Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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RoHS verification
2006
My company is attempting due diligence for RoHS verification but we recognize that we have no clue about conversion coating. How do I tell if the below process leads to a RoHS compliant treatment? What makes a process yield Hex Chromate vs Trivalent Chromate.
1. Polishing
2. Degreasing
3. Acid etching (3% HCL, 50~60s)
4. Chemical oxidation™umaterials : Chromia (CrO3),Boric acid
(H3BO3),Phosphoric acid (H3PO4),Ammonium Bifluoric(NH4HF2),Diammonium Phosphate ((NH4)2HPO4) ™v
5. DI Rinse (PH value = 5.5~8.0)
6. Drying (temperature 90™³;times 10min)
- Warren, New Jersey
2006
That conversion coating is unlikely to be compliant, Joseph. If you balance the oxidation states of CrO3, while recognizing that the oxidation state of oxygen is usually -2, the chromium must be +6 or hexavalent. Presumably the substrate is aluminum? I urge you to consider contacting a supplier of proprietary conversion coating chemistry, as you may find it very difficult to home-brew an acceptable trivalent chromate conversion chemistry.
Although it is possible to do chrome electroplating from a hexavalent plating solution and end up with RoHS-compliant chrome in metallic form, if one uses hexavalent chrome in a conversion coating process, the parts will have a hexavalent chromium conversion coating on them.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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