Micro and macroscopic structure evolution of few-walled carbon nanotube bundled network by high temperature anneal

Abstract

High temperature anneal is of importance to create nanocarbon-based materials with excellent functions and performances. However, a comprehensive understanding on annealed nanocarbon assembly structures has been challenging. We successfully propose the micro and macroscopic structural analysis of 0.8–3.4 nm diameter few-walled carbon nanotube (CNT) bundled network by a multifaceted characterization, which were annealed over 1200–3000 °C in the form of a film as the case study. Up to 1800 °C carbonaceous impurities were removed to secure nanospace among nanotubes, i.e. interstitial channels important to design multiple functions. Beyond 1900 °C nanoscale graphitic particles were generated on the nanotube bundles, then grown to be micro-meter scale toward 3000 °C. Parallel to the particle growth, small diameter (<1.2 nm) nanotubes became undetected at 2200–2400 °C with a decrease in available interstitial channels, finally resulting in the nontubular, graphitized network structures at 2600–3000 °C. The anneal at 1200–1800 °C can afford the high purity CNT bundled network structures, and the higher temperature anneal led to the high crystallinity graphitized network structures. To understand the structural evolution, 14 different analytical methods were employed, and two-dimensional correlation analysis from the collected data revealed the synchronous and asynchronous structural parameters with the annealing temperature. Thus, we found that the structural changes occurred in 3 stages of 1200–1800 °C, 1900–2400 °C, and 2600–3000 °C. On the other hand, the electrical conductivity gradually decreased due to the removed carbonaceous impurities and the structure changes. Our findings can be an asset for carbon material science and pave a way toward nanocarbon applications with the films, fibers, and composites.