Unusually High Thermal Conductivity of Carbon Nanotubes

Combining equilibrium and non-equilibrium molecular dynamics simulations with accurate carbon potentials, we determine the thermal conductivity $\lambda$ of carbon nanotubes and its dependence on temperature. Our results suggest an unusually high value ${\lambda}{\approx}6,600$~W/m$\cdot$K for an isolated (10,10) nanotube at room temperature, comparable to the thermal conductivity of a hypothetical isolated graphene monolayer or diamond. Our results suggest that these high values of $\lambda$ are associated with the large phonon mean free paths in these systems; substantially lower values are predicted and observed for the basal plane of bulk graphite.Comment: 4 pages 3 figures (5 postscript files), submitted for publicatio

Thermal Wave and Raman Characterization of Diamond Films

Diamond films possess many of the attractive properties of bulk diamond such as hardness, thermal conductivity and wide band transparency. This fact plus the recent progress in making these films inexpensively[1,2] has attracted much renewed interest in using them in many different applications which include coatings to machine tools and optical components, heat sinks for high power semiconductor devices. The challenge is then placed on material characterization techniques intended to measure their electrical, optical, thermal, and elastic properties. The challenge on the measurement of thermal properties is especially acute because none of the conventional techniques are appropriate for thin films. The films are usually very thin (of the order of a few to tens of microns) and in intimate thermal contact with the substrate. Even though the diamond films are supposed to have superb thermal conductivity, their contribution to the thermal conductivity of the combined film/substrate composite may still be too small to be detectable by conventional methods. Lifting the film from its substrate and measuring its thermal properties in isolation is not sufficient, because not only is this a destructive procedure, but also it misses the main point. For many applications, it is the in situ thermal properties, together with the coupling to the substrate, which constitute the main focus of interest. The thermal wave mirage method of measuring the thermal diffusivities of solid materials[3,4] meets this challenge very well. In this method a thermal wave is launched at the surface of the sample by a periodic, focused laser beam. The amplitude and phase of the gradient of the temperature field in the surrounding area are then measured with the mirage technique. The thermal properties of the sample/substrate are then deduced by comparing measured values with theoretical model predictions.</p

Contact damage in plasma-sprayed alumina-based coatings

A study of Hertzian contact damage in plasma-sprayed alumina-based ceramic coatings on steel substrates has been made. Presectioned specimens are used to identity subsurface micromechanical damage processes within the coating and substrate layers as a function of increasing contact load, from both postcontact and in situ observations. Damage occurs principally by cracking in the ceramic coating and plastic deformation in the metal substrate, along with delamination at the coating/substrate interface. Coating thickness, cycling loading (fatigue), and processing history (coating microstructure) are shown to be important factors in the damage patterns and ensuing modes of failure. Indentation stress-strain curves are used to measure macroscopic mechanical responses, to quantify the maximum sustainable contact stresses and to determine the relative roles of coating and substrate in the net deformation