ホウ素含有イオン液体による摩擦低減効果

抄録

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.