New Strategies for Corrosion Inhibition Coatings for Lead and Iron Heritage Metal Objects

VICTORIA FLEXER; AHMED, E.; DOWSETT, M.G.; ADRIAENS, A.

Laussane

Conferencia; 65th Annual Meeting of the International Society of Electrochemistry; 2014

International Society of Electrochemistry

Corrosion is the major problem in the degradation of heritage metal objects. The development of appropriate treatment methods to stabilize and protect artefacts is a major scientific challenge. Because inappropriate treatments can cause irreversible damage to irreplaceable objects, it is crucial that the chemical processes involved are fully understood and characterized before any preservation work is undertaken. We aim at the development of environmentally safe corrosion protective coatings for both lead and iron heritage metal objects which are stable, reversible, easy to apply and to remove, and aesthetically justified. An effective protective coating for lead has been found in the use of coatings deposited from solutions of saturated linear monocarboxylates of the type CH3(CH2)n-2COONa (NaCn).[1]  Protection is due to the growth of crystalline lead monocarboxylate layer [CH3(CH2)n-2COO]2Pb which passivates lead surfaces and inhibits corrosion. It was later found that linear monocarboxylates were also protective against iron corrosion, forming similar crystalline layers.[2] For both metals, the degree of inhibition depends on the carbon chain length and on the carboxylate concentration, higher chain length and higher concentrations will result in higher effectiveness. However, the solubility of sodium monocarboxylates drastically decreases with increasing chain length, and therefore C chains longer than NaC10 have not been extensively investigated. The continuous development of nanomaterials and the study of physicochemical phenomena at the nanoscale are creating new approaches to conservation science.[3, 4] Based on these ideas, we have dissolved monocarboxylic acids in nanometre scale microemulsions, which greatly enhance the solubility of these molecules in aqueous solutions. Results show that monocarboxilate microemulsions effectively act as drug-delivery devices. Monocarboxilate molecules are effectively suspended in solution, but the microemulsions are dynamic and monocarboxilate molecules are liberated and react at the metallic surface. Potentiodynamic polarization curves and electrochemical impedance spectroscopy studies show the effectiveness and characteristics of the coatings. Surface analysis of the coatings is currently underway. Time-lapse XRD experiments are currently planned to follow in real time both coating formation and subsequent anticorrosion protection.