Date:         Tue, 9 Oct 2001 11:29:12 EDT
Reply-To:     Blbachman@AOL.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Blaine Bachman <Blbachman@AOL.COM>
Subject:      Re: [vanagon] Re: electrolysis
Comments: To: FrankGRUN@aol.com
Content-Type: text/plain; charset=ISO-8859-1

I knew we'd smoke out a chemist (or similar) in time! <G>

-Blaine

In a message dated Sun, 7 Oct 2001  7:33:17 PM Eastern Daylight Time, FrankGRUN writes:
> Normal tap water, as well as bottled water, has more than adequate conductivity to  support electrolysis even when mixed in a 50/50 solution. The interconnection between two dissimilar metals will lead to corrosion. The key question is the rate. The electron transfer rate (directly related to the mass transfer rate is related to the metal surface potential, the concentration of the solublized ion in solution (Cu2+, Al2+, etc), the voltage drop across the connector (coolant circuit) and the electromotive force difference between the two parent metals. The best way to minimize this transport is to modify the surface potential and minimize the appropriate ion concentration. The additive packages in commercial antifreeze products are designed to do just that (along with buffering and lubrication, and ...). They use surfactants which bind to the exposed metal surface rendering it an exposed semimetal, semiconductor or insulator (take your poison based on your point of view). The net result with surfactants is t
hat the surface is complexed and the equilibrium charge or mass transfer is lowered by factors of 10*3 to 10*5.
>
> A similar chemistry applies to the ion concentration in solution. Here, clathrates or complexing agents are used to bind up the soluble ions. Unfortunately, these compounds are hydrolyzed (react with water) and their concentration falls off with time. At a critical concentration, no more protection exists.
>
> These rates and effective reactions are also a strong function of temperature.
>
> The summary, Copper in a cooling circuit with Aluminum and steel will corrode. The rate could be negligible (higher probability of personal meteor strike than damaging corrosion of Cu component in 5 years or less). Alternative is thick film hydrophobic film as I mentioned in an earlier post.