2072
Corrosion Protection Behavior of Patinas on Copper Alloys in Historical Metal Heritage: Electrochemical Study

Tuesday, 2 October 2018
Universal Ballroom (Expo Center)
D. Arguelles, C. Campechano, R. Galván-Martínez Sr., T. Jimenez, and R. Orozco-Cruz (UNIVERSIDAD VERACRUZANA)
All copper base alloys based copper tend to form a layer of oxide (patina), which gives or not protection to the base metal in the environment where they are exposed, this depends on the interaction with various agents such as chlorides (Cl-), sulfur dioxide (SO2), oxides of nitrogen (NOx) and ozone (O3), as well as the influence of solid particles in suspension such as coal, pollen and microorganisms, etc., which create dust deposits on the patina, which They compact by acting as a sponge, retaining moisture and thus favoring the corrosion phenomenon causing mechanical and chemical damage, originating in some cases soluble corrosion products that due to meteorological conditions such as precipitation can be eliminated, leaving the metal in some areas more exposed and ruining with This is the artistic appearance of the monument. [1-5] In this work, the induction of artificial patinas on Cu base alloys (brass and bronze) was carried out. The aim os this work was analyzing their degradation and evolution mechanisms, being these, characteristics of monuments exposed in atmospheres rich in Cl-, SO2 and NOx to achieve it were used solutions of NH4Cl 33% w, CuSO4 15mM and CuNO3 20% w, respectively. [6] After that, they were exposed to the atmosphere, in the port of Veracruz, Mexico., Having an environment of marine-tropical study, as well as the Cl- and SO2 ppm were monitored in strategic points of the City, this by ISO 9225 Standard. [7] For the study of the corrosion mechanism, electrochemical techniques were used, such as Electrochemical Impedance Spectroscopy (EIS) and Electrochemical Noise (EN). For the measurements, a typical three-electrode cell was used in EIS. A working electrode was used (patinated Cu alloy). ), a reference (Calomel Saturated electrode) and an auxiliary one (graphite), for EN two working electrodes and a reference electrode were used, a representative solution was used as electrolyte, which contained the ppm of contaminants that were monitored monthly, the study was complemented with Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Fourier Transform of Attenuated Total Reflection (FT-ATR). The results showed corrosion products typical of the environments that were desired to be characterized, finding; Brochantite (Cu4SO4 (OH) 6) and Atacamite (CuCl2 · (H3O) while CuNOx were more soluble, this was reflected in EIS, where Nyquist spectra with defined semicircles were found typical of load transfer processes, however for the samples with corrosion products of Cu4SO4 (OH)6 in the Bode diagrams it was possible to observe the increase in the Rtc, and the presence of a second time constant, which is related to the stability and compactness of these products.