Non-isothermal oxidation kinetics of single- and multi-walled carbon nanotubes up to 1273 K in ambient

Non-isothermal oxidation kinetics of single- and multi-walled carbon nanotubes (CNTs) have been studied using thermogravimetry up to 1273 K in ambient using multiple heating rates. One single heating rate based model-fitting technique and four multiple heating rates based model-free isoconversional methods were used for this purpose. Depending on nanotube structure and impurity content, average activation energy (E-a), pre-exponential factor (A), reaction order (n), and degradation mechanism changed considerably. For multi-walled CNTs, E-a and A evaluated using model-fitting technique were ranged from 142.31 to 178.19 kJ mol(-1), respectively, and from 1.71 x 10(5) to 5.81 x 10(7) s(-1), respectively, whereas, E-a for single-walled CNTs ranged from 83.84 to 148.68 kJ mol(-1) and A from 2.55 x 10(2) to 1.18 x 10(7) s(-1). Although, irrespective of CNT type, the model-fitting method resulted in a single kinetic triplet i.e., E-a, A, and reaction mechanism, model-free isoconversional methods suggested that thermal oxidation of these nanotubes could be either a simple single- step mechanism with almost constant activation energy throughout the reaction span or a complex process involving multiple mechanisms that offered varying E-a with extent of conversion. Criado method was employed to predict degradation mechanism(s) of these CNTs.