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Mixed metal oxide (MMO)
Mixed metal oxide (MMO) electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials d ...
s, also called Dimensionally Stable Anodes (DSA), are devices with high conductivity and corrosion resistance for use as anodes
An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...
in electrolysis. They are made by coating a substrate, such as pure titanium plate or expanded mesh, with several kinds of metal oxides. One oxide is usually RuO2, IrO2, or PtO2, which conducts electricity and catalyzes the desired reaction such as the production of chlorine gas. The other metal oxide is typically titanium dioxide
Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound with the chemical formula . When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insolub ...
which does not conduct or catalyze the reaction, but is cheaper and prevents corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
of the interior.
The loading or amount of precious metal on the substrate (that is, other than the titanium) can be in the order of around 10 to 12 grams per square metre.
Applications
Applications include use as anodes in electrolytic cells for producing freechlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
from saltwater in swimming pools, in electrowinning of metals, in printed circuit board manufacture, electrotinning and zinc electro-galvanising of steel, as anodes for cathodic protection of buried or submerged structures.
History
Henri Bernard Beer registered his patent on mixed metal oxide electrodes in 1965. The patent named "Beer 65", also known as "Beer I", which Beer claimed the deposition of Ruthenium oxide, and admixing a soluble titanium compound to the paint, to approximately 50% (with molar percentage RuO2:TiO2 50:50). His second patent, Beer II, reduced the Ruthenium oxide content below 50%.H.B. Beer. Journal of Electrochemical Soc. 127, 1980, 303CSee also
*Chloralkali process
The chloralkali process (also chlor-alkali and chlor alkali) is an industrial process for the electrolysis of sodium chloride (NaCl) solutions. It is the technology used to produce chlorine and sodium hydroxide (caustic soda), which are commodit ...
References