Compounds Lubricant Additive Action

Systematic data on the relation between chemical structure or reactivity of chlorine compounds and lubricant additive performance are sparse. Table 11-11 gives some four-ball test data obtained by Mould, Silver and Syrett [35], with the additives listed in order of increasing effectiveness in terms of the wear/load index. The results show numerous departures from expectations based on chemical structure. For example, there is practically as much difference between the wear/load indices for the two primary chlorides, n-hexadecyl (16.2 kg) and n-hexyl (30.4 kg), as for n-hexyl chloride and t-butyl chloride (46.1 kg). A large difference would be expected on the basis of chemical reactivity between the additive effectiveness of primary and tertiary alkyl chlorides, but only a small difference for the two primary aliphatic chlorides. The overall trends are what would be expected in general, primary and aromatic chlorides are less efficacious than secondary chlorides, which in turn 

Additive Wear/load index, kg (a) Wear scar diameter, mm (b) 

1500 rpm one hour at 15 kg load. Additive furnishes 0.53% chlorine to the lubricant. Data by Mould, Silver and Syrett [35]. 

Some of the factors which complicate the interpretation of the four- 

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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. 

The work of Dorinson [63] on the relation between the basic chemistry and the additive action of sulfurized fatty materials deals with one of the most widely used multicomponent lubricant additives in industry. There are two aspects to the multicomponent nature of products of the sulfurization of ethenoid fatty esters. One is the consequence of the complexity of the sulfurization reaction, so that even if the starting material is a pure fatty ester, the ultimate sulfurized product is a mixture of several species. But the most important aspect of the structure of the sulfurized fatty product is the fact that even were it a single-component substance, it would still be intrinsically multifunctional. For instance, Dorinson [63] reported that the product of the sulfurization of methyl u-undecenoate can be shown to contain at least 50% of the following compounds ... 

Cooperative enhancement is not the only possibility in the interaction of multicomponent additive mixtures. Interference with the antiwear or antiscuff action of a lubricant additive by another component added to the compounded oil as a detergent or an anticorrosion agent is not an unusual experience in the commercial practice of lubrication. The bulk of the experience is empirical good basic studies of inhibition of antiwear or antiscuff functionality are rare. 

The quantitative model for an individual case cannot be divorced from the nature of the particular additive used however, the general principles of wear can be combined with those of additive action to give an acceptable treatment of wear in the presence of compounded lubricants. In Chapters 10 and 11 additive action was shown to fall into two broad categories (a) an interposed film laid down by adsorption or deposition... 

An important aspect of the function of compounded lubricants is to increase the load that can be carried by machinery without catastrophic damage to the rubbing components. Since the typical antiwear additives affect the viscosity of the carrier oil very little, it is not a fluid film effect that is responsible for the load-carrying augmentation. Examination of the various basic wear processes leads to the choice of the adhesive mechanism as the one most likely to respond to the action of boundary or extreme-pressure additives. The type of macroscopically observed severe wear which has this mechanistic process as its primary cause is generally designated as icu i ng (c(S. Chapter 13, Sections 13.4 and 13.6), and it is in this sense, as a description rather than a definition, that the term scuffing is used in the discussion to follow. 

Nitrosoamines or nitrasamines are derivatives of amines, containing V-nitroso groups ( N—N=0)- Typically, a nitrosamine is formed by the reaction of an amine with a nitrite. These substances are also produced by the action of nitrate-reducing bacteria. Nitrosoamines occur in trace quantities in tobacco smoke, processed food, meat products, and salted fish. Many nitrosoamines are used as gasoline and lubricant additives, antioxidants, stabilizers, and softeners for copolymers. These compounds are noncombustible liquids or solids at ambient temperature. The hazardous properties of nitrosoamines are different from those of their parent aliphatic or aromatic amines. 

A combined addition of a chain-breaking inhibitor and a hydroperoxide-breaking substance is widely used to induce a more efficient inhibition of oxidative processes in polyalkenes, rubbers, lubricants, and other materials [3 8]. Kennerly and Patterson [12] were the first to study the combined action of a mixture, phenol (aromatic amine) + zinc dithiophosphate, on the oxidation of mineral oil. Various phenols and aromatic amines can well serve as peroxyl radical scavengers (see Chapter 15), while arylphosphites, thiopropionic ethers, dialkylthio-propionates, zinc and nickel thiophosphates, and other compounds are used to break down hydroperoxide (see Chapter 17). Efficient inhibitory blends are usually prepared empirically, by choosing such blend compositions that induce maximal inhibitory periods [13],... 

Moreover, European regulations in 2005 restricted the sulfur content in diesel fuel to SOmgkg. Sulfur organic compounds are known to provide diesel fuel with a lubricity that will disappear as the regulations take effect. Addition of biodiesel at a level of 1-2% to diesel blends has the effect of restoring lubricity through an antiwear action on engine injection systems, which is specific for polar molecules. 

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