High temperatures gas-solid reactivity of aluminum-carbon nanotubes composites

The gas-solid reactivity of metal-carbon matrix composites such as aluminum-carbon nanotubes (Al-CNT) sintered samples was studied at temperatures below and above the melting point of Al in O-2, synthetic air, CO2, H-2-Ar (5% v/v) and Ar. Small cylindrical samples of different composition with "single-walled" CNTs (SWCNTs) or "multi-walled" (MWCNTs) were sintered in Ar at 625 degrees C and the resulting materials showed densities ranging from 92.2 to 99.0% of the theoretical density of bulk Al. Thermogravimetric analysis (TG) with simultaneous differential thermal analysis (DTA) up to 1200 degrees C shows that the Al-CNT composites do not behave as a two independent phases system. This is mainly demonstrated by the following phenomena: i. The lowering of the melting point of Al, the magnitude of which cannot be explained by the expected very low solubility of C in Al at this temperature; ii. The amount of alpha-Al2O3 grown in oxidizing atmospheres and at the highest temperatures depends from the CNT content in the composite; iii. The formation of Al4C3 occurs only in presence of molten Al as shown by environmental X-ray diffraction "XRD". Field emission scanning electron microscope "FESEM" and high-resolution analytical transmission electron microscopy "HRTEM" investigations confirm that at the sintering temperature no detectable chemical interaction exists between Al and CNT. (C) 2016 Elsevier B.V. All rights reserved.