999 publications from this institution
Nowadays, due to their potential for superior mechanical properties, a considerable interest in bulk ultrafine grained metals exists. One of the possible formation methods for this ultrafine grained material is cryogenic rolling. In this work, the influence of cryogenic rolling on the texture and the microstructure of pure copper is investigated by electron backscatter diffraction (EBSD), both in the deformed and the annealed state. This is done by comparing cryogenically rolled copper with room temperature rolled copper, rolled to the same thickness reductions. A texture difference between the room temperature rolled and cryogenically rolled copper is seen in the deformed state, although the largest texture difference is observed after annealing. These texture differences are mainly attributed to the presence of shear bands in the microstructure of the cryogenically rolled copper. In order to obtain a better understanding of the influence of shear bands on the texture evolution, the grain orientations inside the shear bands are analyzed both experimentally and numerically by applying the visco plastic self-consistent (VPSC) model. A number of shear band specific orientations, which are not observed in the conventional rolling texture of fcc materials, could be identified both in the experimental observations and in the simulations.
The degradation of irradiated human insulin in aqueous solutions was investigated in order to protect the protein against ionizing radiation. The influence of the drug concentration, excipients and irradiation temperature were studied. Aqueous solutions at pH 2 were irradiated by gamma rays or by accelerated electrons. Two different high-performance liquid chromatography (HPLC) methods were used: reverse-phase high-performance liquid chromatography (RP-HPLC)/UV and size exclusion liquid chromatography (SEC/UV) to investigate both the fragmentation and the formation of higher molecular weight proteins. In solution without excipients irradiated at ambient temperature at 10kGy, the loss of human insulin is almost complete. Addition of radio-protecting excipients (free radicals scavengers) and cryo-irradiation allowed to decrease insulin degradation. The best radio-protector used was ascorbic acid in aqueous solution and oxidized glutathione in the frozen solutions. Only the combination of these two approaches (addition of scavenger and freezing) enables the irradiated human insulin in aqueous solution to meet the European Pharmacopoeia requirements for chemical potency (≥90%).
