The experimental system reported in Wang et al. (2013) was modified and adopted, as shown in Fig. 1. Samples were placed evenly on the bottom of a crucible that was put inside an electrically heating furnace, where N2 flush of 5 L/min was adopted to keep an inert atmosphere; and a high-speed IR camera was used to take videos of the samples during the pyrolysis process. The pyrolysis temperature was increased from ambient temperature to 550–600 °C until the reaction finished.