Molybdenum disulfide as a lubricant: A review of the fundamental knowledge

Abstract

This report consists of a review and evaluation of the work presented in the literature over the past 40 years on the behavior of MO!% as a lubricant. The discussion is concerned with the behavior of MO& as a lubricant, its frictional characteristics, the apparent reasons for these characteristics, and the physical and chemical properties which are important to its use as a lubricant The low friction and easy cleavage of molybdenum disulfide is intrinsic to the material and a result of its crystal structure. Although it is clear that the presence of condensable vapors is not required for molybdenum disulfide to exhibit low friction, as it is in the case of graphite, it is true that condensable vapors play an important role in determining the friction and wear characteristics of a lubricant film of MoS2. The presence of oxidizing agents, particularly water vapor and oxygen, tends to reduce the wear life of the MO& film. This is particularly true in the case of burnished films. Although a great deal of knowledge exists concerning the behavior of molybdenum disulfide as a lubricant, there are still voids in our understanding of this subject. CONTENTS * This review is based on an earlier review (October, 1965) by the author which was given limited circulation by the Climax Molybdenum Company of Michigan. Wear, 10 (1967) 422-452 MECHANISM OF FRICTION IN MOLYBDENUM DISULFIDE Although molybdenum disulfide has long been known to exhibit a low coefficient of friction, the reason for this behavior has been the subject of much research and speculation. Because of the similarities between MO& and graphite the early scientists mistook one for the other, and, in recent years, some scientists have at

Nanostructural Aspects of Wear in Ion-Beam Deposited Pb-Mo-S Films

“…This provides the first direct evidence that wear of MoS 2 films can occur by layer-by-layer detachment. This wear mode can be accounted for by the weak Van der Waals bonding between MoS 2 layers, a property which has also been used to explain the low shear strength of MoS 2 [11]. Additionally, this wear mode might account for the very low (sub-nanometer per cycle) wear rates of Pb-Mo-S films [4].…”

Solid lubricant materials for high temperatures—a review

“…Since a large volume of literature exists for these materials (e.g., ref. 2), they will not be discussed in detail here except to emphasize the importance o f chemical reactivity in determining the suitability of a solid lubricant for a specific applicatlon. The maximum useful temperatures for solid lubricants depends strongly on the composition of the ambient atmosphere, the required life at temperature, and factors *Prepared for the Special Issue "Dry Bearings" o f the Tribology International Journal, October 1982.…”

Wear and Friction of Greases Containing Organic and Inorganic Sulfur Carriers

“…MoS2 is a well-known EP additive that has been used extensively in greases [1,5,6,9,18]. The appropriate treat rate employed in the formulation was about 3 mass% for the EP properties to be effective.…”

“…There have been three major theories suggested to understand the mechanism of friction in MoS2 and two of these theories explain the mechanism basing it on the behavior of graphite. The theories used are: a) Intrinsic cleavage mechanism, b) Adsorption mechanism theory and c) Inter-crystallite slip mechanism [1,18]. The coefficient of friction of MoS2 also depends on loading conditions that exist at the asperity contacts.…”