Kinetics of Interfacial Reactions in the Liquid Pd-Mg/α-Al_2O_3 System

摘要

The reactivity at interfaces between α-Al_2O_3 single crystals and molten Pd-Mg alloys at 1823 K under pure argon are investigated for alloys containing typically 10 at% Mg or less. Mg reacts with alumina to form two layers, a magnesia (MgO) layer at the alloy side and a spinel (Al_2MgO_4) layer at the alumina side. We show that it is possible to suppress formation of magnesia layer by adding to the alloy small quantities of Al. The kinetics of the growth in the case of one phase growing (spinel) and of simultaneous growth of two phases (magnesia and spinel) are studied. In both cases the growth of layers obeys the parabolic rate law. Moreover, the presence of magnesia does not constitute a barrier for the growth of spinel. A simple model based on the assumption that the growth of oxide layers is controlled by cation interdiffusion is presented. The average interdiffusion coefficients of Al~(3+) and Mg~(2+) in spinel and magnesia are deduced.