Chemistry

Getting Started with Electroplating



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Electro-deposition, or electroplating is a common and effective solution to prevent the effects of corrosion on different sorts of metals. Basically, it is when an outer layer of elemental metal (or less commonly an alloy) is put over top of a specific object by using electricity to move metal ions around and convert them into different forms. The item that you want to coat with metal is put into a solution of a soluble ionic salt of that metal. That object to be coated gets a negative charge put on it by wiring it to a battery or other source of electricity. This means of course that it is attached to the negative end of a battery, so that electrons will flow into it as a negative electrode. This negative electrode is also referred to as a cathode, and the positive ions of metal are attracted to it. We know that soluble ionic compounds dissociate into ions when they are in aqueous solutions, which means that instead of the metal being in a solid salt compound the solution will have positive metal ions and negative anions in it (such as chlorine).

There is also a positive anode attached to the positive end of the battery that is of the same metal as the ions that are present in the salt solution. By having electrons taken from the anode metal by the battery, the anode metal oxidizes from its elemental state of having an oxidation number of 0, into ion form. Therefore there are positively charged cations produced that are returned back to the solution in equal proportions of the anions already in the mixture.

These metal ions from the anode are used as replacements for the metal in solution that has been plated, and is therefore no longer present in the solution. When there are electrons flowing into the cathode (to be plated with the metal) the positive metal ions in the solution become attracted to it. Reduction (gain of electrons) of the cathode occurs at this point, so that the metal ions return to their 0 oxidation number and valence elemental state. Because the metal ions go over top of the cathode they end up forming a metal layer or plating over top, and the thickness of the electroplated layer will depend on the length of time that you have the whole electroplating process going. If you have the current running for a long period of time the layer will be thicker than a shorter time frame.

Also, for prospective electroplated pieces that have very sharp edges and some indentations, the layer would possibly be uneven over the surface. The metal layer would collect on the sharper edges much more than intended, and in the indentations the layer would be much shallower. This is because electricity tends to flow more easily through thinner pieces of metal, and it has more resistance through thicker pieces. The cathode will therefore have electrons from the battery flow into the narrower edges, making the positive anions attracted to it at a faster rate than other areas.

Quite commonly electroplating is used as a way to prevent corrosion on metal, or to beautify it and improve the finish. An everyday use of this is on cars, when chromium (chrome) is electroplated over top of different pieces in steel. More than one layer of electroplating can be applied, and this serves to further protect the piece as well as making a more pleasing finish. Electroplating is a very effective way to prevent corrosion because it causes the metal that is prone to oxidization to not be exposed outwardly to water or oxygen. These are the substances that it is likely to react with, and will therefore form an oxide coating such as rust that we don't want. If we coat a metal with an element such as gold that doesn't oxidize easily, that layer will permanently protect the metal underneath so long as the layer isn't scratched or scraped. If there is ever a gap in the protective electroplated coating the possibility of rust will reoccur, but all you have to do to fix the problem is to apply another layer of electroplate as soon as possible



If you put on a first layer of nickel and a top layer of chromium, that metal will be very resilient to corrosion and the chrome will make it have a nice luster. You can save a lot of money on jewelery if it is electroplated, because gold generally costs a lot more than, say iron. This means that you can have a relatively inexpensive item that doesn't look the nicest, and then electroplate it with gold to get all the beauty you want without the cost of solid gold. Lighting fixtures that are made of aluminum or even steel are often double electroplated as well, first with nickel as a protection and then with brass or possibly chromium to finish. Cadmium or zinc coatings over top of different items, such as bolts will increase the durability and life length of the item. The functioning of metals used for conducting electricity can be improved as well by electroplating. For example, by electroplating a copper wire with a layer of silver you can dramatically reduce the resistance of electricity and likelihood for oxidation. The reason for this is because silver has a higher electrical potential and is a weaker reducing agent than copper, so the electricity will flow through it more easily and effectively with smaller risk of corrosion.
This is especially helpful on items such as radio frequency connector wires, because of the fact that radio waves tend to flow mostly on the exterior of the electrical medium. The wire will be very sturdy at the core (because copper is physically stronger), conductive, and corrosion resistant on the outside from the properties of silver.

Electroplating does cost money to actually perform, but that cost is outweighed by the amount of money saved on not having to replace a corroded item. You could also have something made out of a less expensive metal with an electroplated coat of a more expensive metal like gold. That would cost a lot less than an item of solid gold, and it would have the same look. The expenses of electroplating stem from the equipment required to perform the task. These things include the tank, electrode (anode), wires, source of electricity and the salt solution of the same metal as the anode. Electroplating is a very inexpensive process that is used quite commonly used. There are electroplating shops that will electroplate various items for people at a very reasonable price

To give a basic idea of how much money electroplating would actually cost:
- You could electroplate your kitchen faucet in 24 karat gold for $10, because the thickness of the layer is around 0.00005". (50 millionths of an inch)
- Silver plate a metal picture frame for $5.
- To plate a light fixture in brass is a few cents.

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