Study On The Preparation Of Low Temperature Expandable Graphite

The expansion temperature of expandable graphite is very high. It always can fully expanded at900-1000℃.This greatly limits the it’s application at cryogenic fire, environmental protection, military and other fields. So it is extremely important that is preparation expandable graphite with high volume at low puffing temperature.This paper studies an improved method of chemical oxidation. The carbon content of flake graphite is85%and its size is+80mesh. The carbon content of the flake graphite is up to99%through the traditional wet purifying. Then perchloric acid is used as intercalation, and permanganate, sodium chlorate is used as oxidant. After flake graphite is oxidized and intercalated by them, it can expand at the lower temperature. The the ratio of graphite and intercalation, oxidant, reaction temperature, reaction time, drying temperature and expansion temperature were discussed to the effect of its expansion ratio. Then the optimum process conditions were found.In this thesis, the carbon content of graphite is85%. The graphite must be purified and make its purity over99%before in oxide intercalation experiment. The low temperature expanded graphite was prepared by filtrating insert and using direct intercalation test method. Then the characterization of natural graphite, expandable graphite and expanded graphite were analyzed with application of the modern instrument. The experiment show:First, natural flake graphite was wet purified with the sulfuric acid and hydrochloric acid method. The best material ratio:graphite(g):sulfuric acid(mL): hydrochloric acid(mL):hydrogen peroxide=(mL)1:3:2.4:3, and the purified graphite carbon content up to99%.Second, the low expandable graphite was prepared by direct intercalation method with the purification of flake graphite as raw material, perchloric acid as intercalation agent and different reagents as oxidizing agent. When the process conditions is the graphite(g):perchloric acid(mL):potassium permanganate(g)=l:5:0.1, reaction temperature was35℃, reaction time was80min, the drying temperature was50℃, the graphite product initiation expansion temperature was110℃, its expanded volume was up to230mL/g at300℃, and its expanded volume was up to380mL/g at 400℃. The addition of40%expandable graphite can make EVA’s oxygen index increase to27.4%from20%.Third, the raw material, intercalation and other condition was same with the second.When the oxidizing agent was potassium permanganate and sodium chlorate, the process conditions:graphite(g):perchloric acid(mL):sodium chlorate(g):potassium permanganate(g)=1:4:0.2:0.08, this graphite product initiation expansion temperature is110℃.Its expanded volume was up to360mL/g when the expansion temperature was300℃. Its expanded volume was up to590mL/g when the expansion temperature was400℃.The addition of40%expandable graphite can make EVA’s oxygen index increase to29.1%.Fourth, characterization of the graphite production was analyzed by SEM. The following conclusions were got thought the analysis of the SEM diagram. After natural flake graphite is oxide intercalated, the layer space is increased, and parts of its edge is crimped. The expanded graphite exhibits wormlike, its layer space has been expanded by hundreds of times, and some properties of is completely different from natural flake graphite. The product has low temperature expansion characteristics. And the preparation process is simple and operated easily. So, it can be applied to fireproof paint, fire control, industrial production.