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Food for thought. Any engineers out there.

S

Smilin' Jack

Well Known Member
Zinc.

While I have been involved in aviation for my whole life. This build stuff is new and it presents an opportunity for a lot of questions and exploration.

I also have owned boats my whole life of various kinds. so my questions deals with corrosion.

If as several of my friends in Alaska have Halibut fishing boats made out of Aluminum that are protected with Zinc Anodes. Why can we not protect an aircraft with a zinc anode. We spend hours zinc cromating out skins and add a couple pounds of paint but could not an anode be used instead?

As noted on a lot of discussions and with Vans themselves they believe that the alclad coatin alone will provide sufficient protection and in fact most single engine Cessna's and Pipers never zinc coated the inside skins and many are still corrosion free 50 years after production.

I realize that the boats are immursed in the salt water. But on the 26 foot
twin 200 Yahamma Halibut boat that my buddy ownes in Alaska he only has about 4 lbs of zinc on it. when it wears down he replaces it. He has had this boat for 26 years and it looks as good as his aircraft does. I popped the question to him and he looked at me and said maybe no one ever thought of it. Probably be to simple :) :) :) :)

Well engineers...... fire away........... we got our helmets on.

Smilin' Jack
Empenage done.
Wings due in 5/16
 
Smilin' Jack said:
Zinc.

I popped the question to him and he looked at me ...


Smilin' Jack
Empenage done.
Wings due in 5/16
Click to expand...

What does this have to do with zinc again?! :D

Anyway....I'm only half engineer so I could be way off base but my understanding is that the boat being immersed in the water actually causes a slight voltage differential between the dissimilar metals. Obviously when you have a voltage differential you have current flowing (very, very small amount obviously) and this is what allows the zinc anode to work. The current flows in such a direction as to break down the zinc, but not the aluminum.

In an aircraft, I don't believe you would have any voltage potential because there is no immersion. Thus, I don't think there would be any induced current and instead of being an anode, the zinc would just be a lump of zinc.
 
good food for thought

This seemed to be a good idea that I knew nothing about. So I did a search and found this statment on Wikipidia.

"For this to work there must be an electron pathway between the anode and the metal to be protected (e.g., a wire or direct contact) and an ion pathway between the anode and the metal to be protected (e.g., water or moist soil) to form a closed circuit; thus simply bolting a piece of active metal such as zinc to a less active metal, such as mild steel, in air will not furnish any protection."
http://en.wikipedia.org/wiki/Galvanic_anode

So, it seems the water is needed to make this work.

I suppose I will open a can of worms here, but I wonder if zink cromate is working on the same theory, and if so, does it ever wear out? Probally not in my lifetime, but it is some more food for thought.
 
Well I guess the zinc anode being bolted directly to the aircraft ei counter balance weights, or on the belly would be a direct path to the aluminum. And since salt laden air is usually very high in mositure would that not be a medium?
All the zinc cromating in the world does not help acid rain.
so the only thing we are combating is salt laden air that we fly in that causes corrosion?
Jack
 
Smilin' Jack said:
Well I guess the zinc anode being bolted directly to the aircraft ei counter balance weights, or on the belly would be a direct path to the aluminum. And since salt laden air is usually very high in mositure would that not be a medium?
Click to expand...

Take a good multimeter and measure the resistance between the probes in some salt water at a fixed distance.


Now hold those two probes up in "salty air" at the same distance and see what you get.
 
There is a good article on this topic in the 27 years of the RVator book on page 44. I also read that zinc chromate does (wear out) eventually. It says that zinc chromate releases chromate ions which neutralize the corrosive salts and prevents electrolytic reaction. The protective elements in zinc chromate are exhausted eventually.
 
Salty air??

I thought when water evaporated it left behind everything but an H2O molecule, hence the salt flats in Utah... Now if you are close to the ocean, you can sure get salt spray which will corrode things really well..

I hate to start something, I really do... Experts?
 
Marine layer

some condensation nuclei is actually salt.

Salt-air that has been thrown about in this thread is a misnomer. When one is close enough to the ocean to smell "ocean air," we cannot say that what a person smells is salt. Rather, what we smell is ocean life-- and of course some of it rotting.

Anytime that you have fog or condensation formed near the coast in and around sea spray--salt will be present at the core of some of the fog as the particle that made condensation possible.

Anytime salt is not part of condensation (fog or clouds) it is fallout or dust.

There you have it. Sea spray, condensation nuclei, fallout, and dust.

And I'm a geek.:D
 
Corrosion-X...

...the airplane every three years or so and forgetaboutit. This stuff is Mil-specked and will wick itself between the skin overlaps.....AFTER you paint it, not before!

Best,
 
I have 11 years experience flying seaplanes in and out of salt water. We use CorrosionX and the 50+ year old planes are in great shape.

Our water rudders do have Zinc attached to them, though.
 
Yes I remember the corrosionX stuff it is a mist they spray and it goes in every crack and nook.
Good stuff.

Smilin' jack
 
There's been some discussion recently about Corrosion-X and ACF-50 causing premature failure of components... The mechanism is that the C-X and ACF-50 get between the surfaces, lubricating them. Anywhere there's just a little movement possible, the parts can fret away at one another and cause rivets to start smoking.

At least, that's the theory. I've seen many older Cessnas with ACF-50 applied, but none that have had it in there for 30 years...
 
I like that... taking one for the team... :)

We all have a little sacrificial anode to be so dedicated to building...:)
Smilin' Jack
 
I seem to remember reading in the book about Ameilia's shoes that they found airplane sheet metal parts from WW2 on the island coated with zinc chromate that were said to look like new. These parts were on an island that the sea washed over at certain times of the year. That sounds like pretty good protection to me. There is also some compelling evidence for the use of zinc chromate in the over the road bus world. Look at the chromated busses from the 50s and 60s that that were used in road salt environs and have lasted well. I have a 1969 GMC that is clean as a pin underneath. My .02
 
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I am not an engineer, but...

I am not an engineer, but I have a bit of experience with different aluminum's.

Most aluminum boats are made from 6061, t6 if I remember correctly.
It is not usually Alclad.

All of our aluminum RV Skins are 2024t3 and are alclad.

They are different for specific purposes.

My belief is that an anode would only be advantageous on the water borne vehicle.

Floatplane operators/mechanics and Material Engineers, help us out a bit here:confused:
 
I know this is an interesting subject.. and after thinking about some of the post I have to inject this thought.
My folks retired in Largo, Fl and the house they bought had a brand new porch and of course Jalousie windows. They were bright and shiney when installed but after a year they started to get pitted. After about 5 years things were falling apart because the aluminum was getting so pitted and eaten up. Their house was not on the water but about 3 miles from it.

The second thought. Our Corporate jet we kept in FT Myers over the New Years and all the pins for the pitot and static holes were pretty well rusted after a 2 week time period. But you have to remember this is on the Gulf side of FL and the winds are generally from the Gulf to the east. I know there are some RV's that are based at FT Myers and I'll check those n numbers out and see if the owners have any issue with the weather there. 2 of them are tied down outside. One is an Blue RV8.



We never have left the aircraft near salt water before and we have left it in AZ, CA, Co and other states many times for 2 week time periods and never had the rusty pins. So I believe that if an area is constantly being exposed to salt air it does have an effect on the aircraft. Simple things such as brake rotators begin to rust. Stuff like this just never happens in Atlanta.

When I was a new flight instructor in 1969 some of our training 150's had chromed rotator so they would not rust up.

Yes our enemy is the salt and acid rains and I don't really think it matters how your aircraft is exposed to it. We always immediatly have out corporate aircraft pressure washed when we return from any coastal State or from the islands.

Smilin' Jack
 
I don't think anyone is saying that salt isn't bad for aluminum.

The real question is whether or not a sacrificial anode will work without immersion in water.
 
Yep your right... and of now the only thought is that the aluminum has to be immersed in the salt water for the anode to work.

Wish we had a chemist out there.

Smilin' Jack
 
Gentlemen,

I am new to the Forum just joined the other day after reading it for months.
I have an Bachelors degree in industrial chemistry and worked as a production chemist for a plant for several years.

So really I know about as much as this stuff as you guys. However I can say this. There is more to Chemistry than meets the eye.

The completion of the circuit is how the ReOX reaction happens. It is this competion of the circuit that occurs when water hits iron. The iron corrosion reaction happens in plain air, with no assistance but its local to the seed point, in other words, without water you just get a rust pin prick spot. With water you get the circuit completing and with salt water you get that nice ion exchange path that someone spoke of earlier.

A physical barrier does a lot to stop this and it doesn't have to be thick. One molecule thick is enough. Then you have sacrificial materials that experience the Oxidation preferencially due to their electro negativity ie you Zinc and Chrome species. They get hit with the electrons coming from the Oxygen instead of your trusty hull or plane.

Now here is the truth. Weird stuff.

Thats right, Chemical species that have really really short lives and and unstable but still get a dance at the party. They still happen. Someone spoke about the smell of the sea being organics? Yep they were right on the money. It isn't much but it is enough to make all the difference.

These high energy species then catalyse other reactions and make a whole soup of interesting reagents that are in low quantity, but after years they have their effect. These are so difficult to understand that us Chemist often don't even try to understand them...... we experiement instead.

Its call suck it and see. (In the 1800 it was actually sucking and actually seeing. There was a material called cinnabar. Highly toxic, tastes sweet. How would you have liked to that evaluation!)

So while conversation of mositure in the atmosphere and sacrificial alloys and salt in the ying yang go on, and they all have some merrit, no one here has said anything silly I can tell you, I would look at what has been experimentally support for a long time.

THATS the real chemistry. The rest is a bunch of us guys in white coats talking BS.

So the summation of all that guff is........If you don't want to coat it, your going to make assumptions that have not been supported by experiementation. It doesn't mean its a dumb idea, its just that there isn't lots of stats to tell you its all good.

GB

PS. Coat the metal, your family are good people and they like ya, stick around for them by going with boring convention and sparying that goop on the fuse.
 
Good,
I think we can put this to rest...

thanks
Smilin' Jack
But maybe I'll attach an anode just to see if it gets eaten up :) :) :) :)
 
Of course!!!

**** now that all this Whoha has been brought up I wanna see what happens too!

I personally like the Zinc, it kinda gives me a feeling like its 1945 and I am building something that is going to fight za germans.
(things ya think about when you have spent too long on something)
 
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