Untersuchungen zur Löslichkeit,Korngrenzensegregation und chemisch-analytischen Bestimmung des Tellurs im Eisen

Die Löslichkeit von Tellur in Eisen wurde durch licht- und elektronenmikroskopische Prüfung von Fe–Te-Legierungen auf Ausscheidungen bestimmt. In α-Eisen bei 700°C sind etwa 50 ppm und bei 850°C 120 ppm löslich, in γ-Eisen lösen sich bei 930°C 5 ppm und bei 1000°C 22 ppm Te. Bei höheren Konzentrationen wird FeTe_0,9 festgestellt. In Fe–Mn–Te-Legierungen wird das Te als Mangantellurid gebunden, dieses bildet Einschlüsse gemeinsam mit Mangansulfid. In Fe–Ti–Te-Legierungen wird nur ein kleiner Anteil Te in Titansulfiden gelöst. Tellur segregiert an die Korngrenzen von α- und γ-Eisen und bewirkt interkristallinen Bruch. Die mit AES bestimmten Korngrenzenkonzentrationen nehmen mit der Lösungskonzentration zu und erreichen bei Überschreiten der Löslichkeit einen Sättigungswert. Die Korngrenzensegregation nimmt mit zunehmender Temperatur ab. Tellur bewirkt eine auffallende Facettierung der Korngrenzflächen, es entstehen Strukturen mit Terrassen und Stufen. Die Proben brechen hierdurch bereits während der Auslagerung an den Korngrenzen auf und zeigen Kornzerfall. In Mn-haltigen Proben wird keine Korngrenzensegregation des Te beobachtet, wenn das Tellur völlig vom Mangan abgebunden ist; in diesem Fall ist der interkristalline Anteil der Bruchflächen sehr gering. Die chemische Bestimmung von Tellur in Eisen und Stählen kann sehr vorteilhaft mit der Atomabsorptionsspektroskopie durchgeführt werden, es wurden die Flammen- und die Graphitrohrmethode untersucht. Die Bestimmung kleiner Tellurgehalte in Stählen durch Atomisieren im Graphitrohr wird durch Chlorid, Chrom, Mangan und Nickel beeinflußt. Zu einer deutlichen Optimierung des Atomisierungsablaufs führt das Atomisieren von einer in das Graphitrohr eingeführten Plattform. Lediglich Mangan vermindert dann die Intensität des Absorptionssignals. Es wird eine Nachweisgrenze von 0,2 ppm Tellur bei einer relativen Standardabweichung von 30% erreicht. Mit der Flammentechnik gelingt die Bestimmung bis zu 50 ppm Tellur.     

Reactive sputter etching of Al in BCl3

Etching of Al is studied in pure BCl₃ as well as in mixtures with other gases in the reactive sputter etching mode in a cryopumped system. Etch rate, selectivity with respect to positive photoresist, SiO₂ and Si and etch profiles are investigated as a function of gas composition, gas pressure, flow rate and plasma power. Plasma chemical processes are monitored by quadrupole mass spectroscopy as well as by optical emission spectroscopy. Perfectly square Al-profiles can be etched if etch rates are kept below 1000 A/min. Al-patterns running over steep steps can also be clearly defined if a certain amount of overetching can be tolerated. The experimental data indicate that the etch process is reactant supply limited. Anisotropic etching is achieved by either a ‘surface inhibitor mechanism’ or the formation of a sidewall protecting film.     

Magnetic Field‐Induced Phase Transformation in NiMnCoIn Magnetic Shape‐Memory Alloys—A New Actuation Mechanism with Large Work Output

Magnetic shape memory alloys (MSMAs) have recently been developed into a new class of functional materials that are capable of magnetic‐field‐induced actuation, mechanical sensing, magnetic refrigeration, and energy harvesting. In the present work, the magnetic &!hyphen;field‐induced martensitic phase transformation (FIPT) in Ni₄₅Mn_36.5Co₅In_13.5 MSMA single crystals is characterized as a new actuation mechanism with potential to result in ultra‐high actuation work outputs. The effects of the applied magnetic field on the transformation temperatures, magnetization, and superelastic response are investigated. The magnetic work output of NiMnCoIn alloys is determined to be more than 1 MJ m^?3 per Tesla, which is one order of magnitude higher than that of the most well‐known MSMAs, i.e., NiMnGa alloys. In addition, the work output of NiMnCoIn alloys is orientation independent, potentially surpassing the need for single crystals, and not limited by a saturation magnetic field, as opposed to NiMnGa MSMAs. Experimental and theoretical transformation strains and magnetostress levels are determined as a function of crystal orientation. It is found that [111]‐oriented crystals can demonstrate a magnetostress level of 140 MPa T^?1 with 1.2% axial strain under compression. These field‐induced stress and strain levels are significantly higher than those from existing piezoelectric and magnetostrictive actuators. A thermodynamical framework is introduced to comprehend the magnetic energy contributions during FIPT. The present work reveals that the magnetic FIPT mechanism is promising for magnetic actuation applications and provides new opportunities for applications requiring high actuation work‐outputs with relatively large actuation frequencies. One potential issue is the requirement for relatively high critical magnetic fields and field intervals (1.5–3 T) for the onset of FIPT and for reversible FIPT, respectively.     

Occurrence of Aflatoxins and Ochratoxin A in Baby Foods in Portugal

Infants have a more restricted diet and they generally consume more food on a body weight basis than adults. Therefore, the significance and potential health risk of any contaminant in foods consumed by infants is increased and diligent attention must be paid to this particular area. The present study aims to determine the occurrence of aflatoxin M₁ (AFM₁), aflatoxin B₁ (AFB₁) and ochratoxin A (OTA) in processed cereal-based foods (flours) and infant formulae (milk powder) available in the Portuguese market, both sold as conventional and organic origin. Mycotoxin determination was carried out using a method previously applied to duplicate diet samples. This method employed chloroform extraction, liquid–liquid extraction, immunoaffinity column (IAC) cleanup and HPLC analysis with fluorescence detection after post-column derivatisation. Quantification limits were 0.014, 0.004 and 0.028 μg kg⁻¹ for AFM₁, AFB₁ and OTA, respectively. These toxins could only be quantified in 12 of 27 analysed samples (15 positive results): two samples with AFM₁, two samples with AFM₁ and OTA, one sample with AFB₁ and OTA and seven samples with OTA. Positive results concerned four for AFM₁ (26%), one for AFB₁ (7%) and ten for OTA (67%). For these samples, contents ranged between 0.017–0.041 μg AFM₁ kg⁻¹, 0.034–0.212 μg OTA kg⁻¹, and one sample had a value of 0.009 μg AFB₁ kg⁻¹. Considering the presented results, we could provisionally conclude that the presence of these mycotoxins in baby foods does not constitute a public health problem. These are the first results concerning the occurrence of mycotoxins in marketed baby foods in Portugal and this is the first study using the HPLC method, proposed for duplicate diets, in baby food sample analysis.     

Modelle für die Berechnung der Ausziehtragfähigkeit von selbstbohrenden Holzschrauben

Equations to calculate the withdrawal capacity of self-tapping screws, arranged in softwood, were determined. Based on results of 1850 withdrawal tests and by means of a regression analysis one equation for the withdrawal resistance and two further equations for the withdrawal parameter (resistance over nominal screw diameter and penetration depth) were derived. Nominal screw diameter, penetration depth and characteristic density of the softwood used are the independent variables in the equations, which are valid for an angle in the range of 45° to 90° between the screw axis and the grain. The equation for the withdrawal resistance delivers, also in comparison with code rules, the most favourable values. It enables now a more accurate estimation of the withdrawal resistance for wood screws with geometrical properties similar to those of the screws used for the tests. Hence, the benefit of this study is the reduction in testing, which is currently necessary for technical approvals.     

Evaluation and simulation of the peel behavior of polyethylene/polybutene‐1 peel systems

The peel characteristics of sealed low‐density polyethylene/isotactic polybutene‐1 (PE‐LD/iPB‐1) films, with different contents of iPB‐1 up to 20 m.‐% (mass percentage), were evaluated and simulated in dependence on the iPB‐1 content, and in dependence on the peel rate. Sealing involves close contact and localized melting of two films for a few seconds. The required force, to separate the local adhered films, is the peel force, which is influenced, among others, by the content of iPB‐1. The peel force decreases exponentially with increasing iPB‐1 content. Transmission electron microscopy studies reveal a favorable dispersion of the iPB‐1 particles within the seal area, for iPB‐1 concentrations ≥6 m.‐%. Here, the iPB‐1 particles form continuous belt‐like structures, which lead to a stable and reproducible peel process. The investigation of the peel rate‐dependency on the peel characteristics is of important interest for practical applications. The peel force increases with increasing peel rate by an exponential law. A numerical simulation of the present material system proves to be useful to comprehend the peel process, and to understand the peel behavior in further detail. Peel tests of different peel samples were simulated, using a two‐dimensional finite element model, including cohesive zone elements. The established finite element model of the peel process was used to simulate the influence of the modulus of elasticity on the peel behavior. The peel force is independent of the modulus of elasticity, however, the peel initiation value increases with increasing modulus of elasticity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Adsorption of antifouling booster biocides on metal oxide nanoparticles: Effect of different metal oxides and solvents

Controlling the release rate of biocides (antifouling agents) from a paint coating is a key issue for the development of multi-season antifouling marine coatings. One promising approach is the use of nanoparticles onto which biocides are adsorbed to prevent premature depletion of the biocide. Adsorption of one novel (Medetomidine) and six commercially available and widely used antifouling biocides (Chlorothalonile, Dichlofluanid, Diuron, Irgarol, Seanine, Tolylfluanid) onto oxide nanoparticles (Al₂O₃, CuO, MgO, SiO₂, TiO₂, ZnO) was investigated by HPLC and NMR in different organic solvents. Large differences in adsorption strength depending on the type of nanoparticle and solvent employed were observed. It was shown that nanoparticles coordinate preferentially with the imidazole moiety of Medetomidine. Independent of the type of particle this interaction was considerably stronger in comparison to the other biocides. However, the interaction strength was strongly dependant on the type of solvent, where the largest strongest interaction was achieved in o-xylene. In addition field tests were performed where a considerable decrease in release rate was displayed from coatings containing Medetomidine adsorbed to nanoparticles compared to coatings containing Medetomidine as single additive.     

基于转角位移法对正交各向异性桥面板内力的分析计算

由于大量的焊接连接件、高度集中荷载作用和它们导致的大量应力循环,正交各向异性桥面板对疲劳破坏非常敏感。在公路桥中,焊接在桥面板的加劲腹板通常易于遭受疲劳破坏。开发了一个分析模型,可以运用转角-位移法计算应力。它构建了一个桥面板的横截面模型,但是其中考虑了整个正交板的水平和竖向刚度以及纵向加劲肋的扭转刚度。这种方法可以计算桥面板横截面上的所有内力。