Papers by Keyword: Paramagnetic Centers

Abstract: High-carbon substances and carbon itself are important structure-forming elements. Of special interest are substances obtained from petroleum feedstock by means of high-temperature treatment. Such substances could include bitumen, pitch, coke, fullerenes, carbon nanotubes and some composition materials. The present article provides a literature review, devoted to structuring in complex multi-component systems, which demonstrated to obtain quasi-crystalline substances in macroscale. In petroleum disperse systems the regulating factor leading to the formation of hierarchy structures is presence in the medium of asphaltenes exerting paramagnetic properties. It was experimentally showed that change of the equivalence ratio of such components as core, salvation shell, and dispersion medium leads to intentional obtainment of various configurations of quasi-crystalline systems. Understanding of macrostructures formation mechanisms under condition of change of medium properties at nanolevel allows constructing new carbon-based constructional materials.

Abstract: Abstract: Formation of electrical conducting channels with paramagnetic properties on the surface of three type polymer plates (phenol-formaldehyde and epoxy resins, polyacrylonitrile) under influence of CO2 laser irradiation at the presence of air have been studied. It is shown that the magnitude of surface resistance of the investigated polymers depends on polymer type and irradiation energy. The appearance of electrical conducting regions in the polymer materials is due to laser-chemical transformations of macromolecular physical and chemical structures near the polymer plate surfaces, leading to formation of double conjugated bonds. These structures are characterized also with paramagnetic properties- by method of ESR the free radicals are discovered in the transformed regions of polymers. The obtained results practically are analogous to ones obtained in such polymers after thermal treatment at high temperatures. However there are some advantages: in the latter case for obtaining of conducting materials on the base of dielectric polymers it is necessary to use a high vacuum. Besides of such method does not allow the formation of conducting channels with desired square and configuration on the surface of polymer plates in very short time (about several seconds) at present of air.

Abstract: EPR and TEM investigations on sublimated solid Alq3, [tris(8- hydroxyquinoline)aluminum(III)] are reported. Different paramagnetic centers in microcrystalline Alq3 fractions as synthesized and annealed are observed. Their nature, thermal treatment dependence, as well as correlation with the crystal structure are analyzed. The existence of randomly oriented triplets and quartets in annealed Alq3 fractions is evidenced from the temperature dependence of X- and Q-band EPR spectra. The spin Hamiltonian parameters are given and proposals for the model structures are made.

Abstract: The advantages and uniqueness of the Inorganic modification of the Sol-Gel method have already been described. Homogeneous nano-composites as well as some exotic glasses, complex-metal-oxides systems with little glass-forming ability, can be produced by this method. Thus, the obtained materials are characterized by a complex structure that leads to the wide variety of physical and chemical properties. Zirconia-containing materials are of utmost interest because of the mechanical toughness and chemical resistance provided by the presence of ZrO2. In the present work, we report on unusual structural peculiarities of the Zr-O, two types of Zr-Ge-O systems (with Zr>Ge and Zr

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