松本 直浩

Improving the wear resistance of polvmer-based materials can lead to high energy efficiency' of transport machineries owing to the higher strength-to-weight ratio. Oxidized wood-utilized synthesized copper-based particles (OWCu) was incorporated into epoxv resin to investigate its effect on the wear resistance of OWCu-incorporated epoxy with the steel counterpart using a ball-on-plate tribometer. OWCu was mainly composed of CuO with a small amount of graphitic carbon, and the average partide size was approximately∗ 0.5 um. A higher wear resistance was observed for the OWCu-incorporated epoxv at more than 0.6 mass% compared to the neat epoxv. The mechanism for the improvement of the wear resistance property was discussed, and it was revealed that the surface roughness of the steel counterpart was maintained at a low level for the OWCu-incorporated epoxy', which played a dominant role in reducing the wear of the OWCu-incorporated epoxv. The polishing effect of OWCu could reduce the surface roughness of the steel counterpart in the friction process. In addition, at higher concentrations of more than 5.0 mass%, OWCu adhered to the steel surface, which decreased the wear of the steel surface. OWCu is a promising material to enhance the wear resistance of polvmer-based materials, especially with low elongation.

In this study, a novel method was developed for in situ scanning electron microscopy (SEM) observations of friction interfaces, from a top view, using a Si3N4 thin film (SiN film), which has high electron transmission ability, and a microtribometer. Nanodiamond (ND) aggregates were adsorbed on the back surface of the SiN film. A JIS-SUS304 ball, on which surface ND aggregates were adsorbed and tribofilms were already formed, contacted and slid with the back surface of the SiN film. An SEM electron beam went through the SiN film, and generated secondary electrons from the ball surface contacting the back surface of the SiN film and the adsorbed ND aggregates. Thereafter, the generated secondary electrons from the ball surface penetrated again through the SiN film and reached the SEM electron detector. In other words, the contacting ball surface and the adsorbed ND aggregates were successfully imaged through the SiN film. Energy dispersive X-ray spectroscopy analyses of the friction interfaces were also accomplished. Moreover, in situ SEM observations of friction interfaces under boundary lubrication, using poly-alpha olefin (PAO) oil with graphene oxide aggregates and lithium grease with MoS2 particles, were successfully accomplished. The PAO oil and lithium grease had electron transmission ability, and the friction interfaces were imaged by SEM as seen with an optical microscope.

Copyright © 2014 John Wiley & Sons, Ltd. Carbon nanoparticles (CNPs) were synthesized by the plasma-based ion implantation method, and structural variations and the synthesis mechanism of CNPs were investigated. CNPs were grown by implanting carbon ions from methane gas into thin silver films. To obtain pure CNPs from the silver matrix, the silver films were evaporated by a thermal process under high vacuum. XPS depth analysis revealed that initially silver atoms were preferably sputtered during implantation, then CNPs gradually started to appear on the silver and carbon atoms concentrated near the surface. Stacked carbons on the surface may prevent silver films from being sputtered and carbon ions from penetrating into the silver matrix. The CNPs grew up to 20 nm, but their size did not increase after the implantation for 2 h. Instead, a membrane cluster among the CNPs was observed after the implantation for 3 h. Thermal process at 750°C for removing silver to obtain only CNPs did not affect CNP growth. Raman spectra indicated that spherical CNPs consist of graphitic structure and long-time implantation yielded amorphous membranes as well as the CNPs.

Metal nanoparticles (NPs) exhibit localized surface plasmon resonance (LSPR) and thus have potential for use in a wide range of applications. A facile technique for the preparation of NP films using an electron-cyclotron-resonance plasma sputtering method without a dewetting process is described. Field emission scanning electron microscopy (FE-SEM) observations revealed that the Au NPs grew independently as island-like particles during the first stage of sputtering and then coalesced with one another as sputtering time increased to ultimately form a continuous film. A plasmon absorption peak was observed via optical measurement of absorption efficiency. The LSPR peak shifted toward longer wavelengths (red shift) with an increase in sputtering time. The cause of this plasmon peak shift was theoretically investigated using the finite-difference time-domain calculation method. A realistic statistical distribution of the particle shapes based on FE-SEM observations was applied for the analysis, which has not been previously reported. It was determined that the change in the shape of the NPs from spheroidal to oval or slender due to coalescence with neighbouring NPs caused the LSPR peak shift. These results may enable the design of LSPR devices by controlling the characteristics of the nanoparticles, such as their size, shape, number density, and coverage. © 2014 AIP Publishing LLC.

In this study, carbon based nanomaterials such as onion-like carbon (OLC), carbon nanotube and buckminsterfullerene (or buckyball) (C60) have been investigated as nanocolloidal additives for liquid lubricants. When tested under a range of contact pressures from 0·51 to 1·10 GPa, OLC provided the best overall friction reducing property in synthetic lubricant, although the friction reducing properties of all nanocarbon materials were dependent on the contact pressure. Detailed transmission electron microscopy revealed that the OLC kept its original structure intact and induced the formation during sliding of a thin 'tribofilm' composed of OLC, nanosized wear debris, amorphous carbon and graphitic layers on the wear debris. This tribofilm seems to be responsible for reduced friction under boundary conditions. © 2012 W. S. Maney & Son Ltd.

This study demonstrated that surfactants can significantly improve the dispersion stability of milled boric acid particles over a broad range of operating temperatures. The tribological performance of boric acid and surfactant [sorbitan trioleate (STOMO)] mixed in the base oil was investigated under cylinder-on-plate line contact set-up using a reciprocating tribological test rig. Several characterisation techniques were used to understand particle distribution and size and composition of tribofilms that resulted from sliding contact. The results showed that surfactant prevented agglomeration of boric acid particles after the milling process and thus, provided good dispersion stability at elevated temperatures. The addition of surfactant in the base oil decreased the friction coefficients by 58 and 42% respectively, and reduced the wear scar diameter by 48 and 34% respectively, as compared to the base oil and fully formulated oil. In addition, the presence of a boron rich boundary film resulting from decomposition of boric acid compounds were detected by XPS and Auger in the wear track inside the wear tracks. © 2012 W. S. Maney & Son Ltd.

In order to investigate a method to increase hydrophilicity on nano-rough carbon surfaces, a nano-rough surface of C60 film and an atomically flat surface of highly oriented pyrolytic graphite (HOPG) were oxidized by hyperthermal oxygen-atom beam exposure and the hydrophilicities of the surfaces were investigated. Superhydrophilicity were achieved on these exposed carbon surfaces, which had low O/C ratio of approximately 28% and surface roughness (Ra) of approximately 3 nm. The direct oxidations on sp2 bonded carbon atoms (basal plane) of these two carbon materials by the exposure of hyperthermal O-atom beam would contribute the superhydrophilicity. © 2011 Elsevier Ltd. All rights reserved.

The carbon nano-onion can be considered as a new kind of interesting lubricating nanoparticle. Used as lubricant additives, carbon nano-onions lead to a strong reduction of both friction and wear, even at low temperature. To better elucidate the mechanisms by which these processes occur, coupled experimental and computational investigations are carried out. In addition, it is found that lubricious iron oxide nanoparticles are generated in the core of the steel contact through mechanisms that are not yet known. The molecular dynamics simulations of carbon onions placed between sliding diamond-like carbon surfaces at high contact pressure indicate that the lubrication mechanism of the onions is based on a coupled process of rolling and sliding inside the contact area. We conclude that most of carbon onions seem to remain intact under friction processes and do not generate graphitic planes, which is in contrast to the previously determined behavior of MoS 2 fullerenes that are mainly exfoliated inside the contact area and liberate lubricating lamellar sheets of h-MoS 2. © 2009 Springer Science+Business Media, LLC.

Fabrication of fullerene C60 nanorings on a highly oriented pyrolytic graphite (HOPG) was carried out by molecular beam epitaxy (MBE). Morphological characteristics of C60 were investigated using an atomic force microscope (AFM). An oxidized HOPG, on which circular etch-pits were formed, was used as the template for the fabrication of fullerene nanorings. Evaporated C60 molecules were selectively adsorbed on the etch-pits edges where the pre-deposited Au islands existed. The diameter of the etch-pits for nanoring template was controlled simply by the oxidation temperature of HOPG. © 2008 Elsevier B.V. All rights reserved.

A new method for the synthesis of very thin onion-like carbon (OLC) film, based on vacuum arc plasma discharge of carbon rods, was presented. To synthesize OLC film from vacuum arc, ultra high vacuum of better than 10-7 Pa was needed. At 10-5 Pa, the influence of CH4 was high enough to cause hydrogenated amorphous carbon. As the fluence of carbon increased, the diameter of OLC increased. The friction coefficient of OLC film was very low at 0.02 under applied forces from 10 to 60 nN. Thus, coating of smooth OLC film is a potential technique to reduce friction. This is an abstract of a paper presented at the World Tribology Congress (Kyoto, Japan 9/6-11/2009).

Since the discovery of carbon nanotubes (CNT), a number of tribological researches made because of their high industrial potentials. CNT have cylinder structures with graphene-sheets (the same as graphite, which is used as good solid lubricants), and have high stiffness. A study on CNT films and sliding tips was carried out. CNT films could sustain the tips at the loads and the friction properties. However, the friction coefficient of CNT films were extremely high. Individual CNT stick the asperities of the tip surfaces and were then bended, thus, the extremely high friction would arise from high repulsive forces due to the bending of CNT. Low-friction forces of CNT could be expected if sticks of CNT in the asperities are avoided. This is an abstract of a paper presented at the 2009 World Tribology Congress (Kyoto, Japan 9/6-11/2009).

Among all the new carbon forms like fullerenes or nanotubes, carbon onions are of particular interest for tribological applications because of their spherical and tiny shape, and their chemical inertness. Used as additives blended to a synthetic base oil, they present excellent anti-wear and friction-reducing properties. In this paper, we compare tribological performances of two kinds of carbon onions with different structural features. Due to the synthesis method used, carbon onions present or not a residual diamond core inside the graphitic shells. Carbon onions without the diamond core present better anti-wear properties. © 2007 Elsevier Ltd. All rights reserved.

The influences of interactions between C₆₀ thin films and Si substrates were investigated using atomic force microscopy (AFM). It was found that higher friction coefficient was obtained at the C₆₀ domains formed on the H-terminated Si(001) substrate and lower ones on the Si(001)-2×1 substrate. Moreover, lowest friction coefficient was found for the C₆₀ film on the Si(001)-2×1 remained after scratching. Therefore, it is thought that higher interactions between C₆₀ and Si substrate caused lower friction coefficient of C₆₀ thin film. The prepared substrate was examined by reflection high energy electron diffraction (RHEED), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES).

The tribological properties of onion-like carbon (OLC) have been investigated on a nanometer scale using an ultra-high vacuum atomic force microscope. In addition, the tribological properties of OLC added to oil were investigated. A viewpoint of the practical application of OLC as a lubricating additive to oil, under both experimental conditions, OLC showed low friction. In the latter case, OLC transformed into a low friction material with long life, and appears to be a promising material as nanolubricant. © 2007 Elsevier B.V. All rights reserved.

Using atom probe field ion microscopy (APFIM), the structure of the apex of single-walled carbon nanotube (SWCNT) and multi-walled carbon nanotube (MWCNT) has been studied. By analyzing the FIM image, it became possible to identify the chirality and conductivity of SWCNT. However, a clear FIM image was not successfully obtained for MWCNT due possibly to the difference in heights of each graphene wall. AP of FIM images showed that ions of carbon clusters, such as C14+, C15+, C18+ and C20+, were field evaporated from SWCNT and MWCNT. Since all of these carbon clusters may include a pentagonal plane, it is considered that, under high electric field, a hexagonal plane of graphene reconstructed into pentagonal plane and consequently these clusters field evaporated by the local concentration of electric field at the protruded pentagonal plane. © 2007 Elsevier B.V. All rights reserved.