Anticorrosive primer pigments and metal passivators u2014 zinc phosphate, benzotriazole, and tolyltriazole u2014 for protecting ferrous and yellow-metal substrates under industrial coatings.
Corrosion inhibitors for coatings are additives that slow the electrochemical breakdown of a metal substrate beneath a paint or primer film. In protective coatings they fall into two working classes: anodic passivating pigments that build a protective layer on steel (zinc phosphate is the workhorse), and adsorption film-formers u2014 the azoles, benzotriazole and tolyltriazole u2014 that protect copper, brass, and other yellow metals. A complete system usually needs both, because each class protects metals the other does not.
Zinc phosphate is the standard chromate-free anticorrosive pigment for primers. It passivates anodic sites on steel and is the compliant replacement for the lead and hexavalent-chromium pigments now restricted across most markets. The trade-off is honest: zinc phosphate is less aggressive than the chromates it replaced, so formulators offset it with film thickness, binder selection, and barrier pigments rather than relying on the inhibitor alone. Specify it where regulatory pressure rules out chromate and where a general-purpose primer is acceptable.
Benzotriazole (BTA) and tolyltriazole (TTA) are yellow-metal inhibitors. They form a thin, insoluble complex on copper and brass surfaces and are used where a coating must protect non-ferrous components or fasteners. Neither azole meaningfully protects bare steel, so they complement u2014 not replace u2014 a passivating pigment. TTA is the liquid-handling counterpart to crystalline BTA and is often preferred in waterborne systems for easier dosing.
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