Hidetaka Nanao

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.

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.

Investigation of the structure and tribological characteristics of monolayers deposited by the Langmuir–Blodgett technique

Abstract A series of partially fluorinated ethyl esters with the same hydrophobic group length were deposited by the Langmuir–Blodgett (LB) technique on an Al plate coated with a NiP film. Film structures were inferred through surface pressure–molecular area isotherms ( π – A isotherms). The results indicate that the film structures are determined by van der Waals forces between hydrophobic chains. Stronger mutual forces lead to stable solid films. Frictional properties and load-carrying capacities of the monolayers were evaluated using a ball-on-plate-type sliding apparatus. The friction coefficient and load-carrying capacity are dependent on the monolayer film structures. The solid film shows a lower friction coefficient and a higher load-carrying capacity. Friction tracks of the monolayers were examined by time-of-flight secondary ion mass spectroscopy (TOF-SIMS). We found that the liquid film may be a fluid monolayer, and that the structure of the solid film changes under frictional force.

Tribological Characteristics and Tribochemical Reactions of Various Ceramics Lubricated with HFC-134a Gas

The role of tribochemical products in the friction and wear reduction of ceramics with different fractional ionic character in CF3CH2F (HFC-134a) gas was investigated using a ball-on-disk type tribometer. Without exposure to air, the wear tracks on the disks were characterized with the aid of a micro-spot X-ray Photoelectron Spectroscope (XPS) whose analytical chamber was connected to the friction chamber of the tribometer. Further, the adsorption and desorption behaviors of HFC-134a molecules on the nascent surfaces of the ceramics were studied using an adsorption test apparatus in high vacuum. It was found that the lubricating effect of HFC-134a gas was closely related to the fractional ionic or covalent characters of the ceramics. HFC-134a gas was more effective in lubricating ionic ceramics than the covalent ceramics. XPS analysis revealed that metal fluorides were mainly formed on the frictional surfaces of the ionic ceramics, whereas the composition of the tribochemical products on the frictional surfaces of the other ceramics was complicated. The adsorption tests proved that HFC-134a was decomposed to an olefin CF2=CHF on the nascent surfaces of the ionic ceramic Al2O3 and the covalent ceramics. However, the formation of organic fluorine-containing compounds was not detected on the frictional surfaces of the ionic ceramics by XPS. This result implies that the mechanism of tribochemical reactions is strongly dependent on the bond type of ceramics. It is concluded that the low friction and wear of the ionic ceramics in HFC-134a gas result from the metal fluorides formed with high surface concentration on the sliding surfaces.

Tribochemical approach toward mechanism for synergism of lubricant additives on antiwear and friction reducing properties

The synergism and antagonism of additives on tribological properties is an important issue for lubricant formulations. In this study, combination effects of anti-wear additives, detergents, and dispersants were evaluated by a block-on-ring type tribometer under the boundary lubrication conditions. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) were employed to study the chemical structure of the boundary film formed on the rubbing surface. The correlation between tribological properties and chemical composition on the worn surface was investigated. Zinc dialkyldithiophosphates (ZnDTP) slightly reduced wear under these conditions. An over-based calcium sulfonate (Ca-Sul) reduced wear and friction remarkably, whereas alkylsuccinimdes (Suc-I) promoted wear. Metal oxides derived from the corresponding additives were found on the wear track lubricated with ZnDTP or Ca-Sul. On the other hand, only iron oxides were detected on the surface lubricated with Suc-I. Combination of Suc-I with ZnDTP or Suc-I with Ca-Sul changes tribological properties and surface contents. Taking the results into account, a classification of additives as “boundary film precursor” or “film formation controller” was proposed.

Tribochemical Reactions and Lubricating Effects of Fluorinated Methanes for Al2O3 Ceramic

It has been found that CF3CH2F (HFC-134a) gas is an effective lubricant for several ceramics because of the formation of fluorine-containing tribochemical products. To understand the influence of the molecular structure of fluorine-containing gases on the lubricating characteristics, the lubricating effects and tribochemical reactions of some fluorinated methanes for Al2O3 ceramic were studied. X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS) were used to identify the chemical structure of tribochemical products. It was found that the friction and wear of Al2O3 ceramic were dependent on the molecular structure of the reacting fluorocarbon gases. The lowest friction was obtained in CH2F2. CHF3 showed the best anti-wear effect. The results of surface analyses indicate that greater amounts of tribochemical products are produced when Al2O3 rubs in CH2F2 than in CF4 and CHF3 gases. C–C/C–H/carbon and AlF3, which are mainly formed on the sliding surface in CH2F2, are responsible for the low friction. The mechanism of tribochemical reactions of the different environmental molecules on the nascent surface of Al2O3 was also discussed.

Effects of End Groups on the Tribochemical Reactions of Lubricants at Head-Disk Interface

Mass spectrometry was used to monitor in-situ gaseous species that were generated at the head-disk interface (HDI) in a high vacuum. It was found that the end groups of the lubricants significantly affected the wear durability at the HDI; piperonyl (–CH2-phe = (O)2 = CH2) terminated Fomblin AM3001 lubricant exhibited longer life than hydroxyl (–OH) terminated Fomblin ZDOL lubricant. The continuous removal of the lubricants resulted in a continuously increasing friction coefficient. Further, the characteristics of tribochemical reactions of the lubricants (Fomblin Z series) with different end groups was investigated in details using Time-of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS) just after the sliding tests. It was found that the decomposition of the end groups was more significant than that of the backbone. The lubricants terminated with the following groups showed the following order of increasing decomposition: –CH2O-CH2-phe = (O)2 = CH2 (AM3001), –CH2OH (ZDOL) < –CH2OCH2CH(OH)CH2OH (Z Tetraol) < –CH2(OCH2CH2)nOH (ZDOL-TX), –COOH (Z Diac). The decomposition of the lubricants appeared to start from the end groups.

Selective Hydrogenation of Cinnamaldehyde Over Platinum Nanosheets Intercalated Between Graphite Layers

Platinum nanosheets between graphite layers were prepared by a thermal treatment of the mixture of platinum chloride (IV) and graphite powder under 0.3 MPa of chlorine at 723 K for 7 days, followed by the reduction under 40 kPa of hydrogen at 573 K for 1 h. Two-dimensional platinum metal nanosheets of 1-3 nm thickness and of 100-200 nm width were intercalated between graphite layers (Pt-GIC). The platinum nanosheets had a number of hexagonal holes and edges with angle of 120°. Liquid phase hydrogenation of cinnamaldehyde (CAL) was studied over Pt-GIC which was compared with that over platinum metal particles supported on graphite layers (Pt/Gmix). The conversion of cinnamaldehyde over Pt-GIC was lower than that over Pt/Gmix; however, the selectivity to cinnamyl alcohol (COL) was higher than that over Pt/Gmix. For similar CAL conversion of around 25% (in 60 min over Pt-GIC and 15 min over Pt/Gmix), the COL selectivities over 5 and 10 wt% Pt-GIC (56 and 54%) were higher than those over 5 and 10 wt% Pt/Gmix (33 and 19%).