Lubricants extreme pressure additives

The role of anti-wear and extreme-pressure additives is to create a solid lubricant at the interface of the metal by chemical reaction. 

In the other market areas, lead naphthenates are used on a limited basis in extreme pressure additives for lubricating oils and greases. Sodium and potassium naphthenates are used in emulsiftable oils, where they have the advantage over fatty acid soaps of having improved disinfectant properties. Catalyst uses include cobalt naphthenate as a cross-linking catalyst in adhesives (52) and manganese naphthenate as an oxidation catalyst (35). Metal naphthenates are also being used in the hydroconversion of heavy petroleum fractions (53,54) and bitumens (55). 

In the lightening of petroleum hydrocarbon oil, esters of mercaptocarboxyhc acids can modify radical behavior during the distillation step (58). Thioesters of dialkanol and trialkanolamine have been found to be effective multihinctional antiwear additives for lubricants and fuels (59). Alkanolamine salts of dithiodipropionic acid [1119-62-6] are available as water-soluble extreme pressure additives in lubricants (60). 

Minor and potential new uses include flue-gas desulfurization (44,45), silver-cleaning formulations (46), thermal-energy storage (47), cyanide antidote (48), cement additive (49), aluminum-etching solutions (50), removal of nitrogen dioxide from flue gas (51), concrete-set accelerator (52), stabilizer for acrylamide polymers (53), extreme pressure additives for lubricants (54), multiple-use heating pads (55), in soap and shampoo compositions (56), and as a flame retardant in polycarbonate compositions (57). Moreover, precious metals can be recovered from difficult ores using thiosulfates (58). Use of thiosulfates avoids the environmentally hazardous cyanides. 

Chlorinated paraffins are versatile materials and are used in widely differing appHcations. As cost-effective plasticizers, they are employed in plastics particularly PVC, mbbers, surface coatings, adhesives, and sealants. Where required they impart the additional features of fire retardance, and chemical and water resistance. In conjunction with antimony trioxide, they constitute one of the most cost-effective fire-retardant systems for polymeric materials, textiles, surface coatings, and paper products. Chlorinated paraffins are also employed as components in fat Hquors used in the leather industry, as extreme pressure additives in metal-working lubricants, and as solvents in carbonless copying paper. 

Metalworking fluids contain mineral oils (refer to p. 80) or synthetic lubricants they are used neat or in admixture with water. They may contain small amounts of biocides, stabilizers, emulsifiers, coiTosion inhibitors, fragrances and extreme pressure additives. The formulations render them suitable for application to metal being worked, generally from a recirculatory system, to provide lubrication, corrosion protection, swarf removal and cooling of the tool and machined surface. 

The performance of soluble oils is made possible not only by their high specific heat and thermal conductivity but by their low viscosity, which permits good penetration into the very fine clearances around the cutting zone. Consequently, these fluids are used mainly where cooling is the primary requirement. Lubricating properties can be improved by polar additives, which are agents that enhance the oiliness or anti-friction characteristics. Further improvements can be effected by EP (extreme-pressure) additives, which are usually compounds of sulfur or chlorine. 

METALWORKING FLUID Eluid applied to a tool and workpiece to cool, lubricate, carry away particles of waste and provide corrosion protection. Generally comprising neat mineral oils, or water-based materials, or a mixture of the two. Eluids may also contain emulsifiers, stabilizers, biocides, corrosion inhibitors, fragrances and extreme pressure additives. 

These are true chemical solutions and are mixtures of soluble polyglycols (to give lubricity), corrosion inhibitors and water soluble extreme pressure additives. They are subject to attack by micro-organisms and as a consequence, they are often formulated with one or more preservatives. 

Extreme pressure additives Chlorinated paraffins Lubricity agents... 

The ability of lubricating oil to reduce wear and prevent damage of interacting solids is the crucial factor controlling lubricant formulations. Chemical reactions of lubricant components, especially of so-called antiwear and extreme-pressure additives, occur during friction. These reactions involve the formation of a film on the contact surface. The film alters the surface s character and thus protects it. 

Under these temperature and pressure conditions, extreme-pressure additives in the residual film chemically react with the metal surfaces to form a surface coating that allows metal-to-metal contact without causing any scuffing or wear. This surface coating acts like a solid lubricant and, hopefully, provides needed lubrication under these conditions. 

The model explains many lubrication phenomena in which antiwear and extreme-pressure additives are involved. It spurs the design of new additives and lubricating compositions. 

X-ray Photoelectron Spectroscopy (XPS) tests were conducted on surfaces lubricated with a sulfur-containing extreme pressure additive, dibenzyl sulfide (Baldwin, 1976 Bird and Galvin, 1976). The films can arise from the use of additives that contain sulfur, phosphorus, chlorine, bromine, or boron and the differences in reactivity are affected by the formation of protective layers. Triboinduced electrons are said to activate the formation of iron halides, iron phosphates and iron sulfides (Dorison and Ludema, 1985 Grunberg, 1966 Kajdas, 2001 McFadden et al., 1998 ). When a chemical reaction takes place, e.g., oxygen interacts with aluminum to form aluminum oxide, a large oxygen peak is seen at approximately 500 eV in the Auger electron spectra (Benndorf et al., 1977 Nakayama et al., 1995). 

Lubricants containing chlorinated hydrocarbons are typically used as antiseizure additives in the metalworking industry. Some chlorine-containing hydrocarbons function by producing iron chloride on the metal surface (Kotvis et al., 1991). The correlation between chemical reactivity and load carrying capacity of oil containing extreme pressure additives can be assumed to be as follows ... 

The differences in antiwear properties of disulfides are related to their ability to be physisorbed about 100 to 1000 times faster than monosulfide on metal surfaces. The differences can be explained in terms of the lower energy needed for the formation of the same number of RS" ions from disulfides (Kajdas,1994). The exposed metal surface is extremely reactive to lubricant components, especially antiwear and extreme-pressure additives resulting the formation of a film on the contact surface. The reaction of emitted electrons of low energy (1 to 4 eV) with molecules of oil additives adsorbed on the friction surface may lead to formation of negative ions and negative ion radicals. The investigator (Kajdas, 1994 and 1985) pointed out the indispensability of the metal oxide film on the rubbing surface from the viewpoint of the theory of sulfide film formation. 

Phosphate esters are widely used in metalworking and lubricants. A C12 h with 6 mol of ethylene oxide (diester) can be used as an emulsifier but also as an extreme pressure additive - it can reduce wear where there is high pressure metal to metal contact. PEs can also show corrosion inhibiting properties, as with petroleum sulphonates and the emulsifying power of PEs with low foam is used in agrochemical formulations. PEs can act as dispersants or hydrotropes in plant protection formulations, allowing the development of easy-to-handle and dilute formulations of both poorly miscible and insoluble herbicides. 

Haltner and Oliver found that several metallic sulphides brought about an improvement in the load-carrying capacity when mixed with molybdenum disulphide. The sulphides included stannic and stannous sulphides, lead sulphide, ferrous suiphide and cuprous and cupric sulphides, and in a standard test procedure there was up to a ten-fold increase in load-carrying capacity. They speculated that the action of the added sulphides was similar to that of extreme-pressure additives in liquid lubricants. This would imply the formation of some protective film on the substrate surface. Pardee later suggested that the effective mechanism was more likely to be oxidation inhibition. An alternative would seem to be the possibility that certain sulphides can act as an additional source of sulphur to form sulphide on the substrate surface, and thus improve adhesion of the molybdenum disulphide, as discussed in the previous chapter. 

The first large scale usage of PCAs began in 1932 when they were incorporated as extreme pressure additives in lubricants [5, 6]. Hardie [20] reported world consumption estimates of 38-50 kt/year in 1961, while in 1977, estimates were reported to be about 230 kt/year [12]. Global consumption estimates for 1993... 

See porpoise oil lubricant, synthetic extreme-pressure additive (2) lube oil additive. 

TPS 20 Di-tert-dodecyl trisulfide CAS 68425-15-0 EINECS 270-335-7 Pale yellow and slightly odorous liquid BP > 200°C (decomposition) d(20/4) = 0.95 Extreme pressure additive for lubricating and cutting oils... 

Synthetic shock loading Heavy or shock loading Heavy or use by most OEMs, especially at operating temperatures exceeding 82°C Preferred for shock loading Heavy or must contain extreme pressure additives Gear lubricant... 

API GL-I. Lubricants intended for manual transmissions operating under such mild conditions that straight petroleum or refined petroleum oil may be used satisfactorily. Oxidation and rust inhibitors, defoamers and pour point depressants may be used to improve the characteristics of these lubricants. Eriction modifiers and extreme pressure additives may not be used. 

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