2012 SH Manual Diesel
Not arguing, offending, or point scoring; just broadening the perspective! And I agree with your rust prevention experience and advice, so no contest there.Salt does not cause rust;
I know that what you are saying can be technically correct in principle, especially for the defined basic chemical reaction. It is also how Redox Reactions are taught in Chemistry (the minimum components required for a straight forward reaction). But where chemistry teachers stop; is where "really!?, how did that happen", begins. It's the sources of the Proton donors (in the textbook, they conveniently just give you these 'Free' Hydrogens, as if they were just standing idly 'waiting for a mate'.); changes in electrical potential (in electrically conductive material or solutes. Galvanic/Daniell cell); intermediatory reactions and by-products; or presence of catalysts; where the salts fit right into the equation(s).
However, in 'bucket Chemistry' (how poop typically happens in real life), chemical reactions can be complex, or very round-about (not straight foward), and can take many routes or intermediatary steps. It's not necessarily obvious how salt cause corrosion; and in some aspects, it can be quite cryptic. You have to think laterally or tangibly, then you see the associations.
To make sense of what I'm saying, you have to consider that; if the salt was not present, then the Redox Reaction would not occur (or not at an accelerated, detrimental rate). And that the Anode and Cathode could be different metals, on different panels or components, or a long way appart. Some example(s), are:
- Bubbling paint, for no apparent reason (no scratch; no hole in panel; no rust any where near the area; surface coating completely intact, and bound all the way around the bubble); but yet corrosion is occuring under the paint;
- Stray current corrosion in cooling systems;
- Rusting bolts, but where no other exposed metal component is corroding.
The following are some of the principles/concepts of how salt provides the required elements of corrosion to start:
- Daniell Cell: salt bridge;
- Salt: weak acid + weak base (include carbonates, nitrates, sulphates, and hydroxides);
- Carbonates, Nitrates, Sulphates: e.g. Carbonic, Nitric acid (acids are corrosive on metals), they also contain Oxygen;
- Hydroxides: Contain Oxygen and Hydrogen ;
- Hydrogen: required for reduction of Oxygen at Cathode;
- Salt: unless anhydrous (Lab supplied), will naturally contain moisture.
And due to electrolysis; rust begets rust!