JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS Vol. 8, No. 2, April 2006, p. 624 - 630 Modification of the structural parameters of coal tar pitch induced by addition of nanocarbon-coated iron at primary carbonization I. ION a.b* , A-M. BONDAR b , Y. KOVALEV a , C. BANCIU b , I. PASUK b a Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research, 141980 Dubna, Russia b Carbon Materials Laboratory , National Institute for Research and Development in electrical engineering, 030138 Bucharest-3, Romania The carbon composite materials consisting of nanocarbon coated iron as additive, in different amount and coal tar pitch as matix, was carbonized at 440 o C with the purpose to obtain materials for electromagnetic interference shielding. The materials structure and the changing induced by addition of different amount of additive were studied by Small-Angle Neutron Scattering, Electron Microscopy. The structural mode proposed exhibit two structural levels characterized by basic structural units (BSU) and fractal clusters, respectively. BSU consist of two polyaromatic molecules piled up parallel to each other. The fractal properties of the clusters depend on the amount of the additive. The effect of additive is negligible to the first level and is strongly manifested at the second level, where the small differences in amount increase the roughness or change the fractal properties from surface to mass fractal. (Received January 18, 2006; accepted March 23, 2006) Keywords: SANS, Carbon composite materials, Mesophase, BSU, Electromagnetic interference shielding 1. Introduction Carbon materials are known to have a wide range of structures, textures and properties and, as a consequence of their diversity, they have wide applications. ’’Carbon material’’ is the generic name for solid materials, which are mainly composed of carbon atoms; and it covers a large variety of materials from amorphous to highly ordered, close to the graphitic structure. In general, due to a wide variety of structures, synthetic graphite and carbon materials were in principally classified according to the possibility to develop graphitic structures and according to the production technology process. The graphitic structures are themselves classified in to non-graphitizing carbon and graphitizing carbon materials. According to the technologic production process, the carbon materials are classified in molded graphite and carbon, glassy carbon, pyrolytic carbon and graphite, carbon fibers, carbon composite, carbon and graphite powder and particles [1]. The graphitizing carbons tend to be soft and nonporous, with relatively high densities, and can be readily transformed into crystalline graphite by heating in the range of 2200-3000 o C. In contrast, the non- graphitizing carbons are hard, low-density materials and cannot be transformed to the crystalline graphite even at 3000 o C and above. The low density of the materials is a consequence of their microporous structure, which gives a high internal surface area. Despite many industrial products and applications, and long term of research, the detailed structure of carbon materials at the atomic level is still poorly understood. One of the closest and most famous microstructural models of carbon material, which is now considered the classical one, was proposed by R. Franklin in 1951 [2]. The Franklin model (Fig. 1) assumed that the microstructure of carbon material consisted either of short fragments of graphite cross-linked by bridging groups or of a twisted network of carbon polyaromatic planar layers. Fig. 1. Franklin model of (a) non-graphitizing, (b) partially graphitizing and (c) graphitizing carbon materials [2], where the straight lines represent the grapheme(planar polyaromatic molecules) layers and the stacks of these graphite fragments.