The protection of galvanised steel using a chromate-free organic inhibitor

• Published in: Anti-corrosion methods and materials Vol. 56; no. 2; pp. 114 - 120
• Main Authors: Angelica Hernandez-Alvarado, Laura, Salvador Hernandez, Luis, Miranda, Juana Maria, Dominguez, Octavio
• Format: Journal Article
• Language: English
• Published: Bradford Emerald Group Publishing Limited 20-03-2009
• Subjects: Aeration; Analytical methods; Aqueous solutions; Chromate coatings; Chromating; Circuits; Conversion coatings; Corrosion; Corrosion inhibitors; Corrosion potential; Corrosion prevention; Corrosion products; Corrosion rate; Electrochemical impedance spectroscopy; Electrochemistry; Electrode polarization; Electrodes; Electrolytes; Environmental impact; Experiments; Fog; Galvanized steel; Galvanized steels; Immersion tests (corrosion); Inhibitors; Linear polarization; Nickel; Organic chemicals; Phosphate coatings; Phosphates; Polarization; Protection; Protective coatings; Sodium chloride; Steel; Submerging; Tests; X-ray diffraction; Zinc; Zinc coatings; Zinc phosphate; United Kingdom > UK; Steel; Coatings; Corrosion protection
• ISSN: 0003-5599; 1758-4221
• DOI: 10.1108/00035590910940113

Purpose - The purpose of this paper is to investigate corrosion protection provided by a water-soluble corrosion inhibitor as a non-toxic alternative to the chromate and phosphate conversion coatings on galvanised steel.Design methodology approach - Untreated galvanised steel samples were assessed simultaneously with galvanised steel samples treated with the chromate-free organic inhibitor, a conventional chromate conversion coating or a zinc phosphate modified with nickel, by means of immersion - weigh loss and electrochemical tests, using a naturally aerated 0.5 M NaCl aqueous solution as corrosive medium. In addition, selected superficial conditions of galvanised steel were submitted to a salt fog test. The electrochemical tests used were: open circuit corrosion potential logging, linear polarization, potentiodynamic polarization and electrochemical impedance spectroscopy. Corrosion products formed on samples withdrawn from the solution at different intervals were characterized using X-ray diffraction.Findings - All tests gave concordant results, indicating that the chromate-free inhibitor showed moderate protective properties in this electrolyte. Among the considered superficial conditions, the phosphate coating showed the most deficient performance. In all cases, it was observed that after moderately intense initial attack, the corrosion rate diminishes due to the formation and growth of insoluble corrosion product layers, which exhibit a passivating action.Research limitations implications - The chromate-free organic corrosion inhibitor protected galvanised steel in this environment but the degree of protection was less than that provided by the chromate conversion coating.Originality value - The paper presents an alternative to the toxic treatments with chromates, since the inhibitor works as an additional coating, sealing pores and other discontinuities found in the zinc coating.