ИСТИНА

Modification of carbon matrixes (natural graphite and carbonized carbon fiber) was carried out by chemical intercalation (in fuming nitric acid) and by anodic oxidation in a nitric acid solution. The process of pyrolytic carbon deposition by CVI technique from methane at original and modified carbon matrices was studied. Intercalation of graphite in 98% HNO3 provides formation of graphite nitrate of stage II with identity period Ic = 11.2 Å. As a result of thermal shock of hydrolyzed graphite nitrate at Т=900оС in the air an expansion with formation of nitric exfoliated graphite EG (N) was observed. Anodic polarization of natural graphite in 58% HNO3 at high potentials (EAg/AgCl>1.5В) provides better oxidation of the carbon matrix and results in a mixture of oxidized graphite and graphite oxide. As a result of thermal shock electrochemical exfoliated graphite EG (E) was obtained. As a result of intercalation, oxidation and subsequent heat treatment crystalline size decreased from Lc=60 to Lc(EG(N))=36 and Lc(EG(E))=24 nm, the specific surface area increased to SBET(EG(N))=89 and SBET(EG(E))=140 m2/g. Modification results in the surface functionalization with hydroxyl groups and in the case of anodic polarization also with ether, carbonyl and carboxyl groups. Similar syntheses were conducted with Zoltek carbonized carbon fibers. Intercalation was not observed in any of the cases because of the small size of the crystallites and the highest functionalization was achieved in 58% HNO3 using anodic polarization. After washing that samples contained 15-20 at.% oxygen and shown specific surface area of about 5 m2/g after heat treatment. Low ordered pyrolytic carbon deposited on the obtained matrix by pulsed pyrolysis of methane. The rate of pyrolytic carbon deposition was shown to depend on the nature of the matrix. The highest deposition rate, other things being equal, were found for the samples of expanded graphite and carbon fiber, obtained by electrochemical modification in a solution of nitric acid. The highest deposition rates were fixed at the initial stages of low-density samples saturation CEG (E) with the most advanced surface. The content of pyrolytic carbon in the composite increases linearly with the increase of SBET of original matrix for both types of expanded graphite in the studied range.