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Structure and stability of binary metal alloys. Precipitation treated via ab-initio calculations

100%

Muller S.

tom Vol. 23, No. 2

347--355

Theoretical studies of substitutional ordering phenomena in binary metal alloys demands the consideration of both huge parameter-spaces ( e. g. for ground-state searches) and systems containing more than a million atoms ( e. g. for precipitation). The combination of density functional theory calculations (DFT) with cluster expansion methods (CE) and Monte-Carlo ( MC) simulations fulfills these requirements. They can be applied to study properties of a metal alloy which possess a delicate temperature-dependence without any empirical parameters, but with such accuracy that quantitative prediction of experimental data becomes possible. The concept is applied to study the structure and distribution of coherent precipitates in binary metal alloys.

Distribution of phosphorus and heavy metals in the sediments of lake arendsee (Altmark, Germany)

51%

Zachmann D. W. , van der Veen A. , Muller S.

2004

tom Vol. 21

179-185

Lake Arendsee is a dimictic lake with a surface area of about 5 km2 and a maximum depth of about 50 m. Due to the input of untreated sewage rich in P the lake turned to eutrophic state in the 1950s. Sediment cores were taken by different methods: short cores (0-50 cm) with a gravity corer, long cores (0-160 cm) with a piston corer. The sediments were sliced into subsamples under argon atmosphere in a glove box. The samples were analysed by ICP-OES and ICP-MS on main and trace elements after digestion in either aqua regia or HF-HNO3-HClO4. Analogous cores were dated by varve counting and radiometric methods. The enforced build-up of industry and agriculture since the 1950s is displayed in the sediment composition. The P concentrations increase from a background of about 600 ppm (oligotrophic state of the lake) to more than 4,000 ppm in a depth of 14 cm, which corresponds to the 1970s. In 1976, a hypolimnetic withdrawal and a sewage plant were built. Above the corresponding depth the concentrations of P and heavy elements decrease in the sediments but are still by far higher than the background values. The bonding form analyses dokument mineral equilibration by diagenetic processes. Stable sulfidic bonding forms become predominant with increasing depth.