmetric stretching vibration modes of tetrahedral species PbBr 4 2− by consulting with the result of neutron diffraction. The shape of Raman spectra did not change drastically with increasing concentration of alkali bromide or a rise of temperature. These results suggest that there existed PbBr 4 2− complex ions in the mixture melts, which might not form further clustering or networking.

Molar volume variation and ionic conduction in molten ZnBr 2–NaBr and ZnBr 2–KBr systems

The molar conductivities of molten ZnBr 2-NaBr and ZnBr 2-KBr systems were evaluated using the data of molar volume and electrical conductivity which were measured by dilatometry and a conventional a.c. technique, respectively. The results suggested that the dimers or more complex clusters of ZnBr 4 2− units existed in the ZnBr 2-rich mixture melts and tended to be dissociated and converted into monomers with increasing alkali bromide concentration or a rise of temperature.

Radiation defects in doped alkali halide microstructures

Photostimulated luminescence (PSL) has been measured in KBr and KI systems doped with Tl and In. The size of grains in microstructures varied from 0.1 to 1.0 μm. Specifics of the photostimulated luminescence mechanisms in these systems are analysed from the viewpoint of their application in miniaturized optoelectronic and photonic devices, including optical chips.

Salt Effects on the Isobaric Vapor−Liquid Equilibrium for Four Binary Systems

An ebulliometer was used to measure the vapor−liquid equilibrium at 101.3 kPa for four binary systems: (1) the acetone−water−CaCl2 system; (2) the 2-propanol−water−potassium acetate system and the 2-propanol−water−KBr system at different salt concentrations; (3) the ethyl acetate−ethanol system saturated with CaCl2; and (4) the acetone−carbon tetrachloride system saturated with CaCl2.The experimental results agree with the common behavior of salt effects on the phase equilibrium. An anomalous crossover between “salting out” and “salting in” effects on acetone had been observed for the acetone−carbon tetrachloride system saturated with CaCl2.

Raman spectroscopic study of molten ZnBr 2KBr mixtures

In this study, Raman spectra of molten ZnBr 2KBr systems were measured at different compositions and temperatures to ensure the existence of tetrahedral ZnBr 4 2− structural units. Each spectrum was deconvoluted in terms of the Gaussian function. Two polarized peaks were identified as the totally symmetric stretching vibration mode of tetrahedral ZnBr 4 2− monomer and its dimer. The relative intensities of these peaks depended on both composition and temperature, probably reflecting the ratio of monomer to dimer in the melts. The relative intensities decreased until the ZnBr 2 composition decreased down to 25 mol.%. and were constant when the composition was less than 25 mol.%. In this work, we discuss the network structure on the basis of the relative intensities of these two peaks.

Electrical double layer properties of hexadecyltrimethylammonium chloride surfaces in aqueous solution

The effect of aqueous KCl concentration on the electrical double layer properties of hexadecyltrimethylammonium chloride (CTAC) surfaces has been investigated. For self-assembled CTAC bilayers adsorbed onto amorphous silica surfaces, flat plate streaming potentials ( ζ s potentials), electrostatic potentials obtained from the electrophoretic mobility of colloid microspheres ( ζ e potentials) and diffuse layer potentials ( ψ d) derived from the force versus separation curves for the interaction of a colloid microsphere with a flat plate (measured with an atomic force microscope) have been analysed. Trends and differences in the ζ s and ζ e potentials have been attributed to incomplete electrical neutralisation of the silica surface by the inner adsorbed monolayer of CTAC, and differences in the silica surface charge density for the colloid and flat plate. It is considered that derived ψ d values highlight the problem created by surface roughness for atomic force microscopy force curve analysis. CTAC micellar surface potentials ( ψ o), which have been determined by a solvatochromic acid-base indicator technique, are greater than the ζ potentials for the planar adsorbed CTAC surfaces. Analyses in terms of a site-binding model and classical electrical double layer theory suggest that the degree of counterion dissociation from the surfactant headgroups (α) is significantly different for highly curved and planar surfaces; α is in the range 0.10–0.15 for the adsorbed CTAC bilayers and in the range 0.41–0.66 for spherical CTAC micelles when activities are used in the calculation. The CTAC critical micelle concentration and the minimum area per CTAC molecule at a planar interface as a function of KCl concentration have been ascertained from air/aqueous solution surface tension curves. The hydrophobic contribution to the free energy of CTAC micellisation has been calculated on the basis that CTAC micelles behave as Nernstian objects in KCl solution with the surfactant monomer acting as a potential determining ion. The results for the CTAC KCl systems have been compared with the results obtained for similar hexadecyltrimethylammonium bromide KBr systems.

Relaxed excited states and anomalous hyperfine structure of muonium centers in KBr

We report on the luminescence induced by positive muons implanted (with 4 MeV) into KBr crystal, which evidences a long-lived (lifetime=13.3 μs excited state produced by muon radiolysis. The temperature dependence of the luminescence yield has a strong correlation with the amplitude of an “anomalous” muonium center: both are observed only below ∼50 K. This correlation strongly suggests that the muonium center is perturbed by the muon-induced excitons to cause the anomalous hyperfine structure. Moreover, the luminescence energy and decay time indicate that the observed luminescence is not associated with the intrinsic or impurity-related self-trapped excitons, but with a relaxed excited state specific to the muon(ium)-KBr system.

Growth of anisotropic shaped superconducting particles in the Tl-Ba-Ca-Cu-O system

Single phase, stoichiometric Tl 2Ba 2CuO 5 (2201) and Tl 2Ba 2CaCu 2O 8 (2212) were successfully formed by molten salt synthesis. A systematic study indicating the effect of reaction temperature and reaction time on the phase formation and particle morphology is reported. Significant morphological differences were observed between powders from solid state reactions and those prepared by molten salt synthesis. The Tl-2212 superconductor was found to be the thermodynamic equilibrium phase and was found to be stable over a very wide compositional range. The best growth conditions from KClNaCl, KCl, KBr and KI salt systems were determined. Sodium containing salts were observed to electrically poison the superconductor. KCl was found to be the best candidate for the optimum growth of Tl-2212 without any deterioration in the superconducting properties.

Muon-induced luminescence in KBr.

The energy spectrum of the luminescence induced by positive muons stopped in KBr has been obtained. This spectrum shows a Gaussian line shape with the peak located at 2.82(2) eV [FWHM, 0.56(5) eV], which is shifted considerably from the 2.28-eV luminescence line due to the lowest triplet state of self-trapped excitons (STE's). This result, together with the temperature dependences of its lifetime and yield, strongly suggests that the initial state of the observed luminescence is a triplet STE state that is specific to the muon(ium)-KBr system.

Studies of new mixed halide glasses

Some new mixed halide glasses, CdF 2PbCl 2, CdF 2PbCl 2, CdF 2PbCl 2KBr, CdBr 2 PbCl 2KI and CdI 2PbCl 2KBr systems, were synthesized. Samples 4 mm thickness could be synthesized in the CdF 2PbCl 2 and CdF 2PbCl 2KBr systems. The infrared cut-off wavelengths of CdF 2PbCl 2KI are 9.5 μm and 18 μm, respectively. The structure of CdF 2PbCl 2 glass was studied by X-ray photoelectron spectroscopy, X-ray diffraction, and infrared and Raman spectral analysis. The Cd 2+ ion in the glasses is coordinated by F and Cl ions, the distance of two Cd 2+ ions being about 4.0 Å and the FCdF angle about 60°. Compared with the [CdF 8] unit in the crystalline state the [CdX n] units in glass have large deformations.

Estimation of the infrared absorption of ZnCl2–KBr glass by molecular dynamics

Molecular dynamic calculations have been made on glasses in the ZnCl2–KBr system in order to estimate the infrared (IR) absorption of these glasses. Oxygen-free glass was estimated to be transparent up to 25 μm. Glasses containing oxygen impurities were estimated to be transparent only up to 16 μm, with a weak absorption band around 10.4 μm. This agrees with experimental results of glasses in the ZnCl2–KBr–PbBr2 system.