Electroplacting

The electroplating is a technique, used mostly in industrial field, that allows to cover a base metal with a thin layer of a more precious metal or noble or more passivable exploiting the electrolytic deposition.
This process is usually used for corrosion protection of metallic structures, but may also have decorative purpose. For example by electroplating it is possible to coat the copper with silver or steel with zinc, tin, nickel or chromium.

Background

The discovery of the galvanic technique begins in 1791 when Luigi Galvani discovered the “electric fluid,” that’s why all the electrolysis process called electroplating derived from his last name Galvani.
The first apparatus for carrying out the electroplating was developed by Johann Wilhelm Ritter in 1800, using the electric current produced by a voltaic pile. During his experiences on electroplating, Ritter discovered that the amount of metal deposited depends on the distance at which the electrodes are placed.
The term “galvanizing” was used for the first time by the French Albert Sorel, who in 1837 obtained the first patents for hot dip galvanizing.
Practical implementation

Following there is the normal procedure to play an electroplating treatment.
In a tank, which constitutes the so-called galvanic bath, containing an aqueous solution of the salt of the metal to be deposited, two electrodes are immersed: the cathode is constituted by the object to be coated, while the anode may be formed from the metal to be deposited , by another inert metal or graphite. To these two electrodes a potential difference is imposed by means of a current generator. In such conditions the metal cations to be deposited will move towards the cathode (negatively charged), while the anions will move towards the anode (positively charged).

The two electrodes have the following phenomena:

• purchase of electrons at the cathode (reduction);
• production of the anode electrons (oxidation).

On the cathode they are then deposited cations, who buy the anode and electrons are transformed into metal atoms. In this way, the cathode is slowly coated with a thin metallic layer and the anode, when it is sacrificial, is slowly consumed by releasing ions in solution. In relation to the metal layer that will be deposited, which is usually of tens of microns or less, for a given value of current density (expressed in A / dm2) to which the working bath and knowing the deposition rate, just set the time necessary to form a deposit of desired thickness. Some bathrooms, like those used for the storage of precious metals such as silver or gold, even using a cyanide ion solution and for this reason are called “cyanide baths.” This type of shower requires, by law, operators authorized the use of cyanide, authorization recognized by the granting of a renewable license. Rhodium, nickel, copper, chromium and zinc are other metals which are commonly used in electroplating.

Some of electroplating applications are:

• zinc plating (or galvanizing): coating with a layer of zinc of ferrous materials, for example steel and mild steel (sometimes improperly called “iron”); It is used to counteract the oxidation (rusting);
• chromium plating: coating with a layer of nickel with a flash of chrome, which is also practiced mainly on steel and mild steel, both to increase resistance is to prevent corrosion;
• nickel plating: overcoating of different metals with a layer of nickel; It contributes to increase the mechanical strength and the corrosion resistance.
• Plating: allows to create uniform gilding with small amounts of gold; It is used in jewelry and electronics industry.