Über die Reduktion von Wüstit mit Wasserstoff-Wasserdampf- und Kohlenmonoxyd-Kohlendioxyd-Gemischen

Herstellung der Wüstitproben und Versuchsdurchführung. Reduktionskinetik des Wüstits bei deckender Eisenschicht. Gaswechselversuche und Bestimmung der kritischen Kohlenstoffaktivität. Reduktionskinetik des Wüstits bei poröser Eisenschicht.     

Surface active betaines as protective agents against denaturation of an enzyme by alkyl sulfate detergents

A homologous series of higher alkyl sulfate surfactants inactivate β-fructofuranosidase (invertase) at levels coinciding with their critical micelle concentrations. It was possible to renature the enzyme by passing it through an anion exchange column. This inactivation was prevented by surface active betaines present at equimolar or higher concentrations than those of the anionics. Effective surfactant betaines include those with carboxylate, sulfonate, or phosphate radicals in their zwitterions. Betaines lacking surface active properties did not prevent denaturation indicating that the effects are due to comicellization. Studies with enzymes may point to appropriate anionic/zwitterionic surfactant ratios in solubilization procedures or detergent applications where biological properties must be preserved and anionic surfactants are required as components.     

Das Ausscheidungsverhalten von hochlegierten austenitischen Stählen mit 6% Molybdän und sein Einfluß auf die Korrosionsbeständigkeit

Precipitation behaviour of high-alloyed austenitic steels with 6% molybdenum and its influence on the corrosion resistance The high-alloy austenitic steels with 6 to 7% Mo, 20 to 21% Cr and 18 to 25% Ni are increasingly used in seawater and chemical applications. This is due to the excellent resistance to pitting and crevice corrosion in chloride-containing neutral and acidic environments. It is the high chromium and molybdenum content which provides the excellent corrosion behaviour but, at the same time favors the tendency to precipitation of intermetallic phases. Therefore, time-temperature-precipitation diagrams have been established for two steels with 6% Mo, 21% Cr, 25% Ni, 0.14 and 0.19% N and for one steel with 6% Mo, 20% Cr, 18% Ni and 0.21% N. The corresponding time-temperature-sensitization diagrams (in accordance to SEP 1877/II) and time-temperature-pitting diagrams (testing in 6% FeCl₃ solution) have been evaluated as well. Precipitation of intermetallics occurs rapidly especially in the range between 700 and 1000°C. In case of the 18% Ni steel and the 25% Ni/0.14% N steel grain boundaries are covered to a large extent with precipitates after only 15 min at 850 or 950°C. In case of the 25% Ni/0.19% N steel precipitation is considerably slower. The precipitates are interpreted to be chi-phase. After very long annealing times additionally small amounts of Laves phase appear. Neither carbides nor nitrides were observed. In spite of the rapid precipitation, sensitization in terms of the 50 m?m grain boundary penetration criterion is observed not before 0.7 h at 850 °C and not before about 2 h at 800°C in case of the 25% Ni/0.19% N steel. After about the same times of annealing also the critical pitting temperature as observed in the FeCl₃-test is dropping below 50°C. Therefore, when welding according to established rules and recommendations, no deterioration of the corrosion resistance in the heat-affected zone is to be expected. If high heat inputs will occur during manufacturing because of hot forming operations or welding of heavy sections, or if more severe test conditions are a requirement, a steel with 25% Ni and about 0.2% N (UNS N 08925, Cronifer hMo) is recommended due to its retarded precipitation and sensitization behaviour when compared to steels with only 18% Ni (UNS S 31 254). Additionally, the steel with 25% Ni has an increased resistance to general corrosion in acids. Notch impact strength of the materials under consideration is increased by the initial precipitation of the intermetallic phases and decreases only after longer times of annealing below the ductility of the solution annealed material.     

205Pb: Accelerator mass spectrometry of a very heavy radioisotope and the solar neutrino problem

To investigate the feasibility of a solar neutrino experiment using ²⁰⁵Tl as a geological detector we have performed a series of measurements at the GSI heavy-ion facility UNILAC studying accelerator mass spectrometry of the heavy radioisotope ²⁰⁵Pb $\text{(T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 14}\text{mio years}$. We observe a suppression of neighbouring masses to better than 10^?16, and an elemental resolution between Pb and Tl through energy-loss difference with a passive-absorber of $\text{Z}\text{ΔZ}\text{～- 100}$. These results, which are possible due to the high energy and good beam quality provided by the UNILAC, suggest the feasibility of detecting neutrino-produced ²⁰⁵Pb provided the overall efficiency of the system — dominated by the low ion source efficiency — can be considerably increased.     

Herstellung und Eigenschaften rheopexer Dispersionen

The report concerns a special kind of anomalous flow of latices being familiar to rheopexy. The rheological properties are characterized by a sudden increase in viscosity of 2 to 3 orders of magnitude within a narrow range of shear rate. The viscosity then decreases again with increasing shear rate with a gradient of —1, corresponding to a maximum shear stress of appx. 0.1 kp · cm^?2. The increase of viscosity and the shear rate at which this increase occurs, depend on the concentration and the temperature of the polymer dispersion. The rheopexy is due to the presence of groups at the surface of the latex particles being able to form hydrogen bonds. At a definite shear rate these groups interact to give a network structure of the latex particles. The network could be demonstrated by electron microscopy.