Evaluation of the thermal/optical reflectance method for discrimination between char- and soot-EC

Many optical, thermal and chemical methods exist for the measurement of elemental carbon (EC) but are unable or neglect to differentiate between the different forms of EC such as char- or soot-EC. The thermal/optical reflectance (TOR) method applies different temperatures for measuring EC and organic carbon (OC) contents through programmed, progressive heating in a controlled atmosphere, making available eight separate carbon fractions - four OC, one pyrolyzed organic carbon, and three EC. These fractions were defined by temperature protocol, oxidation atmosphere, and laser-light reflectance/transmittance. Stepwise thermal evolutional oxidation of the TOR method makes it possible to distinguish char- from soot-EC. In this study, different EC reference materials, including char and soot, were used for testing it. The thermograms of EC reference materials showed that activation energy is lower for char- than soot-EC. Low-temperature EC1 (550 °C in a 98% He/2% O₂ atmosphere) is more abundant for char samples. Diesel and n-hexane soot samples exhibit similar EC2 (700 °C in a 98% He/2% O₂ atmosphere) peaks, while carbon black samples peaks at both EC2 and EC3 (800 °C in a 98% He/2% O₂ atmosphere). These results supported the use of the TOR method to discriminate between char- and soot-EC.