Development of oxidation resistant and mechanically robust carbon nanotube reinforced ceramic composites

摘要

Carbon nanotube (CNT) reinforced bulk ceramic composites are not considered suitable for engineering applications involving exposure to temperatures beyond similar to 500 degrees C in air due to oxidation of the reinforcing CNTs. Against this backdrop, we report here the development of bulk Al2O3-CNT composites that are resistant to oxidation induced degradations at high temperatures in air and are also inherently very 'strong/tough'. SiC-coated multi-walled CNTs (MWCNTs), developed via scalable low temperature route, were incorporated into Al2O3 matrix via an innovative route, which leads to inter- and intra-granular reinforcement of the sintered polycrystalline matrix by the MWCNTs. Such Al2O3-(SiC-coated)MWCNT composites possess enhanced resistance to indentation-induced crack propagation and flexural strength by similar to 41 and similar to 50%, respectively, with respect to monolithic Al2O3; along with improvement in the abrasive wear resistance by similar to 54%. This, in a way, re-confirms the structural compatibility of the SiC-coated MWCNTs with the Al2O3 matrix. In the context of oxidation, the Al2O3 -MWCNT composite counterparts, having uncoated MWCNTs, suffered from nearly complete loss of MWCNTs upon exposure to air at 1000 degrees C (for 1 h), with concomitant reduction in density and reverting back of the fracture mode from transgranular to intergranular (as for monolithic Al2O3). By contrast, the Al2O3-(SiC-coated)MWCNT composites did not suffer from any such oxidation-induced loss/degradation even up to 1000 degrees C in air.