Thermal Conductivities of [bmim][PF<Subscript>6</Subscript>], [hmim][PF<Subscript>6</Subscript>], and [omim][PF<Subscript>6</Subscript>] from 294 to 335 K at Pressures up to 20 MPa

Thermal conductivities are reported for a series of 1-alkyl-3-methylimidazolium hexafluorophosphates having butyl, hexyl, and octyl groups, which are expressed by [bmim][PF₆], [hmim][PF₆], and [omim][PF₆], respectively. The experimental method used was a transient short-hot-wire method. Since only a small amount of sample liquid is required, this method was found to be effective for the thermal-conductivity measurements of ionic liquids (ILs). The experimental temperatures ranged from 294 to 335 K at pressures up to 20 MPa. The values of the thermal conductivities of ILs at normal pressure are similar to those of benzene. It was found that an effect of the length of the alkyl chain on the thermal conductivities in ILs is negligible. From the data for the thermal conductivity and viscosity at 293.15 K and 0.1 MPa of ILs and normal alkanes, a simple correlation was developed based on the Mohanty theory. From comparisons between the thermal conductivities of ILs and those of organic liquids (n-hexane, benzene, and methanol), the temperature and pressure dependences of the thermal conductivity of ILs are relatively weak.     

<Emphasis Type="Italic">Ab initio</Emphasis> studies on [bmim][PF<Subscript>6</Subscript>]-CO<Subscript>2</Subscript> mixture and CO<Subscript>2</Subscript> clusters

Ab initio molecular dynamics studies have been carried out on the room temperature ionic liquid, 1,n-butyl,3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) and supercritical carbon dioxide mixture at room temperature and experimental density. Partial radial distribution functions (RDF) for different sites have been computed to see the organization of CO₂ molecules around the ionic liquid. Several partial RDFs around the carbon atom of CO₂ molecule are compared to find out that the CO₂ has specific interaction with a carbon atom present in the imidazolium ring. The CO₂ is also found to be very well organized around the terminal carbon atom of the butyl chain. The partial RDFs for the oxygen atoms around oxygen and carbon atoms of the CO₂ suggests that there is very good organization of CO₂ molecules around themselves even in the [bmim][PF₆]-CO₂ mixture. The instantaneous quadrupole moment tensor has been calculated for the anion and the cation. The ensemble average of diagonal components of quadrupole moment tensor of the cation have finite values, whereas the off-diagonal components of the cation and both the diagonal and off-diagonal components of the anion have the value of zero with a large standard deviation. The CPMD studies performed on CO₂ clusters reveals the greater tendency of the clusters with more CO₂ units, to deviate from the linear geometry.     

Viscosity of [bmim][PF6] and [bmim][BF4] at High Pressure

The viscosities of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim] [PF₆]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) were measured by using a rolling-ball viscometer. The experimental temperatures were from 293.15 to 353.15 K, and the pressures were from 0.1 to 20.0 MPa.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China.     

液体二氧化碳中的硫化氢、氧硫化碳分析

介绍二氧化碳中的硫化氢、氧硫化碳分析     

Crystal structure of [CH<Subscript>3</Subscript>NH<Subscript>3</Subscript>][(UO<Subscript>2</Subscript>)(H<Subscript>2</Subscript>AsO<Subscript>4</Subscript>)<Subscript>3</Subscript>]

The crystal structure of a previously unknown compound [CH₃NH₃][(UO₂)(H₂AsO₄)₃] was solved by direct methods and refined to R ₁ = 0.038 for 3041 reflections with |F _hkl | >-4σ |F _hkl |. The compound crystallizes in the monoclinic system, space group P2₁/c, a = 8.980(1), b = 21.767(2), c = 7.867(1) Å, β = 115.919(5)°, V = 1383.1(3) ų, Z = 4. In the structure of the compound, pentagonal bipyramids of uranyl ions, sharing bridging atoms with tetrahedral [H₂AsO₄]^? anions, form strongly corrugated layered complexes [(UO₂)(H₂AsO₄)₃]^? arranged parallel to the (100) plane. The protonated methylamine molecules [CH₃NH₃]⁺ form unidimensional tapelike packings parallel to the c axis and linked by hydrophilic-hydro-phobic interactions. The topology of the layered uranyl arsenate complex [(UO₂)(H₂AsO₄)₃]^? is unusual for uranyl compounds and was not observed previously. A specific feature of this topology is the presence of monodentate arsenate “branches” arranged within the layer.     

Synthesis of pure phase Mg<Subscript>1.2</Subscript>Ti<Subscript>1.8</Subscript>O<Subscript>5</Subscript> and MgTiO<Subscript>3</Subscript> nanocrystals for photocatalytic hydrogen production

Synthesis of pure phase Mg_1.2Ti_1.8O₅ and MgTiO₃ nanocrystals has proven to be challenging. Here, pure phase Mg_1.2Ti_1.8O₅ and MgTiO₃ nanocrystals were prepared. Furthermore, a new magnesium titanate, Mg_1.2Ti_1.8O₅, was synthesized via a solution-based route for the first time. As hydrogen evolution photocatalysts, both pure phase Mg_1.2Ti_1.8O₅ and MgTiO₃ nanocrystals exhibit excellent hydrogen production efficiency. In comparison with pure MgTiO₃ nanocrystals, the asprepared Mg_1.2Ti_1.8O₅ nanocrystals exhibited four times as much photocatalytic hydrogen production activity, up to 40 μmol·h^–1. Photoelectrochemical analysis, including linear sweep voltammetry, transient photocurrent measurement, electrochemical impedance spectroscopy, and construction of Mott-Schottky plots, demonstrated that the enhanced photocatalytic activity was attributed to the large surface area, fast photoelectron transfer, higher carrier density, and efficient charge separation of the Mg_1.2Ti_1.8O₅ nanocrystals.

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Crystal structure of a complex of Pu(VI) nitrate with triphenylphosphine oxide, [PuO<Subscript>2</Subscript>(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>(OP(C<Subscript>6</Subscript>H<Subscript>5</Subscript>)<Subscript>3</Subscript>)<Subscript>2</Subscript>]

Single crystals of [PuO₂(NO₃)₂(TPPO)₂] (TPPO = OPPh₃) isostructural to the related compounds of uranyl and neptunyl were isolated, and the structure of this complex was determined. Contrary to the complexes [AnO₂(TPPO)₄](ClO₄)₂ studied previously, the interatomic distances and volumes of coordination polyhedra of An in these compounds somewhat decrease in the series U-Np-Pu. This difference was attributed to a change in the number of TPPO ligands in the compounds and weakening of their interaction with oxygen atoms of the AnO ₂ ²⁺ groups in passing from [AnO₂(TPPO)₂](ClO₄)₂ to [AnO₂(No₃)₂(TPPO)₂].     

紫外荧光法检测溶解乙炔中硫化氢含量的研究

鉴于溶解乙炔中硫化氢、磷化氢杂质超标造成的极大危害以及目前溶解乙炔中硫化氢含量的检测方法存在着诸多不足,探讨了准确测定溶解乙炔中硫化氢含量的新方法——紫外荧光法,此检测方法具有操作简单、分析高效等特点,适用于溶解乙炔中硫化氢含量的定量分析。     

Solubility of UF<Subscript>4</Subscript>, ThF<Subscript>4</Subscript>, and CeF<Subscript>3</Subscript> in a LiF-NaF-KF melt

The solubility of UF₄, ThF₄, and CeF₃ in fluoride melt of the composition 45 mol % LiF-12 mol % NaF-43 mol % KF in the temperature interval 773–973 K was determined. The solubility of the fluorides increases with an increase in the melt temperature. The CeF₃ solubility in the LiF-NaF-KF system is high: 19.9 mol % at 923 K and 23.3 mol % at 973 K. Experimental data on the solubility of CeF₃ (PuF₃ imitator) were compared to the calculated data on the PuF₃ solubility in the LiF-NaF-KF melt. The results showed that CeF3 can be considered as PuF3 imitator in FLINAK melt.     

Properties of CdSe films produced via spray pyrolysis of [Cd((NH<Subscript>2</Subscript>)<Subscript>2</Subscript>CSe)<Subscript>2</Subscript>Cl<Subscript>2</Subscript>]

Data are presented on microwave photoconductivity kinetics in CdSe films prepared via spray pyrolysis of aqueous solutions of thiourea complexes on quartz and glass-ceramic substrates at temperatures from 300 to 600°C. The films were characterized by x-ray diffraction and optical absorption and reflection spectroscopies. Microwave photoconductivity (excitation with 8-ns laser pulses at 337 nm) was measured at 295 K by a resonator method in the 9-and 36-GHz ranges. The results indicate that the photoresponse decay kinetics depend on deposition temperature and incident intensity. In the films deposited below 400°C, the photoresponse decay follows a first-order rate law. At deposition temperatures above 450°C, the photoresponse decay cannot be represented by a first-or second-order rate law at low excitation intensities and approaches second-order kinetics at high intensities (> 10¹⁵ photons/cm² per pulse). Analysis of the photoresponse decay kinetics in terms of the interaction between free and trapped electrons, holes, and ions allowed us to formulate a model for the processes involved and to evaluate the rate constant of electron-hole recombination in CdSe: (4–6) × 10^?11 cm³/s.     

Crystallization kinetics of amorphous Te<Subscript>x</Subscript>(Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript>)<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript> glasses

The activation energy plays a dominant role in deciding the utility of the material for the specific purpose—here storage. The dependence of the peak temperature of crystallization (T _p)on the composition and heating rate (β) has been studied here. From the heating rate dependence,T _p the activation energy for crystallization (E _c)has been evaluated. The activation energy,E _ccalculated using three different approaches is found to decrease with the increase in Bi content. This analysis helps in finding the suitability of an alloy to be used in phase transition optical memories/switches. The results have been analysed using Kissinger’s equation for non-isothermal crystallization of materials.     

Phase relations in the Ag<Subscript>8</Subscript>SnS<Subscript>6</Subscript>-Ag<Subscript>2</Subscript>SnS<Subscript>3</Subscript>-AgBr system and crystal structure of Ag<Subscript>6</Subscript>SnS<Subscript>4</Subscript>Br<Subscript>2</Subscript>

The T-x phase diagram of the Ag-Sn-S-Br system has been studied in the composition region Ag₈SnS₆-Ag₂SnS₃-AgBr, and a compound of composition Ag₆SnS₄Br₂ has been identified. Ag₆SnS₄Br₂ has a new structure, closely related to that of Ag₆GeS₄Br₂: sp. gr. Pnma, a = 6.67050(10), b = 7.82095(9), c = 23.1404(3) Å, Z = 4, R _B = 0.0519, R _wp = 0.0782, χ² = 1.36.     

Spectral parameters of Nd<Superscript>3+</Superscript> ion in Sr<Subscript>6</Subscript>NdSc(BO<Subscript>3</Subscript>)<Subscript>6</Subscript> crystal

The spectroscopic study of Nd³⁺ in Sr₆NdSc(BO₃)₆ crystal had been performed. Based on the Judd-Ofelt theory to analyze the optical strengths measured in absorption spectra, the following spectral parameters were obtained: intensity parameters are ₂ = 1.108 × 10^–20 cm², ₄ = 2.884 × 10^–20 cm², ₆ = 3.085 × 10^–20 cm², the radiative lifetime is 385 s, the quantum efficiency is 12.5%. The fluorescence branch ratios were calculated: ₁ = 0.423, ₂ = 0.482, ₃ = 0.092, ₄ = 0.005.     

Electrical Conductivity and Viscosity of 1-Hexyl-3-methylimidazolium Bis(trifluorosulfonyl)imide, [C<Subscript>6</Subscript>mim] [(CF<Subscript>3</Subscript>SO<Subscript>2</Subscript>)<Subscript>2</Subscript>N] (CAS-RN# 382150-50-7)

The electrical conductivity and viscosity of 1-hexyl-3-methylimidazolium bis(trifluorosulfonyl)imide, [C₆mim] [(CF₃SO₂)₂N], were measured at atmospheric pressure, between 270 K and 350 K, for samples with an amount of water not exceeding 200 ppm, as part of International Union of Pure and Applied Chemistry Project 2002-005-1-100. Water content was monitored before and after measurements, by coulometric Karl–Fisher titration. Special care was taken with ionic liquid manipulation in view of the measurement uncertainty budget. The uncertainties of the electrical conductivity measurements and of the viscosity measurements are estimated to be better than 2.0 % and 0.5 %, respectively. Results were compared with data from other authors, and all data were correlated as a function of temperature.     

Etching behavior of CdTe in aqueous H<Subscript>2</Subscript>O<Subscript>2</Subscript>-HI-C<Subscript>6</Subscript>H<Subscript>8</Subscript>O<Subscript>7</Subscript> solutions

This paper examines the dissolution behavior of the (111)A, (111)B, (110), and (100) surfaces of CdTe single crystals in aqueous H₂O₂-HI-C₆H₈O₇ (citric acid) solutions. We have determined the dissolution rate of the crystals as a function of temperature and solution concentration, located the composition regions of polishing and selective etchants, and studied the microstructure and roughness of surfaces polished with optimized etchants. The etching behavior of CdTe is shown to depend on its crystallographic orientation.     

A Thermodynamic Property Model for the Binary Mixture of Methane and Hydrogen Sulfide

A thermodynamic property model with new mixing rules using the Helmholtz free energy is presented for the binary mixture of methane and hydrogen sulfide based on experimental P_ρ T_x data, vapor–liquid equilibrium data, and critical-point properties. The binary mixture of methane and hydrogen sulfide shows vapor–liquid–liquid equilibria and a divergence of the critical curve. The model represents the existing experimental data accurately and describes the complicated behavior of the phase equilibria and the critical curve. The uncertainty in density calculations is estimated to be 2%. The uncertainty in vapor–liquid equilibrium calculations is 0.02 mole fraction in the liquid phase and 0.03 mole fraction in the vapor phase. The model also represents the critical points with an uncertainty of 2% in temperature and 3% in pressure. Graphical and statistical comparisons between experimental data and the available thermodynamic models are discussed     

Thermal conductivity of LaB<Subscript>6</Subscript> and SmB<Subscript>6</Subscript> in the range 6–300 K

The thermal conductivity of LaB₆ and SmB₆ crystals has been measured from 6 to 300 K. The electronic and lattice contributions to the thermal conductivity of SmB₆ and the temperature-dependent phonon mean free path in this hexaboride have been evaluated. The results indicate strong phonon scattering by structural defects, presumably those typical of hexaborides.     

Enhanced photocatalytic activity of Bi<Subscript>12</Subscript>O<Subscript>17</Subscript>Cl<Subscript>2</Subscript> preferentially oriented growth along [200] with various surfactants

In this study, Bi₁₂O₁₇Cl₂ nanosheets preferentially oriented growth along [200] were successfully synthesized through a facile hydrothermal method in the presence of various surfactants, including PVP, CTAB and CTAC. The crystallization behavior, band gap structure and morphology of Bi₁₂O₁₇Cl₂ could be modulated by the addition of surfactants. Bi₁₂O₁₇Cl₂ with surfactants displays superior visible light photocatalytic performance than pristine sample for photodegrading RhB and 2-chlorophenol. Moreover, Bi₁₂O₁₇Cl₂ preferentially oriented growth along [200] maintained stable and recyclable in the photocatalytic process, demonstrating their promising application in environment remediation.