Comparative XPS Study of Silver and Copper Surfaces Exposed to Flowing Air Containing Low Concentration of Sulfur Dioxide

Abstract

Sulfur dioxide (SO 2 ), a typical gaseous compound found in the atmosphere, corrodes metals, particularly outdoors. When SO 2 adsorbs on the surface electrolyte, it easily dissolves, resulting in the formation of protons (H ) and bisulfite ions (HSO 3 ). The former reduces the pH of the surface electrolyte, which promotes metal dissolution.Silver and copper are commonly used in the electronic components and devices typically found in telecommunication equipment. Since silver and copper are affected by SO 2 , it is important to know the effects of SO 2 on their corrosion behavior to predict the life expectancy of the equipment. Such knowledge would also be useful for coping with anomalous situations, such as volcanic eruptions, in which the SO 2 concentration can exceed several hundred ppb. A previous study showed that silver and copper plates exposed to the atmosphere were severely corroded following the volcanic eruption on Miyake Island in 2000. 1)Much effort has been expended on clarifying the effects of SO 2 on atmospheric silver and copper corrosion. A number of laboratory experiments have been reported regarding the effects of exposure to high SO 2 concentrations. 2) 15)Using infrared reflection absorption spectroscopy (IRAS), Persson and Leygraf showed that sulfite formed on the surface of copper during the initial stage when it was exposed to 0.21 ppm SO 2 in flowing air at 80 relative humidity (RH).16) In situ analysis using IRAS and a quartz crystal microbalance by Ito et al.17) 18) revealed that sulfite like CuSO 3 Cu 2 SO 3 2H 2 O (Chevreul's salt) and sulfate CuSO 4 5H 2 O formed as corrosion products on copper exposed to flowing air containing 10 ppm SO 2 at 80 RH. Moreover, the formation rate of sulfite was higher than that of sulfate in the very early stage. 17) 18) In contrast, the sulfidation rate by SO 2 for silver is much lower than that by reduced sulfur species, such as H 2 S and COS. 12) Since SO 2 is considered to be a weak corrosive agent for silver, the effect of SO 2 on atmospheric silver corrosion in the initial stage has received little attention.In this study, the chemical state of the sulfur was investigated when silver and copper plates were exposed for one hour to flowing air containing low concentrations of SO 2 . Since the electrochemical reactions occur at the metal/ electrolyte interface in the early stage of corrosion, X-ray photoelectron spectroscopy (XPS) was used. The SO 2 concentrations were 18 and 148 ppb ; the former is at least one order of magnitude lower than those in previous studies. 16) 18)The silver and copper plates were 99.99 pure and 5 5 0.1 mm in size. Their surfaces were sputtered with 3 kV Ar ions to clean them. The sputtering was conducted until both carbon and oxygen were not detected in the XPS spectra, as described elsewhere. Sulfur dioxide (SO 2 ) is a typical gas affecting the atmospheric corrosion of metals, particularly outdoors. Although many studies have investigated the effect of SO 2 on the atmospheric corrosion of silver and copper, little is ...

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An experimental set-up to apply polarization modulation to infrared reflection absorption spectroscopy for improved in situ studies of atmospheric corrosion processes

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