Oxidation and annealing of thin FeTi layers covered with Pd

The hydrogen storage material FeTi has the disadvantage to lose its sorption capacity in contact with impurities such as O2 and H2O. A possibility to overcome this problem is to coat it with an anti-corrosive layer which is permeable for hydrogen. In this study we prepared FeTi layers covered with a 4 or 20 nm.thin Pd layer. We used ion beam and sputter profiling techniques, X-ray photoelectron spectrometry and scanning probe techniques to investigate the response of these bi-layers upon annealing up to 3008C in vacuum, air and 10y5 mbar O2. The layered structure remains intact up to 1508C. At 2008C in air and O2, Fe and some.Ti move towards the Pd surface where they form oxide regions. At higher temperatures thicker oxide regions, presumably along the Pd grains, are formed. These processes are more pronounced for the case of 4 nm Pd. A model is presented to explain the observed phenomena. We conclude that up to 1508C 4 nm of Pd is sufficient to act as a protective layer. For a temperature of 2008C, 20 nm Pd may still provide sufficient protection against oxidation. q1999 Elsevier Science B.V. All rights reserved.