Triboluminescence flashes from high-speed ruptures in carbon nanotube Macro-Yarns

• Published in: Materials letters Vol. 213; pp. 298 - 302
• Main Authors: Gspann, Thurid S., Ngern, Nigel H.H., Fowler, Andrew, Windle, Alan H., Tan, Vincent B.C., Elliott, James A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.02.2018; Elsevier BV
• Subjects: Carbon nanotube; Carbon nanotubes; Crystals; Electron microscopy; Failure mode; Fracture surfaces; Heating; Materials science; Nanotubes; Strain rate; Strain rate effect; Tensile tests; Thermal conductivity; Triboluminescence; Yarn structure; Yarns; Carbon nanotube; Failure mode; Triboluminescence; Yarn structure; Strain rate effect
• ISSN: 0167-577X; 1873-4979
• DOI: 10.1016/j.matlet.2017.11.066

[Display omitted] •Triboluminescence flashes at point of rupture.•Observed for the first time in carbon nanotube yarn-structures.•Strain related overall heating followed by localized heating to 1800 K.•Yarn-like structure combined with high strain rates leads to highly localized strain energy.•CNT filament fracture leads to burst of white light emission. During tensile tests of carbon nanotube (CNT) macrostructures (ribbons, ropes and tows) under dynamic strain rates (1000 s–1), we recorded temporally sporadic, spatially localized visible light emissions (“flashes”) of less than 1.5 µs duration. The flashes occurred at the fracture sites and were, depending on the sample morphology, either distributed randomly over time (for tows) or occurred all at once over larger areas of several pixels (for ribbons). In situ thermal camera measurements, as well as ex situ analysis by electron microscopy reveal a hierarchical mechanism of overall heating over the whole sample length during straining, and localized heating around the fracture surfaces. Temperatures around the fracture tip were calculated to be of 1800 K in average. We propose that the flashes are caused by charge separation due to CNT bond fracture and gas discharge of the surrounding gases. Triboluminescence, known for larger sugar crystals, has not been observed for carbon nanotubes previously. It results from the yarn-like morphology, the ultra-high strength and thermal conductivity of our CNT fibers, which at high strain rates concentrate the strain at CNT level and lead to CNT fracture, rather than bundle sliding.