Packing lubricant graphite

Table 9 Hsts the quantities and doUar values of natural graphite used in the United States in 1988—1989 by product groups (7,15). Refractories and cmcibles account for about half of the known use. Natural graphite has its next greatest use (ca 15%) in lubricants and packings, including expandable graphite.

MoS2 has a structure built of close-packed layers of sulfur atoms stacked to create trigonal prismatic interstices which are occupied by Mo atoms. The stacking is such as to permit easy slippage of alternate layers and thus MoS2 has mechanical properties (lubricity) similar to those of graphite. 

MoS is a black powder insoluble in most solvents. It crystallizes like graphite with hexagonal layer molecules MoSj infinitely extended in two dimensions (Figure 25.4). Within the layer the sulfur atoms are effectively close packed and the molybdenum atoms are situated in the octahedral holes. The layers are bound to each other by very weak van der Waals forces. Because of this the layers slip easily against each other and the sulfide has lubricant properties. It is an essential component in solid lubricants that can be used at much higher temperatures than conventional lubricants. They lubricate up to 350°C in air and 1200°C in vacuum or in an inert atmosphere. Molybdenum disulfide lubricants can also be suspended in special oils and used as lubricating aerosol sprays. 

---