Role of point defects in self-diffusion along low-angle twist boundaries in fcc metals: A molecular dynamics study

The interaction of point defects with low-angle (100), (110) and (111) twist boundaries in fcc metals Ni, Cu, Al and role of the point defects in self-diffusion along considered boundaries were studied by the molecular dynamics method. The binding energies of point defects with low-angle twist boundaries were calculated. It was found that the point defects are mainly fixed in the nodes of grain-boundary screw dislocations network. It was shown that the introduced vacancies play an important role in diffusion along twist grain boundaries. The contribution of introduced interstitial atoms to grain-boundary diffusion under thermodynamic equilibrium condition is less by several orders of magnitude in comparison with the contribution of vacancies.

A GENERAL RELATIVISTIC THOMAS FERMI TREATMENT OF NEUTRON STAR CORES II: GENERALIZED FERMI ENERGIES AND BETA EQUILIBRIUM

We formulate the set of self-consistent ground-state equilibrium equations of a system of degenerate neutrons, protons and electrons in beta equilibrium taking into account quantum statistics, electro-weak, and strong interactions, within the framework of general relativity. The strong interaction between nucleons is modeled through sigma-omega-rho meson exchange in the context of the extended Walecka model, all duly expressed in general relativity. We demonstrate that, as in the non-interacting case, the thermodynamic equilibrium condition given by the constancy of the Fermi energy of each particle-specie can be properly generalized to include the contribution of all fields.

Pressure Gradient Variations During Reflux Condensation in a Closed Thermosyphon

The heat and mass transfer in the condenser region of a variable conductance thermosyphon, consisting of two components (R11 + R113) has been studied and special attention has been devoted to pressure drop during reflux condensation. The mass, energy, and species conservation equations in conjunction with the overall mass conservation and continuity of momentum at liquid-vapor interface constraints and the thermodynamic equilibrium condition have been solved numerically by use of the integral method. In contrast to the flat-front model which assumes a sharp interface between the active and shut-off portions in a variable conductance thermosyphon, in this paper a continuous model has been used. In this model a continuous variation of physical properties with condensation of both components along condenser is assumed. The results of the present study have been compared with available numerical and experimental results of other investigators and pressure gradient profiles have been achieved. A calculation of the frictional, accelerational and gravitational components of the pressure drop shows that the gravitational component has the greatest magnitude due to the relatively high density of the vapor.

Aluminium corrosion studies. IV. Pitting corrosion

Measurements are reported for the variation of the open-circuit potential, Er, of aluminium in oxygen-saturated sodium salt solutions. The value of Er was independent of SO42- and NO3- concentrations and similar to the value obtained for water (0.04 (s.h.e.)). Er was a function of chloride concentration given by ������������������� Er = -0.475-0.060log[Cl-] V (s.h.e.) at 25�C. There was a less well defined relationship between Er and NO2-, I- and Br-, and a complex relationship with F-. ��� The potentiodynamic characteristics are reported for aluminium in 1-0.01 mol l-1 Cl- oxygen-saturated solutions. Functional relationships were found for E0, Ep, Es and E0' with chloride activity at 5, 25, 50 and 75°C. Hysteresis effects are reported. ��� The experimental results are interpreted in terms of a thermodynamic equilibrium condition between the surface oxide and soluble aluminium chloride. As the system oscillates across the equilibrium conditions the surface will passivate or pit. A critical bulk solution chloride concentration is necessary to maintain the growth of the pit; the experimental value was 1.6 mol l-1 Cl- and the corresponding open-circuit potential was Ecrit = -0.48 V (s.h.e.). The pitting potential, Ev, was interpreted as an overpotential, ηp, given by η = Ep,- Ep-Ecrit.

Steady Two-Dimensional Heat and Mass Transfer in the Vapor-Gas Region of a Gas-Loaded Heat Pipe

A numerical analysis is made of the steady two-dimensional heat and mass transfer in the vapor-gas region of a gas-loaded heat pipe. Consideration is given to a cylindrical heat pipe with typical evaporator, condenser, and noncondensible-gas sections and with negligible axial conduction through the wall and the liquid-wick matrix. The elliptical mass, momentum, energy, and species conservation equations have been solved in conjunction with the overall energy and mass conservation constraints and the thermodynamic equilibrium condition for three heat pipe cases with different working fluids and diameters. The results show that in certain gas-loaded heat pipes, such as liquid-metal heat pipes, vapor-gas diffusion and two-dimensionality must be considered in the analysis. Extension of the present numerical framework to more general cases such as including the axial wall conduction is indicated.