Assessing Friction Stress on a Liquid Lubricant by Stable Isotope Analysis
Memorandum rept. 1 Oct 2008-30 Sep 2010
NAVAL RESEARCH LAB WASHINGTON DC CHEMISTRY DIV
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Compound-specific stable isotope analysis CSIA was applied to a pentaerythritol ester lubricant to determine if predictable fractionation effects could be related to friction stress. A pin-on-disk tribometer was used to expose the lubricant to five doubly-increasing sliding distances up to 36 km. PCA was used to ordinate multivariate data and test if significant isotopic shifts or FTIR spectral changes could be related to sliding cycles. 13C Isotope ratios only were found to be statistically different P 0.05 between treatments. PCA gave a primary score PC1 containing 44 of the 13C-isotopic variability, which correlated exponentially with sliding cycles r2 0.96. A peak, not present in unexposed lubricant, became evident and showed increasing 13C depletion with increasing length of sliding exposure.
- Lubricants and Hydraulic Fluids