Figure 4 The color evolution of the PAO and DIOS oil samples with antioxidants (T501, T531 and Tz516 mentioned in Experimental Section) after oxidized at 175 oC
Both 928 and 50-1-4Φ aviation lubrication oil have the viscosity of 3 cSt at 100 oC, however, the base oil of two lubrication oils is quite different. The base oil of 928 aviation lubrication oil is mainly poly-α-olefin (known as PAO), and the base oil of 50-1-4Φ aviation lubrication oil is synthetic ester (in this paper is di-iso-octyl sebacate, DIOS), as shown in Figure 3.
In the same appliance, the PAO and DIOS (both kinematic viscosity of the base oils is 3 cSt at 100 oC) is comparatively oxidized at 175 oC for the reasons mentioned before. The oxidation temperature is maintained at 175 oC which is coincident with the maximum operation temperature of 50-1-4Φ aviation lubrication oil. As shown in Figure 4, the oxidized PAO and DIOS oil samples with antioxidants (T501, T531 and Tz516 mentioned in Experimental Section) have significant color darkening phenomena after antioxidants were applied in the pure PAO and DIOS. It should be noted that the antioxidants T501, Tz516 are used in 928 and T531 applied in 50-1-4Φ aviation lubrication oil, respectively.