Development of pressureless sintered and hot-pressed CNT/alumina composites including mechanical characterization

Abstract

A process for the production of carbon nanotube (CNT)/alumina composites on the basis of an aqueous suspension and without any extensive pretreatment was developed. Pressureless sintering and hot-pressing of the nanocomposites were extensively researched and optimized. The influence of varying CNT contents, different alumina powders, sintering temperature and pressure on mechanical properties were investigated. Optimal hot-pressing conditions are specified at 1550°C, 15 min dwell time, and 80 MPa applied pressure. Dense nanocomposites up to 3 wt.% and 0.5 wt.% CNT content were achieved by hot-pressing and pressureless sintering, respectively. Furthermore, a 20% increase in hardness for CNT contents below 1.0 wt.% was detected, which is independent from the applied force and the alumina matrix. A highly anisotropic fracture toughness at increased CNT contents was detected by an indentation-based method. The developed process provides a possibility to produce CNT/alumina composites with improved mechanical properties under reasonable effort, which could also be used for industrial production.