Corrosion protection inhibition

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. 

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. 

Additionally, crevice corrosion can be reduced by two techniques used successfully on most aqueous corrosion—chemical inhibition and cathodic protection. However, both these techniques may be cost prohibitive. 

Clean surfaces are almost always easier to protect chemically from corrosion. Chemical inhibition and inhibitors are often tested on relatively clean surfaces, for a variety of reasons. The effectiveness of almost all commonly used corrosion inhibitors increases as surface cleanliness improves. 

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... 

Epoxy based primer systems remain the best suited for the corrosion protection of magnesium. Cathodic epoxy electrophoretic paints , chromate inhibited epoxy-polyamide primers and high temperature stoving epoxy sealers are used to provide protection up to 180°C. For higher temperature applications up to 300°C, epoxy silicone or polyimide based systems can be used. 

Provide effective means of corrosion protection of components consistent with operational circumstances. This may involve cathodic protection, inhibition, coatings or combinations of these. 

One example is the use of rigid selfexpanding closed cell polyurethane foams as a method to inhibit corrosion of the interior surfaces of metal (steel, etc.) structural cavities exposed to seawater and moisture is one of many example of plastic providing corrosion protection. Unfilled metal cavities are a general feature of various structures or products used in the marine, building, electronics,... 

Adsorption versus Polymerization. It is instructive to examine further the time dependence of the corrosion inhibition. In acid corrosion inhibition tests, steady state is customarily assumed to be reached within 10 to 20 min after initial exposure of the metal specimen. Since the inhibitors function by reducing the available active surface area, we expect an increase in and a corresponding decrease in P. The degree of corrosion protection the inhibitor provides is given by... 

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... 

There is a large potential for conducting polymers as corrosion-inhibiting coatings. For instance, the corrosion protection ability of polyaniline is pH-dependent. At lower pH polyaniline-coated steel corrodes about 100 times more slowly than noncoated steel. By comparison, at a pH of about 7 the corrosion protection time is only twice for polyaniline-coated steel. Another area of application involves creation of solid state rechargeable batteries and electrochromic cells. Polyheterocycles have been cycled thousands of times with retention of over 50% of the electrochromic activity for some materials after 10,000 cycles. IR polarizers based on polyaniline have been shown to be as good as metal wire polarizers. 

The corrosion process can be inhibited by the addition of phosphate or polyphosphate ions [344], inorganic inhibitors as, for example, chromate ions [336], adsorbed alcohols [345], adsorbed amines, competing with anions for adsorption sites [339,] as well as saturated linear aliphatic mono-carboxylate anions, CH3(CH2)n-2COO , n = 7 — 11, [24]. In the latter case, the formation of the passive layer requires Pb oxidation to Pb + by dissolved oxygen and then precipitation of hardly soluble lead carboxylate on the metal surface. The corrosion protection can also be related to the hydrophobic character of carboxylate anions, which reduce the wetting of the metal surface. 

It is important not to leave the system empty of water for any long period, as rapid surface rusting will take place. As soon as the closed-loop system is declared free of contamination, sufficient corrosion inhibitor is added to provide long-term corrosion protection. The corrosion inhibitor is usually an anodic, passivating formulation, typically based on nitrite or tannin (and often in combination with phosphate, silicate, borate, or molybdate, etc.). Finally, after confirmation that the entire system is adequately treated (which usually requires the inhibited water in the system to be recirculated for a further 16 to 24 hours), the system is signed off and handed over. 

Inhibiting the corrosion of aluminum alloys by adding 1-5% of transition metals is a dramatic case of corrosion protection because of the small amounts of additives that are successful in reducing the corrosion rate by 1-2 orders of magnitude. It turns out that the alloying materials shift the pzc toward the positive side on the potential scale. Thus, in many practical situations, the alloys of the transition metals are in a... 

Recently, the mechanism of corrosion protection by soluble chromate inhibitors has been the subject of active research, which has attempted to understand and replicate its inhibiting functions with less toxic chemical substances. In this section, some recent findings on chromate corrosion inhibition are reviewed, particularly as they pertain to corrosion of light metals, with a focus on the use of techniques that are useful for studying mechanisms of inhibition. 

Using the HSAB principle, one can rationalize the corrosion inhibition of iron and aluminum by phosphate in which iron phosphate and aluminum phosphate are produced. Ferric and Al3+ are hard acids, and they react with phosphate, a hard inhibitor and give corrosion protection. Corrosion inhibition of Cu2+ and Zn2+ by amines can be rationalized by the formation of amine complexes of Cu2+ and Zn2+, and this is in accord with the principle that Cu2+ and Zn2+ are borderline acids reacting with amines which belong to borderline inhibitors. Corrosion protection of copper (soft acid) by mercapto-benzothiazole (soft inhibitor) is also in keeping with the HSAB principle. 

Corrosion protection by an inhibitive primer may be envisaged as shown in Figure 1.67. Inhibitive metal primers are designed with relatively high pigment volumes to allow sufficient water absorption to dissolve the passivating inhibitor and yet prevent aggressive ions such as chloride which interfere in the passive oxide formation process. 

Corrosion protection measures involve washing the metal object with reagents such as sodium sulfate or silicate, which form lead sulfate or lead silicate film. Whenever galvanic effects are envisaged use of insulation is recommended. Sodium silicate has been successfully used to inhibit release of lead from the solder in copper pipes carrying domestic water supplies. 

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