Sulfur-free Ash-free Expandable Graphite

The expandable graphite that used concentrated sulfuric acid as the inserting reagenterodes the metals when used as sealing materials. Low sulfur or sulfur-free expandablegraphite was paid more attention. In this study, the preparation of sulfur-free expandablegraphite was made using the nitric acid as the oxidant and inserting reagent. Furthermore,Sulfur-free expandable graphite was prepared by using the mixed acids of nitric acid andhydrogen peroxide as the oxidation-intercalation agent and using acetic acid as the assistintercalation agent.The influence factors were discussed in detail, such as the concentration of nitricacid, the amount of nitric acid, the ratio of materials, reaction time, temperature, theamount of free acid, pH value, the forms of washing and drying conditions. The bestreaction conditions were obtained by using the orthogonal test method. The optimumtechnological conditions are as follows: The nitric acid concentration is 98%, the weightratio of nitric acid and natural flake graphite is 2.4: 1.0, reaction time is 15min, reactiontemperature is 30℃, The descending order of affecting factors is weight ratio of nitricacid and natural flake graphite, the concentration of nitric acid, reaction time, and reactiontemperature. The Exfoliated volume is 180 ml·g^-1.Sulfur-free expandable graphite was also obtained by using the mixed acids of nitricacid and hydrogen peroxide as the oxidation-intercalation agent and using acetic acid asthe assist intercalation agent in based on previous experiments, The factors that influenceexfoliated volume were discussed, such as the amount and concentration of nitric acid, theamount of hydrogen peroxide, oxidation time, temperature and the concentration of aceticacid. The optimum conditions of processing were obtained as follows: hydrogen peroxide:nitric acid(98%): graphite: acetic acid(85%)=1ml:12ml:5g:7ml, oxidant reaction time islh, inserting reaction time is 15min, reaction temperature is 25℃, The contents of water,volatile, ash, sulfur and pH values were tested. The exfoliated volume is over 300 ml·g^-1,no sulfur and no ash. The quality of the product is high.