Wachstum von Silber-Ausscheidungen in Aluminium unter Last und Temperatur

Die Temperaturabhängigkeit des Ausscheidungswachstums wurde an zwei Legierungen Al-2at%Ag und Al-6at%Ag untersucht. Es wurde die Änderung der Radien und der Abstände der Ausscheidungen einmal mit Hilfe des "Guinier Fits" und einmal mit Hilfe des "Hard-Sphere-Modells" bestimmt, graphisch dargestellt und verglichen. Um das Experiment zu realisieren, wurde im Rahmen der Diplomarbeit ein Ofen entwickelt, der in eine Zugmaschine einbaubar und röntgendurchlässig ist. Damit war es möglich, die Probe während eines Zugversuches zu beheizen, um eine eventuelle Änderung in der Ausscheidungsform in Abhängigkeit einer von außen angelegten Kraft und einer Temperatur zu untersuchen. Es wurde festgestellt, dass im Rahmen der Auflösungsgrenze von etwa 1% keine messbare Änderung in der Form stattfindet. Alle Versuche wurden in der Röntgenkleinwinkelanlage "NANO-STAR" der Firma Bruker-AXS durchgeführt.The temperature dependence of the precipitation growth was investigated by two alloys: Al-2at%Ag and Al-6at%Ag. Changes in radii and the mean distance between the precipitations were, firstly, determined by "Guinier-fits" and afterwards by using the "Hard-Sphere-Model". The results of both calculation methods are depicted in graphics and are compared with each other. To realize the experiment, an X-Ray transparent furnace was developed which could be mounted on the tensile machine. Due to this furnace, the investigation of the precipitations' shape modification in dependence of external load and temperature was possible. It was found out that there were no measurable changes in shape within a resolution limit of 1%. All experiments were carried out in the Small Angle X-Ray Scattering-machine "NANO-STAR" by Bruker-AXS

Timescales of self-healing in human bone tissue and polymeric ionic liquids

Strain (stress-free) relaxation in mechanically prestrained bone has a time constant of 75 s. It occurs by a reorganization of the proteoglycan-glycoprotein matrix between collagen fibers, which requires ionic interactions. Dissolving and relinking the ionic bonds is thus an important tool of nature to enable plastic deformation and to develop self-healing tissues. A way to transfer this approach to technical materials is the attachment of ionic end groups to polymeric chains. In these classes of materials, the so-called polymeric ionic liquids, structural recovery of thermally disorganized material is observed. A time constant between minutes and a week could be achieved, also by ionic rearrangement. The same mechanism, rearrangement of ionic bonds, can lead to vastly different relaxation times when the ionic interaction is varied by exchange of the cationic end groups or the anions

Inorganic–organic hybrid materials through post-synthesis modification: Impact of the treatment with azides on the mesopore structure

Hybrid, hierarchically organized, monolithic silica gels, comprising periodically arranged mesopores and a cellular macroscopic network, have been prepared through a co-condensation reaction of tetrakis(2-hydroxyethyl)orthosilicate with chloromethyl-trimethoxysilane or 3-(chloropropyl)-triethoxysilane. Subsequent conversion of the chloro groups into azido groups, by nucleophilic substitution with NaN3 in N,N-dimethylformamide, was conducted upon preservation of the monolithic structure. However, treatment with NaN3 had a strong influence on the structure in the mesoporous regime, with changes such as an increase of mesopore diameter, pore volume and lattice constants, as well as a concomitant decrease of the pore wall thickness, as confirmed by small angle X-ray scattering, transmission electron microscopy, and nitrogen sorption analysis. Similar effects were observed for unmodified silica gels by simple ageing in azide-containing media, whether a relatively small or a sterically demanding counter ion (Na+ or (H3C)4N+) was used. The structural modification did not seem to depend greatly on whether an organic aprotic solvent (N,N-dimethylformamide, 1,1,3,3-tetramethylurea, 1,3-dimethyl-2-imidazolidinone) or a protic solvent that can form hydrogen bonds, such as water, was used

Hierarchically Nanostructured Polyisobutylene-Based Ionic Liquids

A new type of highly temperature stable ionic liquid (IL) with strongly temperature dependent nanostructures is reported. The molecular design relies on the use of a liquid polymer with an ionic liquid headgroup, introducing liquid properties by both the polymeric and the ionic liquid (IL) headgroup. The IL polymers (poly­(isobutylene)­s) <b>3a</b>–<b>3c</b> (PIB-ILs) were prepared by a combination of living carbocationic polymerization (LCCP) and subsequent “click” chemistry for attachment of methylimidazolium (<b>3a</b>), pyrrolidinium (<b>3b</b>), and triethylammonium cations (<b>3c</b>). All three investigated PIB-ILs exhibited pronounced nanostructural organization at room temperature depending strongly on the nature of the anchored cation. Whereas the morphology of the imidazolium-based PIB-IL <b>3a</b> shows high thermal stability up to the decomposition temperature, order–order (OOT) and lattice disorder–order transitions (LDOT) characteristic for common ionomers could be observed in the case of pyrrolidinium <b>3b</b> and ammonium-based <b>3c</b> PIB-ILs. Control of flow behavior as well as adjustable relaxation times from the liquid to the viscoelastic regime can be adjusted by choice of the appropriate IL headgroup