Evaluation of the oxidative reactivity and electrical properties of soot particles

Abstract This paper focuses on the correlation between the oxidative reactivity and electrical properties of soot particles. Soot particles were produced from an n-heptane inverse diffusion flame and were sampled at different heights above the burner (HAB) using a thermophoretic and probe sampling techniques. The electrical properties were characterized by the electrical conductivity and work function, which were evaluated by an atomic force microscopy. The soot reactivity was assessed in terms of activation energy (Ea) and characteristic oxidation temperatures, including peak temperature (TP) and burnout temperature (Tb), using thermogravimetric analysis. As the soot particles gradually age, they have various electrical conductivity distributions. The average electrical conductivity presents an increase by three orders of magnitude when increasing the HAB from 10 to 60 mm. The work function of bulk soot particles shows an increase with the soot maturation. The soot reactivity gradually reduces during the soot maturation process because the values of Ea, TP, and Tb show increases with the increase in HAB. For the soot particles, the Ea and Tp have strongly positive correlations with the work function and with the logarithm of the electrical conductivity. Thus, electrical properties can serve as an indicator of soot reactivity.