LAUSR

The thermo-oxidative degradation of a multiply-alkylated cyclopentane (MAC) lubricant for space applications is investigated. Accelerated aging tests at temperature levels between 60 °C and 150 °C are performed and the aging behavior is investigated in detail with spectroscopic, mass spectrometric and chromatographic techniques as well as tribological testing on a ball-on-disk setup. The degree of oxidative aging of the MAC lubricant is monitored with the carbonyl index (CI), which is shown to be well-suited to monitor the degree of degradation of the lubricant. Gas chromatography/mass spectrometry (GC/MS) analysis is applied to identify 9-nonadecanone as the main volatile degradation product in all aged samples, suggesting a similar decomposition pathway at all tested temperatures. Size exclusion chromatography (SEC) is further applied to confirm the formation of higher molecular weight degradation products upon aging, affecting the viscosity of the lubricant. In the subsequent ball-on-disk tests, a good correlation of the performance loss with the FTIR measurements is seen and CI values of approx. 0.64 are regarded as threshold for the complete loss of performance at the selected test conditions. The determined CI values in dependence of the aging duration are further used to perform a time–temperature superposition (TTS) to acquire a master curve for accelerated aging. In the resulting Arrhenius plot, non-linear behavior is observed, highlighting the importance of a precise control of accelerated aging parameters for reliable lifetime estimations.