11MSE 2090: Introduction to Materials ScienceChapter 5, DiffusionDiffusion - how do atoms move through solids?Diffusion mechanisms¾Vacancy diffusion ¾Interstitial diffusion¾ImpuritiesThe mathematics of diffusion¾Steady-state diffusion (Fick’s first law)¾Nonsteady-State Diffusion (Fick’s second law)Factors that influence diffusion¾Diffusing species¾Host solid¾Temperature¾MicrostructureChapter Outline2MSE 2090: Introduction to Materials ScienceChapter 5, DiffusionDiffusion is material transport by atomic motion.Inhomogeneous materials can become homogeneous by diffusion. For an active diffusion to occur, the temperature should be high enough to overcome energy barriers to atomic motion.What is diffusion?results of an atomistic simulation of atomic mixinghomework project in MSE 4592/62703MSE 2090: Introduction to Materials ScienceChapter 5, DiffusionInterdiffusion(or impurity diffusion)occurs in response to a concentration gradient.Self-diffusionis diffusion in one-component material, when all atoms that exchange positions are of the same type.Interdiffusion and Self-diffusionBeforeAfter(Heat)4MSE 2090: Introduction to Materials ScienceChapter 5, DiffusionVacancy diffusion mechanismTo jump from lattice site to lattice site, atoms need energy to break bonds with neighbors, and to cause the necessary lattice distortions during jump. This energy comes from the thermal energy of atomic vibrations (Eav~ kBT)The direction of flow of atoms is opposite the vacancy flow direction.Diffusion Mechanisms (I)Atom migrationVacancy migrationAfterBefore
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