"Measurements of a Trace Amount of Indoor Corrosion Using Kelvin Probe and QCM Methods"

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New methods for measuring a trace amount of corrosion, which are based on Kelvin prove and quartz crystal microbalance (QCM) methods, have been developed to clarify the mechanisms of indoor corrosion in electronic equipments.This study is divided into three chapters.(1) "Development of a Vibrating reference electrode system" A new technique for measuring the potential distribution on a metal without touching the surface has been developed. We found that the use of parasitic capacitance is effective to reduce to time for measurement. By using this equipment, the surface potential of aluminum embedded in a copper sheet was measured.(2) "oxygen reduction under thin water layer" The reduction mechanisms of oxygen on metals with thin water layer have been investigated by Kelvin probe method. Particular attention has been given to the dependence of the oxygen reduction rate on the thickness of water layer. It was found that the reduction rate increases with decreasing the thickness of water layer down to the thickness of several tens mum. When the thickness is decreased further, it is independent of the thickness. It can be explained by a decrease of oxygen solvability and a pH change of water film.(3) "Impedance characteristics of metal corrosion under thin water layer"The impedance characteristics of steels and copper have been monitored in wet/dry cycle condition. This is capable of monitoring the corrosion rate simultaneously with the thickness of water layer. We found that the corrosion rate increases sharply, immediately after the dried surface is reimmersed into a solution and shortly before the surface dried out, and that it exhibits a maximum around the water layer thickness of 20 mum.