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<< Lancair Builders' Mail List >>
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Just a few thoughts about using the Titanium rod.
FROM http://www.pemnet.com/design_information/galvanic.html
Since TI is at the lower end of the chart and Stainless Steel
is 4 to 5 levels above I would think the electronegativity
difference would yield very little corrosion potential. Aluminum
is at the top end of the chart. Aluminum forms a protective
oxide with the air that prevents further corrosion. Oxygen
and Nitrogen would be way, way off the top of the chart.
FROM http://www.deutschetitan.de/eng/profi/kb21.html
Contact corrosion in titanium materials
In the active condition titanium is a relatively unnoble metal
whose standard potential at <1.75 V lies between those of
aluminum and magnesium. However, already at room temperature
titanium forms a firmly adherent and dense passive layer on
the surface which characterizes its corrosion properties.
In oxidizing and neutral media, as well as in reducing media
containing amounts of oxidizing components (inhibitors) which
allow formation of the passive layer and inhibit its destruction,
titanium displays high corrosion resistance.
Due to this passive layer there is no significant difference in
electrochemical potential between titanium and the corrosion
resistant 18/8-CrNi steels, Monel and Hastelloy.
The risk of contact corrosion on surfaces of roughly the same
size in seawater and chloride-containing solutions for example
is therefore extremely slight. However galvanic contact of
titanium with magnesium, aluminum, copper and their alloys
can result in increased corrosive attack on these partner metals.
Deutsche Titan, Nov. 2000
FROM http://www.webspinners.futura.net/apurdy/periodic_tabl.htm
Using the periodic table you can select an element and look up
the electronegativity. This will give the galvanic potential
between the elements and the tendency for corrosion to develop.
The electronegativity of TI is 1.54 and the FE is 1.9. For reference
Oxygen is 3.44, Nitrogen is 3.04, Aluminum is 1.61, and Carbon
is 2.55. Corrosion potential is the difference between the
electronegativity of the two metals.
Example: 1.9 (FE) - 1.61 (AL) = 0.29 (Do you have the aluminum
elevator brackets with the press fit bearing and
steel bolts?)
1.9 (FE) - 1.54 (TI) = 0.36 Slightly greater than AL / FE
3.44 (O) - 1.90 (FE) = 1.54 (Makes rust)
2.55 (C) - 1.61 (AL) = 1.06
What does all this mean?? For myself, I would use the Ti rod with
a light coat of grease.
Just my 2 cents.
Ranny
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LML website: http://www.olsusa.com/mkaye/maillist.html
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Please send your photos and drawings to marvkaye@olsusa.com.
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