Passive Film

Definition

A protective oxide layer on a metal surface that holds the metal in place and resists corrosion, maintained by water chemistry.

A hydroxide rich, higher pH environment favors passive film stability, so general corrosion rates on mild steel decrease as pH rises. Conversely, low pH dissolves protective films and increases general corrosion, showing up as rising iron and worsening coupons. Maintaining the passive film is a central aim of corrosion control.

Related concepts

pH Drift · Oxygen Differential Cell · Microbiologically Influenced Corrosion

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Part of The Blueprint of Water · ⚡ electrochemistry