Oxidation and recrystallization of platinum group metals (Pt, Pd, Rh) in oxygen. Surface and subsurface reconstruction of polycrystalline platinum during annealing in the O_2 atmosphere over the temperature range of 600-1400K

摘要

Scanning electron microscopy, energy-dispersive and X-ray photoelectron spectroscopies, as well as X-ray diffraction analysis were used to study the morphology, microstructure and chemical composition of surface and subsurface layers of Pt(poly) after treatment in O-2 at T = 600-1400 K. It was found that the Pt(poly) microstructure is determined by the reaction of O-2 with the surface carbon and platinum recrystallization. At T = 600-1000 K a part of the surface graphite-like film is removed and the surface microstructure remains virtually unchanged. The fcc lattice parameter of platinum (a), the size of the coherent scattering region (D), and microdistortion of the metal lattice (epsilon) virtually do not change and are equal to 3.920 angstrom, 100 nm and 0.05%, respectively. At T 1000 K, the a value remains virtually constant and sizes of D, grains and microfacets substantially increase to ca. 500-600 nm, 40 and 1 mu m whereas the E value decreases to ca. 0.014%. At T = 600-1400 K, dissolution of oxygen in the platinum lattice and formation of bulk PtO2 oxide are not observed; however, oxygen is able to accumulate at grain boundaries and other defects in the amount of 5-10 at.%.