Journal of Phase Equilibria and Diffusion

A probe has been developed to determine the solubility of hydrogen in metals. The method is based on mass balance and high-pressure hydrogen produced in situ partitioning between a zirconium probe and the metal. As an example, the solubility of hydrogen in copper, SH in Cu, has been determined between 350 and 450 °C: $$ S_{\text{H\,in\,Cu}} = (1000 \pm 200)\exp \left( { - \frac{43000 \pm 1300}{RT}} \right){\text{ [mol H}}_{2} /{\text{m}}^{3} \sqrt {\text{MPa}} ]. $$ This solubility agrees with permeation and diffusivity measurements spanning 10 and 6 orders of magnitude, respectively.

The processes taking place during supersaturation of the Al-4.7mass%Cu alloy have been studied by the methods of quantitative metallography and dilatometry. The grain growth activation energy was about 95 kJ/mol, and the exponent of time, n, was close to 0.4. Dissolution of precipitates caused two-stage shrinkage of the sample, which had activation energies of 90 kJ/mol (first stage, n=0.8) and 63 kJ/mol (second stage, n=0.4). The kinetics of the phase transformation during aging of the Al-4.7mass%Cu alloy has been studied by the dilatometry and differential thermal analysis The activation energy of the precipitation processes within the range of 50–320 °C varied between 50 and 100 kJ/mol and confirmed the results obtained previously. For the precipitation processes within the range of 320–462 °C, the activation energy varied from 226 to 300 kJ/mol. The results obtained were compared with literature data with good agreement.

The solid-liquid equilibria of the ternary system H2O-Cu(NO3)2-Al(NO3)3 were studied by using a synthetic method based on conductivity measurements. Five isotherms between 10 and 50 °C were established and stoichiometric phases which appear are, respectively: At 10 and 20 °C: Al(NO3)3·9H2O and Cu(NO3)2·6H2O. At 30, 40, and 50 °C: Al(NO3)3·9H2O and Cu(NO3)2·3H2O.

The thermodynamic properties of the HoRhO3 were determined in the temperature range from 900 to 1300 K by using a solid-state electrochemical cell incorporating calcia-stabilized zirconia as the electrolyte. The standard Gibbs free energy of formation of orthorhombic perovskite HoRhO3, from Ho2O3 with C-rare earth structure and Rh2O3 with orthorhombic structure, can be expressed by the equation; $$ \Updelta G_{{{\text{f}}({\text{ox}})}}^{ \circ } \left( { \pm 78} \right)/({\text{J}}/{\text{mol}}) = - 50535 + 3.85\left( {T/{\text{K}}} \right) $$ Using the thermodynamic data of HoRhO3 and auxiliary data for binary oxides from the literature, the phase relations in the Ho-Rh-O system were computed at 1273 K. Thermodynamic data for intermetallic phases in the binary Ho-Rh were estimated from experimental enthalpy of formation for three compositions from the literature and Miedema’s model, consistent with the phase diagram. The oxygen potential-composition diagram and three-dimensional chemical potential diagram at 1273 K, and temperature-composition diagrams at constant oxygen partial pressures were computed for the system Ho-Rh-O. The decomposition temperature of HoRhO3 is 1717(±2) K in pure O2 and 1610(±2) K in air at a total pressure p o = 0.1 MPa.

Thermodynamics of critical phenomena in a system is well understood in terms of the divergence of molar quantities with respect to potentials. However, the prediction and the microscopic mechanisms of critical points and the associated property anomaly remain elusive. It is shown that while the critical point is typically considered to represent the limit of stability of a system when the system is approached from a homogenous state to the critical point, it can also be considered to represent the convergence of several homogeneous subsystems to become a macro-homogeneous system when the critical point is approached from a macro-heterogeneous system. Through the understanding of statistic characteristics of entropy in different scales, it is demonstrated that the statistic competition of key representative configurations results in the divergence of molar quantities when metastable configurations have higher entropy than the stable configuration. Furthermore, the connection between change of configurations and the change of information is discussed, which provides a quantitative framework to study complex, dissipative systems.

The parameters of nuclear γ resonance (Mössbauer) spectra on 119mSn nuclei inserted into grain boundaries of polycrystalline Nb have been determined at the annealing temperatures of 680 to 994 K [0.25–0.36 melting temperature (T m)]. Two components are observed in the nuclear emission γ resonance spectra at all of the annealing temperatures considered. One of them (component 1) is suggested to result from the 119mSn atomic probes localized in grain boundary cores, while the other one (component 2) corresponds to that located in the near-boundary areas. Diffusion annealing temperature dependences of both components parameters have been analyzed. The coefficients and enthalpy of Sn grain-boundary segregation are determined based on this analysis, as well as the ratio of the diffusion pumping zone extension to the grain boundary width and the enthalpy of the atomic probes “pumping” from grain boundaries into the bulk.