Summary for trivalent passivates baking Discussion
trivalent passivates baking: Ted Mooney reports that five trivalent passivates were baked for one hour at 400 °F, then checked for hexavalent chromium using ISO 3613 Test Method 5.5 with Test Solution C (diphenylcarbazide). Four of the five samples tested positive, while a blank sample without passivate tested negative. The question is whether this is typical or an anomaly. In the excerpt, no one gives a direct explanation yet, but Ian MacMoy says ASTM B08 will be testing the issue and looking at whether the ASTM B850 hydrogen-embrittlement release bake-out can cause trivalent coatings to flip to hexavalent chromium, and at what rate. The thread therefore frames the result as a real concern under investigation rather than a settled conclusion.
We have done some work on baking trivalent passivates. (Many of you may have read our work on trivalent passivates, heard it at Sur/Fin 2009, or at least heard of it.) We tested five trivalent passivates. After passivating, we subjected them to one hour at 400 °F. We tested each surface for hexavalent chromium by the ISO 3613 Test Method 5.5 using ISO 3613 Test Solution C (diphenylcarbazide). Four of the five samples tested positive for hexavalent chromium. (We also tested a ‘blank’ – a sample with no passivate, which tested negative.) Are these results consistent with the results others have obtained or are they an anomaly?
Tom Rochester
CTO – Jackson, Michigan, USA
Plating Systems & Technologies, Inc.
June 23, 2009
! Well, this is an issue if I’m applying trivalent on bolting going to a REACH Nation that requires <.1% hexavalent chrome.
Ian MacMoy
Technical Authority – Houston,Texas
April 4, 2025
A. Indeed. Tom has long been concerned that the trivalent chromium conversion coating processes may not deliver as much of their vaunted freedom from hexavalent chromium as we think.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
 | It has been 18 years since my seminal work on this issue. There are a number of ways to respond constructively to this query: political, technical, and pragmatic. Political: It is accepted by the automakers and the EU that once articles leave the production line free from hex chrome, they are REACH-compliant. (This is almost universally the case.) Technical: Hexavalent chromium is an extraordinarily effective corrosion inhibitor. Once trivalent passivates are in corrosive environments, they will almost always generate hexavalent chromium in small but effective amounts. Pragmatic: Don’t look under the rock.
Workshop in ASTM B08 in May. We will be testing this and seeing if ASTM B850, internal hydrogen embrittlement release bake out is a cause of the trivalent flip to hexavalent and what percentage flips. -Ian MacMoy Ian MacMoy [returning] |