(Invited) Synthesis and Properties of All SWCNT Metallic Nanotube Wire

Abstract

Copper and aluminum wire conductors are the principal means of conducting electricity. However, they add weight, possess poor fatigue and corrosion resistance and suffer from electromigration under severe conditions. Carbon nanotube (CNT) conductors have long been thought able to replace metals but still fall short of copper in electrical conductivity. CNT wires have so far displaced metal conductors in only a few high value-added applications. In this presentation, we outline an approach to create CNT conductors that address copper shortcomings. These carbon-based wires are made by a new high rate process to grow all metallic (armchair) CNT single wall tubes which are spun into wire in situ within the reactor all in one step, thereby keeping air away from the contacting surfaces of the tubes. We discuss a model of growth in terms of entropy of formation and radiation induced sympathetic vibration. In all other CNT yarn formation methods known to us, multistep processes are required which add cost or omit spinning. This latter process is necessary to add strength and improve conductivity. The innovations described in this talk include (1) methods for synthesis of nearly all metallic single chirality carbon nanotubes, and (2) the in situ spinning of these nanotubes within the reactor to a finished wire. We describe their properties determined by Raman, TGA, and structure by SEM and TEM. The conductivity of CNT wires depends on CNT alignment, surface contamination, control over the interfaces (Schottky barriers), and density. Yarns made from nanotubes of exactly the same diameters are also expected to pack well in the wire and provide better properties than the more typical random and larger diameters sometimes made. The combination of Boronite’s approach to create all CNT wire from uniform nanotubes with metallic chirality with the increasing commercial pressure to reduce weight, increase strength, and operational temperature, opens up commercial opportunities for very lightweight wiring in applications from aircraft to rotating machinery used at high temperatures. Weight saving in a variety of products is especially important for aircraft, cars, and even for large electric systems required to deliver very high current pulses. Boronite has also developed a unique method for infiltrating CNT spun yarn with copper, silver or aluminum to create electromigration resistant materials that can carry extreme currents.