Revelations about zinc electrodes.

Read carefully...very carefully. PASSIVATION is a new term for you. And it is not clear exactly what you said.

Iron is a manufacturing contaminate. Great lengths are gone to avoid this iron contamination to achieve milspec anode class. . The molten zinc is handled with graphite ladles and in graphite molds. The mil spec anode alloy contains added alum and cadmium.

MilSpec Marine anodes are precision manufactured , not simply lumps of zinc.

 

This is what you wrote:

Now you contradict yourself and say that they are not alloys but pure. This post is typical of yours. When you are found to be wrong, you change position and engage on personal attacks. Grow up boy.

 

From here:

http://www.boatzincs.com/use_milspec_a18001k.html

 

That is correct, it can have more impurities than originally thought. However, the key word is "tolerated".

 

The Al and Cd are intentionally added though, so it is indeed an engineered ally. The Fe is a tolerated contaminant.

 

Depending on the installation, iron deposits may or not be a problem. Some need aluminum or magnesium instead of zinc. For example, outdrives and outboards. Also, the salinity of the water has a lot of importance in the choice.

 

I think the keyword here is histrionics.

This whole discussion about Mil spec doesn't make sense to me. The idea behind Mil specs is a bureaucratic instrument to ensure the army gets the best the industry has to offer. Which of course they don't, they only pay more.

Zinc simply is a very cheap metal, suitable for only two applications: to protect iron and steel and be sacrificed doing that, or serve as the negative electrode in a primary cell, where it is also eaten by the electrolyte.

 

Thankyou again for your reply CDK ,the reason I asked the question was that many years ago I was told by a person who's knowledge I respected that the correct way to protect aluminium ,LM25 in this case ,in seawater was to use mild steel fittings to the anodes. I never asked why ,and I will admit it didn't make sense at the time.Your reasoning for using stainless is logical and does make sense. Since I only use GRP jets in GRP hulls now the question to me is academic, but it is something I have wondered about.

 

You indeed use mild steel with aluminium underwater...the galvanic scale indicates that Aluminium and mild steel are most compatible.
...
magnesium,
zinc,
aluminum,
mild steel,
cast iron,
stainless steel (type 410, active),
lead,
Monel,
Muntzmetal,
manganese bronze,
naval brass, yellow brass,
aluminum bronze,
copper,
silicon bronze,
nickel,
stainless steel (types 304, 316, and 410, passive).

 

Good article, again zincs, like all metals today, the importance of purchasing from a reputiable manufacturer is so important, content is simply something printed on a label. A topic i stressed on another thread regarding stainless. In this part of the world i am a fanatic about where my marine products are manufactured and don't mind paying a little more for a good product. Two important points made in this thread,#1 good electrical bonding of the zinc. #2 zincs are sacrifical and after a normal sailing season,(5 to 6 m),should show some signs of being eaten away, if not recheck your bonding to be sure. If completely dissolved before that time suspect unwanted electrical activity either with your own vessel (not good but something you have a degree of control over) or stray activity in the area you keep you boat for long periods of time (something you most likely don't have much control over, so haul out mid season and replace your zincs. As a former owner of an aluminium hull on it's first season afloat,i was a fanatic about checking the zincs, donning fins and mask once a month. Speaking of stray electrical activity, there a big debate by wooden boat owners regarding weather or not to bond thru hulls. Good topic, maybe this little teaser will keep it going into the field of zincs and hull materials and proper electrical practices within ones own craft. Geo

 

Outboards and outdrives have stainless bolts on their factory install anodes. They perform well. Carbon steel will corrode and be almost impossible to remove.

 

Outboards are cast alloy and are closer to ss on the scale. Refer to the above metals table for Al Si Bronze alloys
Outboard casting are A367.0 or A368.0 AlSi alloy .

 

I can't think of anything on a boat, except maybe a frying pan, that would not be an alloy and just plain aluminum.

 

I can think of an example thats not an alloy, the whole boat it's 99.9999%gold, and in many cases fools gold or at least it's weight in gold to produce it. My frying pan is cast iron, useful in repelling borders but the downside is when it's in the hands of an iriate wife.

 

304 is not higher than nickel and monel. That list is wrong.