Formation of oxidation resistant graphite flakes by ultrathin silicone coating

Abstract

Two types of silicone compounds and a trace amount of Pt catalyst were impregnated into exfoliated graphite (EG) by sorption and cured under different conditions. By this process, graphite sheets composing EG were coated with very thin (≪1 μm) silicone layer. Thus, obtained precursors were converted to oxidation resistant graphite flakes by the heat-treatment at a temperature in a range of 1000–1300 °C for 1 h in inert atmosphere. The coatings were intact and they were mixtures of Si–C–O glass-like composites and amorphous silica, which were confirmed by SEM, XRD and MAS-NMR. As formed graphite flakes showed instantaneous mass losses of 5–13% by oxidation at 1000 °C for 1 h in pure O 2, but after that the mass change was very small. By removing free carbons on the surface beforehand, the mass loss became less than 1% for all products. The mass loss of the sample molded into a disk-shape was about 1% after the first cycle (1 h) of repetitive oxidation at 1000 °C in air but from the second cycle an appreciable mass loss was not observed up to 20 h. The present method is promising for the production of oxidation resistant graphite flakes.