Inhibition anodic

Copper Corrosion Inhibitors. The most effective corrosion inhibitors for copper and its alloys are the aromatic triazoles, such as benzotriazole (BZT) and tolyltriazole (TTA). These compounds bond direcdy with cuprous oxide (CU2O) at the metal surface, forming a "chemisorbed" film. The plane of the triazole Hes parallel to the metal surface, thus each molecule covers a relatively large surface area. The exact mechanism of inhibition is unknown. Various studies indicate anodic inhibition, cathodic inhibition, or a combination of the two. Other studies indicate the formation of an insulating layer between the water surface and the metal surface. A recent study supports the idea of an electronic stabilization mechanism. The protective cuprous oxide layer is prevented from oxidizing to the nonprotective cupric oxide. This is an anodic mechanism. However, the triazole film exhibits some cathodic properties as well. 

A anodic inhibition, which prevents the reduction of the metal... 

A special kind of anodic film formation is called passivation and it is itself the best example of anodic protection. So important has passivation been over the years, and so puzzling its mechanism, that the subject (which implicitly presents anodic inhibition) will be treated in a separate section (12.4). 

One of the methods used in corrosion control is anodic inhibition. The method applies in particular to iron and its steels. The electrode is moved in the anodic direction (at first stimulating the corrosion rate), but soon an oxide film forms and reduces the dissolution current. There are certain types of oxide film, passive films, that are particularly protective. Indeed, such films are involved in the way metals preserve themselves in nature. There is much to be found out about these films (why they are so protective) and some of the material that allows us to understand them and their eventual breakdown by aggressive ions such as chloride, has been given in this chapter. 

Dichromate does not function as an anodic inhibitor during crevice propagation in these experiments. Dichromate is not expected to be an inhibitor at the applied potentials used here, but estimates of the potential drop place the bottom of the crevice at a potential ranging from -0.5 to -0.8 V. In this potential range, anodic inhibition might be expected, provided the chromate chloride ratio is sufficiently large. 

Overall, these results indicate that chromates inhibit corrosion by elevating the pitting potential on aluminum with respect to the corrosion potential, which decreases the probability for the formation of stable pits. In general a chromate chloride concentration ratio in excess of 0.1 is necessary to observe significant anodic inhibition. 

A Catalytic Mechanism of Anodic Inhibition in Metallic Corrosion... 

These ideas are shown to apply to other metals in addition to aluminum and explain a number of facts which are inconsistent with existing theories of anodic inhibition. 

Figure 3. Inhibition (top) cathodic inhibition (bottom) anodic inhibition...

Anodic inhibition of stress corrosion cracking was first provided on an industrial scale in a large plant for the production of hydrogen by electrolysis of potassium hydroxide solution. After preliminary trials on a laboratory scale, the chemical industry s first anodically protected large-scale plant, a sodium hydroxide solution evaporator with a capacity of 142 t, was put into operation in 1968. Since then, plants have been equipped in the same way (Grafen 1971). 

Inhibition is a method of corrosion protection by molecules that are adsorbed on the metal surface and reduce the rate of either metal dissolution (anodic inhibition) or the rate of the... 

More generally, acidic depolymerization products can be leached out of many films of paint, unless suitable pigments are incorporated. Zinc dust plus zinc oxide was the original acid scavenger. Zinc phosphate, zinc ferrite, and calcium borosilicate will each exert an anodic inhibitive function at pH values exceeding 7 while zinc chromate, zinc tetroxychromate, and strontium chromate act independently of pH value (Van Eijnsbergen, 1988). In general, the pH of aqueous paint film extracts should be between 7.5 and 8.5 and certainly not below 6 or above 10. 

Corrosion in neutral environments is most often due to the reaction of dissolved oxygen with the metal. The risk of attack is therefore considerably reduced if one limits the access of oxygen to the metal surface (cathodic inhibition). Alternatively, one can diminish the rate of corrosion by bringing about passivation of the metal (anodic inhibition). Corrosion can also be reduced by inhibitors that adsorb onto the surface and block the reactive sites. 

The corrosion potential of carbon steel is shifted in the anodic direction by the addition of HEDP due to the anodic inhibition effect of the phosphonate. In the presence of Zn " or Ca ", the corrosion potential tends to shift in the cathodic direction. By combined application of HEDP and or... 

Figure 2.2 Principle of anodic inhibition. When no anodic inhibitor has been added, the corrosion current (rate) is h. When an anodic inhibitor is added, the anodic potential is modified and rotates up so that the corrosion rate is reduced (I2)...

---