Benzotriazole for copper and yellow metals, with sodium molybdate and sodium nitrite for ferrous protection in metalworking fluids and closed systems.
Les inhibiteurs de corrosion sont des additifs qui ralentissent la corrosion électrochimique des pièces et des équipements métalliques dans les fluides aqueux. In industrial manufacturing they split by the metal they protect: azole film-formers such as benzotriazole guard copper, brass, and other yellow metals, while anodic inhibitors such as sodium nitrite and sodium molybdate passivate ferrous surfaces. A mixed-metal system u2014 a cast-iron machine wetted with brass fittings u2014 usually needs both a yellow-metal azole and a ferrous inhibitor, because each protects metals the other does not.
Benzotriazole (BTA) is the standard yellow-metal inhibitor. It forms a thin, insoluble complex on copper and brass that blocks the corrosion reaction, and it stays effective at low dose, often a fraction of a percent of the fluid. Specify BTA wherever a metalworking fluid, coolant, or cleaner contacts copper alloys. It does little for bare steel, so it complements rather than replaces a ferrous inhibitor.
For ferrous protection the choice is between sodium nitrite and sodium molybdate, and that is the real trade-off on this page. Sodium nitrite is a strong, low-cost anodic inhibitor, but it is not used in fluids containing secondary amines, because the two can react to form N-nitrosamines; many modern water-soluble metalworking fluids use sodium molybdate or amine-carboxylate chemistry instead. Molybdate works at higher dose and cost but avoids that reaction. Confirm regulatory status for your application and jurisdiction.
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