Wettability and reactivity between molten aluminum and randomly aligned carbon nanotubes

The wettability and reactivity between molten aluminum (Al) and carbon nanotubes (CNTs) are a key issue in the preparation of CNTs-reinforced Al-matrix composites using a solidification route. In this work, we measured the wettability of randomly aligned multi-walled carbon nanotubes (buckypaper) by molten Al at 973–1173 K in a high vacuum using a modified sessile-drop method and examined their interactions using a droplet-sucking technique. The wettability between Al and CNTs is even worse than that of the Al/graphite system. The contact angles are basically larger than 140° and show only a sluggish decrease with time during isothermal dwelling. The chemical stability of CNTs in contact with Al is closely related to their structural integrity. The CNTs with good crystallinity and structural integrity have relatively high chemical stability and exhibit only a weak interfacial reaction with Al at 973 K. However, the stability of structural defective parts is much lower. They are readily eroded by molten Al, leading to the fragmentation of the CNTs. These CNT fragments having an open tubular structure are then rapidly dissolved in molten Al along the axial and radial directions. Simultaneously, a large amount of Al4C3 is formed at the interfaces.