>mineral hungry distilled water> (sorry for length)
Basically, that is incorrect. To some extent, ions (or minerals) will tend
to be attracted in the direction that tends to neutralize any ionic
imbalance. This is a similar process to the one that causes your skin to
wrinkle when you are in water for too long. The (relatively) salty chemical
balance of your body fluids is higher content of ions than the surrounding
water. The ions within your fluids migrate toward the lower chemical state
of the water. You end up somewhat dehydrated. A similar process works in the
coolant in your engine. Mineral ions (like rust) tend to move in a direction
that wants to make the entire system reach equilibrium. Of course, any free
iron on the surface of the coolant passageways chemically wants to combine
with oxygen in the water to form iron oxide which is a more stable chemical
compound than the free iron or the free oxygen. This is all relatively
dictated by the chemical "laws" indicated in the periodic table of elements.
I used to work with nuclear reactors. To fight corrosion, several things
were done.
First, use corrosion resistant materials such as stainless steels and
non-ferrous steel alloys containing chromium, nickel, copper, etc.
Second, reduce or eliminate free oxygen by mixing in certain chemical
compounds that "strip" free oxygen. Without free oxygen, it is very
difficult to form oxides (various forms of "rust" where oxygen has combined
with the base metals). You also would want to eliminate any air from the
system (so limit free oxygen -- not necessarily practical in a car since you
have to then have a way to compensate for the expansion/contraction of the
coolant with temperature -- the water expansion can burst things).
Third, you fight any acidic compound formation by adding chemicals that make
the coolant a base, as opposed to an acid, thus you want a pH that is much
greater than 7.0 (which is neutral and is what pure deionized water pH is).
Fourth, you add chemicals or include a de-ionizer to strip away certain free
radical ions that are corrosion producing compounds.
Fifth, you include a filtration scheme to remove any corrosion products that
do happen to occur.
Sixth, you do a process called "passivation" where you temporarily run
something like hydrogen peroxide or ammonium compounds mixed in pure,
de-ionized water at elevated temperatures to "passivate" the metal surfaces.
This process chemically "binds up" any free iron molecules on the exposed
surfaces to form iron or nickel oxides that are tightly adherent and prevent
further corrosion of the underlying base metal. A passivated surface
sometimes looks "dull black" sometimes you can't tell.
The industry uses what is called "DI Water" this is shorthand for
"de-ionized water". It is water that has been distilled to pH = 7.0,
filtered and treated to remove contaminants and ions. It is "pure water" and
hence is very low conductivity. This water is "tasteless and clear".
Minerals are what give "regular water" its taste and color.
Roy
'60 TR3a (TS63103LO) in restoration
techman@metrolink.net
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