7 results
Now showing1 - 7 of 7
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Ultra-hoch gefüllte und orientierte CNT- und 3D-vernetzte Aerographit Epoxidkomposite: Synthese, Herstellung und EigenschaftenIn this work two different polymer nanocomposites (PNCs) with graphitic fillers in epoxy matrix are characterized. Both PNCs possess structural features, which are used to address open scientific questions in the field of carbon nanotube (CNT) based PNCs. The PNCs of this work use in-house synthesized nanoparticles, which are: mm-long, unidirectional aligned carbon nanotubes (CNTs) and covalently 3D interconnected graphite-based networks ('Aerographite', AG). For CNT-based PNCs (CNT-PNCs) a manufacturing method is introduced (patented), which allows to embed very high amounts of CNTs in epoxy matrix (Φ= 10-70 wt.%). Two different structures are given for these CNT-based PNCs: APNCs: PNCs with unidirectional alignment of mm-long, in-house produced CNTs (anisotropic). RPNCs: PNCs with randomly oriented CNTs (mm-long in-house produced CNTs or µm-long commercial CNT) (isotropic). AG-PNCs: Aerographite-based PNCs are PNCs with an isotropic, covalently interconnected graphite filler network embedded in epoxy matrix (Φ<1 wt.%) (isotropic). Here different orientations, different aspect ratios and different qualities of CNTs are directly compared. The scaling of electrical conductivity and Young's moduli in respect to filler loadings are in focus of the investigations (σ (Φ) , E(Φ)). The piezoresistive and thermoelectric behavior of CNT-based PNCs with filler loadings Φ >5 wt.% are investigated here for the first time. The findings for CNT-PNCs are combined with the results on AG-PNCs. The influence of inner network topologies on electrical conduction is discussed in detail. If the graphitic networks of AGs are infiltrated with epoxy, AG-PNCs of low filler loading and isotropic structure result. Inner graphite elements of AGs are covalently interconnected. Therefore AG-PNCs can be used to investigate the influence of reduced electron tunneling on the electrical conduction and piezoresistive behavior of PNCs. It can be shown, that highly filled APNCs can lead to highly improved material properties like electrical conductivities up to σ= 37000 S/m and Youngs's moduli up to E= 36 GPa. On the other hand APNCs are shown to follow similar scaling rules of electrical conduction (σ(Φ)), as they had been derived from dispersed CNT-PNCs in the last two decades of research. The inner interconnections of AG lead to - compared to all of today's CNT-based PNCs - effective electrical conduction (σ/Φ). Appendix: Aerographite (AG): In the year 2010 first time a metal oxide (ZnO) was shown to be a feasible substrate for graphite deposition via a chemical vapor deposition process (CVD). Technically no other synthesis offers following combination: (i) structuring by tailored ceramic networks & graphite deposition with in situ removal of template. The density and inner structure of AG can be altered by the CVD-process. Scientifically the details of nucleation and growth of graphite within the CVD-process is not yet fully understood. To continue the research, the appendix deal with following contents: Development of synthesis & outlook on structuring Statistics of CVD-processes (2010-2015) & introduction of one control parameter for selecting variant and density of AGs Structural analyses (SEM, TEM, SAEDs, XRD,…) & introduction of a hypothetical growth modelPublicationtype: Doctoral Thesis749 387 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Nanomechanics of individual aerographite tetrapods(Nature Publishing Group, 2017-04-12); ; ; ; Carbon-based three-dimensional aerographite networks, built from interconnected hollow tubular tetrapods of multilayer graphene, are ultra-lightweight materials recently discovered and ideal for advanced multifunctional applications. In order to predict the bulk mechanical behaviour of networks it is very important to understand the mechanics of their individual building blocks. Here we characterize the mechanical response of single aerographite tetrapods via in situ scanning electron and atomic force microscopy measurements. To understand the acquired results, which show that the overall behaviour of the tetrapod is governed by the buckling of the central joint, a mechanical nonlinear model was developed, introducing the concept of the buckling hinge. Finite element method simulations elucidate the governing buckling phenomena. The results are then generalized for tetrapods of different size-scales and shapes. These basic findings will permit better understanding of the mechanical response of the related networks and the design of similar aerogels based on graphene and other two-dimensional materials.Publicationtype: Journal ArticleScopus© Citations 30 425 515 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Low powered, tunable and ultra-light aerographite sensor for climate relevant gas monitoring(Royal Society of Chemistry (RSC), 2016-09-27); ; ; ; Increasing atmospheric CO2 gas pollution and emergence of new types of green energy sources require continuous environmental monitoring. In this context, fast, efficient, light, robust, and reliable gas sensors that can work at room temperature are in high demand. We report on a low-powered type of ultra-light sensor, based on a 3-D-microtube network from a 2-D graphene/nanographite, called aerographite, and a method to tune the nanosensor’s selectivity by a simple variation of the applied bias voltage. Adequate selectivity to CO2 and ultra-fast sensing of H2 by applying 1 V and 5 V, respectively, is obtained. At ultra-low applied bias voltages (1–100 mV) only very low power consumption (z3.6 nW for 1 mV) is needed. This is most important, as it can be run by energy harvesting methods. The presented results are of the highest interest in terms of low-cost production of ultra-light and ultra-low-power consumption gas sensors for environmental monitoring of greenhouse gases and their simplicity from the technological/engineering points of view.Publicationtype: Journal ArticleScopus© Citations 49 388 422 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Strong light scattering and broadband (UV to IR) photoabsorption in stretchable 3D hybrid architectures based on Aerographite decorated by ZnO nanocrystallites(Nature Publishing Group, 2016-09-12); ; ; ; In present work, the nano- and microscale tetrapods from zinc oxide were integrated on the surface of Aerographite material (as backbone) in carbon-metal oxide hybrid hierarchical network via a simple and single step magnetron sputtering process. The fabricated hybrid networks are characterized for morphology, microstructural and optical properties. The cathodoluminescence investigations revealed interesting luminescence features related to carbon impurities and inherent host defects in zinc oxide. Because of the wide bandgap of zinc oxide and its intrinsic defects, the hybrid network absorbs light in the UV and visible regions, however, this broadband photoabsorption behavior extends to the infrared (IR) region due to the dependence of the optical properties of ZnO architectures upon size and shape of constituent nanostructures and their doping by carbon impurities. Such a phenomenon of broadband photoabsorption ranging from UV to IR for zinc oxide based hybrid materials is novel. Additionally, the fabricated network exhibits strong visible light scattering behavior. The developed Aerographite/nanocrystalline ZnO hybrid network materials, equipped with broadband photoabsorption and strong light scattering, are very promising candidates for optoelectronic technologies.Publicationtype: Journal ArticleScopus© Citations 54 257 406 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A tunable scaffold of microtubular graphite for 3D cell growth(Soc., 2016-06-03); ; ; ; Aerographite (AG) is a novel carbon-based material that exists as a self-supportive 3D network of interconnected hollow microtubules. It can be synthesized in a variety of architectures tailored by the growth conditions. This flexibility in creating structures presents interesting bioengineering possibilities such as the generation of an artificial extracellular matrix. Here we have explored the feasibility and potential of AG as a scaffold for 3D cell growth employing cyclic RGD (cRGD) peptides coupled to poly(ethylene glycol) (PEG) conjugated phospholipids for surface functionalization to promote specific adhesion of fibroblast cells. Successful growth and invasion of the bulk material was followed over a period of 4 days.Publicationtype: Journal ArticleScopus© Citations 24 295 408 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Three-dimensional Aerographite-GaN hybrid networks: single step fabrication of porous and mechanically flexible materials for multifunctional applications(Nature Publishing Group, 2015-03-06); ; ; ; Three dimensional (3D) elastic hybrid networks built from interconnected nano- and microstructure building units, in the form of semiconducting-carbonaceous materials, are potential candidates for advanced technological applications. However, fabrication of these 3D hybrid networks by simple and versatile methods is a challenging task due to the involvement of complex and multiple synthesis processes. In this paper, we demonstrate the growth of Aerographite-GaN 3D hybrid networks using ultralight and extremely porous carbon based Aerographite material as templates by a single step hydride vapor phase epitaxy process. The GaN nano- and microstructures grow on the surface of Aerographite tubes and follow the network architecture of the Aerographite template without agglomeration. The synthesized 3D networks are integrated with the properties from both, i.e., nanoscale GaN structures and Aerographite in the form of flexible and semiconducting composites which could be exploited as next generation materials for electronic, photonic, and sensors applications.Publicationtype: Journal ArticleScopus© Citations 46 250 390 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Influence of small cyclic and DC electrical loads on the fracture toughness of ferroelectric ceramicsThe present work investigates the influence of small AC, unipolar cyclic and DC electric loads on the fracture toughness of a ferroelectric ceramic. Single-edge-notched beams (SENB) of a poled and unpoled lead zirconate titanate (PZT) ceramic were fractured in a four-point-bending device under conditions of controlled crack growth. During crack advance the different electrical loads were applied perpendicular to the crack faces. The applied nominal electric field amplitudes were less than one third of the coercive field and maximum frequencies of 20 kHz were applied. The measured R-curves show that even for these low amplitudes, electrical AC loading causes a drop in the critical mechanical load of up to 25%. The drop increases with increasing amplitude and frequency. Possible mechanisms to explain the results are discussed.Publicationtype: Journal ArticleScopus© Citations 14 2106 1177