12 results
Now showing1 - 10 of 12
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Production of magnetite-polyvinyl butyral composites using a Nano Spray DryerBio composites as nacre show outstanding mechanical properties which surpasses those of their single constituents. This is due to their complex structure, in which the small building blocks of the hard component are embedded in a softer matrix, thus combining strength and toughness. This combination makes such materials interesting for various applications, e.g. for tooth replacement materials but also for industrial structural materials. Therefore, the interest is to develop scalable processes for the production of artificial composites. In this work a Nano Spray Dryer is used to produce polymer-encapsulated magnetite particles from a magnetite-polymer-suspension. A Design of Experiment study is conducted which identified the suspension composition as the major influencing factor on the product properties. The particles are then warm-compacted and the composite pellets are examined for their mechanical properties and structure. With this method composites with bending strength of 91.2 MPa and Young's modulus of 9.2 GPa were produced.Publicationtype: Journal Article162 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Influence of pores arrangement on stability of photonic structures during sintering(Elsevier, 2020-05-11); ; ; ; Discrete Element Method (DEM) has been used for numerical investigation of sintering-induced structural deformations occurring in inverse opal photonic structures. The influence of the initial arrangement of template particles on the stability of highly porous inverse opal α-Al2O3 structures has been analyzed. The material transport, densification, as well as formation of defects and cracks have been compared for various case studies. Three different stages of defects formation have been distinguished starting with local defects ending with intrapore cracks. The results show that the packing of the template particles defined during the template self-assembly process play a crucial role in the later structural deformation upon thermal exposure. The simulation results are in very good agreement with experimental data obtained from SEM images and previous studies by ptychographic X-ray tomography.Publicationtype: Journal ArticleScopus© Citations 7 202 243 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Fabrication of highly filled composites with an innovative miniaturized spouted bed(Multidisciplinary Digital Publishing Institute (MDPI), 2020-04-28); ; ; In nature bio-composites such as nacre show remarkable mechanical properties due to their complex hierarchical structure and high-volume fraction of its hard component. These composites are highly interesting for structural applications in different branches of industries for mechanical engineering and process technology. The aim of this work was to provide a scalable method for the production of highly filled composites by mimicking the structure of bio-composites. Therefore, composites from iron oxide (Fe2O3) and SBC-polymer (styrene-butadiene block copolymer) were fabricated by using a miniaturized spouted bed with an innovative fluidization gap design. Small iron oxide particles (25–45 μm) were fluidized in the spouted bed and coated with a polymer solution via a bottom spray nozzle. Afterwards the coated granules were hot-pressed and the mechanical properties of the obtained composites were tested. By this method composites with a bending strength of up to 6 MPa were fabricated. Although the mechanical properties of these artificial composites are still lower than those of the natural role models, it was shown that the spouted bed is a suitable technique for the fabrication of highly filled composites. For further optimization of the mechanical properties more complex and tailor-made starting materials will be used in following studies.Publicationtype: Journal ArticleScopus© Citations 3 209 201 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of particle shape and size on mechanical properties in copper-polymer composites(2018-11); ; In this contribution, the influence of the particle aspect ratio on mechanical properties of composites is investigated. As example, copper-polyvinyl butyral (PVB) composites are studied. Copper particles in two different sizes, 29.5 μm and 260 μm, are coated in a spouted bed with PVB and the produced granules are then directly pressed to a bulk material or they are firstly rolled, to increase the aspect ratio, and then pressed. For the bulk material the mechanical properties, such as Young's modulus, strength, strain and fracture toughness, are determined. The results show that elongation at break, strength and fracture toughness increase with increasing aspect ratio. For the coarser particles, the bending strength could be doubled at 72 vol. % of copper. The maximal increase for the toughness in the composites with fine particles is about 65 vol. %. In the composites with coarser particles the maximal increase is even 80 vol. %. The fracture toughness increases with increasing crack length due to effects inside of the composites. The optimal composition is between 72 and 75 vol. % of copper.Publicationtype: Journal Article157 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Photonic glass for high contrast structural color(Macmillan Publishers Limited, part of Springer Nature, 2018-05-17); ; ; ; Non-iridescent structural colors based on disordered arrangement of monodisperse spherical particles, also called photonic glass, show low color saturation due to gradual transition in the reflectivity spectrum. No significant improvement is usually expected from particles optimization, as Mie resonances are broad for small dielectric particles with moderate refractive index. Moreover, the short range order of a photonic glass alone is also insufficient to cause sharp spectral features. We show here, that the combination of a well-chosen particle geometry with the short range order of a photonic glass has strong synergetic effects. Using a first-order approximation and an Ewald sphere construction the reflectivity of such structures can be related to the Fourier transform of the permittivity distribution. The Fourier transform required for a highly saturated color can be achieved by tailoring the substructure of the motif. We show that this can be obtained by choosing core-shell particles with a non-monotonous refractive index distribution from the center of the particle through the shell and into the background material. The first-order theoretical predictions are confirmed by numerical simulations.Publicationtype: Journal ArticleScopus© Citations 46 535 501 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Using a spouted bed spray granulation process to study the influence of aspect ratio on fracture toughness in composites(2017-05); ; ; In this work the fracture toughness of copper-composite materials was studied. The volume fraction of copper was between 69 and 76 %. The study was carried out with two types of composites. The first type were composites containing spherical copper particles. The second type were composites with copper particles, which were rolled before they were pressed to a bulk material. The analysis of fracture toughness shows, that the composites with spherical particles have a mean fracture toughness of 1.69 MPam 1/2 . The composites with higher aspect ratios of particles have a fracture toughness of 2.66 MPam 1/2 . It corresponds to an increasing of approximatively 55 % for the toughness referred to composites with spherical particles.Publicationtype: Conference Paper87 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Improvement of mechanical properties by a polydopamine interface in highly filled hierarchical composites of titanium dioxide particles and poly(vinyl butyral)(Elsevier, 2017-04-15); ; ; ; In this work, the preparation and properties of hierarchical composites of titanium dioxide (TiO2) particles (rutile modification) and poly(vinyl butyral) (PVB) are discussed. The volume fraction of the ceramic particles was approximately 60%. Two types of composites with different fillers were examined, i.e. TiO2 particles with and without a thin coating of polydopamine (PDA). A variety of characterization methods was applied in order to analyze the properties of the particles and the composites. Infrared spectroscopy is used to verify the functionalization of the particles with a thin polydopamine layer. Thermal analysis provides information on the thermal stability and the degree of functionalization of the coated particles and the composites. Scanning electron microscopy investigations reveal that the functionalized TiO2 particles with PDA form larger agglomerates which enable the coating of the TiO2 particles with PVB via the spouted bed technique. Nanoindentation experiments show that the final hierarchical composite material with the use of non-coated TiO2 particles exhibits a hardness of 0.75 ± 0.04 GPa and a Young's modulus of 29.5 ± 1.0 GPa. The composites containing polydopamine coated TiO2 particles show an increase of approximately 40% in hardness and 25% in Young's modulus in comparison to the composites with uncoated TiO2.Publicationtype: Journal Article163 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Sintering Simulation of Periodic Macro Porous Alumina(Wiley-Blackwell, 2015); ; ; ; Three-dimensionally ordered macroporous (3DOM) ceramic materials are considered for a variety of applications. One of its many subclasses, inverse opals, is constituted by the ordered arrangement of the pores, resulting in the functionality of a photonic crystal and leading to strong reflection of incident electromagnetic radiation. Exposing these porous structures to high temperatures, however, can lead to sintering of the desired structure and loss of functionality. Therefore, discrete element method (DEM) simulations are performed on inverse opal structures with random homogenous distributed alumina particles forming the struts and nodes. Grain-boundary diffusion as well as surface diffusion are modeled via respective parameters of a contact model applied in MUSEN-DEM. Furthermore, the void to particle size ratio is varied to simulate fine and coarse grained 3DOM ceramics. Results indicate that nodes densify at higher rates and to a larger extent when compared to struts. An increase in the void to particle size ratio results in similar trends but with lower densification rates. This behavior is observed regardless whether surface or grain-boundary diffusion is considered as the dominant transport mechanism, with the latter giving higher densification rates. Variations in particle coordination due to the initial random packing favor local desintering, thereby causing the formation of defects/crack nuclei.Publicationtype: Journal Article95 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Attritor-milling of poly(amide imide) suspensionsThe milling behavior of poly(amide imide), which serves as a prototypical hydrophilic high-performance polymer with a high glass transition temperature, was investigated. Various milling conditions (milling times up to 7 h, stirrer tip speeds of 3.4-4.9 m/s, and mass concentrations of 5-20%) were tested, and particle sizes as low as d50,3 ∼ 3 μm were obtained. The milling was performed at 11°C in an attritor. Differential scanning calorimetry and thermogravimetric analysis were performed before and after milling to investigate the effect of milling on the glass transition temperature and on the decomposition behavior of the polymer. The suspension obtained after milling was observed to be stable without the addition of stabilizers or the adjustment of the pH value, and no negative effect of milling on the polymer properties was observed. The attritor technique proved to be an adequate and efficient milling tool for the production of micrometer-sized high-performance polymer suspensions.Publicationtype: Journal ArticleScopus© Citations 18 281 423 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Novel, highly-filled ceramic–polymer composites synthesized by a spouted bed spray granulation process(Elsevier, 2014-01-10); ; ; ; We present a novel processing route to synthesize homogeneous ceramic polymer composites with ultrahigh (~78 vol.%) packing density by using the spouted bed granulation technology and subsequent warm pressing. In the granulation process, two ceramic particle size fractions (alpha-Al2O3) and a thermoplastic polymer (polyvinyl butyral) are assembled to granules. In the process, lm-sized particles are coated with a layer of polymer which contains a second, nm-sized ceramic particles fraction. The mass fractions of each constituents can be adjusted independently. During the warm pressing, the nm-sized particle fraction along with polymer is pressed into the void volume of the lm-sized particles, thus achieving a homogeneous, isotropic composite structure with a very high packing density of ceramic particles. The material, which can easily be produced in large quantities, combines a high modulus of elasticity (up to 69 GPa), tensile strength (~50 MPa), and pronounced fracture strain (~0.1%) with an isotropic, biocompatible, metal-free composition. Possible failure mechanisms are discussed, including failure due to necking of the polymer, and failure due to limited polymer–particle-interfacial strength.Publicationtype: Journal ArticleScopus© Citations 55 493 589