Molybdenum dithiophosphate

Table 5.15. Protective tribofilm formation from degradation of molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate (MoDDP) and molybdenum amine-ester complex (MoAC) directly and in combination with ZDDPs or sulfur compounds...

The various types of compound and their mechanisms of action have been reviewed by Mitchell . He concluded that the question of the extent to which the molybdenum additives decompose to produce molybdenum disulphide, if at all, was not yet resolved and certainly depended on the type of compound and the operating conditions. There was little doubt that molybdenum dithiocarbamates form molybdenum disulphide, probably by decomposition at hot spots caused by asperity interactions. It was less certain that molybdenum dithiophosphates form molybdenum disulphide, although mixtures of zinc dialkyidithiophosphate and molybdenum complexes had been shown to do so . 

Formation of M0S2 single sheets inside the contact area has already explained friction-reducing properties of several additives the molybdenum dilhiocarbamate (MoDTC) and the molybdenum dithiophosphate (MoDTP) [58]. Grossioid et al. showed the presence of M0S2 sheets in a carbon matrix or a phosphate matrix, these sheets coming from the chemical decomposition of the molecule of additive. Only a few sheets are necessary to obtain low friction. With these two additives, a low coefficient of friction is obtained after only several minutes of test, which corresponds to the activation time of the additive [98]. Moreover, these additives are efficient only if they are thermally activated (70 °C), whereas IFs are efficient at ambient temperature. In the case of IF, low friction is obtained from the first cycles. 

The action of lubricant additives has been analysed under boundary lubrication on metal couples of Cr-bearing steel plates and cast iron pins in reciprocating mode using model oil systems. Tribological parameters have been measured in addition to analyses of the wear films lubricated with different oils base oil, oil+ZDDP (Zinc Dialkyldithiophosphate), oil+ZDDP plus addition of Ca-sulphonate detergent and oil+MoDTP (Molybdenum Dithiophosphate). 

R.Unnikrishnan, M.C.jain, A.K.Harinarayan, A.K.Mehta, Additive-additive interaction an XPS study of the effect of ZDDP an the A W/EP characteristics of Molybdenum based additives . Wear 252,240-249, 2002. Y.Yamamoto, S.Gondo, T.Kamakura, N.Tanaka, Frictional characteristics of molybdenum dithiophosphates . Wear, 112, 79-87, 1986. 

More recendy, molecular molybdenum-sulfur complexes and clusters have been used as soluble precursors for M0S2 in the formulation of lubricating oils for a variety of appHcations (70). Presumably, the oil-soluble molybdenum—sulfur-containing precursors decompose under shear, pressure, or temperature stress at the wear surface to give beneficial coatings. In several cases it has been shown that the soluble precursors are trifunctional in that they not only display antifriction properties, but have antiwear and antioxidant characteristics as weU. In most cases, the ligands for the Mo are of the 1,1-dithiolate type, including dithiocarbamates, dithiophosphates, and xanthates (55,71). 

Physical Form, brown to black oily liquid new mineral-based crankcase oil contains petrochemicals (straight-chain hydrocarbons, aromatic hydrocarbons, and polyaromatic hydrocarbons or PAH) plus stabilizers and detergents including zinc dithiophosphate, zinc diaryl or dialkyl dithiophosphates (ZTDP), calcium alkyl phenates, magnesium, sodium, and calcium sulfonates, tricresyl phosphates, molybdenum disulfide, heavy metal soaps, cadmium, and zinc. ... 

Mo(V) complex disproportionates as it dissociates to produce mononuclear Mo (IV) and Mo (VI). As Mo (IV) and Mo (VI) are directly interconvertible by an oxo transfer reaction, they are viable participants in catalytic cycles. A dinuclear Mo(V) species of this nature can thus supply either the oxidizing or reducing member of this couple and presents a mechanism by which molybdenum enzymes can channel reducing or oxidizing power. Several inorganic reactions have recently been explained using this scheme (80, 81). To date, however, Reaction 12 only applies when the ligand is a dithiocarbamate or dithiophosphate. Nevertheless, were there known dinuclear active sites in enzymes, this would be an important mechanism to consider. 

K Kubo, M Kibukawa, Y Shimakawa, Effect on friction of lubricants containing zinc dithiophosphate and organo-molybdenum compound I Mech E Conference Publictions (Institution of Mechanical Engineers), 1985, pp 121-131... 

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