Extreme pressure additives ZDDPs

Four-Ball Machine later to study the interaction between molybdenum disulphide and several anti-wear and extreme-pressure additives and detergent/dispersant additives in a mineral oil. Unfortunately these results are difficult to compare directly with those of Thorp because he only reported wear scar diameters at two load levels. He found that at high load (lOOON) with 1 % of molybdenum disulphide, the combination with a ZDDP gave a wear scar diameter higher than either additive separately, and comparable to that of the base oil, and he described this as an antagonistic effect between the two additives. 

The only RR-based antioxidants are reaction products of sulfur or phosphorus pentasulfide with - terpenes (ot-pinene), resin oils and unsaturated esters. Reaction of alcohols (Cg) with phoshorus pentasulfide, followed by a reaction with zinc oxide yields salts of dialkyl dithiophosphoric acid (ZDDP), which are widely used, not only as antioxidants but also as corrosion inhibitors and extreme-pressure additives. Longer-chain alcohols enhance oil solubility. 

The lubrication system is extremely complex. The mechanism of lubrication is partly dictated by the nature of interactions between the lubricant and the solid surface. Additives blended into lubricating oil formulations either adsorb onto the sliding surfaces, eg., fatty alcohols, fatty amines, amides, phosphoric acid esters (friction modifiers), or react with the surface, eg., ZDDP, MoDTC, MoDDP organic phosphates (extreme pressure). Some interactions affecting the surfaces of metals include adsorption, chemisorption, and tribochemical reactions-these form new compounds on the surface and lubrication by reaction products (Bhushan and Gupta, 1991 Briscoe et al., 1973 Briscoe and Evens, 1982 Heinicke, 1984 Hsu and Klaus, 1978 and 1979 Klaus and Tewksbury, 1987 Lansdown, 1990 Liston, 1993 McFadden et al., 1998 Studt, 1989). 

In the selection of an appropriate corrosion inhibitor, an important consideration is the problem of adverse competition with other additives designed to adsorb on the liquid-metal interface. Extreme pressure and/or antiwear agents compete for the same sites as the corrosion inhibitor. Eatty amines are good corrosion inhibitors in this type of environment. However, their adverse effect on the performance of ZDDP additives often prohibits their use. Half esters or amides of dodecylsuccinic acid, phosphate esters or thiophosphates are frequently employed. A combination of inhibitors is sometimes used, for example, fatty carboxylic acids or the dimer/trimer analogues of the unsaturated acids, e.g. oleic, used in conjunction with an amine such as an ethanolamine or alkyl amine, or amide such as alkyl imidazoline and sarcosines, Eig. 6.7. Shorter chain carboxylic acid and amines are used as volatile corrosion inhibitors. 

The Ui method permits a better understanding of the interactions observed between ZDDP (zinc dialkyldithiophosphates) additives and various mineral base oils [17]. This applies for the anti-wear (AW), extreme pressure (EP) and antioxidant functions of ZDDP. The viscosity of base oils was shown to be a factor controlling these relationships. The o method has also been found useful in showing the directions of the relationships. For the case when an observed change should be considered as a complex one, the influence of the tested medium on it may be expressed as a sum as follows ... 

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