Chrome plating as a high school science project

A. Hi, Mike,

There is a lot of info on this site, including our Introduction to Chrome Plating, which I hope you'll look at, and an FAQ about zinc and copper plating for science projects. To start well though, I'd suggest you skip chrome plating and decide you are going to try zinc plating or copper plating, then search the site for threads on the subject. Good luck!

A. Mike, you may have an e-mail problem because we advised you 3 weeks ago that we had responded here.

If you are careful, and with supervision from your chemistry teacher, you could do a project on zinc plating, or possibly copper or nickel plating, if electroplating interests you. You could perhaps do cobalt plating or gold plating too!

But high school students should not do chrome plating as a science project. The hazards are too many and too severe; for example, people who work with chrome plating must receive periodic blood tests and medical monitoring. Best of luck.

A. Speaking as the father of a High School student, I must urge you to listen to the sage advice given previously.

I encourage you to learn more about chrome plating by another means such as reading. Many good books exist on the subject, and you can find references on various search engines on the internet.

Actual chrome plating should only be done by trained professional Surface Finishers. These people have all the proper equipment, exhaust equipment, waste treatment, and knowledge to do this kind of plating. NEVER EVER should it be undertaken by anyone else. EVER.

I have to disagree with the spirit of Mr. Mooney and Mr. Budman's sage advice. Although chrome plating is a technically complex (not really) and potentially dangerous (know what you're doing/how to dispose of chemicals properly) I don't think chrome plating should be held out of reach of High School students. I am not myself a high school student anymore, but when I was I was successfully chrome plating model airplane engine parts. I did a lot of research on my own, through books mainly, as that was in a time when the Internet wasn't very prevalent. I would have however, been thoroughly upset had an "expert" rudely proclaim that I should not attempt such a thing, without rhyme or reason. My father very fortunately was very supportive of my scientific ventures, and would never tell me not to screw around with sulfuric acid, or other things that might get me hurt, that would have prevented much greater things from happening. In a country built on ingenuity, discovery, and child prodigies, it is discouraging to hear people say such things. In the defense of Mr Mooney and Budman, it did sound like Mr. Moore might be in a little over his head. Even still, that is no reason to discourage scientific thinking, without just cause. Shame on you.

"Hard Chromium plating"
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A. You are welcome to your opinion, Jon, which we are happy to post here. But I asked Mike to see our "Introduction to Chrome Plating" for the "rhyme and reason". Please consider:

- the fumes from chrome plating are carcinogenic; there have been 100 years of research reports on this. They have no place in a high school lab where other children will be exposed to them; you may feel that teenagers should be allowed to give themselves cancer if they feel like it, but they still shouldn't give it to their classmates; as I told Mike on this page, anyone exposed to the chrome electroplating process is required to have blood tests and medical surveillance. Is that remotely practical for a high school science project?

- the solution evolves messy "ginger ale" droplets of hexavalent chrome that will spread all over the high school lab; this material is carcinogenic and also causes chrome sores and chrome ulcers; the surface tension of chrome plating baths must, by law, be measured with proper instrumentation and controlled every day to try to minimize this problem;

- chrome plating solution is the same hexavalent chromium that made Erin Brockovich [affil link to Amazonaffil links] a household name, but in much much more concentrated form; at 32 oz. per gallon, it's more than 100x as concentrated as the cooling water that Brockovich was involved with;

- the use of hexavalent chromium plating is being drastically curtailed everywhere around the world; the airframe and aerospace industry, and the military, is spending countless millions of dollars completely eliminating the use of chromium electroplating on even the most critical flight hardware where it was formerly deemed indispensable;

- just one broken large beaker of chrome is enough to ruin the wells for blocks around; millions of dollars of pollution;

- it's simply ridiculous to believe that school authorities will let him demonstrate this project anyway.

That's my first half dozen reasons why school children should not do chrome plating. Do you still think I should be ashamed for suggesting that Mike do zinc plating, copper plating, nickel plating, or cobalt electroplating instead?

A. In my experience, Ted Mooney is absolutely correct. My parents are both chemistry teachers and I myself know a lot about chemistry. Chrome plating is no doubt a particularly dangerous job, especially dangerous since it is being done in the hands of a high school student, who doesn't have the experience, proper equipment, safety procedures, etc. All these factors could not possibly be accessible to a student. Chrome plating should NEVER be undertaken by any high school student. You should ask a professional. But on the other hand, you could ask your science teacher and practice with copper plating, cobalt plating, etc. Although you specifically said that you need to do chrome plating, I wouldn't take any chances because in the end, it is your health and well-being at risk.

A. Hi, Simon.

You can electroplate some stuff with zinc or copper for your science project. For instructions, please see our FAQ on How Electroplating Works.

But chrome is not quite the right thing for the project fair. Chrome plating requires the use of toxic and carcinogenic process solutions, and the school won't let you bring into the gymnasium the chemical that made Erin Brockovich [affil link to Amazonaffil links] famous.

You can learn what is involved in chrome plating on our Introduction to Chrome Plating page if you are curious. Good luck with the project!

A. Hi Luke. Yes "chrome" is merely slang for chromium. Chromium plating is one of the more difficult finishes, Luke, and the chemicals are toxic and carcinogenic, so it's probably not the best plating for a science project. Maybe you could try zinc plating per our FAQ "How Electroplating Works" in addition to your copper plating?

A. It is possible to electrodeposit chromium metal from a simple solution of 250g/l CrO3 and 2.5g/l H2SO4. There are other solutions available that have fluorosilicates added. The solution is very acidic and not very nice to handle unless you know what you are doing. The efficiency is generally quite low, about 20-25%, so a lot of hydrogen is also produced. This causes gassing and unless it is suppressed by a suitable additive (e.g., Chromomist) it can be a significant health hazard. The major problem is airborne chromic acid vapors that, in extreme circumstances can cause attack of the nose and even the lungs. Chrome is a shortened term for chromium and the two are often interchanged. However, when chromium plating is done on automobiles, there are sublayers of copper and duplex nickel. The duplex nickel is one layer of lamellar nickel and one of columnar; these layers offer improved corrosion protection to the substrate.

Chromium is an interesting metal is as much as when it gets damaged, it self heals. That is, the metal is covered in a metal oxide that prevents it from rapid corrosion, but if the oxide is damaged, the exposed metal quickly forms another oxide film, thereby reducing the rate of subsequent corrosion.

A. Hi Trevor,

I usually hear of "self healing" used to describe the process by which a chromate conversion coating will protect the underlying metal by supposedly having some reaction at the exposed surface of the metal similar to the original conversion coating. In that case, the base metal is supposed to initiate the reaction along with moisture in the air over it. Never having seen it myself, I have always believed the reaction to exist.

Oxide formation of the surface of many common metals is somewhat adherent, protective, and self-forming. Nickel oxide ruins the shine of the metal and must be continuously polished. Certainly, chromium and aluminum are known to have an extremely thin and "decorative" oxide, in that we don't notice it by looks.

Regards,

A. Hi Amy. Since you read the FAQ, you know that there are two general types of chrome plating: hard chrome plating, for engineering purposes, which is deposited directly on hardened steel components; and decorative chrome plating which always includes nickel plating first.

Conceptually it isn't difficult if you don't dig too deep: after the parts are thoroughly clean and free of oxides, they are immersed into a vat of about 32 oz./gal H₂CrO₄ in water, and DC electricity is applied, with the parts attached to the negative (cathodic) pole. The excess electrons from the applied electricity neutralize the positive charge of the Cr⁺⁶ ions and reduce them to Cr⁰ metallic form. It's that easy!

But if you dig deeper, it is exceptionally complex from a theoretical standpoint; as you study, you will learn that the reaction will not occur unless the solution contains a catalyst at almost exactly the right concentration. The earliest and best known catalyst is sulphate which must be present in a ratio of almost exactly 1 part sulphate to 100 parts chromate for the deposition to proceed. Significantly too little, no plating occurs; significantly too much, no plating occurs; even a little too much or too little and the plating is crummy. And on top of that, for reasons we don't quite know, the "plating efficiency" is only 10 to 25 percent at best; what that means is 75 to 90 percent of the electricity applied goes to liberating hydrogen from the water in the plating solution rather than going towards reducing the chromium ions to metal :-)

Post-doctoral level theses have attempted to explain precisely how it works, but even they are incomplete and partially in doubt. For a year 12 student, it should be sufficient to note that the chromium is in solution as H₂CrO₄, and the oxidation state of the chromium is +6 such that 6 electrons must be added to reduce one atom of Chromium to metallic state. You might try to get your hands on a plating book, Amy, as that's where you'll find in depth info on what you're looking for. Good luck.