Hydrogen-induced phase transformation in internally oxidized (Pd0.8Rh0.2)0.97Ce0.03

Samples of a (Pd(0.8)Rho)(0.97)Ce-0.03 alloy which had been cold worked and internally oxidized for 72 h at 1073 K were submitted to high hydrogen pressure, at 3.5 GPa for 5 h at 1073 K. The phase transformations were analysed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The X-ray results for the internally oxidized sample revealed the formation of PdO and PdRhO2. In the samples submitted to high hydrogen pressure, it was observed that in both cases, a phase separation had been induced by hydrogen at high temperature, which suggests the formation of Pd-rich hydride phase and a Rh-rich phase. The TEM analysis of these samples revealed the formation of a Rh-Pd phase, which presented some faceted semi-coherent interfaces with Pd matrix. The formation of this ordered compound, which possesses Rh3Pd stoichiometry, is attributed to hydrogen induced vacancies in the alloy. (C) 2003 Elsevier B.V. All rights reserved.