Zinc is an important alloying element in the 7000 series aluminium alloys. It is also an element that may enrich near the alloy surface during treatments of aluminium alloys by processes such as electropolishing, alkaline anodic etching and alkaline etching. The enrichment may occur since the change in Gibbs free energy per equivalent for formation of ZnO is less negative than that for formation of Al 2 O 3 . The enriched alloying element is present in an alloy layer up to ∼5 nm thick located immediately beneath the alloy/film interface. In the present study, the dependence of the enrichment of zinc on the grain orientation of the alloy is investigated for a solid solution Al-1.1at.%Zn alloy. The enrichment of the zinc is developed by alkaline etching of the alloy. The grain orientation is determined by electron backscattering diffraction, with enrichments quantified on selected grains by Rutherford backscattering spectroscopy and medium energy ion scattering. The morphologies of the surfaces of the etched grains are characterised by scanning electron microscopy and atomic force microscopy. The findings reveal that the zinc enrichment ranges from 1.7 × 10 15 atoms/cm 2 to 3.9 × 10 15 atoms/cm 2 , with the greatest enrichment occurring on a grain of (100) orientation, while differing surface topographical textures are developed on the various grains.

a b s t r a c tIn this work the palladium interaction with silicon carbide is investigated by means of complementary analytical techniques such as thermogravimetry (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).Thermoscans were carried out on pellets of palladium, a-SiC and b-SiC high purity powders in the temperature range comprised between 293 K and 1773 K, in order to study the effect of temperature on the palladium-silicon carbide reaction.Thermoscans of a-SiC pellets containing 5 at.%Pd show that during differential calorimetry scans three exothermic peaks occurred at 773 K, 1144 K and 1615 K, while thermoscans of b-SiC pellets containing 3 at.%Pd and 5 at.%Pd do not show peaks. For the pellet a-SiC-5 at.%Pd XRD spectra reveal that the first peak is associated with the formation of Pd 3 Si and SiO 2 phases, while the second peak and the third peak are correlated with the formation of Pd 2 Si phase and the active oxidation of silicon carbide respectively. Thermogravimetry scans show weight gain and weight loss peaks due to the SiO 2 phase formation and the active oxidation. Additionally XPS fittings reveal the development of SiC x O y phase during the first exothermic peak up to the temperature of 873 K. The experimental data reveals that alpha silicon carbide is attacked by palladium at lower temperatures than beta silicon carbide and the reaction mechanism between silicon carbide and palladium is strongly affected by silicon carbide oxidation.

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The determination of S‐carboxymethyl‐(R)‐cysteine (SCMC) in human plasma during extended bioequivalence studies demands a rapid, accurate and selective assay technique. A liquid chromatographic/mass spectrometric method was developed which involves rough protein precipitation followed by high‐performance liquid chromatographic separation with an ion‐exchange column and atmospheric pressure ionization (API) mass spectrometric detection, with the instrument operating with electrospray ionization (ESI) and in the selected‐ion monitoring mode. The drug and the internal standard S‐[(R)‐1‐carboxyethyl]‐(R)‐cysteine (SCEC) are detected by focusing the first quadrupole of the triple stage system on MH+ ions, thus permitting elimination of endogenous interfering substances and allowing a detection limit of 0.05 μg ml‐1. The chromatographic run time is 16 min and the method has sufficient sensitivity, precision, accuracy and selectivity for routine analyses of clinical plasma samples containing SCMC at concentrations in the range 0.2–20 μg ml‐1. In summary, this LC/MS‐based assay of SCMC demonstrates advantages of easy sample preparation, low limit of quantification (200 ng per ml of human plasma) without any derivatization step, high specificity and rapid sample analysis with an overall throughput of more than 60 analyses per day. © 1997 by John Wiley & Sons, Ltd.