Corrosion inhibitor

Abstract

The present invention relates to a corrosion inhibitor and a corrosion inhibiting coating provided for coating a metal, particularly but not exclusively steel. The inhibitors pigment will also protect aluminium and magnesium alloys. The corrosion inhibitor particularly protects a sacrificial coating such as zinc or zinc alloy on galvanised steel, which in turn therefore provides improved corrosion resistance to the underlying steel. The present invention comprises an organic cation in a cation exchange resin.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a corrosion inhibitor and a corrosion inhibiting coating provided for coating a metal, particularly but not exclusively steel. The inhibitors pigment will also protect aluminium and magnesium alloys. The corrosion inhibitor particularly protects a sacrificial coating such as zinc or zinc alloy on galvanised steel, which in turn therefore provides improved corrosion resistance to the underlying steel.BACKGROUND OF THE INVENTION[0002]Corrosion inhibitors sometimes referred to as corrosion inhibitive pigments in the form of sparingly soluble inorganic salt powders, dispersed within an organic coating have been traditionally used to protect a wide range of metallic surfaces, including steel and galvanised steel. A typical steel coating system is shown in FIG. 1 and comprises a steel substrate 2, a metallic coating 4 (to sacrificially protect the steel substrate, typically comprising zinc or a zinc alloy), a conversion coating ...

AI Technical Summary

Benefits of technology

[0011]Organic cations are any cations that fit the general definition of an organic compound, which comprise at least carbon and hydrogen atoms. An organic cation in a cation exchange resin provides a corrosion inhibitor having the beneficial properties of acting as a smart release corrosion inhibitor with improved capability for providing corrosion resistance whilst also being environmentally acceptable. Such a corrosion inhibitor is capable of allowing dissociation of the organic cation from the cation exchange resin under the conditions of a corrosive electrolyte becoming present, and sequesters ions (preferably benzotriazole) in a protonated form to form a precipitate or barrier layer by deprotonation to prevent further corrosion.

[0012]The finding of the beneficial corrosion inhibition properties of a corrosion inhibitor comprising an organic cation in a cation exchange resin is contrary to expected and known teachings. In a corrosion environment the ions released are generally metal cations due to the loss of electrons in the corrosion process. Accordingly, in order to address the presence of metal cations and form an insoluble precipitate the expected and taught solution is to provide anions which would readily combine with the metal cations or surface. However, the present invention teaches instead to release cations which would ordinarily repel the metal cations and thus have no desirable effect upon the metal cations and not result in the formation of an insoluble precipitate to prevent further corrosion.

[0013]It has been found however that as the organic cation is released it is deprotonated by the corrosive environment to become neutral, and if the environment is alkaline may be deprotonated again into an anionic form and react with the metal cation to form the desired insoluble precipitate. The use of an organic cation in a cation exchange resin such as Amberlite®, allows the manufacturing process to have no solution waste stream, as the cationic exchange resin does not have a chloride counterion. By using a cationic resin, the corrosion inhibitor also enables an enhanced cure for a coating into which the inhibitor is added.

[0014]A further benefit associated with a corrosion inhibitor comprising an organic cation in a cation exchange resin is the effect of improving the cure of a coating on a metal substrate. The curing process has been found to be enhanced, leading to improved physical properties as a result of the enhanced cure.

[0015]In the protection of galvanised steel, the organic cation dissociates to provide protection to be zinc or zinc oxide sacrificial layer. This improves the lifespan of the sacrificial layer.

Problems solved by technology

Current anti-corrosion inhibitors comprise sparingly soluble chromium salts such as zinc or strontium chromate, which have a degree of toxicity which is not environmentally acceptable.

Although alternative, environmentally acceptable (Cr (vi)-free) inhibitive pigments, typically based on sparingly soluble phosphate slat technologies are available, they are invariably less effective than their chromate counterparts.

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