The Growth of Thin Lubricating Films of Plant Oils

Abstract

The extreme conditions of high pressure and shear imposed in a lubricated sliding contact could influence tribochemical reactions that could occur over long sliding distances and time scales, possibly leading to changes in both friction and film thickness. Experiments conducted with 12 plant oils reveal for the first time, that thin lubricating films of some plant oils can grow to thicknesses much greater than what is predicted from either elastohydrodyamic theory or their adsorbed molecular heights. Some films grew as much as 25 times in thickness (unrefined canola oil), while others remained roughly unchanged (flaxseed and olive oil), or grew slightly and then collapsed during the test (safflower oil). The absence of a loss in film thickness and the viscoelastic-like behavior of the film when speeds are reduced to zero, support the view that polymerization could be the main mechanism of film growth. However, the lack of correlation between the degree of unsaturation and the film growth rate suggests that other mechanisms could also be at work.

Preparation of the electroless Ni–P and Ni–Cu–P coatings on engine cylinder and their tribological behaviors under bio-oil lubricated conditions

“…8. It can be found that both of the contents of C and O increased with increasing slide speed, indicating the adsorbed oil film turned thicker [26]. Moreover, in HL regimes (e.g.…”

Surface‐Enhanced Raman Spectroscopy of Tribochemically Formed Boundary Films of Refined and Unrefined Canola Oils

“…The apparatus used for the sliding experiments was an in-house developed ball-on-disc tribometer. The tribological conditions used were kept the same as that described in an earlier work [8], except that the bearing ball used was replaced with a silver coated bearing ball ( Fig. 1).…”

“…These oxidative processes could possibly be accelerated at the interface during a metallic sliding contact, resulting in the formation of thick viscous boundary films. This hypothesis was first tested in an earlier work by measuring the boundary film thickness, using the capacitance method, of four refined oils and nine cold-pressed unrefined oils in a ball-on-disk tribometer setup [8]. The tests were conducted under moderate tribological conditions of a steel-on-steel sliding contact for 18 h. It was revealed, for the first time, that boundary film thicknesses of most plant oils do thicken over long sliding distances.…”

Tribological and Chemical–Physical Behavior of a Novel Palm Grease Blended with Zinc Oxide and Reduced Graphene Oxide Nano-Additives

“…Many researchers investigated the tribological and chemical-physical properties of vegetable oils to replace mineral ones in industrial applications [22][23][24][25]. For example, experimental investigation tested 12 different plant oils for tribological properties and showed that some vegetable oils can form thicker lubricating films than that predicted from elastohydrodynamic theory [26]. Another recent finding proved that vegetable oilbased grease produces a stable and consistent hydrodynamic film lubricant with higher load-carrying capacity in comparison with commercial lithium grease [27,28].…”