The effect of mullite coating and microwave sintering on high temperature oxidation resistance of MWCNTs

Multi-walled carbon nanotubes (MWCNTs) are considered as a promising material for nanocomposites fabrica-tion due to their magnificent characteristics. However, challenges including low oxidation resistance (oxidized above 530 C in the air) and weak interfacial adhesion, etc, restrict their use at high temperatures. Coating the surface of MWCNTs seems a promising way to control its oxidation and to increase interfacial adhesion. To the best of our knowledge, the coating of MWCNTs by mullite has not been reported yet, so that in this paper, mullite-coated MWCNTs (20 wt %) was fabricated by sol-gel method to improved oxidation resistance of MWCNTs. The uniform mullite shell was sintered through two methods of microwave and conventional heating. The effect of sintering temperature and type of heating on mullitization, crystallization and oxidation resistance of MWCNTs were investigated. Microstructural investigations revealed that the surface of MWCNTs is uniformly covered by mullite and TGA results showed the increase in oxidation temperature (asymptotic to 300 C). In addition, the obtained results confirm that the microwave method could be a better technique for obtaining a dense, smooth and crystallized coating layer than the conventional one for improving oxidation resistance of MWCNTs.

Automated summary

In this study, mullite-coated MWCNTs were fabricated by sol-gel method to improve the oxidation resistance. The results showed that the mullite coating, synthesized using microwave heating, exhibited a uniform and dense structure with higher crystallinity, resulting in an increase in the oxidation temperature of MWCNTs.