The local structure, many-body effect, and charge redistribution of Pt and Ni in Pt–Ni alloys (Pt–Ni = 3:1, 1:1, and 1:3) have been studied by X-ray absorption spectroscopy and X-ray photoelectron spectroscopy (XPS). It is found that upon alloying, the skew many-body line shape of Pt 4f peaks in Pt metal becomes more symmetric in Pt alloys, while the associated Ni 2p peaks become more asymmetric and are accompanied by more intense shake-up satellites. This is because Pt gains while Ni loses valence d electrons, resulting in different phase shift of electrons scattered near the Fermi level. Meanwhile, the redistribution of the density of states (DOS) is confirmed by experiment and density functional theory calculations, suggesting that the centroid Ni d states tend to shift closer to the Fermi level, while Pt d states are down-shifted in alloys. This DOS redistribution causes the anomalous binding energy shift for both Pt and Ni core levels in XPS, which has not been well explained in the literature. These findings also suggest that the d-band centroid shift originates from two different mechanisms for Pt-based alloys and Pt-skinned core–shell catalysts.
Experimental investigations of nano-scale spatio-temporal effects that occur on the friction surface under extreme tribological stimuli, in combination with thermodynamic modeling of the self-organization process, are presented in this paper. The study was performed on adaptive PVD (physical vapor deposited) coatings represented by the TiAlCrSiYN/TiAlCrN nano-multilayer PVD coating. A detailed analysis of the worn surface was conducted using scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) methods. It was demonstrated that the coating studied exhibits a very fast adaptive response to the extreme external stimuli through the formation of an increased amount of protective surface tribo-films at the very beginning of the running-in stage of wear. Analysis performed on the friction surface indicates that all of the tribo-film formation processes occur in the nanoscopic scale. The tribo-films form as thermal barrier tribo-ceramics with a complex composition and very low thermal conductivity under high operating temperatures, thus demonstrating reduced friction which results in low cutting forces and wear values. This process presents an opportunity for the surface layer to attain a strong non-equilibrium state. This leads to the stabilization of the exchanging interactions between the tool and environment at a low wear level. This effect is the consequence of the synergistic behavior of complex matter represented by the dynamically formed nano-scale tribo-film layer.
Mononuclear cationic rhodium complexes of dioxygen have been synthesized and characterized. Crystallographic, spectroscopic, and computational results support the conclusion that these complexes are best described as Rh III {O 2 2− } (rhodium(III) peroxo) complexes, in contrast to recently reported neutral analogues that are best described as Rh I { 1 O 2 } adducts. The nature of the ligand trans to the O 2 ligand is crucial in defining the electronic nature of the RhO 2 bonding. It is determined that π-donor ligands such as the halidesin conjunction with sufficient steric bulkcan stabilize the formation of Rh I { 1 O 2 } adducts, whereas stronger field ligands lead to the stabilization of asymmetric O 2 binding that ultimately favors formation of higher coordinate Rh III peroxo species. The factors that control the relative stabilization of Rh III {O 2 2− } versus Rh I { 1 O 2 } species are related to the well-established Dewar−Chatt−Duncanson model that has been successfully used to describe the bonding in isoelectronic transition-metal alkene complexes. The specific factors that control the stabilization of one electromer (resonance structure) over another are explored and discussed in detail.
An extensive study of surface/interface phenomena during wear of an adaptive TiAlCrSiYN/TiAlCrN nano-multilayer coating deposited using physical vapor deposition was undertaken under increasingly severe tribological conditions associated with dry end milling of H13 hardened tool steel. The results of FEM modeling on the temperature/stress distribution at different cutting speeds outline actual cutting conditions on the both rake and flank frictional surfaces of the coated tool. Studies of the surface/interface phenomena were made by means of SEM/high-resolution transmission electron microscopy/XPS analyses. Results demonstrate that intensifying tribological conditions facilitates improved wear performance of the adaptive coating layer. In extreme tribological conditions of ultra-performance machining (cutting speed of 500 m/min), the self-organization process establishes entirely through the formation of a nano-scale layer of dynamically re-generating tribo-ceramic films. The formation of these surface nano-films results in exceptionally efficient protection of the underlying coating layers. In response to the extreme external environment, the coating layer remained almost undamaged during a long run, demonstrating the capacity to efficiently replenish necessary tribo-ceramic films. In this way, interconnection of various surface and undersurface processes is established in the hierarchically structured tribo-films/coating layer. This integral performance is responsible for exceptional wear resistance under intensifying and extreme tribological conditions.
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