Results 1 - 10 of 44253
Results 1 - 10 of 44253. Search took: 0.065 seconds
|Sort by: date | relevance|
[en] Due to an oversight, the Surname of Haya Alhummiany was incorrectly spelled in the published online version. The correct surname is “Alhummiany”, instead of “Alhumminay”. The correct spelling is also shown above.
[en] Organized meso porous materials represent a class of molecular sieves because of its high potential for commercial applications in adsorption and catalysis. In this study, organized meso porous alumina was synthesized by the sol-gel method using various organic templates, i.e. cationic, neutral and anionic surfactants. Surface porosity of the synthesized alumina obtained exhibit materials in the meso pore ranges. The morphology of the samples consists of wormhole-like meso structure in the nano-region (20 - 70 nm). Sample with cetyl trimethylammonium bromide as cationic templates has the narrowest pore distribution centred at 8 nm as compared to samples synthesized with Triton X-114 (neutral) and stearic acid (anionic). All samples showed only Lewis acidity. Acidity and meso porous character present in these meso porous alumina samples showed that this material has potential as catalyst support and also used in Lewis acid catalyzed reactions. Study showed that the cationic surfactant is a better template to obtain uniform meso porous alumina that might be due to the weak interaction between the template and the surface of the alumina. (author)
[en] The phenomenon of electrostatic charge in ceramic powders takes place when the particle surfaces enter in contact between them or with the containers. The accumulation of electrostatic charge is of relevance in ceramic powders in view of their insulating character and the risk of explosions during the material handling. In this work the main factors that affect the appearance of intrinsic charge and tribo-charge in ceramic powder have been studied. In ceramic powders of alumina it has been verified that the smallest particle sizes present an increase of the electrostatic charge of negative polarity. A correlation has been observed between the nature of the OH -surface groups and the electrostatic charge. The intrinsic charge and the tribocharge in ceramic powders can be diminished by compensating the surface groups that support the charge. The dry dispersion of nanoparticles on microparticles allows surface charge compensation with a noticeable modification of the powder agglomeration. (Author) 19 refs.
[en] Recent results have strongly suggested that the ballistic-resistance of different comminuted ceramics is similar, independent of the original strength of the material. In particular, experimental work focused on the ballistic response of such materials has suggested that ballistic response is largely controlled by shattered material morphology. Consequently, it has been postulated that control of the nature of ceramic fragmentation should provide a potential route to optimise post-impact ballistic resistance. In particular, such an approach would open up a route to control in multi-hit capabilities. Here, ballistic tests into pre-formed 'fragmented-ceramic' analogues assembled from compacted alumina powders with two differing morphologies were conducted. Strong hints of a morphology-based contribution to ballistic resistance were apparent, although there was insufficient fidelity in the experimental data set to categorically identify the nature of this contribution.
[en] The description of strength behavior and failure behavior of ceramics by means of fracture-mechanical data was based up to now mainly on data obtained for the propagation behavior of single cracks in a material defined otherwise as crack-free. It turned out that in case of failure processes dominated by the single crack event one also has to take into account cracks already existing in the material. An effect of main importance behind the crack tip is discussed first, namely R-curve effect due to crack edge interaction. Furthermore, an effect which essentially considers interaction between main crack and microcracks in the range of the crack tip in the so-called process region has to be considered. This problem was examined experimentally and in theory. The work reported here examined the strength of pre-damaged test pieces and the influence of different crack configurations, which are pre-set by macrocracks and different microcrack fields, on the crack resistance behavior, i.e. on displacement of the KI-intervals in the double torsional test. (orig.) With 3 tabs., 12 figs., 7 refs
[de]In der Beschreibung des Festigkeits- und Versagensverhaltens keramischer Werkstoffe auf bruchmechanischer Grundlage wurde bisher hauptsaechlich das Ausbreitungsverhalten von Einzelrissen in einem ansonsten als rissfrei angesehenen Material betrachtet. Es zeigt sich jedoch zunehmend, dass bei Versagensvorgaengen mit dem Einzelrissereignis auch das Zusammenwirken von im Material vorhandenen Rissen Beruecksichtigung finden muss. Zum einen steht ein Effekt zur Diskussion, der im wesentlichen hinter der Rissspitze Bedeutung hat, naemlich der R-Kurveneffekt infolge der Rissflankenwechselwirkung. Zum anderen muss ein Effekt betrachtet werden, der im wesentlichen im Bereich der Rissspitze in der sogenannten Prozesszone die Wechselwirkung zwischen Hauptriss und Mikrorissen beruecksichtigt. Diese Problemstellung wurde experimentell und theoretisch untersucht. Dazu wurden die Festigkeit vorgeschaedigter Proben und der Einfluss verschiedener Risskonfigurationen, die durch Makrorisse und unterschiedliche Mikrorissfelder vorgegeben sind, auf das Risswiderstandsverhalten und damit auf die Verschiebung der KI-Intervalle im Doppeltorsionsexperiment untersucht. (orig.) With 3 tabs., 12 figs., 7 refs