The Development and Mechanical Properties of Carbon Nanotube Fibers
Dr. Michael Jaffe
New Jersey Institute of Technology
Thursday, July 14, 2005, 3:00 pm
Ben Bandy Conference Center
Center for Applied Energy Research
Abstract: Many routes have been developed for the synthesis of carbon nanotubes, but their assembly into continuous fibers has so far been achieved only through post-processing methods. In this work, carbon nanotube fibers were obtained by directly spinning an aerogel of carbon nanotubes formed during chemical vapor deposition synthesis (1). Typically a mixture of ethanol, ferrocene and thiophene is injected into a hot hydrogen atmosphere (1150 °C) and these compounds rapidly react to form carbon nanotubes. The carbon nanotubes then interact to form a continuous sock-like aerogel that travels down the reaction zone without sticking on the furnace walls. The sock is then spun into a fiber using a variety of spindle orientations. Overall, this process can be split broadly into three stages; the initial chemical vapor deposition reaction, the formation of sock and the drawing and properties of the fiber. Each process will be addressed in the talk.
Different hydrocarbons have been used for the reaction, with the yield and products being found to vary greatly with the feedstock used. These products were characterized using Raman spectroscopy and electron microscopy. The presence of small amounts of oxygen was found to be enhance sock formation and hence fiber spinning. Also, the process parameters were found to have a strong effect on whether multi-walled or single-walled nanotubes are produced.
Physical properties of the fibers were also assessed, with special emphasis on tensile strength and electrical conductivity. Tensile strengths are greatly dependant on process conditions and therefore, the different microstructures observed. On average, values lie in the range of 0.7 ± 0.2 GPa, with the maximum tensile strength reaching 1.5 GPa. The electrical conductivity of the carbon nanotube fiber is consistently higher than for carbon fibers, ranging from 2.5 to 8.3 per Ohms per meter. All experimental evidence points to the fact that very significant improvements in properties can be accomplished by better controlling the synthesis process.
1. Li et al., Science, 304, 276, 2004