The mending effect and mechanism of metal nano-particles in an area undergoing wear are quite important for both the fundamental theory of nano-tribology and the development of lubricant additives. This paper presents research on the mending effect of copper nano-particles added to lubricant oil. Pin-on-disk experiments and Scanning Electron Microscopy (SEM) observations show that copper nano-particles do display an excellent mending effect. The observation by Scanning Tunnelling Microscopy (STM) reveals that the mending effect results from the deposition of copper nano-particles onto the wear scar. It has also been disclosed by heating simulation that, due to nano-scale effects, which bring about decrease in the diffusion temperature of copper nano-particles, the heat generated by friction leads to the diffusion of copper nano-particles and their subsequent deposition, which finally results in the so-called mending effect.

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The lifetime behavior of a H 2 /O 2 proton exchange membrane (PEM) fuel cell with polystyrene sulfonic acid (PSSA) membrane have been investigated in order to give an insight into the degradation mechanism of the PSSA membrane. The distribution of sulfur concentration in the cross section of the PSSA membrane was measured by energy dispersive analysis of X-ray, and the chemical composition of the PSSA membrane was characterized by infrared spectroscopy before and after the lifetime experiment. The degradation mechanism of the PSSA membrane is postulated as: the oxygen reduction at the cathode proceeds through some peroxide intermediates during the fuel cell operation, and these intermediates have strong oxidative ability and may chemically attack the tertiary hydrogen at the a-carbon of the PSSA; the degradation of the PSSA membrane mainly takes place at the cathode side of the cell, and the loss of the aromatic rings and the SO 3 À groups simultaneously occurs from the PSSA membrane. A new kind of the PSSA-Nafion composite membrane, where the Nafion membrane is bonded with the PSSA membrane and located at the cathode of the cell, was designed to prevent oxidation degradation of the PSSA membrane in fuel cells. The performances of fuel cells with PSSA-Nafion101 and PSSA-recast Nafion composite membranes are demonstrated to be stable after 835 h and 240 h, respectively.

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In this study, the properties of novel acid-base blend membranes from polybenzimidazole PBI and self-prepared sulfonated nonfluorinated and partially fluorinated arylene main chain polymers from the polymer classes of aromatic polyethers, polyetherketones, polyethersulfones, and polyphosphine oxides are comparatively discussed. The aims of this study were to (1) determine the influence of the chemical structure of the polymers on their thermal and chemical stabilities and to identify polymeric structures having stabilities as high as possible, and (2) determine the effect of the addition of PBI to sulfonated arylene ionomers in terms of improving of their chemical, thermal, and dimensional stabilities. The working hypothesis of the study was that partially fluorinated arylene main-chain ionomers should have better chemical and thermal stabilities than the F-free ionomers, due to the much higher stability of CÀ ÀF bonds, compared to that of CÀ ÀH bonds. Improved procedures have been used for the polycondensation reactions, by applying an excess of K 2 CO 3 deprotonation compound; the use of a dehydration agent like toluene or benzene was not required. Further, reactions could be performed at lower temperatures than is usually required for such polycondensation reactions; most of the polycondensations were made in a temperature range between 80 and 130 8C. The following properties of the polymers and blend membranes have been determined: proton conductivity, water uptake, swelling, thermal stability including thermal stability of sulfonic acid groups and of the polymer backbone, and oxidative stability by H 2 O 2 treatment. The result of these investigations was that polymers containing fluorinated building blocks and/or phosphine oxide building blocks had the best stabilities. Selected acid-base blend membranes were made from PBI and these aromatic polymers showed proton conductivities of up to 0.1 S/cm, water uptake values of not more than 40%, and starting temperatures for SO 3 H group splitting-off approaching 290 8C. Moreover, PBI-sulfonated polymer blend membranes showed much less weight loss after H 2 O 2 treatment than does the sulfonated polymers alone, indicating a radical attack-stabilizing effect of PBI. M5: PBI/7b with IEC calc ¼ 1.23 meq/g M6: PBI/8b with IEC calc ¼ 1.23 meq/g M7: PBI/7b with IEC calc ¼ 1.35 meq/g M8: PBI/8b with IEC calc ¼ 1.35 meq/g M9: PBI/5b with IEC calc ¼ 1.23 meq/g M10: PBI/5b with IEC calc ¼ 1.35 meq/g M17: 7b with IEC overall ¼ 2.35 meq/g M31: 9b with IEC calc ¼ 1.35 meq/g 2322 KERRES, XING, AND SCHÖ NBERGER