Q1: Galvanic corrosion

ANS:A - occurs in a bimetal couple.

Galvanic corrosion occurs in a bimetal couple. Explanation:

1. Galvanic Corrosion: Galvanic corrosion, also known as bimetallic corrosion, is an electrochemical process that occurs when two different metals are in electrical contact with each other in the presence of an electrolyte, such as moisture or an aqueous solution. In this process, one metal acts as the anode (the more reactive metal) and undergoes corrosion, while the other metal acts as the cathode and is protected from corrosion.
2. Bimetal Couple: Galvanic corrosion specifically occurs in a bimetal couple, which refers to two different metals that are electrically connected or in contact with each other. The potential difference between the two metals in the couple leads to the flow of electric current, causing corrosion of the more reactive metal.
3. Examples of Galvanic Corrosion:
   • A common example of galvanic corrosion is the corrosion of iron nails or screws when they are used to fasten copper or aluminum components. In this scenario, iron acts as the anode, while copper or aluminum acts as the cathode.
   • Galvanic corrosion can also occur in plumbing systems when dissimilar metals, such as copper pipes and galvanized steel fittings, are in contact with each other and exposed to water or moisture.
4. Caustic Embrittlement and Dezincification: Caustic embrittlement of boiler tubes and dezincification are specific types of corrosion phenomena but are not synonymous with galvanic corrosion.
   • Caustic Embrittlement: Caustic embrittlement is a form of stress corrosion cracking that occurs in boiler tubes subjected to high temperatures and caustic environments. It is caused by the combined effects of stress, temperature, and the presence of caustic agents in the boiler water.
   • Dezincification: Dezincification is a form of corrosion that specifically affects brass alloys containing zinc. It involves the selective removal of zinc from the alloy, leaving behind a porous copper structure. While dezincification can occur in plumbing systems where brass components are exposed to aggressive environments, it is not directly related to galvanic corrosion.

In summary, galvanic corrosion occurs in a bimetal couple when two different metals are in contact with each other and exposed to an electrolyte. It is a distinct corrosion mechanism from caustic embrittlement and dezincification, although these phenomena may occur in specific applications or environments.