Leung-Griffiths model for the thermodynamic properties of mixtures of CO2 and C2H6 near the gas-liquid critical line

Leung and Griffiths have proposed a fundamental thermodynamic equation for a binary mixture near the critical line and have successfully applied it to the mixture of He³ and He⁴ in which the critical line is a nearly linear function of composition. We have used a Leung-Griffiths type equation of state to describe the thermodynamic properties of the mixture of carbon dioxide and ethane. The critical line of this mixture is, unlike that of He³ and He⁴, a nonlinear function of composition, and the azeotropic line extends to the critical line. Comparison of the predictions of the equation to experimental data shows a good agreement for the mixture of CO₂ and C₂H₆.     

Isochoric Heat Capacity Measurements for 0.5 H2O+0.5 D2O Mixture in the Critical Region

The isochoric heat capacity C _V of an equimolar H₂O+D₂O mixture was measured in the temperature range from 391 to 655 K, at near-critical liquid and vapor densities between 274.05 and 385.36 kgm^–3. A high-temperature, high-pressure, nearly constant-volume adiabatic calorimeter was used. The measurements were performed in the one- and two-phase regions including the coexistence curve. The uncertainty of the heat-capacity measurement is estimated to be ±2%. The liquid and vapor one- and two-phase isochoric heat capacities, temperatures, and densities at saturation were extracted from the experimental data for each measured isochore. The critical temperature and the critical density for the equimolar H₂O+D₂O mixture were obtained from isochoric heat capacity measurements using the method of quasi-static thermograms. The measurements were compared with a crossover equation of state for H₂O+D₂O mixtures. The near-critical isochoric heat capacity behavior for the 0.5 H₂O+0.5 D₂O mixture was studied using the principle of isomorphism of critical phenomena. The experimental isochoric heat capacity data for the 0.5 H₂O+0.5 D₂O mixture exhibit a weak singularity, like that of both pure components. The reliability of the experimental method was confirmed with measurements on pure light water, for which the isochoric heat capacity was measured on the critical isochore (321.96 kgm^–3) in both the one- and two-phase regions. The result for the phase-transition temperature (the critical temperature, T _{C, this work}=647.104±0.003 K) agreed, within experimental uncertainty, with the critical temperature (T _{C, IAPWS}=647.096 K) adopted by IAPWS.     

Effect of the Consolute Point of Isobutyric Acid+Water on the Rate of an SN1 Hydrolysis Reaction

The rate constant for the S _N 1 hydrolysis of 2-chloro-2-methylbutane was measured near the consolute point of the liquid mixture isobutyric acid+water. At temperatures far from the upper critical solution temperature, T _c, of this mixture, the rate constant obeyed the Arrhenius equation. In the one-phase region just above T _c, however, the rate constant decreased below the Arrhenius background, while in the two-phase region below T _c, it increased. This combination of slowing-down with speeding-up appears to be beyond the scope of explanation of the current theories of dynamic critical slowing-down.     

Formation mechanism of titanium silicide by mechanical alloying

The syntheses of five titanium silicides (Ti₃Si, TiSi₂, Ti₅Si₄, Ti₅Si₃, and TiSi) by mechanical alloying (MA) have been investigated. Rapid, self-propagating high temperature synthesis (SHS) reactions were involved in producing the last three materials during room temperature high-energy ball-milling of elemental powders. Such reactions appeared to occur through ignition by mechanical impact in the fine powder mixture formed after a critical milling period. From in-situ thermal analyses, each critical milling period for the formation of Ti₅Si₄, Ti₅Si₃, and TiSi was observed to be 22, 35.5 and 53.5 minutes, respectively. However, the formation of Ti₃Si and TiSi₂ did not occur even after 360 minutes of milling of as-received Ti and Si powder mixture, due to the lack of homogeneity of the powder mixture. Other ball-milling procedures were employed for the syntheses of Ti₃Si and TiSi₂ using different sizes of Si powder and milling medium materials. Ti₃Si was synthesized by milling a Ti and 60 minutes premilled Si powder mixture for 240 minutes. -TiSi₂ and TiSi₂ were produced by high energy partially stabilized zirconia (PSZ) ball-milling for 360 minutes in a steel vial followed by jar-milling of a Ti and 60 min premilled Si powder mixture for 48 hr. The formation of Ti₃Si and TiSi₂ occurs through a slow solid state diffusion reaction, and the product(s) and reactants coexist for a certain period of time. The formation of titanium silicides by MA and the reaction rate appeared to depend on the homogeneity of the powder mixture, milling medium materials, and heat of formation of the product involved.     

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     

Effects of Y2BaCuO5 on the directional growth of YBa2Cu3Ox superconductor

The effects of Y₂BaCuO₅ on the microstructure and superconducting properties of YBa₂Cu₃O_x samples, textured using the directional growth of Y₂BaCuO₅, BaCuO₂ and CuO powder mixtures, were studied. Y₂BaCuO₅ moved downward as the sample passed up through the hot zone, and this downward movement affected the superconducting properties of the directionally grown samples. The critical temperature increased, and the resistance transition width decreased as the excess 211 content in the powder mixture increased up to a value, beyond which the temperature decreased and the width increased. The critical current densities of the directionally grown samples were scattered because of the presence of uncontrollable severe cracks perpendicular to the growth direction. As the hot-zone temperature increased, the critical current density of the directionally grown sample increased up to a maximum value (>6000 A cm^–2) beyond which the critical current density decreased. Compared to data from other studies, the hot-zone temperature required to produce a maximum critical current density was lower.     

Experimental Study of the Critical Behavior of the Isochoric Heat Capacity of Aqueous Ammonia Mixture

The isochoric heat capacity of a NH₃ + H₂O (0.2607 mole fraction of ammonia) mixture has been measured in the near- and supercritical regions. Measurements were made in the single- and two-phase regions including the coexistence curve using a high-temperature, high-pressure, nearly constant-volume adiabatic calorimeter. Measurements were made along 38 liquid and vapor isochores in the range from 120.03 kg · m⁻³ to 671.23 kg · m⁻³ and at temperatures from 478 K to 634 K and at pressures up to 28 MPa. Temperatures at the liquid–gas phase transition curve, T _S(ρ), for each measured density (isochore) and the critical parameters (T _C and ρ _C) for the 0.2607 NH₃ + 0.7393  H₂O mixture were obtained using the quasi-static thermograms technique. The expanded uncertainty of the heat-capacity measurements at the 95 % confidence level with a coverage factor of k = 2 is estimated to be 2 % to 3 % in the near-critical and supercritical regions, 1.0 % to 1.5 % in the liquid phase, and 3 % to 4 % in the vapor phase. Uncertainties of the density, temperature, and concentration measurements are estimated to be 0.06 %, 15mK, and 5×10⁻⁵ mole fraction, respectively. An unusual behavior of the isochoric heat capacity of the mixture was found near the maxcondetherm point (in the retrograde region). The value of the Krichevskii parameter was calculated using the critical properties data for the mixture and vapor-pressure data for the pure solvent (H₂O). The derived value of the Krichevskii parameter was used to analyze the critical behavior of the strong (C _P , K _T ) and weakly (C _V ) singular properties in terms of the principle of isomorphism of critical phenomena in binary mixtures. The values of the characteristic parameters (K ₁, K ₂), temperatures (τ ₁, τ ₂), and the characteristic density differences (Δρ ₁, Δρ ₂) were calculated for the NH₃ + H₂O mixture by using the critical-curve data.     

Self-flux synthesis and photoluminescent properties of LiAl5O8

Pure-phase LiAl₅O₈ was selected as an oxide ceramic red phosphor material without dopants (color centers) and was synthesized using a self-flux method. The LiAl₅O₈ was formed by heating a powder mixture consisting of γ-Al₂O₃:Li₂SO₄ = 1:2 (molar ratio) at over 1100 °C for 1 h. Photoluminescence (PL) properties for the synthesized LiAl₅O₈ were investigated. The maximum intensity of the excitation spectrum for the photoluminescent emission of LiAl₅O₈ synthesized was at 274 nm. The peak intensity of the emission spectrum was at a wavelength of 667 nm (red color). The intensity of the peak emission spectrum increased with the heating temperature, i.e., the maximum peak intensity of the red emission spectrum was detected for the LiAl₅O₈ synthesized by heating at 1500 °C for 1 h.     

Critical curves in mixtures of carbon dioxide with ethane and ethylene based on a generalized fluctuation form of the van der waals equation of state

Critical curves of CO₂-C₂H₄ and CO₂-C₂H₄ mixtures are investigated using a new fluctuation equation of state. Particular attention is paid to the behavior of thermodynamic sensitives in the vicinity of the critical azeotropic points, at which the derivative of the molar volume with respect to the composition, which has no special features in the vicinity of the critical points of the pure components, becomes zero. Reliable agreement between the results of describing the critical curves of the mixtures and the known (including volumetric measurements) experiment is obtained. Possible intensification of supercritical extraction in using the CO₂-C₂H₆ mixture in the vicinity of the azeotropic point is predicted. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 2, pp. 407–413, March–April, 2000.     

The Viscosity Anomaly Near the Lower Critical Consolute Point

Shear viscosity measurements for a critical mixture of 3-methylpyridine + heavy water near a lower critical consolute point are reported. The background contribution was determined from viscosity measurements of mixture at a noncritical composition. In the entire investigated temperature range T _c – T 15.6 K, the viscosity of the critical mixture exceeds the background contribution, and the critical enhancement is important. The increase of the viscosity near critical is found in the temperature range T _c–T 1.82 K. The critical exponent y = 0.0415 ± 0.002 and the wave number Q = (0.40 ± 0.07) nm^–1 are determined.     

Mass spectrometric study of gas-phase chemistry in the hot-wire CVD processes of SiH4/NH3 mixtures

The gas-phase reaction products of SiH₄, NH₃ and their mixtures from a hot-wire CVD chamber were investigated using laser ionization time-of-flight mass spectrometry. Both vacuum ultraviolet laser single photon ionization and laser-induced electron impact ionization were used. The main products observed from a 50% NH₃/He sample were H₂ and N₂. The study of an NH₃/SiH₄ mixture (P_NH3:P_SiH4 = 100:1) has shown that the NH₃ dissociation on the filament was suppressed by the presence of SiH₄ in the system. Signals from Si(NH₂)₄ and Si(NH₂)₃ species were identified as products from the 100:1 NH₃/SiH₄ mixture. The spectrum for a 1:1 NH₃/SiH₄ mixture was dominated by mass peaks characteristic of SiH₄ chemistry in the reactor, i.e. H₂, Si₂H₆, and Si₃H₈, at low temperatures. The extent to which the decomposition of NH₃ is suppressed is enhanced with more SiH₄ molecules in the system.     

X-ray absorption fine structure combined with X-ray fluorescence spectrometry: Part 18. Tin site structure of Pt-Sn catalyst

Sn Kα₁-detecting Sn K-edge XANES spectrum was successfully measured for Pt-Sn/SiO₂ catalyst (2.5 wt.% Pt, Sn/Pt atomic ratio 1.0) in the energy resolution 5.0 eV using Rowland-type fluorescence spectrometer equipped with Ge(13,13,13) bent crystal. The steeper, more clearly resolved XANES spectrum thus obtained could be compared quantitatively to theoretical XANES spectra generated by ab initio calculations for thirteen plausible Pt-Sn site models (alloy, adsorbed Sn, and mixture models). This spectral simulation suggested that fluorescence-detecting XANES is a simple method to judge the plausible site structure without detailed spectral analyses. The comparison supported an adsorbed Sn site model structure on highly dispersed Pt[-Sn] nanoparticles on SiO₂.     

Saturation vapor pressure and critical constants of H2O,D2O,T2O,and their isotopic mixtures

Reliable data on the vapor pressure and critical constants of H₂O isotopes and their isotopic mixtures are required for the generation of thermophysical properties data over a wide range of temperatures and pressures. In this study, vapor pressure equations for D₂O and T₂O have been developed based on the latest experimental and theoretical information. Considering the similarity among H₂O isotopes, the functional form of the Saul and Wagner equation, fully proven for H₂O, has been employed. The present equation for D₂O shows a lower trend by up to 0.09% than the widely used Hill and MacMillan equation at temperatures below 150°C. For the vapor pressure of the isotopic mixtures, the available experimental data have been examined for the validity of Raoult's law. Then it has been shown that the critical temperature and the critical pressure of the isotopic mixture can also be predicted as simple mole-fraction average values.     

Fabrication of YBa2Cu3Ox superconductor using Y2BaCuO5, BaCuO2 and CuO

YBa₂Cu₃O _x superconductor was synthesized using Y₂BaCuO₅, BaCuO₂, and CuO powder mixture. Reaction temperatures were identified using differential thermal analysis (DTA) and thermogravimetry (TG) for syntheses of precursor powders and the powder mixtures. Appropriate reaction temperatures for Y₂BaCuO₅ and BaCuO₂ precursor powders were 950 and 930°C, respectively. Two endothermic reactions involving melt formations were identified on the DTA and TG curves of the powder mixture, and the liquid increased the reactivity of the YBa₂Cu₃O _x formation. Powder mixture samples were sintered at various temperatures ranging from 880 to 1000°C. Microstructural and X-ray powder diffraction studies showed YBa₂Cu₃O _x and impurities to be formed in the samples sintered at various temperatures. The samples sintered at 990 and 1000°C showed dense microstructures. The critical temperature was 84 K for the sample sintered at 880°C and rose to 92 K as the sintering temperature increased.     

A simple route to synthesize nanocrystalline TiO2 films at room temperature

At room temperature, TiO₂ films were deposited by direct current pulse magnetron sputtering. Varying the O₂/Ar flow ratio, TiO₂ films with different crystalline structures and surface morphologies were obtained. X-ray diffraction spectra and atomic force microscopy showed TiO₂ films mainly existed as amorphous and crystalline structures when the O₂/Ar flow ratio was less and more than 6/14, respectively. With these results, a critical point was found at O₂/Ar = 6/14. The film growth behavior was controlled by the shadowing effect and the mixture of crystallographic orientation and grain growth effects, when the O₂/Ar flow ratio was less and more than the critical point, respectively. The present work reveals a simple way to prepare the high quality anatase phase TiO₂ films at room temperature, as well as the growth mechanism behind it.     

Superflow and the depairing critical current for spin singlet-triplet states of superfluid Fermi liquid

The unitary states of superfluid Fermi liquid with singlet D and triplet P type of pairing are investigated in the framework of the weak coupling approximation. The superflow pair-breaking critical current is calculated at zero temperature and in the Ginzburg-Landau region for various values of the respective strengths of singlet and triplet components of the pairing interaction. The dependence of the mass superflow on the a ₁ (F ₁ ^s ) Landau amplitude is determined. The mixed singlet-triplet states BS (a mixture of BW anisotropic and D-wave states) and 2DS (a mixture of 2D planar and D-wave states) are found to be stable for some region of the superfluid velocity.     

Structure and superconductivity of Bi-(Pb)-Ca-Sr-Cu-O ceramics processed by arc melting

The Bi-(Pb)-Ca-Sr-Cu-O ceramics of typical cation composition 2 (0.4) 223, presintered at 800°C, are formed by arc melting and rapidly cooling the 2021 superconducting phase, CaO, and Cu₂O. The arc-melted samples sintered in air at 840°C exhibit a solid-state structural transformation of the components and a mixture of 2122 and 2223 superconducting phases, and small amounts of Ca₂CuO₃, Ca₂PbO₄, and CuO appear. When the arc melting is used as an intermediate stage in the preparation of the high-T _c superconductors in this system, a significant increase in density (from 3.7 to 5.7 g/cm³) and in critical current density (from 28 to 60 A/cm² in zero field and at liquid-nitrogen temperature) is observed, while the critical temperature remains practically unchanged (–104 K).     

Oil mass fraction measurement of CO2/PAG mixture

In this study, a method of using a capacitance sensor was investigated as a means to measure the mass fraction of a type of PAG oil flowing with CO₂ in a transcritical cycle. The test facility equipped with the capacitance sensor was fabricated to establish and maintain a known oil mass fraction and to measure the capacitance of the CO₂/oil mixture. By using this facility, the relationship among three parameters (reduced CO₂ density (CO₂ density divided by the critical density of CO₂), oil mass fraction, and relative dielectric constant of the CO₂/PAG oil mixture) was developed. For the range of oil mass fraction 0–0.07, the error of new measurement method was within 0.005 for a wide range of pressures and temperatures tested. This study established the method of measuring the oil mass fraction continuously in the transcritical CO₂ cycle without affecting the cycle performance. Through this method, the effect of oil mass fraction on the characteristics of the oil circulation behavior and the performance of the transcritical CO₂ cycle can be investigated.     

Ga2O3 nanowires grown on GaN-Ga2O3 core-shell nanoparticles using a new method: Structure, morphology, and composition

Ga₂O₃ nanowires grown on GaN-Ga₂O₃ core-shell nanoparticles were prepared through heat-treating GaN powder method which comprises a pre-nitridation process in the flow of N₂ gas and a post-oxidation process in the air at 1200 °C. XRD and EDS patterns indicated that the heat-treated GaN powders were a powder mixture of GaN and Ga₂O₃. SEM, TEM, HRTEM and SAED images revealed that some nanowires that grow out from the edge of the GaN-Ga₂O₃ core-shell nanostructures with atomically smooth interfaces were monoclinic Ga₂O₃. Large blue-shifts in vibration frequency of Ga-N bonds observed in the FTIR spectrum could be contributed to size confinement effect and internal strains in GaN nanoparticles.