Question

During metallography, Nital is the most commonly used for etching _____________.

• A. Bronze
• B. Brass
• C. Mild Steel
• D. Aluminium

Hint:

Nital is a nitric acid and alcohol mixture; it is the go-to etchant for revealing ferrite and pearlite in carbon and low alloy steels, not for copper alloys or aluminium.

Answer 1

The Correct Option is C

Step 1: Recall the purpose of etching in metallography.
After a metal sample is polished to a mirror finish, it still looks featureless under a microscope because all grains reflect light the same way. Etching uses a chemical reagent to attack the polished surface selectively, mainly along grain boundaries and different phases, so the microstructure (grains, phases, boundaries) becomes visible under the microscope.

Step 2: Recall what Nital is.
Nital is a mixture of nitric acid (\(\text{HNO}_3\)), typically 2 to 5 percent by volume, dissolved in ethanol or methanol. It is one of the simplest and most widely used etchants in a metallurgical laboratory.

Step 3: Recall which metals Nital is used on.
Nital attacks the ferrite phase boundaries and darkens pearlite in plain carbon and low alloy steels, which makes it the standard, go-to etchant for revealing ferrite, pearlite, martensite, and grain boundaries in mild steel and other carbon steels.

Step 4: Analyze the other options.
(A) Bronze: A copper-tin alloy, usually etched with reagents based on ferric chloride (\(\text{FeCl}_3\)) in acid, not Nital.
(B) Brass: A copper-zinc alloy, also typically etched with ferric chloride based reagents, not Nital.
(D) Aluminium: Usually etched with reagents such as Keller's reagent (a mix of hydrofluoric, hydrochloric, and nitric acids in water) or sodium hydroxide solution, not Nital.

Step 5: Final conclusion.
Nital is the standard etchant for revealing the microstructure of
\[ \boxed{\text{Mild Steel}} \]
Hence, the correct option is (C).