Kinetic Features of Reactive Diffusion in Binary Systems

摘要

The temperature dependence of the kinetics of the reactive diffusion was numerically analyzed for a hypothetical binary system composed of one compound phase (β) and two primary solid solution phases (α and γ). The growth rate of the β phase during the reactive diffusion between α and γ phases in a semi-infinite diffusion couple was expressed as a function of the interdiffusion coefficient D~θ and the solubility range of the θ phase (θ = α, β, γ). For the reactive diffusion controlled by volume diffusion, the thickness l of the β phase is described as a function of the annealing time t by the parabolic relationship l~2 = Kt. The equations K = K_0 exp(-Q_K/RT) and D~θ = D_0~θ exp(-Q~θ/RT) were adopted to express K and D~0 as functions of temperature T, respectively. The relationship between the temperature dependence of K and that of D~θ was evaluated according to the following assumptions: the molar volume, the solubility range and the value of D_0~θ are constant and equivalent for all the phases. When Q~α or Q~γ is smaller than Q~β, Q_K is greater than Q~β. On the other hand, Q_K is close to Q~β if both Q~α and Q~γ are greater than Q~β. In such a case, the temperature dependence of the kinetics represents that of interdiffusion in the growing compound.