The role of nitrogen atoms in forming the carbon structure in the carbonization of polymer composites

Abstract

Data have been used from X-ray photoelectron spectroscopy, small-angle X-ray spectroscopy, nuclear magnetic resonance, IR Fourier spectroscopy, electron spectroscopy, and other current methods for polyacrylonitrile, polypyromellitimide, hydrated cellulose, hard coals, and various model compounds to examine the effects of the nitrogen atoms on carbonization and graphitization. The nitrogen atoms are found to have multiple effects on the thermochemical and thermophysical parameters of the polymer carbonization over a wide temperature range. In the derivation of the carbon structures, the nitrogen acts as a messenger combined agent, which gives rise to heterorings, which are transformed into intermediate aromatic compounds, which form the basis of the matrix synthesis consisting of ordered graphite-type structures.Polymer carbonization is a thermochemical process with a long history. The first researches in this area were simultaneous with the determination of the macromolecular nature of coal.Analyses of hard coals with various degrees of metamorphism show that in addition to carbon they contain various heteroatoms, amongst which nitrogen and sulfur are counted fairly frequently no matter what the local origin of the coal. One trend in coal chemistry was research on thermal treatment, which alters the coal composition and structure. It alters the basic applied parameters of coal as a fuel. From the viewpoint of the chemistry and physics of macromolecular compounds, the changes occurring in coals involve thermophysical and thermochemical reactions. The multiplet composition found in coals means that these processes are inseparable and have effects on the composition and properties of the heat-treatment products. Numerous researches [1][2][3] have shown that competition between destruction and structuring determines the trend in thermochemical processes. The heating conditions determine whether the coal will burn almost completely up to a certain temperature and be converted to gaseous and readily volatile products from thermal and thermal-oxidative destruction. With special technologies, a hard coal can be converted to carbon-saturated products, from which carbon materials and components are formed that are used in many branches of industry.The transformations in the polymers forming the main part of a coal are dependent on many factors, amongst which a considerable part is played by the elemental and functional compositions. Accumulated analytical data for the area have enabled one to build up qualitative and quantitative pictures of the transformation of the constituent elements over wide temperature ranges. The data allow one to observe fairly novel properties of the nitrogen atoms: they are preserved in the carbonized products, whereas the atoms of hydrogen, oxygen, sulfur, and certain other elements almost completely leave the sphere of thermochemical reactions up to temperatures of 1000-1200°C. However, most researchers have not drawn any further conclusions from the unusual thermal stability of nitrogen in th...

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