Leonard Yowell

Survivability of single-walled carbon nanotubes during friction stir processing

Single-walled carbon nanotubes (SWCNTs) were added to aluminium using friction stir processing (FSP). The SWCNTs survived the thermal and stress cycles involved with friction stir processing. The Raman spectroscopy and SEM results are presented. Potential applications of nanotubes inserted into metals by this method are discussed.

Enhanced Raman microprobe imaging of single-wall carbon nanotubes

We explore Raman microprobe capabilities of visualizing single-wall carbon nanotubes (SWCNTs). Although this technique is limited to the micron scale, we demonstrate that images of individual SWCNTs, bundles, or their agglomerates can be generated by mapping Raman active elementary excitations. We measured the Raman response from carbon vibrations in SWCNTs excited by confocal scanning of a focused laser beam. Carbon vibrations reveal key characteristics of SWCNTs such as the nanotube diameter distribution (radial breathing modes (RBM), 100?300?cm?1), the presence of defects and functional groups (D-mode, 1300?1350?cm?1), strain and oxidation states of SWCNTs, as well as the metallic or semiconducting character of the tubes encoded in the lineshape of the G-modes at 1520?1600?cm?1. In addition, SWCNTs are highly anisotropic scatterers. The Raman response from a SWCNT is maximal for incident light polarization parallel to the tube axis and vanishing for perpendicular directions. We show that the SWCNT bundle shape or direction can be determined, with some limitations, from a set of Raman images taken for two orthogonal directions of the incident light polarization.

Advanced life support for space exploration: Air revitalization using amine coated single wall carbon nanotubes.

The challenges posed by long duration human space flight have made regenerable air revitalization a critical technology. Current systems using disposable lithium hydroxide do not address the difficulties presented by long duration missions. Solid amine systems offer the capability to regeneratively adsorb CO 2 using an amine—impregnated porous substrate. Desorption of CO 2 is then achieved by exposing the system to vacuum or by increasing temperature. However, thermal inefficiencies and system size constraints prevent adoption of regenerable systems on current and future space vehicles. A key challenge is the thermal management of the adsorbing bed. The adsorbing surface increases in temperature which reduces adsorbing efficiency. The removal of CO 2 reduces temperature, which in turn produces a loss in regeneration efficiency. These thermal inefficiencies necessitate prohibitively large volumes of traditional solid-amine materials, which do not have optimized surface areas and pore distributions. Single-wall carbon nanotubes (SWCNTs) may provide a means to increase surface area of the amine support and thermal efficiency. Recent work by Cinke et. al. provided a method of functionalizing SWCNTs and increasing the surface area to the order of 1500 m 2 /g [1]. We will report on the production of free standing, high surface area carbon nanotube structures currently being impregnated with amines. This novel SWCNT/amine approach will be compared with the current state of the art polymer structure-based system and characterized using SEM, TEM, surface area analysis through Brunauer-Emmett-Teller (BET), and also thermogravimetric equilibrium absorption. Results of SWCNT material improvements from processing modifications will also be presented.

Application of Carbon Nanotubes and Fullerenes for Thermal Management in Ceramics

New techniques for thermal management in ceramics at the nanoscale level have been investigated using low percentages of carbon nanotubes to reduce thermal conductivity of bulk ceramics. Samples of yttria-stabilized zirconia containing purified single-walled carbon nanotubes (SWNT) or vapor grown carbon fibers (VGCF) have been prepared by tape casting and analyzed using the laser flash method to evaluate reductions in thermal conductivity at high temperatures. New features in the samples due to the presence of carbon nanotubes have been characterized using Raman, SEM, TEM and, in the case of VGCFs, are related to significant reductions in thermal conductivity (>25%). The inclusion of a low percentage of nanoscale carbon fibers, the intimate relationship between the fibers and ceramic particles, and the indication that the fibers possess a crystalline overcoating, all contribute to the lowering of the thermal conductivity.