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Date: Wed, 11 Jul 2001 10:43:35 -0500
From: "Fullinwider RR (Ranson)" <RRFullinwider@equiva.com>
Subject: Re: Ti rudder pin rod for IV series a/c
To: "'lancair.list@olsusa.com'" <lancair.list@olsusa.com>
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Reply-To: lancair.list@olsusa.com

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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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