Rapid Oxidation of Copper 2

What exactly are you trying to accomplish?
Produce a black oxide coating, a pink oxide coating, a blue-green patina, an antique finish, or something else?

For oxidation via heating in air, see
thread367-38946
Thread330-38947

Nitric acid rapidly oxidizes copper (along with nasty fumes): to produce Cu[sup]+2[/sup] ions in solution, but that's probably not what you want.

If you want to use a chemical solution to produce a colored finish, see the article "Antiquing of Brass, Copper, and Bronze" at

Also, do a search at
Re your medical question. I checked an MSDS for Cu powder
"Reproductive Effects: No information available."
"California No Significant Risk Level: None of the chemicals in this product are listed." (any evidence that it was a reproductive hazard would place it on California's Proposition 65 list.)
Also checked an MSDS for a soluble compound (copper sulfate) which has more health effects, but it is similarly not known to be a reproductive hazard.

Trying to determine if creating an oxide layer on the surface of copper will prevent sperm samples from becoming immobile. The information I have so far suggests that any oxide that forms on the surface of copper is merely superficial, which sounds reasonable in my opinion.

OK,
I think I understand the situation. Will bodily fluid, e.g., semen, corrode copper, and would the copper ions resulting from the corrosion have a deleterious effect on said bodily fluid? Also, would an oxidative treatment of the copper prevent such an effect?

To begin, presumably the sperm samples are in semen or a solution of equivalent salinity, similar to seawater. From the uses of copper-containing anti-fouling paints on ships and copper sulfate as an algaecide, I would expect copper to have a negative effect on the sperm.

Second, a layer of copper oxide is more chemically resistant than bare copper. However, I would not consider this layer to be sufficiently inert or protective for your purpose without extensive testing ($$$), and I doubt that the FDA would either. There might be a problem in sterilizing medical instruments due to oxide porosity.

Finally, I don’t know of any use of copper in medical instruments used internally or in contact with fluid samples, etc. Suggest using an alloy that is already in general use for medical instruments or surgical implants. It’s probably too expensive to use an implant alloy, e.g., Co-28Cr-6Mo as specified by ASTM F1537 and F75, but a suitable material might be electropolished 316 stainless steel. I suggest getting the booklet Biodur® and Other Specialty Alloys for Medical Applications from Carpenter Technologies.

Kenvlach

First of all thanks for the information you have provided.

We manufacture cell culture incubators and the majority of them have an electropolished stainless steel interior. We also provide an incubator with a copper interior to prevent anything from growing on the surface as we know that most things won't grow on it.

I would assume that our customer is placing the samples in plastic dishes within the copper interior and they are finding that their samples are becoming immobile. I am a mech engineer and my knowledge of biochemistry is limited to say the least so I am assuming things that maybe I shouldn't. Also I only have half the story and I don't fully understand how our customer ended up with a copper interior incubator when we know that they are not suitable for incubating sperm samples. We are now in the awkward position of trying to find out if an oxidised layer on the surface of the copper interior will still effect sperm samples without being able to test it.

From some further research yesterday I have discovered that copper causes something called Metal-Induced lipid peroxidation. I don't know if I am going along the correct lines but it would seem that this process causes an increase in free radicals that causes a chain reaction in taking electrons from other cells that have an unpaired electron available. This may be why the sperm samples are dying/becoming immobile. I am beginning to think that there is no way of curing this as we would need to try and make the copper inert which would cause other problems with cleaning and sterilisation as you suggested.

Does lipid peroxidation mean anything to you and do you think I am heading along the correct lines?

First, I really would not count on oxidation making the copper inert. There is a good chance that the copper oxide surface would be catalytically active. Most biologically active forms of copper seem to be Cu(II)-containing proteins that function as enzymes in oxidation reactions, as in the example you mentioned, although some employ the Cu(I)-Cu(II) redox reaction, as in hemocyanins which transport oxygen in lobsters, etc. I have a book on Organometallic Transition Chemistry, but it is rather heavy reading, so I am referring to Advanced Inorganic Chemistry, 5th Edn., pp. 1363-1369. A number of the active sites involve coupled molecules, each with a Cu(II) sharing an adsorbed O[sub]2[/sub] molecule.

Second, I am not sure copper is the problem. “our customer is placing the samples in plastic dishes within the copper interior and they are finding that their samples are becoming immobile.” Is the sperm sample not in direct contact with the copper? Perhaps the problem is the plastic dishes. It could be the wrong material or a bad batch, with residual monomer (most are toxic). I presume that a plasticizer is not used in these. Does the protocol require that these plastic containers go through a clean and steam cycle prior to use to sterilize and remove volatiles?

With regard to making the copper inert, you could have it coated with Teflon® or gold-plated (with a diffusion barrier of Ni between the Cu and Au). Cr plating might work. A sputter coating of either the Co-28Cr-6Mo implant alloy or Ti would also work, but probably quite expensive. An electroplated tin coating would be the least expensive, but I’m not sure that it would be inert, just figure that it’s safe for food so possibly OK.
Ken

""Second, I am not sure copper is the problem. “our customer is placing the samples in plastic dishes within the copper interior and they are finding that their samples are becoming immobile.” Is the sperm sample not in direct contact with the copper? Perhaps the problem is the plastic dishes.""

This is the bit that I do not understand. If the user is placing a sample in the incubator within a plastic sterile container, then how can copper that is not directly in contact with it effect it?? Osmosis??

I am beginning to think that the customer is perhaps not doing things correctly or not telling us the full story.

Kenvlach

I have finally managed to find out what kind of finish we are looking to produce. We would like the copper surface to turn black. Could you tell me what process would be best to produce this?

Thanks once again.

While I don’t believe CuO is a good finish for an incubator, it may work if not subjected to hot water or steam. Several alternatives, but I’d go with the hot oxide process mentioned first below.

A CuO finish is best produced by a hot, caustic oxidizing solution: 240[sup]o[/sup]F, caustic soda and sodium nitrate – Metal Finishing Guidebook, p. 382 (2003),online: Proprietary solutions are normally used. This is more of a specialty service than is the hot black oxide finish on steels To locate a shop, try this ‘Jobshops’ link If unsuccessful, go to EPI’s site They have a suitable product:
“Ultra-Blak 420 for Copper/Brass — Oxidizing salt mixture for blackening copper, brass and bronze. Used at a concentration of 2 pounds per gallon of water at temperatures of 200° to 210° F to blacken copper surfaces with a deep black, abrasion resistant finish.”
Either use yourself or ask EPI for their nearest customer in your area.
Another, well-known product is ‘Ebonol C.’ It is/had been made by Enthone-OMI, but I couldn’t find on their site. Some ‘Ebonol C’ info is at and
I looked at all 27 recipes for black/brown/gray finishes on Cu given in The Colouring, Bronzing and Patination of Metals, R. Hughes and M. Rowe, Thames and Hudson (1991). 17 of these produce a sulfide, not an oxide. All 27 mention that a wax finish may or must be applied, surely not good for an incubator.

A number of art sites show a black copper finish which looks to be produced by heat, e.g.,
Finally, here is a less dangerous, Do-it-Yourself recipe for a blue-black finish:
“Copper carbonate, 1 pound
Ammonia, 1 quart
Water, 2.5 quarts
Temperature, 175[sup]o[/sup]F

The copper carbonate and the ammonia are thoroughly mixed before adding the water. An excess of copper must be present. The color, which is a blue-black, may be fixed by a subsequent dip in a 2.5% solution of caustic soda.”
-- Metal Finishing Guidebook (1998), p. 461.

Good luck, let us know the outcome.
Ken