Oxygen activity dependent dissolution of nickel from nickel oxide into platinum
Journal of Physics and Chemistry of Solids(1995)
摘要
The oxygen activity dependent dissolution of the metallic component of a metal oxide into platinum was experimentally studied in the model system PtNiO. Thermogravimetric measurements were performed on PtNi1 − ΔO composite and on Ni1 − ΔO samples to determine mass changes as a function of oxygen activity at 1200, 1300 and 1400 °C. (For the sake of simplicity, Ni1 − ΔO is in this article often denoted as NiO, except in cases where Δ is important.) The mass changes of the PtNiO composite samples were found to be almost entirely due to the dissolution of Ni from NiO into Pt rather than due to changes in the deviation from stoichiometry in Ni1 − ΔO, especially at low oxygen activities. The experimental results suggest that the mole fraction of Ni in PtNi increases with decreasing oxygen activity. From the experimental data, the activity of Ni in PtNi alloys and the corresponding activity coefficients were determined as a function of composition and compared with data from the literature. By switching oxygen activities between two values it was observed that the equilibration of PtNiO composites occurs much slower in the reducing direction than in the oxidizing direction. At low oxygen activities the kinetics of the reduction of PtNiO composite samples were found to be extremely slow. These slow kinetics are likely due to a very slow incorporation of Ni from NiO into PtNi alloys.
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关键词
A. oxides,D. thermodynamic properties,D. phase equilibria
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