Metallographic Ceramic Etchants
The anti-corrosive properties of most ceramics make them difficult to etch by standard metallographic etching techniques. Most useful etching techniques for ceramics include: thermal, molten salt and plasma etching. A good resouce for additional etchants can be found with the etchant database provided by PACE Technologies:
CAUTION: Safety is very important when etching. Be sure to wear the appropriate protective clothing and observe all WARNINGS on chemical manufacuters SDS (Safety Data Sheets). Also review the COMMENTS and CONDITIONS Section for each etchant.
Sample Preparation:
Engineering ceramics are very hard, therefore specimen preparation procedures generally use a CMP (chemical mechanical polishing) component to remove induced microstructural damage.
Recommended Etchants
Oxide Ceramics (e.g alumina, zirconia, etc.)
| Etchant | Conc. | Conditions | Comments |
|---|---|---|---|
| Thermal etching in air |
|
Minutes to hours at 100-200°C below the sintering temperature |
AL2O3,
Al2O3-MgO |
|
Molten Salt
Potassium hydrogen fluoride melt |
|
5-10 minutes in Pt crucible |
Al2O3,
Al2SiO5 |
|
Distilled water
Phosphoric acid |
15 ml
85 ml |
Boiling for 5 minutes to 2 hours |
Al2O3 |
|
Distilled water
Sulfuric acid |
50 ml
50 ml |
Boiling for 1-5 minutes | ZrO2 |
Carbide Ceramics (e.g silicon carbide, tungsten carbide)
| Etchant | Conc. | Conditions | Comments |
|---|---|---|---|
|
Molten Salt
Sodium or potassium bicarbonate melt |
| 10 minutes in Pt crucible | SiC |
|
Hydrochloric acid
Hydrogen peroxide (30%) |
10 ml
10 ml |
Seconds to minutes | WC |
Nitride Ceramics (e.g. silicon nitride)
| Etchant | Conc. | Conditions | Comments |
|---|---|---|---|
|
Thermal etching in high purity nitrogen |
|
Several hours at 1600° C |
Si3N4 |
|
Molten Salt
Potassium hydroxide melt |
|
Seconds to minutes in Pt crucible |
>Si3N4
|
| Hydrofluoric acid |
100% |
10-15 minutes | Si3N4 |
Boride Ceramics (e.g. zirconium boride, titanium boride)
| Etchant | Conc. | Conditions | Comments |
|---|---|---|---|
|
Latic acid
Nitric acid Hydrofluoric acid |
30 ml
10 ml 10 ml |
Seconds to minutes | ZrB2 ,TiB2 |
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