Prestone Antifreeze question for 1990 200tq
Stephane.Livolsi at investorsgroup.com
Wed Mar 5 09:31:57 EST 2003
You know, when I see posts like this, demonstrating the vast array of
knowledge and expertise that various listers have, I think there is nothing
we can't do if we all got together sometime....
thanks for sharing the info Robert
> Aluminum metal spontaneously reacts with water to form Aluminum hydroxide
> [Al(OH)3] and hydrogen gas. The only reason that a block of aluminum in
> contact with water does not do this to any great extent is that the
> spontaneously decomposes in an equilibrium process to form aluminum oxide
> Al2O3. This forms a quite refractory coating of aluminum oxide on the
> surface of the metal which prevents contact between the aluminum metal and
> the water in much the same way a good coat of paint can protect a piece of
> steel from rusting when exposed to moist air.
> 1. 2 Al + 3 H2O --> 2 Al(OH)3 + 3 H2
> 2. 2 Al(OH)3 <==> Al2O3 + 3 H2O (with a large Keq)
> 3. Al(OH)3 <==> Al+3 + 3 OH- (with a small Keq thus
> a very low but essentially constant amount of Al+3 ions in solution))
> Now enters the phosphate ion from phosphate containing antifreeze.
> 4. Al+3 + PO4-3 <==> AlPO4 (with a VERY large Keq - aluminum
> phosphate is EXTREMELY insoluble in water)
> This last process tends to lower the Al+3 concentration and this, in turn,
> causing equation 3 above to shift to the right in order to form more Al+3
> ions to keep the system in a proper state of equilibrium. This, in effect
> then effectively "cleans" the surface of the aluminum block and allows
> of the metal to react with water in an effort to keep everything in
> as far as the complementary equilibria go. The end result after a long
> term is that the metal of the aluminum block gets ":eaten away". This is
> not a particularly desirable result for an aluminum engine.
More information about the quattro