Thursday, 18 June 2020Speaker: Prof. Alexander B. FreidinInstitute for Problems in Mechanical Engineering of Russian Academy of Sciences Chemical affinity tensor in mechanochemistry |
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Abstract
Chemomechanics or mechanochemistry – i.e. coupling between chemical reactions and mechanical stresses – problems have been studied intensively during last decades. Among the examples one could mention are: the oxidation of silicon in integrated-circuit technology with reaction retardation produced by stresses in silicon microspheres and nano-wires, the oxidation and accompanying damage in microscale parts of MEMS, the formation of intermetallic phases in solders and lithiation in lithium-ion batteries. It should be emphasized that stresses may arise in mechanochemistry due to strains produced by chemical reactions in the absence of external mechanical loading. Furthermore, accurate formulations and solutions of mechanochemistry problems are motivated by applications involving miniaturization in electronics and mechatronics.
In this talk the interaction between solid and movable diffusive constituents is discussed within the framework of mechanics of configurational forces. At first, the fundamental notions of chemical kinetics are recalled, including the notion of chemical affinity which controls the chemical reaction rate in classical physical chemistry. We subsequently show from balance laws and the second law of thermodynamics that in the case of chemical reactions in deformable solids the chemical affinity is a tensor. The normal component of the affinity tensor acts as a configurational force driving the reaction front propagation, while stresses affect the reaction rate through the affinity tensor. A kinetic equation in the form of the dependence of the reaction front velocity on the affinity tensor together with constitutive equations for the solid reactants, mechanical equilibrium equations and diffusion equation form the system of governing equations for the coupled problem “diffusion – chemistry – mechanics”. In the last part of the talk are presented solutions of coupled problems for elastic and inelastic solid reactants, showing how mechanical stresses can accelerate, retard or block the propagation front. Finally, the reaction front instabilities and arising damage problems are also discussed and applications are presented.
Biography
Prof. Alexander Freidin obtained his Diploma in Mechanical Engineering from Leningrad Polytechnic Institute in 1976. He continued as a graduate student in fracture mechanics at the Novosibirsk Electrical Engineering Institute studying under A.I. Chudnovsky and I.A. Kunin. In 1979 he came back to Leningrad (St. Petersburg) to work for the polymer industry at Plastpolymer Research Institute until 1992. He obtained his PhD in Physics and Mechanics at Moscow Physical and Technical Institute in 1987. In 1993 he joined the Institute for Problems in Mechanical Engineering of the Russian Academy of Sciences where, in 1997, he was awarded a Doctoral Habilitation in Physics and Mechanics. He also holds the position of Professor at Peter the Great St. Petersburg Polytechnic University (Institute of Applied Mathematics and Mechanics) and St. Petersburg University (Faculty of Mathematics and Mechanics). His research interests are in nonlinear mechanics and thermodynamics of materials including multidisciplinary problems of stress-induced phase transitions and stress-affected chemical reactions.