Kinetic Features of Reactive Diffusion in Binary Systems

Abstract:

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 Dθ 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 l2 = Kt. The equations K = K0 exp(−QK/RT) and Dθ = D0 θexp(−Qθ/RT) were adopted to express K and Dθ as functions of temperature T, respectively. The relationship between the temperature dependence of K and that of Dθ was evaluated according to the following assumptions: the molar volume, the solubility range and the value of D0 θ are constant and equivalent for all the phases. When Qα or Qγ is smaller than Qβ, QK is greater than Qβ. On the other hand, QK is close to Qβ, if both Qα and Qγ are greater than Qβ. In such a case, the temperature dependence of the kinetics represents that of interdiffusion in the growing compound.