Thermal conductivity of carbon nanotube (CNT) films and micro-fibres synthesised by floating catalyst chemical vapour deposition was measured by the parallel thermal conductance method. CNT films showed in-plane thermal conductivities of 110 W m 1 K 1. Online condensation into a micro-fibre morphology-a two-dimensional reduction in the transverse plane, including some axial stretching during solvent evaporation-resulted in room-temperature thermal conductivity values as high as 770 ± 10 W m 1 K 1 , which is the highest thermal conductivity reported for CNT bulk materials to date. In specific terms, this matches the maximum thermal conductivity of heattreated carbon fibre, but with a higher onset temperature for Umklapp scattering processes (300 K rather than 150 K). We selected four sample types to investigate effects of alignment, purity, and single-or multi-wall character on their thermal conductivity. For both the electrical and thermal conductivity of as-spun material, i.e. without any post-synthesis treatment, we show that the density and quality of CNT bundle alignment are still the predominant factors affecting these properties, outweighing the influence of single-or multi-walled character of the nanotubes. This raises the promise that, with optimal alignment and junction points, even higher values of thermal conductivity are achievable for macroscopic CNT fibres.
The physical properties of dry-spun MWCNT yarns with diameters from 35 to 60 μm were systematically determined as a function of annealing up to 2700 °C. Raman spectroscopy showed a ~5 fold increase in relative CNT crystallinity after annealing. Electrical conductivity and magnetoresistance (in fields up to 9 T) were measured from 2 K to 390 K. Thermal conductivity from 50 K to 300 K was determined using the parallel thermal conductance method. The electrical and thermal conductivities of the yarns both increased by over 100 % after annealing to 2700 °C. The influence of adsorbed species on the electrical properties of the yarns was also studied.
Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions? Contact the NRC Publications Archive team atPublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. NRC Publications Record / Notice d'Archives des publications de CNRC:http://nparc.cisti-icist.nrc-cnrc.gc.ca/eng/view/object/?id=01e4ef00-e2d0-4de6-aa56-efc8eba12c43 http://nparc.cisti-icist.nrc-cnrc.gc.ca/fra/voir/objet/?id=01e4ef00-e2d0-4de6-aa56-efc8eba12c43Copyright line will be provided by the publisher pss-Header will be provided by the publisher Review copy -not for distribution (pss-logo will be inserted here by the publisher) The thermal conductivity of bulk, self-supporting boron nitride nanotube (BNNT) sheets composed of nominally 100% BNNTs oriented randomly in-plane was measured by a steady-state, parallel thermal conductance method. The sheets were either collected directly during synthesis or produced by dispersion and filtration. Differences between the effective thermal conductivities of filtrationproduced BNNT buckypaper (~1.5 W m -1 K -1) and lower-density as-synthesized sheets (~0.75 W m -1 K -1 ), which are both porous materials, were primarily due to their density. The measured results indicate similar thermal conductivity, in the range of 7 to 12 W m -1 K -1, for the BNNT network in these sheets. High BNNT-content composites (~30 wt.% BNNTs) produced by epoxy impregnation of the porous BNNT network gave 2 to 3 W m -1 K -1 , more than 10 the baseline epoxy. The combination of manufacturability, thermal conductivity, and electrical insulation offers exciting potential for electrically insulating, thermally conductive coatings and packaging.
An elastic sheet that deforms near a solid substrate in a viscous fluid is a situation relevant to various dynamical processes in biology, geophysics and engineering. Here, we study the relaxation dynamics of an elastic plate resting on a thin viscous film that is supported by a solid substrate. By combining scaling analysis, numerical simulations and experiments, we identify asymptotic regimes for the elastohydrodynamic leveling of a surface perturbation of the form of a bump, when the flow is driven by either the elastic bending of the plate or thermal fluctuations. In both cases, two distinct regimes are identified when the bump height is either much larger or much smaller than the thickness of the pre-wetted viscous film. Our analysis reveals a distinct crossover between the similarity exponents with the ratio of the perturbation height to the film height. * acarlson@math.uio.no
We present the results of experimental determination of the heat capacity of the pyrochlore Er 2 Ti 2 O 7 as a function of temperature (0.35–300 K) and magnetic field (up to 9 T), and for magnetically diluted solid solutions of the general formula (Er 1− x Y x ) 2 Ti 2 O 7 ( x ≤0.471). On either doping or increase of magnetic field, or both, the Néel temperature first shifts to lower temperature until a critical point above which there is no well-defined transition but a Schottky-like anomaly associated with the splitting of the ground state Kramers doublet. By taking into account details of the lattice contribution to the heat capacity, we accurately isolate the magnetic contribution to the heat capacity and hence to the entropy. For pure Er 2 Ti 2 O 7 and for (Er 1− x Y x ) 2 Ti 2 O 7 , the magnetic entropy as a function of temperature evolves with two plateaus: the first at R ln 2 , and the other at R ln 16 . When a very high magnetic field is applied, the first plateau is washed out. The influence of dilution at low values is similar to the increase of magnetic field, as we show by examination of the critical temperature versus critical field curve in reduced terms.
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