Disulfide, molybdenum

A number of substances such as graphite, talc, and molybdenum disulfide have sheetlike crystal structures, and it might be supposed that the shear strength along such layers would be small and hence the coefficient of friction. It is true... 

The structurally similar molybdenum disulfide also has a low coefficient of friction, but now not increased in vacuum [2,30]. The interlayer forces are, however, much weaker than for graphite, and the mechanism of friction may be different. With molecularly smooth mica surfaces, the coefficient of friction is very dependent on load and may rise to extremely high values at small loads [4] at normal loads and in the presence of air, n drops to a near normal level. 

Moissanite, see Silicon carbide Molybdenite, see Molybdenum disulfide Molybdite, see Molybdenum(VI) oxide Molysite, see Iron(III) chloride Montroydite, see Mercury(II) oxide Morenosite, see Nickel sulfate 7-water Mosaic gold, see Tin disulfide Muriatic acid, see Hydrogen chloride, aqueous solutions... 

Dry lubricants are usually added to the powder in order to decrease the friction effects. The more common lubricants include zinc stearate [557-05-17, lithium stearate [4485-12-5] calcium stearate [1592-23-0] stearic acid [57-11-4] paraffin, graphite, and molybdenum disulfide [1317-33-5]. Lubricants are generally added to the powder in a dry state in amounts of 0.25—1.0 wt % of the metal powder. Some lubricants are added by drying and screening a slurry of powder and lubricant. In some instances, lubricants are appHed in Hquid form to the die wall. 

A small portion of molybdenite concentrate production is purified to yield lubricant-grade molybdenum disulfide, a widely used soHd-state lubricant. 

The most important compound of Mo (TV) is molybdenum disulfide [1317-33-5] M0S2 (21). The layered stmcture of M0S2 is reflected in the flat plate-like hexagonal gray-black crystaUites found in natural and synthetic samples. The stmcture consists of pairs of close-packed layers of sulfur which are echpsed with respect to each other. The close-packed sulfur surfaces are naturally hydrophobic, which faciUtates the extraction of M0S2 ore by flotation. 

T. J. Risdon, Properties of Molybdenum Disulfide, MoS (IMolybdenite) Bulletin C-5c, Climax Molybdenum Co., Ann Arbor, Mich., Aug. 1989. 

Titanium disulfide has been proposed as a soHd lubricant. The coefficient of friction between steel surfaces is 0.3, compared to only 0.2 for molybdenum disulfide. However, because it does not adhere strongly to metal surfaces, TiS2 is generally less effective than molybdenum sulfide. 

Tungsten disulfide forms adherent, soft, continuous films on a variety of surfaces and exhibits good lubricating properties similar to molybdenum disulfide and graphite (51) (see also Lubrication and lubricants). Itis also reported to be a semiconductor (qv). 

SoHd lubricants ate added to help control high friction characteristics in high speed or heavy-duty appHcations where high temperatures are generated. Molybdenum disulfide [1317-33-5] M0S2, may be used alone or in a complex compound formed by grinding with fine natural graphite, and zinc sulfide [1314-98-3] ZnS. Other compounds include calcium fluoride, cryoHte [15096-52-3] Na AlF, rare-earth oxides, and metal sulfides, eg, iron, antimony, or zinc (see LUBRICATION AND LUBRICANTS). 

A number ot aryl trifluoromethyl ethers are synthesized by fluormation of aryl chlorothioformates with molybdenum hexafluoride. The reagents are progressively heated from -25 to 130 C, and the products are distilled off. Molybdenum disulfide and carbon disulfide are the by-products [12] (equation 16)... 

Secondary lithium-metal batteries which have a lithium-metal anode are attractive because their energy density is theoretically higher than that of lithium-ion batteries. Lithium-molybdenum disulfide batteries were the world s first secondary cylindrical lithium—metal batteries. However, the batteries were recalled in 1989 because of an overheating defect. Lithium-manganese dioxide batteries are the only secondary cylindrical lithium—metal batteries which are manufactured at present. Lithium-vanadium oxide batteries are being researched and developed. Furthermore, electrolytes, electrolyte additives and lithium surface treatments are being studied to improve safety and recharge-ability. 

Molybdenum disulfide (M0S2) and tungsten diselenide ( VSe2) are used for their excellent dry lubricant properties. 

Carbon monofluoride has found use as a lubricant. Studies by Fusaro and Sliney FI, F2) and Gisser (G2) showed that carbon monofluoride is superior to molybdenum disulfide under many conditions. Grafting of monomers can further improve lubricity (B4). Electrochemical applications are discussed later. 

Miyake, S., Sekine, Y., Noshiro, J., and Watanabe, S., Low-Friction and Long-Life Solid Lubricant Films Structured of Nanoperiod Tungsten Disulfide and Molybdenum Disulfide Multilayer, Jpn. J. Appl. Rhys., Vol. 43, 2004, pp. 4338-4343. 

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