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Author Topic: Aluminum corrosion in sea water in the presence of other metals  (Read 579 times)

Matt Revington

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Aluminum corrosion in sea water in the presence of other metals
« on: November 14, 2019, 02:10:08 PM »

Just an idea that has been in the back of my mind for a while.

One possibility for the fate of the Electra in the TIGHAR hypothesis would be that after washing off the reef  it's debris could have eventually ended up being caught up in the submerged debris of the Norwich City.   This might explain the absence of aluminum debris on the underwater slope of the reef.  The large structural components of the Norwich City would have been ( I believe ) steel.  In a marine environment aluminum by itself is much more corrosion resistant than steel but due to the difference in the oxidation potential of the metals iron and steel can actually react with the aluminum and cause it to corrode.  I mention this because while looking for  something else  I came across the use of "sacrificial anodes" made of aluminum or zinc.  Because of their relative oxidation potentials the aluminum or zinc actually will corrode more quickly and protect the steel or iron from corrosion.  This is done in industry to protect underwater metal structures  and I have found  articles where they are being used to preserve WWII wrecks in the Pacific.  To be an efficient anode ( and corrode) there must be direct contact between the aluminum and the other metals but if the  debris of the Electra was among the remains of the NC for years on the slope of the reef much of the aluminum could have eventally corroded away or been broken down into smaller hard to identify pieces. 

https://galvanizeit.org/corrosion/corrosion-protection/sacrificial-anodes
« Last Edit: November 14, 2019, 04:20:56 PM by Matt Revington »
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J West

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Re: Aluminum corrosion in sea water in the presence of other metals
« Reply #1 on: November 14, 2019, 07:24:03 PM »

Just an idea that has been in the back of my mind for a while.

One possibility for the fate of the Electra in the TIGHAR hypothesis would be that after washing off the reef  it's debris could have eventually ended up being caught up in the submerged debris of the Norwich City.   This might explain the absence of aluminum debris on the underwater slope of the reef.  The large structural components of the Norwich City would have been ( I believe ) steel.  In a marine environment aluminum by itself is much more corrosion resistant than steel but due to the difference in the oxidation potential of the metals iron and steel can actually react with the aluminum and cause it to corrode.  I mention this because while looking for  something else  I came across the use of "sacrificial anodes" made of aluminum or zinc.  Because of their relative oxidation potentials the aluminum or zinc actually will corrode more quickly and protect the steel or iron from corrosion.  This is done in industry to protect underwater metal structures  and I have found  articles where they are being used to preserve WWII wrecks in the Pacific.  To be an efficient anode ( and corrode) there must be direct contact between the aluminum and the other metals but if the  debris of the Electra was among the remains of the NC for years on the slope of the reef much of the aluminum could have eventally corroded away or been broken down into smaller hard to identify pieces. 

https://galvanizeit.org/corrosion/corrosion-protection/sacrificial-anodes

Indeed, every saltwater boat or ship with exposed [usually] underwater metal parts uses sacrificial anodes to protect them. Stray currents flowing around the vessel can eat a prop off in weeks. Even if the hull is fiberglass, the props, shafts, thruhulls, etc., will rapidly corrode without those anodes as an easier target.

The Navy ran into a major corrosion problem in the late '50s or '60s with retrofitting some destroyers with aluminum superstructure [deckhouses, bridges, etc]. They replaced the old steel superstructure to save weight [tophamper], due to adding/changing armament.
Then Ma Nature saved even more weight by eating some of that replacement aluminum up.
There was a more recent example with the USN Littoral Combat Ship USS Independence-class vessels [see link below].

I just happened to be looking into this area earlier today and came across a rather novel example: a "lasagna cell":
https://en.wikipedia.org/wiki/Galvanic_corrosion#Lasagna_cell
"A "lasagna cell" is accidentally produced when salty moist food such as lasagna is stored in a steel baking pan and is covered with aluminum foil. After a few hours the foil develops small holes where it touches the lasagna, and the food surface becomes covered with small spots composed of corroded aluminum.[14] "
Yum.
John
TIGHAR #5152R
 
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Jeff Lange

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Re: Aluminum corrosion in sea water in the presence of other metals
« Reply #2 on: November 14, 2019, 09:16:29 PM »

I have noticed that for years with our lasagna pans John. Even had a favorite pan that we HAD been in the habit of leaving the leftovers in for a day or so. It now has several pinholes along its' sides at the level of the top of the food. Only used for dry storage now! ;)
Jeff Lange

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Don White

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Re: Aluminum corrosion in sea water in the presence of other metals
« Reply #3 on: November 15, 2019, 08:15:21 PM »

On the topic -- this is another possible reason there might be little or nothing of the Electra to find under water.

Off topic (of the Electra) -- Stainless steel and plain steel have different galvanic indices. If stainless fasteners are used in steel structures -- such as is often done in antique car restorations -- and are in contact with the plain steel, it can accelerate the corrosion of the plain steel, which is rather the opposite of the restorer's intention in replacing plain steel fasteners with stainless.

Off off topic -- Lasagna is also acidic as are most Italian foods, which also creates a galvanic battery effect. My grandmother (1900-1997) '/=[made spaghetti sauce in a Wear-Ever aluminum pot. I have the pot today. It is heavily pitted inside. I don't use it to make spaghetti sauce.

LTM (who remains stainless and uncorroded),
Don
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Randy Conrad

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Re: Aluminum corrosion in sea water in the presence of other metals
« Reply #4 on: November 17, 2019, 06:28:45 AM »

After reading Matt and Don's posting, it had me thinking about the possibility that the water on Gardner Island/Niku may have become acidic at some point in 1937  due to small eruptions or gas releases from an extinct volcano. This is just a theory. But, what are the chances that the Electra did indeed fall into a small wading pool and was overcome with toxic acid spewing from the rock and over a small time was destroyed.                                                                                               

https://www.usgs.gov/faqs/can-lakes-near-volcanoes-become-acidic-enough-be-dangerous-people-and-animals?qt-news_science_products=0#qt-news_science_products

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Randy Jacobson

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Re: Aluminum corrosion in sea water in the presence of other metals
« Reply #5 on: November 17, 2019, 06:53:17 AM »

After reading Matt and Don's posting, it had me thinking about the possibility that the water on Gardner Island/Niku may have become acidic at some point in 1937  due to small eruptions or gas releases from an extinct volcano. This is just a theory. But, what are the chances that the Electra did indeed fall into a small wading pool and was overcome with toxic acid spewing from the rock and over a small time was destroyed.                                                                                               

https://www.usgs.gov/faqs/can-lakes-near-volcanoes-become-acidic-enough-be-dangerous-people-and-animals?qt-news_science_products=0#qt-news_science_products
Extremely far-fetched.  Niku is a coral atoll, whose volcanic base is millions of years old and has been inactive for a very very long time.  What was described in the article are lakes on active volcanoes.  Hydrothermal water circulation is a primary cause of the acidity, and the chances of active, deep-seated hydrothermal circulation on Niku is improbable.
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Bill Mangus

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Re: Aluminum corrosion in sea water in the presence of other metals
« Reply #6 on: November 17, 2019, 07:13:29 AM »

I'm not sure and I don't know if this makes a difference, but wasn't Norwich City constructed with iron , not steel? As was Titanic.
Bill Mangus
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Don White

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Re: Aluminum corrosion in sea water in the presence of other metals
« Reply #7 on: November 17, 2019, 08:05:26 AM »

The Titanic (and her sisters) and the Norwich City were both made with steel plating and framing, which had replaced iron in those applications by then. It was likely a similar kind of steel in both, as they were both built in Britain around the same time. There was also iron used in many places, such as cast iron in the engine. For this discussion, it doesn't make much difference, as the galvanic number of iron and low-carbon steel is the same (-85). The discussion here is whether galvanic corrosion could have hastened the disappearance of aluminum, which we can say it well might have, if in contact with ferrous metal, that is if Electra debris ended up in contact with Norwich City debris. Our reconstruction of events suggests that is possible. There are other possibilities, including (and not limited to) that it's somewhere we haven't looked, or buried underwater by fallen material (man-made and natural), or so broken up that we haven't recognized the pieces.

LTM,
Don

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Bill Mangus

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Re: Aluminum corrosion in sea water in the presence of other metals
« Reply #8 on: November 17, 2019, 12:06:28 PM »

Thanks for the answer, Don.  I was wondering because of the vast difference in the way the two wrecks appear now.  Titanic is covered in those "rusticiles" (excuse the spelling) while what we've seen of Norwich City is not, perhaps because of the action of the sand and silt filtering down from the reef.

Thanks for the explanation.
Bill Mangus
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Matt Revington

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Re: Aluminum corrosion in sea water in the presence of other metals
« Reply #9 on: November 17, 2019, 04:36:51 PM »

The environment makes a big difference, in particular the higher oxygen concentration which drives oxidation, biological activity( barnacles, coral)  and the increased physical activity (waves, currents etc) near the surface at the Norwich City versus the very different deep ocean environment near the Titanic.
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