Characterization and Tribological Properties of MoS2Powders and of Related Chalcogenides

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Abstract
Surface and bulk properties of MoS2 Technical Grades and of their fractions are compared. The water vapour adsorption isotherm is a sensitive indicator of hydrophilic impurities. Inconsistencies in current purchase specifications are pointed out. The endurance of fractions and Grades of MoS2 is compared with that of several synthetic chalcogenides at the same layer thickness and in dry atmospheres. Failure can occur (i) already at very low loads, during rubbing-in, (ii) during running-in to full load, or (iii) at different, but high load levels. A classification of solid lubricants, based on these observations, is proposed. While “infant death” of the lubricant film can have many causes, fully loaded lubricants, natural MoS2 as well as the synthetic chalcogenides, fail alike by a surface fatigue process: dynamic blister formation. The minimum endurance value of an effective MoS2 layer, when tested in dry air, depends on the ratio of pin to ring hardness and on surface roughness. There is also interaction between these parameters.