Etching
Etching is a process for revealing the structure of the material, common etching techniques include:
- Chemical
- Electrolytic
- Thermal
- Plasma
- Molten salt
- Magnetic
Common Etchants
There are a number of more common etching solutions. Several of them are listed in the folowing table.
The following table lists the most commonly used etchants
Etchant |
Composition |
Conc. |
Conditions |
Comments |
ASTM No. 30 |
Ammonia |
62.5 ml |
Mix Ammonia and water before adding peroxide. Must be used fresh. Swab 5-45 seconds |
For etching copper, copper alloys and copper-silver alloys. |
Kalling's No. 2 |
CuCl2 |
5 grams |
Immersion or swabbing etch at 20 degrees Celcius |
For etching duplex and 400 series stainless steels and Ni-Cu alloys and superalloys. |
Carpenters Stainless Steel Etch |
FeCl3 |
8.5 grams |
Immersion etching at 20 degrees Celcius |
For etching duplex and 300 series stainless steels. |
Kellers Etch |
Distilled water |
190 ml |
10-30 second immersion. Use only fresh etchant |
Excellent for aluminum and titanium alloys. |
Klemm's Reagent |
Sodium thiosulfate |
250 ml Saturated |
Etch for a few seconds to minutes | For etching alpha-beta brass, bonze, tin, cast iron phosphides, ferrite, martensite, retained austenite, zinc and steel temper embrittlement. |
Kroll’s Reagent |
Distilled water |
92 ml |
Swab specimen up to 20 seconds |
Excellent for titanium and alloys. |
Nital |
Ethanol |
100 ml |
Immersion up to a few minutes. |
Most common etchant for Fe, carbon and alloys steels and cast iron - Immerse sample up from seconds to minutes; Mn-Fe, MnNi, Mn-Cu, Mn-Co alloys. |
Marble's Reagent |
CuSO4 |
10 grams |
Immerse or swab for |
For etching Ni, Ni-Cu and Ni-Fe alloys and superalloys. Add a few drops of H2SO4 to increase activity. |
Murakami's |
K3Fe(CN)6 |
10 grams |
Pre-mix KOH and water before adding |
Cr and alloys (use fresh and immerse); iron and steels reveals carbides; Mo and alloys uses fresh and immerse; Ni-Cu alloys for alpha phases use at 75 Celcius; W and alloys use fresh and immerse; WC-Co and complex sintered carbides. |
Picral |
Ethanol |
100 ml |
Seconds to minutes |
Recommended for microstructures containing ferrite, carbide, pearlite, martensite and bainite. Also useful for magnetic alloys, cast iron, high alloy stainless steels and magnesium. |
Vilella’s Reagent |
Picric Acid |
1 gram |
Seconds to minutes |
Good for ferrite-carbide structures (tempered martensite) in iron and steel |
Guide to Acid Concentrations
Acid / Base |
Specific gravity |
Concentration |
|
Nitric (HNO3) |
1.4 |
68-70% |
Hydrofluoric (HF) |
- |
40% |
Hydrochloric (HCl) |
- |
37-38% |
|
Ammonium Hydroxide |
- |
35% |
Etchant Database CD
For more specific etchants, PACE Technologies offers an CD etchant database containing over 2200 etchants.
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| Metallographic etchant and training CD | ||
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| Etchant database search result | Metallographic training basics | |
ETCHING PRODUCT DESCRIPTIONS
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ETCHING / SPECIMEN PREPARATION |
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|
Description |
Quantity |
Catalog Number |
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|
Etchant / Specimen preparation CD |
each |
CD-ETCH |
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