Kinetic description of the transition from a one-phase to a two-phase growth regime in Al/Pd lateral diffusion couples

Abstract

The kinetics of the solid-state reaction between Al and Pd is studied in the geometry of a lateral Al-Pd diffusion couple in the temperature range between 250 and 430 °C. The first reaction phase is the crystalline Al3Pd2(δ) phase. After the growth of Al3Pd2 reaches a critical length, the quasicrystalline decagonal Al3Pd(γ′) phase starts to grow in between the Al and the Al3Pd2 phases, and the Al3Pd2 and Al3Pd phase continue to grow simultaneously. We have fitted this simultaneous growth with a recently proposed model of kinetic suppression on the basis of interfacial reaction barriers. Excellent agreement between the data and the model is found. From the analysis the effective interface growth constant for the Al3Pd is extracted as a function of temperature.