ИСТИНА

Graphite intercalation by acids has been attracted great attention of scientist and technologists since they were synthesized for the first time. Recent researches were pointed to establishment of structural parameters, physical properties, surface area, sorption ability, practical application etc. Therefore, there is still a lack of information about graphite morphology transformations under chemical and thermal treatment. In present work the influence of intercalation and exfoliation conditions on graphite micro-, macro- and pore structure was studied. Natural graphite, expandable graphite and exfoliated graphite were characterized by means of X-ray diffraction (XRD), optical and scanning electron microscopy, Raman spectroscopy, electron energy loss spectroscopy (EELS) and nitrogen adsorption. Expandable graphite of two types was prepared by graphite intercalation with 98 % nitric acid (EG-1) or graphite anodic oxidation in 60 % nitric acid (EG-2). Exfoliated graphite (EGT-1 and EGT-2) was obtained by EG thermal treatment at 250 – 900 oC. According to microscopy studies, chemical intercalation is accompanied by defect appearance at particle edges. Electrochemical treatment has a prepotent effect on graphite macrostructure and promotes particles split followed by diameter and thickness reduction. Thermal exfoliation causes particle expansion and, in case of EG-2→EGT-2 transition, further dispersion along c-axis. XRD data evidences that crystalline size reduces 2 or 6 times when graphite matrix is oxidized up to I-II stages or 350 – 1500 C/g in case of chemical and electrochemical intercalation correspondingly. Besides, graphite oxide phase occurs as a result of graphite polarization as early as at 350 C/g. Raman spectroscopy and EELS revealed small amount of amorphous carbon in EGT-1 and about 60 % in EGT-2. Nitrogen adsorption shows that only exfoliation process leads to pore structure development. Surface area and pore volume of EG900-1 and EG900-2 are of 20 m2/g (0.006 cm3/g) and 95 m2/g (0.14 cm3/g) correspondingly.