Abstract: A method of inhibiting corrosion of a metal surface in an aqueous system comprising introducing corrosion inhibiting cations into the aqueous system. The corrosion inhibiting cations are selected from the group comprising cations of yttrium and cations of the metals of the lanthanum series which metals have atomic numbers from 57 to 71 inclusive. The cations may be introduced in the form of water soluble salts. Alternatively the cations may be releasably bound by ion exchange to a substrate and the ion-exchanged substrate introduced into the aqueous system.

Abstract: A corrosion inhibitor comprises particles of an inorganic oxide having cations of yttrium or cations of one or more metals of the lanthanide group chemically bound to the particles by ion-exchange. The cations are released by ion-exchange with other cations and not by the water solubility of the corrosion inhibitor.The corrosion inhibiting particles may be prepared by contacting particles of the inorganic oxide with an aqueous solution containing the required cations. Alternatively, the particles of the inorganic oxide may be contacted with an aqueous solution of an alkali metal so that alkali metal ions are exchanged onto the surface of the oxide and then contacting the alkali metal exchanged oxide with a solution of the required cations so that the required cations replace the alkali metal cations.The corrosion inhibiting particles may be incorporated into protective coatings e.g. paints based on epoxy resins, alkyd resins, vinyl resins or chlorinated rubbers in amounts up to 80% wt.