WARNING! This material is of a highly technical nature, and has a tendency to
make one's head hurt. There are a lot of big words used, but that's
unavoidable
as I am not smart enough to know the small ones, nor eloquent enough to be
briefer. - {9-> Steve
pamelam@connix.com wrote:
> I traveled with one of our experts this week that has 20 years experience
> pumping Category I DI water through electrolyzers and fuel cells.
>
> He thought that straight DI would be a risk, especially to a pitted
> radiator. It will take ions out of the metals until the solution reaches
> equilbrium.
>
> However, adding rust inhibitor, antifreeze, pump lube to the water puts
> ions in the water again. It is a good idea to use good water (I have to, as
> my well water is high in minerals) to prevent scaling and subsequent
> degradation of the ability to exchange heat.
>
> Bob Melusky
Thank you, Bob
I was thinking over your friends comment on the affinity for DI (distilled?)
water
for having a propensity for taking ions out of metals being riskier than "good
water". I am not sure what that is, but "de-ionized" water has ions removed as
well.
If I recall my Chemistry 101 correctly, a solvent will reach equilibrium with
any
material that is soluble in it. Once saturated to it's capacity for that
material, it stops. That does not, however, prevent it from dissolving a
different soluble material to it's own solubility limit. If I have reached
saturation in dissolving table salt, NaCl, that does not prevent me from also
reaching the equilibrium point with sugar. Although it wouldn't taste too good.
I doubt very much that any normal water has much aluminum ions in, it. Maybe
some
copper, maybe some iron. In any event, the actual solubility of these materials
is extremely small, so the fluid would soon be saturated with minuscule amounts,
even if it had none to begin with.
I think what we are facing here is NOT solubility, as much as electrolysis. And
this should not be confused with scale, which are deposits of materials having
reached super saturation, or just plain evaporation, or oxidation.
Electrolysis depends on the relative location in the electrolytic activity
table,
and the electrical conductivity of the fluid. Distilled water is a very poor
electrical conductor, as opposed to a thermal conductor. Ionized water is much
better conductor because of the dissolved ions.
Some materials will electrolyticly react with a conductive fluid. But the most
active materials will be absorbed by the electro-chemical reaction first.
Aluminum will dissolve before the iron. That's why the aluminum heads and pumps
go, but this reduces the electrolysis of the cast iron.
The use of a material higher in the electrolytic table, such as zinc or
magnesium,
will cause those materials to be sacrificial anodes before the materials lower
on
the scale, like aluminum, copper, iron are affected
Salt water cooled engines use sacrificial zinc in their system to prevent the
iron
from going, and sea water is highly conductive.
J. C. Whitney (Warshowskies) still sells zinc/magnesium radiator rods with a
stainless tie to the water inlet for fishing out the remains. The sacrificial
electrolytic erosion of this material will prevent the copper, aluminum, and
iron
materials, all lower on the scale, from being electrolyticly attacked.
Try this simple example out on your friend, and see how he responds. Chem. 101
was a long time ago.
Bob Palmer may be fresher at this than I am.
Steve
--
Steve Laifman < Find out what is most >
B9472289 < important in your life >
< and don't let it get away!>
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