A Novel, Highly Effective, Chrome-Free, Smart-Release, Economically Viable Corrosion Inhibitor- from Lab Kinetics through to Industrial Coating Incorporation

Abstract

Novel, smart-release in-coating corrosion-inhibiting pigments for hot dip galvanised (HDG) steel, were investigated as a low cost replacements for hexavalent chromate. Organic anions were exchanged into the smart-release divynl benzene resin based pigment, dispersed in a model coating and analysed using an in-situ scanning kelvin probe (SKP) technique, for their effectiveness at preventing cathodic delamination. SKP allows rapid screening of the inhibitor-containing pigment when dispersed in a model organic polyvinyl butyral (PVB) coating. Each experiment lasts 24 hours, enabling a larger experimental through-put in comparison to traditional screening techniques, such as EIS or salt spray (ASTM-B117). SKP gives spacially resolved corrosion potential (Ecorr) profiles enabling identification of the delamination front and subsequent measurement of its progression and rate kinetics. Figure 1 shows plots of delamination distance vs. time for the anions screened in these experiments. Results indicate that a benzotriazolate-containing pigment system is the most effective, where delamination rates were reduced by 95% and the onset of cathodic delamination was increased by ca. 2160 hours from the point of initiation with an external electrolyte. It has been reported previously that benzotriazole is an effective corrosion inhibitor for a range of metals when in solution (1-5), the divynl benzene matrix allows benzotriazolate to be stored and released only when the coating encounters a corrosive electrolyte, via ion exchange mechanisms. Open circuit potential measurements show an increase in Ecorr measurements where benzotriazole is present in the experimental electrolyte suggesting anodic inhibition. Results from salt-spray testing carried out on a commercial coil coating are also presented where benzotriazole is shown to be effective after a period of 1000 hours. The current study suggests that a benzotriazolate-containing pigment system is a strong, environmentally friendly, contender to replace chromate for the inhibition of corrosion on hot dip galvanised steel. 1. Finšgar M, Milošev I (2010) Corros Sci 52:2737–2749. 2. Kosec T, Merl DK, Milošev I (2008) Corros Sci 50:1987–1997. 3. Aramaki K (2001) Corros Sci 43:1985–2000. 4. Müller B, Imblo G (1996) Corros Sci 38:293–300. 5. LEROY RL (1978) Corrosion 34:98–110. Figure 1