A theory of the heat of solution of hydrogen in simple metals is developed and results are presented for the cases of aluminum and magnesium. The electronic contribution to the heat of solution is treated within the framework of local pseudopotential theory and is based on linear screening. For the proton contribution it is necessary to use nonlinear theory for the screening of the proton and a convenient framework for this is the density functional formalism with exchange and correlation corrections included approximately. The calculated value of the heat of solution for aluminum is 0,45 eV which compares favorably with the experimental value of 0.66 eV. The result for magnesium, -0.05 eV, is also in reasonable agreement with the experimental value of 0.25 eV bearing in mind that the hydrogen heat of solution is obtained as the difference of two energies of about 15 eV. The energy has also been investigated as a function of the position of the proton in the lattice.Calculated energy barriers are used to estimate proton diffusion parameters.
I. INTRODUCI'IONMost simple metals dissolve hydrogen only in very small quantities.For example, the metals which are the subject of this investigation, namely Mg and Al, dissolve about 700 parts per million atomic and 1 (ppma), respectively, of hydrogen at Btomospheric pressure near their melting points. In spite of the small quantities dissolved, hydrogen in metals is of practical interest because of problems that arise in manufacturing processes. One example is the formation of gas bubbles in the metal after solidification due to dissolved hydrogen. ' In the ease of Al, bubbles form near the surface and lead to blistering.Hydrogen-metal systems are also of interest because hydrogen is dissociated upon solution and leads to the simplest possible impurities. The H' ion, the proton, is a point charge for our purposes with no complicating core electron structure. However, from a theoretical point of view, there are difficulties in treating this impurity because the proton-electron interaction is very strong and cannot be substituted by a weak potential with the same scattering properties. This replacement is the foundation of the pseudopotential method which allows us to treat the properties of simple metals by perturbation theory.Apart from the relevance to hydrogen-metal systems, the behavior of a heavy particle with unit positive charge in a metal is also relevant to the positive p. meson which has recently been used as a solid-state probe.~The p, meson with a mass of about 200 electron masses will interact with the ions and electrons of a metal in an identical way to the proton and will differ only in its vibration motion. Apart from negligible effective-mass eorreetions, the heats of solution, migration energies for diffusion, and the like will be the same for the proton and positive p. meson, but an important difference will be the larger effective jump frequency of the p meson. The diffusion coefficient for the p meson will be larger than for the proton by a, factor of a...
Fast-neutron irradiation damage at 1.74 °K and its recovery to 100 °K have been investigated in Al and Au by means of residual electrical resistivity measurements. The effects of impurities, quenched-in vacancies, and dislocations were studied. It was found that the damage rate of Al was unchanged by impurity concentrations of less than 0.5 at. % and quenched-in vacancy concentrations of less than 0.002 at. %. Dislocation concentrations of ~2 × 1010/cm2 in Al and ~1011/cm2 in Au increased their damage rates by 35%and 50% respectively. Small amounts of impurity (~0.02 at. %) in Au increased its damage rate by 15% and suppressed the enhancement caused by deformation. The stage I recovery of Al and Au was only slightly increased by extra dislocations, but was increased considerably by quenched-in vacancies. An impurity concentration of ~0.5 at. % suppressed the stage I recovery of Al, but not that of Au. The results are interpreted in terms of channeling in Al and collision chains in Au.
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