Chromium Plating

Reflections on a motorcycle

Reflections on a motorcycle (Photo credit: Wikipedia)

English: Rear bumper on a 1971 Dodge Dart Pure (99.999%) chromium crystals, produced by ...

English: Rear bumper on a 1971 Dodge Dart (Photo credit: Wikipedia)

Have you ever looked at a shiny new car bumper and wondered how they got it to be so shiny and bright? It was done by being plated with chromium, a hard metal that takes a beautiful polish. Unfortunately, this metal cannot be used for the whole bumper, for two reasons: one, it is not cheap enough to be used so extensively, and two, it would dent WAY too easily for a car bumper. But how do they get the Chromium on? 

First, the steel bumper is cleaned and any oxides are sanded off and polished to a high brightness, then it is dumped into a liquid solution that transports elecrical currents well. Next to it, but not touching it, is a large lump of chromium in anionic form (meaning it has more electrons than protons, and so is negatively charged). Anyway, so they are both placed into the solution.

Now they are both hooked up with electricity, the bumper is hooked up with a positively charged flow and the chromium gets negative, and so the plating begins.

What happens? On the negative end, the elecricity sucks in oxygen, which hooks onto the chromium, becoming chromium oxide. This is now able to dissolve into the solution, which it does, and, being negative, is attracted where? To the car bumper. Once there against the car bumper, the positive electricity seperates the oxygen away, and the Chromium is plated evenly over the whole bumper, aligning exactly how the steel is aligned, and comes out polished to a beautiful finsh, and is sent to wherever cars are made.

One interesting fact is that whatever chromium is still in the solution when the bumper is lifted out forms little chromium crystals at the bottom, which are very bright and beautiful. Some tourists are allowed to keep these, otherwise they are just broken off and used again.

 

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