Problem 8.4: Explain how a phosphatebased inhibitor can

From Chapter 8 Problem Set. Level 1: Conceptual Mastery.

Question

Explain how a phosphate-based inhibitor can itself become a source of scale. Name the scaling salt involved.

Answer

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Polyphosphates hydrolyze into orthophosphate at elevated temperatures. Phosphonates can also revert under thermal or oxidative stress. The resulting orthophosphate reacts with calcium at elevated pH to precipitate calcium phosphate - Ca₃(PO₄)₂. The inhibitor chemistry itself becomes the source of a scaling ion.