Definition
In lubricant and fluid formulations, corrosion inhibitors protect non-ferrous metal surfaces — primarily copper, copper alloys (brass, bronze), and aluminum — from chemical attack by acidic compounds, sulfur species, and other reactive components in the formulation.
The primary class is metal deactivators:
- Benzotriazole (BTA) and tolyltriazole (TTA) — form stable coordination complexes with copper surface atoms, creating a passive barrier film
- Thiadiazoles — used in gear oils and metalworking fluids for copper and copper alloy protection
Sulfur-containing EP additives and certain antioxidants can corrode copper — corrosion inhibitors counteract this effect. Copper corrosion testing (ASTM D130, IP 154) is standard in lubricant formulation qualification.