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Galvanic Corrosion Current -
History: It took three famous minds and some chance (unintended) observations/discoveries to unravel the mysteries of galvanic current, induced when two dissimilar metals/alloys are electrically connected and in contact with an electrolyte. Luigi Galvani (1737-1798) Galvani, an Italian physiologist, observed that dead frogs "twitched" when coming into contact with dissimilar metals. Galvani (incorrectly) attributed this effect to electricity produced by the animals' muscular and nervous systems ("animal electricity").
Alesandro Volta (1745-1827) Volta became fascinated by Galvani's experiments and came to the insight that the generated electricity originated from the dissimilar metals in contact with the frogs (electrolyte), rather than from the animals themselves. Volta's work included the development of batteries (generators of electric current) consisting of two dissimilar metals in contact with an electrolyte. Only a limited number of metals were available to Volta at the time, notably copper and zinc with their relatively high separation in the galvanic series. The generation of current by Volta's galvanic cells (referred to as a "pile") was described in a paper to the Royal Society in 1799. The terminology of "anode" and "cathode" used for the two electrodes in a galvanic cell has been attributed to William Whewell, only introduced some 50 years after Volta's experiments. (Sir) Humphry Davy (1778-1829) Davy made the breakthrough discovery that current was generated by chemical reaction in Volta's cells (he noticed oxidation of the zinc anode). Reportedly, Volta had assumed that mere contact of the dissimilar metals with the electrolyte was sufficient to generate current, when these metals were connected. Also of importance is the reverse principle that an electrical current can induce a chemical reaction - as applied in electroplating. Davy produced potassium, by plating it out on a platinum cathode in a galvanic cell. Other metals were also subsequently isolated by Davy in this manner. Humphry Davy's connection to Michael Faraday Davy hired another famous scientist, none other than Michael Faraday, in 1813. Faraday is accredited with the rule of proportionality between the mass of material deposited (or dissolved) and the current flowing in a cell. This law is known as Faraday's Law of Electrolysis and still used to convert corrosion current densities to mass loss - refer to ASTM G102: Standard Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements. After many years of working together, an unhealed rift reportedly occurred towards the end of Davy's career. References: T. Crump: "A Brief History of Science - As seen through the development of scientific instruments", Robinson, London, 2002.
Galvanic Corrosion Testing - History: The ASTM G149 standard (Standard Practice for Conducting the Washer Test for Atmospheric Galvanic Corrosion) reportedly evolved from washer (disk) testing by H.O. Teeple in 1949. Source: ASTM International (www.astm.org) Links:
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