Anodic polarization method was applied for the investigation of pinhole defects in a gold-plated or a nickel-plated layer of FFCs (Flexible Flat Cables). Pinhole defects in a gold-plated layer were quantitatively determined using 5 M H2SO4 as the electrolyte. The ratio of pinhole defects over 0.05% could be evaluated. Although pinhole defects in a gold-plated layer tend to decrease with an increase of the plating thickness, an excessive use of gold results in a cost problem. But generally, pinhole defects in a gold-plated layer are considered to decrease adequately, if the qualities of a base nickel-plated layer are high enough. The method of measuring pinhole defects in a nickel-plated layer was also developed for the quality estimation. In the case with acidic electrolytes, the anodic dissolution of nickel started before that of copper. However, the use of an alkaline electrolyte (i.e., 7 M KOH) enabled us to detect the current peak due to the formation of a copper oxide without the interference of the anodic reaction of a nickel-plated layer. The evaluation lower limit of the ratio of nickel pinhole defects was around 0.01%.
The goal of this paper is to evaluate the environment within concrete nondestructively related to corrosion of reinforcing bar using the newly developed magnetic corrosion probe which is introduced into concrete to raise a magnetic signal. The probe was prepared by electroplating of iron onto a copper bar, which was subsequently heat treated at 423 K for 30 min to stabilize the residual magnetization. The residual magnetization from the probe, as detected by superconducting interference device (SQUID) decreased with progress of corrosion of the probe. The electrochemical behavior of the magnetic corrosion probe was also evaluated in a saturated Ca(OH)2 solution. The as plated probe showed a large active current density and residual magnetization. The heat treatment of the probe resulted in reduction of the active current density and residual magnetization. Meanwhile the passive current density of the probe was still higher as compared with that of an iron bar even after the heat treatment. This means that the probe is more sensitive to corrosive environment than reinforcing bars. Thus, the developed probe is expected to give a magnetic warning against degradation of surroundings in advance of the corrosion of reinforcing bar.