Kroll's Etchant
Kroll's Reagent
Material Specific
Composition
Hydrogen fluoride 1–5%, Nitric acid 4–8%
PACE product, by weight
Method
Swab
Time
3–15 s
Alternative Names
Tags
Reveals
Alpha and beta phases in titanium alloys (alpha light, beta dark); transformed beta colonies; grain boundaries; alpha-2 Ti3Al
Typical Results
The standard etchant for titanium alloys (CP-Ti, Ti-6Al-4V, Ti-5Al-2.5Sn, Ti-6242). Reveals alpha / beta distribution clearly. Standard composition: ~2 mL HF + ~6 mL HNO3 + 100 mL H2O. Also works on zirconium and Zircaloy.
Application Method
Method:Swab
Typical Time:3–15 s
Preparation Notes
PACE Kroll's Reagent is supplied ready-to-use. Composition (by weight):
| Ingredient | CAS No. | % | Hazardous |
|---|---|---|---|
| Hydrogen fluoride | 7664-39-3 | 1–5% | Yes |
| Nitric acid | 7697-37-2 | 4–8% | Yes |
| Water | 7732-18-5 | 90–95% | No |
Application Notes
Swab 3–15 s at room temperature. Do not immerse; HF over-attacks. Rinse copiously with cold water.
Troubleshooting
HF burns may be delayed; keep calcium gluconate gel on hand and treat any contact immediately. Use PE containers only; HF etches glass. Alpha-2 Ti3Al phase in Ti-6242 needs the longer end of the dwell.
Storage Notes
PE / PP bottle at room temperature, labeled with HF symbol. Stable many months.
Alternative Etchants
- Modified Kroll's Reagent
- Ti-AP-16 (attack-polish, different workflow)
Similar Etchants
- Modified Kroll's Reagent