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THERMODYNAMIC METHOD OF DESCRIBING THE STATE OF BUILDING COMPOSITES AS A MACROSCOPIC SYSTEM

Arkady Ayzenshtadt

Abstract

In materials science, composites (nanocomposites) are materials consisting of a combination of two or more micro (nano-) and / or macrocomponents, which are different in shape, chemical composition and do not have significant mutual solubility. A distinctive feature of composites that determine their importance is that two or more noticeably different components when combined form a system that has significantly improved properties compared to the properties of its individual components. It is known that for most polycrystalline materials the hardness and elastic limit increase with decreasing average particle size (Hall-Petch law). Therefore, the possibility of the existence of such a system is determined by the interaction forces between the structural parts when they are brought closer to sufficiently small distances. For the emergence of a stable structure of a solid, it is necessary to provide conditions under which the forces of attraction (van der Waals forces) will prevent the removal of the components particles from each other. Any solid body is a system consisting of a huge number of microparticles. In such systems exhibit specific patterns. To describe the state of the formations, you can use the thermodynamic approach, which considers the macroscopic structure as a whole, and not its individual parts. In this case, the magnitude of the potential of attraction (van der Waals) determines the possibility of the appearance of structural bonds at the interface. The thermodynamic criterion for evaluating such component compatibility is the Hamaker constant (A), as a criterion for the energy of dispersion interaction of highly dispersed particles. This approach allows solving two fundamental problems of building materials science: optimize the composition when creating composites of various in nature substances and predict the phenomena associated with changes in the properties (composition) of the finished composite during its operation, caused by technogenic metasomatism. In previous studies, we have shown the possibility of experimentally determining the magnitude of the complex Hamaker constant (?), which characterizes the energy of dispersion interaction of a solid surface when it comes in contact with a water-ethanol (slightly polar) solution (?01). This value is functionally related to the properties of the solution (?00) and the solid phase itself (?11). In this paper, we present an algorithm and the results of calculating ?11, as a constant of the dispersive interaction of the components that make up the solid phase. Due to the fact that one of the most common composites used in the construction industry are concrete and wood (a natural composite consisting of cellulose fibers bound by a polymer matrix, which is mainly lignin), these materials were used as pilot objects for research.

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DOI resolver: doi.org/10.5593/sgem2019/6.1/s24.061

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