Abstract
The elemental depth profiling of tarnish films were analyzed at the early stages of atmospheric copper corrosion by glow discharge optical emission spectroscopy (GDOES), where the tarnish films had been formed by exposing copper plates to various outdoor environments, i.e., urban, rural/coastal, and hot-spring sites, for 1 month. Since GDOES probed a large surface area, on the order of millimeters, the depth profiles reflected macroscopic-averaged characteristics over this area, which are representative of real corroded surfaces. GDOES complemented previous analyses, i.e., Auger electron spectroscopy (AES), x-ray diffraction, field-emission scanning electron microscopy (FE-SEM), coulometric reduction, and x-ray photoelectron spectroscopy, and provided a better understanding of these tarnish films. In particular, the previous findings from microscopic FE-SEM observation and AES depth profiling were well supported by the GDOES results. With GDOES we observed the generation and distribution of cuprite [Cu2O] and posnjakite (Cu4SO4[OH]6·H2O), which had formed through the influence of sea salt at the urban site. The posnjakite was mostly located on the top of cuprite particles in the tarnish film. The tarnish film extended over 2 μm in depth at the rural/coastal site due to the higher atmospheric sea-salt concentration and humidity. In addition, chlorine, which promotes copper corrosion, was incorporated into the tarnish film with the growth of the oxide. Sulfide and oxides were generated at the hot-spring site, and the tarnish film extended to >5 μm, where apart of sulfide was oxidized to become sulfate.
