Study On Surface Oxidation Of Cerium Metal By XPS

Researches on the surface properties of cerium metal and cerium-lanthanum alloy have been carried out mainly by X-ray photoelectron spectroscopy (XPS), and then, compared the properties with those of plutonium and its alloys. As some similarities have been found between these two elements, we discuss the possibility of cerium and its alloy as a surrogate of plutonium and its alloys. The conclusions are followed:Studies of in situ oxidation of cerium metal under ultra-high vacuum (UHV) condition show that the chemical specie firstly formed upon Ce to O₂ is Ce₂O₃; near saturation a thin layer of CeO₂ is formed over Ce₂O₃ layer, and its oxides' structure from outside to inside is CeO₂, Ce₂O₃ and Ce. The core level Ce 3dXPS spectrum is single-peak for pure cerium metal, but during oxidation, the 3d spectra show multi-split. That's to say, there are two peaks in each region, 3d_3/2 and 3d_5/2. When there are some CeO₂ on the surface, the spectra are more complex. Study of X-ray diffraction (XRD) of Ce-La alloy shows the phase in the bulk is γ-phase. That's to say, some addition of La to Ce don't take a phase transition in room temperature, and that is not analogical to that of plutonium, because some addition of aluminum or gallium to plutonium will stable the high temperature δ-phase down to room temperature.As cerium and plutonium metal have many similarities to each other, and in order to discuss the properties of cerium as a surrogate of plutonium we do some work on the redox of cerium dioxide. The storage research of oxides on the surface of cerium metal under UHV condition shows: no reduction was found in room temperature, while heated to 673K or higher, CeO₂ reduced to Ce₂O₃. When compared the properties of Ce and Pu with each other, some similarities have been found, such as similar oxidation, the same oxides structure and the similar reduction under UHV condition, so cerium metal can be as a surrogate of plutonium in some surface corrosion experiment, such as oxidation, redox, hydrogenation and so on. And whether Ce₂O₃ interface catalyse the redox of CeO₂ need more experiments' support.