SAMPLE PREPARATION AND ETCHANTS

Preparation of test specimen

1. Clean the specimen to remove any scale/ pit or foreign material that might crush or flow under test pressure and so affect the result.
2. Polish the tested surface with Alumina Surry to ensure the surface condition of the specimen before etching

Procedure of etching

1. Differential the material of the specimen
2. Refer to Table 1 to check what kind of etchant should be used for etching.
3. Correct handling of chemicals.
4. After preparing the etchant, place or fix the specimen securely by a tong special for etching.
5. Immerse the specimen into the etchant by the duration of etching which is specified for certain material or purpose.
6. Adjust the duration of etching until a clear microstructure has been observed.

Etchants for general purpose

Table 1. Etchants for different type of materials

Material	Etchant	Duration (s)
Tool steel Oil hardened steel Carbon steel Wrought irons	2-10% Nital 2-10% by volume of conc. HNO3 in ethanol	10-15s or until the surface becomes a silvery color
Stainless steel	Mix 50mL HCl, 25mL HNO3, 25mL of distil water	40-60s
Pure Zinc, Impure Zinc	50% conc. HCl acid	5-30s
Copper alloys	Alcoholic ferric chloride 5gm FeCl3, 2mL HCl, 95mL ethanol or Ammonia/ Hydrogen peroxide 1 part NH4OH, 1 part H2O2 3%, 2 parts distil water	60-90s
		5-20s or until surface is noticeably darkened
Aluminum alloys	Mixed acid reagent 95 mL Water, 1.5mL HCl, 2.5mL HNO3, 0.5mL HF 48%	15-.20s