Surface Properties and Lubricating Action of Graphite and MoS2

Abstract

Examination of adsorptive properties of graphite and MoS₂ revealed that their surfaces are composed of two distinct sites, i.e., basal plane and edge sites, having different affinities for polar compounds and paraffmic hydrocarbons. It was therefore of interest to investigate the relationship between the proportions of the individual surface sites and the lubricating action of these solids. This was done by preparing special graphite and MoS₂ powders having a high proportion of basal plane surface and comparing their lubricating properties to those of the powders having a relatively high ratio of edge to basal plane surface area. It was found that the proportion of basal plane surface is an important factor in the lubricating performance of both graphite and MoS₂ and that the powders having predominantly basal plane surface have significantly better antiwear properties than the powders having a high ratio of polar to basal plane surface. The basal plane surface in MoS₂ plays an exceptionally important role in lubrication, and its contamination with strongly adsorbed paraffins reduces substantially the lubricating action of the powder.