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A tube of commercial graphite powder lubricant with molybdenum disulfide additive (called "molybdenum") [33] Due to weak van der Waals interactions between the sheets of sulfide atoms, MoS 2 has a low coefficient of friction. MoS 2 in particle sizes in the range of 1–100 μm is a common dry lubricant. [34]
Such materials can operate up to 350 °C (662 °F) in oxidizing environments and even higher in reducing / non-oxidizing environments (molybdenum disulfide up to 1100 °C, 2012 °F). The low-friction characteristics of most dry lubricants are attributed to a layered structure on the molecular level with weak bonding between layers.
The potassium intercalated molybdenum ditelluride becomes superconducting below 2.8 K. [36] As a lubricant molybdenum ditelluride can function well in a vacuum and at temperatures up to 500 °C with a coefficient of friction below 0.1. However molybdenum disulfide has a lower friction, and molybdenum diselenide can function at higher temperatures.
Some molybdenum disulfide containing additives to lubricating oils are claimed to reduce friction, bond to metal, or have anti-wear properties. MoS 2 particles can be shear-welded on steel surface and some engine components were even treated with MoS 2 layer during manufacture, namely liners in engines.
Organo-molybdenum compounds, were initially developed as antiwear additives but were later recognized to be very effective in reducing boundary friction. [3] They are currently used in many engine oils and, more recently, in gear oils. [1] They reduce friction by forming two-dimensional molybdenum disulphide layers on rubbing surfaces. [4]
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In general a filler is selected to decrease the friction coefficient of the material. Particle size and shape are contributing factors. Smaller particle size increase wear resistance because they cause less debris. silica, alumina, molybdenum disulfide, and graphite powder are common fillers that improve wear resistance. [13]