Thermodynamic study of mixtures containing oxygenated compounds

Excess volumes, V^E, isentropic compressibility deviations, Δκ_S, and excess enthalpies, H^E, of 1-butanol or 2-butanol with tetrahydrofuran have been determined at the temperatures 283.15 K, 298.15 K and 313.15 K, for 2-butanol H^E are also given at 290.15 K and 305.15 K. A brief discussion of the results is given in terms of molecular interactions.     

Thermodynamic analysis of the quantum critical behavior of Ce-lattice compounds

A systematic analysis of low-temperature magnetic phase diagrams of Ce compounds is performed in order to recognize the thermodynamic conditions to be fulfilled by those systems to reach a quantum critical regime or, alternatively, to identify other kinds of low-temperature behavior. Based on specific heat (C _m ) and entropy results, three different types of phase diagrams are recognized: (i) with the entropy involved in the ordered phase (S _MO) decreasing proportionally to the ordering temperature (T _MO); (ii) those showing a transference of degrees of freedom from the ordered phase to a non-magnetic component, with their C _m (T _MO) jumps (ΔC _m ) vanishing at finite temperature; and (iii) those ending at a critical point at finite temperature because their ΔC _m do not decrease sufficiently with T _MO, producing an entropy accumulation at low temperature.

Only those systems belonging to the first case, i.e. with S _MO?→?0 as T _MO?→?0, can be regarded as candidates for quantum critical behavior. Their magnetic phase boundaries deviate from the classical negative curvature below T?≈?2.5?K, denouncing monotonic misleading extrapolations down to T?=?0. Different characteristic concentrations are recognized and analyzed for Ce-ligand alloyed systems. In particular, a pre-critical region is identified where the nature of the magnetic transition undergoes significant modifications, with its ?C _m /?T discontinuity strongly affected by the magnetic field and showing an increasing remnant entropy at T?→?0. Physical constraints arising from the third law at T?→?0 are discussed and recognized from experimental results.     

Thermodynamic study on the composition of the gas phase over melts of an aluminum-scandium system

The vapor pressure of the gas phase components over Al-Sc melts was studied. The temperatures and the variation of the enthalpy upon “melt-gas” phase transformations were determined. The simulation was performed in an initial medium of argon at a total pressure of 10⁵ Pa and temperatures T = 1873−4000 K.     

Thermodynamic behavior of the system benzene-ethylene dichloride

The Maron theory of nonelectrolyte solutions has been used to analyze the thermodynamic behavior of the system benzene-ethylene dichloride. Excellent agreement with experiment has been obtained for all the thermodynamic properties involved. The analysis also shows that the interaction parameter for this system is small and positive, but it varies sharply with both concentration and temperature. As a result the system is nonideal and complex in behavior, despite the fact that vapor pressure data would tend to suggest near ideality.     

Thermodynamic assessment of the K-Na and Cr-V system

The assessment of the thermodynamic properties of K-Na and Cr-V molten alloys has been theoretically examined using a simple statistical mechanical model based on pairwise interaction to obtain higher-order conditional probabilities that describe the occupation of the neighbouring atoms in molten binary alloys. The optimised values of order energy ω obtained are used to describe a number of thermodynamic quantities computed for different concentrations in the alloys at 384 and 1550 K, respectively. The study shows that there is a tendency for homocoordination (like atoms pairing as nearest neighbour) in K-Na and the existence of heterocoordination in Cr-V at all concentrations. Thus, the consistency between calculated and reported experimental thermodynamic values enforces the legitimacy of the findings.     

Thermodynamic modelling of the cerium–oxygen system

The published data for the thermochemical properties and phase relationships of the cerium–oxygen system have been critically examined. No major inconsistencies in the experimental database have been found. Thermodynamic model parameters of all phases, i.e., liquid, fcc-Ce, bcc-Ce, A-, H-, and X-Ce₂O_3−x, Ce₃O_5±x (Mn₂O₃-type), CeO_2−x, as well as Ce₁₁O₂₀, Ce₆₂O₁₁₂, Ce₄₀O₇₂, Ce₁₉O₃₄, Ce₉O₁₆, and Ce₇O₁₂ have been derived by the least-squares minimization procedure using Thermo-Calc® software. The models are simple to be compatible with the standard Gibbs energy minimization procedure, but provide enough flexibility to account for the crystal structure, defect chemistry, and thermodynamic properties of phases in the Ce–O system. The backward compatibility of the refined parameters with experimental data has been demonstrated by calculation of phase and property diagrams. The Ce–O phase diagram in the whole range of compositions and at elevated temperature, a complete list of invariant reactions as well as the enthalpy and entropy of formation of Ce_nO_2n −2m phases are presented for the first time.     

Thermodynamic phase diagram of the quantum hall skyrmion system

We numerically study the interacting quantum Hall Skyrmion system based on the Chern-Simons action. By noticing that the action is invariant under global spin rotations in the spin space with respect to the magnetic field direction, we obtain the low-energy effective action for a many-Skyrmion system. Performing extensive molecular dynamics simulations, we establish the thermodynamic phase diagram for a many-Skyrmion system.     

Thermodynamic arrow for a mixing system

The purpose of this paper is to study the appearance of time asymmetry in dynamical systems. The systems are harmonic oscillators and a certain mixing flow on the torus. The asymmetry is a kind of frictional force, but we emphasize that the boundary conditions, a usual source of asymmetry in studies of this sort, are taken to be time symmetric. For the mixing flow the response of the system, as reflected in its entropy as a function of time, occurs only subsequent to the friction, while for the oscillators the effects are both before and after. Some general discussion also takes up the question of which of the foregoing systems is a better model of the physical world for purposes of correlating arrows of time.Work supported in part by U.S. Army Research Office (Durham, N.C.).     

Thermodynamic properties and phase diagram of the graphite-diamond-liquid carbon system

Abstract

We review work performed on a three-phase theoretical carbon equation of state. The algorithm has been used, with good success, in a chemical equilibrium code of mixtures (of solids, liquids, and gasses), in which the gas phase is modeled by a statistical mechanical theory of mixtures. We use simple Grüneisen models for the solid phases and compute the corresponding liquid phases with a “scaling” theory. A modified Lindemann model is used in the scaling theory to predict melting properties. The liquid carbon consists of a mixture of expanded graphitic and diamond-like forms. Terms that describe the electronic energy change of the liquid have been estimated with the INFERNO code. Both experimental and theoretical work has been used to determine the best equation of state parameters. The resulting model yields a phase diagram consistent with all known mutually consistent data. Significant uncertainties still exist in the melting data.     

Thermodynamic properties of a spin half ladder system

A complete dimerized state exists for one kind of two-leg spin half ladders, which has local antiferromagnetic ordering and frustration effect at the same time. The system’s low-lying excitations can be obtained exactly which enables us to calculate thermodynamic quantities such as specific heat and magnetic susceptibility at low temperatures. Our results also show that the subset energy spectrum is a good approximation to the whole spectrum even for the usual two-leg spin half ladder without frustration.     

Thermodynamic stability of equilibrium system and critical state

On the basis of general Gibbs conditions of stability, the requirements of critical state stability that are applied to adiabatic coefficient of stability (ACS) and their derivatives are obtained. The examination of these conditions with critical state definition establishes the existence of four alternative types of critical behaviour of the thermodynamic system. These types are classified by the critical behaviour of ACS and K_C, which is connected with ACS. Analysis of the asymptotic behaviour of adiabatic quantity (AQ), which is consistent with stability requirements, demonstrates that both analytic and nonanalytic behaviours are possible.     

Thermodynamic properties of a spin half ladder system

A complete dimerized state exists for one kind of two-leg spin half ladders, which has local antiferromagnetic ordering and frustration effect at the same time. The system’s low-lying excitations can be obtained exactly which enables us to calculate thermodynamic quantities such as specific heat and magnetic susceptibility at low temperatures. Our results also show that the subset energy spectrum is a good approximation to the whole spectrum even for the usual two-leg spin half ladder without frustration.     

Thermodynamic limit for a system with dipole-dipole interactions

The free energy at constant magnetization of a simple cubic lattice of Ising spins with dipole-dipole interactions in periodic boundary conditions is related to the free energy at constant magnetization with no periodicity. The relationship is not one of equality.     

Thermodynamic magnetization of a strongly correlated two-dimensional electron system

We measure thermodynamic magnetization of a low-disordered, strongly correlated two-dimensional electron system in silicon. Pauli spin susceptibility is observed to grow critically at low electron densities—behavior that is characteristic of the existence of a phase transition. A new, parameter-free method is used to directly determine the spectrum characteristics (Landé g-factor and the cyclotron mass) when the Fermi level lies outside the spectral gaps and the inter-level interactions between quasiparticles are avoided. It turns out that, unlike in the Stoner scenario, the critical growth of the spin susceptibility originates from the dramatic enhancement of the effective mass, while the enhancement of the g-factor is weak and practically independent of the electron density.     

Thermodynamic analysis of the decomposition of a supersaturated solid solution of the Fe-Cu system

The structure of Fe-5.5% Cu alloy is studied after eutectoid reaction and aging of the martensite. The thermodynamic analysis of decomposition of the supersaturated solid solution with copper release is peformed for different types of crystal lattice. The free energy of solid solutions and phase separation diagrams of the BCC and FCC phases of copper is calculated. Barriers for the nucleation of copper particles with BCC and FCC lattices are evaluated. The factors that favor the appearance of intermediate structural forms of copper preceding the formation of stable FCC phase are discussed.     

Thermodynamic stability of interacting fermions system with matrix eigenvalue method

A matrix eigenvalue method is applied to analyse the thermodynamic stability of two-component interacting fermions. The non-relativistic and ultra-relativistic d=1, 2,3 dimensions have been discussed in detail, respectively. The corresponding stability region has been given according to the two-body interaction strength and the particle number density ratio.     

Thermodynamic and kinetic properties of an icosahedral quasicrystalline phase in the Al-Pd-Tc system

The properties of a quasicrystalline phase in the Al-Pd-Tc system are studied for the first time. X-ray investigations demonstrate that the quasicrystalline phase in the Al₇₀Pd₂₁Tc₉ alloy has a face-centered icosahedral quasi-lattice with parameter a=6.514 ?. Annealing experiments have revealed that this icosahedral phase is thermodynamically stable. The heat capacity of an Al₇₀Pd₂₁Tc₉ sample is measured in the temperature range 3–30 K. The electrical resistivity and magnetic susceptibility are determined in the temperature range 2–300 K. The electrical resistivity is found to be high (600 μΩ cm at room temperature), which is typical of quasicrystals. The temperature coefficient of electrical resistivity is small and positive at temperatures above 50 K and negative at temperatures below 50 K. The magnetic susceptibility has a weakly paramagnetic character. The coefficient of linear contribution to heat capacity (γ=0.24 mJ/(g-atom K²)) and the Debye characteristic temperature (Θ=410 K) are determined. The origin of the specific features in the vibrational spectrum of the quasicrystals is discussed. __________ Translated from Fizika Tverdogo Tela, Vol. 42, No. 12, 2000, pp. 2113–2119. Original Russian Text Copyright ? 2000 by Mikheeva, Panova, Teplov, Khlopkin, Chernoplekov, Shikov.