Dépôt de fil fondu | EPFL Graph Search

Le dépôt de fil fondu (DFF) ou Fused deposition modeling (FDM) ou encore Fused Filament Fabrication (FFF) est une technologie d'impression 3D. On appelle aussi ce procédé impression 3D par extrusion de matériau Material Extrusion 3D printing (MEX). Cette technologie consiste à déposer de la matière à l'état liquide couche par couche. La technologie utilise le plus souvent un filament de matière polymère qui est fondu puis extrudé pour construire une pièce couche par couche. Le matériau d’apport est extrudé au travers d’une buse sur la table de la machine. Le mouvement de la table ou de la buse permet de créer une couche de matériau ayant la géométrie désirée. La succession des différentes couches permet de créer la pièce finale. Les filaments peuvent être composés de diverses matières, mais les plus communes sont le PLA et l’ABS. Le MEX permet aussi de mettre en forme des mélanges de polymères et de poudres métalliques ou céramiques. Pour la production de pièce de céramique ou métall

Recycled Glass Fiber Composites from Wind Turbine Waste for 3D Printing Feedstock: Effects of Fiber Content and Interface on Mechanical Performance

Kazem Fayazbakhsh, Rodolphe Henri

This research validates the viability of a recycling and reusing process for end-of-life glass fiber reinforced wind turbine blades. Short glass fibers from scrap turbine blades are reclaimed and mixed with polylactic acid (PLA) through a double extrusion process to produce composite feedstock with recycled glass fibers for fused filament fabrication (FFF) 3D printing. Reinforced filaments with different fiber contents, as high as 25% by weight, are extruded and used to 3D print tensile specimens per ASTM D638-14. For 25 wt% reinforcement, the samples showed up to 74% increase in specific stiffness compared to pure PLA samples, while there was a reduction of 42% and 65% in specific tensile strength and failure strain, respectively. To capture the level of impregnation of the non-pyrolyzed recycled fibers and PLA, samples made from reinforced filaments with virgin and recycled fibers are fabricated and assessed in terms of mechanical properties and interface. For the composite specimens out of reinforced PLA with recycled glass fibers, it was found that the specific modulus and tensile strength are respectively 18% and 19% higher than those of samples reinforced with virgin glass fibers. The cause for this observation is mainly attributed to the fact that the surface of recycled fibers is partially covered with epoxy particles, a phenomenon that allows for favorable interactions between the molecules of PLA and epoxy, thus improving the interface bonding between the fibers and PLA.

2019

Fabrication of clamped-clamped beam resonators with embedded fluidic nanochannel

Annalisa De Pastina, Damien Maillard, Philippe Renaud, Carlo Ricciardi, Davide Scaiola, Stefano Stassi, Stefano Silvio Giovanni Varricchio, Luis Guillermo Villanueva Torrijo

Suspended nanochannel resonators (SNRs) are promising devices able to characterize mass down to the attogram scale, thus being able to detect nanoparticles or biomolecules. In this paper, we present a flexible fabrication process for SNRs based on a sacrificial layer approach that allows to easily tailor the dimensions of the nanochannel by changing the thickness of the sacrificial layer or its patterning during the lithographic step. The resonance properties of the fabricated SNR are investigated in terms of resonance frequency and frequency stability (Allan deviation). Liquids of different densities are injected in the device and, from the shift of the resonance peaks, the mass responsivity of the resonators is assessed to be up to 3.90 mHz/ag. To the best of our knowledge, the devices here presented are the first example of suspended nanochannel resonators with a channel height as low as 50 nm fabricated with a top-down approach.

ELSEVIER2020

Molecular Engineering of Electrode Surfaces for Electrocatalysis

Patrick Eduard Alexa

Electrocatalysts play an important part on the route towards environmental friendly energy sources. They support modern technologies like fuel cells to move further away from the utilization of fossil fuels and the resulting CO2 emission into our atmosphere. The main principle of such energy conversion technologies is to store chemical energy within chemical bonds and to release it as electric energy to fulfill the energy demand of today's society. However energy conversion chemistry in such technologies requires catalysts in order to be effective by providing an alternative reaction pathway that lowers activation energies and maximizes the energy output. Providing suitable catalyst surfaces requires a fundamental knowledge of the interaction of reactants and reaction intermediates with the catalyst surfaces. This concern is addressed in this thesis by fabricating specifically tailored molecular components on metal surfaces, which act as organic/inorganic hybrid electrodes for various energy conversion reactions in electrocatalysis. Characterizing the electrode surface is crucial in order to identify active sites of the catalyst. The molecular structure is investigated by surface sensitive techniques, such as STM and XPS in combination with a home-build transfer system, which enables electrode fabrication in UHV and electrocatalytic experiments in a liquid environment. A detailed characterization of organic polymer components on electrode surfaces is obtained by combining experimental data with MD simulations. The morphology of polymer networks can be successfully mimicked and depending on the chemical composition and the structure, spatial correlations on short length scales are reported. Hybrid electrodes with organic polymer co-catalysts reveal an increased catalytic activity for the HER by providing suitable docking sites that act as catalytic active sites. Reactants and reaction intermediates are stabilized via hydrogen bonding, which results in a higher catalytic turnover. The specific designed structure of the organic co-catalyst helps to identify a fraction of the reaction mechanism and highlights the importance of molecular components in electrocatalysis. The utilization of organic units on electrocatalysts provides also an excellent opportunity in order to use single metal atoms as catalysts. Engineering large pi-systems has no significant impact on the ORR activity, while the distance between active sites and the underlying electrode are crucial for enhancing the catalytic activity. A significant factor in using molecular components in electrocatalysis is the stability of the organics. Using electrografting allows to design organic/inorganic hybrid electrodes with covalent bonds between the molecular component and the metal substrate. Attaching empty porphyrin molecules to substrates introduces a powerful technique in molecular engineering, since empty porphyrin cycles can be metallized with various metal centers that can act as electrocatalysts for different electrochemical reactions. In summary, this thesis provides multiple engineering aspects, which are useful in designing molecular components on metal electrodes for energy conversion. Such hybrid catalyst surfaces are capable of improving the catalytic activity and allow to study the mechanism of catalytic reactions. Implementing organic components provides new routes for tailoring novel materials, which deliver new insight into the complex field of electrocatalysis.

EPFL2020

Molecular Engineering of Electrode Surfaces for Electrocatalysis

Patrick Eduard Alexa

EPFL2020