中性子反射率法を用いた金属表面における添加剤吸着層の厚みおよび密度測定とそのトライボロジー特性

概要

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Thicknesses and densities of additive adsorbed layers on metal surfaces under lubrication were directly measured by neutron reflectometry. Two kinds of metal surfaces, iron and copper, on ultra-flat silicon blocks were prepared by physical vacuum deposition. After that, each target surface was analyzed by neutron reflectometer SUIREN in air, in base oil (poli-alpha-olefin) and in base oil with deuterated acids as additives. Fitting operation based on Parratts theory showed that the thicknesses of additive adsorbed layer on the iron and copper surfaces were quite thin, only 1.5-2.0 nm. The friction coefficients of the metal surfaces, measured by a ball-on-disk friction tester, decreased considerably when the additive was added to the base oil. We concluded that the additive adsorbed layers on the metal surfaces considerably affected friction properties despite being only several nanometers thick.