Detection of Corrosion‐Related Defects in Aluminum Using Positron Annihilation Spectroscopy

Near‐surface atomic‐scale defects in aluminum foils of at least 99.98% purity were characterized with positron annihilation spectroscopy measurements of the Doppler‐broadening parameter S. Profiles of S vs. positron beam energy (i.e., vs. depth into the sample) were analyzed with a model for positron diffusion and trapping in order to characterize the defect layer structure. As‐received foils were shown to possess a defect layer within 10 to 100 nm of the oxide film/metal interface. Both dissolution in aqueous sodium hydroxide solution and anodic pitting corrosion in caused significant changes in the position spectra which were interpreted as increases in the defect population. On the basis of isochronal annealing, the defects were impurity‐complexed voids or vacancy clusters, or else interfacial voids at the metal/film boundary located at surface roughness features. Either case suggests a possible role for the defects as pit sites, since both near‐surface impurities and surface roughness are known to influence the number of pits on a surface. Defects found after pitting may be present in layers surrounding individual pits, and might have been produced in the process of pit initiation

Positron Annihilation Spectroscopy Study of Interfacial Defects Formed by Anodic Oxidation of Aluminum

Positron annihilation spectroscopy (PAS) measurements were carried out to characterize open-volume defects associated with anodic oxidation of aluminum. The annihilation fractions with low and high momentum electrons (S and W spectral lineshape parameters, respectively) of the annihilation photopeak were determined, as a function of the positron beam energy. A subsurface defect layer, containing nanometer-scale voids in the metal near the metal/oxide film interface, was found after oxide growth, and was shown to contain new voids created by anodizing. Such interfacial voids in the metal are of interest because of their possible role as corrosion initiation sites. The Sparameter characterizing the defect-containing layer (Sd) was obtained by simulation of the S-energy profiles. On samples with two different surface conditions, Sd remained constant at its initial value during anodizing. Because Sd is related to the void volume fraction in the interfacial metallic layer containing the voids, that result suggests that formation of metallic voids, and their subsequent incorporation into the growing oxide layer, occurred repeatedly at specific favored sites. © 2003 The Electrochemical Society. All rights reserved

Depletion induced isotropic-isotropic phase separation in suspensions of rod-like colloids

When non-adsorbing polymers are added to an isotropic suspension of rod-like colloids, the colloids effectively attract each other via depletion forces. We performed Monte Carlo simulations to study the phase diagram of such rod-polymer mixture. The colloidal rods were modelled as hard spherocylinders; the polymers were described as spheres of the same diameter as the rods. The polymers may overlap with no energy cost, while overlap of polymers and rods is forbidden. Large amounts of depletant cause phase separation of the mixture. We estimated the phase boundaries of isotropic-isotropic coexistence both, in the bulk and in confinement. To determine the phase boundaries we applied the grand canonical ensemble using successive umbrella sampling [J. Chem. Phys. 120, 10925 (2004)], and we performed a finite-size scaling analysis to estimate the location of the critical point. The results are compared with predictions of the free volume theory developed by Lekkerkerker and Stroobants [Nuovo Cimento D 16, 949 (1994)]. We also give estimates for the interfacial tension between the coexisting isotropic phases and analyse its power-law behaviour on approach of the critical point

Copper Layers Deposited on Aluminum by Galvanic Displacement

Metallization layers nanometers to tens of nanometers thick are desirable for semiconductor interconnects, among other technologically relevant nanostructures. Whereas aqueous deposition of such films is economically attractive, fabrication of continuous layers is particularly challenging on oxidized substrates used in many applications. Here it is demonstrated that galvanic displacement can deposit thin adherent copper layers on aluminum foils and thin films from alkaline copper sulfate baths. According to scanning electron microscopy and quartz crystal microbalance measurements, the use of relatively low CuSO4 concentrations produced films composed of copper nanoparticles overlying a uniform continuous copper layer on the order of nanometers in thickness. It seems that there are no precedents for such thin layers formed by aqueous deposition on oxidized metals. The thin copper layers are explained by a mechanism in which copper ions are reduced by surface aluminum hydride on Al during alkaline dissolution

Australian Sphingidae – DNA Barcodes Challenge Current Species Boundaries and Distributions

© 2014 Rougerie et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The attached file is the published version of the article

The 2006 July 17 Java (Indonesia) tsunami from satellite imagery and numerical modelling: A single or complex source?

The Mw 7.8 2006 July 17 earthquake off the southern coast of Java, Indonesia, has been responsible for a very large tsunami causing more than 700 casualties. The tsunami has been observed on at least 200 km of coastline in the region of Pangandaran (Wes

A Prediction Model for Reflection on Varnished Metallic Plates

Several models predict the reflectance of a rough metallic surface. They are however not adapted to the surfaces used in the packaging industry, such as boxes made of printed metallic plates. For printing purposes, metallic surfaces need to be varnished. Light reflection properties are therefore modified. We propose methods which adapt existing reflectance models to varnished surfaces. We also present a correction capable of predicting the reflectance even if incident light is not collimated, i.e. not composed of parallel rays

Experimental Limit on the Cosmic Diffuse Ultra-high Energy Neutrino Flux

We report results from 120 hours of livetime with the Goldstone Lunar Ultra-high energy neutrino Experiment (GLUE). The experiment searches for <10 ns microwave pulses from the lunar regolith, appearing in coincidence at two large radio telescopes separated by 22 km and linked by optical fiber. Such pulses would arise from subsurface electromagnetic cascades induced by interactions of >= 100 EeV neutrinos in the lunar regolith. No candidates are yet seen, and the implied limits constrain several current models for ultra-high energy neutrino fluxes.Comment: 4 pages, 4 figures, revtex4 style. New intro section, Fig. 2, Fig 4; in final PRL revie