Electroplating 101

A Small Introduction to Plating and Coating

These descriptions of electroplating are summaries taken from other sites. For more details please visit the linked pages

Electroplating is a process for coating a conductive object with a thin layer of a material, such as a metal. An electrical current is used to reduce cations of a desired material from a solution onto the object. Electroplating is primarily used for depositing a layer of material to bestow a desired property (e.g., abrasion , wear resistance, corrosion protection, lubricity, aesthetic qualities, etc.) to a surface that otherwise lacks that property. Another application uses electroplating to build up thickness on undersized parts.

The process used in electroplating is called electrodeposition. It is analogous to a galvanic cell acting in reverse. The part to be plated is the cathode of the circuit. The anode is made of the metal to be plated on the part. Both components are immersed in a solution called an electrolyte containing one or more dissolved metal salts as well as other ions that permit the flow of electricity. A power supply supplies a direct current to the anode, oxidizing the metal atoms that comprise it and allowing them to dissolve in the solution. At the cathode, the dissolved metal ions in the electrolyte solution are reduced at the interface between the solution and the cathode, such that they "plate out" onto the cathode. The current flowing through the circuit sets the rate that the anode is dissolved and plated onto the cathode. In this manner, the ions in the electrolyte bath are continuously replenished by the anode. Other electroplating processes may use a nonconsumable anode such as lead. In these techniques, ions of the metal to be plated must be periodically replenished in the bath as they are drawn out of the solution.

From Wikipedia - Electroplating

Process of coating with metal by means of an electric current. Plating metal may be transferred to conductive surfaces (e.g., metals) or to nonconductive surfaces (e.g., plastics, wood, leather) if a conductive coating has been applied. Usually the current deposits a given amount of metal on the cathode (workpiece) and the anode (source of metal) dissolves to the same extent, maintaining a fairly uniform solution. Silver plating is used on tableware, electrical contacts, and engine bearings. The most extensive use of gold plating is on jewelry and watch cases. Zinc coatings prevent the corrosion of steel articles, and nickel and chromium plate are used on automobiles and household appliances.

For more information on electroplating, visit Britannica.com.

The process of electroplating takes place as metals in ionic form move from a positive to negative electrode. An electric current passing through the solution causes objects at the cathode or work piece to be coated by the metal in the solution.

Electroplating is done for many reasons, usually to beautify, insulate or to protect and to increase the corrosion resistance, conductivity solder ability of metal objects. Plating protects by one of two ways, either sacrificially or mechanically.  Zinc and cadmium protect the base metals they cover sacrificially. They are more reactive to corrosion than iron or copper alloys so they corrode first, before the base metals. Copper, nickel, chromium and most other metals protect the base metals mechanically. They protect the base metals by forming a protective coating, therefore the protection is good only as long as that coating is intact. If there is defect or break in the protective coating the base metal will corrode before the plating. The most common metals used in plating are copper, nickel, gold. silver, chrome, zinc and tin.

Copper Plating, is the most common of all metals to be plated on to another metal. It's finish is soft, red, ductile and solder able. It is seldom used as a final plate because it tarnishes easily. Copper is an excellent choice as an under plate since it is easy to buff or polish and it will cover small imperfections on the surface. A high polish on the copper helps to give your next layer a good appearance. Copper is highly conductive and makes a great coating for printed circuit or over steel wire that is used to conduct electricity. Copper is often used as a base for a conduct coating when electroforming. Copper has a high plating efficiency resulting in excellent coverage over difficult surfaces. It is about the only metal that will plate over zinc diecast.

Nickel Plating, is a yellowish white, hard, reflective finish used for wear resistance, solder ability, or dimensional restoration. Nickel plate often used over copper and under chromium for a decorative finish. Nickel is a very hard metal with poor ductility, therefore parts that are to be plated with nickel should be bent into their final shape before plating whenever possible. Nickel should be plated over copper before gold plating to reduce the corrosion or darkening of the gold.

Silver plating, besides being decorative, has the highest electrical and thermal conductivity of any metal. In most cases it is plated out looking white or pickled and can be polished with silver polish to bring out a shine.

Gold Plating, is sometimes made in different karat colors such as 14kt, 18kt, and 24kt.

Chrome Plating, or chromium plating as it sometimes is called has a blue-white color that may be applied over copper and nickel for decorative purposes. It may be applied directly on the base metal for engineering purposes. Chrome plating may be either shiny or dull and tends to highlight imperfections the same way that a painted surface will still show scratches and such after painting if proper preparation isn't taken. For decorative purposes the finish or shine that is on the nickel will determine the finish on the chrome.

Zinc Plating, is a soft, ductile, decorative, marginally solder able, corrosion resistant finish. Unlike most commonly plated metals, zinc protects the piece by sacrificing itself and thus corrodes before the base metal. This means that zinc will protect even if the zinc coating sustains miner damage such as scratches and punctures. This is sometimes an advantage over other types of plating. Zinc is the most reactive of all common metals and may be attacked or dissolved by ordinary liquids such as soft drinks and vinegar.

Cadmium Plating, Used for corrosion protection on Aircraft landing gear and other ultra high strength steel parts.

Cobalt, deposit has a low coefficient of friction. Provides good wear resistance at elevated temperatures. Used as a touch-up for chromium plating.

From Dalmar.com - Electroplating

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