The corrosion of ferrous metals is an electrochemical process that requires one of the reactants to be water. It therefore follows that when water is made available to a metal surface as a result of condensation, leakage or in some other way, corrosion will result unless the metal surface is protected. There is a surfeit of data which indicate that fluids such as hydrocarbons, esters and silicones cannot by themselves prevent corrosion because they are not strongly adsorbed on the surface of the metal and are thus readily displaced from the metal surface by water which is strongly adsorbed. It is essential therefore that such fluids be fortified with compounds which are soluble in the fluids, relatively insoluble in water and so configured as to have a polar component which can be strongly adsorbed on the metal oxide surface and a hydrocarbon component, hydrophobic in nature, which extends into the fluid. A metal immersed in a fluid containing these amphipathic molecules will be protected from the corrosive effects of dispersed and/or dissolved water by a close packed and vertically oriented monolayer on the surface of the metal(1,2,3,4) which is capable of significantly reducing the diffusion of water from the liquid phase to the surface of the metal. Metal salts of hydrocarbons displaying a large variety of structural configurations have been studied for their rust inhibiting properties(4,5, 6,7,8) and a great deal of data have been accumulated which indicate that an adsorbed monolayer of rust inhibitor can be made less permeable to water and oxygen, if the size of the hydrocarbon chain is increased and stearic effects are reduced in order to facilitate close packing. Conversely there is comparatively little data relative to the performance of a rust inhibitor as a function of the metal component of the molecule or of the type of fluid in which the inhibitor is dissolved.
