Study on Thermal Oxidation and Viscosity Degradation for Synthetic Aviation Lubricant Fluids

Abstract

The thermal oxidation and viscosity degradation for poly-α-olefins (PAO) and di-esters (DOS) was studied under the GC/MS investigation. Through the oxidative pyrolysis conditions, these two synthetic base fluids were characterized to get their simulated “areo-engine” conditions’ for thermal stability, such as oxidative and kinematic viscosity variation. The experimental results suggests that the oxidation products generated from oxidation reactions of DOS is mainly single esters, di-esters, ketone, ether, organic acids and alcohol, which results much bigger total acid values than that of PAO treated in similar conditions. The substantial increment of the kinematic viscosity of DOS reveals its limited thermal oxidation stability compared to PAO.

Oxidation of lubricating oil and its influence on the aging behaviors of fluorine rubber

“…During the aging process of the lubricating oil, the small molecule antioxidants could be oxidized and become ineffective, which further causes the oxidation of the main composition of the base oil and strong polar substances such as carboxylic acids and aldehydes could be formed. Therefore, the changed polarity of the aged lubricating oil shows lower contact angle and stronger interaction with FKM 29 . Which indicates that the aged oil medium has a stronger force with the FKM samples and is easier to diffuse into the FKM samples.…”

“…With the prolongation of aging time, the acid value increases, which indicates that acid substances are generated during the aging process. These acidic substances are most likely carboxylic acids and aldehydes 29,30 …”

“…So in the infrared spectrum no noticeable change in FITR spectrum. 29 presents It can be seen from the spectra that I 2930 /I 1740 and I 1162 /I 1740 basically remain unchanged in the aging process, which means that the characteristic peak of lubricating oil medium does not change before and after aging.…”

“…These acidic substances are most likely carboxylic acids and aldehydes. 29,30 With the prolongation of aging time of the lubricating oil medium, the contact angle that between the pure oil medium and the FKM samples decreases gradually as shown in Figure 1c. During the aging process of the lubricating oil, the small molecule antioxidants could be oxidized and become ineffective, which further causes the oxidation of the main composition of the base oil and strong polar substances such as carboxylic acids and aldehydes could be formed.…”

“…Therefore, the changed polarity of the aged lubricating oil shows lower contact angle and stronger interaction with FKM. 29 Which indicates that the aged oil medium has a stronger force with the FKM samples and is easier to diffuse into the FKM samples. In addition, as shown in Figure 1d, the viscosity of the pure lubricating oil has almost no change, indicating that the molecular chain of the aged oil has not been broken and the molecular weight has not changed much, but only the groups on the main chain of the molecule are oxidized to acidic groups such as aldehydes and carboxylic acids.…”