NaCl Phase Research Articles

SnO2–CuO–NaCl/SiO2 Catalysts for Propylene Epoxidation

The discovery of heterogeneous catalysts capable of direct gas-phase production of propylene oxide (PO) from propylene and molecular oxygen remains a challenge in industrial catalysis. The SnO2–CuO–NaCl/SiO2 system has been shown to produce PO at 55–60% selectivity with propylene conversion of 1% at 250 °C and 1 bar. A product shift toward CO2, found to occur during continuous operation, was counteracted by cofeeding 10–50 ppm 1-chloropropane, maintaining peak PO selectivities for 12 h. Temperature-programmed-reduction (TPR) studies indicated that Na increases copper dispersion. Additional catalyst characterization studies performed by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed the presence of distinct phases of CuO, SnO2, and NaCl.

First principles study of structural, electronic and elastic properties of group IB metal nitrides TMNx (TM=Cu, Ag and Au: x=1, 2)

Abstract The structural, electronic and elastic properties of group IB transition metal nitrides (TMN x : TM = Cu, Ag, Au and x = 1, 2) are investigated by first principles calculation using the Vienna ab initio simulation package. The lattice constants, cohesive energy, bulk modulus, band structures and the density of states are obtained. The calculated lattice parameters are in good agreement with the available results. The electronic structure reveals that these materials exhibit metallic behaviour. A pressure-induced structural phase transition from NaCl to CsCl phase in AgN at 6 GPa, NaCl to ZB phase in AuN at 34.2 GPa and ZB to NaCl phase in CuN at 36.2 GPa is observed. In group IB metal di-nitrides, CaF 2 to AlB 2 phase transition is predicted. The computed elastic constants indicate that these nitrides are mechanically stable at ambient pressure. The calculated Debye temperature values are in good agreement with experimental and other theoretical results.

The high pCO2 Caprese Reservoir (Northern Apennines, Italy): Relationships between present- and paleo-fluid geochemistry and structural setting

The chemical and isotopic compositions of (i) CO2-rich fluids exploited from the ~5,000m deep Pieve Santo Stefano 1 (PSS1) borehole located in the Upper Tiber Basin (Northern Apennines, Italy) and (ii) natural gas seeps located in its surroundings, mainly in the Mt. Fungaia ophiolitic-bearing complex (Ligurian Unit), are presented and discussed. Deep seismic profiles have allowed to identify a thrust-related antiform (Caprese Antiform), a regional geological structure trapping the pressurized deep fluids. Fluids from the Caprese Reservoir (CR) consist of a CO2-, N2-rich gas phase sourced by both mantle degassing and thermal degradation of carbonate rocks and organic-rich sediments of the Umbro–Tuscan sedimentary series and a Na–Cl saline (up to 82g/L of TDS) brine. Gases naturally discharging in the study area are related to those present in the CR. These gases, during their uprising toward the surface, mix with shallow aquifers. Addition of (i) H2 and H2S, derived by the interaction with ophiolite-bearing Ligurian Units, and (ii) thermogenic hydrocarbons, originated from the degradation of organic matter contained in the turbiditic (sandstone-rich) formations (Cervarola–Falterona Unit) was also evidenced. Fluid inclusions, trapped in calcite and quartz crystals from the PSS1 drill-core at the depth of 3864 to 3867m, contain CO2–N2 and H2O–NaCl phases. The different paleo CO2–N2 contents and densities found with respect to the fluids currently exploited from the CR have been related to the evolution of the reservoir throughout the time. Compositional data of fluids exploited from PSS1 borehole provide a unique opportunity to better characterize chemical–physical processes and source regions of past and present deep fluids circulating in Northern Apennines.

Epitaxial Growth of Cubic and Hexagonal InN Thin Films via Plasma-Assisted Atomic Layer Epitaxy

InN thin films possessing either a novel cubic or a hexagonal phase were grown by plasma-assisted atomic layer epitaxy on an a-plane sapphire, Si(111), and GaN/sapphire templates, simultaneously. Two ALE growth temperature windows were found between 175–185 °C and 220–260 °C, in which the growth process is self-limiting. In the lower temperature ALE window, InN on an a-plane sapphire crystallized in a face-centered cubic lattice with a NaCl type structure, which has never been previously reported. InN grown on other substrates formed the more common hexagonal phase. In the higher temperature ALE window, the InN films grown on all substrates were of hexagonal phase. The NaCl phase and the epitaxial nature of the InN thin films on the a-plane sapphire grown at 183 °C are confirmed independently by X-ray diffraction, transmission electron microscopy, and numerical simulations. These results are very promising and demonstrate the tremendous potential for the PA-ALE in the growth of crystalline III-N materials with novel phases unachievable by other deposition techniques.

Kinetically driven ordered phase formation in binary colloidal crystals

The aggregation of binary colloids of the same size and balanced charges is studied by Brownian dynamics simulations for dilute suspensions. It is shown that, under appropriate conditions, the formation of colloidal crystals is dominated by kinetic effects leading to the growth of well-ordered crystallites of the sodium-chloride (NaCl) bulk phase. These crystallites form with very high probability even when the cesium-chloride (CsCl) phase is more stable thermodynamically. Global optimization searches show that this result is not related to the most favorable structures of small clusters, which are either amorphous or of the CsCl structure. The formation of the NaCl phase is related to the specific kinetics of the crystallization process, which takes place by a two-step mechanism. In this mechanism, dense fluid aggregates form at first and then crystallization follows. It is shown that the type of short-range order in these dense fluid aggregates determines which phase is finally formed in the crystallites. The role of hydrodynamic effects in the aggregation process is analyzed by stochastic rotation dynamics - molecular dynamics simulations, and we find that these effects do not play a major role in the formation of the crystallites.

Dynamical stability and phase transition of ZrC under pressure

A comprehensive first principles study of structural, elastic, electronic, and phonon properties of zirconium carbide (ZrC) is reported within the density functional theory scheme. The aim is to primarily focus on the vibrational properties of this transition metal carbide to understand the mechanism of phase transition. The ground state properties such as lattice constant, elastic constants, bulk modulus, shear modulus, electronic band structure, and phonon dispersion curves (PDC) of ZrC in rock-salt (RS) and high-pressure CsCl structures are determined. The pressure-dependent PDCs are also reported in NaCl phase. The phonon modes become softer and finally attain imaginary frequency with the increase of pressure. The lattice degree of freedom is used to explain the phase transition. Static calculations predict the RS to CsCl phase transition to occur at 308 GPa at 0 K. Dynamical calculations lower this pressure by about 40 GPa. The phonon density of states, electron–phonon interaction coefficient, and Eliashberg's function are also presented. The calculated electron–phonon coupling constant λ and superconducting transition temperature agree reasonably well with the available experimental data.

High-pressure structures and metallization of sodium chloride

Sodium chloride (NaCl) is known as salt and an ionic insulator at ambient conditions. The high-pressure structures of NaCl have been extensively explored through a particle swarm structural search at zero temperature and pressure range of 0–800 GPa. In addition to the known low-pressure insulating phases, we find three novel orthorhombic high-pressure structures: oC8 (stable at 322–645 GPa), oI8 (stable at 645–683 GPa), and oP16 (stable at above 683 GPa). The oC8 structure can be metallized via band-gap closure under high pressure, while both oI8 and oP16 are metallic in their stable pressure ranges. Intriguingly, our predicted metallic high-pressure phases of NaCl retain predominant ionic behaviors. The peculiar conductive behaviors can be attributed to the extended anion sublattice.

Infrared Optical Constants of Crystalline Sodium Chloride Dihydrate: Application To Study the Crystallization of Aqueous Sodium Chloride Solution Droplets at Low Temperatures

Complex refractive indices of sodium chloride dihydrate, NaCl·2H(2)O, have been retrieved in the 6000-800 cm(-1) wavenumber regime from the infrared extinction spectra of crystallized aqueous NaCl solution droplets. The data set is valid in the temperature range from 235 to 216 K and was inferred from crystallization experiments with airborne particles performed in the large coolable aerosol and cloud chamber AIDA at the Karlsruhe Institute of Technology. The retrieval concept was based on the Kramers-Kronig relationship for a complex function of the optical constants n and k whose imaginary part is proportional to the optical depth of a small particle absorption spectrum in the Rayleigh approximation. The appropriate proportionality factor was inferred from a fitting algorithm applied to the extinction spectra of about 1 μm sized particles, which, apart from absorption, also featured a pronounced scattering contribution. NaCl·2H(2)O is the thermodynamically stable crystalline solid in the sodium chloride-water system below the peritectic at 273.3 K; above 273.3 K, the anhydrous NaCl is more stable. In contrast to anhydrous NaCl crystals, the dihydrate particles reveal prominent absorption signatures at mid-infrared wavelengths due to the hydration water molecules. Formation of NaCl·2H(2)O was only detected at temperatures clearly below the peritectic and was first evidenced in a crystallization experiment conducted at 235 K. We have employed the retrieved refractive indices of NaCl·2H(2)O to quantify the temperature dependent partitioning between anhydrous and dihydrate NaCl particles upon crystallization of aqueous NaCl solution droplets. It was found that the temperature range from 235 to 216 K represents the transition regime where the composition of the crystallized particle ensemble changes from almost only NaCl to almost only NaCl·2H(2)O particles. Compared to the findings on the NaCl/NaCl·2H(2)O partitioning from a recent study conducted with micron-sized NaCl particles deposited onto a surface, the transition regime from NaCl to NaCl·2H(2)O is shifted by about 13 K to lower temperatures in our study. This is obviously related to the different experimental conditions of the two studies. The partitioning between the two solid phases of NaCl is essential for predicting the deliquescence and ice nucleation behavior of a crystalline aerosol population which is subjected to an increasing relative humidity.

Biodegradable Microcapsules Prepared by Self-Healing of Porous Microspheres.

A method is herein proposed to produce biodegradable microcapsules by a self-healing of porous microspheres, which were prepared from water-in-oil-in-water (W1/O/W2) double-emulsion templates. Methoxypoly(ethylene glycol)-b-poly-dl-lactide (PELA) was dissolved in ethyl acetate (EA) as the oil phase (O) of double emulsion, NaCl and poly(vinyl acetate) aqueous solutions serving as internal and external water phases (W1 and W2), respectively. Porous PELA microspheres were prepared by a two-step emulsification and solvent extraction method. Core materials, such as proteins or latex particles, could then be loaded by diffusion from the external water phase. Eventually, the pores in the surface could heal up triggered by a solvent swelling or infrared irradiation to form closed microcapsules. Compared with traditional encapsulations which are based on the two-step emulsification, the proposed posthealing approach could overcome some drawbacks, such as the shear destruction, solvent erosion to delicate core materials, or even their unexpected release during the emulsification. Besides PELA, poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) microcapsules were also proved feasible to fulfill such an approach.

High pressure structural phase transitions of PbPo

Abstract First-principles calculations have been performed to investigate the high pressure phase transitions and dynamical properties of the less known lead polonium compound. The calculated ground state parameters for the NaCl phase show good agreement with the experimental data. The obtained results show that the intermediate phase transition for this compound is the orthorhombic Pnma phase. The PbPo undergoes from the rocksalt to Pnma phase at 4.20 GPa. Further structural phase transition from intermediate to CsCl phase has been found at 8.5 GPa. In addition, phonon dispersion spectra were derived from linear-response to density functional theory. In particular, we show that the dynamical properties of PbPo exhibit some peculiar features compared to other III–V compounds. Finally, thermodynamics properties have been also addressed from quasiharmonic approximation.

Structural, Electrical, and Optical Properties of PbTe Thin Films Prepared by Simple Flash Evaporation Method

Lead telluride (PbTe) films have been prepared on glass substrates by flash evaporation method. Structure of the film is found to possess stable face-centered cubic (fcc) NaCl phase in which the grains predominantly grow in the direction of (200) plane. The calculated grain size was in the range 19 nm. The electrical resistivity as a function of temperature was measured using four-probe technique. The electrical conductivity was calculated, and the value is found to be from 67.11 to 344.82 S/cm in the temperature range 303–453 K. The value of mobility was evaluated, and it is found to be0.329×10-3 cm2·V−1 S−1. An optical study reveals that the PbTe thin films exhibit large blue shift. The optical constants such as absorption coefficient and refractive index have been estimated, and the results are discussed.

Effect of Sputtering Current on Structure and Morphology of (Ti1-xCrx)N Thin Films Deposited by Reactive Unbalanced Magnetron Co-sputtering

(Ti1-xCrx)N thin films were deposited with various chromium currents (ICr = 0.4-1.0 A) on Si (100) wafers and glass slides by reactive unbalanced magnetron co-sputtering technique without heating and biasing the substrates. The effects of sputtering current on the structure and morphology of (Ti1-xCrx)N films was studied. The films were grown on the substrates using titanium and chromium targets in a mixed Ar and N2 atmosphere. The structure of the films was investigated by x-ray diffraction (XRD). The surface and cross-sectional morphologies of the films were examined by atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM), respectively. Furthermore, the chemical composition of the films was analyzed using energy dispersive x-ray spectroscopy (EDS). The results revealed that the (Ti1-xCrx)N thin films formed solid solutions with the fcc NaCl phase and relative Cr content (x) was figured out in the range from 0.46 to 0.81. The crystal sizes of the films calculated from Scherrer formula are about 12-13nm. AFM results indicated increasing of the roughness from 3 to 7 nm corresponding to the thickness increased from 400 to 900nm when ICr was increased. In addition, the crosssectional morphology showed dense and compact columnar.

The Effect of Ultrasonic Treatment on the Particle Size and Specific Surface Area of LaCoO3

It is well known that the properties of the materials depend on the synthesis process. The controlled synthesis concern particle size and specific surface area of LaCoO3 material is necessary in many applications, such as catalysis and gas sensitivity. Since the activity of a catalysis strongly depends on the particle size and specific surface area. In this study, LaCoO3 powder was synthesized by grinding, heating and washing operations. Firstly, mixture powder of starting materials, LaCl3, CoCl2 and Na2CO3 was ground by using a planetary ball mill grind at speed 300rpm for 2h. Secondly, the ground sample was calcined at 600oC for 90minutes. Finally, the sample product was washed with distilled water under ultrasonic for different treatment times to remove the NaCl phase. The ultrasonic bath was sonicated at a frequency of 40kHz with a total nominal output power of 95W for 0, 2, 4 and 6minutes. All prepared samples were characterized by XRD, particle size analyzer, BET and SEM analysis. XRD patterns clearly showed the complete formation of LaCoO3 with a single-phase of perovskite structure from this synthesis. Moreover, it was found that increasing of the sonication treatment time increases the specific surface area of the prepared samples while decreasing the average particle size D[4,3]. In addition, SEM micrographs also revealed that the morphology is significantly influenced by the sonication time of treatment.

Structural, electronic, optical and thermodynamic properties of Na xRb 1− xH and Na xK 1− xH alloys

A theoretical study of the structural, electronic, optical and thermodynamic properties of Na x Rb 1 −x H and Na x K 1 −x H ternary alloys in NaCl phase has been carried out using the first-principles method. We modeled the alloys at some selected compositions with ordered structures described in terms of periodically repeated supercells. The dependences on the composition of the lattice constant, band gap, dielectric constant, refractive index, Debye temperature, mixing entropy and heat capacities were analyzed for x=0, 0.25, 0.50, 0.75 and 1. The lattice constants of Na x Rb 1 −x H and Na x K 1 −x H exhibit a marginal deviation from Vegard's law. A strong deviation of the bulk modulus from linear concentration dependence was observed for both alloys. We found that the composition dependence of the energy band gap is highly non linear and the large bowing coefficient for Na x Rb 1− x H is sensitive to the composition. Using the approach of Zunger and co-workers, the microscopic origins of the gap bowing were detailed and explained. The thermodynamic stability of these alloys was investigated by calculating the phase diagram. The thermal effect on some macroscopic properties was investigated using the quasi-harmonic Debye model. There is a good agreement between our results and the available experimental data for the binary compounds, which is a support for those of the ternary alloys that we report for the first time.

Mechanism of Molten-Salt-Controlled Thermite Reactions

The present work was undertaken to study the chemistry and phase formation mechanism in the salt-controlled MoO3 + Mg + NaCl thermite reaction. It was found that the structure and phase formation mechanism in the studied system primarily depend on the salt content in the initial mixtures. In salt-poor mixtures, nucleation of product particles takes place in the molten magnesium, whereas under salt-rich conditions, products are mainly formed in molten sodium chloride. Analyses of combustion temperature profiles and product microstructures and thermal analysis of reacting mixtures suggested that the molybdenum oxide reacts with the salt at early stages of the process. The formed intermediate molybdenum oxychloride and sodium molybdate then react with magnesium, yielding Mo, MgO, and NaCl phases. The low value of the activation energy (50 kJ/mol) of the combustion process also suggests that gaseous (liquid) intermediates play an important role in the phase formation mechanism.

First-principles investigation of electronic, vibrational, elastic, and structural properties of ThN and UN up to 100 GPa

We have investigated the electronic properties, phonon dispersion relations, elastic constants, structural phase transitions, and pressure-volume equations-of-state of thorium (Th) and uranium (U) mononitrides (ThN and UN) under pressure (0\ensuremath{-}100 GPa) using pseudopotential density functional theoretical methods. The generalized gradient approximation (GGA) is found to describe the ground-state and high-pressure experimental data much better than the local density approximation (LDA) for both compounds. ThN shows acoustic mode phonon softening along the \ensuremath{\Gamma}\ensuremath{-}X direction of the Brillouin zone in the NaCl phase under pressure, followed by a transition to a CsCl structure at 72.5 GPa. Detailed electronic structure analysis revealed an electronic topological transition under pressure that could be responsible for acoustic mode phonon softening and structural phase transition. Unlike ThN, UN shows a structural phase transition from an NaCl to R-3m structure at a much smaller pressure (18 GPa), and the calculated ${C}_{44}$ shear elastic constant decreases with pressure and becomes negative at 15 GPa. A Peierls-like distortion, due to $f$ states, is found responsible for elastic instability and structural phase transition. Our results are in reasonably good agreement with available experimental data. We have also tested the effect of on-site Coulomb interactions on a few ground-state properties and on the phase-transition behavior of UN.

High pressure lattice dynamics, dielectric and thermodynamic properties of SrO

Using density functional theory and density functional perturbation theory we have studied the effects of hydrostatic pressure on lattice dynamics, dielectric and thermodynamic properties of the rocksalt (NaCl) and CsCl phases of SrO. The stability of the NiAs type structure, experimentally confirmed to be stable in BaO, is also investigated. Studying the lattice dynamics of the NaCl and CsCl phases at various pressures, in the range of the phase stability, we have found the lattice dynamical instabilities which govern the phase transitions between NaCl and CsCl phases with increasing and decreasing pressure. By monitoring the behaviour of the found soft modes, we have calculated the transition pressures upon compression and decompression of SrO crystal. Lattice dynamics calculations reveal that the rocksalt and CsCl structures are unstable with respect to the soft transversal acoustic modes at single points of the Brillouin zone, which points to the fact that the transitions are of displacive type. Responses to electric fields and thermodynamic properties at high pressures are also given and discussed. All our results are in a good agreement with experimental data where applicable.

Dynamical stability and high pressure phases of platinum carbide

Using the density-functional linear response method, we study the dynamical properties of ground state zinc-blende and high pressure NaCl phases of platinum carbide (PtC). The calculated phonon dispersion curve does not show any soft modes for all wave vectors, indicating the dynamic stability of the ground state zinc-blende phase. The high pressure rock-salt phase exhibits imaginary frequencies, practically along all directions of the Brillouin zone, which means that PtC cannot exist in the NaCl phase at least up to a high pressure of 100 GPa.

The first principles study on the TmSb compound

The structural, elastic, electronic, thermodynamic, and phonon properties of TmSb which crystallizes in NaCl (B1) phase were analyzed by performing ab-initio calculations based on density functional theory using the Vienna Ab-initio Simulation Package (VASP). The exchange correlation potential within the generalized-gradient approximation (GGA) of Perdew–Burke–Ernzerhof (PBE) was used. The calculated structural parameters, such as the lattice constant, bulk modulus and its pressure derivative, cohesive energy, and second-order elastic constants are presented for B1 and CsCl (B2). This compound exhibits crystallographic phase transition from the B1 to B2 structure at pressure 29.13 GPa. In order to gain further information, for B1 phase, we investigated the elastic properties such as, Zener anisotropy factor, Poisson’s ratio, Young’s modulus, and shear modulus; the thermodynamic properties such as, the pressure and temperature dependent behavior of the normalized volume, bulk modulus, heat capacity, thermal expansion coefficient, Debye temperature, Grüneisen parameter, and entropy over a pressure range of 0–18 GPa and a temperature range of 0–1000 K. The electronic band structure, total density of states, phonon dispersion curves and one-phonon density of states of B1 phase are also presented. The obtained results are compared with the available experimental and theoretical data.

Ab initio study of structural, elastic and vibrational properties of praseodymium chalcogenides

The plane-wave pseudopotential approach to the density-functional theory within the GGA approximation implemented in Vienna Ab-initio Simulation Package (VASP) code have been used to calculate structural, elastic and lattice dynamical properties of praseodymium chalcogenides: PrS, PrSe and PrTe. The structural properties are performed in five different crystal structures: NaCl (space group Fm3m(225)), CsCl (space group Pm3m(221)), ZB (space group F43m(216)), WC (space group P6m2(187)) and CuAu (P4/mmm(123)). Our results showed that these chalcogenides are stable in NaCl phase which are in agreement with the experimental works. The phonon dispersion curves are showed that the gap between the optic and acoustic branches decreases on going from PrS to PrTe. We have also estimated some thermodynamical properties such as entropy and heat capacity at the temperature range 0–1000K.