Preparation of Exfoliated Graphite from Alkaline Metal-Graphite-Tetrahydrofurane Ternary Compounds

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Abstract
The exfoliated graphite was prepared from the ternary intercalation compounds of alkaline metal and tetrahydrofurane (THF).The degree of exfoliation at high temperatures was discussed in relation to the stability of the compounds.The properties of the sheets from these exfoliated graphites were compared with those of the sheets produced by con-ventional process (using acides as intercalant).The starting ternary compounds of Na-C-THF and K-C-THF were prepared through the reaction between the natural graphite (average particle size of 140μm, thickness of ca.20μm) and either Na-or K-naphthalene in THF at 25°C.The reaction products after 48 hours were the mixtures of 1st and 2nd stage intercalation compounds and unreacted graphite.The compound of Na-C-THF was found to be stable even after exposing in air and to need high temperatures to get high degree of exfoliation.The degree of exfoliation reached to about 350 times (in thickness) of the original graphite.From these exfoliated graphites, the sheets were obtained by simple compression, of which properties were very similar to those of commercial sheets.The thermal conductivity along the normal to the sheet showed strong dependence on the orientation of basal planes, suggesting, the importance of rolling process in order to get high degree of orientation and therefore low conductivity.From the point of engineering view, the Na-C-THF intercalation compound is concluded to be preferable, because of air stability and low cost of sodium metal itself, and also of air stability of ternary intercalation compound, even though long time for synthesis of ternary compound and a little high temperature for exfoliation are required.

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