Molybdenum sulfide films

The goal of lubrication is elimination of this wear and minimizing friction otherwise encountered in dry sliding. This is accompHshed ideally with complete separation of the mbbing surfaces with a full film of lubricant. When complete hill-film separation is impossible, surface chemical effects of a lubricating oil and its additives, or solid-film lubricants such as graphite and molybdenum sulfide, can assist. 

Although supported Pd catalysts have been the most extensively studied for butadiene hydrogenation, a number of other catalysts have also been the object of research studies. Some examples are Pd film catalysts, molybdenum sulfide, metal catalysts containing Fe, Co, Ni, Ru, Rh, Os, Ir, Pt, Cu, MgO, HCo(CN) on supports, and LaCoC Perovskite. There are many others (79—85). Studies on the weU-characteri2ed Mo(II) monomer and Mo(II) dimer on siUca carrier catalysts have shown wide variations not only in catalyst performance, but also of activation energies (86). 

The friction coefficient drops to a value below 0.05, characteristic of ultralow friction. This is a well known phenomenon encountered when using MoDDP additives in lubricating tests (Tung et al., 1988 Zheng et al., 1986). This demonstrates that the ultralow friction is mainly due to a tribochemical transformation of the solid reaction film. In the ASE spectrum analysis a molybdenum sulfide tribofilm formed on the wear scar showed a S Mo peak ratio near 9, which is in agreement with a pure MoS2 spectrum. 

Both XPS and Auger analyses were performed for tribofilm. The Auger results revealed higher concentration of Fe, Zn, Mg and P, but lower levels of carbon relative to XPS. Phosphorus is present in phosphate form and sulfur as sulfide in unmodified oil. The oil containing a soluble molybdenum friction modifier additive formed films which were thinner and less continuous than films formed from the unmodified oil. The film was dominated by magnesium phosphate which was identified by AES, and by the combination of XPS and IR. Sulfur was present as sulfate and sulfide while molybdenum was present as Mo+4 and Mo+6, as shown in Fig. 4.8 (Lindsay et al., 1993). 

Metal dithiocarbamates have been investigated as single-source precursors for MOCVD nanosized particles of metal sulfides, such as PtS and PdS,43 PbS,437,4 8 and Bi2S3,439 and tin sulfide thin films.440 In this respect the termochemistry of dithiocarbamates (periodically reviewed441 144) is important. Molybdenum dialkyldithiocarbamates are highly effective antiwear, antiseize, and antifriction additives for lubricating oils,445 and are used as vulcanization accelerators.446... 

The molybdenum neopentyUdene complex Mo(CHBu )(NR)(OBu )2 is the active catalyst used in a fascinating development for the synthesis of 11-Vt semiconductor clusters (ZnS, CdS, PbS) and silver and gold nanoclusters of predictable size within microdomains in films of block copolymers prepared by ROMP. Block copolymers of norbomene and a functionalized norbomene that wiU complex with a metal-containing compound were prepared and characterized as monodisperse materials. The functionalized component (amine, alkoxide, or thiolate) then sequestered the metal and the metallated block copolymer was cast into a film which was subsequently treated with H2S to convert the metal into the sulfide. The molybdenum complexes have also featured in the development of the synthesis of side-chain liquid crystal polymers by living ROMP.98 99... 

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