Zinc pest

From Wikipedia, the free encyclopedia

Zinc pest, (from German Zinkpest), is a destructive, intercrystalline corrosion process of zinc alloys of poor purity.

Zinc pest affects primarily die-cast zinc articles that were manufactured during the 1930s, 1940s, and early 1950s. In Germany, articles made from ZAMAK, a zinc alloy that also contains aluminum, magnesium, and copper, may be affected when produced during WWII and several years thereafter ^[1] Purer alloys were not available for the manufacturers as they were used for the war effort, or , after the war, just not on the market. While impurities of the alloy seem to be the cause of the problem, environmetal conditions such as warm humidity (greater than 65 %) may accelerate the process.^[2] Also, significant temperature changes can be damaging.

Affected objects may show surface irregularities such as blisters or pitting, they expand, buckle, tear, and in the end crumble. The irreversible process will eventually destroy the object. Due to the expansion process, attached normal material may be damaged secondarily. Zinc pest is different from a superficial white oxidation process (“Weissrost”) that may affect some zinc articles.

Zinc pest is a dreaded condition for collectors of old model trains, toys, or radios where the zinc die-cast process was used. Valuable items are rendered worthless but for their residual parts. Also part of engines of older vehicles or airplanes and military medals may be affected. Fortunately many articles of the time period at risk show no signs of zinc pest and seem to be stable.

Articles made after 1960 are generally considered free of the risk of zinc pest. Use of purer materials and more controlled manufacturing conditions make it unlikely that modern zinc article will encounter degradation by zinkpest.^[2]

Zinc pest is not related to tin pest.