Preparation Of Sulfur-free & High Anti-oxidation Expandable Graphite

The early expanded graphite contains sulfur which can erode the metal when used as sealing materials.In addition,on the condition of high temperature and ample oxidant,the expanded graphite can easily be oxidized that causes the effect of seal to drop.Therefore,the study on sulfur-free & anti-oxidation expandable graphite preparation has been paid more attention.By adopting the step method,the sulfur-free & anti-oxidation expandable graphite was prepared using hydrogen peroxide and potassium permanganate as the oxidants respectively,nitric acid and phosphoric acid as the reagent and different solutions as the impregnant and a series of capabilities were tested.The influence factors were discussed in detail,such as the quantity of nitric acid, the kind of oxidants and quantity,the oxidation temperature and time,the quantity of phosphoric acid,the insertion temperature and time,the torrefaction temperature and time,the expanded temperature and time.The best reaction conditions were obtained by using the orthogonal test method respectively.The optimum technological conditions are as follows:Graphite(g):HNO₃(ml):H₂O₂(ml):H₃PO₄(ml)=5:12:0.5:7, the reaction time is 60min,reaction temperature is 25℃;Graphite(g):HNO₃(ml): KMnO₄(g):H₃PO₄(ml)=5:12:0.6:7,the reaction time is 80min,reaction temperature is 35℃.On these condition,the expanded volumes are 270 mL·g^-1 and 280 mL·g^-1 respectively.On the basis of the former optimum technological conditions,the sulfur-free & anti-oxidation expandable graphite was prepared with different solutions as the impregnant.The results show the expandable graphite prepared using hydrogen peroxide as the oxidant,sodium dihydrogen phosphate,boric acid and phosphoric acid mixture as the impregnant has high expanded volume and maximum anti-oxidation.The sulfur-free & anti-oxidation expandable graphite that was prepared with hydrogen peroxide as the oxidant has higher anti-oxidation than the potassium permanganate did.The contents of water,volatile and ash were tested.The products have no sulfur or ash,and the qualities are high.