Morphology, Microstructure and Chemical Composition of Oxide Phases on Polycrystalline Rhodium in Oxygen Atmosphere at 1100 K
摘要
Polycrystalline rhodium Rh(poly) is oxidized in the O2 atmosphere under the pressure PO2 of 1 bar and a temperature of 1100 K, and then the morphology, microstructure and chemical composition of oxide phases were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). According to the XRD data, rhodium exists in the metallic state and contains subgrains with a size of ~43 nm and as large as ~10 µm in the bulk of the sample. The XPS data indicate that the recorded Rh 3d5/2 and O 1s peaks with an electron binding energy (Eb) of 308.6 eV and 530.1 eV correspond to Rh3+ and O2– in the composition of the surface Rh2O3 oxide. Morphology, phase and chemical compositions of a ~35 nm thick surface oxide layer and a rhodium corrosion layer located below the oxide layer at a depth of ~230 nm are characterized by SEM and EDS methods using the probe electron energy (E0) of 5 keV and 20 keV. The Rh(poly) surface contains 20-50 nm (~35 nm) Rh2O3 oxide particles that are formed on ~43 nm rhodium subgrains and form a continuous oxide layer. This layer includes 20-50 µm regions containing spherical Rh2O3 oxide agglomerates with a size of ~150 nm. A corrosion rhodium layer containing 20-50 nm large Rh subgrains and nanocrystals is found under the oxide layer. The same layer contains 100-200 nm (~150 nm) rhodium crystals on which oxide agglomerates are formed.