Effect of structure on tribomechanical properties of sintered (Al-12Si)-Sn composites

The structure, mechanical and tribological properties of sintered (Al-12Si)-xSn composites were investigated in the present study. The composites were obtained by sintering of the briquettes made of aluminum (Al-12Si) and tin powders mixture. It was found that the hot densification substantially increases the strength of sintered composites and also makes much higher their wear resistance under the dry friction against a steel counterbody. The mechanical properties of the obtained materials slowly decrease with an increasing of tin content up to 40 wt. %, while their wear resistance increases

Influence of the duration of aging the system Ti/Al2O3 in a hydrogen atmosphere on hydrogen sorption, adhesion, tribology, and electrical conductivity of the film

Publisher's version (útgefin grein)This paper reports results on the interaction between an aluminum oxide film, deposited on technically pure titanium of grade VT1-0 by the magnetron reactive sputtering method, and a hydrogen-containing atmosphere. Such a study is important in order to find protective coatings that would prevent the penetration of hydrogen inside a product. A given system aged in a hydrogen atmosphere in the interval of 1‒4 hours at a pressure of 2∙105 Pa (2 bar) and a temperature of 400 °C. We have acquired data on the distribution of hydrogen along a film thickness and its content in a thin-film system. It is shown that hydrogen diffuses into the film and builds up in it up to three hours, and only then it begins to penetrate the substrate. We have managed to increase aging duration in a hydrogen-containing environment and increase the temperature of heating up to the stage of film destruction. In the case of the starting film and after aging from 1 to 3 hours the adhesion force between a film and a substrate increases, apparently due to the formation of hydrogen bonds film-substrate. The adsorption of hydrogen atoms at the surface of the Al2О3 film is accompanied by an increase in its conductivity by not larger than 4 % with the increased time of aging. Such a change in the conductivity of the Al2О3 film can be explained based on the formation of a zone structure. Thin oxide films may possess continuous one-side conductivity, but in the case the film is thick (0.5 µm and above), it is not possible to argue about the one-side conductivity. The data acquired on the influence of aging duration in a hydrogen atmosphere indicate an increase in adhesive strength by almost 6 times within 3 hours and by 2.5 times in 4 hours. The determined coefficient of film friction increases by not larger than 2.5 times. By measuring the electrical conductivity of the film surface, it was found that it increases with an increase in the time of aging in a hydrogen atmosphere. This pattern is obviously linked to the creation of transitions of the p-n-type in the film of aluminum oxide at the expense of hydrogen ionsPeer Reviewe

A disintegrin derivative as a case study for PHIP labeling of disulfide bridged biomolecules

A specific labeling strategy for bioactive molecules is presented for eptifibatide (integrilin) an antiplatelet aggregation inhibitor, which derives from the disintegrin protein barbourin in the venom of certain rattlesnakes. By specifically labeling the disulfide bridge this molecule becomes accessible for the nuclear spin hyperpolarization method of parahydrogen induced polarization (PHIP). The PHIP-label was synthesized and inserted into the disulfide bridge of eptifibatide via reduction of the peptide and insertion by a double Michael addition under physiological conditions. This procedure is universally applicable for disulfide-containing biomolecules and preserves their tertiary structure with a minimum of change. HPLC and MS spectra prove the successful insertion of the label. 1H-PHIP-NMR experiments yield a factor of over 1000 as lower limit for the enhancement factor. These results demonstrate the high potential of the labeling strategy for the introduction of site selective PHIP-labels into biomolecules’ disulfide bonds