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This paper investigates the reaction steps involved in tribochemical wear of SiO(2) surfaces in humid ambient conditions and the mechanism of wear prevention due to alcohol adsorption. The friction and wear behaviors of SiO(2) were tested in three distinct gaseous environments at room temperature: dry argon, argon with 50% relative humidity (RH), and argon with n-pentanol vapor pressure 50% relative to the saturation pressure (P/P(sat)). Adsorbed gas molecules have significant chemical influences on the wear of the surface. The SiO(2) surface wears more readily in humid ambient compared to the dry case; however, it does not show any measurable wear in 50% P/P(sat) n-pentanol vapor at the same nominal contact load tested in the dry and humid environments. The tribochemical wear of the SiO(2) surface can be considered the Si-O-Si bond cleavage upon reactions with the impinging vapor molecules under tribological stress. DFT calculations were used to estimate the apparent activation energy needed to cleave the Si-O-Si bond at beta-cristobalite (111) and alpha-quartz (001) surfaces by reactions with impinging water and alcohol vapor molecules. The alkoxide termination of the SiO(2) surfaces increases the energy barrier required to cleave the Si-O-Si bonds when compared to hydroxyl-terminated SiO(2) surfaces.

The boundary film formation and lubrication effects of low molecular weight silicone lubricant molecules with cationic side groups were studied. Poly(N,N,N-trimethylamine-3-propylmethylsiloxane-co-dimethylsiloxane) iodide was synthesized and deposited on silicon oxide surfaces to form a bound-and-mobile lubricant film. The bound nature was investigated with ellipsometry, water contact angle, and X-ray photoelectron spectroscopy for the polymers with cationic mole percent of 6, 15, and 30 mol % (monomer based). The bound layer thickness decreased as the cationic content increased. The quaternary ammonium cations in this layer were electrostatically bound to the substrate surface. The mobile nature of the multilayers was explored with scanning polarization force microscopy. The multilayer films exhibited characteristic topographic features due to ionic interactions within the polymer film. Contact scratching of these films altered the multilayer topography within the contact scanned area. Even after high load contact scanning, the bound layer was not removed from the scanned region. These results implied that the molecules in the first layer are strongly bound and the molecules in the multilayers are mobile. Both nanoscale and macroscale tribological tests of these films revealed that the polymer with 15 mol % cationic groups gives lower friction and adhesion than the 6 and 30 mol % cationic polymers as well as the polydimethylsiloxane control sample. This seems to be due to a synergistic effect between the bound and the mobile layers.

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Ruddlesden-Popper phase, La n+1 Ni n O 3n+1 (n=1, 2, and ∞) compounds were prepared by citrate sol-gel method. We revealed the origin of the variation of the electrical conductivities in La n+1 Ni n O 3n+1 (n=1, 2, and ∞) using resistivity measurements, Rietveld analysis, and X-ray absorption spectroscopy. According to the XANES spectra, it is found that the degree of 4p π -4p σ energy splitting between 8345 eV and 8350 eV is qualitatively proportional to the elongation of the out-of-plane Ni-O bond length. With the decrease of 4p π -4p σ splitting, the strong hybridization of the σ-bonding between Ni-3d and O-2p orbitals creates narrow antibonding σ* bands, which finally results in the lower electrical resistivity.

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