Trace element analysis of high-purity copper

Summary In copper samples trace impurities of the elements As, Bi, Cr, Fe, Pb, Sb, Se and Te in the low g/g range were coprecipitated with lanthanum hydroxide and determined by flame AAS (Fe) and electrothermal AAS (other elements). Reduction of the sample weight results in a considerable saving of time compared to elder procedures and allows to apply centrifugation instead of filtration as separation technique, by which the risk of contamination is decreased. The completeness of separation was examined by analyzing standard solutions. Additionally radio tracer experiments were employed with Sb and Se. Based on recovery data, a classification scheme was set up with regard to adsorption behaviour. High-purity copper samples were analyzed by the procedure described; INAA and ICP-MS were used as comparison methods. Parameters affecting the precision were examined; the main influence was caused by the separation step. The procedure is well suitable for the determination of 2–10 g/g As, Cr and Pb and 5–50 g/g Fe in high-purity copper.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Zum mechanismus des strahlenchemischen abbaus von polytetrafluorethylen

The present work studies the changes in polymer structure and the mechanism of the decomposition of polytetrafluoroethylene resin (PTFE) exposed to high energy radiation (electron beam). Spectroscopic and kinetic observations are used to interpret the degradation process. For the first time the decomposition of PTFE has been carried out on a preparative scale and new results obtained by analysing the degradation products. The radiation-induced degradation of PTFE is accompanied by thermal degradation under certain irradiation conditions. This is due to an increase in temperature of the polymer caused by retardation of highly accelerated electrons (heat accumulation effect).The kinetics are discussed in terms of the reactions and recombination of radicals produced by high-energy radiation both in the polymer melt and the polymer surface. These are related to the overall rate of decomposition.The primary radicals formed by decomposition of PTFE in an inert atmosphere (N₂, Ar) react to produce perfluorinated alkanes and alkenes. In the presence of reactive gases the decomposition fragments originated will react rapidly; e.g. if oxygen is present in the reactive area the radicals form perflourinated peroxyl and oxyl radicals which finally stabilize themselves by CC-scission to perfluorocarbon acid fluorides and carbonyldifluorides.