Diffusion in Solid

Diffusion is…
• The transport of atoms through matter
• The mechanism by which many important
processes occur in materials:
• Case hardening of steel
• Doping of semiconductors
• Oxidation of metals
• Solid-state formation of compounds from
individual components
• Sintering — the process by which an object
made from powders becomes dense and
strong
• Types of diffusion in solids
• Self-diffusion — movement of atoms through their
own lattice
• Interdiffusion (a.k.a. impurity diffusion) — e.g.,
movement of Ni through the lattice of Cu


Kinetics (DIFFUSION in SOLID}
• Basic concepts in kinetics
o Kinetics of phase transformations
o Activation free energy barrier
o Arrhenius rate equation

• Diffusion in solids - phenomenological description
o Driving force for diffusion in ideal and regular solutions
o Flux, steady-state diffusion, Fick’s first law
o Diffusion coefficient, Einstein relation
o Nonsteady-state diffusion, Fick’s second law

• Thermodynamics of diffusion
o Driving force for diffusion
o Diffusion against the concentration gradient: Spinodal decomposition

• Solutions to the diffusion equation
o Numerical integration
o Analytical solution
o Applications
? Chemical homogenization
? Carburization of steel

• Atomic mechanisms of diffusion
o Substitutional diffusion
o Interstitial diffusion
o Temperature dependence
o High diffusivity paths (grain boundaries, free surfaces, dislocations