The composition of natural saliva is strongly variable and unstable outside the oral cavity, therefore corrosion tests are usually performed in artificial saliva solutions. In this study the effect of the composition of various saliva solutions on the corrosion behavior of a CuZn37 alloy, exposed for 1, 3, and 16 h to the solutions, is investigated by using electrochemical measurements, optical microscopy, and X-ray photoelectron spectroscopy (XPS). The solutions investigated in this study are: Darvell, Carter-Brugirard, and SALMO, selected for their composition that mainly differs in the organic compounds' content. Electrochemical measurements show that the open circuit potential and the polarization resistance increase with exposure time in the solutions, indicating a decrease in the corrosion rate. The corrosion rate (µm/year) in the Darvell solution is found to be two times higher than the other artificial saliva formulations and varies in the order: Darvell > Carter-Brugirard > SALMO. These data suggest that the presence of different organic compounds might limit the formation of a stable protective surface film as confirmed by XPS surface analyses.

Several formulations of artificial saliva have been used for corrosion studies. The present work focuses on the effect of different saliva formulations on the composition of the surface film formed on CuZn37 brass alloy by X-ray photoelectron spectroscopy (XPS), in order to clarify the corrosion mechanism of historical brass wind instruments when used. Three different saliva solutions, Darvell (D), Carter-Brugirard (C-B) and SALMO, were selected. They differ for the content of the organic compounds. The XPS results show the presence of a film made of CuSCN and zinc-phosphate on the brass exposed to C-B and SALMO. In the case of samples exposed to D formulation, phosphorus is not revealed, a decrease in the zinc content in the film is detected and the S 2p shows the presence of a second component together with the one ascribed to CuSCN. A comparison with the results obtained on the pure metals in the presence of the organic compounds suggests that the formation of zinc and copper complexes may lead to thin and less protective surface film and thus to the observed high corrosion rates.

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