In situ synchrotron X-ray diffraction of carbon nanotube wires under tension: Microstrain and graphitic order

Carbon nanotube wires are promising candidates for next-generation beam instrumentation because of their ultralow mass, radiation tolerance, and potential for stable mechanical and structural behaviour under extreme operating conditions. However, their performance is strongly influenced by catalyst contamination, graphitic disorder, and residual microstrain inherited from fabrication and bundle architecture. Understanding how these factors vary across different CNT wire architectures is essential for developing reliable low-density conductors for future accelerator systems. This study presents a comparative structural and mechanical investigation of carbon nanotube wires spanning distinct nanotube types, fabrication routes, and diameters from 10 μ m to 50 μ m , examined before and after nitric-acid purification and twist fixation. Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray analysis, tensile testing, and in situ synchrotron X-ray diffraction were combined to quantify graphitic order, lattice spacing, and spatial heterogeneity. Strong architecture-dependent behaviour was observed. The 10 μ m wire exhibited compressed basal-plane spacing and large spatial variability, whereas the 50 μ m multi-walled-dominant wire remained close to relaxed turbostratic spacing. Purification reduced impurity content, improved graphitic coherence, and enhanced tensile stiffness, including an increase from 30.8 GPa to 68.4 GPa in the 10 μ m wire, while preserving the underlying hierarchy of residual strain across suppliers. The results demonstrate that purification improves structural uniformity and mechanical consistency, but that the dominant lattice strain state is primarily governed by nanotube architecture and bundle topology rather than chemical treatment.