Inst. Werkstoffwissenschaften und -technologien

124 Items

Recent Submissions
Surface chemistry and stability of metastable corundum-type In2O3

Köck, Eva-Maria ; Kogler, Michaela ; Zhuo, Chen ; Schlicker, Lukas ; Bekheet, Maged F. ; Doran, Andrew ; Gurlo, Aleksander ; Penner, Simon (2017)

To account for the explanation of an eventual sensing and catalytic behavior of rhombohedral In2O3 (rh-In2O3) and the dependence of the metastability of the latter on gas atmospheres, in situ electrochemical impedance spectroscopic (EIS), Fourier-transform infrared spectroscopic (FT-IR), in situ X-ray diffraction and in situ thermogravimetric analyses in inert (helium) and reactive gases (hydro...

High resolution pore size analysis in metallic powders by X-ray tomography

Heim, Korbinian ; Bernier, F. ; Pelletier, R. ; Lefebvre, L.-P. (2016)

The deployment of additive manufacturing processes relies on part quality, specifically the absence of internal defects. Some of those defects have been associated with porosities in the powder feedstock. Since the level of porosity in the powder is generally very low, standard characterisation techniques such as pycnometry and metallography are not suitable for quantification. However, the qua...

Structure and molecular dynamics of thin films of homopolymers and miscible polymer blends

Madkour, Sherif A. (2018)

In recent years, research on nanoscale confinement of polymers has witnessed topical investigations in attempt to tune polymer properties on demand. One of the most studied forms of nanoconfinement are thin films, where 1D confinement results from the reduction of the film thickness. For these systems, it is crucial to understand how confinement affects the glass transition phenomenon and the a...

Der Schäumprozess von Aluminiumlegierungen: Tomoskopische Untersuchung der Gasnukleation

Kamm, Paul Hans (2018)

Die Verbesserung der Struktur metallischer Schäume und damit ihrer Eigenschaften bedarf eines tieferen Verständnisses der während des Schäumens und der späteren Degradation ablaufenden Mechanismen. Um diesen dynamischen Prozess in seiner dreidimensionalen Komplexität und zeitlichen Veränderung zu erfassen wurde in dieser Arbeit das Verfahren der zeitaufgelösten Tomographie (Tomoskopie: Ein Kuns...

Tribologisch induzierte Oberflächenveränderungen im Reib-Verschleiß-Kontakt Kolbenring gegen Zylinderlaufbahn

Biberger, Julian (2017)

In Verbrennungsmotoren ist der Tribokontakt Topring gegen Zylinderlaufbahn einer der am höchsten beanspruchten Kontakte. Die Anforderungen an Reibungsoptimierung und geringen Verschleiß bei gleichzeitig hoher Laufzeit erfordern ein detailliertes Verständnis dieses tribologischen Kontaktes. Aus diesem Grund ist es erforderlich, unterschiedliche Kolbenringbeschichtungen auf ihr tribologisches Ver...

Ultramicroporous silicon nitride ceramics for CO2 capture

Schitco, Cristina ; Seifollahi Bazarjani, Mahdi ; Riedel, Ralf ; Gurlo, Aleksander (2015)

Carbon dioxide (CO2) capture is regarded as one of the biggest challenges of the 21st century; therefore, intense research effort has been dedicated in the area of developing new materials for efficient CO2 capture. Here, we report high CO2 capture capacity in the low region of applied CO2 pressures observed with ultramicroporous silicon nitride-based material. The latter is synthesized by a fa...

Suitability of various complex hydrides for foaming aluminum alloys

Kamm, Paul H. ; García-Moreno, Francisco ; Jiménez, Catalina ; Banhart, John (2013)

Some hydrides that could replace TiH2 as the hitherto most suitable blowing agent for foaming aluminum alloys were investigated. Hydrides taken from the group MBH4 (M = Li, Na, K) and LiAlH4 were selected since these have not been studied in the past although their decomposition characteristics appear to be suitable. Foamable precursors of alloy AlSi8Mg4 were manufactured by pressing blends of ...

A study on the thermal conversion of scheelite-type ABO(4) into perovskite-type AB(O,N)(3)

Li, Wenjie ; Li, Duan ; Gao, Xin ; Gurlo, Aleksander ; Zander, Stefan ; Jones, Philip ; Navrotsky, Alexandra ; Shen, Zhijian ; Riedel, Ralf ; Ionescu, Emanuel (2015)

Phase-pure scheelite AMoO(4) and AWO(4) (A = Ba, Sr, Ca) were thermally treated under an ammonia atmosphere at 400 to 900 degrees C. SrMoO4 and SrWO4 were shown to convert into cubic perovskite SrMoO2N and SrWO1.5N1.5, at 700 degrees C and 900 degrees C respectively, and to form metastable intermediate phases (scheelite SrMoO4-xNx and SrWO4-xNx), as revealed by X-ray diffraction (XRD), elementa...

Slow crystallisation of a monodisperse foam stabilised against coarsening

Meagher, Aaron J. ; Whyte, David ; Banhart, John ; Hutzler, Stefan ; Weaire, Denis ; García-Moreno, Francisco (2015)

The evolution of a three-dimensional monodisperse foam was investigated using X-ray tomography over the course of seven days. The coarsening of the sample was inhibited through the use of perfluorohexane gas. The internal configuration of bubbles is seen to change markedly, evolving from a disordered arrangement towards a more ordered state. We chart this ordering process through the use of the...

Annihilation of structural defects in chalcogenide absorber films for high-efficiency solar cells

Mainz, Roland ; Sanli, Ekin Simsek ; Stange, Helena ; Azulay, Doron ; Brunken, Stephan ; Greiner, Dieter ; Hajaj, Shir ; Heinemann, Marc D. ; Kaufmann, Christian A. ; Klaus, Manuela ; Ramasse, Quentin M. ; Rodriguez-Alvarez, Humberto ; Weber, Alfons ; Balberg, Isaac ; Millo, Oded ; Aken, Peter A. van ; Abou-Ras, Daniel (2016)

In polycrystalline semiconductor absorbers for thin-film solar cells, structural defects may enhance electron-hole recombination and hence lower the resulting energy conversion efficiency. To be able to efficiently design and optimize fabrication processes that result in high-quality materials, knowledge of the nature of structural defects as well as their formation and annihilation during film...

The contrasting effect of the Ta/Nb ratio in (111)-layered B-site deficient hexagonal perovskite Ba5Nb4-xTaxO15 crystals on visible-light-induced photocatalytic water oxidation activity of their oxynitride derivatives

Hojamberdiev, Mirabbos ; Bekheet, Maged F. ; Zahedi, Ehsan ; Wagata, Hajime ; Vequizo, Junie Jhon M. ; Yamakata, Akira ; Yubuta, Kunio ; Gurlo, Aleksander ; Domen, Kazunari ; Teshima, Katsuya (2016)

The effect of the Ta/Nb ratio in the (111)-layered B-site deficient hexagonal perovskite Ba5Nb4-xTaxO15 (0 <= x <= 4) crystals grown by a KCl flux method on visible-light-induced photocatalytic water oxidation activity of their oxynitride derivatives BaNb1-xTaxO2N (0 <= x <= 1) was investigated. The Rietveld refinement of X-ray data revealed that all Ba5Nb4-xTaxO15 samples were well crystallize...

Characterization and mechanical properties investigation of the cellulose/gypsum composite

Nindiyasari, Fitriana ; Griesshaber, Erika ; Zimmermann, Tanja ; Manian, Avinash Pradip ; Randow, Clemens ; Zehbe, Rolf ; Fernandez-Diaz, Lurdes ; Ziegler, Andreas ; Fleck, Claudia ; Schmahl, Wolfgang W. (2016)

We synthesized cellulose/gypsum composites in the presence and absence of sodium alginate and investigated the interaction between the composite components as well as the mechanical properties of the final composites. Four different types of cellulose fiber materials were used: cellulose UFC100, cellulose B400, nanofibrillated cellulose, and Lyocell fiber. For all investigated composites the to...

Über den Wirkmechanismus von Polyethylenglykol als Additiv zur Gefügeverdichtung im Rotationsformverfahren

Rohnstock, Falk (2018)

Eines der Hauptprobleme beim Rotationsformen sind verbleibende eingeschlossene Luftblasen, die die Sinterzeit verlängern und die Festigkeit, aber auch die Ästhetik des Bauteils beeinträchtigen. Überraschenderweise konnten Kulikov und Kollegen (2009) zeigen, dass der Zusatz einer geringen Menge von Polyethylenglykol (PEG) den Sinterprozess erheblich beschleunigt und den Anteil verbleibender Luft...

Untersuchungen zum Strangpressen von Aluminiumhohlprofilen mit axial variabler Wandstärke

Negendank, Maik (2017)

Ein möglichst ressourcenschonender Umgang mit den auf der Erde vorhandenen natürlichen Rohstoffen, insbesondere den fossilen Energieträgern, dem Ziel einer Minderung der globalen CO2-Emmissionen und einer Begrenzung der Erderwärmung machen im industriellen Transportsektor innovative Leichtbauentwicklungen notwendig. Aluminiumlegierungen sind derzeit im Leichtbaubereich der am häufigsten eingese...

Radiographic and tomographic investigation of water transport in operating polymer electrolyte membrane fuel cells

Alrwashdeh, Saad Sabe' (2017)

Fuel cells are foreseen to play a leading role in many future sustainable energy strategies as they allow for environmental friendly and locally pollutant-free energy conversion systems. One of the most important and prevalent types is the polymer electrolyte membrane fuel cell (PEMFC). One of the key issues of the PEM fuel cell is the water management since efficiency, cell performance and...

Changes of valence state and local structure in anode materials for lithium-ion batteries by X-ray absorption spectroscopy

Zhou, Dong (2017)

Electronic and local structural changes in three different promising anode materials (porous NiSi2/Si composite, nano-crystalline NiFe2O4 and ZnFe2O4) for lithium ion batteries are investigated by X-ray absorption spectroscopy. The lithium storage mechanism and associated structural changes are derived not only from the average valence states of the absorption atoms (Ni, Fe and Zn) estimated fr...

Optimierung der mechanischen Eigenschaften von 7xxx-Aluminiumlegierungen durch gezielte Einstellung der Mikrostruktur

Paulisch, Melanie Cornelia (2017)

In der vorliegenden Arbeit werden die Einflüsse des Strangpressens und Wärmebehandelns auf die Mikrostruktur und die mechanischen Eigenschaften vier verschiedener ausscheidungshärtbarer 7xxx-Legierungen (7108, 7020, 7021B und 7175) untersucht. Darüber hinaus wurde das quasistatische und dynamische Verformungsverhalten bezüglich Veränderungen in der Kornmorphologie und Textur analysiert. Dazu wu...

X-ray radiographic and tomographic investigations of cycled lithium ion batteries

Sun, Fu (2017)

Lithium ion batteries (LIBs) have become the predominant power supplies in portable electronic devices such as cell phones, laptops and tablets. They are regarded as promising candidates to power future electric vehicles and to store the intermittent and fluctuating energy harvested from solar and wind sources. Unfortunately, the current LIB technology fails to meet the growing energy demand re...

Alterung und Lebensdauervorhersage von O-Ring-Dichtungen

Kömmling, Anja (2017)

In some applications, elastomer seals have to remain leak tight over extended time periods (up to several decades) as an exchange of the seals is not practical. Therefore, it is necessary to be able to predict the lifetime of such seals reliably. For this reason, ageing experiments with O-rings and sheets based on hydrogenated acrylonitrile butadiene rubber (HNBR), ethylene propylene diene rubb...

Charakterisierung von Glas-Polymer Verbundmaterialien für die Hochdruckspeicherung von Wasserstoff

Prewitz, Marc (2017)

This thesis investigates glass capillaries and structures consisting of borosilicate glass (Simax) for high pressure hydrogen storage. The finite element method (FEM) is used for the mechanical analyses and the design optimization. The necessary characteristic values for the material descriptions are determined by experimental tests. The strength, the shear strength of the interface glass/adhe...