Communication lines are usually composed of steel and other metallic components and are built outdoors. To determine whether local corrosion is inhibited in coastal areas, which are tough on metals, we conducted a longterm (23 years) exposure test on Miyake Island. The test candidate was steel suspension wire used for suspending communication cables on telephone poles. For preventing corrosion such wires, Zn coating had been used. However, some steel wire strands located in coastal areas still corroded. This is because air born sea salt particles from the ocean are blown by the wind and adhere to the surface of metals. To protect steel wires against atmospheric corrosion, Al coating was applied because of its higher corrosion resistance compared with that of Zn coating. This coating still did not prevent corrosion at specific points in the coastal areas. We compared three types of steel wire strands, Zn coated and Al coated, which are currently used for protecting steel wires, and one Al coated with sacrificial anode tape was efficient in preventing on steel wires had efficacy as protecting corrosion by conducting the exposure test in Miyake Island for 23 years.
A new voltammetric method for determination of the oxides on tin was proposed. In an ammonia buffer solution (0.5 M NH4OH+0.5 M NH4Cl), well-defined reduction peaks for SnO and hydrated SnO2 (denoted as SnO2･nH2O) were observed in a current-potential curve. The peak potentials were fully separated by -0.3 V, since NH4+ ions facilitated the reduction of SnO2･nH2O. On the other hand, in a borate buffer solution, which has been frequently used as the supporting electrolyte for this purpose, and in 1 M KCl containing higher concentration of ions, the peak of SnO2･nH2O was not detected. By using the ammonia buffer solution, we found that the main corrosion products formed on tin in air were SnO and SnO2･nH2O. It was also found that SnO was formed in air at a temperature higher than 100℃, while SnO2･nH2O was formed at a temperature below 100℃ with a higher relative humidity of 90%. The amounts of the respective oxides increased with temperature and relative humidity. In addition, the film thicknesses of tin oxides estimated from the areas of reduction peaks were close agreement with FIB/SEM data.