Solved cryptogram

Aluminum corrodes instantly, then stops. The oxide layer it forms seals the metal underneath.

Chemistry Facts, sourced to Royal Society of Chemistry.

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What it means

Fresh aluminum is highly reactive, and a clean surface oxidizes in a fraction of a second. The oxide happens to be tough, transparent and tightly bonded to the metal below, so the reaction stops itself after a layer a few atoms thick. Iron oxide flakes off instead and lets the attack continue, which is the whole difference between a rusted car and an old ladder.

The claim comes from Royal Society of Chemistry.

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