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Difference between MIL-C-5541 Class 1a and MIL-DTL-5541 Type 2 Class 1a

January 28, 2008

Q. What is the difference between these two mil standards? Is one for a clear RoHS compliant and the other for a yellow RoHS compliant? Or is the Mil-C-5541 for clear RoHS and Mil-DTL-5541 [link by ed. to spec at TechStreet] for yellow hex. Please let me know. Thank you.

Mike Logan
plating shop employee - Minneapolis, Minnesota

February 4, 2008

A. Mike, Hi.
Type I - Compositions containing Hex Chrome
Type II - Compositions containing no Hex Chrome
Class 1A - For maximum protection against corrosion, painted or unpainted.

Mil-C-5541 did not mention Type I or II whereas Mil-DTL-5541 [link by ed. to spec at TechStreet] does. Class 1A is the same for both standards. For Mil-DTL-5541, it is very clear when Type II is mentioned, the conversion coating shall not contain Hexavalent Chrome, hence, RoHS compliant. When Type I is mentioned, the conversion coat contains Hexavalent Chrome but it may not necessarily be yellow. There are clear conversion coatings out there which are Hexavalent chromium based. As far as I am concerned, there is no yellow conversion coat (yellow chromate if you prefer) that is Type II. If you have time check out and check out some excellent trivalent chromium base conversion coats (Henkel, Surtec, Macdermid, Luster On ) which can, incidentally be classified as Type II.

Cheah Sin Kooi
- Penang, Malaysia

February 28, 2008

A. Mike,
Further readings on earlier posts at, apparently, there are yellow conversion coating that is Type II - clear conversion coating with yellow dye.

SK Cheah
MST - Penang Malaysia

November 2013

A. Hi Cheah. I think the confusion is that there are RoHS compliant trivalent conversion coatings which are yellow (through the addition of dye) -- but they are not compliant with MIL-DTL-5541. So it probably isn't correct to call them Type II ... just call them yellow and RoHS-compliant :-)


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Ted Mooney, P.E. RET
Pine Beach, New Jersey

August 27, 2009appended

Q. Can anyone tell me what are the differences in the new standards (Mil-DTL-5541 [link by ed. to spec at TechStreet]F) as compared to the old.

Thomas Joseph
Precision Metal Fabricator - Singapore

November 2013

A. Hi Thomas. We appended your question to thread where Cheah Sin Kooi had answered the question: RoHS-compliant, Type II coatings did not exist in the old Mil-C-5541 standards. Good luck.


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Ted Mooney, P.E. RET
Pine Beach, New Jersey

December 6, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Is Irridite per MIL-C-5541E, class 1A compliant with RoHS?

Senthil Kumar
- Bangalore, INDIA

December 9, 2013

A. Hi Senthil. We appended your question to a thread which answers it. No, Mil-C-5541E, class 1A is NOT RoHS compliant. Good luck.


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Ted Mooney, P.E. RET
Pine Beach, New Jersey

September 26, 2014

Q. Is the part processed per type I hazardous in any way? Or just the chemical solution used in the process? We have parts processed per type I versus required type II. The customer is giving us a hard time. Thanks.

david ho
- milford, Connecticut, usa

September 2014

A. Hi David. RoHS is short for the European Parliament's directives on Reduction of Hazardous Substances, and refers to the constitution of the parts, not the processes used to manufacture the parts. The situation is simply that parts processed in Type II solutions do not put hexavalent chromium on the parts, so the parts are very likely to be RoHS complaint. Processing parts per Type I does put hexavalent chromate on the parts, and they are unlikely to pass a test of their RoHS compliance.

Many domestic and non-European customers are requiring RoHS compliance, so it is understandable that the customer is giving you a hard time -- he may not be able to use the parts.

"...hazardous in any way?" is a loaded and qualitative question which I don't think anyone can authoritatively answer. A former governor of NJ once remarked that " 'toxic' is a matter of statute, not opinion", and I think we can look at the word 'hazardous' the same way. Good luck.


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Ted Mooney, P.E. RET
Pine Beach, New Jersey

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