S. Mori

Investigation of Tribo-Chemistry by Means of Stable Isotopic Tracers, Part 2: Lubrication Mechanism of Friction Modifiers on Diamond-Like Carbon

A solution of glycerol monooleate (GMO) in polyalphaolefin (PAO) considerably reduced the friction between the steel and the diamond-like carbon (DLC) under boundary conditions. The combination of the material-oil-additive is of importance. Model additives composed of a stable isotope ( 2 H or 13 C) were employed to trace the additive molecule by time-of-flight secondary ion mass spectroscopy (TOF-SIMS). It was found that the additive interacted with DLC surfaces in the form of an ester. Inclusion of PAO in the boundary film on DLC was found by TOF-SIMS analysis.The utility of the isotopic tracer technique in tribo-chemistry was demonstrated in this study.

Effects of molecular structure of aliphatic diols and polyalkylene glycol as lubricants on the wear of aluminum

Abstract The lubrication characteristics of aliphatic diols and polyalkylene glycol on the aluminum-steel friction surface were investigated by using a FALEX machine. Aluminum wear is not influenced by the viscosity of diol and polyalkylene glycol, but the molecular structure dose have a significant effect. The lubricant compounds having OH groups on both ends of molecule increased aluminum wear but the wear substantially decreased when OH groups were etherificated with alkyl groups. Wear also decreased when alkyl group(s) was added to the diol. The nascent aluminum surface reacts with alcohol to partially form aluminum alkoxide. As a result, the oxidation layer declines, and wear increases. Furthermore, the wear of aluminum is increased by such a molecular structure that makes it difficult for an anti-wear layer to form on the friction surface.

Chemical analysis of wear tracks on magnetic disks by TOF-SIMS

Surface reactions on magnetic recording disks have been studied during sliding with ceramic sliders in the main chamber of TOF-SIMS. Chemical change of lubricant oil in the wear track was observed by the chemical image of TOF-SIMS. The magnetic disk surface was covered with perfluoroalkyl polyether lubricant (Fomblin Zdol). The Si tip slider surface was covered with Al 2 O 3 , DLC, TiN or c-BN coating. Experimental conditions were as follows: 0.8 mN of load and a sliding speed of 0.01 m/s. Lubricant oils were decomposed with A1 2 0 3 and TiN slider surfaces. Metal (Al, Ti) fluorides were detected by TOF-SIMS in the sliding track. Material transfer occurred by chemical wear of slider material. From TOF-SIMS observation, the decomposition of lubricant molecules was initiated at the end group of molecules (-CF 2 CH 2 OHj. On the other hand, DLC and c-BN sliders suppressed the decomposition reaction of PFPE oils. In conclusion, hard and chemical inert materials such as DLC and c-BN are suitable for a long-life HDI.

Exoelectron emission: Possible relation to seismic geo-electromagnetic activities as a microscopic aspect in geotribology

Abstract The present study investigates the source mechanism of the seismic geo-electromagnetic activities that occur in a geotribosystem. It was shown that granite generates thermally stimulated exoelectron emission (TSEE) at temperatures ranging from 300 to 400 °C. This emission is released from the trapped levels at intrinsic and extrinsic centres in the minerals. Possible heat sources are discussed in terms of the frictional heating of the precursor slip. Fracture-induced transient electric signals (FTESs), propagated through the rock, could be detected; the intensity of the signals decayed inversely proportionally to the distance from the fracture zone. Less FTES was detected for granite annealed at a temperature of 400 °C, where the piezoelectric effect was unchanged but the exoelectron sites were reset. This confirms that the main source of FTES and seismic geo-electric activity is probably the trapped electrons.

Tribochemical decomposition of formic acid on the nascent surfaces of steel formed by scratching

The nascent surfaces of steel were formed by scratching mechanically under high vacuum conditions and adsorption and decomposition of formic acid on the surfaces were carried out at room temperature. The changes in partial pressures of the related compounds were monitored with a quadruple mass spectrometer. The results showed that the chemisorption rate of formic acid on the nascent surfaces was much higher than the formation rate of the reaction products, carbon dioxide and hydrogen. The analyses of adsorption and desorption activities of the compounds on (from) the nascent surfaces showed that the desorption activity of the products were as high as about 20 times the adsorption activity of formic acid. It is proposed that two types of sites might exist on the nascent surfaces. Although the active sites on the nascent surfaces could chemisorb formic acid molecules, only a portion could contribute to the decomposition of formic acid.

Tribochemical reactions of very thin layers on magnetic recording disks

Abstract Surface reactions of thin oil layers on magnetic recording disks have been studied during sliding with an Mn-Zn ferrite slider under high vacuum conditions. Gaseous products, fluorinated carbons, CO2 and H2 were detected with a quadrupole mass spectrometer, even at a low load of 9.8 × 10−2 N. Surface analysis by X-ray photoelectron spectroscopy with a small spot size revealed that metal fluorides were formed on the wear track. This is good evidence for the tribochemical reaction of fluorinated oils with the disk surface. There was marked gas formation after 4300 repeated sliding cycles and, at the same time, the coefficient of friction increased from 0.3 to 0.6. It is concluded that thin layers of perfluorinated oil were removed from the disk surface through chemical means during sliding. It is found that the disappearance of the oil layer was accelerated by the tribochemical reaction and that the carbon layer acted as a protective layer for the reaction of oil. Fresh metal surfaces formed by friction with a slider play an important role in the reaction.