Dear Vinooth Rajendran

A full corrosion process normally involves two half-proceses, the anodic oxidation of a metal and the cathodic reduction of species from the environment. In deaerated media, the most common cathodic reaction is the reduction of H+ to H2, while in aerated media the reduction of O2 to OH- is expected.

So, in the anodic sites there is a release of metal ions that, through hydrolysis, may form metal hydroxides, releasing H+ (with local decrease of pH), while in the cathodic sites the reductions of H+ to H2 or O2 to OH- will lead to local increase of pH.

One of the cases where the localised acidification at anodic sites is very important is pitting corrosion. In this case, the fact that oxidation proceeds inside the pit leads to the creation of a local environment with very low pH which is responsible for the autocatalytic growth of the pit.

On the contrary, if corrosion proceeds is a well mixed electrolyte, the contributions of the anodic process to pH decrease and of the cathodic process to pH increase may cancel, with no sensible change of pH.

Best regards

Dear Vinooth Rajendran . See the following useful RG link: Article Modeling of pH Distribution Over Corrosion Sites

Kindly see also the following useful link: https://hal-ifp.archives-ouvertes.fr/hal-02464447/document

Also check please the following useful link: https://www.materialsperformance.com/articles/cathodic-protection/2017/04/an-alternative-view-of-the-cathodic-protection-mechanism-on-buried-pipelines

Dear Vinooth Rajendran

As soon as H2O, O2, and corrosive ions (i.e. Na+ and Cl─) come in contact with the metal surface, the cathodic and anodic reactions begin, causing the formation of OH─ and Fe2+/Fe3+ ions. As a result of the interaction of hydroxyl radicals and Fe2+/Fe3+ions with Na+ and Cl─, the NaOH and various species of hydrated ferrite can be respectively formed, leading to the generation of high alkaline and/or low acidic environment in some specific zones of the metal substrate.

In this regard, I recommend you to read the following publications:

- Novel bi-functional RGO-HPSE-Zn@ epoxy nanocomposite with superior corrosion protection potency.

- Rational design of a novel multi-functional carbon-based nano-carrier based on multi-walled-CNT-oxide/polydopamine/chitosan for epoxy composite with robust pH-sensitive active anti-corrosion properties

- Metal-doped 2D rGO nano-sheets fabrication utilizing plant source bio-molecules and application in the epoxy anti-corrosive coating: Combined experimental and DFT-D modeling investigations

corrosion rate of carbon steel decreases with increasing pH value toward the alkaline end while increases with increasing AC current density. When the solution pH becomes highly alkaline, say, 12, passivation occurs on carbon steel surfaces, with an enlarging passive region as pH increases. However, it is worth noting that the passive film suffers from mechanical breakdown

The higher the concentration of H + ions in an acidic solution, the lower the pH. Carbonation induced corrosion will decrease pH.