Improving reinforcement properties of CNTs in aluminium matrix composites: a case of surface modification through AlN nano-particle grafting

This paper accentuates a newer approach to modify the surfaces of pristine multiwall carbon nanotubes (CNTs) by two-phase acid treatment, followed by silanization and grafting of functionalized AlN nano-particles onto the CNT surfaces, as a preparatory treatment before reinforcing in liquid metallurgy processed aluminium matrix composites (AMCs) without disrupting their structural integrity. Besides, the surface modified CNTs will have the strong potential to improve their dispersion uniformity, wettability and matrix-reinforcement bonding strength in the AMCs. The AlN nano-particle grafted CNTs were characterized through dispersion stability test, UV-Visible spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) analysis, Raman spectroscopy and Thermogravimetric analysis (TGA). Microstructure and elemental analysis were conducted through Scanning electron microscope (SEM) embedded with Energy dispersive X-ray spectroscope (EDS), Field emission scanning electron microscope (FESEM) and Transmission electron microscope (TEM). The aforementioned characteristics of AlN nano-particle grafted CNTs were compared with those of the pristine CNTs, acid treated CNTs and silanized CNTs to demonstrate the effectiveness of AlN nano-particle grafting on the CNT surfaces. Results revealed improvement of dispersion stability, covalent attachment of AlN nano-particles onto CNT surfaces (FTIR spectroscopy), existence of AlN on the CNT sidewalls (XRD analysis) and peaks corresponding to Al and N (EDS). Evidence of AlN on the CNT surfaces was also established through SEM, FESEM, TEM and EDS. Though there was a paltry degradation of CNT surfaces after the acid treatment, it was recovered substantially during silanization, and there was no evidence of tube shortening or fragmentations in SEM of silanized and AlN grafted CNTs.