Lubricating oils degrade by various factors under operation. Degradation causes of lubricating oils are roughly classified into two types, one is caused by solid particles and the other by oil oxidation products. Amine antioxidants are generally added in turbine oils to prevent formation of sludge. Degradation of base oil progresses rapidly, when antioxidant is used up. Thus, an on-site degradation diagnosis method of antioxidant is significant to maintain fluid property of lubricating oil. There are several methods such as a chromatography and ASTM D2272 in order to measure the residual ratio of antioxidant, but these methods cannot be used as an on-site degradation diagnosis method and need the particular experience and long time. On the other hand, ASTM D6810 can measure it in a short time. In our laboratory, we have reported that there is a good relationship between the degradation of lubricating oil and color of the membrane patch. Furthermore, we have developed degradation diagnosis method of the lubricating oils focusing on the coloration of the membrane patches with contamination. In this study, we investigated relations between oxidized products of amine antioxidant captured with membrane filter and color of membrane patch and we discussed the possibility of new depletion diagnosis method of amine antioxidants.
Colorimetric analysis, Membrane patch, Amine antioxidant, On-site degradation diagnosis
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