On lower-nitrogen expandable graphite

The intercalation reaction of a mixture of HNO3 and acetic anhydride to form expandable graphite was investigated. Expandable graphites were prepared from the intercalation compounds (GICs) by rapid heating up to 900°C. The effects of reaction conditions on the quality of the expandable graphites were studied and the optimum conditions for the procedure were as follows: weight ratio of natural flake graphite:acetic anhydride:nitric acid:potassium permanganate, 1.0:0.8:0.5:0.07; reaction temperature, 30°C; and time, 40 min. X-ray diffraction patterns showed the intercalation product was a stage 4 compound. Mass spectra showed that nitric and acetic acids were intercalated into graphite layers. Expandable graphite with 280 ml/g expansion volume and 1.27% nitrogen was obtained.