Pasichnyy M. New Models of the Initial Stages of Solid State Reactions in Thin Films and Nanoparticles

The thesis is devoted to development of the computer simulation methods of nucleation and growth of ordered phases at the initial stages of diffusive solid-state reactions in nanosize binary systems. The Monte-Carlo model of reactive diffusion is proposed. The main peculiarity of this model is the sharp dependence of the pair interaction energy on the local environment. It was confirmed that the formation of first intermediate phase consists of the concentration preparation, lateral growth and normal growth. An incubation period increases with the period of multilayer, and tends to the asymptotical value for thick films. The polymorphic mode of nucleation was confirmed. The delay of phase Al9Co2 appearance in diffusion couple Al-Co was explained by thermodynamic inhibition of nucleation in the field of concentration gradient. The lateral growth of intermediate phase during the reactive diffusion due to "chemical" driving force was analyzed. Asymptotical thickness phase layer just after lateral stage was proved to be proportional to the square root of ratio of interphase diffusivity and reaction rate constant at interphase boundary. The thermal hysteresis of decomposition in binary nano-particles was investigated. It was confirmed that the width of hysteresis loop depends on the size of particle, rate of temperature change, thermodynamic and kinetic parameters.