1,721,350 research outputs found
Il Progetto MWCVI: stato di avanzamento e prospettive
No full textAtti del Centro Interdipartimentale di Ingegneria dei Material
Modeling and development of a microwave heated pilot plant for the production of SiC-based ceramic matrix composites
No full textThis paper outlines the development of a microwave heated apparatus for the production of silicon carbide (SiC) based ceramic matrix composites via chemical vapor infiltration. An innovative pilot scale reactor was designed and built. A coupled thermal and electromagnetic model was developed in order to predict the temperature profile inside the reactor. The results obtained from the model demonstrated that the electric field inside the sample was constant. This fact is particularly important in order to prevent the thermal instabilities (run-aways) that are typical in the case of microwave heating. Therefore the heating was uniform with the aid of a mode stirrer that achieved a better distribution of the microwave power and then improved the process efficiency. The infiltration cycles were carried out on SiC fiber preforms and resulted in an excellent average weight increase with respect to the initial sample. By using microwave heating, the treatment times were considerably reduced with respect to the conventional process times reported in the literature. The microstructure of the SiC composites were observed by scanning the electron microscopy in order to evaluate the quality and the degree of densification which was achieved within the fiber tows. The SiC deposition inside of the sample was sufficiently homogeneous and compact, even if a certain degree of inter-tow porosity was still evident
On the use of dynamic mechanical thermal analysis (DMTA) for measuring glass transition temperature of polymer matrix fibre reinforced composites
No full textDer Einfluss einer Oberflächenbeschichtung von gefälltem Calciumcarbonat auf die mechanischen Eigenschaften von polymeren Nanocomposites
No full textPrecipitated calcium carbonate particles coated with stearin prepared in the aqueous medium were investigated in this work. The surface characterisation indicated that the adsorption of stearin onto the PCCs surface was controlled by a micelle-adsorption mechanism, which resulted in two types of coating layers with different chemicalphysical properties: a chemisorbed monolayer bonded directly with the PCC surface and one or more physisorbed stearate layers linked with the monolayer. More interestingly, the monolayer yielded by the water coating process showed a non-complete surface coverage. The surface energy of the coated PCC particles was also analysed in this research to find that stearin coating can effectively decrease the surface tension of the PCCs nanoparticles. HDPE/PCCs composites were prepared in this work, and the influence of the surface coating amount on the mechanical properties was discussed. Compared to the composites with pure PCCs, the impact toughness of the HDPE/PCCs increased as the surface stearin coating amount increased. The improved toughness of the composites filled by coated PCCs with respect to the uncoated PCCs was attributed to the weaker interfacial adhesion with the matrix and to the good dispersion of PCCs particles due to the stearin surface coating.In dieser Arbeit wurden die Partikel von gefälltem Calciumcarbonat (Precipitated Calcium Carbonate = PCC), die in wässrigem Medium mit Stearin beschichtet wurden, untersucht. Die Oberflächengestaltung führt zu der Annahme, dass die Adsorption von Stearin auf der Oberfläche der PCC-Partikel durch einen Mizellen-Adsorptionsmechanismus gesteuert wird, der zu zwei Typen von Beschichtungslagen mit unterschiedlichen chemisch-physikalischen Eigenschaften führt: eine chemisch adsorbierte Monoschicht, die direkt an die PCC-Oberfläche gebunden ist und eine oder mehrere physikalisch adsorbierte Stearatschichten, die mit der Monoschicht verbunden sind. Interessanter ist, dass die beim wässrigen Beschichtungsprozess aufgebrachte Monoschicht die Oberfläche nicht vollständig bedeckt. Die Oberflächenenergie der beschichteten PCC-Teilchen wurde in dieser Untersuchung auch analysiert, wobei sich herausstellte, dass die Stearinbeschichtung die Oberflächenspannung der PCC-Nanopartikel stark herabsetzt. Es wurden für diese Studie HDPE/PCC-Composites hergestellt und der Einfluss der Höhe der Oberflächenbeschichtung auf die mechanischen Eigenschaften wird diskutiert. Verglichen mit den Composites mit reinen PPCs wuchs die Schlagzähigkeit der HDPE/PCCs mit wachsender Stärke der Stearinoberflächenbeschichtung. Die verbesserte Zähigkeit der Composites mit beschichteten PCCs gegenüber unbeschichteten PCCs wurde auf die schwächere Grenzflächenadhäsion an der Matrix und auf die gute Dispersion der PCC-Partikel aufgrund der Stearinoberflächenschicht zurückgeführt
The Effect of Surface Interactions on Morphology and Fracture Behaviour of Ultrafine CaCO3/High Density Polyethylene Nanocomposites
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Processi di cavitazione nei sistemi polimerici multifase: modellazione e risultati sperimentali
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