Effect of drying methods on the structure and thermal decomposition behavior of ammonium perchlorate/graphene composites

Graphene hydrogels were prepared by the sol-gel method, and then used to prepare ammonium perchlorate (AP)/graphene composites by the incorporation of AP. The composites were dried naturally in air, freeze-dried, or dried with supercritical CO₂. Scanning electron microscopy (SEM), elemental analyses (EA), and X-ray diffraction (XRD) were used to characterize the structure of the AP/graphene composites dried using different methods. Furthermore, the thermal decomposition behavior of the AP/graphene composites was investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis/infrared spectroscopy (TG-FTIR). Drying method had an obvious influence on the morphology of the AP/graphene composites; only the AP/graphene composites dried with supercritical CO₂ showed similar three-dimensional networks and porous structure to graphene aerogels. Elemental analyses revealed that the AP contents in the AP/graphene composites prepared by drying naturally, freeze-drying, and supercritical CO₂ drying were 89.97%, 92.41%, and 94.40%, respectively. XRD results showed that AP was dispersed homogeneously on the nanoscale in the AP/graphene composites dried with supercritical CO₂ and the average particle diameter of AP was about 69 nm. DSC and TG-FTIR analyses indicated that graphene could promote the thermal decomposition of AP, particularly for the sample dried with supercritical CO₂. Independent of drying method, the low-temperature decomposition of the as-prepared AP/graphene composites was not observed and the high-temperature decomposition was accelerated. Compared to the other two drying methods, graphene in the AP/graphene composites dried with supercritical CO₂ showed most obvious promoting effects. The high-temperature decomposition temperature of the AP/graphene composites dried with supercritical CO₂ decreased by 83.7 °C compared with that of pure AP, and the total heat release reached 2110 J·g^-1. Moreover, graphene also took part in the oxidation reactions with oxidizing products, which was confirmed by the generation of CO₂.