Electrochemical evaluation of temporary protection by using natural compounds as corrosion inhibitors, used for the preservation of bronze metallic heritage

摘要

The corrosion phenomena that occurs on cultural heritage metals, represent an irreplaceable loss of history, that is the importance of controlling it or stopping it through methods of protection. To avoid further degradation and in general the appearance of corrosion products, a more or less insulating barrier must be created on the metallic surface between the object and the atmosphere. Varnishes are generally applied as a final protection system for artifact conservation in museums under controlled environmental conditions. Corrosion inhibitors are another method that conservation-restoration professionals have had available to protect and to extend the life for those artifacts. The inhibitors and layers of protection do not comply with the general criteria of the conservation. Many of them are practically irreversible, change the appearance of the metal. New researches in the use of inhibitors of natural origin show them as good option because their use can be reversible, does not change the appearance and do not harm human health, although its use of the restoration has not been very investigated. This research presents the effectiveness of temporary Paraloid B72 films with addition of two natural compounds as inhibitors. Caffeine and nicotine to provide better corrosion resistance for the conservation of metallic elements of the cultural heritage were used. A coupled multielectrode monitor has been used, which allows monitoring of time - of- wetness and behavior of temporary protections against corrosion in controlled outdoor exposure, testing on different relative humidity 40% and 99%. The micros tructure of the bronze and the corrosion products was investigated by SEM/EDX. The structural characterization of different protections was done by infrared spectroscopy technique. The difference between the performances of the inhibitors was determined by electrochemical noise technique. The results showed that the application of inhibitor compounds allows the formation of a thin passive layer which can retard the anodic and/or cathodic reactions responsible for corrosion. It was found that both investigated compounds inhibited the corrosion. Increased efficiency notably of Paraloid B72 used in metallic heritage conservation, adding caffeine and nicotine as an alternative of corrosion inhibitors.