Additives for Corrosion Inhibition

In 2002, Ube Indnstries, Ltd. discovered that adding small quantities of dinitriles (such as adiponitrile (161)) to electrolytes reduces the corrosion of metal parts of the battery, snch as the battery container and the electrodes [36]. 

Subsequently, demand increased abruptly, and various electrolytes mixed with small quantities of dinitriles and other additives were discovered from 2004 onward. For example, in 2004, LG Chem Ltd. discovered that compounds such as succinonitrile (162) and sebaconitrile (163) can be combined with compounds such as 2-fluorotolu-ene (164) and 3-fluorotoluene (165) [150]. In the same year, Samsung SDI discovered that succinonitrile (162) is effective for protecting Cu current collector [151]. 

1 Nitrogen-Containing (Imide Anion) Lithium Salts 

In 1986, Hydro-Quebec discovered lithium salts containing imide anions, such as lithium bis(trifluoromethanesulfonyl)imide (166) [154]. 

In 1998, Chemetall GmbH found lithium bis(oxalato)borate (170) [158]. 

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These are the roles of additives for corrosion inhibition and the modification of electrodeposits. For electrode reactions where the overall sequence includes chemical steps, however, the role of the adsorbate layer may be quite different. Rather it may be to create an environment which is more favourable than the bulk solution for a particular reaction. For example, the proton availability may be different it is not unusual for an adsorbate layer to be relatively aprotic compared with an aqueous electrolyte and such modifications of electrode processes have been used in the following. 

In this section, we present additives for wettability improvement, additives for corrosion inhibition, and lithium salts. 

Calcium nitrate is used in explosives, matches and pyrotechnics. Other applications are in the manufacture of incandescent mantle and as an additive to diesel fuel for corrosion inhibition. 

Control of fouling because of corrosion is possible by the employment of additives. For corrosion to occur, all the elements of the electrochemical circuit must be complete, so that an imposed electrical barrier in the circuit prevents the movement of ions and electrons, which is fundamental to the fouling mechanism. A thin layer of metal oxide can act as such a barrier, provided that the layer is continuous. The protective layer is itself a product of limited corrosion, its presence inhibiting further attack. 

Of the 120 million market for corrosion-inhibiting additives, 90 million is spent on an additive that is used for 560 billion liters (150 billion gallons) of motor fuel (both gasoline and diesel). The consumption of gasoline is growing at a slow rate because of a steady increase in fuel-efficiency of automobiles since the early 1980s. 

The third circuit (Fig. 7.25c) has been proposed to describe EIS results containing two relaxation time constants. Such behavior is commonly encountered for corrosion under coatings or under scale, for corrosion-inhibited systems, or even for localized corrosion. The meaning of the circuit elements in Fig. 7.25c will vary with the physical systems represented, but their significance has been validated through additional measurements and calculations. Figure 7.30 illustrates the model circuit in Fig. 7.25c with simulated data obtained with Rs = 10 fi, = 40 kfl, and Qi = 40 piF with exponent ra = 1, i 2 = 20 kfi, and Q2 = 20 p-F with exponent n = 1. Figure 7.31 is a Bode representation of the same data illustrated in Fig. 7.30 in complex-plane format. 

Surface-modified nanoparticles are good candidates for corrosion-inhibiting additives. Nanoparticles have high smface areas (high loadings of organic corrosion inhibitors) and novel surface ehemistries (enhanced chemical reactivity) and offer multiple properly enhancements without trade-offs. However, there are also some praetieal limitations to the use of nanopartioles as corrosion inhibitors. These inelude eost (paints are a conunodity product), accessible surface chemistry (one needs to tether the eorrosion inhibitor to the nanopartiele surface) and a release meehanism. 

Oil field uses are primarily imidazolines for surfactant and corrosion inhibition (see Petroleum). Besides the lubrication market for metal salts, the miscellaneous market is comprised of free acids used ia concrete additives, motor oil lubricants, and asphalt-paving applications (47) (see Asphalt Lubrication AND lubricants). Naphthenic acid has also been studied ia ore flotation for recovery of rare-earth metals (48) (see Flotation Lanthanides). 

Cyclohexylamine is miscible with water, with which it forms an azeotrope (55.8% H2O) at 96.4°C, making it especially suitable for low pressure steam systems in which it acts as a protective film-former in addition to being a neutralizing amine. Nearly two-thirds of 1989 U.S. production of 5000 —6000 t/yr cyclohexylamine serviced this appHcation (69). Carbon dioxide corrosion is inhibited by deposition of nonwettable film on metal (70). In high pressure systems CHA is chemically more stable than morpholine [110-91-8] (71). A primary amine, CHA does not directiy generate nitrosamine upon nitrite exposure as does morpholine. CHA is used for corrosion inhibitor radiator alcohol solutions, also in paper- and metal-coating industries for moisture and oxidation protection. 

Petroleum sulfonates are widely used as solubilizers, dispersants (qv), emulsifiers, and corrosion inhibitors (see Corrosion and corrosion inhibitors). More recentiy, they have emerged as the principal surfactant associated with expanding operations in enhanced oil recovery (66). Alkaline-earth salts of petroleum sulfonates are used in large volumes as additives in lubricating fluids for sludge dispersion, detergency, corrosion inhibition, and micellar solubilization of water. The chemistry and properties of petroleum sulfonates have been described (67,68). Principal U.S. manufacturers include Exxon and Shell, which produce natural petroleum sulfonates, and Pilot, which produces synthetics. 

Corrosion Inhibition. Another important property of antifreeze solutions is the corrosion protection they provide. Most cooling systems contain varied materials of constmction including multiple metals, elastomeric materials, and rigid polymeric materials. The antifreeze chosen must contain corrosion inhibitors that are compatible with all the materials in a system. Additionally, the fluid and its corrosion inhibitor package must be suitable for the operating temperatures and conditions of the system. 

Other dimer acid markets include intermediates for nitriles, amines and diisocyanates. Dimers are also used in polyurethanes, in corrosion inhibition uses other than for downweU equipment, as a "mildness" additive for metal-working lubricants, and in fiber glass manufacture. 

With the exception of coupling agent technology, primers for structural adhesive bonding have received little theoretical treatment in the literature beyond a discussion of mechanisms of corrosion inhibition by primer additives and limited discussion about statistical techniques for primer formulation. Perhaps because of the much more widespread use and greater economic importance of corrosion-protective coatings, the design and function of primers for these systems have... 

Literature Recent additions to the literature on the principles and practice of inhibition include books concerned with the subject as a whole, and reports of conferences and papers, or reports concentrating on particular aspects of the subject. Books include the volume by the late Professor I. L. Rozenfel d and collected data in the form of references, patents etc. from various sources Conferences include the recent quinquennial events at the University of Ferrara S, each providing substantial contributions to all aspects of corrosion inhibition. The uses of molybdates as inhibitors have been reviewed by Vukasovich and Farr in a paper with 221 references and test methods for inhibitors in a report from the European Federation of Corrosion with 49 references . 

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. 

Other common poly glycol-based antifoams include certain derivatives of polyethylene glycol (PEG), which are condensation polymers of ethylene glycol. An example is polyethylene glycol-8 dioleate. Apart from its antifoam properties, PEG-8 dioleate is also used in cooling water inhibitor formulations as a surface cleaner, in the formation of a corrosion-inhibiting surface film. Additionally, it is employed as an oil-soluble emulsifier for other defoamer chemistries. 

The mechanism of developing corrosion protective properties in an inorganic coating principally consists of forming insoluble oxides on the netal surface. Additionally, oxides must have certain corrosion inhibition (redox) properties which can protect the nnetal substrate from corrosive species like Cl and 804 . In the case of chromate conversion coating, OCC, the oxides of aluminum and chromium have been responsible for their corrosion inhibitive properties which were derived from their soluble and insoluble portions of the... 

Nitroaromatic compounds (NACs) are one of the widespread contaminants in the environments. Sources of NACs are numerous they originate from insecticides, herbicides, explosives, pharmaceuticals, feedstock, and chemicals for dyes (Agrawal and Tratnyek, 1996). Under anaerobic conditions, the dominant action is nitro reduction by zero-valent iron to the amine. Other pathways do exist, such as the formation of azo and azoxy compounds, which is followed by the reduction of azo compounds to form amines. Also, in addition to the possibility of azo and azoxy compounds, phenylhydrox-ylamine may be an additional intermediate (Agrawal and Tratnyek, 1996). Nitrobenzene reduction forms the amine aniline. Known for its corrosion inhibition properties, aniline cannot be further reduced by iron. Additionally, it interferes with the mass transport of the contaminant to the surface of the iron. The overall reaction is as follows ... 

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