Thermodynamic Stability Limit Research Articles

Role of microwave oxygen plasma in the low-temperature growth of HoBa 2Cu 3O x thin films

The oxidizing activity of ECR oxygen plasma is investigated by evaluating the oxidation state of the HoBa 2Cu 3O χ (HBCO) thin films annealed in this plasma. The conditions under which these films grow and under which they are thermodynamically stable were determined in molecular oxygen and in oxygen plasma. The oxidizing activity of oxygen plasma is equivalent to that of molecular oxygen at a pressure three orders of magnitude higher. Oxygen plasma expands the thermodynamic stability limit toward higher temperatures and the oxidizing activity limit toward lower oxygen pressures.

Mechanism of formation of diamond crystals in iron-carbon alloys

In accordance with the phase diagram of carbon the graphite {r_arrow} diamond polymorphic trans-formation is possible at a pressure of {similar_to}130 kbar and temperature of {similar_to}1200{degrees}C. However, in the presence of iron the processes of formation of diamond from graphite and a number of non-graphite forms of carbon (soot, coke, carbon glasses, etc.) occur even at a pressure of 40-60 kbar, that is, in the area of thermodynamic stability of graphite. The physicochemical nature of the processes leading to formation of diamond crystals under these conditions i still not clear. Nevertheless it is assumed that in the given case polymorphic transformation of graphite into diamond, on which iron has some catalytic action causing a decrease in the necessary pressure within the limits of thermodynamic stability of diamond, occurs. A number of hypotheses have been proposed. 9 refs., 3 figs.

Thin Film Growth of High Tc Superconductors by Microwave Plasma Assisted Reactive Evaporation

ABSTRACTThe oxidizing activity of an oxygen plasma is investigated in terms of the oxygen content of HoBa2Cu3Ox. thin films. The thermodynamically stable region of HoBa2Cu3Ox. and the region where the HoBa2Cu2Ox films are formed are also determined both in molecular oxygen and in an oxygen plasma. The oxidizing activity of an oxygen plasma is equivalent to that of molecular oxygen at three orders of magnitude higher pressure. The oxygen plasma expands the thermodynamic stability limit toward higher temperatures and the oxidizing activity limit toward lower oxygen pressures. In addition, the interfacial reaction between an oxide superconductor and silicon is investigated. The oxygen ions in HoBa2Cu3O film diffuse into Si even at room temperature, probably enhanced by the strong affinity of silicon for oxygen ions.

Thermodynamic investigation of the phase separation behaviour of ethylene‐vinyl acetate copolymers in diphenyl ether

AbstractLiquid‐liquid phase separation in solutions of ethylene‐vinyl acetate (EVA) random copolymers is investigated for different VA content using diphenyl ether (DPE) as the solvent. Cloud‐point curves (CPC's), spinodal curves (SC's) and critical conditions (CC's) were experimentally established by visual observation, pulse‐induced critical scattering (PICS) and phase‐volume ratio method, respectively. It is found that the miscibility gap, which is of the Upper Critical Solution Temperature (UCST) type, shifts to lower temperatures as the VA content in the copolymer increases. The limits of thermodynamic stability (spinodals) could be reasonably well described by means of the classical rigid lattice model, provided allowance is made for the various constitutional repeating units (CRU's) to differ in nearest‐neighbour contacts. Using this description, CC's and SC's could be predicted in a qualitative way. Further, measured CPC's can be nearly described in a quantitative sense when the value of the higher molecular weight average M̄z is adjusted well above the value suggested by GPC measurements.

Thermodynamic incompatibility of the 11S fraction of soybean globulin and pectinate in aqueous medium

The phase analysis method was used to determine a binodal curve in the system comprising soybean globulin (glycinin), pectinate (degree of esterification 58%), water ( I = 0.3 mol/dm 3 NaCl, pH 8.0, 0.01 mol/dm 3 mercaptoethanol). The coordinates of the critical point and the threshold of phase separation were deduced from experimental results. The thermodynamic parameters of pah-interaction (the second virial coefficients A 12, A 14, A 24 and Flory's interaction parameters χ 12, χ 14, χ 24) were estimated using elastic light scattering data. The limit of thermodynamic stability of the system (spinodal curve) and the coordinates of the critical point were calculated assuming the virial expansion to be limited by the second virial coefficient. Experimental data were in good agreement with calculated results. Due to the different affinity of these biopolymers to the solvent (χ 12 ≠ χ 14; Δ χ, effect) the distribution of solvent in two equilibrium phases was in favour of the phase that was richer in the polymer that exhibited the higher solvent-polymer interaction (the phase of the pectinate).

Liquid-film instabilities in confined geometries.

Sol-gel methods combined with specific thermal treatments were used to fabricate porous glasses with extremely uniform pore diameters and high internal surface areas. Low-temperature adsorption isotherm measurements reveal the dynamic and thermodynamic stability limits of the liquid films as a function of evolving pore diameter. Contrary to classical predictions, the results are in remarkable agreement with a universal hydrodynamic theory of film behavior which includes substrate interactions.

Thermodynamic Modeling of Quaternary Systems: Oil/Brine/Surfactant/Alcohol

Abstract Surfactant flooding for EOR results in multiphase oil/brine/surfactant/alcohol mixtures. Because alcohol and surfactant do not partition among the phases in constant proportion, thermodynamic modeling of quaternary systems is necessary in an accurate treatment of phase equilibria in these systems. We describe here the quaternary version of a free-energy-based equation of state (EOS). The systematic computation of phase equilibria in a quaternary system begins on the binary edges and ternary faces and proceeds by numerical continuation through the higher dimensional composition space. We expedite the computation with knowledge of the limits of thermodynamic stability—the spinodal surfaces—and all critical points that lie on those surfaces. This preliminary calculation indicates those regions in which solution of the nonlinear equations of phase equilibria will suffer from slow numerical convergence. Multiphase equilibria are searched out by both parametric and compositional continuation. The results provide the basis for understanding the trends of three- and four-phase equilibria in oil/brine/surfactant/alcohol mixtures.

Single‐Crystal Elastic Constants of Yttria‐Stabilized Zirconia in the Range 20° to 700°C

Elastic constants of single crystals of yttria‐stabilized zirconia were determined through the temperature range 20° to 700°C. Crystals containing 8.1, 11.1,12.1, 15.5, and 17.9 mol% Y203were measured. The elastic constant C11 was found to decrease and C12 and C44 to increase with increasing Y2O3 content; this appears to be due to decreasing coulombic interaction as Y3+ replaces Zr4+. Except for the 8.1 mol% Y2O3 crystal, the conventional elastic constants all showed normal monotonic decreases with increasing temperature. In the case of the 8.1 mol% Y2O3 crystal, measurements as a function of temperature were not reproducible, and it is likely that this composition at room temperature is below the composition limit of thermodynamic stability of the cubic fluorite phase.

Power Law Behavior of the Pressure Dependence of Expansivity in the Liquid Hexane as a Model for Liquids. Limit of Thermodynamic Stability

ABSTRACTIn this work a power lay is used to fit the isothermal pressure dependence of the expansivity α = V−1(∂V/∂T)p of liquid hexane. This functional form is also observed to fit the expansivity and the isothermal compressibility KT = −V−1(∂V/∂P)T data of the three liquids : hexane, argon, carbon dioxide.

Electric-field-induced nucleation: a phenomenon used for determining the boundary of stability of liquids

The limit of absolute thermodynamic stability and tensile strength of liquids (n-hexane, n-pentane and iso-pentane) have been determined using the phenomenon of electric-field-induced nucleation. An extrapolation of the curves of critical voltage applied to the liquid against temperature to the points of zero critical voltage gives the limiting value of the superheat temperature at a given pressure. The locus of these limiting values in the p-t plane, terminating at the critical point, gives the boundary of absolute thermodynamic stability (spinodal) of the liquid. The electrical forces at the interface corresponding to various critical voltages have been proposed to give the limiting negative pressures (tensile strengths). The energy contributed by the electric field over the volume of a vapour nucleus of critical size is in agreement with the value of the thermal energy required for the formation of the nucleus of the same size de novo in a liquid.

Excitation Spectrum and Thermodynamic Properties of Liquid Films in Cylindrical Pores

We examine the dynamic and thermodynamic properties of adsorbed liquid films in cylindrical cavities. We find a dynamical stability limit for the thickness of films adsorbed uniformly on the walls. This limit is shown to coincide with a thermodynamic stability limit which depends on both substrate and capillary forces. The Kelvin equation describing capillary condensation is generalized to include the substrate interaction. The low-temperature properties of the films are calculated.

Design and development of a bubble chamber technique for the study of electric-field induced nucleation in liquids

A description is given of a method for the study of electric-field induced nucleation (phase transition) in liquids. The device used is a miniature bubble chamber in which intense electric stress is applied to the liquid by means of a sharp edge of thin ( approximately 10-5 cm), transparent and highly conducting film of tin oxide. A capacitor manometer has been used for the dynamic pressure measurements. The change in scattered light intensity from the liquid at 90 degrees to the incident light is utilized as an indication of the nucleation. The instantaneous pressure, scattered light intensity and the instant of the application of the electric field are registered simultaneously on the oscilloscope. Typical sets of results are shown at different temperatures and pressures for three organic liquids namely n-hexane, n-pentane and iso-pentane. The extrapolation of these results to the zero value of external electric field gives the limit of thermodynamic stability of the liquids. The results thus obtained are compared with those obtained from kinetic and Furth's theories of liquids.

Determination of the limit of absolute thermodynamic stability of liquid using external electric fields as perturbation

A relationship between the pressure and temperature of superheated liquid n-hexane and the critical electrostatic field required for inducing nucleation in it is obtained experimentally. This relation is used for the determination of the limit of stability of the liquid.