British Historic Cannonballs 5

[dik]

Any suggestions on how to keep the cannonballs from corroding on exposure to air?

From the BBC:

The Mary Rose sank in 1545 and was raised from the sea in 1982. The cannonballs on board are difficult to conserve because chlorine has got into them from being in the sea. The chemical has got in all the way to its core. This means that they start to corrode if they are exposed to the air.

Dr Schofield's team has tried to remove the chlorine by soaking some cannonballs in solution. But the researchers found that although they had extracted some they hadn't removed it all. They discovered this when the cannonballs began to disintegrate when they were put on display.

http://www.bbc.com/news/science-environment-43334700

Dik

 

[bimr]

Remember reading an article about the conservation of the Hunley artifacts. The procedure is outlined in this article. Don't have an update on the procedure but would expect that it would work for the cannonballs as well.

Hunley

 

Such extensive corrosion would not have all happened after exposure to air, but I don't doubt that whatever has gotten in through the cracks could be difficult to remove.
To paraphrase Monty Python, this is an ex-cannonball.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[dik]

Thanks, gentlemen

Dik

 

[dik]

bimr:
Sent your info on to the MaryRose.org

Ironic metallurgist:
Sent your info on to John Cleese

thanks... Dik

 

[stevenal]

Why display them in air? There must a suitable neutral transparent fluid that could be used. And even ex-parrots can be mounted for display.

 

[dik]

Why display them in air?

Should have replied... thanks for the info... have passed it on, too.

Dik

 

[Chumpes]

I maybe stupid but if the cannonballs have been preserved in low oxygen seawater for so long, maybe keeping them into the same environment will avoid further corrosion ?
what about coating with resin ?

 

[dik]

what about coating with resin ?

Sent the information about displaying them in a fluid and added the suggestion of a coating system... heard nothing back from them. From the photos of the deteriorated cannonballs, I would never have guessed that they would have deteriorated like that...

Dik

 

[bimr]

I maybe stupid but if the cannonballs have been preserved in low oxygen seawater for so long, maybe keeping them into the same environment will avoid further corrosion ?

That is generally what is typically done, to maintain the item in storage until the item undergoes conservation.

what about coating with resin ?

Problem with this solution is that exhibit visitors want to see the real thing. You could also show images of the item too, but exhibit visitors want to see the real thing.

 

[EdStainless]

I recall that they have used electrochemical treatments to recover encrusted and heavily corroded artifacts.
The fact that these are intact as found and only crumble on exposure to air tells me that it is the oxidation of the internal phases that are driving the destruction.
Perhaps an applied electrical current while submerged in hot water would be a way to 'de-tox' these.
I presume that a sample has been core drilled from one for detailed chemical and structural analysis?
Sounds like a job for someone working on a PhD in electrochemistry.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[dik]

EdStainless...
Will pass that info on...

 

[WKTaylor]

Carbon depletion?

Consider baking at least 1 or 2 balls in a inert atmosphere [dry argon] at 180F for at least 90+ days.



Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[3DDave]

Seems to be entirely from chlorine infiltration and the subsequent corrosion on exposure to oxygen and moisture.

"Cl can remain trapped in pores within the metal, in the form of hibbingite, b-Fe2(OH)3Cl. On exposure to oxygen at near-neutral pH, this phase rapidly oxidises to b-FeO(OH)."

https://onlinelibrary.wiley.com/doi/abs/10.1002/ange.201713120

I don't know enough chemistry to understand how much energy is required to break the Cl bonds in the hibbingite.

Here's a lengthy paper on the problem

https://orca.cf.ac.uk/54986/1/U585375.pdf

It's a 200+ page dissertation.

Investigating the treatment of chloride-infested archaeological iron objects
Melanie B. Rimmer
Thesis submitted to Cardiff University
in candidature for the degree of PhD

 

[dik]

Thanks very much Dave; I'll pass it on.

Dik

 

[djhurayt]

Have you talked with the folks restoring the H.L. Hunley?

 

[dik]

I don't know... I've just passed the information on. I figgured that this is an 'international site' and that there would be lots of engineers that could offer solutions. Same reason I went to university... you cannot be among 20,000 academics and not learn something.

Dik

 

[bimr]

Have you talked with the folks restoring the H.L. Hunley?

The 2nd post above mentioned the Hunley procedures.

 

[dik]

I'm going to have to re-connect with Mary Rose... tried logging in this AM and they had no record of my email address. Maybe that's a reason for not hearing back... just sort of a one way conversation.

Dik

 

[georgeverghese]

If this corrosion requires oxygen, then would blanketing the air tight display container with nitrogen do the job? You could purge out the old N2 every few days or so and replace with fresh N2 for about a month or so, just in case there is some residual air in the pores?