Buried-interfacial reactivity of palladium-coated Fe<sub>2</sub>O<sub>3</sub>/FeTi thin films during vacuum or hydrogen annealing
J H Sanders; B J Tatarchuk; J H Sanders; Dept. of Chem. Eng., Auburn Univ., AL, USA; B J Tatarchuk; Dept. of Chem. Eng., Auburn Univ., AL, USA
Журнал:
Journal of Physics: Condensed Matter
Дата:
1990-07-02
Аннотация:
FeTi is considered a good material for solid state hydrogen storage; however, it must undergo an initial activation by either a vacuum or hydrogen annealing procedure after preparation or exposure to air. Previous studies indicate that the initial activation in vacuum causes a reduction of surface iron oxides by a solid state reaction with FeTi to produce TiO<sub>2</sub>. Palladium has also been shown to be an effective barrier for eliminating O<sub>2</sub> or H<sub>2</sub> impurities in typical H<sub>2</sub> charging gases from reaching active FeTi. These impurities cause FeTi decomposition to iron and TiO<sub>2</sub>. In this study, experiments have been performed to investigate interfacial reactions that occur between Fe<sub>2</sub>O<sub>3</sub> and FeTi layers located below protective palladium overlayers. Vacuum annealing procedures were found to crack the palladium overlayer while forming both iron and titanium oxides below the surface. Hydrogen annealing procedures allowed reduction of the subsurface Fe<sub>2</sub>O<sub>3</sub> by FeTi without evidence of cracking within the palladium overlayer. Both procedures produced Fe-Pd alloys, the latter procedure also forming Fe-Pd hydrides at >or=623 K. Results indicate that the application of palladium overlayers on FeTi may be successfully used provide the initial activation is performed in hydrogen environments.
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