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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Black Oxide finish versus Conductivity
Q. I am working on a product that requires good conductivity. For an aesthetic point of view, I wanted to finish some parts using black oxide. Is black oxide very good for conductivity or should I use something else and what other type of finish should I use? Thanks for your help.
Best regards,
Electronics mfgr - Gatineau, Québec, Canada
2004
A. A black oxide finish is basically a controlled rust finish. It is very thin (millionths of an inch) but is still non conductive because oxides are not metallic. A zinc-iron finish with black chromate, a black nickel, or a black chrome plating are examples of conductive finishes; all are aesthetic finishes. Good luck.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004
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Ed. note 10/5/09: A reader read this to mean that a black oxide coating would be a good thin insulative coating, and we want to disavow that interpretation. We were saying that the coating is much too thin and wrong in nature to serve as a conductive contact surface, but we were certainly not claiming that it can be used as an electrical insulator.
Q. Though it's technically not conductive, when you screw a black oxide screw in (as long as the tapped hole is tight enough), the oxide will get grounded off enough to make a decent connection? I wouldn't try it on anything you are trying to get UL listed, because it might not pass the hipot test?
Please don't put too much stock in what I just said though (why I used question marks instead of periods). I myself am also just starting to put out some products and am dealing with different black oxide fasteners and am getting some parts black oxide-ed.
I hope others will not blast me for my ignorance, but instead part with actual useful information that we can all use. thanks.
audio mfgr. - Chicago, Illinois, USA
May 2, 2011
A. Hi, Daniel.
I guess something that may be confusing here is that we are talking about a quantitative parameter, surface resistivity, as if it were a qualitative go/no-go parameter. I suppose that the only finishes that are truly conductive are gold and other precious metals that do not tarnish at all. And, in fact, for very low voltage, very low current applications where extremely reliable contact is required, like signal levels in electronic circuits, only gold plating will do. For somewhat higher voltage and current applications like charging contacts on dry cell batteries, electroless nickel plating is ubiquitous. Then we get to the plated black finishes that I mentioned, bare copper, etc.
As we talk about finishes for steel substrates, we're no longer talking about very low resistance anyway, because steel would not be used as a conductor of a signal except, as you mentioned, when it's screwed in tight. I don't have test results but I would expect that a black oxide finish would work on screw terminals for an audio level signal like speaker wires.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 5, 2011
Q. Hello all. I need to know what ill effect (if any) blackodised hardware will have on the genset earthing. So far I've seen zinc coated fasteners. Your early response will be much appreciated.
Pandurang K- Pune, Maharashtra, India
June 20, 2013
Need black surface that is conductive
I have a similar issue where I have a requirement to have a black surface that is conductive. It looks like black nickel is the only finish that I could find that would work. I plan to use either an aluminum parts (using the black nickel) or stainless steel (I have not found something that will work). Do you have a suggestion? This is not a structural application
Primary requirements:
- Resistance of 400 ohm or less between two points 1" apart.
- Black
- Matte (not shiny)
Thank you --- Cyrus
- Fallston, Maryland, USA
March 31, 2014
A. Hi Cyrus,
You may consider black ruthenium which is widely used as final finishing for spectacle frame.
Regards,
David
David Shiu
- Singapore
April 1, 2014
Q. Thank you David. Is this expensive? And it is electrically conductive? That's the most important property
Cyrus Etemad-Moghadam [returning]- Fallston, Maryland USA
April 3, 2014
A. Hi Cyrus,
Ruthenium is one of platinum group elements with high electrical conductance and corrosion resistance. Latest price is around US $72/oz which is almost 4 times of silver (around US $20/oz).
Regards,
David
David Shiu
- Singapore
April 6, 2014
Thanks for the quick response. That's very expensive compared to the alternate finishes suggested. I will try Black Nickel.
Regards,
Cyrus
- Fallston, Maryland USA
April 7, 2014
A. A Blackened Electroless Nickel finish will meet your requirements.
The finish is black and electrical conductive.
Other options are Black Nickel Electroplating .
- Bnei Berak,Israel
April 18, 2014
Thanks Gabriel. That is what we are leaning toward. Regards -> Cyrus
- Fallston, Maryland USA
April 21, 2014
A. Cyrus,
You can do black electroless nickel on either aluminum or stainless steel. The pricing is a touch higher than regular electroless nickel, which I would suspect is cheaper than black ruthenium. I don't have the answer for the conductivity test, but could look into it.
- Schaumburg, Illinois USA
May 21, 2014
Thanks Jim. We went with the black electroless nickel over aluminum.
Regards, Cyrus
- Fallston, Maryland, USA
May 22, 2014
Q. Hi David Shiu,
Small question on your post for my own learning: ruthenium being conductive applied on spectacle frame, wonder why one needs a conductive frame? Thanks, Ahmed
electronics - santa clara, California, us
June 1, 2016
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