Abstract
The present work focuses on the characterization of brass surfaces after contact with artificial saliva solution at pH 7.4 and phosphate buffer solution at pH 7 simulating two extreme conditions that might occur when playing ancient brass wind instruments in the context of historically informed performance practice. The composition and the morphology of the film formed following the contact with the solutions for 1, 3, and 16 h were investigated by ex situ X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to shed a light on the surface changes upon time. In situ electrochemical impedance spectroscopy (EIS) was used to study the mechanism of corrosion and protection of the alloys. The results could be interpreted using a reliable equivalent electrical circuit; they provided evidence that the alloys behave differently when in contact to the various solutions. In saliva solution the formation on the brass surface of a thick surface film was observed, composed of crystallites of about 200 nm size mainly composed of CuSCN and Zn3(PO4)2. This layer hinders the alloy dissolution. The contact of the alloys with the buffer solution originated a much thinner layer composed of Cu2O, ZnO, and a small amount of Zn3(PO4)2. This film is rapidly formed and does not evolve upon time in a protective film.
Highlights
This work is part of a larger project whose overall goal was the development of an electrochemical sensor to understand the mechanism of corrosion and to monitor its evolution over time on brass musical instruments of the nineteenth and twentieth century1
The surface of the alloy after the exposure to the saliva solution was homogeneously covered by particles of about 0.2 μm in size; in contrast to the buffer solution no scratches were detectable on the surface of the metal
The surface chemical state and composition of the brass samples after the exposure to the two neutral solutions was investigated by X-ray photoelectron spectroscopy (XPS)/XAES surface analysis
Summary
This work is part of a larger project whose overall goal was the development of an electrochemical sensor to understand the mechanism of corrosion and to monitor its evolution over time on brass musical instruments of the nineteenth and twentieth century. To verify the efficiency of preventive conservation measures and to obtain information on the corrosion state and rate inside the instruments, non-destructive electrochemical techniques were chosen. The work (Elsener et al, 2016b) has involved the development of the electrochemical sensor and subsequently its calibration; afterward the sensor has been applied on reference materials and used on the historical brass musical instruments (Elsener et al, 2016a). The surface state inside the tuning slides is unknown and it is difficult to find a technique able to characterize for instance the inside surface of the trumpets
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