Theory of Spin-Resolved Auger-Electron Spectroscopy from Ferromagnetic 3d-Transition Metals

CVV Auger electron spectra are calculated for a multi-band Hubbard model including correlations among the valence electrons as well as correlations between core and valence electrons. The interest is focused on the ferromagnetic 3d-transition metals. The Auger line shape is calculated from a three-particle Green function. A realistic one-particle input is taken from tight-binding band-structure calculations. Within a diagrammatic approach we can distinguish between the \textit{direct} correlations among those electrons participating in the Auger process and the \textit{indirect} correlations in the rest system. The indirect correlations are treated within second-order perturbation theory for the self-energy. The direct correlations are treated using the valence-valence ladder approximation and the first-order perturbation theory with respect to valence-valence and core-valence interactions. The theory is evaluated numerically for ferromagnetic Ni. We discuss the spin-resolved quasi-particle band structure and the Auger spectra and investigate the influence of the core hole.Comment: LaTeX, 12 pages, 8 eps figures included, Phys. Rev. B (in press

Corrosion Resistance Studies of Sintered and Cast Cobalt-Chromium-Molybdenum Alloys for Surgical Implants.

The principal aim of the work described in this thesis was to produce a sintered cobalt-chromium-molybdenum alloy, and to study its corrosion resistance in order to assess its value as a surgical implant material. A literature and clinical survey indicated that sintering, as opposed to casting, the alloy produces a required increase in mechanical properties but that the sintered alloy had not been shown to have sufficient corrosion resistance for use in the human body. A potentiostatic method of corrosion testing was chosen for this work after a consideration of the theory of aqueous corrosion and a review of previously used techniques. Preliminary tests were carried out on specimens of Vitallium and these provided information about the corrosion resistance of the cast alloy as well as helping to standardise a testing procedure. Specimens of the sintered alloy were produced by the author using a previously developed method. This material was found to be unsuitable for use in the body by virtue of its low passive breakdown potential in Hanks' balanced salt solution. Electron probe analysis suggested that this inadequate corrosion resistance was the result of an unexpected low chromium content. A sintered alloy with an increased chromium content was produced but this was found to have similarly low corrosion resistance. Further corrosion tests indicated that this was the result of a chromium deficient phase within the grain boundaries. It was concluded that, without further development, the powder metallurgy technique was incapable of producing a cobalt-chromium-molybdenum alloy with sufficient corrosion resistance for surgical implants. The metallurgical examination of several removed cast Vitallium implants is described. The results, together with those of further laboratory corrosion tests, suggest that the cast alloy is susceptible to crevice corrosion in the human body

Corrosion Resistance Studies of Sintered and Cast Cobalt-Chromium-Molybdenum Alloys for Surgical Implants.

The principal aim of the work described in this thesis was to produce a sintered cobalt-chromium-molybdenum alloy, and to study its corrosion resistance in order to assess its value as a surgical implant material. A literature and clinical survey indicated that sintering, as opposed to casting, the alloy produces a required increase in mechanical properties but that the sintered alloy had not been shown to have sufficient corrosion resistance for use in the human body. A potentiostatic method of corrosion testing was chosen for this work after a consideration of the theory of aqueous corrosion and a review of previously used techniques. Preliminary tests were carried out on specimens of Vitallium and these provided information about the corrosion resistance of the cast alloy as well as helping to standardise a testing procedure. Specimens of the sintered alloy were produced by the author using a previously developed method. This material was found to be unsuitable for use in the body by virtue of its low passive breakdown potential in Hanks' balanced salt solution. Electron probe analysis suggested that this inadequate corrosion resistance was the result of an unexpected low chromium content. A sintered alloy with an increased chromium content was produced but this was found to have similarly low corrosion resistance. Further corrosion tests indicated that this was the result of a chromium deficient phase within the grain boundaries. It was concluded that, without further development, the powder metallurgy technique was incapable of producing a cobalt-chromium-molybdenum alloy with sufficient corrosion resistance for surgical implants. The metallurgical examination of several removed cast Vitallium implants is described. The results, together with those of further laboratory corrosion tests, suggest that the cast alloy is susceptible to crevice corrosion in the human body

Purification and characterization of a bacterial dehalogenase with activity toward halogenated alkanes, alcohols and ethers

An enzyme that is capable of hydrolytic conversion of halogenated aliphatic hydrocarbons to their corresponding alcohols was purified from a 1,6-dichlorohexane-degrading bacterium. The dehalogenase was found to be a monomeric protein of relative molecular mass 28000. The affinity for its substrates was relatively low with Km values for short-chain haloalkanes in the range 0.1-0.9 mM. The aliphatic dehalogenase showed a much broader substrate range than has been reported for halidohydrolases so far. Novel classes of substrates include dihalomethanes, C5-C9 1-halo-n-alkanes, secondary alkylhalides, halogenated alcohols and chlorinated ethers. Several of these compounds are important environmental pollutants, e. g. methylbromide, dibromomethane, 1,2-dibromoethane, 1,3-dichloropropene, and bis(2-chloroethyl)ether. The degradation of chiral 2-bromoalkanes appeared to proceed without stereochemical preference. Optically active 2-bromobutane was converted with inversion of configuration at the chiral carbon atom, suggesting that the dehalogenase reaction proceeds by a nucleophilic substitution involving a carboxyl group or base catalysis.