The SS-30 material from Jet-Lube is not intended for use with aluminum where
galvanic corrosion could be a significant issue, as per their spec sheet. For
aluminum interfaces the product they suggest is Zinc Dust Petrolatum.
Paul - W2NMI
----- Original Message -----
From: john@kk9a.com
To: towertalk@contesting.com
Sent: Fri, 16 Feb 2018 13:23:08 -0500 (EST)
Subject: Re: [TowerTalk] Al-to-Al
Penetrox has zinc particles and the SS-30 that K3LR uses has copper. Zinc
is much closer on the galvanic chart to aluminum than copper which
concerns me.
John KK9A
To: towertalk@contesting.com
Subject:Re: [TowerTalk] Al-to-Al
From: Patrick Greenlee <patrick_g@windstream.net>
Date: Fri, 16 Feb 2018 09:42:52 -0600
Conductors (at least metals) are rated on an electromotive scale. The
farther apart they are on the scale the greater the voltage generated when
an electrolyte is present. Stick a piece of aluminum into a lemon (citric
acid solution for electrolyte) and also stick in a piece of copper and
touch the two metals with your multimeter probes and note the voltage.
Switch over to current measurement and see the short circuit current the
little battery will produce.
When dissimilar metals (different ratings on the electromotive scale)
touch in the presence of an electrolyte (acid rain, salty ocean breeze,
etc current flows and the less noble metal is eaten away by electrolysis
(AKA electrolytic corrosion.)
Zinc particles in an oil or grease base are protected from contact with an
electrolyte. When a joint has Penetrox or other equivalent zinc particle
bearing paste in it and is tightened the zinc particles are in contact
with the two substrate materials to be joined, promoting good conductance
and are protected from galvanic action by the oil/grease. By itself zinc
is not magic and will corrode easily. You wouldn't want to use zinc
washers in place of the zinc particle loaded paste.
Replaceable pieces of zinc are used on prop shafts and propellors to
protect the shaft and prop from damage by electrolysis. The zinc is
considered a "sacrificial element" as it is eaten away by electrolysis
while protecting the prop and shaft. Many of the 6 gal water heaters found
on RVs have replaceable sacrificial zinc rods in them. In that service
corrosion of the replaceable zinc is intentional to protect other
components. In joining aluminum antenna components you don't want
corrosion and the zinc in the paste is not intended to be sacrificed to
protect the aluminum.
Anyone want to design sacrificial zincs to put on antennas?
Patrick NJ5G
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