Kinetics of phase transitions in porous materials

The effect of pore radius on the shifts of melting temperature in amorphous and crystalline porous materials and on solid phase crystallization kinetics in amorphous materials is analysed. For the calculation of the free energy of porous silicon the surface free energy at the walls of pores is added to the free energy of bulk material known from empirical data. It is estimated that the temperature of the phase transition from amorphous to crystalline state is by 120 K lower and the melting temperature is by 200 K lower for porous Si (with pore size 1 nm) in comparison with bulk Si. The computer simulated structure of porous silicon was used to take into account the size and shape distribution of pores.