Agreed.
A surface coating of aluminium oxide (Al2O3) is reasonably impervious to air and moisture, protecting the metal underneath from further oxidation.
The situation with iron/steel is very different. Iron oxidizes in air to ferric oxide (Fe2O3, rust), which is porous, and gives no protection at all.
John
Depends on the steel. Corten (sp?) steel rusts a little, then no more.
On my understanding, this surface discoloration of Corten steel is not rust. Stainless steel likewise does not rust.
John
Sure looks like rust anyway. We used to have a building in Maryland built of Corten. It was known in the company as "The Rusty Bucket".
Chuck Tribolet
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