Would our life and technology be the same without conductive copper wires, aluminum containers, galvanized sheet metal, microelectronic circuits and magnesium alloys?
And what do all these materials have in common with gold or silver plated costume jewelry and American pennies? The common denominator is that the production process of all of them involves electrolysis, an industrial operation that is an example of applied chemistry.
Around 1800, the Englishman Humphry Davy carried out the first studies on electrochemistry. It was Michael Faraday (1791-1867), Davy's early assistant, who enunciated the laws that allow understanding and quantifying these processes. Around 1842, Werner von Siemens, a Prussian artillery officer and industrial pioneer, developed electroplating processes.
But what is an electrolysis process? Basically it is a chemical reaction of oxide reduction, during the course of which electrons are transferred from one chemical species to another. As it is a non-spontaneous chemical process, electrical energy is required for the reaction to take place. This expenditure of electricity is offset by the properties and costs of the materials manufactured during electrolysis. Such a process is capable of transforming such inexpensive raw materials as salt and water into industrially valuable products such as NaOH (caustic soda), Cl2 (chlorine) and H2 (hydrogen). This method, industrially known as chlor-alkali, consumes 0.5% of all electrical energy produced in the USA.
Magnesium, essential for the production of light structural metal alloys, is mainly found in seawater, combined in the form of a dissolved salt, magnesium chloride (MgCl2). This salt is separated from the seawater by fractional crystallization and from it magnesium is prepared in the metallic state by a process of electrolysis. Thus the combined element gains electrons (is reduced) and is transformed to the metallic state. At the same time, the chlorides are oxidized and chlorine is obtained as a by-product.
Another application is the electrolytic bath or deposit. By this procedure, a metal, generally of low cost, is coated by a thin layer of another metal, of higher cost and better properties, during an electrolytic process, for decorative purposes or as protection against corrosion.
The industrial process of electrolytic refining is another application of electrolysis. In this way, pure metallic copper is obtained.
In this case, an anode of impure copper and a cathode of pure copper, both immersed in a solution of a copper compound, are used. As the electric current flows, the impure anode dissolves and copper is deposited on the cathode, but in its pure state. The impurities, which settle in the electrolytic vat, are called anode sludge and are rich in gold and silver. By recovering the precious metals from these sludges, the cost of electrolysis is offset.
Some plastics can also be electrolytically coated with metal. To do this, it is first necessary to make the plastic conductive by adhering a layer of graphite powder (allotropic variety of carbon) to its surface. The electrolytic deposition of copper on plastic has made it possible to improve the quality of microelectronic circuits.
Until 1884, aluminum was considered a semi-precious metal. The cost of production was about twenty dollars per kilogram, and it was used exclusively in jewelry and ornamental works. But in 1886, with the development of the Hall Héroult process, which made it possible to obtain very pure aluminum by means of an electrolytic method, the technological applications of this metal began to develop. In our country, one of the most important metallurgical industries is the one dedicated to the electrolytic production of aluminum. The metallurgical process used obtains the metal from bauxite, a mineral that contains aluminum oxide (Al2O3) as raw material and iron oxide (Fe2O3) as the main impurity. The oxides are separated by alkaline dissolution of the aluminum and pure aluminum oxide is obtained again. This is subjected to an electrolytic process mixed with cryolite (Na3AlF6) to lower the high melting point of the oxide. The result is aluminum with a purity of more than 99%.
The installation of this type of aluminum plants is generally carried out near hydroelectric plants, due to the fact that approximately 15,000 kWh are consumed per ton of aluminum.
Source: Estela Mónica López Sardi Professor of the Faculty of Engineering - UP