Which one of the following is not true for anodizing process?
It makes aluminium corrosion resistant.
Metals like aluminium, titanium and magnesium can be anodized.
Clean aluminium article is the anode and oxygen gas is evolved at the cathode.
It is used in aircraft industry.
Answer is Wrong!
Answer is Right!
This question was previously asked in
UPSC CDS-1 – 2023
A) It makes aluminium corrosion resistant. This is true. The artificially thickened oxide layer is more robust and protective than the natural oxide layer, providing enhanced corrosion resistance.
B) Metals like aluminium, titanium and magnesium can be anodized. This is true. These are common metals that form stable oxide layers and are frequently anodized.
C) Clean aluminium article is the anode and oxygen gas is evolved at the cathode. In the anodizing process, the aluminium article to be anodized is made the anode (positive electrode). Oxidation occurs at the anode, forming the oxide layer on the aluminium surface. The cathode (negative electrode) is typically an inert material like graphite or lead. At the cathode, reduction occurs, which involves the reduction of water to hydrogen gas and hydroxide ions ($2H_2O + 2e^- \rightarrow H_2 + 2OH^-$) or the reduction of H⁺ ions to hydrogen gas ($2H^+ + 2e^- \rightarrow H_2$). Oxygen gas is evolved at the *anode* if the process involves the electrolysis of water ($2H_2O \rightarrow O_2 + 4H^+ + 4e^-$) as part of the overall reaction, which contributes to the oxide layer formation ($2Al + 3H_2O \rightarrow Al_2O_3 + 6H^+$). However, the primary anodic reaction is the formation of Al₂O₃. Oxygen gas evolution typically occurs at the cathode, especially if there are other species present, or as a side reaction. More accurately, hydrogen gas is evolved at the cathode. Therefore, the statement that oxygen gas is evolved at the cathode is *not* true.
D) It is used in aircraft industry. This is true. Anodizing is widely used in the aerospace industry to improve the corrosion resistance, wear resistance, and paint adhesion of aluminium alloys used in aircraft components.
The statement that is NOT true is C, specifically regarding oxygen evolution at the cathode.
– Anodizing enhances corrosion resistance, wear resistance, and allows for dyeing.
– Hydrogen gas is typically evolved at the cathode during anodizing.