Improving the water-wettability and oxidation resistance of graphite using Al2O3/SiO2 sol-gel coatings

Transparent Al2O3, Al2O3–SiO2 and SiO2 sols were prepared via hydration of TEOS and Al(OC3H7)3 in distilled water and used to coat natural flake graphite. Graphite coated with these sols was dried at 120 °C for 12 h and heat-treated at 500 °C for 2 h to gel the sols. Water-wettability and oxidation resistance of as-received (uncoated) and coated graphites were examined. Al2O3, Al2O3–SiO2 and SiO2 coatings improved graphites water-wettability and SiO2-coated graphite showed the best water-wettability. All the coatings also improved the graphites oxidation resistance, especially at high temperatures (>1100 °C). Addition of Si greatly improved the oxidation resistance of as-received graphite whereas the oxidation resistance of the coated graphites was only slightly improved, suggesting that it is possible to decrease the level of antioxidant used in commercial castable systems.