This is a copy of the slides presented at the meeting but not formally written up for the volume.

Description: Interfacial reactions in the Cu/Mg/Cu trilayer system during constant heat treatment have been in-situ studied by specular x-ray reflectivity (XRR). The evolution of interface interdiffusion/roughness and the nucleation and growth of CuMg2 phase have been analysed through the simultaneous refinement of selected parameters of several reflectivity scans measured during the heat treatment. Synchrotron radiation and an special experimental setup allowed scan times of 110s which covered a temperature range of 3.7 K when heating the sample at 2 K/min from room temperature to 603 K. By this method, significant differences in the behavior of both interfaces, Cu on Mg and Mg on Cu, have been observed during the nucleation and growth of the intermetallic phase, in complete accordance with previous calorimetric measurements.