Zinc anticorrosion

[Werner]

I was reading in our Calling All Ship Fans section about various anticorrosion techniques in the 1880s-1900s. The author did not mention zinc anodes.

Does anyone know when cathodic protection for ship hulls was perfected, and when zinc anodes replaced copper plates and wood, bronze fixtures or other methods for protecting hulls from oxidation? Chuck?

[Ron Smith]

The first photographic evidence I can recall seeing is from the mid-1920's, that does not mean it didn't happen earlier. From at least 1905 through the end of WWII antifouling and anticorrosion methods are constantly proposed and tested by the USN.

Probably the scariest antifouling proposed was a system of small ports to inject "mercury chloride" at several places along the length of the hull into the boundary layer. Ostensibly it would "...so poison the water that marine growth on the hull would be impossible."

[Werner]

"What a fascinating modern age we live in...". Captain Jack Aubrey.

[HMAS]

from Corrosion and Electrochemistry of Zinc. 1996 By Xiaoge Gregory Zhang, pg 403
he states zinc anodes were used on copper plated hulls a century & a half ago.

[Foeth]

From at least 1905 through the end of WWII antifouling and anticorrosion methods are constantly proposed and tested by the USN.

Paint technology is still an active field, especially with the ban on tributyltin compounds in 2008 by IMO. There's a host of foul release and anti-fouling paints avaible, each with their (dis)advantages. Zinc anodes are---by the way---not to counter oxidation, but to prevent electrochemical corrosion. The potential from various metals in a seawater solution leads to a bit of current, dissolved the least noble material. This is usual iron (used initially to nail the cupper plates to old hulls), with the brass propeller acting as the main source of the electrical potential problem. Zinc is only used as a sacrifical material on passive systems to be dissolved first, with active-current systems on more modern ships. It stands separately from anti-fouling technology.

Slip-release coatins are non-toxix, so that most fouling is washed away as the ships sails. This helps against grasses and shellfish, but not against slime formation.

[Seasick]

Ocean water contains: (% by mass)
Chlorine 1.94
Sodium 1.08
Magnesium 0.1292
Sulfur 0.091
Calcium 0.04
Potassium 0.04
Bromine 0.0067

Sodium, magnesium, calcium, and potassium are some of the most reactive metals in the world. Because of the natural properties of water the chlorine is cut off from these metals. Therefore they look for another substance to neutralize themselves with. The anodes and cathodes interfear with the normal process and inhibit corosion.

[richter111]

forgive my stupidity,

What about Teflon???

Ric

[Werner]

Um, the recent UN recommendations on further reduction in ozone depleting chemicals will make the manufacture of Teflon impossible.

http://news.bbc.co.uk/1/hi/sci/tech/7010280.stm

[Guest]

Electrolytic protection is definitely something that's been in use since at least the days of the clipper ships, when they were used to protect the copper fastenings on the outside of the hull. However, I guess it is possible that the use of electrolytic protection was discontinued for a while when iron hulls became popular, and was reinvented a while later.

[Shaun Carter]

Your question got me looking and I found this site "http://www.jcse.org/Volume4/Preprints/V4Preprint2.pdf" . It gives a brief history of zinc anodes. It looks like the 1820's was the first use, but it wasn't until the 1930's that they were developed into a reliable system by the USN. At least, that is what the article implies.

Hope this helps
Shaun