tailieunhanh - Kinetics of Materials - R. Balluff_ S. Allen_ W. Carter (Wiley_ 2005) Episode 2

Tham khảo tài liệu 'kinetics of materials - r. balluff_ s. allen_ w. carter (wiley_ 2005) episode 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 22 Microscopic and mechanistic aspects of diffusion are treated in Chapters 7-10. An expression for the basic jump rate of an atom or molecule in a condensed system is obtained and various aspects of the displacements of migrating particles are described Chapter 7 . Discussions are then given of atomistic models for diffusivities and diffusion in bulk crystalline materials Chapter 8 along line and planar imperfections in crystalline materials Chapter 9 and in bulk noncrystalline materials Chapter 10 . CHAPTER 2 IRREVERSIBLE THERMODYNAMICS AND COUPLING BETWEEN FORCES AND FLUXES The foundation of irreversible thermodynamics is the concept of entropy production. The consequences of entropy production in a dynamic system lead to a natural and general coupling of the driving forces and corresponding fluxes that are present in a nonequilibrium system. ENTROPY AND ENTROPY PRODUCTION The existence of a conserved internal energy is a consequence of the first law of thermodynamics. Numerical values of a system s energy are always specified with respect to a reference energy. The existence of the entropy state function is a consequence of the second law of thermodynamics. In classical thermodynamics the value of a system s entropy is not directly measurable but can be calculated by devising a reversible path from a reference state to the system s state and integrating dS 5qĩev T along that path. For a nonequilibrium system a reversible path is generally unavailable. In statistical mechanics entropy is related to the number of microscopic states available at a fixed energy. Thus a state-counting device would be required to compute entropy for a particular system but no such device is generally available for the irreversible case. To obtain a local quantification of entropy in a nonequilibrium material consider a continuous system that has gradients in temperature chemical potential and other intensive thermodynamic quantities. Fluxes of heat mass and other extensive .