Rodolfo A. Pérez

Ru Self-Diffusion and Ru Diffusion in Al

The self-diffusion of Ru in the temperature range of (1267-1373) K and the Ru diffusion in pure aluminum in the temperature range of (632-873) K is reported. Difficulties were encountered when working with Ru as matrix (its brittleness at room temperature impeded a good sectioning) and they are the reason why only the order of magnitude of the self-diffusion in the small range of temperature studied is given. For Ru diffusion in aluminum, two experimental techniques were used: the conventional serial sectioning with use of a radiotracer, 103Ru, for the highest temperatures and Heavy Ions Rutherford Backscattering Spectrometry (HIRBS) for the lowest ones. The diffusion parameters are: Q = 199.4 kJ/mol and D0 = 4.1x10-2 m2/s. A comparison is made with Ru diffusion behavior in copper and silver.

Diffusion of Pd in α-Ti studied by means of Rutherford back-scattering and channelling techniques

Abstract The diffusion of implanted Pd in α-Ti has been studied in the 723–1073K temperature range by using Rutherford back-scattering and channelling techniques. The measurements show that the diffusion coefficient follows a linear Arrhenius rule D(T) = D 0exp(—Q/RT), where D 0 = (2.0 ± 0.5) × 10−3 m−2s−1 and Q = 264 ± 9 kJmol−1. In addition. channelling experiments performed in the 673–973K temperature interval show that, independent of the annealing temperature, at least 30% of the Pd atoms are at interstitial sites of the Ti matrix. A comparison of the present and previous published data indicates that Pd diffuses more rapidly than substitutional elements but more slowly than the interstitial elements Fe, Co and Mn do. These two features indicate that the diffusion mechanism is not purely substitutional but has a mixed character.

Experimental determination of U diffusion in α-Ti

α-spectrometry was used in order to measure the diffusion of U in bulk α-Ti in the temperature range 863–1123 K (540–850 °C). A straight Arrhenius plot was found, giving diffusion parameters Q = 297 kJ/mol and D 0 = 5 × 10−3 m2/s, which are similar to the α-Ti self-diffusion ones, when measured in Ti samples with a similar impurity content than presently. This behaviour is compatible with the hypothesis of U diffusing via a vacancy-assisted mechanism in the α-Ti lattice and contrasts with older results in which the activation energy is almost a third the self-diffusion one, even lower than the vacancy formation energy.

Uranium Diffusion in Metals Used in Nuclear Facilities - A New Approach

Diffusion at infinite dilution of U in metals, with particular emphasis in those used in nuclear facilities, is revisited. Early works present some particularities such as activation enthalpies lower than the vacancy formation enthalpy in the matrix, large differences with self-diffusion in the base material, up to four orders of magnitude differences between measurements performed by different authors in similar temperature ranges, etc. In particular U self-diffusion was qualified as abnormal when compared with other metals. Recent studies by means of α-spectrometry reveal a normal behaviour: activation enthalpies and pre-exponential factors similar to the self-diffusion one and diffusion coefficient values in the same order of magnitude than self-diffusion. The possible influence of short circuits, impurities and/or uncertainties in the techniques used in the early works is discussed in order to explain the differences obtained.

Diffusion in Very Dilute Zr-Fe Alloys

The diffusion process in hcp Zr with low amounts of Fe being in solution or forming very dilute Zr-Fe alloys is analysed and discussed. The enhancement of the diffusion coefficient in alloys with increasing amounts of Fe is studied using both experimental and theoretical results. In contraposition with the assumption made in the literature that the Fe in solution in the hcp Zr lattice is the responsible, this enhancement seems to be more related with the total amount of Fe present in the samples. This idea is supported by measurements of Au diffusion in Zr with 50 to 150 gr/gr of Fe which shows increments in the diffusion coefficients even at the lower temperatures where the reported Fe solubility in -Zr is negligible. Ab initio calculations using SIESTA and WIEN2k codes show several stable and meta-stable configurations for the Fe in the hcp Zr lattice in interstitial and off-centre positions, resembling the last ones a Zr3Fe like arrangement. These configurations are used in order to analyze the mechanism of both, self-diffusion enhancement and ultra-fast diffusion of Fe in -Zr.

Study of Diffusion and Reaction Diffusion in the Fe-C-Nb System

Experiments of niobium diffusion at infinite dilution and Nb reaction-diffusion in pure iron and in ferrites with different amounts of carbon were performed, for comparison, in order to understand the influence of carbon on the diffusion process in the Nb-Fe system. A proportional decrease of the diffusion coefficient with the increasing amount of carbon was found. This effect seems to be stronger than in the self-diffusion analyzing the literature; moreover SIMS measurements in niobium- implanted samples show a redistribution of carbon during the first steps of the diffusion process. For those reasons, a stronger effect of carbon-niobium interaction over the carbon-vacancy interaction seems to be responsible for the decrease in the diffusion coefficient.