Fugitive Calcium Carbonate Film

Definition

The fugitive calcium carbonate film is a thin, discontinuous, self-renewing layer that precipitates at the cathode where rising pH shifts carbonate equilibria. It interferes with oxygen access and electron transfer.

It is not permanent but fugitive, dissolving back into the bulk water when conditions change and reforming when they return, so its protection comes from equilibrium. It requires water with sufficient calcium and alkalinity, which is why ultra-soft, low-alkalinity water tends to be corrosive. Phosphonates are added to stabilize and refine this film into a thin, dispersed, less insulating boundary layer.

Related concepts

Alkalinity · Threshold Inhibition · Phosphonates

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Part of The Blueprint of Water · 🧪 chemistry