Lubricant additive action

LUBRICANT ADDITIVE ACTION. I. BASIC CATEGORIES AND MECHANISMS... 

However, in a rigorous discussion of chemisorbed films and their role in lubricant additive action we must be more precise. A chemical reaction cannot be specified without specifying the reactants. In the case of metals in ordinary ambient surroundings, we must consider as pos-... 

The concept of the interaction film in lubricant additive action is based on the postulate that material in the rubbing surface and the additive both contribute to the formation of the film by extensive chemical reaction with each other. The additives contain characteristic elements l. g. sulfur, chlorine, phosphorus) in characteristic chemical structures. The material in the rubbing surface is usually metallic iron is the metal most frequently encountered in technological practice. 

R. M. Matveevsky [56] discussed the influence of temperature on lubricant additive action in terms of whether the additive functions by an adsorption/desorption mechanism or by a chemical reaction mechanism. If the additive is a blend of two components, one of which acts via adsorption and the other by reaction, and if the critical temperature of desorption is lower than the temperature at which the rate of chemical reaction of the other additive will contribute substantially to the lubrication process, then the critical desorption temperature will control lubricant failure. Thus, if the load induces frictional heating at the rubbing interface so that the conjunction temperature exceeds the critical desorption temperature, this will be the critical failure load. But if the surface exposed by desorption of the first additive reacts with the second additive at the temperature prevailing there, the failure load will be raised. Cameron and his co-workers [48, 57] used these concepts, although not as explicitly proposed by Matveevsky, to explain the behavior of multicomponent compounded lubricants containing dibenzyl disulfide and a commercial calcium petroleum sulfonate as the additives. The failure temperature characteristic of the calcium sulfonate as the sole additive was 468 K (195 C), whereas failure with dibenzyl disulfide was observed at 543 K (270 C). With the two-component additive, incipient failure began at ca. 473-493 K, which seems to mark a balance between desorption of the sulfonate and chemical reaction of the disulfide. As the temperature increased above 493 K, the reactivity of the disulfide became more apparent and the coefficient of friction decreased, until at 543 K, the temperature observed for the failure of the disulfide alone, the rubbing pieces scuffed. 

---