Abstract
A new formulation is proposed to lubricate tribopairs in extreme conditions where the amount of lubricant is small and the lubricating region highly confined. It is composed of non-magnetic solid lubricants dispersed in an oil-based ferrofluid. When this inverse ferrofluid (IFF) is magnetically activated, the lubricant particles are subjected to magnetophoretic forces. By using appropriate magnetic field gradients, they can be driven to the region of interest and thus control the friction locally. The rheological and tribological performances of three IFF formulations are evaluated in several conditions of applied magnetic field strength and shear flow rates.
Highlights
It is a well-known fact that the use of nanofluids, dispersions of nanoparticles in a carrier, as lubricants entails several advantages in their tribological performance [1]
The rheological behaviour of inverse ferrofluid (IFF) can be understood by using the mean magnetisation (MM) approximation [24,29] in which each non-magnetic particle is viewed as a magnetic dipole placed at its centre
This is in agreement with XPS analyses demonstrating a larger concentration of fluor when the field is applied in the 4.4 wt% PTFE-based IFF sample; an atomic concentration of fluor of 0.29% is measured in the contact in the absence of a magnetic field while a concentration of 0.34% is measured
Summary
It is a well-known fact that the use of nanofluids, dispersions of nanoparticles in a carrier, as lubricants entails several advantages in their tribological performance [1]. A possible solution to these shortcomings could be the synthesis of dilute lubricant nanofluids whose concentration would be tuned locally so that it reaches the required value, and the targeted tribological prop erties, only in the system areas where wear takes place Such a “smart” lubricant has already been conceived using, for example, the so-called magnetorheological (MR) fluids under external magnetic fields [8]. The main objective of this manuscript is to elucidate if an external magnetic field of proper strength and gradient is capable to tune the rheological and tribological performances of solid lubricant-based IFFs at specific posi tions. With this in mind, one can hope to apply the method to narrow spaces and to control friction in moving mechanical parts
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