This is the basis of galvanising - coating steel with zinc. It is not a
mechanical barrier as I once thought, but a sacrificial layer. Strangely,
for this discussion, corrugated steel roofing here in Aus. is now coated
with Zincalume - I assume a zinc-aluminium alloy -which is much longer
lived than the old zinc-on-iron style.
Andrew
> You are slightly off target on this one also. Metal hulled ships in
>the oceans of the world form an electrical cell with the saltwater being
>the electrolyte. A minor flow of electrons will leave the ship's hull
>from areas determined by physical factors but generally aft in the
>propulsion and rudder areas or in free flood areas of little
>turbulence. The sacrificial metal is almost always zinc ingots (called
>zinc anodes) are molded onto steel straps which are welded to the hull
>or ingots of various forms with steel sleeved bolt holes meant to be
>bolted onto the hull in the chosen area.
> I suppose that aluminium could work for this but I have never seen or
>heard of it my 25 years of marine engineering. For sure, that it
>wouldn't last very long though. Mostly changing of sacrificial anodes
>is done in drydock.
>Rand E.
>
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>~~~~
>> > Yes, the oxidation is not much of a surprise to me. The rounds have been
>> > lying in the fields (exposed to rain etc.) for several years. They seem to
>> > have been made for the majority of a metal which contains iron (as
>>they show
>> > rust), probably this part is regular (or hardened steel), and
>>something of a
>> > light shade of metal, which most closely resembles aluminium. Now,
>>supposing
>> > this is aluminium, I seem to remember that (sea) ships use blocks of
>> > aluminium as so-called "sacrificial metal", the idea is that aluminium
>>is a
>> > stronger reductor than the metal of the ship it self, causing the
>>aluminium
>> > to get oxidised rather than the ship (a simple yet effective trick) [I
>>hope
>> > I remembered all this correctly from my high school chemistry
>>classes]. So,
>> > it's not strange indeed to see that the tips of these bullets also got
>> > oxidised.
>
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