Effect of lubricant ageing on lubricants' physical and chemical properties and tribological performance; Part I: effect of lubricant chemistry

Purpose - Ageing has been known to affect the performance of lubricants. However, there is a lot of debate as to whether ageing is beneficial or detrimental to the wear performance of lubricants. Design/methodology/approach - The purpose of this research is to evaluate the effect of ageing on the viscosity, total acid number and Fourier-transform infrared spectroscopy information of a series of lubricants. The tribological performance (friction and wear) of the aged lubricants is also studied, followed by X-ray photoelectron spectroscopy analysis on the selected post-test samples to study the tribochemical features of the tribofilm. Findings - The results show that ageing has a different impact on lubricants and tribological performances based on the physical and chemical properties. Originality/value - These findings will be compared with the research on the role of water in lubricant ageing (Part II of this study).