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71.
Hilmar K. Danielsen John Hald Flemming B. Grumsen Marcel A. J. Somers 《Metallurgical and Materials Transactions A》2006,37(9):2633-2640
TheZ-phase Cr(V,Nb)N particles in various 9 to 12 pct Cr creep-resistant steels were investigated with electron diffraction, energy
dispersive spectroscopy (EDS), and electron energy loss spectroscopy (EELS). In addition to the well-known tetragonal crystal
structure forZ phase, a cubic crystal structure was identified for Cr(V,Nb)N and CrVN particles, but not for CrNbN. The tetragonal and cubic
crystal structures were observed to coexist within the same particles, and the orientation relationship between the two lattices
was determined. Understanding and controlling the nucleation of Cr(V,Nb)N particles could be of crucial importance to enable
improvement of the long-term creep stability of 9 to 12 pct Cr martensitic steels. 相似文献
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For organically modified montmorillonite (OMM)-epoxy nanocomposites, maximal montmorillonite dispersion is found to depend synergistically on the mechanical processing history of the resin mixture and the chemistry at the OMM surface. Specifically, Cloisite 30A (quaternary ammonium OMM) and I30.E (primary ammonium OMM), each containing surfactants with different catalytic effects on the curing chemistry of Epon 862, are compared. Irrespective of the OMM, conventional solvent-free processing methodologies, including sonication, result in an inhomogeneous distribution of OMM on the micron scale. Even though the primary ammonium alkyls within I30.E enhance intragallery reactivity, this only results in extensive swelling of tactoids (interlayer distance ∼10-20 nm), and thus retention of layer-layer correlations, leading to ‘hybrid’ micron scale reinforcing particles, not nanoscale dispersion of individual layers. In contrast, sub-ambient temperature (cryo) compounding had substantial impact on the ability to reduce tactoid and agglomerate size and increase homogeneity of dispersion for Cloisite 30A. The reactivity near Cloisite 30A is similar to that in the bulk and thus localized gelation around the layer-stacks does not retard particulate refinement. In all cases, alteration of the global epoxy network structure was ruled out by FTIR and NMR measurements. For nanocomposites with similar OMM content, however, the final thermal-mechanical properties does not coherently relate to one characteristic of the morphology. The coefficient of thermal expansion (T>Tg) and hardness (T<Tg) depend only weakly on morphology, where as the glass transition temperature depends strongly on the extent of OMM dispersion and interfacial chemistry. In general, the inter-relationships between mechanical processing, OMM surface chemistry and the desired property enhancements are not linear and thus must be considered in light of a final application to evaluate the optimal ‘nanocomposite’ fabrication methodology to achieve maximal benefit. 相似文献
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Hilmar W. Duerbeck 《NTM》2004,12(4):251-253
Ohne Zusammenfassung 相似文献
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Remotely actuated polymer nanocomposites--stress-recovery of carbon-nanotube-filled thermoplastic elastomers 总被引:1,自引:0,他引:1
Stimuli-responsive (active) materials undergo large-scale shape or property changes in response to an external stimulus such as stress, temperature, light or pH. Technological uses range from durable, shape-recovery eye-glass frames, to temperature-sensitive switches, to the generation of stress to induce mechanical motion. Here, we demonstrate that the uniform dispersion of 1-5 vol.% of carbon nanotubes in a thermoplastic elastomer yields nanocomposites that can store and subsequently release, through remote means, up to 50% more recovery stress than the pristine resin. The anisotropic nanotubes increase the rubbery modulus by a factor of 2 to 5 (for 1-5 vol.%) and improve shape fixity by enhancing strain-induced crystallization. Non-radiative decay of infrared photons absorbed by the nanotubes raises the internal temperature, melting strain-induced polymer crystallites (which act as physical crosslinks that secure the deformed shape) and remotely trigger the release of the stored strain energy. Comparable effects occur for electrically induced actuation associated with Joule heating of the matrix when a current is passed through the conductive percolative network of the nanotubes within the resin. This unique combination of properties, directly arising from the nanocomposite morphology, demonstrates new opportunities for the design and fabrication of stimuli-responsive polymers, which are otherwise not available in one material system. 相似文献
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Anja Rey Jörg Rothe Hilmar Schadrack Lena Schend 《Annals of Mathematics and Artificial Intelligence》2016,77(3-4):317-333
We study the computational complexity of the existence and the verification problem for wonderfully stable partitions (WSPE and WSPV) and of the existence problem for strictly core stable coalition structures (SCSCS) in enemy-oriented hedonic games. In this note, we show that WSPV is NP-complete and both WSPE and SCSCS are DP-hard, where DP is the second level of the boolean hierarchy, and we discuss an approach for classifying the latter two problems in terms of their complexity. 相似文献
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Enhanced power from chambered benthic microbial fuel cells 总被引:1,自引:0,他引:1
We describe a new chamber-based benthic microbial fuel cell (BMFC) that incorporates a suspended, high surface area and semi-enclosed anode to improve performance. In Yaquina Bay, OR, two chambered BMFC prototypes generated current continuously for over 200 days. One BMFC was pumped intermittently, which produced power densities more than an order of magnitude greater than those achieved by previous BMFCs with single buried graphite-plate anodes. On average, the continuous power densities with pumping were 233 mW/m2 (2.3 W/m3); peak values were 380 mW/m2 (3.8 W/m3), and performance improved over the time of the deployments. Without pumping, high power densities could similarly be achieved after either BMFC was allowed to rest at open circuit. A third chambered BMFC with a 0.4 m2 footprint was deployed at a cold seep in Monterey Canyon, CA to test the new design in an environment with natural advection. The power density increased 5-fold (140 mW/m2 vs 28 mW/m2) when low-pressure check valves allowed unidirectional flow through the chamber. 相似文献
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