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Figure 2. SEM images of the surface of the silver cleaned with a) CaCO, b) thiourea-H;PO, solution, c) electrochemical reduction in Na;H(CO3),. eee eee eee ee eee eee Mechanical methods left silver brighter than chemical and electrochemical. Pre-Lim© and calcium carbonate were the slowest methods, but the visual result was homogeneous and shiny. The silver surface was smoother than the original and the tarnished coupons (Fig. 2a), even though some lineal scratches related with the abrasive could be observed on the surface. In the largest holes and scratches, remains of Ag»S were detected because the manual system did not reach to clean them (Fig. 2a). The silver coupon cleaned by polishing presented irregular marks associated with the rubber point, therefore this method is not recommended for smooth areas.

Figure 2 SEM images of the surface of the silver cleaned with a) CaCO, b) thiourea-H;PO, solution, c) electrochemical reduction in Na;H(CO3),. eee eee eee ee eee eee Mechanical methods left silver brighter than chemical and electrochemical. Pre-Lim© and calcium carbonate were the slowest methods, but the visual result was homogeneous and shiny. The silver surface was smoother than the original and the tarnished coupons (Fig. 2a), even though some lineal scratches related with the abrasive could be observed on the surface. In the largest holes and scratches, remains of Ag»S were detected because the manual system did not reach to clean them (Fig. 2a). The silver coupon cleaned by polishing presented irregular marks associated with the rubber point, therefore this method is not recommended for smooth areas.

Related Figures (3)

Figure 1. SEM images of the surface of a) original silver, b) tarnished silver. The original silver coupon presented some scratches related with the preparation (Fig. la). Af- ter tarnishing, all the silver coupons presented a brownish and dark layer associated with the formation of Ag»S on their surface. The surface of the tarnished silver was rougher than the original silver (Fig. 1b) because of the reaction of the silver surface with the sulphur vapor. The crystals of AgoS were observed at high magnification.
Figure 1. SEM images of the surface of a) original silver, b) tarnished silver. The original silver coupon presented some scratches related with the preparation (Fig. la). Af- ter tarnishing, all the silver coupons presented a brownish and dark layer associated with the formation of Ag»S on their surface. The surface of the tarnished silver was rougher than the original silver (Fig. 1b) because of the reaction of the silver surface with the sulphur vapor. The crystals of AgoS were observed at high magnification.
Figure 3. AFM images (10 x 10 pm) of the surface of the coupons original, tarnished, mechanical cleaned with Prelim© (MP) and electrochemical cleaned in NaNO; (EN). ae ee te ste ee eee I Eg I DN IE EES AFM showed similar results to SEM. The original coupon presented scratches from the preparation (Fig. 3). Tarnishing produces a fine-grained texture over these scratches related with the formation of AgS layer. The electrochemical cleaning with NaNO; as electrolyte (EN) preserved the texture of the tarnished coupon, as opposed to the mechanical cleaning with Pre- lim© (MP), which polished the surface, eliminating the features of the original coupon (Fig. 3).
Figure 3. AFM images (10 x 10 pm) of the surface of the coupons original, tarnished, mechanical cleaned with Prelim© (MP) and electrochemical cleaned in NaNO; (EN). ae ee te ste ee eee I Eg I DN IE EES AFM showed similar results to SEM. The original coupon presented scratches from the preparation (Fig. 3). Tarnishing produces a fine-grained texture over these scratches related with the formation of AgS layer. The electrochemical cleaning with NaNO; as electrolyte (EN) preserved the texture of the tarnished coupon, as opposed to the mechanical cleaning with Pre- lim© (MP), which polished the surface, eliminating the features of the original coupon (Fig. 3).
Figure 4. a) S2, XPS spectra of the coupons: original, tarnished, mechanical cleaned with Prelim© (MP), chemically cleaned with DTPA+Triton X-100 (CC) and electrochemical cleaned in NaNO; (EN). b) Mass variation in function of the cycle number. The silver coupons cleaned with mechanical and chemical methods showed loss of mass, while the weight of the coupons cleaned with electrochemical met hods were almost constant (Fig. 4b). The most abrasive method was polishing with the rubber point mounted on a rotary tool and softly abraded with Pre-Lim©, which removed ~1.0 % of mass in 6 cycles. The mechanical abrasion with Pre-Lim© and with calcium carbonate were bo h similar, they abraded over the 0.5 % of silver after six cycles of tarnishing/cleaning. The thiourea acid solutions produced 4 loss of silver mass similar to the soft abrasives (Fig. 4b). The hiourea-H3PO, acid solution ex- tracted slightly more mass than thiourea-HCOOH acid solution because of its slightly high re- activity. However, as it was shown in SEM images, while in t loss is uniformly distributed on the surface, the mass loss of t selective corrosion, leaving a non-uniform surface. he mechanical methods the mass hiourea-acid methods is due to 2
Figure 4. a) S2, XPS spectra of the coupons: original, tarnished, mechanical cleaned with Prelim© (MP), chemically cleaned with DTPA+Triton X-100 (CC) and electrochemical cleaned in NaNO; (EN). b) Mass variation in function of the cycle number. The silver coupons cleaned with mechanical and chemical methods showed loss of mass, while the weight of the coupons cleaned with electrochemical met hods were almost constant (Fig. 4b). The most abrasive method was polishing with the rubber point mounted on a rotary tool and softly abraded with Pre-Lim©, which removed ~1.0 % of mass in 6 cycles. The mechanical abrasion with Pre-Lim© and with calcium carbonate were bo h similar, they abraded over the 0.5 % of silver after six cycles of tarnishing/cleaning. The thiourea acid solutions produced 4 loss of silver mass similar to the soft abrasives (Fig. 4b). The hiourea-H3PO, acid solution ex- tracted slightly more mass than thiourea-HCOOH acid solution because of its slightly high re- activity. However, as it was shown in SEM images, while in t loss is uniformly distributed on the surface, the mass loss of t selective corrosion, leaving a non-uniform surface. he mechanical methods the mass hiourea-acid methods is due to 2
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