Molybdenum lubricating material

A vast amount of information has been published on the testing of molybdenum disulphide materials for space use. It seems probable that most if not all American satellites and spacecraft have contained some application of molybdenum disulphide, and a number of space applications are listed in Table 1.1. A notable early example was its use on the extendible legs of the Apollo Lunar Module in 1969. Application of molybdenum disulphide in more conventional bearing systems is described in Chapters 9 to 13, but the wide variety of lubricant uses is shown in Table 1.2 by a list of applications not described in more detail elsewhere in the book. 

The compound occurs as the mineral molybdenite which after refining is also used as lubricating material. The principle of action of molybdenum sulfide is based on... 

It has been a dream for a tribologiest to create a motion with a super low friction or even no friction between two contact surfaces. In order to reduce friction, great efforts have been made to seek materials that can exhibit lower friction coefficients. It is well known that friction coefficients of high quality lubricants, e.g., polytetrafluoroethylene (PTFE), graphite, molybdenum disulphide (M0S2), etc., are hardly reduced below a limit of 0,01,... 

Molybdenum disulhde (M0S2), graphite, hexagonal boron nitride, and boric acid are examples of lamella materials commonly applied as solid lubricants. The self-lubricating nature of the materials results from the lamella crystalline structure that can shear easily to provide low friction. Some of these materials used to be added to oils and greases in powder forms to enhance their lubricity. Attention has been shifted in recent years to the production and use of nanosize particles of M0S2, WS2, and graphite to be dispersed in liquid lubricants, which yields substantial decreases in friction and wear. 

In tests of materials saturated with liq oxygen and subjected to 71-75 lb drop weight tests, the following were found acceptable (one de-tonation/40 impacts or none/20) fluorocarbon oils greases, graphite, halogenated biphenyl molybdenum disulfide lubricants, polyethylene... 

As the coefficient of friction can be reduced by the use of a lubricant, it is generally beneficial to use a suitable oil or grease when required. The addition of a modifier to the prepolymer itself must be done with care, as the material will reduce the overall properties including aging and may influence the bond ability of the material. Additives that have been employed in this application include molybdenum disulfide, graphite, and silicone oil. They must be used at the lowest level possible. 

Bullet jacket materials include gilding metal cupronickel cupronickel-coated steel nickel zinc-, chromium-, or copper-coated steel lacquered steel brass nickel- or chromium-plated brass copper bronze aluminum/alumi-num alloy Nylon (Nyclad), Teflon- and cadmium-coated steel (rare). Black Talon bullets have a black molybdenum disulfide coating over the metal bullet jacket which acts as a dry lubricant. Steel jackets are frequently coated both inside and outside as an anticorrosion measure. Gilding metal is by far the most common bullet jacket material. Tin is claimed to have lubricating properties and is sometimes incorporated in bullet jacket material. The alloy is known as Lubaloy or Nobaloy and contains 90% copper, 8% zinc, and 2% tin. 

The purpose of the study was to assess this material as a potential source for lubricant grade molybdenum disulphide, because of the steady increase in its use in lubricants. However, the total consumption for lubricant use represents less than 4% of the primary molybdenite production. It seems unlikely, therefore, that the demand will justify even the low quoted cost of upgrading the by-product material, except where the availability of the indigenous source is important. 

For effective solid lubrication, it is not enough to have a material with low internal or external friction. It is also necessary for it to form films with sufficient adhesion to a substrate, and internal cohesion, to withstand rubbing under high loads. Molybdenum disulphide has this ability to a very high degree. It can be made to adhere readily and firmly to a substrate, forming a strong, cohesive film. 

Molybdenum disulphide is intrinsically an excellent lubricant. No details exist about the way in which it was used in the distant past, but almost certainly it was first used as a free solid. While not deliberately mixed with any other material, it would have been fairly impure. In recent years it has become usual for it to be used in conjunction with other substances to improve some specific property or to overcome some specific problem. From such points of view as ease of application, re-supply, quality control, corrosion prevention or service life, there can be significant advantages in using it in combination with other materials. Nevertheless, there are still many situations for which its use unmixed with other substances can provide a satisfactory, or even optimum, solution. 

Similar materials were used by Skeldon et al to produce a self-lubricating surface film on aluminium. They first produced a porous alumina film on the surface by anodizing, and then re-anodized in an electrolyte containing 0.01 M ammonium tetrathiomolybdate. They then found that the pores of the primary anodized film contained mainly amorphous molybdenum trisulphide, and this was converted by vacuum annealing to hexagonal molybdenum disulphide. The film gave a marked improvement in wear resistance. 

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