Verhalten von Gasturbinenschaufelwerkstoffen bei mechanischer Langzeitbeanspruchung unter Heißgaskorrosion. Teil 2: Metallkundliche Nachuntersuchungen

Behaviour of gas turbine blade materials under mechanical long term loading and hot gas corrosion. Part 2: Metallographical and microanalytical investigations Results of metallographical and microanalytical investigations on selected specimens after mechanical long term creep and LCF-loading under hot gas corrosion conditions will be presented. Uncoated and MCrAlY or Al-diffusion coated specimens of the polycristalline materials IN-738 LC and IN-939 and the single crystal alloys M 002 mod., CM-SX-6 and B 1914 were investigated. The corrosion attack increases with increasing impurities of the hot gas. Internal nitridation and sulphidation of base material or coating is observed after deterioration of the protective scales rich in Cr₂O₃ and/or Al₂O₃.     

Berechnung der Schubspannungs-Abgleitungs-Kurven aus Druckversuchen an mittelorientierten Einkristallen

Mittelorientierte Einkristalle verformen sich im Druckversuch über ihre Länge nicht homogen. Es wird ein Rechenverfahren angegeben, in dem diese Inhomogenitäten berücksichtigt werden und Schubspannungs-Abgleitungskurven für den homogen verformten Teil der Probe errechnet werden können. Die Rechnung wird an experimentellen Ergebnissen von Fe—6 Gew.% Si überprüft.     

Pore bifurcation, growth and pore termination in nanoporous alumina with concave and convex surfaces

The growth of nanoporous alumina on concave or convex aluminium surfaces has been investigated. The number of pores during anodic oxidation increases or decreases almost linearly with the thickness of the oxide which is due to bifurcation or termination of single pores during alumina growth. The anodic oxidation has been constantly conducted in oxalic acid at 40 V. Therefore the average interpore distance has not changed during alumina growth. In earlier papers it has been shown that a bifurcation of pores is the result of the change of voltage and the electrolyte. In this work we have demonstrated that a termination or a bifurcation of pores is also possible by structuring the aluminium to a curved surface with concave or convex properties before oxidation. Those results do not depend on the substrate characteristics or on the alumina preparation techniques.     

Optical characterization of ultrananocrystalline diamond films

Optical properties of the ultrananocrystalline diamond films were studied by multi-sample method based on the combination of variable angle spectroscopic ellipsometry and spectroscopic reflectometry applied in the range 0.6–6.5 eV. The films were deposited by PECVD in a conventional bell jar (ASTeX type) reactor using dual frequency discharge, microwave cavity plasma and radio frequency plasma inducing dc self-bias at a substrate holder. The optical model of the samples included a surface roughness described by the Rayleigh–Rice theory and a refractive index profile in which Drude approximation was used. The results conformed with the present understanding of the polycrystalline diamond growth on the silicon substrate because the existence of silicon carbide and amorphous hydrogenated carbon film between the silicon substrate and nucleation layer was proved.     

Kommentar II

Ohne Zusammenfassung     

A study on the sorption of NO3− and F− on the carboxymethylated starch‐based hydrogels loaded with Fe2+ ions

Using the principle of geochemistry of fluoride, green and cost effective anion adsorbents were developed for the removal of F^? from water systems. The scheme was further applied for the removal of NO₃^? also. Carboxymethylated starch functionalized through network formation with acrylamide was used as adsorbent, and the resultant hydrogels were loaded with Fe²⁺ ions to generate anchorage for the anions. Sorption of Fe²⁺ was studied as a function of different factors such as time, temperature, pH, and ion strength. The network having the highest Fe²⁺ uptake was loaded with the Fe²⁺ ions under optimum conditions and used for the sorption of F^? and NO₃^?. High efficiency has been observed for F^?, as even up to 100% uptake has been observed within just 10 minutes. The support shows high selectivity for NO₃^?, which was used as anion reference. Thermodynamics of sorption confirms low order and low energy processes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Differences in prevalence of tobacco use among Indian urban youth: the role of socioeconomic status

This study examined whether the distribution of tobacco use and related psychosocial risk factors among youth in urban India vary by socioeconomic status (SES). Data were derived from a cross-sectional survey of students enrolled in the 6th and 8th grades in 32 schools in Delhi and Chennai (N = 11,642). The survey was conducted in 2004, before the implementation of a program designed to prevent and reduce tobacco use (MYTRI). Mixed-effect regression models were used (a) to determine the prevalence of tobacco use among private (higher SES) and government (lower SES) school students, (b) to investigate whether certain psychosocial factors were associated with increased tobacco use, and (c) to determine how these factors varied by school type. Ever-use of multiple forms of tobacco (e.g., gutkha, bidis, and cigarettes) was more prevalent among government school students than private school students. After adjusting for city, gender, grade, and age, we found the prevalence rate for ever-use of any tobacco product to be 18.9% for government school students, compared with 12.2% for private school students (p<.01). Students in government schools scored lower than private school students on most psychosocial risk factors for tobacco use studied here, indicating higher risk. Government school students scored the lowest for refusal skills, self-efficacy, and reasons not to use tobacco. Social susceptibility to chewing tobacco and social susceptibility to smoking were strong correlates of current tobacco use among government school students. Exposure to tobacco advertising was also a strong correlate of current tobacco use for government school students but not private school students. In two large cities of India, students attending government schools are using many forms of tobacco at higher rates than private school students. The psychosocial risk profile of government school students suggests they are more vulnerable to initiation and use and to outside influences that encourage use.     

The Impact of Zeta Potential and Physicochemical Properties of TiO2‐Based Nanocomposites on Their Biological Activity

The aim of this research was to observe the relationship between zeta potential, morphology, surface area, porosity, chemical composition, and ecotoxicity of nanocomposite powders such as Au/TiO₂, Ag₂O/TiO₂, PdO/TiO₂, Ag/TiO₂/SiO₂, Ag/N(C)TiO₂, and SiO₂/TiO₂ from which Ag₂O/TiO₂, Ag/N(C)/TiO_2, and Ag/TiO₂/SiO₂ were exhibiting good antimicrobial properties. It was observed, that nanomaterials characterized by similar morphology and zeta potential revealed the similar toxic behavior. The samples of higher agglomeration and higher zeta potential, especially Ag/TiO₂/SiO₂ xerogel and TiO₂/SiO₂ aerogel were generally less ecotoxic to water organisms and plants. They were also not genotoxic in concentrations up to 500 and 250 mg/L, respectively.