Anti-corrosion additives

ANTI-CORROSIVE ADDITIVE - A lubricant additive to reduce corrosion. 

Jenkinson JR and Zaczek BJ, Anti-Corrosion Additives in Oil Fired Boilers. European Meeting, Corrosion by Hot Gases and Combustion Products, DACHEMA, Frankfurt, Germany, April 1965. 

Several salts of dialkylphosphorodithioic acids (Chapter 9.10) have applications as anti-wear and anti-corrosion additives to lubricating oils. Zinc salts of this kind, Zn[(RO)2PSS]2, R = hexyl, for example, are made by adding zinc oxide to the acid which is itself obtained from P4S,o and the appropriate alcohol (4.104). These zinc salts are believed to react with the metal surfaces of gears and moving engine parts to give smoother surfaces which have improved wear and corrosion resistance. 

Tank ruptured (2) Intensive corrosion of tank materia] Excessive pressure (4) Excessive temperature Butene is released, fire, explosion same as (2) same as (2) (b) No measures required since tank material is well suited and anti-corrosion additive is adequate (c) Check safety valve on the tank (d) Measure connected with TIAS adequate... 

Scheerder J, Breur R, Slaghek T, Holtman W, Vennik M, Ferrari G (2012) Exopolysaccharides (EPS) as anti-corrosive additives for coatings. Prog Org Coat 75 224-230... 

If, however, the cerinm salt is very solnble, this limits its ability to provide long-term corrosion inhibition. " It can also disrapt the stractirre of the gel or of the overlying paint layer. Organics snch as benzotriazole can also adversely affect the stability and barrier properties of hybrid gels, so this is not a phenomenon confined to inorganic anti-corrosion additives. 

Paints are complex formulations of polymeric binders with additives including anti-corrosion pigments, colors, plasticizers, ultraviolet absorbers, flame-retardant chemicals, etc. Almost all binders are organic materials such as resins based on epoxy, polyurethanes, alkyds, esters, chlorinated rubber and acrylics. The common inorganic binder is the silicate used in inorganic zinc silicate primer for steel. Specific formulations are available for application to aluminum and for galvanized steel substrates. 

Despite the introduction of new, improved methods of refining it has been necessary to enhance the performance of lubricants by the use of additives, either to reinforce existing qualities or to confer additional properties. Once additives were regarded with some suspicion —an oil that needed an additive was necessarily an inferior oil today they are an accepted feature of lubricants. Almost all quality lubricants on sale today contain one or more additives. An enormous range of additives are available for use in lubricants " , some produced by the oil companies and others provided by specialist manufacturers. Additives are usually named after their particular function, but many additives are multifunctional. Thus, an anti-wear additive may also protect a surface against corrosion. The main types of additives that can enhance the anti-corrosion behaviour of lubricants are listed in Table 2.22. 

Table 2.22 Additives that can enhance the anti-corrosion behaviour of lubricants...

The deposits formed in internal combustion engines by high-octane petrols may be classed as ashes they consist of mixtures of lead oxides, bromides and sulphates derived from the anti-knock additives and, of course, exert their main corrosive effect on the parts operating at the highest temperature the exhaust valves and the sparking-plug electrodes. 

There has been much activity in this field of corrosion inhibition in recent years which appears to have been prompted by health and safety requirements. As with engine coolants, the use of nitrites, particularly where amines may also be present, needs to be considered carefully. Nitrites have been widely used in cutting, grinding, penetrating, drawing and hydraulic oils. Suggested replacements for nitrites and/or amines make use, inter alia, of various borate compounds, e.g. monoalkanolamide borates. Molybdates have also been proposed in conjunction with other inhibitors, e.g. carbox-ylates, phosphates, etc . Water-based metalworking fluids usually contain other additives in addition to corrosion inhibitors, e.g. for hard-water stability, anti-foam, bactericidal proderties and so on. Thus, claims are made for oil-in-water emulsions with bactericidal and anti-corrosion properties. 

Enhanced anti-corrosion properties are also reportedly achieved by mill additions of lithium titanate, lithium aluminate or magnesium titanate to the host glass frit . 

These results must be treated with caution. ZDDP s are anti-wear additives, as well as anti-oxidants and corrosion inhibitors, but are not particularly effective in increasing load-carrying capacity, so that the comparison between the two additives in this case is not a very demanding one. On the other hand, the highest concentration of molybdenum disulphide used was only 1 %, well below the concentrations normally used for load-carrying performance, which would typically be greater than 5%. 

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