Surface Coating Formation on the Multi-walled Carbon Nanotubes and Its Oxidation Resistance

Coating formation on multi-walled carbon nanotubes (MWCNTs) treated in a coke bed in the temperature range of 1000 similar to 1500 degrees C using silicon powder (Si) and the mixture of aluminum and silicon powders (Al+Si) as the silicon sources and its oxidation resistance were investigated by means of X-ray diffraction, high resolution transmission electron microscopy equipped with energy dispersive X-ray spectroscopy and thermogravimetric analysis-differential scanning calorimetry. Results show that using Si as a silicon source, SiC coating forms on the surface of MWCNTs after treated below 1400 degrees C. At 1500 degrees C, most of MWCNTs have transformed into solid SiC nanowires. Using Al+Si as a silicon source, the thickness of the coating increases at the same treated temperature compared with Si source. In addition, transformation of MWCNTs is prevented after treated at 1500 degrees C. The oxidation resistance of the treated MWCNTs improves compared with the as-received ones, and it gets better with increasing the thickness of the coating. Non-isothermal kinetics shows that oxidation activation energy of the as-received MWCNTs is 157.69 kJ/mol, while they are 202.39 k.J/mol and 230.70 kJ/mol after MWCNTs treated at 1400 degrees C using Si and Al+Si as the silicon sources, respectively.