Growth Stresses in the Oxide Scales on TiAl Alloys at 800 and 900°C

In the oxidation of TiAl alloys, the role of scale-growth stresses formed during oxidation has, thus far, been unknown. In the present paper the oxide-growth stresses were investigated by the deflection-test method in monofacial oxidation (DTMO) accompanied by acoustic-emission measurements. On unmodified surfaces the growth stresses are compressive and reach levels of around –100 MPa. At the same time, significant acoustic emission occurs indicating that even under isothermal conditions, stresses are relieved by a scale-cracking mechanism. For oxide scales on TiAl surfaces, which had been ion implanted with chlorine before oxidation, a very thin protective alumina layer is formed which, however, develops growth stresses in the range of several GPa, accompanied by intensive acoustic emission. In all stress–time curves, a dynamic situation is observed. This consists of phases of stress relief by scale microcracking and phases of stresses increase due to crack healing and further oxide growth. As a result, the level of stress as a function of oxidation time, is characterized by an oscillating course.     

Vom freiwilligen Seminar zur Q2-Pflichtveranstaltung

Definition of the problem: Ethical reasoning cannot be enforced. Voluntary understanding is a basic condition for the development of ethical competencies and attitudes. The aim of this survey was to investigate whether the presence of those students who attended our seminars compulsorily would have a negative effect upon the quality of the course. Methods and results: The participants of our small-group seminars in medical ethics were asked to complete a questionnaire on teaching aims, seminar atmosphere, moderation and importance of subjects. One hundred and ninety-two voluntary participants (2001/2) and 293 compulsory participants (2002/3) completed the questionnaire and were statistically compared. There was no significant difference between voluntary and compulsory participants in any of the important items. However, there were considerable differences in some items between male and female participants. Conclusion: We were surprised that there was no difference between the two groups. This leads us to hope that our concept of case-based small-group seminars will prove capable of realising our teaching aims for all students. The difference between male and female participants may have important didactic consequences and will be the subject of further studies.     

Buchbesprechungen

Ohne Zusammenfassung     

Retention of Escherichia coli in municipal sewage by means of planted soil filters in two-stage pilot plant systems.

Different types of constructed wetlands in a pilot-plant system were fed with identical municipal waste water to compare the sanitisation process in two-stage systems. With combinations of a vertical and a horizontal flow filter an E. coli reduction of 5 log10 with an E. coli influent concentration of 10(7) MPN/100 ml was achieved. Using different filter materials in each stage the total performance of the two-stage system was independent from the sequence of these materials. However, using coarser filter material in the first stage makes the filter less prone to clogging and is thus the preferential option with regard to operational reliability.     

Preparation and Characterization of Novel Polyimides from 2,6-bis[1-(p-dimethylaminophenylimino)ethyl] pyridine for the Selective Extraction of some Metals

Summary A group of new polyimides has been prepared by solution condensation of 2,6-bis[1-(p-dimethylaminophenylimino)ethyl] pyridine containing pendant NMe₂ units and various dianhyrides in N-methylpyrrolidone (NMP). The tridentate (N-N′-N) pydim ligands were prepared by Schiff-base condensation of 2,6-diacetylpyridine and 4-dimethylaminoaniline in the presence of formic acid as catalyst. These polymers were investigated for their extraction capabilities for Zn(II), Mn(II), Cu(II), Cd (II) and Ni(II) and at different pH. Under different conditions enhanced selectivity was observed. Up to 98% quantitative recoveries were observed for all metals.     

“Ärztliche Freiheit und Berufsethos“ — Hängen ärztliche Berufsfreiheit und ärztliches Berufsethos zusammen?

Ohne Zusammenfassung     

Production of maraging steel grades and the influence of specified and nonspecified elements for special applications

The material properties of maraging steels are greatly affected by the alloy and inclusion content and hence by the production route. This paper describes various past and current production routes at Böhler Edelstahl GmbH and the effect of these routes on the specified element (alloy) and non-specified element (inclusion) contents. Non-metallic inclusions were investigated by EDX analysis. The effects of various alloying and tramp elements on the material properties are presented as a statistical evaluation of previous melts. Nitrogen solubility was calculated with Thermo–Calc for maraging steel Mat.-No. 1.6354 and the precipitation of nitrides is discussed. A proposal is made for the production of melts with improved properties.     

Phase relations in the ternary system Cu-In-Se

The phase relations of the ternary system Cu-In-Se were studied at 750° C by quenching experiments. Special attention was given to the region CuInSe₂In₂Se₃-In₄Se₃. Only four ternary phases with extended homogeneity ranges were found to exist. They were characterized by X-ray powder diffraction, electron microprobe analysis (EK8PA)' end optical microscopy. Differential thermal analysis (DTA) investigations allowed us to construct theT-x diagram of the Cu₂Se-In₂Se₃. out between 47 and 100 mol% In₂Se₃. Besides, it was also possible to give a tentative diagram of the solid-liquid equilibria at 750° C and to get some information on the sub-solid existence fields beside the Cu₂Se-In₂Se₃ cut.