Micro‐Raman investigations of early stage silver corrosion products occurring in sulfur containing atmospheres

Abstract

Silver is a soft, lustrous metal with the highest electrical and thermal conductivity. Due to these properties, it has many applications as a precious material both in pure and alloy form (ornaments, jewellery, utensils, coins), but also in several technological fields, considering silver compounds (e.g. photography, electric and electronic industry). As a consequence of this, silver and its by‐products are regularly exposed to different atmospheres where a wide spectrum of agents (e.g. moisture, temperature, air pollutants, UV light) may cause metal corrosion and alteration of their surface characteristics and properties. The aim of this research is to deepen the potential and applicability of micro‐Raman spectroscopy as a surface‐sensitive technique to investigate the initial steps of atmospheric corrosion throughout the identification of surface chemical reactions and corrosion products formed on silver substrates. In a previous study, micro‐Raman analysis was carried out on pure silver powder compounds, selected among the most expected corrosion products occurring on silver substrates, in order to optimize experimental conditions and to obtain reference spectra [1]. Subsequently highly pure silver samples were exposed for 24 h to different controlled laboratory atmospheres (synthetic air, relative humidity, SO2, H2S), particularly focusing on sulfur containing gases, and the resulting surface reactions. The experiments highlight micro‐Raman spectroscopy as a highly surface‐sensitive technique enabling to detect both adsorbed chemical species and crystalline corrosion products of only several monolayers of thickness. Furthermore, these investigations could show the trends of primary and secondary corrosion mechanisms and their mutual interaction occurring on silver substrates. Copyright © 2013 John Wiley & Sons, Ltd.

Evaluation of laser cleaning for the restoration of tarnished silver artifacts

“…a) Ag 3d and b) S 2p for pure silver; c) Ag 3d, d) S 2p, e) Cu 2p and f) Cu Auger LMM for sterling silver. [43,44]. The presence of this compound testifies the high tendency of silver to oxidation under ambient conditions.…”

“…7c) results in the appearance of a couple of bands at 185 and 237 cm −1 that are assigned to the Ag-S stretching and bending vibrations modes of Ag 2 S, respectively [43,44]. At 1064 nm, the Raman spectra reveal slight differences in the intensity of the Ag 2 S bands.…”

“…The band at 463 cm −1 is assigned to the O-S-O bending vibration. As the absence of bands at 964 or 970 cm −1 rules out the presence of Ag 2 SO 3 and Ag 2 SO 4 compounds respectively [44], it is possible to assign the vibration at 463 cm −1 to cluster species composed of sulfur and oxygen atoms. The shoulder at 473 cm −1 corresponds to the vibrational modes of the S-S bond of S 8 (with orthorhombic crystal structure) [8,45].…”

Chemical stability of plasmon-active silver tips for tip-enhanced Raman spectroscopy

“…However, silver sulfide (Ag 2 S) and silver sulfate (Ag 2 SO 4 ) are common atmospheric silver corrosion products that form on the probe surface. Their Raman bands, which appear around 188, 243, and 273 cm -1 for Ag 2 S and 432, 460, 595, 623, 970 (strong), and 1079 cm -1 for Ag 2 SO 4 [2], can coincide with spectral regions of interest such as the radial breathing mode of carbon nanotubes (CNT) [3]. It was also shown that the electric field enhancement decreases with the aging of the silver surface [4]; the thickness of Ag 2 S increases over time as it is not a self-limiting process confined to the surface [5].…”

Recent advances in linear and nonlinear Raman spectroscopy. Part VIII

“…carried out a micro‐Raman investigation of early‐stage silver corrosion products occurring in sulfur containing atmospheres. The experiments highlight micro‐Raman spectroscopy as a highly surface‐sensitive technique enabling the detection of both adsorbed chemical species and crystalline corrosion products of only several monolayers of thickness . Sanson and coworkers studied carrier concentration profiles in Al‐implanted Ge by micro‐Raman spectroscopy using different excitation wavelengths.…”