Oberfl?chenanalytik an Anlauffarben auf nichtrostenden St?hlen

Zusammenfassung Bei der kurzzeitigen Hochtemperaturbeaufschlagung nichtrostender Stähle (z.B. Durchlaufglühen, Schweißen) in Atmosphären mit verschiedenen O₂-Partialdrucken können oxidische Deckschichten entstehen, die eine solche Dicke erreichen, daß sie optisch wahrgenommen werden. Zusammenhängende Schichten sind häufig farbig. Dies ist überwiegend auf Interferenz, z.T. aber auch auf Absorption des Lichts zurückzuführen. Bei nicht zusammenhängenden inselförmigen Schichten entsteht der Eindruck eines Grauschleiers. Die Zusammensetzung der Schichten ist je nach Werkstoff, Temperatur und Atmosphäre sehr unterschiedlich nd kann im Detail nicht vohergesagt werden. Analytische Untersuchungen erfolgten mit ESCA und Mikro-AES. Wo es auf die Analyse farblich differenzierter Bereiche ankam, die sich im Kontrast im REM-Bild nicht unterschieden, wurde zusätzlich LAMMA eingesetzt. Diese Methode gestattet darüber hinaus den empfindlichen Nachweis auch der leichten Elemente bei hohem räumlichen Auflösungsvermögen.

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Surface analysis on stainless steels exhibiting annealing colours

Summary When stainless steels are exposed for short periods to high temperatures (as in welding and continuous annealing), oxide layers sufficiently thick to be visible may be formed in atmospheres with various O₂ partial pressures. Continuous layers are often coloured. This arises mainly from interference, but to some extent from absorption of the light also. Non-continuous layers consisting of islands give the surface an appearance of grey haze. The composition of the layers differs very much according to the material, temperature, and atmosphere, and cannot be accurately predicted. We investigated the layers analytically by ESCA and micro-AES. Where it was necessary to investigate differently coloured areas that could not be distinguished in the SEM picture, LAMMA was used also. This method additionally enables even the light elements to be detected very sensitively and gives high spatial resolution.

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Herrn Professor Dr. H. Hartmann zum 70. Geburtstag gewidmet     

Gauge-invariant poisson brackets for chromohydrodynamics

Noncanonical hamiltonian structures are presented both for Yang-Mills Vlasov plasmas, and for ideal fluids interacting with Yang-Mills fields. These hamiltonian structures are given Lie-algebraic interpretations.     

The enthalpy of mixing of liquid NaF and NaMgF3 from drop calorimetry

The enthalpy of mixing of three liquid mixtures of NaF and NaMgF₃ has been measured by drop calorimetry and was found to be negative. This energy release is attributed to a change in the equilibrium

Mg_1/4[MgF²⁻₄]_3/4+f⁻ å MgF²⁻₄ to the formation of complex MgF²⁻₄-ions. A ΔH^M diagram for the system NaF-MgF₂ up to 50 mol % MgF₂ has been constructed.     

Converging finite-strength shocks

The converging shock problem was first solved by Guderley and later by Landau and Stanyukovich for infinitely strong shocks in an ideal gas with spherical and cylindrical symmetry. This problem is solved herein for finite-strength shocks and a non-ideal-gas equation of state with an adiabatic bulk modulus of the type $\text{B}{}_{\mathrm{s}}\text{=}\text{?}\text{v}\text{?}\text{p}\text{?}\text{v}\text{|}{}_{\mathrm{<mtext>s</mtext>}}\text{= (}\text{p +B}\text{)}\text{f}\text{(}\text{v}\text{)}$, where B is a constant with the dimensions of pressure, and f(v) is an arbitrary function of the specific volume. Self-similar profiles of the particle velocity and thermodynamic variables are studied explicitly for two cases with constant specific heat at constant volume; the Tait-Kirkwood-Murnaghan equation, f(v) = constant, and the Walsh equation, f(v) = v/A, where A = constant. The first case reduces to the ideal gas when B = 0. In both cases the flow behind the shock front exhibits an unbalanced buoyant force instability at a critical Mach number which depends upon equation-of-state parameters.     

The reaction 6Li (d, α)α with a new highly polarized 6Li target

A highly polarized ⁶Li target with a new polarizing principe has been developed. A surface is used to store polarized lithium particles from an atomic beam source. The maximum target tensor polarization is P_zz = 0.81 ± 0.06 and the thickness 3 × 10¹⁴ ions per cm².     

Surface analysis of AgSn alloys by ESCA

The surface composition of AgSn alloys with low Cu and Zn contents was investigated by ESCA following various pretreatments. Exposure to air, especially at elevated temperatures, resulted in the surface being enriched, not only by Sn, but particularly by the Zn and Cu contents in the form of oxides. Zn and Cu enrichment is less pronounced when heating in a vacuum (10^?6 Torr). Any tin oxide present is partially reduced. The results obtained are compared with model concepts established by various authors from studies of binary alloys.     

Elucidation of the thermochemical properties of triphenyl- or tributyl-substituted Si-, Ge-, and Sn-centered radicals by means of electrochemical approaches and computations

Redox potentials of a number of triphenyl- or tributyl-substituted Si-, Ge-, or Sn-centered radicals, R(3)M(*), have been measured in acetonitrile, tetrahydrofuran, or dimethyl sulfoxide by photomodulated voltammetry or through a study of the oxidation process of the corresponding anions in linear sweep voltammetry. For the results pertaining to the Ph(3)M(*) series (including literature data for M = C), the order of reduction potentials follows Sn > Ge > C > Si, while for the two oxidation potentials, it is C > Si. The effect of the R group on the redox properties of R(3)Sn(*) is pronounced in that the reduction potential is more negative by 490 mV in tetrahydrofuran (390 mV in dimethyl sulfoxide) when R is a butyl rather than a phenyl group. The experimental trends have been substantiated through quantum chemical calculations, and they can be explained qualitatively by considering a combination of effects, such as charge capacity being most pronounced for the heavier elements, resonance stabilization present for the planar Ph(3)C(*) and all R(3)M(+)(), and finally a contribution from solvation. The solvation of R(3)M(-) is observed to be relatively strong because of a rather localized negative charge in the pyramidal geometry. However, there is no evidence in the calculations to support the existence of covalent interactions between solvent and anions. The solvation of R(3)M(+)() is relatively weak, which may be attributed to the planar geometry around the center atom, leading to more spread out charge than that for a pyramidal geometry. Although the calculated solvation energies based on the polarizable continuum model approach exhibit the expected trends, they are not able to reproduce the experimentally derived values on a detailed level for these types of ions. An evaluation of the general performance of the continuum model is provided on the basis of present and previous studies.