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Item type:Publication, Access status: without files , 47 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Shear Strength and Interfacial Toughness Characterization of Sapphire-Epoxy Interfaces for Nacre-Inspired Composites(American Chemical Society (ACS), 2016-09-15); ; ; The common tensile lap-shear test for adhesive joints is inappropriate for brittle substrates such as glasses or ceramics where stress intensifications due to clamping and additional bending moments invalidate results. Nevertheless, bonding of glasses and ceramics is still important in display applications for electronics, in safety glass and ballistic armor, for dental braces and restoratives, or in recently developed bioinspired composites. To mechanically characterize adhesive bondings in these fields nonetheless, a novel approach based on the so-called Schwickerath test for dental sintered joints is used. This new method not only matches data from conventional analysis but also uniquely combines the accurate determination of interfacial shear strength and toughness in one simple test. The approach is verified for sapphire-epoxy joints that are of interest for bioinspired composites. For these, the procedure not only provides quantitative interfacial properties for the first time, it also exemplarily suggests annealing of sapphire at 1000 °C for 10 h for mechanically and economically effective improvements of the interfacial bond strength and toughness. With increases of strength and toughness from approximately 8 to 29 MPa and from 2.6 to 35 J/m2, respectively, this thermal modification drastically enhances the properties of unmodified sapphire-epoxy interfaces. At the same time, it is much more convenient than wet-chemical approaches such as silanization. Hence, besides the introduction of a new testing procedure for adhesive joints of brittle or expensive substrates, a new and facile annealing process for improvements of the adhesive properties of sapphire is suggested and quantitative data for the mechanical properties of sapphire-epoxy interfaces that are common in synthetic nacre-inspired composites are provided for the first time.Publicationtype: Journal Article74 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Tailoring Toughness and Mechanical Reliability by Controlled Defects: Nature-Inspired Composite Laminates of Laser-Perforated Yttria-Stabilized ZirconiaResearchers investigate the role of nature-inspired composite laminates of laser-perforated yttria-stabilized zirconia in tailoring toughness and mechanical reliability by controlled defects. They attempt to combine advantages of both continuously reinforced multilayered ceramic composites like sponge spicule and discontinuously reinforced nacre. For this purpose, they use laserperforated strips of 3-mol% yttria-stabilized zirconia (3YSZ) and laminate them with toughened epoxy. In these composites, the laser-perforation guides the crack for a higher density of crack deflections and pull-outs and thus higher toughness while the ceramic bridges remaining between holes cause the perforation to stay considerably stiff and strong.Publicationtype: Journal Article168 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Large-scale parallel alignment of platelet-shaped particles through gravitational sedimentation(2015-05-18); ; ; ; Parallel and concentric alignment of microscopic building blocks into several orders of magnitude larger structures is commonly observed in nature. However, if similarly aligned structures are artificially produced their thickness is generally limited to just about one or two orders of magnitude more than the dimensions of the smallest element. We show that sedimentation provides a promising approach to manufacture solid materials consisting of well-aligned platelet-shaped particles while being more than 30 000 times thicker than the individual particle. Such sediments contain up to 28 vol% of particles without any further treatment and can be densified to 67 vol% particle fraction by subsequent unidirectional pressing. The degree of orientation of the platelet-shaped particles within the sediments was tracked by high-energy X-ray diffraction measurements. The Hermans orientation parameter, a statistical measure of the quality of alignment, was determined to be 0.63 ± 0.03 already for as-sedimented samples while the standard deviation of the orientation distribution of particles, another measure of average misalignment, was found to be (21.5 ± 1.4)°. After pressing, these values further improved to (0.81 ± 0.01) and (14.6 ± 0.4)°, respectively. Such quality of alignment competes with, if not even exceeds, values reported in the literature.Publicationtype: Journal ArticleScopus© Citations 40 406 364 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Highly-structured, additive-free lithium-ion cathodes by freeze-casting technologyStoring large amounts of energy for mobile applications is an ongoing problem in research and development. This especially holds for transportation purposes where the charging and discharging profiles can be rather fast, a characteristic that physically contradicts high effective capacities. Furthermore, conventional fabrication methods for lithium-ion cathodes include the use of significant amounts of additives to consolidate the active materials powders without sintering. These additives hinder the movement of ions within the battery and represent dead volume that is lost to the purpose of energy storage. In the following study, the technology called freeze-casting or ice- Templating was applied to create additive-free, sintered cathodes with highly aligned porosity was applied. By controlling and varying the freezing rate in the freeze-casting process, the solids loading in the freezing slurry, and the sintering parameters, it was possible to obtain cathodes that solely contain active material and highly aligned pores that are fast channels for transporting lithium ions. These cathodes are highly promising for providing a unique combination of high capacity as well as fast charging and discharging capabilities.Publicationtype: Journal Article109 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Dielectric behaviour and conductivity of high-filled BaTiO3-PMMA composites and the facile route of emulsion polymerization in synthesizing the same(Royal Society of Chemistry (RSC), 2013-05-21); ; ; Poly(methyl methacrylate)-BaTiO3 composites were prepared by a combined process of free radical emulsion polymerization and hot pressing. Using a cationic surfactant, emulsion polymerization was proven to be an easy and fast method to synthesize core-shell hybrid particles. By subsequent hot pressing of powders with different amounts of polymers, composites with barium titanate filler contents up to 65 vol% with uniform microstructures could be achieved, as determined by thermogravimetric analysis and scanning electron microscopy. The dielectric properties were characterized for frequencies and temperatures ranging from 100 Hz to 1 MHz and -30 to 80 °C, respectively. Composites exhibited a significant increase in dielectric constant up to 85 with BaTiO3 content and low loss tangents of 0.06 at 1 kHz. Dc conductivity measurements reveal increasing leakage currents with BaTiO 3 contents, enhanced by cationic surfactant influences.Publicationtype: Journal Article136