Abstract

Carbon nanotube (CNT) bulk conductors have been proposed as an alternative material to metals for power and data transmission applications due to their light weight, flexure tolerance, and chemical stability. However, current fabrication technologies prevent bulk CNT wires from matching the electrical properties of individual CNTs, providing opportunity for researchers to improve CNT wire fabrication.

In this work, CNT conductors have been advanced using high-purity laser-vaporized single wall carbon nanotubes (SWCNTs). Acid dispersion and extrusion of SWCNTs into a coagulant bath was used to fabricate wires and systematic modification of the process has determined that coagulation dynamics govern the resulting wire properties. Extrusion of highly aligned and dense, acid-doped SWCNT wires yielded wires with record-setting electrical conductivities of 5.1 MS/m. An extrusion apparatus has been designed and built to scale up the fabrication process and has reduced variability in wire conductivity from 30% to 6% for samples 10’s of meters long. The high-current behavior of extruded SWCNT wires and commercially available CNT yarns has been investigated in a variety of ambient conditions. Comparison of electrical testing scenarios has determined that voltage-controlled testing is the proper method of characterizing CNT wires at high currents. Maximum current densities of 420 MA/m2 for extruded SWCNT wires were reached in helium, 10x greater than that reached in helium by commercial CNT yarns and exceeding fuse-law behavior for aluminum wires of equivalent diameter.

Further work to enhance CNT electrical conductivity was conducted using IBr chemical doping. Electrical enhancement of commercial CNT sheets and dopant adsorption were correlated and determined to be solvent dependent. A mechanism is proposed where low-dipole moment solvent systems favor the IBr-CNT interaction over the IBr-solvent and the solvent-CNT interactions. The optimal IBr doping conditions from the work were applied to commercial CNT yarns leading to an improvement in conductivity of 13.4x to a value of 1.4 MS/m. High voltage testing in air shows a 36% increase in maximum current, compared to as-received commercial CNT yarns. This dissertation research demonstrates the importance of SWCNT purity and selection of coagulation conditions to promote high-density, aligned SWCNT wires. Delivery of chemical dopants with high electrochemical potential through solvents which favor dopant-CNT interactions enhances electrical conductivity and maximum current density, achieving CNT wires capable of competing with metal conductors for electrical transmission applications.

Publication Date

3-6-2018

Document Type

Dissertation

Student Type

Graduate

Degree Name

Microsystems Engineering (Ph.D.)

Department, Program, or Center

Microsystems Engineering (KGCOE)

Advisor

Brian J. Landi

Advisor/Committee Member

Stefan F. Preble

Advisor/Committee Member

Reginald E. Rogers

Campus

RIT – Main Campus

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