Microemulsions as a new strategies for corrosion inhibition coatings for lead

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

Viena

Conferencia; 3rd International Conference for Chemistry for Cultural Heritage; 2014

Institute of Science and Technology in Art of the Academy of Fine Arts Vienna

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 are currently working in the development of environmentally safe corrosion protective coatings for lead heritage 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. 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.2-3 Based on these ideas, we have dissolved monocarboxylic acids in nanometer scale microemulsions, which greatly enhance the solubility of these molecules in aqueous solutions. Results show that monocarboxilate microemulsions effectively encapsulate the insoluble monocarboxilate molecules. Monocarboxilate molecules are effectively suspended in solution. However the microemulsions are dynamic and monocarboxilate molecules are liberated and react at the metallic surface. Therefore, the microemulsions effectively act as drug-delivery devices. Potentiodynamic polarization curves and electrochemical impedance spectroscopy studies in corrosive media show the effectiveness of the coatings. The coatings have been further characterized by FT-IR spectroscopy and X-ray diffraction.