Investigation of artificially produced and natural copper patina layers

Abstract

Patina layers artificially produced by chemical treatment of copper and bronze were characterized using ion-beam analysis techniques. In order to simulate the corrosion process, the samples were electrochemically treated in 0.5 M Na₂SO₄ solution at ambient temperature. The corrosion behavior of artificial Cu patina layers prepared on copper and bronze substrates was studied using potentiodynamic, potentiostatic, and cyclic voltammetric techniques. The composition of the patina layers, which mainly consisted of phases corresponding to the minerals cuprite, antlerite, and brochantite, was determined by energy dispersive spectroscopy and scanning electron microscopy was used to examine their surface morphology prior to and after the corrosion tests. A natural patina sample was also investigated in the same way for comparison purposes. Characterization of the untreated and the electrochemically treated samples was also performed by Rutherford backscattering spectroscopy and nuclear reaction analysis techniques. Backscattering of protons and deuterons, as well as the ¹⁶O(d,p)¹⁷O, ³²S(p,p′γ)³²S and ⁶³Cu(p,nγ)⁶³Zn nuclear reactions were used for the profiling of oxygen, sulfur, and copper in the patina layers under investigation. The measurements indicate that the composition of the artificially prepared antlerite and brochantite patina layers is very close to that expected stoichiometrically. The antlerite patinas are transformed during the electrochemical treatment in 0.5 M Na₂SO₄ solution to brochantite, whereas the brochantite patinas seem to remain unchanged.