A quantitative evaluation of inorganic boundary films formed in engine oils by TOF-SIMS depth profiling with low energy Cs sputtering

Quantitative evaluation of lubrication boundary films was investigated by time-of-flight secondary ion mass spectrometry depth profiling with low energy Cs sputtering. Relative sensitivity correction coefficient (RSC) for calcium phosphate, calcium carbonate, or calcium sulfate was determined by measuring the pellets of the mixture of these compounds. The RSCs for the three calcium salts varied with measurement conditions such as sputter energy and primary ion species. By using the RSC determined in this investigation, the depth profiles of the boundary films formed in real engine oil were corrected to quantitative profiles. The difference of structures between two lubrication boundary films on the different substrate materials formed in the same engine oil was clarified.