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.     

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.     

<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.     

Thermal Conductivities of Imidazolium-Based Ionic Liquid + CO<Subscript>2</Subscript> Mixtures

Experimental results for the thermal conductivities of imidazolium-based ionic liquid + CO₂ mixtures are reported. The thermal conductivities were measured with a transient short-hot-wire method. The experimental temperatures were from 294 K to 334 K, and pressures were 10.0 MPa and 20.0 MPa. The CO₂ mole fractions of the mixtures covered a range up to 0.42. It was found that the thermal conductivities of ionic liquids have a very small CO₂ mole fraction dependence.     

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     

Viscosity Measurements and Correlation of the Squalane + CO<Subscript>2</Subscript> Mixture

Experimental results for the viscosity of squalane + CO₂ mixtures are reported. The viscosities were measured using a rolling ball viscometer. The experimental temperatures were 293.15, 313.15, 333.15, and 353.15 K, and pressures were 10.0, 15.0, and 20.0 MPa. The CO₂ mole fraction of the mixtures varied from 0 to 0.417. The experimental uncertainties in viscosity were estimated to be within ±3.0%. The viscosity of the mixtures decreased with an increase in the CO₂ mole fraction. The experimental data were compared with predictions from the Grunberg–Nissan and McAllister equations, which correlated the experimental data with maximum deviations of 10 and 8.7%, respectively.     

New insights into anatase crystallization behavior in ionothermal synthesis of nanostructured TiO<Subscript>2</Subscript>

The anatase crystallization behaviors in ionothermal synthesis (sol–gel method containing ionic liquid) of nanostructured TiO₂ were studied in this paper. It was found that the specific physical chemical characteristics of the water/ionic liquid mixture caused the formation path and crystallinity of anatase TiO₂ to depend on the H₂O/titanium dioxide precursor (titanium tetraisopropoxide, TIP) molar ratio. Hydroxylated titanium compound was a key intermediate for forming anatase TiO₂. It could be directly formed from hydrolysis of titanium dioxide precursor or ionic liquid-induced water dissolution of the condensation product. X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) data indicated that a higher hydroxyl group ratio content of hydroxylated titanium compound was obtained at medium H₂O/TIP molar ratio and from the system containing hydrophilic ionic liquid, such as 1-butyl-3-methylimidazolium tetrafluoroborate ([BuMIm]⁺[BF₄]⁻). The self organization ability of ionic liquid drove anatase crystallization through dehydration of the Ti–OH group of hydroxylated titanium compound in the thermal annealing process. As for the particle size of TiO₂, TEM results indicated smaller particle size of TiO₂ was obtained at medium H₂O/TIP molar ratio case.     

The solubility of solid chlorine,hydrogen sulphide,sulphur dioxide,and ammonia in liquid nitrogen in the temperature range 77.4–63.5 K

The filtration method was used to study the solubility of solid chlorine, hydrogen sulphide, sulphur dioxide, and ammonia in liquid nitrogen. SO₂ and NH₃ were found to be insoluble in LN₂ at 77.4 K. The solubility of solid chlorine in LN₂ changes over the range 2.13 × 10^?7 mole fraction at 77.4 K to 0.57 × 10^?7 mole fraction at 63.5 K. The solubility of solid hydrogen sulphide in LN₂ changes within the range of 15.6 × 10^?8 mole fraction at 77.4 K and 0.87 × 10^?8 mole fraction at 63.5 K.The experimental results were compared with the solubilities calculated on the basis of the Scatchard-Hildebrand equation.     

Hydrogen-induced phase transformations in alloys based on Sm Co<Subscript>5</Subscript> under pressures of up to 650 kPA

The interaction of alloys based on SmCo₅ with hydrogen is studied by the methods of differential thermal and X-ray phase diffraction analyses under initial pressures of hydrogen of 200, 300, 400, 500, and 650 kPa at temperatures of up to 1223°K. The hydride of the alloy is formed up to a temperature of 343°K. Within the temperature ranges 388–408°K and 488–523°K, hydrogen is released from the hydrides of phases of the alloy. Within the temperature range 823–863°K, the alloy partially disproportionates into Sm H_x and Co. At 1008–1053°K, SmH_x undergoes partial decomposition and the SmCo₅ and Sm₂Co₁₇ phases are detected. The Co, SmCo₅, and Sm₂Co₁₇ phases exist at temperatures above 1168–1188°K. The compositions of the phases depend on the duration of interaction of the alloy with hydrogen. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 1, pp. 94–98, January–February, 2007.     

Synthesis and characterization of new glasses based on Li<Subscript>2</Subscript>S-P<Subscript>2</Subscript>S<Subscript>5</Subscript>-Sb<Subscript>2</Subscript>S<Subscript>3</Subscript> system

There is great interest in sulfide glasses because of their high lithium ion conductivity. New sulfide glasses based on Li₂S-P₂S₅-Sb₂S₃ system have been synthesized by a classical quenching technique. A summary of thermal and structural characterization is presented. Electrical conductivities of the samples have been determined by Impedance Spectroscopy. The compositions of low lithium content (below 20% mol) have presented low electronic conductivities close to 10⁻⁸ S/cm at room temperature. The compositions of medium lithium content (30–50% mol) have presented mixed ionic-electronic behavior with predominant on ionic conductivity with a maximum values around 10⁻⁶ S/cm for samples up to 50% Li₂S at room temperature. Arrhenius behavior is verified between 25°C and T_g for all glasses with activation energies about 0.55–0.64 eV. A comparative study of conductivities with glasses belonging to the other chalcogenide systems has been undertaken.     

Synthesis of Mg<Subscript>2</Subscript>Ni nanoparticles in a KCl-NaCl-MgCl<Subscript>2</Subscript> melt

The reaction between magnesium and nickel powders in a KCl-NaCl-MgCl₂ ionic melt at 970 K (reaction time, 5 h) has been studied by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray microanalysis, and chemical analysis. According to scanning electron microscopy data, the synthesized Mg₂Ni powder consists of particles 70–75 nm in size, in reasonable agreement with the equivalent particle diameter, ≃ 64 nm, determined from the specific surface area of the Mg₂Ni powder and with the crystallite size, D _hkl ≃ 65 nm, evaluated from X-ray diffraction data. The hydrogen sorption properties of the Mg₂Ni obtained in a KCl-NaCl-MgCl₂ ionic melt are identical to those of Mg₂Ni powder prepared by a standard method, but the former reacts with hydrogen far more rapidly.     

Composition range and thermodynamic properties of Tl<Subscript>5</Subscript>Se<Subscript>2</Subscript>Br-based solid solutions

The equilibrium subsolidus phase diagram of the TlBr-Tl₂Se-TlSe system has been mapped out using X-ray diffraction analysis and emf measurements on thallium concentration cells. Tl₅Se₂Br has been shown to have a broad homogeneity region. The emf results are used to evaluate the relative partial thermodynamic functions of the thallium in the alloys studied and the standard integral thermodynamic functions (ΔG ⁰(298 K), ΔH ⁰(298 K), S ⁰(298 K)) of the Tl₅Se₂Br-based solid solutions.     

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.     

Effect of heating rate on the microstructural and magnetic properties of nanocrystalline Fe<Subscript>81</Subscript>Si<Subscript>4</Subscript>B<Subscript>12</Subscript>P<Subscript>2</Subscript>Cu<Subscript>1</Subscript> alloys

The effect of heating rate on the structural and magnetic properties of the nanocrystalline Fe₈₁Si₄B₁₂P₂Cu₁ alloy has been investigated. Amorphous Fe₈₁Si₄B₁₂P₂Cu₁ alloy was annealed at 753 K for 180 s at different heating rates ranging from 0.05 to 5 K/s in protective argon atmosphere. The structural and magnetic properties of the as-quenched and annealed alloys were studied using X-ray diffractometer (XRD), differential scanning calorimeter (DSC), vibrating sample magnetometer (VSM), and B–H loop tracer, respectively. Amorphous precursor prepared by industry-grade raw materials is obtained. The increase of heating rate is found to be significantly effective in decreasing the grain size of α-Fe(Si) phase, but the grain size increases at higher heating rate. The volume fraction of α-Fe(Si) phase shows a monotonic decrease with the increase of the heating rate. The coercivity H _c markedly decreases with increasing heating rate and exhibits a minimum at the heating rate of 0.5 K/s, while the saturation magnetization, M _s, shows a slight decrease. These results suggest that the effect of heating rate on H _c and M _s is originated from the changes of grain size and the volume fraction of α-Fe(Si) phase.     

Viscosity of Imidazolium-Based Ionic Liquids at Elevated Pressures: Cation and Anion Effects

The viscosity of imidazolium-based ionic liquids with four different cations and three different anions was measured to pressures of 126 MPa and at three temperatures (298.15 K, 323.15 K, and 343.15 K). The high-pressure viscosity of 1-ethyl-3-methylimidazolium ([EMIm]), 1-n-hexyl-3-methylimidazolium ([HMIm]), and 1-n-decyl-3-methylimidazolium ([DMIm]) cations with a common anion, bis(trifluoromethylsulfonyl)imide ([Tf₂N]), was measured to determine the alkyl-chain length effect of the cation. An increase in the alkyl-chain length increased the viscosity at elevated pressures. [DMIm] exhibited a larger nonlinear increase with pressure over the shorter alkyl substituents. Anion effects were investigated with [HMIm] as a common cation and anions of [Tf₂N], hexafluorophosphate ([PF₆]), and tetrafluoroborate ([BF₄]). [HMIm][PF₆], with the highest viscosity, demonstrated a very nonlinear pressure dependence even at relatively moderate pressures (to 30 MPa), similar to the results for [BMIm][PF₆]. A combined Litovitz and Tait equation was utilized to describe the viscosity of the ionic liquids with pressure and temperature and demonstrated good correlation with the experimental data.     

Al-doped Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles and Their Magnetic Properties

Al-doped Fe₃O₄ nanoparticles were synthesized for the first time via the Composite-Hydroxide-Mediated (CHM) method from Fe₃O₄ and Al₂O₃ without using any capping agent. The synthesis technique was one-step and cost effective. The obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersion spectroscopy (EDS). Samples with a tunable size of 500–1500 nm, 200–800 nm, and 100–700 nm could be obtained by adjusting the reaction time and temperature. Magnetic property of the as-synthesized Al-doped Fe₃O₄ nanoparticles was investigated. Magnetic hysteresis loops measured in the field range of −10 kOe<H<10 kOe, indicated the ferromagnetic behavior with coercivity (H _c) of 470 and 110 Oe and remanence magnetization (M _r) of 13 and 6.4 emu/g at the temperature of 5 and 300 K, respectively. The saturation intensity (M _s) was 46.1 emu/g at 5 K, while it was about 43.6 emu/g at 300 K.     

An Experimental Study of the <Emphasis Type="Italic">pVTx</Emphasis> Properties for Aqueous Solutions of Ammonia Focusing on the Maximum Density Region

An experimental study of the pressure–volume–temperature-composition (pVTx) properties for the aqueous solution of ammonia, namely NH₃–H₂O mixtures, has been conducted with the use of a constant-volume apparatus, especially focusing on the maximum density behavior, in the range of temperatures from 253 to 309 K, pressures from 0.47 to 16.93 MPa, densities from 950 to 1007 kg · m⁻³ and compositions from 0 to 0.1436 mole fraction of ammonia. The behavior of the maximum densities for the aqueous solution of ammonia has been investigated for the first time by the present experimental study, and the available equations of state do not represent the pVTx properties of the present measured data adequately near the maximum density region. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

Interaction of ZrFe<Subscript>2</Subscript> doped with Ti and Al with hydrogen

The influence of doping with Ti and Al on the structure and hydrogen sorption properties of ZrFe₂ was studied by XRD, XRSMA, and measurement of hydrogen absorption and desorption isotherms at pressure up to 300 MPa. The hydrogen capacity and equilibrium desorption pressures of hydrides decrease with increasing Al content at a constant ratio of Ti and Zr. The increase in the Ti content at a constant content of Al in alloys also leads to a decrease in hydrogen capacity; however, the equilibrium desorption pressures of hydrides increase considerably. Zr_1−x Ti _x (Fe_1−y Al _y )₂ (x= 0.2–0.8; y = 0.05–0.4) alloys were investigated.     

Pressure-pulsed chemical vapour infiltration of SiC into two-dimensional-Tyranno/SiC particulate preforms from SiCl4–CH4–H2

SiC was infiltrated in two-dimensionally woven Tyranno/SiC particulate preforms from SiCl₄–CH₄–H₂ using pressure-pulsed chemical vapour infiltration (PCVI) in the temperature range 1348–1423 K. Above 1373 K, only β-SiC was deposited, whereas, at 1348 K, Si codeposition was found. At 1423 K, a macrosurface film was formed in the early stage of PCVI. At 1373 K, residual porosity decreased from 30% to 7.5% irrespective of the sample size. Three point flexural strength increased with decreasing residual porosity and increasing fibre volume fraction in the sample. Flexural strength of the sample having 48% fibre volume fraction reached about 325 MPa after 5 × 10⁴ pulses of CVI at 1373 K. Inter-laminar shear strength of the sample obtained at 1373 K reached 40 MPa at 7 × 10⁴ pulses. This revised version was published online in November 2006 with corrections to the Cover Date.     

Hydration of Non-electrolytes in H<Subscript>2</Subscript>O and D<Subscript>2</Subscript>O Investigated by Passynski’s Method

Passynski’s hydration numbers were calculated for 1-propanol, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 2,6-dimethylpyridine, and 2,4, 6-trimethylpyridine in H₂O and D₂O, for the temperature range from 277K to 313 K. Correlations between the hydration numbers and the association energies of 1:1 water–amine complexes as well as the net atomic charges on the nitrogen atom were found. It seems probable that the O–H· · ·N bond promotes the structure due to the strengthening of the O–H· · ·O bonds between water molecules neighboring that of amine. The higher the O–H· · ·N bond energy, the stronger is the promoting effect. The calculated hydration numbers in H₂O are lower than their counterparts in D₂O. ThusD₂O appears more sensitive than H₂O to the solute-induced changes of structure.