On Sun, 10 Apr 2005 14:30:04 -0700, Roy Lewallen
wrote:

Another corrosion-inhibiting coating for aluminum is iridite. There are
conductive and non-conductive versions, something I learned the hard way
long ago.

Tell me about it [g].

I was the engineer responsible for transferring the design of the then
new Phoenix Missile IMPATT diode transmitter from the development lab
to the production floor.

The transmitter had three stages: a single diode driven by a
phase-locked Gunn oscillator fed a three diode cavity that drove a 16
diode cavity.

The development hardware used aluminum cavities that were comprised of
two pieces, with third copper piece that mounted the sixteen diodes.
So there was one aluminum-to-aluminum and one aluminum-to-copper
interface in each sandwich. Since this was a product for the U.S.
military, "passivation" was required for all aluminum parts.

I won't go into the considerable amount of detective work that it took
to decide that despite being "conductive" Alodine and its ilk are not
suitable coatings for rf components.

Gold is your friend, if of course, it's thicker than a few skin
depths, which is another long story. [g]


Roy Lewallen, W7EL

axolotl wrote:
Jim Miller wrote:
there is another type of coating for aluminum called alodyne

which protects the same way as anodizing but is electrically
conductive.



Alodine (R) coatings are not conductive. You can specify a "type 3"
coating that is thin enough that fasteners will usually punch through
the coating layer.

See MIL-C-5541 chromate conversion coatings.

Kevin Gallimore

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