Carbon nanotubes: Amino functionalization and its application in the fabrication of Al-matrix composites

Al-matrix composites reinforced with amino-functionalized multiwalled carbon nanotubes (fCNTs) have been fabricated using the powder metallurgy process. Using this method fCNTs (1.5 wt.%) were dispersed in Al powder by high energy ball milling. Al–fCNTs composites (1.5 wt.%) were fabricated by the consolidation of powders at 550 MPa followed by sintering at 620 °C under a vacuum of 10− 2 Torr for 2 h. Functionalization of the nanotubes was carried out by ball milling multi-walled carbon nanotubes (MWCNTs) in the presence of ammonium bicarbonate. It was observed that the dispersion of fCNTs in Al-matrix was much higher than those of non-functionalized MWCNTs. Microhardness measurements showed that a microhardness value of about 400 kg/mm2 could be obtained for Al-matrix composites loaded with 1.5 wt.% fCNTs. Microstructure observations using scanning electron microscopy (SEM) and high-resolution electron microscopy (HRTEM) confirmed that the sintered composites had a good dispersion of fCNTs in Al matrix and they do not agglomerate with each other. Further, the HRTEM characterization of these composites revealed the formation of a thin transition layer of Al4C3 between fCNTs and Al matrix, which is believed to be responsible for load transfer from Al matrix to fCNTs. A thorough characterization of MWCNTs and fCNTs synthesized in the present work was carried out using XRD, SEM, TGA, HRTEM, FTIR, SIMS and Raman spectroscopy.