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The Unexpected Role of Carbonate Impurities in Polyphosphate Corrosion Inhibition

The Unexpected Role of Carbonate Impurities in Polyphosphate Corrosion Inhibition

Suzanne Morsch, Seyedgholamreza Emad, Lee A Farren, Matthew D Goodall, Stuart B Lyon, Simon R Gibbon

Sci Rep. 2018 Nov 28;8(1):17450.

PMID: 30487636

Abstract:

Polyphosphate corrosion inhibitors are increasingly marketed as chromate replacements for coil coated steel. The mechanisms underpinning corrosion prevention by these species is, however, not fully understood; corrosion inhibition is ordinarily assessed using electrochemical techniques, followed by ex-situ surface analysis. As a result, the formation of a clear film over cathodic sites is known to contribute to corrosion prevention, but little is known about its formation. Here, we apply advanced microscopy techniques (in-situ fluid cell AFM, SEM-EDX, and AFM-IR nano-chemical analysis) to examine early cathodic film formation by strontium aluminium polyphosphate (SAPP) in detail. For a model cut edge system, it is found that cathodic inhibition dominates during the first 24 hours of immersion, and surprisingly, that strontium carbonate impurities play a significant role. Rapidly precipitated zinc carbonate provides protection almost immediately after immersion, before the film structure evolves to include (poly)phosphate species. This suggests that the purposeful inclusion of carbonates may provide a new, environmentally sound approach to enhancing inhibitor efficacy.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP1633052	Strontium carbonate		1633-05-2	Price

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