Rust Inhibitors
Table of Contents
Physical & Chemical Properties

Since water is a common contaminant in mineral oil lubricated systems used on earth, anti-rust additives are used. Rust inhibitors prevent the formation of rust (hydrated iron oxide) on iron surfaces by the formation of protective films, or by the neutralization of acids. Typical anti-rust compounds are highly basic compounds, sulfonates, phosphates, organic acids, esters or amines. The rusting of ferrous parts in a lubricated system is undesirable. The rust contributes to sludge, causes loss of metal, sticking of metal parts, and the formation of solid particles of rust that are abrasive. Rust indicates the presence of water in the system.

The ability of treated oil to prevent rusting may be measured by ASTM D 665, entitled Rust Prevention Characteristics. A 300 ml sample of lubricant is introduced into a beaker containing 30 ml of either salt or fresh water. A specially prepared bullet-shaped steel rod is placed in the beaker along with the oil/ water mixture. The mixture is heated and stirred for 24 to 48 hours to promote rust on the steel bullet. At the end of the test time the bullet is carefully inspected and rated for any sign of rust.

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