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<p>[QUOTE="NSP, post: 3377998, member: 74849"]Regarding brass corrosion, alloys have a “parting limit,” which is the minimum concentration of the more noble metal (in this case Cu) above which the more active metal won’t corrode preferentially. In other words, below this minimum Cu concentration threshold, Zn corrodes preferentially to Cu. This preferential corrosion of alloys is called “dealloying.” For brasses, this is called “dezincification.” The parting limit for Cu/Zn is around 85% Cu, so this coin would be susceptible to dezincification. See the following links for more information about parting limits and dezincification. </p><p><br /></p><p><a href="https://www.corrosionpedia.com/definition/856/parting-limit" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://www.corrosionpedia.com/definition/856/parting-limit" rel="nofollow">https://www.corrosionpedia.com/definition/856/parting-limit</a></p><p><br /></p><p><a href="https://www.nace.org/Corrosion-Central/Corrosion-101/Dezincification/" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://www.nace.org/Corrosion-Central/Corrosion-101/Dezincification/" rel="nofollow">https://www.nace.org/Corrosion-Central/Corrosion-101/Dezincification/</a></p><p><br /></p><p>As for whether or not the Zn preferentially corroded... I’m not sure. The reddish brown corrosion products don’t look like the usual Zn corrosion products (Zn oxide is white), so it’s hard to tell for sure without knowing what environment the coin was stored in.[/QUOTE]</p><p><br /></p>
[QUOTE="NSP, post: 3377998, member: 74849"]Regarding brass corrosion, alloys have a “parting limit,” which is the minimum concentration of the more noble metal (in this case Cu) above which the more active metal won’t corrode preferentially. In other words, below this minimum Cu concentration threshold, Zn corrodes preferentially to Cu. This preferential corrosion of alloys is called “dealloying.” For brasses, this is called “dezincification.” The parting limit for Cu/Zn is around 85% Cu, so this coin would be susceptible to dezincification. See the following links for more information about parting limits and dezincification. [url]https://www.corrosionpedia.com/definition/856/parting-limit[/url] [url]https://www.nace.org/Corrosion-Central/Corrosion-101/Dezincification/[/url] As for whether or not the Zn preferentially corroded... I’m not sure. The reddish brown corrosion products don’t look like the usual Zn corrosion products (Zn oxide is white), so it’s hard to tell for sure without knowing what environment the coin was stored in.[/QUOTE]
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