Time-dependent electrical properties of carbon nanotube yarns

Carbon nanotubes (CNTs) are projected as a desirable option to transmit electrical power where specific conductivity is an important consideration. A CNT-yarn was therefore characterized for its ability to transmit power as a function of time. A current-voltage (I-V) relationship was established that showed three distinct regions: linear, non-linear and finally its degradation. The linear region shows a low and constant resistance. The output current did not change with time when the applied constant voltage was in the linear region of the I-V relationship. However, when the applied constant voltage was in the non-linear region the current decreased exponentially and leveled off with time. Under constant current tests, voltage increased only when current level was in the non-linear region. These time-dependent electrical conducting properties can be accounted for by short circuits occurring from the development of a localized red-hot spots in the CNT-yarn in the non-linear region, leading to thermal degradation, as revealed by thermal imaging of the yarn, thermal gravimetric analysis of the CNTs, and SEM images and EDAX of the thermally degraded CNT-yarn.