Thermally induced variations in the nanostructure and reactivity of soot particles emitted from a diesel engine

This work focuses on the thermally induced variation in the nanostructure, size of primary particles and oxidative reactivity of diesel soot and a commercial carbon black in an inert gas environment at temperatures ranging from 600 to 1000 °C. Soot nanostructure and size were characterized by high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The soot reactivity was evaluated with respect to activation energy (E_a) and characteristic oxidation temperature, including peak temperature (T_P) and burnout temperature (T_b), using thermogravimetric analysis (TGA). The mass loss of diesel soot and carbon black rises when increasing the thermal treatment temperature, especially at 1000 °C, and a significant quantity of mass loss can be observed, which is primarily due to thermal fragmentation and the desorption of chemical species on soot surfaces. The HRTEM and XRD results all indicate that the thermally treated soot samples have more ordered nanostructure than the untreated samples. There is a reduction in the size of primary particles as thermal treatment temperature increases. The soot reactivity decreases after thermal treatment, as manifested by the elevation in E_a, T_P, and T_b values. Moreover, the oxidation reactivity of soot samples is closely associated with the fringe length, tortuosity, and fringe tortuosity. Compared to carbon black, diesel soot with a more disorder structure has a higher oxidative reactivity.