Effect of sintering temperature and nanotube concentration on microstructure and properties of carbon nanotube/alumina nanocomposites

Multiwalled carbon nanotube (MWCNT)/alumina (Al2O3) nanocomposites were prepared by simple wet mixing of MWCNT and Al2O3 powder followed by pressureless sintering in static Argon. X-ray diffraction (XRD) line broadening analyses using Williamson–Hall (W –H ) technique revealed a polynomial dependence of crystallite size (D V) on sintering temperature (T sin) and volume percent CNT added (V CNT) as DV≈[0.9(Tsin)−770]+[−1.1(Tsin)+1489](VCNT)+[0.4(Tsin)−547]2(VCNT)DV≈[0.9(Tsin)−770]+[−1.1(Tsin)+1489](VCNT)+[0.4(Tsin)−547](VCNT)2. While the highest increase (~14%) in Vickers hardness (HV) over pure Al2O3 was offered by 0.15 vol% MWCNT/Al2O3 specimen, the highest fracture toughness (KIC~5 MPa m0.5) and flexural strength (σFS~260 MPa) were obtained for nanocomposite containing 0.3 vol% MWCNT which were ~26% and ~16% higher, respectively, than those of pure Al2O3. The 0.15 vol% MWCNT/Al2O3 specimen also offered maximum increase (~22%) in thermal conductivity over unreinforced Al2O3 (~39 W/m K). Electrical percolation in nanocomposites was observed between 0.6 and 1.2 vol% CNT loading.