Microstructural evolution of multi-walled carbon nanotubes in the presence of mixture of silicon and silica powders at high temperatures

Abstract

Microstructural evolution of multi-walled carbon nanotubes (MWCNTs) in the presence of mixture of silicon and silica powders in a coke bed is studied in the temperature range of 1000–1500°C by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and thermogravimetry–differential scanning calorimetry (TG–DSC). The results showed that a thin amorphous SiO2 coating was formed on the surface of MWCNTs at the temperature below 1300°C. With the increase of the treated temperature, the coating became thicker, 3–7nm in thickness at 1400°C and a maximum of 10nm at 1500°C. Meanwhile, SiC nanowires and SiC nanocrystals around Ni catalyst at the tip of MWCNTs were formed at 1400°C and 1500°C, which were related to the vapor–vapor (V–V) and vapor–liquid–solid (V–L–S) reactions between SiO (g) and CO (g) or C (s), respectively. The oxidation resistance of all the treated MWCNTs was better than that of as-received ones. The oxidation peak temperature reached 804.2°C for the treated MWCNTs, much higher than 652.2°C for as-received ones.