Definition
Rust inhibitors prevent the formation of iron oxide (rust/corrosion) on ferrous metal surfaces by displacing water and forming a protective adsorption film. They are critical in lubricants, hydraulic fluids, and metalworking fluids that may contact water or operate in humid environments.
Common chemical types:
- Sulfonates — also function as detergents; the most widely used rust inhibitors
- Amine phosphates — used in soluble metalworking fluids
- Carboxylate salts — sodium or amine salts of fatty acids
- Imidazolines — effective at low concentrations for ferrous protection
Rust inhibitors should be distinguished from corrosion inhibitors, which protect non-ferrous metals (copper, brass, aluminum). A formulation for mixed-metal systems requires both types.