We use chemical potential to define the equilibrium condition and chemical potential gradient to define the driving force of phase change. For binary elements forming phases with different compositions, we need to define enthalpy and entropy of mixing, then Gibbs free energy of mixing. Simple phase diagrams such as solid solution, miscibility gap, and eutectic system can be obtained. The two basic concepts that are essential to the understanding of kinetic processes are atomic diffusion and interfaces. Nucleation forms a new interface.
Growth is the atomic process of migration of an interface.
Spinodel decomposition involves up-hill diffusion in a diffusive interface. In part A and B, we discuss diffusion and interfaces, respectively. In part C, we discuss phase changes in solidification and in solid state. One centimeter long pieces are cut from the 0-ring. One piece is mounted and its cross-section is polished and etched for microstructure observation and hardness measurement.