Surface Force Apparatus Studies of Adsorbed Borate Films

Abstract

The Lyon molecular tribometer, a very stiff and sensitive surface force apparatus, was used to investigate the structure, mechanical properties, and some Tribological characteristics of two different dispersions of potassium triborate adsorbed on cobalt oxide surfaces. Two suspensions in PAO were prepared using two different dispersants. Light scattering measurements on the suspensions showed one to be monodisperse and one to be a bimodal dispersion. For the monodisperse suspension, it was concluded that a single layer of adsorbed micelles separated the contact surfaces at maximum pressure. Also, the monodisperse suspension under compression formed a layer of high viscosity liquid containing a higher concentration of borate micelles than the bulk liquid, adjacent to the layer of adsorbed micelles on each surface. No interpretation in terms of micelle size was possible for the adsorbed layers of the bimodal dispersion between the contact surfaces at maximum pressure. No viscous layer was observed for the bimodal dispersion; the viscosity was constant (and equal to the bulk liquid viscosity) down to contact between the surfaces. Mechanical properties of the adsorbed films were determined. Friction and wear during reciprocating sliding under load were measured. Compared to the bimodal dispersion, the monodisperse suspension showed a decrease in friction, rather than an increase, and lower wear. It is hypothesized that the layer of higher viscosity adjacent to the contact surfaces contributed to the lower friction and wear for the monodisperse suspension.

Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Cancun, Mexico October 27–30, 2002

KEY WORDS:

• Boundary Lubrication
• Gear Lubricants
• Additives
• Friction
• Wear

Notes

Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Cancun, Mexico October 27–30, 2002