A pulsed liquid ionization chamber filled with Xe,Ar and CH4

A pulsed liquid ionization chamber filled with Xe, Ar and CH₄ is described and its characteristics are presented. The energy resolution for the detection of γ-quanta with an energy of 1836 keV amount to 4.9%, 4.1% and 6.2% for the xenon, argon and methane fillings, respectively. Dependences of the yields of free electrons from the electron tracks in the liquids (Xe, Ar, CH₄) on the electric field strength and the electron energy are obtained.     

Predicting the virial coefficients and thermodynamic properties of a multicomponent mixture with application to the ternary mixture of CH2F2+CF3CHF2+CF3CH2F

A model for estimating second and third virial coefficients, which has been used successfully to represent the behavior of pure gases and binary mixtures, was applied to a ternary mixture. An estimate for the ternary third virial coefficient.C ₁₂₃, was added to the model. Three experimentally determined binary interaction parameters were also used. The model has been applied to the ternary mixture CH₂F₂+CF₃CHF₂+CF₃CH₂F (R32+R125+R134a). The results are useful for calculating gas-phase densities, thermodynamic properties, and fugacities for phase equilibrium calculations. The use of such models leads to a considerable economy of effort in the case of multicomponent mixtures. Examples of the thermodynamic properties are given for the equimolar ternary mixture in the range from the dew-point temperature to 400 K at pressures of 0.5, 1, and 2 MPa. Calculated densities and speeds of sound are compared with new experimental values for a near-equimolar composition.     

Second and third interaction virial coefficients of the (methane+propane) system determined from the speed of sound

The speed of sound has been measured in the binary gaseous mixture (0.85CH₄+0.15C₃H₈) along seven isotherms at temperatures between 225 and 375 K and at pressures up to 1.4 M Pa. From the measurements, second and third acoustic virial coefficients of the mixture were obtained. These results were analyzed together with values of the second and third acoustic virial coefficients of the two pure components to obtain a set of model intermolecular potential-energy functions for the methane-propane system. Nonpairwise additivity of the intermolecular forces was included in this analysis. Ordinary second and third interaction virial coefficients calculated from the model are reported, as are the second and third virial coefficients of the pure components. Gas densities calculated by means of these virial coefficients for the mixture (0.9298CH₄+0.0702C₃H₈) were found to agree with experimental values at temperatures between 280 and 330 K to within 0.02% at pressures up to 3 MPa and to within 0.08% at 4MPa.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Transport properties of refrigerants R32, R125, R134a, and R125+R32 mixtures in and beyond the critical regionPropriétés de transport des frigorigènes R32, R125, R134a et des mélanges de R125+R32 dans et au-delà la région critique

A practical representation for the transport coefficients of pure refrigerants R32, R125, R134a, and R125+R32 mixtures is presented which is valid in the vapor–liquid critical region. The crossover expressions for the transport coefficients incorporate scaling laws near the critical point and are transformed to regular background values far away from the critical point. The regular background parts of the transport coefficients of pure refrigerants are obtained from independently fitting pure fluid data. For the calculation of the background contributions of the transport coefficients in binary mixtures, corresponding-states correlations are used. The transport property model is compared with thermal conductivity and thermal diffusivity data for pure refrigerants, and with thermal conductivity data for R125+R32 mixtures. The average relative deviations between the calculated values of the thermal conductivity and experimental data are less than 4–5% at densities ρ0.1ρ_c and temperatures up to T=2T_c.     

Comparison of Lorentz–Berthelot and Tang–Toennies Mixing Rules Using an Isotropic Temperature-Dependent Potential Applied to the Thermophysical Properties of Binary Gas Mixtures of CH4, CF4, SF6, and C(CH3)4 with Ar, Kr, and Xe

In this paper the isotropic temperature-dependent potential (ITDP) approach and the concepts introduced in our previous papers have been used to calculate equilibrium and transport properties of low-density gas mixtures. The twelve binary mixtures considered here are: Ar–CH₄, Ar–CF₄, Ar–SF₆, Ar–C(CH₃)₄, Kr–CH₄, Kr–CF₄, Kr–SF₆, Kr–C(CH₃)₄, Xe–CH₄, Xe–CF₄, Xe–SF₆ and Xe–C(CH₃)₄. The (n–6) Lennard–Jones potential parameters n (repulsive parameter), R_m (equilibrium distance), and (potential well depth) of the pure noble gases Ar, Kr, and Xe are obtained by a minimization of the sum of squared deviations between experimental and calculated viscosity (), and second pVT (B) and acoustic () virial coefficients normalized to their relative experimental error a_exp. The number of included experimental points for B, , was N = 305, 210, and 167 for Ar, Kr, and Xe, respectively. For the pure globular gases the potential parameters were taken from previous publications. The calculations of B, , and D₁₂ of binary mixtures were compared with experimental data by using two different mixing rules (Lorentz–Berthelot and Tang–Toennies). Recommended sets and fitting formulae for the potential parameters that can be used for the calculation of low-pressure thermophysical properties of these mixtures are provided.     

Thermal Conductivity of Solid Methane with Krypton Impurity

The time–relaxation model was proposed to describes the thermal conductivity of a low temperature phase of both pure solid CH ₄ and with an impurity of Kr. On the basis of the model the conclusion are made about the phonon–rotation interaction in solid CH ₄ and influence of impurity of Kr on transformation of the rotational motion of methane molecules.     

Preparation of high yield multi-walled carbon nanotubes by microwave plasma chemical vapor deposition at low temperature

Vertically-aligned carbon nanotubes(CNTs) with multi-walled structure were successfully grown on a Fe-deposited Si substrate at low temperature below 330°C by using the microwave plasma chemical vapor deposition of methane and carbon dioxide gas mixture. This is apparently different from the conventional reaction in gas mixtures of hydrogen and methane, hydrogen and acetylene, and hydrogen and benzene ... etc. High quality carbon nanotubes were grown at lower temperature with CO₂ and CH₄ gas mixture than those used by the previous. After deposition, the microstructure morphology of carbon nanotubes was observed with scanning electron microscope and high-resolution transmission electron microscope. The characteristics of carbon nanotubes were analyzed by laser Raman spectroscopy. The results showed the variation of the flow rate ratio of CH₄/CO₂ from 28.5 sccm/30 sccm to 30/30 sccm and the DC bias voltage from –150 V to –200 V, at 300 W microwave power, 1.3–2.0 kPa range of total gas pressure, and substrate temperatures between 300°C and 350°C. Vertically aligned carbon nanotubes with the diameter of about 15 nm and multi-walled structure were illustrated by SEM and HRTEM. However, the highest yield of carbon nanotubes of about 50% was obtained at low temperature below 330°C by MPCVD for the CH₄/CO₂ gas mixture with properly controlled parameters.     

Quantum effects and properties of the Helium-Ammonia mixture for neutral gas absorption refrigeration

Zusammenfassung The present work considers the thermodynamic and transport properties of theHe/NH ₃ gas mixture. The values obtained assume virial form of the equation of state. The existing experimental data have been used too. A detailed calculation of the second virial coefficients is presented taking in account the quantum effects interactions. The results obtained are valid for a total pressure of25 bar and a temperature range of −40°C to +50°C.

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Heat transfer in liquid nitrogen—methane mixtures under pressure

Heat transfer in nitrogen—methane mixtures (0 to 100 molar per cent CH₄) was studied in the bubble boiling range under pressures up to 3.5 MPa.For a given heat flux density in all mixtures the temperature differences are higher than in the adjacent pure componentThe maximum heat flux densities have a maximum between 90 and 70 molar per cent methane (for lower and higher pressures, respectively) with the absolute values being higher than for the pure components     

Vortices in Doped 4He Clusters

We investigate the properties of liquid ⁴ He_N clusters hosting a quantized vortex pinned to a dopant atom (Ne or Xe) or molecule (SF ₆ or HCN). A density functional theory is used to calculate the stationary configurations of pure and doped clusters, with and without vortex, up to N=1000. A liquid drop formula is then proposed that accurately describes the total energy of the complex and allows one to extrapolate the results to larger N values. We find that forming a dopant+vortex+ ⁴ He_N complex is energetically favored below a critical size N _cr , which strongly depends on the type of dopant.     

Influence of methane and carbon dioxide on in-flight particle behavior of cast iron powder by atmospheric plasma spraying

Graphite degradation in plasma sprayed cast iron coatings is a technological barrier for achieving superior wear resistant coatings. Therefore, there is a need to understand the in-flight particle behavior of cast iron powder. In this study, methane (CH₄) and methane/carbon dioxide (CO₂) mixture has been introduced into the plasma flame to decrease the in-flight particle temperature of cast iron powder in order to prevent the oxidation and dissolution of graphite as well as provide additional free carbon. It has been observed that, CH₄ and CH₄/CO₂ addition remarkably decreases the in-flight particle temperature as a result of the in-situ endothermic reactions. Also, results demonstrate that while CH₄ and CH₄/CO₂ addition does not alter the microstructure, it slightly increases the graphite content in cast iron coatings.     

Photocatalytic transformation of CO2 to CH4 and CO on acidic surface of TiO2 anatase

Recently, many studies have demonstrated that carbon dioxide can be converted to methane on TiO₂ surface by a photocatalytic process. We show that such a photo-reduction can be significantly affected by the presence of an acidic proton in powder samples of titania. Using in situ absorption gas-phase rovibrational spectroscopic detection of CH₄, CO and CO₂, we demonstrate that proton enhancement positively affects transformation of intermediate derivatives to methane during the photo-irradiation process via several reactions in which the electron transfer inside titania is coupled to oxygen transfer to the Ti³⁺ centers of TiO₂ structure. The yield of CH₄ or CO depends on the surface conditioning of titania: the formation of CH₄ is boosted by a presence of adsorbed HCl, while the formation of CO is boosted by adsorbed H₂SO₄.     

Possibility of methane decomposition in a gas discharge

The possibility of using a gas discharge such as a corona discharge or a barrier discharge for decomposition of methane in different gaseous mixtures is investigated theoretically. The effect of preheating of the gas to a temperature of 1200 K on the degree of methane conversion in the discharge is studied. A kinetic model that describes the processes of methane decomposition and oxidation in CH₄/CO₂, CH₄/H₂O, and CH₄/O₂ mixtures is developed. The effect of the discharge parameters and gas additives on the efficiency of methane decomposition is investigated. The optimum temperature of the mixture, particle lifetime, and initial concentration of oxygen for the production of hydrogen molecules are found. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 6, pp. 1016–1023, November–December, 1998.     

Determination of the compressibility factorZ(p,T) of three methane-ethane mixtures using the dielectric constant method

The compressibility behavior of three mixtures of the CH₄ C₂ H₆, system has been investigated experimentally by means of the dielectric constant method. Precise ( ± 1 ppm) measurements of the dielectric constant () as a function of the pressure (P) along one isotherm (T) are combined with the first three dielectric virial coefficients (A,B, andC) in order to obtain accurate values of the molar density (p). The compressibility factorZ=P/( _p RT) was obtained from the measured values ofp,P, andT. The coefficientA, is determined from the measurements of as a function ofP, while the higher-order coefficients (B, andC,) are obtained by an expansion technique. We report the measured values ofZ at 295.15 K up to 12 MPa for three mixtures of CH₄-C₂-H₆ containing, respectively. 9.54, 35.3, and 75.4% (molar) of ethane. Their exact composition was determined by weighing during the mixing process. The first three dielectric virial coefficients and the mixed second dielectric virial coefficient for the CH₄,-C₂, H₆ system agree with the calculated or the literature values within the limits of uncertainties. For the mixture containing 90.46% CH₄+C₂H₆, deviations in compressibility are of the order of 0.4% from GERG.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Virial Coefficients from Burnett Measurements for the R116 + CO<Subscript>2</Subscript> System

PVTx measurements for the R116 + CO₂ system for four isotherms (283, 304, 325 and 346 K) were performed. In total, 16 runs were performed in a pressure range from 5100 to 140 kPa. Seven runs along four isotherms in a pressure range from 3400 to 280 kPa were performed for pure hexafluoroethane (R116), and the second and third virial coefficients were derived. The values of the virial coefficients for CO₂ were adopted from our previous measurements. The second and third virial coefficients along with the second and third cross-virial coefficients were derived from the mixture results. The Burnett apparatus was calibrated using helium. The experimental uncertainty in second and third virial coefficients was estimated to be within ±2 cm³· mol^–1 and ±500 cm⁶ ·mol ^–2, respectively.     

Effects of enhanced nucleation on the growth and thermal performance of diamond films deposited on BeO by hot filament CVD technique

A method of controlling the feeding concentration of methane was applied in a hot-filament chemical vapor deposition (HFCVD) in order to improve the nucleation of diamond on the beryllium oxide substrates. The nucleation density and the morphologies of diamond were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) while the thermal conductivities of substrates and the composites were detected by laser-diathermometer. The results show that the diamond thin film is in larger grain size with lower roughness when CH₄ and H₂ enter the chamber, respectively, rather than as a mixture, and the composites’ conductivity soared by 21%–31% compared with BeO substrates. At the conditions of separated gas entry, several projects with changes of the CH₄ flux during depositing were designed to discuss the influence of CH₄ concentration on diamond nucleation. The uniform and compact diamond thin films were acquired when the ratio of CH₄:H₂ at nucleation stage was in the range of 4%–8%.     

Reduced Interface‐Mediated Recombination for High Open‐Circuit Voltages in CH3NH3PbI3 Solar Cells

Perovskite solar cells with all‐organic transport layers exhibit efficiencies rivaling their counterparts that employ inorganic transport layers, while avoiding high‐temperature processing. Herein, it is investigated how the choice of the fullerene derivative employed in the electron‐transporting layer of inverted perovskite cells affects the open‐circuit voltage (V_OC). It is shown that nonradiative recombination mediated by the electron‐transporting layer is the limiting factor for the V_OC in the cells. By inserting an ultrathin layer of an insulating polymer between the active CH₃NH₃PbI₃ perovskite and the fullerene, an external radiative efficiency of up to 0.3%, a V_OC as high as 1.16 V, and a power conversion efficiency of 19.4% are realized. The results show that the reduction of nonradiative recombination due to charge‐blocking at the perovskite/organic interface is more important than proper level alignment in the search for ideal selective contacts toward high V_OC and efficiency.     

Effects of oxygen on multiwall carbon nanotubes growth by PECVD

Multiwall carbon nanotubes (MWCNTs) were grown by dielectric barrier discharge (DBD)-type plasma enhanced chemical vapor deposition (PECVD) method in downstream. The temperature was 973 K and the compositions of gases were methane, hydrogen and oxygen in the total pressure of 0.05 MPa. The effect of O₂ concentration in the mixture on the configuration of carbon nanotubes (CNTs) was investigated in detail. Results from scanning electron microscope (SEM) and transmission electron microscope (TEM) showed that CNTs grown in CH₄/H₂ (38.6%/61.4%, volume) mixture have many defects and contained disordered graphitic materials. With the addition of appropriate amount of O₂ (∼0.67%), high-purity CNTs could be obtained. However, no CNT, even no carbon matrix existed under the condition of an excessive oxygen concentration (>1.0%, volume) in the mixture. In order to understand the role of O₂ during CNTs growth, optical emission spectroscopy (OES) was in-situ employed and the results predicted that the improvement of CNTs quality in O₂ addition was attributed to the effect of OH oxidation from the reaction of atomic oxygen with hydrogen in the plasma.     

Two-step growth of high-quality nano-diamond films using CH4/H2 gas mixture

Diamond films with fine grain size and good quality were successfully deposited on pure titanium substrate using a novel two-step growth technique in microwave plasma-assisted chemical vapor deposition (MWPCVD) system. The films were grown with varying the methane (CH₄) concentration at the stage of bias-enhanced nucleation (BEN) and nano-diamond film deposition. It was found that nano-diamond nuclei were formed at a relatively high methane concentration, causing a secondary nucleation at the accompanying growth step. Nano-diamond film deposition on pure titanium was always very hard due to the high diffusion coefficient of carbon in Ti, the big difference between thermal expansion coefficients of diamond and Ti, the complex nature of the interlayer created during diamond deposition, and the difficulty in achieving very high nucleation density. A smooth and well-adhered nano-diamond film was successfully obtained on pure Ti substrate. Detailed experimental results on the synthesis, characterization and successful deposition of the nano-diamond film on pure Ti are discussed.     

Study of the law of corresponding states of viscous properties of classical liquids

The law of corresponding states is studied for the coefficients of shear η* _S and volume η* _V viscosities of classical liquids (Ar, Kr, Xe, O₂, N₂, CH₄); the analytical expressions are derived on the basis of kinetic equations for one- and two-particle distribution functions. The reduced iso-frequency coefficients Φ(|r|) and g(|r|) for liquid Ar, Kr, Xe, O₂, N₂, and CH₄ are numerically calculated in a wide range of variations at the reduced temperatures T* and densities ρ*, which satisfy the law of corresponding states, at a definite choice of the intermolecular interaction potential η _S * and radial distribution function η _V *.