Coke contains phosphoric acid, which chemically breaks down iron oxide (rust) into iron phosphate. And Diet Coke isn’t sticky like Coke. And aluminum loses electrons and oxidizes, while the iron oxide (rust) gains electrons. This chemical reduction fundamentally changes the rust back into a form that easily breaks away from the base metal.
Craig French recommends soaking rusty typewriter springs in Diet Coke and then wiping them with aluminum foil to remove rust.
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