Sichere Druckwasserstoff-Logistik — Speicherung und Transport

Safe handling of pressurized hydrogen – storage and transport. For the necessary future transition to non-fossile energy sources hydrogen is considered to be the ideal energy vector and will therefore assume ever-increasing importance. However, safe handling of the gas will be a basic requirement. A particular difficulty with pressurized hydrogen is its relative incompatibility with many materials which are commonly used for pressure vessels, either for transportation or for storage. The paper summarizes the major factors instrumental in hydrogen embrittlement. In particular, it stresses the role played by service conditions and by the quality of the internal surface of the vessels when exposed to the gas. On the basis of these findings a number of recommendations are given with respect to vessel design and operating measures in order to secure safe working with high pressure hydrogen gas.     

Eine charakterisierung der lochfraßkorrosion des nickels—I. Die bestimmung der lochfraßpotentiale in neutralen und alkalischen lösungen

Quasistationary values for the characteristic pitting potentials for nickel were determined by means of potentiokinetic polarization measurements and their dependence on chloride and hydroxide ion concentration was investigated. The pit nucleation potential U_np is a linear function of the logarithm of the anion concentration. The value being determined by the adsorption equilibrium of the anions on the passivated metal surface.The critical pitting potential U_cp depends on the pH of the solution only. Above pH 6-5 U_cp decreases with increasing pH. On the basis of the mechanism for crevice corrosion this behaviour may be explained by the influence of OH^?-ions being known to take part in the ionization of the metal atoms.     

Cavitary aspergillosis as a complication of AIDS

The authors report a case of type 2 dissection, strictly confined to the terminal portion of the ascending aorta, not seen by transesophageal echocardiography because of the existence of a blind spot and responsible for a false negative. The role of TEE in the diagnostic approach to dissections is reviewed, as are its limitations, of which it is important to be aware because of the poor prognosis of pathology of this type.     

Technological application of the martensitic transformation of some austenitic stainless steels

The final heat treatment of austenitic stainless steels of types X 5 CrNi 18 9 (1.4301) and X 2 CrNi 18 10 (1.4306) normally is annealing at 1050°C and subsequent water quenching. The resulting structure is of a metastable fcc-type. Plastic deformation, especially at low temperatures, causes martensitic transformation of these metastable structures. The transformation is accompanied by a substantial flow stress increase. This strengthening mechanism should be used in practice, e.g. to save weight. The deformed structure consists of tetragonal α′-martensite, austenite and hcp ε-martensite. Whereas α′-martensite increases continuously with deformation, the content of ε-martensite reaches a maximum value at about 5% plastic strain at 77 K. The hcp phase is only detectable by means of X-ray analysis, whilst α′-martensite can be determined quantitatively by saturation magnetisation measurement. The flow stress increase during low temperature deformation of metastable austenitic stainless steels is based on normal work-hardening by dislocation accumulation, in addition to a distinct amount of work-hardening due to martensitic transformation. Analysis of the work-hardening behaviour in the range of stable deformation (T > M_D) can be used to predict the amount of normal work-hardening when deformation is performed in the instable temperature regime. Separation of the flow stress contributions according to the procedure described above enables the possible savings in weight to be predicted when using cryogenically stretched instable austenitic steels in comparison with stable grades deformed under the same conditions.     

The impact of visual layout factors on performance in Web pages: a cross-language study

Visual layout has a strong impact on performance and is a critical factor in the design of graphical user interfaces (GUIs) and Web pages. Many design guidelines employed in Web page design were inherited from human performance literature and GUI design studies and practices. However, few studies have investigated the more specific patterns of performance with Web pages that may reflect some differences between Web page and GUI design. We investigated interactions among four visual layout factors in Web page design (quantity of links, alignment, grouping indications, and density) in two experiments: one with pages in Hebrew, entailing right-to-left reading, and the other with English pages, entailing left-to-right reading. Some performance patterns (measured by search times and eye movements) were similar between languages. Performance was particularly poor in pages with many links and variable densities, but it improved with the presence of uniform density. Alignment was not shown to be a performance-enhancing factor. The findings are discussed in terms of the similarities and differences in the impact of layout factors between GUIs and Web pages. Actual or potential applications of this research include specific guidelines for Web page design.     

Eine Charakterisierung Der Lochfraßkorrosion Des Nickels-II. Wachstumskinetik Und Lochmorphologie In Neutralen Sulfat- Und Perchloratlösungen

Potentiostatic current-time-measurements in sulphate and perchlorate solutions result in a quadratic time dependence for the growth of single pits on high purity nickel. In connection with studies of the pit morphology a new model for the propagation of pits is suggested. According to this model the development of a pit depends on the formation of a hydroxide or oxide layer at the opening of the pit or within the pit area. The model permits a new interpretation of the critical pitting potential and its observed pH-dependence. Furthermore, it gives a qualitative explanation of the influence of solution agitation on pitting corrosion.