Zinc pest (from German ''Zinkpest'' "zinc plague"), also known as zinc rot, mazak rot and zamak rot, is a destructive, intercrystalline

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 engine ...

process of

zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...

alloy An alloy is a mixture of chemical elements of which in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...

s containing lead impurities. Prepared under the direction of the ASM International Handbook Committee. While impurities of the alloy are the primary cause of the problem, environmental conditions such as high

humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...

(greater than 65%) may accelerate the process. It was first discovered to be a problem in 1923, and primarily affects die-cast zinc articles that were manufactured during the 1920s through 1950s. The New Jersey Zinc Company developed

zamak ZAMAK (or Zamac, formerly trademarked as MAZAK) is an eclectic family of alloys with a base metal of zinc and alloying elements of aluminium, magnesium, and copper. Zamak alloys are part of the zinc aluminium alloy family; they are distinguished ...

alloys in 1929 using 99.99% pure zinc metal to avoid the problem, and articles made after 1960 are usually considered free of the risk of zinc pest since the use of purer materials and more controlled manufacturing conditions make zinc pest degradation unlikely. Affected objects may show surface irregularities such as small cracks and fractures, blisters or pitting. Over time, the material slowly expands, cracking, buckling and warping in an

irreversible process In thermodynamics, an irreversible process is a thermodynamic processes, process that cannot be undone. All complex natural processes are irreversible, although a phase transition at the coexistence temperature (e.g. melting of ice cubes in wate ...

that makes the object exceedingly brittle and prone to fracture, and can eventually shatter the object, destroying it altogether. Due to the expansion process, attached normal material may also be damaged. The occurrence and severity of zinc pest in articles made of susceptible zinc alloys depends both on the concentration of lead impurities in the metal and on the storage conditions of the article in the ensuing decades. Zinc pest is dreaded by

collectors Collector(s) may refer to: Arts and entertainment * Collector (2011 film), ''Collector'' (2011 film), an Indian Malayalam film * Collector (2016 film), ''Collector'' (2016 film), a Russian film * Collectors (film), ''Collectors'' (film), a 2020 So ...

of vintage die-cast model trains, toys, or radios, because rare or otherwise valuable items can inescapably be rendered worthless as the process of zinc pest destroys them. Because castings of the same object were usually made from various batches of metal over the production process, some examples of a given toy or model may survive today completely unaffected, while other identical examples may have completely disintegrated. It has also affected carburetors, hubcaps, door handles and automobile trim on cars of the 1920s and 1930s. Since the 1940s, some model railroad hobbyists have claimed, with varying degrees of success, that a method of "pickling" zinc alloy parts by soaking them in

vinegar Vinegar () is an aqueous solution of diluted acetic acid and trace compounds that may include flavorings. Vinegar typically contains from 5% to 18% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation, converting ...

oxalic acid Oxalic acid is an organic acid with the systematic name ethanedioic acid and chemical formula , also written as or or . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name i ...

solution for several minutes before painting and assembling them could prevent or delay the effects of zinc pest. Engine parts of older vehicles or airplanes, and military medals made of zinc alloys, may also be affected. In addition, the post-1982 copper-plated zinc

Lincoln cent The Lincoln cent (sometimes called the Lincoln penny) is a one-cent coin that has been struck by the United States Mint every year since 1909. The obverse and reverse, obverse, or heads, side was designed by Victor David Brenner, as was the origi ...

s have been known to be affected. Zinc pest is not related to

tin pest Tin pest is an autocatalytic, allotropic transformation of the element tin, which causes deterioration of tin objects at low temperatures. Tin pest has also been called ''tin disease'', ''tin blight'', ''tin plague'', or ''tin leprosy''. It is ...

, and is also different from a superficial white corrosion oxidation process ("''Weissrost''") that affects some zinc articles.

References

{{reflist Zinc Corrosion

See also

References