Phase behavior of mixtures at very high pressures

The invention of the diamond anvil cell (DAC) has been an enormous stimulus to high-pressure research. This technique has only recently been used to investigate the behavior of binary systems, probably because of the extra experimental problems which arise in the study of mixtures. It will be shown that a variety of aspects of the behavior of the mixture can, nevertheless, be studied under extreme conditions. Although the first investigations were carried out only recently, some very interesting results have already been obtained. A variety of two-components systems has been studied, e.g., He-Kr, Ne-Xe, He-H₂, NH₃-H₂O, and N₂-He₂. Some of these results are discussed. Finally, a comparison is made between experimental results and theoretical calculations.Invited paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Thermal conductivity of argon and argon-neon mixtures at high temperature

The thermal conductivity of neon and argon-neon mixtures is studied in the temperature range 400–1500°K. This is the first recording of such data above 793°K.Notation T_g true temperature drop in gas layer °K - ¯T temperature, °K, Q, effective thermal flux, W - Q_t, Qr thermal flux transmitted by thermal conductivity and radiation, respectively, W - T_sh correction for temperature shift, % - thermal conductivity of gas mixture, W/m·°K - x_i a molar concentration of neon - _i, _i, _ij, _ij potential function parameters for inter molecular interaction of homogeneous and inhomogeneous molecules - slope of exponential repulsion term Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 5, pp. 848–856, November, 1977.     

Viscosity of mixtures of fluoroalcohols and water at high pressures

Viscosities of aqueous solutions of 2,2,2,-trifluoroethanol, 2,2,3,3-tetrafluoropropanol and 2,2,3,3,3-pentafluoropropanol have been measured with a falling-body viscometer. Measurements were performed at temperatures from 298 to 323 K and at pressures up to 80 MPa with an estimated uncertainty of ±2%. Viscosities obtained for these mixtures are represented by a simple empirical equation within the experimental uncertainty. The composition dependence of the viscosity is compared with that for mixtures of hydrocarbon alcohols and water.Paper dedicated to Professor Joseph Kestin.     

Study of plasma-solid interaction in electronegative gas mixtures at higher pressures

Surface treatment at higher pressures has become an important issue of plasma science and technology. The analysis of processes in such plasmas is now often based on computer modelling; however, the main problem of simulation in medium and higher pressures is the increasing number of collisions among plasma particles and because of this, decreasing efficiency of simulations. A combination of experimental and computational approaches was used for the study of this problem in the present work. The measurements were performed in the positive column of a DC glow discharge in oxygen, both pure and in mixtures with rare gases, at medium pressures. These experiments were completed by computer simulations, where an attempt was made to extend the particle simulation technique to higher pressures. It was shown that the standard Particle-In-Cell/Monte Carlo simulation technique loses its applicability at higher pressures and must be replaced by more sophisticated computational methods. In the present work new algorithms for particle treatment in plasma at higher pressures were suggested and successfully tested.     

Volumetric properties of mixtures of fluoroalcohols and water at high pressures

Densities of aqueous solutions of 2,2,2-trifluoroethanol, 2,2,3,3-tetranuoropropanol, and 2,2,3,3,3-pentanuoropropanol have been measured with a vibrating-tube densitometer. Measurements were performed at temperatures of 298 and 323 K and at pressures up to 80 MPa with an estimated uncertainty of ±0.2 %. Molar volumes obtained for these mixtures are correlated with pressure by the Tait equation within the experimental uncertainty. Excess molar volume, isothermal compressibility, and partial molar volume of these mixtures are determined in terms of this correlation equation and compared with those of the aqueous solutions of hydrocarbon alcohols. Composition dependence of partial molar volume is discussed in comparison with that of Raman spectroscopic data.     

Acoustic velocity in and density of binary helium-argon mixtures

The acoustic velocity in four different mixtures of the helium-argon system and the specific volume of two different mixtures of this system were measured over the 298.16–473.16°K temperature range under pressures from 50 to 400 MPa.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 6, pp. 1090–1094, December, 1980.     

Features of nucleation kinetics in vapor-gas mixtures at increased pressures of gas

The kinetics of nucleation in a vapor-gas mixture at increased pressures of the gas-ballast (at Knudsen numbers determined from the radius of a critical nucleus below unity) is theoretically investigated. Interpolation expressions for the nucleation rate at arbitrary Knudsen numbers are obtained.Academic Scientific Complex A. V. Luikov Institute of Heat and Mass Transfer of the Academy of Sciences Belarus, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 64, No. 5, pp. 577–582, May, 1993.     

Volumetric properties of mixtures of 1,4-dioxane and water at high pressures

Densities of aqueous of 1,4-dioxane have been measured at temperatures from 298 to 348 K and at pressures up to 40 MPa by a vibrating-tube method. Molar volumes obtained with an estimated uncertainty of ±0.2°,% are correlated with pressure by the Tait equation within the experimental uncertainty. Pressure and composition dependences of the excess molar volume, partial molar volume, and isothermal compressibility are determined and they are compared with those of other aqueous solutions.     

Heat-conduction coefficient of gas mixtures at high densities

An approximate formula is obtained to compute the heat-conduction coefficient of multicomponent dense gas mixtures.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 48, No. 3, pp. 418–424, March, 1985.     

Premelting of iron at high pressures under conditions of contact with amorphous argon

Experiments involving shock-wave loading systematically produce higher melting temperatures than those obtained in experiments involving the use of diamond anvils (DAC). The melting temperature in DAC experiments is determined by structural changes on the surface of a solid in contact with another substance (for example, with argon). We use the method of molecular dynamics to investigate the process of iron melting from the surface in single-component and two-component (in the presence of argon as medium) cases at pressures of ～100 GPa. In the argon-iron two-component model aimed at reproducing the conditions of static DAC measurements, premelting is observed at a temperature below T _m . The layer of iron adjacent to argon may make a transition to disordered state under certain conditions. The temperature interval at constant pressure, in which this effect is observed, is comparable in magnitude with the difference between the melting temperatures obtained as a result of dynamic and static measurements. Therefore, this effect may be one of the reasons for discrepancy between the experimental results for the melting curve of iron and other metals.     

Isotope effects on fluid-fluid separation of H2-He mixtures at high pressures

The fluid-fluid phase separation of H₂-He mixtures has been studied theoretically at 100 K. It is found that phase separation is promoted by heavier helium isotopes or by lighter hydrogen isotopes. This can be accounted for by a simple size analysis of the components.     

Ultrasonic speed in mixtures of monochlorodifluoromethane and monochloropentafluoroethane under high pressures

The ultrasonic speed u of [(1 -) CHClF₂(1) + C₂ClF₅(1)] including the azeotropic mixture [CHClF₂(1) + C₂ClF₅(1)] was measured at pressures up to 51 MPa within the temperature range 283.15 to 373.15 K, using a sing-around technique operated at a frequency of 2 MHz with an estimated uncertainty of less that ±2.4 m·s^–1. For = 0.1537 and 0.6268, measurements of the vapor pressure are also reported.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

The thermal conductivity of pure nitrogen and of mixtures of nitrogen and carbon dioxide at elevated temperatures and pressures

The thermal conductivities of nitrogen at 470 K and six mixtures of nitrogen and carbon dioxide at various temperatures have been measured as a function of pressure up to 25 MPa. The mixtures were measured at the following temperatures: one at 302 K, three at 380 K, one at 430 K, and one at 470 K. The data were used to test three prediction methods for the thermal conductivity of gas mixtures under pressure. Surprisingly good agreement was found with predictions using the corresponding-states method of Ely and Hanley. The predictions of the more theoretically based method of Mason et al. were low throughout, due partly to its use of the Hirschfelder-Eucken equation as the low-density limit, but also because the predicted density dependence rises too slowly. The simplified version of this method proposed by Svojskij gave slightly worse predictions, particularly at higher densities. The zero- density results for nitrogen are examined by comparing the zero-and first-density coefficients with the trends shown at lower temperatures.     

Gas scattering effects and microstructural evaluation of electron beam evaporated titanium coatings in neon and argon at different gas pressures

Titanium coatings were deposited on stainless steel and glass substrates by electron beam evaporation in vacuum (4×10⁻⁴ Pa) and at different neon and argon gas pressures (from 0.33 to 2.00 Pa). The effect of background gas pressure and type on film microstructure was evaluated by scanning electron microscopy (SEM). Since it was not feasible to maintain a constant evaporation rate for all runs, the ‘deposition efficacy’, a parameter defined as the ratio between coating thickness and mass of material evaporated, was statistically modelled using non-linear regression analysis to determine the effects of gas scattering. The results revealed that neon and argon promote similar scattering of the titanium vapour and this may point to a lower likelihood of gas-phase metal cluster formation in neon. The coating microstructure was found to change from a tapered grain structure, obtained under vacuum conditions, to a faceted one at low gas pressure (0.33 Pa), becoming more porous as gas pressure increased. For a given gas pressure, no significant differences could be observed in coating microstructure between the use of argon or neon. These findings may be significant when considering the use of neon as an alternative gas to argon, for improving reactive gas ionisation (through Penning mechanisms) in Plasma-Assisted Physical Vapour Deposition.     

Surface desublimation of carbon dioxide from binary gas mixtures

The results of an experimental investigation of the time evolution of the main characteristics of the process of surface desublimation of carbon dioxide from N₂-CO₂ and He-CO₂ gas mixtures are given.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 6, pp. 965–970, December, 1986.