Zinc pest, (from German Zinkpest), is a destructive, intercrystalline corrosion process of zinc alloys containing lead impurities. While impurities of the alloy are the primary cause of the problem, environmental conditions such as high humidity (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 1930s, 1940s, and early 1950s. The New Jersey Zinc Company developed zamak alloys in 1929 using 99.99% pure zinc metal to avoid the problem, and articles made after 1960 are generally 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 blisters or pitting, and they expand, buckle, tear, in an irreversible process that will eventually destroy the object. Due to the expansion process, attached normal material may also be damaged. Zinc pest is dreaded by collectors of old die-cast process model trains, toys, or radios because otherwise valuable items can be rendered worthless but for their residual parts. Engine parts of older vehicles or airplanes, and military medals made of zinc alloys may also be affected.
- Tin pest (chemically unrelated but similar in its progressiveness and irreversibility)
- Bronze disease (chemically unrelated but similar in its near-inexorable progressiveness and irreversibility)
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- prepared under the direction of the ASM International Handbook Committee ; Stephen D. Cramer and Bernard S. Covino, Jr., volume editors. (2005). ASM Handbook 13B. ASM International. p. 37. ISBN 0-87170-707-1..
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- Wanhill, R.J.H.; Hattenberg, T. (May 2005), Corrosion-induced cracking of model train zinc-aluminium die castings (PDF), National Aerospace Laboratory NLR, NLR-TP-2005-205, archived from the original (PDF) on 2011-07-16.