Coating aluminum

".Blueskies." wrote in message
om...

"Lou" wrote in message
oups.com...
So, let me get this right,
acid bad
Alodine good.


Alodine is acid - chromic acid.

Now that I didn't know...or had forgotten!
--
Jim in NC

"Lou" wrote in message
oups.com...
Thanks everyone, I'll be ordering the solution this week.

Good choice. Alodine treatment is the clear cut industry standard.

It is interesting to hear about the Navy's anti corrosion cycle. Given,
they operate airplanes in some of the harshest environments in the world.

A good friend of mine was a Master Chief in the Navy, working on aircraft
from Vikings to A-6's, to FA-18's. Another note of interest is that he
never served on a nuclear carrier. They had?have (how many now, I don't
know, anyone else know?) a lot of conventional carriers out there, even
though all you hear about are the Nukes. The conventional carriers add
another negative impact on the maintenance of the aircraft. The fuel burned
for propulsion is an added factor accelerating corrosion.

Airplanes are regularly taken out of service, and either areas, or the whole
airplane is completely stripped down, and the parts are stripped, retreated
and reassembled. If they did not do this, I'm quite sure that their
airplanes would indeed start falling out of the air.
--
Jim in NC

Alodine is acid - chromic acid.

Now that I didn't know...or had forgotten

And the acid etch applied before alodining to remove any
corrosion products is phosphoric acid.
Aluminum is never found in the free state as many other metals
sometimes might be. And it doesn't smelt easily, requiring huge amounts
of electricity to electrolyze it out of the ore. So it's a relatively
recent metal, being rather scarce (and super-expensive) 100 years ago,
in spite of the fact that it's one of the most abundant elements in the
earth's crust.
I suppose we don't find it in its free state in nature because
it reacts so easily with just about anything else and returns to its
former oxides or sulphates or chlorides or whatever. And I imagine
that's why it hasn't seen wide service in cars, what with all the road
salt used in many areas. Even inside an airplane wing we find surface
corrosion on uncoated 2024, just from condensation. Any good floatplane
will have its interior zinc-chromated.

Dan

..Blueskies. wrote:
"Lou" wrote in message oups.com...

So, let me get this right,
acid bad
Alodine good.



Alodine is acid - chromic acid.



I hear the confusion, Lou. Yes, alodine is also acid, but what your
doing is using the acid in a CONTROLLED environment. You put the piece
in the alodine bath for only a short time. Leaving it there for
extended periods IS bad. It'll eat your part up.

After you get the surface coated with a good layer of whatever chromium
compound it is that the alodine leaves behind, you pull it out of the
solution and wash it with clean water. As soon as it is good and dry,
you put a coat of primer on it.

The post about bases is spot on, except that you don't find them in the
air much. Most of the acid in the rain is put there either by burning
coal or diesel fuel. As Morgans pointed out, the air around diesel
driven air carriers has given the Navy fits for decades.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."