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Table 1 Identical sterling silver coupons with a polished surface were exposed to five different sulfidation environments. Based on the discoloration of the sur- face, the corrosive environments were arranged from slow to fast proceeding corrosion

Table 1 Identical sterling silver coupons with a polished surface were exposed to five different sulfidation environments. Based on the discoloration of the sur- face, the corrosive environments were arranged from slow to fast proceeding corrosion

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Figure 1 Calculated colour change of Ag925 coupons exposed to residential and laboratory environments in comparison with a freshly polished Ag925 coupon. a Change in colour (AE) over time; b the colour as described by a* and b* values, indicating a more yellow (Residence environment and a more reddish corrosion colour development (Laboratory environment); values with numbers 1-6 correspond to the exposure time in months as ina.
Figure 1 Calculated colour change of Ag925 coupons exposed to residential and laboratory environments in comparison with a freshly polished Ag925 coupon. a Change in colour (AE) over time; b the colour as described by a* and b* values, indicating a more yellow (Residence environment and a more reddish corrosion colour development (Laboratory environment); values with numbers 1-6 correspond to the exposure time in months as ina.
Figure 2 Corrosion on the samples after 6 months of exposure; a residential environment, b Laboratory environment. (Images AXES, Antwerp).
Figure 2 Corrosion on the samples after 6 months of exposure; a residential environment, b Laboratory environment. (Images AXES, Antwerp).
Figure 4 Change in colour relative to the polished metal as a func- tion of exposure time.
Figure 4 Change in colour relative to the polished metal as a func- tion of exposure time.
Figure 3 EDX spectra collected on the general area of the presented images (Figure 2) show in both cases no S but an enrichment in Cu and O, moderate in the residential environment (Cu 9.6, O 1.2, S 0.1 and Ag 89.1 wt%), but strong in the laboratory environment (Cu 20.8, O 15.7, N 2.5, S 0.1 and Ag 60.9 wt%). Reference values for a non-exposed sample is Cu 5.3 and Ag 94.6; O, N and S: 0.0 wt%). A summarizing table is given at the end of the ‘Results’ part.
Figure 3 EDX spectra collected on the general area of the presented images (Figure 2) show in both cases no S but an enrichment in Cu and O, moderate in the residential environment (Cu 9.6, O 1.2, S 0.1 and Ag 89.1 wt%), but strong in the laboratory environment (Cu 20.8, O 15.7, N 2.5, S 0.1 and Ag 60.9 wt%). Reference values for a non-exposed sample is Cu 5.3 and Ag 94.6; O, N and S: 0.0 wt%). A summarizing table is given at the end of the ‘Results’ part.
Figure 5 SEM-FIB investigations of an Ag925 coupon after an exposure of 168 h according to method 3. In these FIB-cross-sectioned samples, the bulk metal is located at the bottom of the image and the sulfide layer is located between the bulk metal and the platinum evaporated on top of the surface. a the FIB cut showing different phases in arrows 1 and 3 in the metal (bottom of the image) and the sulfide layer (arrow 2); b high magnifica- tion image showing a compact sulfide layer with brighter inclusions. (Images CEST, WrNeustadt).
Figure 5 SEM-FIB investigations of an Ag925 coupon after an exposure of 168 h according to method 3. In these FIB-cross-sectioned samples, the bulk metal is located at the bottom of the image and the sulfide layer is located between the bulk metal and the platinum evaporated on top of the surface. a the FIB cut showing different phases in arrows 1 and 3 in the metal (bottom of the image) and the sulfide layer (arrow 2); b high magnifica- tion image showing a compact sulfide layer with brighter inclusions. (Images CEST, WrNeustadt).
Figure 6 Secondary electron images of the tarnishing/corrosion layer obtained by method 3 (TAA procedure), illustrating the change in morphol- ogy on the surface, left column. The right column shows the corresponding FIB-cross sections, showing the increase in voids at the interface. (Images CEST, Wr. Neustadt).
Figure 6 Secondary electron images of the tarnishing/corrosion layer obtained by method 3 (TAA procedure), illustrating the change in morphol- ogy on the surface, left column. The right column shows the corresponding FIB-cross sections, showing the increase in voids at the interface. (Images CEST, Wr. Neustadt).
Table2 Summary of quantitative results obtained from SEM-EDX spectra collected from the surfaces after sulfidation according to the respective methods 1-5, values in wt%. Since the penetration depth of electrons might be deeper than the thickness of the sulfide layer, interference with the substrate cannot be avoided
Table2 Summary of quantitative results obtained from SEM-EDX spectra collected from the surfaces after sulfidation according to the respective methods 1-5, values in wt%. Since the penetration depth of electrons might be deeper than the thickness of the sulfide layer, interference with the substrate cannot be avoided
Figure 7 Secondary electron images of the surface of polished sterling silver after exposure to synthetic air, 90% RH and 500 ppb H,S for 24 h, fol- lowed by 90% RH and 500 ppb SO, for another 48 h (Images CEST, Wr.Neustadt).
Figure 7 Secondary electron images of the surface of polished sterling silver after exposure to synthetic air, 90% RH and 500 ppb H,S for 24 h, fol- lowed by 90% RH and 500 ppb SO, for another 48 h (Images CEST, Wr.Neustadt).
Figure 8 FIB SEM-EDX Analyses of Ag925 exposed to synthetic air, 90% RH and 500 ppb H,S for 24 h, followed by 90% RH and 500 ppb SO, for another 48 h. a SEM SE image x40,000of FIB cut cross section, b BSE image and EDX measuring point analyses of FIB cross section, x 20,000 (Images CEST, Wr.Neustadt).
Figure 8 FIB SEM-EDX Analyses of Ag925 exposed to synthetic air, 90% RH and 500 ppb H,S for 24 h, followed by 90% RH and 500 ppb SO, for another 48 h. a SEM SE image x40,000of FIB cut cross section, b BSE image and EDX measuring point analyses of FIB cross section, x 20,000 (Images CEST, Wr.Neustadt).
Figure 9 Change in colour relative to the polished metal as a func- tion of exposure time.
Figure 9 Change in colour relative to the polished metal as a func- tion of exposure time.
Figure 10 Backscattered electron images of a FIB cut of sterling silver sulfidized with the Na,S method for 60 min: a a surface area with moderate Cu content in the sulfide layer; b an area with a higher Cu-content in the sulfide layer. (Images CEST, Wr.Neustadt).
Figure 10 Backscattered electron images of a FIB cut of sterling silver sulfidized with the Na,S method for 60 min: a a surface area with moderate Cu content in the sulfide layer; b an area with a higher Cu-content in the sulfide layer. (Images CEST, Wr.Neustadt).
Figure 11 SEM images of the evolution of the tarnish layer over time after 3 min (a), 9 min (b), 60 min (€) and 300 min (d). (Images CEST, Wr.Neustadt).
Figure 11 SEM images of the evolution of the tarnish layer over time after 3 min (a), 9 min (b), 60 min (€) and 300 min (d). (Images CEST, Wr.Neustadt).
Figure 12 Evolution of the tarnishing layer as function of time with SEM-FIB. The images correspond to the ones in Figure 11. (Images CEST, Wr.Neustadt).
Figure 12 Evolution of the tarnishing layer as function of time with SEM-FIB. The images correspond to the ones in Figure 11. (Images CEST, Wr.Neustadt).
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