Ultrasound-Enhanced Anodic Stripping Voltammetry Using Perfluorosulfonated Ionomer-Coated Mercury Thin-Film Electrodes

The high mass transport caused by ultrasonic radiation in the preconcentration of trace metal species in anodic stripping voltammetry (ASV), leads to an order of magnitude enhancement in sensitivity. A Nafion-coated mercury thin-film working electrode is placed in a specially designed small-volume sonovoltammetric cell. The preparation and curing procedure for the Nafion film on a glassy carbon electrode substrate as well as ultrasound-enhanced mercury deposition through the Nafion film are optimized. The resulting electrode assembly is stable under ultrasonic irradiation. Optical microscopy observations show the formation of closely spaced mercury droplets of micrometer dimensions under the Nafion film. The performance characteristics of ultrasound-enhanced ASV at the Nafion-coated mercury thin-film electrode are studied in detail. The detection limit obtained for lead and cadmium test species is 3 × 10-11 M (30 s preconcentration in the presence of ultrasound). A relative standard deviation of 1.2% is obtained for repetitive determinations of 10 nM Cd2+ (n = 9)

Positron-lifetime investigation of thermal stability of ultra-fine grained nickel

Thermal stability of ultra-fine grained (UFG) nickel (mean grain size 114 nm) prepared by high pressure torsion was studied by means of positron-lifetime spectroscopy (PLS) combined with TEM. The experimental results obtained by PLS are interpreted using the diffusion trapping model, which allows for determination of important physical parameters characterizing the specimens. The microstructure of the material studied is strongly inhomogeneous. The grain interiors with low dislocation density are separated by distorted regions with high numbers of dislocations. We have found that positrons are trapped at dislocations inside the distorted regions and in the microvoids situated inside the grains. Structure evolution with increasing temperature was studied in details using isochronal annealing of the specimen. We have found that recovery of the UFG structure involves the abnormal grain growth followed by further recrystallization in the whole volume of samples. It was shown that PLS is sensitive to structure changes, caused by the magnetostriction phenomenon