Copper Corrosion in Telephone Switching Centers and Their Outdoors

摘要

Copper plates were exposed both in telephone switching centers and their outdoors to investigate the corrosion behavior of copper. We selected eight telephone switching centers and outdoor locations in the Kanto area including Tokyo (urban), Saitama (urban), Ibaraki (rural), and Tochigi (hot spring). The copper plates were exposed for a month and the experiments were conducted over the course of a year. After exposure, the amounts of sulfur and chlorine on the copper plates were determined by means of X-ray fluorescence analysis (XRF). We also analyzed the corrosion products formed during outdoor exposure using X-ray diffraction (XRD). Our results can be summarized as follows. 1) The amounts of sulfur and chlorine on the copper plates exposed in the telephone switching centers were one to two orders of magnitude lower than that on the plates exposed outdoors. 2) The amounts of sulfur and chlorine on the copper plates exposed outdoors in Tokyo and Saitama (urban areas) exhibited significant seasonal variations. The seasonal change in the sulfur was caused by the change in the sulfate ion concentration in fine airborne particles. By contrast, we attributed the seasonal change in the chlorine to changes in the sea salt aerosol concentration. 3) The corrosion products on the copper plates exposed in Tokyo, Saitama, and Ibaraki in summer were found to be cuprite (Cu_2O) and posnjakite (Cu_4SO_4(OH)_6 centre dot H_2O). We found that the formation of posnjakite depended on the amount of sulfur on the copper plate.