Non-destructive electrochemical evaluation of corrosion protection systems subjected to accelerated ageing tests: a strategy for the conservation of colonial Mexican metal alloys

In this study we used Electrochemical Impedance Spectroscopy (EIS) to assess the protective capacity of different conservation treatments: benzotriazole, tannic acid and a polyurethane coating. They were applied on corroded coupons that replicate colonial Mexican brass and cast-iron alloys which were subjected to an accelerated ageing process under UVB/condensation exposure cycles. Electrochemical analysis was complemented with colorimetric measurements and FTIR analysis for information on the structural level before and after ageing. EIS results indicate that although the inhibitor systems prevent corrosion in early stages of the ageing, after 600 h they degrade, and corrosion products are formed resulting in low protective capacities. The selected polyurethane coating provided high protective capacities measured by EIS and agreed with no chemical degradation registered by FTIR and colour aspect. This investigation was performed with a methodology that can be replicated on site since it is non-destructive and the data can be employed for planning conservation strategies.