Magnetite protective film

Definition

Magnetite is an iron oxide, Fe3O4, that forms a thin protective film on carbon steel in closed loops. It holds together in alkaline water and dissolves as pH falls.

The film is the steel’s defense against corrosion, stable only while the water stays alkaline. As pH approaches neutral the magnetite dissolves, exposing fresh metal and releasing iron into solution. Maintaining alkaline pH is therefore central to protecting carbon steel systems.

Related concepts

Corrosion control by pH · pH controls chemistry

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Part of The Blueprint of Water · 🧱 materials