High-temperature resistivity of aluminum–carbon nanotube composites

The resistivity and thermal coefficient of resistivity (TCR), of metallic matrix composites, MMCs, aluminum–carbon nanotube, Al-CNT, were studied under high vacuum in the temperature interval from RT to 800 K. The samples shaped as small cylinders and containing single-walled CNTs or multi-walled CNTs were sintered at 625 °C. The resistivity of sintered samples of pure Al was found three orders of magnitude higher with respect to bulk, having the former a density value equal to 98.8 % of bulk Al. The explored range of the CNT concentration was within 5 wt%. At the highest CNT concentrations, the trend of resistivity against temperature was found negative being more pronounced for composites with MWCNTs. For Al-SWCNT composites, at around 3.3 wt% (4.2 vol%), TCR is practically independent from temperature; for Al-MWCNT, the TCR zero-crossing occurs at different compositions depending on temperature. Higher is the temperature, lower is the TCR zero-crossing composition. Resistivity data were discussed in the framework of the Matthiessen’s rule and sound evidences were shown that no Al₄C₃ formation was detected at working temperatures.