Technology Products Processes
About Us News Contact Us Search
Subject on This Issue:
* Steels & Properties
* Heat Treatment


Picture
 

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

 
Home | Last Issues | Feedback | Links
Copyright © 2006 TPP Information Centre.  All Rights Reserved.