Carbon nanotube wires with continuous current rating exceeding 20 Amperes

A process to fabricate carbon nanotube (CNT) wires with diameters greater than 1 cm and continuous current carrying capability exceeding 20A is demonstrated. Wires larger than 5mm are formed using a multi-step radial densification process that begins with a densified CNT wire core followed by successive wrapping of additional CNT material to increase the wire size. This process allows for a wide range of wire diameters to be fabricated, with and without potassium tetrabromoaurate (KAuBr4) chemical doping, and the resulting electrical and thermal properties to be characterized. Electrical measurements are performed with on/off current steps to obtain the maximum current before reaching a peak CNT wire temperature of 100 degrees C and before failure, yielding values of instantaneous currents in excess of 45A for KAuBr4 doped CNT wires with a diameter of 6mm achieved prior to failure. The peak temperature of the wires at failure (similar to 530 degrees C) is correlated with the primary decomposition peak observed in thermal gravimetric analysis of a wire sample confirming that oxidation is the primary failure mode of CNT wires operated in air. The in operando stability of doped CNT wires is confirmed by monitoring the resistance and temperature, which remain largely unaltered over 40 days and 1 day for wires with 1.5mm and 11.2mm diameters, respectively. The 100 C continuous current rating, or ampacity, is measured for a range of doped CNT wire diameters and corresponding linear mass densities rho(L). To describe the results, a new form of the fuse-law, where the critical current is defined as I infinity rho(3/4)(L), is developed and shows good agreement with the experimental data. Ultimately, CNT wires are shown to be stable electrical conductors, with failure current densities in excess of 50A in the case of a convectively cooled 11.2mm doped CNT wire, and amenable for use in applications that have long-term, high-current demands.