In-situ studies of O2 and O radical oxidation of carbon black using thermogravimetric analysis and environmental transmission electron microscopy

Abstract

Understanding carbon black's oxidation behavior and resistance is crucial to its effective manufacturing, aftertreatment, and applications. This study combines well established bulk oxidation techniques, with novel in situ electron microscopy to visualize and establish oxidation pathways dependent on nanostructure and oxidation species. Three sample batches of carbon black were prepared; untreated, heat treated at 1400∘C, and 1600∘C. Heat treatment of the samples generated a graphitic shell highly resistant to oxidation by molecular oxygen. The sample oxidation pathways were then fully characterized using thermogravimetric analysis (TGA) and environmental transmission electron microscopy (ETEM). The TGA allowed for ex situ reactivity studies with molecular oxygen. The ETEM provided a real-time topographical and cross-sectional view of the particles as they oxidized under ionized O radicals and O2. Oxidation for all samples followed a three-step pathway: surface oxidation, nanotunnel formation through the surface, and bulk, diffusive carbon oxidation by O2. Amorphous samples oxidized rapidly with molecular O2. However, when O radicals were present, the amorphous sample reacted with O radicals to form a resilient carbon oxide, slowing oxidation. The heat-treated samples followed opposite trends; they resisted oxidation with O2 and reacted quickly with O radicals, as the radicals stripped away the graphitic shell.