We report the mechanical properties and microstructures of multi-walled carbon nanotube (MWCNT)/alumina composites made with MWCNTs that absorb negatively charged functional groups at the MWCNT ends and along their length from an acid treatment. We conducted the fracture surface observations of the composites, in order to evaluate the effects of the acid treatment conditions of MWCNTs on the mechanical properties of the composites and the microstructures such as dispersibility and protrusion

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... gth of MWCNTs. According to the SEM observations, it was found that the dispersibility of MWCNTs affected the mechanical properties of the composites, and the protrusion length of MWCNTs decreased with increasing of the acid treatment time of MWCNTs. These observations revealed that the high structural homogeneity rather than pullout behavior of MWCNTs leads to an increase in the mechanical properties of the MWCNT/alumina composite. There is an optimal acid treatment time for improving the mechanical properties of the composites. The dispersibility of the MWCNTs and mechanical properties of the composites was increased by the acid treatment with treated for 2 hours compared to the pristine MWCNTs and acid treatment MWCNTs with treated for 0, 0.5, 1, 3 and 4 hours.