Shigeyuki Mori

Tribological reactions of perfluoroalkyl polyether oils with stainless steel under ultrahigh vacuum conditions at room temperature

Abstract Perfluoroalkyl polyether oils have been allowed to react with stainless steel (440C) under sliding conditions. Type F oil, which contains an acetal group (-OCF 2 O-), was decomposed during sliding and gaseous products were liberated during the sliding experiments. The components of the gaseous products were COF 2 and low molecular weight perfluoroethers which were detected using a quadrupole mass spectrometer. The amount of evolved gas increased with increasing load and sliding speed. Metal fluorides were detected on the wear track after each sliding experiment using small spot-size X-ray photoelectron spectroscopy. In the case of type D and K oils, reactions with stainless steel occurred and metal fluorides were formed at the sliding contacts, but no gaseous product was detected. From the experimental results it is concluded that the tribological reaction of the perfluoroethers is mainly affected by the activity of mechanically formed fresh surfaces of metals rather than the heat generated at the sliding contacts. The metal fluorides formed on the specimen surfaces acted as a catalyst during the decomposition of the F oil. Moreover, the fluorides formed on the wear track act as a boundary layer, reducing the friction coefficient.

Relationship between tribological performance of liquid crystals and their molecular structure

Abstract The tribological behaviour of nematic and smectic liquid crystals was observed using a two-roller friction tester under the conditions of 735 N load and 220 rpm rotational speed. Each liquid crystal has two typical structures: a flexible structure (alkyl chain) and a rigid structure (cyanophenyl group). Structural features of the liquid crystals were (1) alkyl cyanobiphenyl (CB), (2) alkoxyl cyanobiphenyl (ECB) and (3) alkyl cyanophenyl cyclohexane (CPC). The frictional coefficient of the test samples was lower and the estimated film thickness was larger than those of synthetic oils. The friction coefficient was not affected by the carbon number of the alkyl chain, but was closely dependent on the molecular structure of the rigid part of the liquid crystal module. The frictional coefficient of CB which has a biphenyl group was 0.035, but CPC had a higher friction coefficient of 0.045. The molecular orientation of the rigid group was observed under shearing conditions. It is concluded that the flat structure of the biphenyl group plays an important role on the tribological behaviour.

Adsorption of Model Compounds of Lubricant on Nascent Surfaces of Mild and Stainless Steels under Dynamic Conditions

Mild steel and stainless steel specimens were activated mechanically by cutting under high vacuum at room temperature, and sub-monolayer levels were adsorbed. It was found that the compounds could be divided into two groups according to their adsorption activity on the cut surface. Benzene, 1-hexene, methyl proprionate and diethyl disulfide exhibited a high adsorption activity, while the polar compounds propionic acid, propylamine, trimethyl phosphate and trimethyl phosphite exhibited comparatively low activity. The functional groups of the former compounds have a higher polarizability than that of the latter compounds. The results are discussed on the basis of the Pearsons HSAB (Hard and Soft Acids and Bases) principle. It was found that the nascent surface was so active that benzene decomposition and the reaction of diethyl disulfide with the surface occurred even at room temperature.

Decomposition of Perfluoroalkylpolyethers (PFPE) in Ultra-High Vacuum Under Sliding Conditions

Reactions of three different types of perfluoroalkylpolyether (PFPE) liquids were studied during sliding contact with stainless steel (440C) specimens under ultra-high vacuum conditions. All three liquids reacted with the steel specimens during sliding. One PFPE liquid, which has acetal linkages, decomposed under the sliding conditions and generated gaseous products, namely, COF2 and fluorinated carbons, which were detected by a quadrupole mass spectrometer. Gaseous products were not detected for the other two PFPE liquids (these two liquids lacked the acetal linkages). The amount of gaseous products from the acetal containing PFPE liquid increased with increasing sliding speed. At the end of the sliding experiments, the specimens were removed from the vacuum chamber and the wear scar and the deposits on the specimens were examined by small-spot-size X-ray photoemission spectroscopy (XPS). The oxide layer on the specimen surface was removed during sliding, and metal fluorides were formed on the worn surfa...

Adsorption of benzene on the fresh steel surface formed by cutting under high vacuum

Abstract The adsorption of benzene on a fresh steel surface was carried out in high vacuum at room temperature. The fresh surface was formed by cutting in a high vacuum chamber, and benzene was allowed to adsorb on the surface during cutting. The adsorption and the surface reaction of benzene was monitored with a quadrupole mass spectrometer. It was found that the cut surface was so active that the catalytic decomposition of benzene occured even at room temperature. The adsorption rate and the sticking probability of benzene were estimated. The adsorption rate linearly increased with cutting speed, that is, the formation rate of the fresh steel surface. It was found that the adsorbed amount was under the monolayer level, and that the adsorption activity of toluene on the fresh surface was about two times larger than that of benzene.

Decomposition of Aromatic Compounds on Cut Nickel Surface

The absorption and decomposition of several aromatic compounds was studied on a nickel surface under dynamic conditions at room temperature. Nickel was activated by cutting under high vacuum. The aromatic compounds decomposed on the cut nickel surface, and hydrogen was evolved even at room temperature. However, decomposition was not observed with saturated hydrocarbons such as normal hexane and cyclohexane. It was elucidated that hydrogen evolution was the result of catalytic decomposition of aromatic compounds on the cut nickel surface as well as the thermal decomposition of adsorbed water. It was found that aromatic decomposition was closely dependent on the structure of the aromatics. The nature of chemical activity of nickel under dynamic conditions is discussed. Presented at the 42nd Annual Meeting in Anaheim, California May 11–14, 1987

Molecular Design of Environmentally Adapted Lubricants: Antiwear Additives Derived from Natural Amino Acids

Novel environmentally adapted lubricant additives were synthesized from cystine (Cys 2 ), an essential amino acid obtained from natural sources. The structural feature of cystine is a dimeric amino acid with a central disulfide bond. The carboxyl groups in Cys 2 were converted to corresponding esters by reaction with long-chain alcohols. The resultant diesters were soluble in poly-alpha-olefin (PAO) and ester-type synthetic oils. The structural features of the new additives include multifunctional groups on the same molecule, such as disulfide as a tribologically active moiety and polar functional groups as anchors to friction surfaces. The additives consist of hydrogen, carbon, nitrogen, oxygen, and sulfur; they are free of phosphorus, chlorine, and metals. The tribological properties of the additives in a solution of synthetic oil were evaluated by performing laboratory tribotests under boundary conditions. The Cys 2 -derived additives exhibited comparable antiwear properties to the conventional additive zinc dialkyldithiophosphate (ZnDTP). The additives showed good antiwear properties even at low concentrations of sulfur (160 ppm) in synthetic hydrocarbons such as PAOs. A high concentration of sulfur (640 ppm) was required to obtain an optimized antiwear performance of the synthetic esters as a base oil. The new additives reduced the friction coefficient of PAOs and synthetic esters. A saturated ester of Cys 2 reduced the friction of PAOs and synthetic esters up to oil temperatures of 150°C. The lubrication mechanism was discussed with respect to the role of functional groups in the additive molecule. The use of amino acids as versatile building blocks for the synthesis of environmentally adapted additives was also pointed out.

Tribochemical activation of gold surface by scratching

Abstract Fresh gold surfaces were formed by scratching under high vacuum conditions, and adsorption and reactions of organic compounds on the surface were monitored with a quadrupole mass spectrometer. It was found that the gold surface was activated tribochemically by scratching, and various organic compounds chemisorbed on the fresh surface. The estimated chemisorption activities were closely related to the functional group of the organic compounds. Hydrogen evolution due to decomposition of adsorbed molecules was observed even after the termination of scratching. Hydrocarbons were also evolved on adsorption of organic iodide. It is conclude that gold surface becomes so active by scratching that chemisorption and decomposition of organic compounds occur on it even at room temperature.

X-ray photoelectron spectroscopy peak assignment for perfluoropolyether oils

Perfluoroalkylpolyether (PFPE) oils are increasingly being used as vacuum pump oils and as lubricants for magnetic recording media and instrumentation for satellites. In this paper, the relative binding energies of three PFPE oils are determined. When sample oils are continuously irradiated during X-ray spectroscopy (XPS) measurements, the relative peak intensity of the spectra is altered significantly, indicating that gaseous products form from the oils during XPS measurements. Thus, attention should be paid to chemical changes when XPE is used to characterize fluorinated carbons such as PFPE oils.

Effects of film characteristics on frictional properties of carboxylic acid monolayers

Monolayers of long-chain carboxylic acids, with various fluorination ratios, were deposited on solid substrates to investigate the effects of surface properties on frictional behavior. It is found that a lower surface free energy correlates to a lower friction coefficient for the monolayers of partially fluorinated carboxylic acids. However, a stearic acid (C17H35COOH) monolayer shows the lowest friction coefficient, although its surface free energy is relative high. The two-dimensional elastic modulus, which might be used as a parameter to quantitatively characterize the film strength, was developed. Friction coefficients of the monolayers show a strong correlation with their elastic modulus, that is, the higher the elastic modulus, the lower the friction coefficient. The research results indicate that frictional properties of ultrathin films are mainly dependent on film strength. Enhancement of intermolecular attractive force might be a more effective way to improve the lubricating properties of ultrathin films.