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<p>[QUOTE=&quot;-jeffB, post: 1079973, member: 27832&quot;]Actually, it&#039;s used as a sacrificial anode. Zinc <i>is</i> more reactive than iron or copper; but, when it&#039;s bound to one of those metals -- that is, in good electrical contact with it -- it gets attacked before the less-active metal.</p><p><br /></p><p>So, if you&#039;ve got a part made of galvanized steel, the zinc will slowly corrode off it. But you don&#039;t notice unsightly deposits, because the products of zinc corrosion are colorless and water-soluble; and, until most or all of the zinc is gone, the iron remains intact.</p><p><br /></p><p>On a copper-coated zinc penny, if you puncture the copper layer, the zinc immediately starts getting attacked. In fact, I imagine it gets attacked <i>faster</i> than the coating on galvanized steel, because the difference in &quot;electronegativity&quot; is greater with copper than with iron. Any acid, or even a strong base, will speed things along considerably. (Zinc oxide is &quot;amphoteric&quot;, meaning it can react either as a base or an acid.)</p><p><br /></p><p>So, yeah -- punch through the copper coating, and you get pits that grow rapidly (by coin-decay standards, anyhow).</p><p><br /></p><p>Maybe BadThad can fact-check me on this...?[/QUOTE]</p><p><br /></p>

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