Investigation of diffusion and electromigration of hydrogen in palladium and PdAg alloy

Abstract Diffusion and electromigration of hydrogen in PdH 0.1 , Pd 77 Ag 23 H 0.1 and Pd 50 Ag 50 H 0.1 alloy were measured by means of resistivity method. It is known that hydrogen migrates towards the cathode within the temperature range of 300–473 K in the PdH 0.1 and Pd 77 Ag 23 H 0.1 system. In Pd 50 Ag 50 H 0.1 , hydrogen migrates towards the cathode below 400 K, but towards the anode at higher temperatures. Its effective valency increases together with temperature. At the same time it satisfies the linear dependence on inverse specific resistance ρ : Z eff = Z i +( k / ρ ). The constants Z i and k have the following values: (1.05±0.01) and −(3.81±0.04)×10 −8 Ω m for hydrogen in PdH …

Positron Annihilation in Metals Defected by Action of the Tensile Force

Results of experimental investigations of uniaxially elongated mono- and polycrystalline samples of several metals (Fe, Ta, Pd, Ag, and Au), performed using the positron annihilation methods, are reviewed. The dependences of the S-parameters and positron lifetimes on the relative elongation of the samples were presented. The data obtained for polycrystalline samples indicate that in the proportionality and limited proportionality regions the changes in the physical properties are governed mainly by generation of vacancies and by kinetics of formation and transformations of vacancy clusters occurring flrst of all on the grain boundaries of monocrystallites. In the region of plastic deformati…

Positron Annihilation in Defected Monocrystalline Gold Samples

Angular distribution of the positron annihilation quanta was measured for monocrystalline gold samples, oriented in (110) and (111) directions. The samples were deformed by elongation for different deformation degrees. The S and W parameters as a function of deformation degree of the sample were determined. It was found that the dynamics of the dislocations and vacancy generation during the sliding of some crystallographic planes, depends on the crystallographic direction.

Melting Process of the Sn-45 wt.% In and Sn-77 wt.% In Alloys as Viewed by Positron Annihilation

The temperature dependences of the positron annihilation parameters F and R were determined for Sn–45 wt.% In and Sn–77 wt.% In alloys. The obtained results enabled to verify the vacancy and the quasicrystalline models of the melting process. It was found that for metals transforming into the liquid state from the structures different than the close packed structure, the melting transition are hardly explainable in terms of the vacancy model of melting. The strong trapping of positrons in metallic liquids is an indication of the presence of microvoids (vacancy clusters) or microcrystals containing defects more immense than vacancies. The share of these positron trapping centers in the volum…

Positron Annihilation in Steel Samples Deformed by Uniaxial Tension

Angular distributions of the positron annihilation quanta were measured for steel ST2 SAL samples deformed by uniaxial tension up to difierent deformation degrees. The dependences of the S parameter on the relative elongation of the samples are presented. The positron annihilation data for steel are compared with the results obtained previously for polycrystalline iron samples deformed by uniaxial tension up to difierent deformation degrees in the proportionality and limited proportionality regions.

Positron Annihilation in Deformed and Hydrogenated Pd-23%atcu Alloy

Positron Annihilation in Solid and Liquid Bi40Sn60Alloy

Measurements of Positrons Lifetimes in Corroded Nickel

It is over twenty years now that the nuclear method of conducting investigations into defects in the volume and on the surface of solids, based on positron annihilation phenomenon, has been developing on a quite intensive scale [1-3]. The present work is an attempt at adopting positron annihilation to investigations of the phenomenon of pitting corrosion in metals. Pitting occurs mainly in environments containing chlorides and affects metals and alloys covered with passivating oxide layers. Research carried out for many years by the use of various methods . has proved that pittings, which could — after some time — take sizes as large as the tenth of the millimeter order, are formed in the p…

Positron Annihilation with Electrons of Admixture Atoms in Some Binary Nickel Alloys

Weighted difference curves have been shortly presented as a proper tool allowing to analyze in another way two-detector Doppler spectra regarding positron annihilation with admixture electrons in some nickel alloys. The analysis of low and middle momentum parts of Doppler spectra for investigated alloys reflects the annihilation of positrons with admixture electrons. There is no distinct signal of annihilations with admixture electrons from the positron lifetime data for well-annealed samples.

A two-detector spectrometer for measurements of Doppler broadened positron annihilation spectra

Abstract A two-detector spectrometer for measurements of Doppler broadened positron annihilation spectra has been constructed and tested. The energy difference of the annihilation quanta is measured in the analogue, not in the digital manner. The peak to background ratio in the measured spectra is of the order of 10 6 , the FWHM representing the energy resolution, equals to 1.1 keV , thus enabling the very subtle physical effects to be revealed. Some information on electronic structure of the investigated 3-d metals (Ti, V, Cr, Fe, Ni, Cu and Zn) has been determined using this spectrometer. It has been shown that the apparatus permits to detect the impurity-vacancy pairs in dilute nickel al…

Positron Lifetime in Hostaphan

Positron lifetime measurements in hostaphan RNK, used for encapsulation of Na positron sources, were performed. It was found that the parameter of positron lifetime spectra in hostaphan RNK differ markedly from those for other forms of polyethylene terephthalate. The maximum penetration depth of positrons from RNK hostaphan amounts 0.42 mm. The information gained in the present study is of great importance for experimenters using hostaphan RNK for encapsulation of positron sources.

Investigation of the Absorption of Annihilation Quanta in Solid and Liquid Ga and BiSn Alloy

Test Measurements of Modernized Version of Two-Detector Doppler Spectrometer

The quality of the annihilation quanta energy measurements (Doppler effect) has greatly increased when experimenters have begun to introduce Doppler apparatus modifications. In the basic version, the experimental set-up consisted of high energy resolution Ge(Li) detector, amplifier and multichannel analyser. A simple construction and short time of data acquisition were the main advantages of that version of the apparatus. Competitive, angular correlation of annihilation radiation (ACAR) method was better from the resolution point of view and not worse when considering the range of momentum distribution, but the ACAR method required high activity positron sources and data acquisition time wa…

Studying of Nickel Alloys with 1 at.% of Ge, Zn, In, Zr and Pb by Positron Annihilation Methods

Positron Annihilation in Polycrystalline Metals Deformed by Uniaxial Tension

Angular distributions of the positron annihilation quanta were measured for polycrystalline samples deformed by uniaxial tension up to difierent deformation degrees. The S parameter as a function of the W parameter was determined. The data obtained for samples elongated up to difierent elongation degrees indicate that in the proportionality and limited proportionality regions the changes in the physical properties of samples are governed mainly by generation of vacancies and formation and kinetics of transformations of vacancy clusters occurring flrst of all on the grains of monocrystallites. In the region of plastic deformations the dominant defects are dislocations and vacancies and their…