Study on preparation and inoxidizability of sulfurfree expandable graphite

Sulfur-free and high inoxidizability expandable graphite has been prepared by chemical method using non-high purity mixture grain size natural flake graphite. The conditions for preparing the expandable graphite have been optimized and influence factors have been obtained. Results showed that the optimum conditions were the ratio of flake graphite(g) : potassium permanganate(g) : nitric acid(ml) being 1:0.2:6, oxidation time of 60 min, oxidation temperature of 40°C, 2ml hydrogen peroxide and 10 ml antioxidant. The maximum expansion volume was 280 ml·g^-1. The inoxidizability and expansion volume change of expandable graphite added antioxidants have been researched. Results showed that mixture solution of phosphoric acid and boric acid as antioxidant had the best antioxidant capacity, followed by mixture solution of phosphoric acid and potassium dihydrogen phosphate, then phosphoric acid.