Preparation Of Exfoliated Graphite And Study The Conductive Capability Of The Product

Exfoliated graphite (EG) is a porous and conductive material which is produced by natural flake graphite by means of oxidation, inserting, watering, dryness and expansion. In this thesis, what to study was to synthesize EG by chemical and electrochemical methods. The influence factors were discussed in detail,and the best reaction conditions were obtained by orthogonal tests. Specifications of graphite intercalation compounds (GICs) were tested. In addition, the structure and apparent performance of GICs were studied by means of XRD, SEM, TGA, and IR. In the present investigation,three acrylic resin / graphite conductive coatings were prepared from natural flake graphite, EG prepared by chemical method and EG prepared by electrochemical method, respectively. Surface resistivity was tested, and relationships of content and surface resistivity were investigated. The main research work was as follows:1) EG were prepared by a chemical method from natural flake graphite, using sulfuric acid and nitric acid mixing as intercalation agent and potassium permanganate as oxidant. EG with 290 ml/g exfoliation volume at 900℃was obtained in the best process condition. The optimum conditions of processing were obtained as follows: the amount of mixed acid was 60g, weight ratio of nitric acid to sulfuric acid in mixed acid was 1:3, 2.5 g of KMnO₄ was the best amount, and reaction time was 50 min. The exfoliated domain had a multilayer structure with many diamond-shaped pores. EG is worm-like or accordion-like and microcells are held together at their edges. Crystalline of graphite was damaged because of oxidation intercalation, but the C-C bond was not undermined. The medial strength feature diffraction peak of GICs at 2θ=29.5o was also determined by the damaged graphite crystalline. Sulfuric acid and nitric acid were intercalated into the graphite layers. The thermal event in GICs occurred at 71 500℃,which attained 21.45%, which seemed to be evidence for a removal of the intercalate from GICs.2) EG with 300 ml/g exfoliation volume at 900℃was obtained, which was prepared by the step method in the best process condition. The optimum technological conditions are as follows: the amount of mixed acid was 60g, weight ratio of nitric acid to sulfuric acid in mixed acid was 1:3, 2.2 g of KMnO4 was the best amount, reaction time was 50 min, and it was dipped in formic acid for two hours. Graphite layers of GICs appeared relatively looser than that of natural flake graphite,and EG possessed better pore structure. Crystalline of graphite was damaged because of oxidation intercalation, but the C-C bond was not undermined. The medial strength feature diffraction peak of GICs at 2θ=28.5o was also determined by the damaged graphite crystalline. Sulfuric acid, nitric acid and formic acid were intercalated into graphite layers. The thermal event in GICs occurred at 89 500℃,which attained 21.45%, which seemed to be evidence for a removal of the intercalate from GICs.3) EG with 200 ml/g exfoliation volume at 900℃was obtained, which was prepared by the electrochemical method in the best process condition. Experimental results show that the best process conditions were following: the current intensity was 0.75 A/m2, the sulfuric acid concentration was 75%,m(H2SO4):m(KMnO4)=90:1,and reaction time was 5 hours. Graphite layers of GICs appeared relatively looser than that of natural flake graphite. Crystalline of graphite was damaged because of oxidation intercalation, but the C-C bond was not undermined. The medial strength feature diffraction peak of GICs at 2θ=29.6o was also determined by the damaged graphite crystalline. Sulfuric acid was intercalated into the graphite layers. The thermal event in GICs occurred at 266 500℃,which attained 10.766%, which seemed to be evidence for a removal of the intercalate from GICs.4) When natural flake graphite was used as conductive filler, percolation threshold of coating was 33.33 wt. % and surface resistivity was decreased obviously to 1.76×10⁴Ω·cm^-2. The coating with EG as conductive filler possessed a lower percolation threshold (0.5 wt. %) and a better electrical conductivity, reaching about 20.8Ω·cm^-2Ω, which was nearly independent of the amount of the EG.