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Due to its simplicity, speed and ability to obtain a particle number size distribution, single particle ICP-MS (spICP-MS) has emerged as an important tool for the analysis of nanoparticles (NPs). However, when NPs are suspended in a complex, unknown solution, matrix effects can occur affecting the instrument’s sensitivity. As a result, an over- or underestimation of the particle size is possible.
In this work, a proof-of-concept study of the combination of isotopic dilution analysis (IDA) and spICP-MS compensating for possible matrix effects is presented. As an example, an isotopically enriched 109Ag standard solution was added to silver NPs (Ag NP) suspensions. Different NP suspensions with mean particle diameters between 30 and 80 nm were chosen. The mixtures were analyzed using a quadrupole ICP-MS instrument. Both Ag isotopes (107Ag and 109Ag) were monitored during one experiment. The result show a good agreement with the diameters obtained using conventional spICP-MS.
In a second step, the Ag NPs were suspended in a simulated seawater matrix. Using conventional spICP-MS, a great reduction in the signal intensities and consequently in the particle sizes, was monitored. The application of the IDA-spICP-MS approach on these samples was able to obtain similar diameters compared to the samples without matrix.
Impact of biocomponents in the fuel and heating oil on the compatibility of sealing materials
(2016)
The objective of this research was to determine the resistance of frequently used sealing materials such as FKM, FVMQ, VMQ, EPDM, CR, CSM, IIR, PA, NBR and PUR in fuels and heating oil with and without admixtures of biogenic sources such as E10, diesel fuel with 5 % biodiesel, non-aged and 2 year aged B10 (heating oil with 10 % biodiesel), pure diesel, standard heating oil and premium grade fuel Super plus at 20 °C, 40 °C and 70 °C.
Mass, tensile strength and breaking elongation of the test specimens were determined before and after the exposure for 84 days in the fuels. The visual examination of some elastomer test specimens clearly showed the great volume increase until break or partial dissolution. Shore hardness A and D (for PA) were determined before and after exposure of the test specimens in the biofuels for 42 days.
There is not determined a threshold for the reduction in tensile properties and Shore hardness in the international standards. Therefore a threshold of 15 % was determined for the evaluation of the compatibility.
In summary, it can be therefore stated that the chemical resistance of the fluoropolymers FKM and FVMQ in fuels and biofuels is the best one.
Höherfester Feinkornbaustahl (FKB) mit Streckgrenzen ≥ 690 MPa ist als Konstruktionswerkstoff in vielen Industriebranchen unentbehrlich geworden. Anzuführen sind bspw. der Kran-, Nutzfahrzeug-, Brücken-/Anlagenbau und zunehmend auch der allgemeine Stahlbau. Wesentliche Schwerpunkte sind die Maximierung der Nutzlasten (z.B. Trage-, Hublasten usw.) und damit verbundene Ressourceneinsparungen. Eine Werkstoffsubstitution der niederfesten (S235) mit höherfesten Stahlgüten ermöglicht bei gleicher Beanspruchbarkeit eine Reduzierung des Werkstoffeinsatzes von bis zu 70% und kann zu einem Schweißkostenverhältnis von 6 zu 1 führen. Mit zunehmender Festigkeit der FKB werden deutlich höhere Anforderungen an deren schweißtechnische Verarbeitung gestellt. Dies betrifft die Wärmeführung beim Schweißen und die damit verbundene Kaltrissvermeidung. So kam es in der Vergangenheit leider immer wieder zu Schadensfällen, weil gerade die Sensibilität gegenüber einer Degradation der mechanischen Eigenschaften der höherfesten FKB, durch den im Lichtbogen aufgenommenen Wasserstoff, mit steigender Festigkeit signifikant zunimmt und zu wasserstoffunterstützten Kaltrissen führen kann. Für konventionelle MSG-Schweißprozesse liegen bereits Erfahrungen und Regelwerke zur Wärmeführung und entsprechende Wasserstoffgrenzwerte vor. Diese Kenntnisse sind jedoch nicht auf moderne Lichtbogenprozesse mit modifizierten Sprühlichtbogen (mod. SLB) aufgrund deren Prozesscharakteristik übertragbar.
Die schädigende Alkali-Kieselsäure-Reaktion (AKR) im Beton stellt in Teilbereichen nach wie vor ein Problem bei der Bewertung der Dauerhaftigkeit von Beton dar. Eine der häufigsten Fragestellungen ist immer noch eine schnelle und sichere Beurteilung der Alkaliempfindlichkeit von Gesteinskörnungen für die Betonherstellung. In der Präsentation wird gezeigt, welchen Beitrag die Gesteinskörnung zur AKR im Beton hat. Dabei wird die Alkaliempfindlichkeit von Gesteinskörnungen quantifiziert und die zu erwartende Schädigung des Betons durch die Gesteinskörnung detaillierter als bisher möglich klassifiziert. Im Vordergrund der Präsentation steht dabei das Verständnis der Auflösungsprozesse von Gesteinskörnungen in KOH-Lösungen (pH ≥ 13) bei unterschiedlichen Reaktionsbedingungen.
Anhand von Löseversuchen an den originalen Lieferkörnungen der Gesteinskörnungen bei 40 °C und mit 1,0 M KOH-Lösung ist es möglich, die Reaktivität der Gesteinskörnungen mit den ermittelten SiO2- und Al2O3-Konzentrationen der alkalischen Lösungen zu beschreiben. Durch eine erhöhte Temperatur von 80 °C und eine abgesenkte Konzentration der KOH-Lösung von 0,1 M können innerhalb von 56 Tagen vergleichbare Ergebnisse zu den Resultaten der Löseversuche bei 40 °C und 1,0 M KOH-Lösung erreicht werden.
In der alkalischen Lösung wird ein bestimmter Teil des gelösten SiO2 durch ebenfalls vorhandenes Al2O3 alumosilikatisch gebunden. Der verbleibende Teil des gelösten SiO2 steht für eine AKR zur Verfügung. Aus der zeitabhängigen Darstellung dieser SiO2-Konzentration wird die Lösegeschwindigkeit ermittelt. Dabei werden vier aufeinanderfolgende Phasen dem Dehnungs- und Rissbreitenverlauf der Probekörper des 40 °C-Betonversuchs zugeordnet. Zur Beurteilung der Alkaliempfindlichkeit einer Gesteinskörnung sind die Lösegeschwindigkeiten der letzten drei Phasen entscheidend.
Die Methode bietet eine Möglichkeit, die Alkaliempfindlichkeit einer Gesteinskörnung schnell, sicher und genauer als bisher zu bestimmen. Besonders vorteilhaft sind dabei die direkte Prüfung der Gesteinskörnung an der originalen Korngröße (Lieferkörnung), die zementunabhängige Prüfung, sowie die einfache experimentelle Durchführung und Auswertung.
Despite the many controversial discussions about the nanometric confinement effect and the predictions of the three-layer model, much remain not understood and/or experimentally unproven. Here, a combination of Broadband Dielectric Spectroscopy (BDS), Specific Heat Spectroscopy (SHS), and ellipsometry was utilized to investigate the glassy dynamics of ultra-thin films of Poly (vinyl methyl ether) (PVME) and PVME/Polystyrene (PS) 50:50 wt-% miscible blend (thicknesses: 8nm - 200nm). For BDS measurements, a recently developed nano-structured sample arrangement; where ultra-thin films are spin-coated on an ultra-flat highly conductive silicon wafer and sandwiched between a wafer with nanostructured silica nano-spacers, was used. For PVME films, two processes were observed and interpreted to be the α-processes of a bulk-like layer and an absorbed layer to the substrate. BDS and SHS showed that glassy dynamics are bulk-like. However, for films lower than 15nm, BDS showed weakly slowed dynamics. For PVME/PS blend, by a self-assembling process, a nanometer-thin surface layer with a higher molecular mobility is formed at the polymer/air interface. By measuring the dynamic Tg in dependence on the film thickness, both BDS and SHS, showed that the Tg of the whole film was strongly influenced by that nanometer thick surface layer, with a lower Tg.
A novel process to structure the surfaces of low temperature co-fired ceramics (LTCC) is presented. Lowered and raised structures are formed by hot-embossing with glass-like carbon molds during pressure-assisted sintering. Molding is driven by viscous flow of the LTCC glassy phase above the glass transition temperature. For accurate molding of embossments on the LTCC surface, proper filling of cavities in the glass-like carbon mold is necessary. Therefore, de-airing of the mold cavity has to be assured. Two strategies have been investigated: (i) hot-embossing at 850 °C after termination of LTCC shrinkage with de-airing through vent holes in the mold; and (ii) hot-embossing of open porous LTCC at 775 °C with dense molds, de-airing through pore channels in the LTCC, and subsequent densification by further heating to 850 °C. Circular embossments with 10 mm diameter were molded on a commercially available LTCC (Ceramtape GC, CeramTec GmbH, Marktredwitz, Germany). The sintered height was measured using optical profilometry. Image processing was used to evaluate porosity distributions in the sintered structures. The influence of embossing temperature on LTCC viscosity and mold filling behavior is discussed. Successful molding of 47 µm high raised grids and characters by hot embossing with 0.41 MPa at 775 °C and further heating to 850 °C under constant load is demonstrated. Thereby, the high potential of hot-embossing for precise structuring of LTCC surfaces is illustrated.
Currently, residual stresses in welded HSLA (high strength low alloyed steels) are considerded by simplified “robust” procedures fixed in common standards (such as Eurocode 3). The models are mostly based on specimens from mild steel with lower strength. For HSLA, necessary material data is less available for realistic assessment of the appearing residual stresses in typical I-girders. Hence, the economic benefit of HSLA steels in scope of load bearing capacity cannot fully be exploit. Thus, the scope of this work is the measurement of weld residual stresses in component-like I-girders S355 and S690 by sectioning method and subsequent verification by global structural welding simulation.
Epoxy/Carbon nanotube (CNT) composites are interesting materials that could be used in a wide variety of applications. In this study, CNT contents of 0.25, 0.5, 1 and 2 wt% were used for reinforcing epoxy. A nanoindentation device and a temperature regulating system were developed in order to investigate the effect of CNTs on the time-dependent properties of epoxy using relaxations and creep tests on the nano scale. The relaxation tests showed a significant shift for the relaxation spectrum towards shorter times with introducing a low CNT content of 0.25 wt%. Additionally, creep tests showed that both the holding time at a constant load and the unloading velocity have a major effect on the contact stiffness. However, there was no effect for the CNTs on the creep behavior with contents lower than 1 wt%, which was related to the presence of a percolation threshold around this value.
Hydrogen can cause unexpected material failure under consideration of stresses (external/internal) during manufacturing, processing or service of the materials. This failure is mostly based on a certain degradation of the mechanical properties. Thus, the correlation of hydrogen trapping vs. a respective microstructure is necessary for high strength steels. Thus, the scope of this work is the improvement of existing hydrogen trap models by verification of activation energies for hydrogen traps as well as the influence of the determination method. In this scope, the thermal desorption method is appropriate to distinguish between different hydrogen traps. Nevertheless, the specimen temperature has to be accounted very carefully in case of calculating the necessary trap energy.
Experimental simulation of dissimilar weld metal in high manganese steels by arc metling technique
(2016)
High manganese steels have great potential for use in automotive lightweight constructions (like car body structures) due to their superior strength and formability. In this scope, welding is the most common joining technique for sheet metal with challenges especially of dissimilar weld joints. In this case, the formation of martensite has to be considered resulting in a certain propability of brittle fracture in a respective load condition. In addition, no reliable weld metal microstructure prediction is possible with currently available constitution diagrams like the Schaeffler or WRC1992-diagram. Thus, the arc melting technique offers the possibility to investigate the effects of dilution on microstructures and properties of weld metal of high manganese steels. The results suggested that a complex indentification of microstructures is possible by directed experiments using the arc metling technique