Ionic liquids containing halogens have good lubricity, however, they are reported to cause corrosive wear. In contrast, halogen-free ionic liquids do not cause such corrosive wear, but they do not have good lubricity comparable to the halogen-containing counterparts. In this study, we focused on specific halogen-free boron-containing ionic liquids that exhibited low friction performance. The performance was mainly due to its boron-containing anions, because it was realized with both phosphonium-based and ammonium-based cations. Surface analysis and scratch test with atomic force microscope (AFM) were conducted with phosphonium-based cations to clarify the low friction mechanism. The boron-containing ionic liquid, [BOB][P66614], showed lower friction of around 0.01, which was much lower than MoDTC-containing engine oils did. The cause of the ultra-low friction with [BOB] [P66614] is thought to be due to the fact that the reaction film formed by friction has a very smooth surface and suppresses contact between metals. On the other hand, another boron-containing ionic liquid [BMB] [P66614], which did not form a smooth surface, showed relatively high friction compared to [BOB] [P66614]. Scratch tests with AFM indicated that the softer reaction film derived from [BOB] [P66614] led to the formation of a smooth sliding surface.
The vapor phase carbon coating such as diamond-like carbon (DLC) coating can form a hard carbon layer with a uniform and large area on the base materials, and is widely used in industry. However, it is impossible to perform carbon coating on a powder or a structure having a complicated shape by the vapor phase carbon coating method. Further, since the vapor phase carbon coating method is expensive and not suitable for mass production, therefore it is required the development of an inexpensive liquid phase carbon coating method. In this study, we developed a liquid-phase carbon coating method that enables uniform and ultrathin carbon coating on silica spherical particles by using a soluble carbon material derived from phloroglucinol, and developed carbon-coated silica spherical particles that have both high lubricity and wear suppression ability. The carbon coated silica spherical particles exhibited high lubrication characteristics as a dispersion of low and high viscosity or the form of a spray.
Carbonaceous hard coatings have promising tribological properties, such as low friction, high hardness and high wear resistance. In particular, CNx (Carbon Nitride) coating and a-C:H (hydrogenated amorphous carbon) coating show ultra low friction coefficient (µ<0.01) in dry nitrogen gas. However, the mechanism of ultra low friction has not clarified. We have developed the in-situ measurement method on friction area during sliding to clarify the ultra low friction mechanism of carbonaceous hard coating. In this research, we demonstrated in-situ measurement of surface energy on friction area during friction by manufacturing friction tester in ESEM (Environmental Scanning Electron Microscope) chamber. Moreover, we estimated the effect of surface energy on friction property of carbonaceous hard coatings. We used UV irradiation to prepare the carbonaceous hard coatings, which have different surface energy. From the results, friction coefficient of carbonaceous hard coating decreased with surface energy, however the approximate line which showed the relationship between friction coefficient and surface energy did not pass through the origin. It suggested that friction occurred beneath the sliding surface in coatings or transferred layers not on the surface. Moreover, surface energy of carbonaceous hard coatings approached the value of graphite when carbonaceous hard coatings showed low friction. It suggested that structure of carbonaceous hard coatings had become graphite-like structure.