*2.5. Galvanic Corrosion*

In the first stage, to establish a galvanic series in artificial sweat the open circuit potentials of eighteen alloys were measured:

Precious metal alloys used in jewelry: Pt 950CoNi (950‰Pt, 18‰Co, 32‰Ni), AuPdCu150 (750‰Au, 100‰Pd, 150‰Cu), AuAgNi109 (750‰Au, 141‰Ag, 109‰Ni), AuCuNi130 (750‰Au, 120‰Cu, 130‰Ni), AuNiCu142 (750‰Au, 108‰ Ni, 142‰Cu), AuNiCu112 (750‰Au, 138‰Ni, 112‰Cu) and AuCuZn374 (585‰Au 41‰Cu, 374‰Zn).

Steels: 1.4441, 1.4435, 316 L F, 316 L F Cu, 1.4301, 1.4305, Sandvik 1802, 1.4104. 1.4105, 1.4539 and 12/12.

The samples, in form of 10-mm-diameter discs, were "mirror" polished, washed with a mixture of acetone and ethanol, and rinsed with deionized water 18 MΩ·cm. After drying with hot air, the samples were introduced into the PTFE sample holder, specially designed for the rotating electrode test. The electrochemical measurements were made with a potentiostatic assembly of three electrodes: a working electrode (rotating electrode), a platinum counter-electrode and a reference SCE electrode. Given that diffusion phenomena play a major role with regard to the changes produced at the metal/solution interface and consequently to the state and composition of the metal surfaces layers, readings were made in a laminar system (criterion of Re = 3200) with a limit current iL = 56 mA, and a rotational velocity of 300 rpm, to control the mass transfer phenomena. The open circuit potentials (Eoc) were measured after 24 h of immersion.

In the second stage, our interest was focused on galvanic couplings in the assembly of steel watch strap links with precious metal alloys (18K gold). The evaluation was indirectly made, by measuring the quantities of nickel released after 7 days of immersion in artificial sweat, according to standard EN 1811-2011+A1:2015 [50]. The tests were carried out on 27 gold-steel links (Figure 4), 5N18 (18K gold alloy)-1.4441 (316L) and 5N18 (18K alloy)-1.4539 (904L).

**Figure 4.** Link, steel-gold assembly with pins.

The microscopy investigations (scanning electron microscopy/energy-dispersive X-ray spectroscopy SEM/EDX) were carried out using a JEOL JSM-6300 SEM (JEOL, Peabody, MA, USA) equipped with an Oxford INCA EDS system (Oxford Instruments, Abingdon, UK) for local phase analysis.
