Two plateaus are found in the potential vs. time curve when the duplex copper oxide film is cathodically reduced at a constant current density. However, there are contradictory mechanisms to assign these two plateaus. We must solve this problem to use catholic reduction for characterization of the duplex copper oxide film. The sub-committee for catholic reduction of copper oxide films constituted in 2002 and has been discussing the reduction sequence in catholic reduction of the duplex copper oxide film. We performed round robin experiments in three companies to determine the reduction sequence in the potential vs. time curve. In these experiments, the electrolyte was 0.1M KCl and reduction current density was 50μA/cm2. The specimens for catholic reduction were oxidized in a constant temperature humidity chamber at 60°C and 90%RH for 72h. The change in the XPS spectra of specimen surfaces revealed that cupric oxide was reduced in the first plateau, while cuprous oxide was reduced in the second plateau. Furthermore, we found that the cupric oxide was directly reduced to metallic copper by an experiment using the standard CuO/Cu specimen.
Corrosion diagnosis and the corrosion mechanism investigations of carbon steel covered with mill scale in distilled water and aqueous solution containing various component (Cl-, SO42-, HCO3-, SiO2) were performed by using ENA. It has been clarified that the corrosion patterns could be discriminated by the measurements of potential time series and that the effects of the water quality factor on the corrosion could be discussed. Bicarbonate ions whose concentration is less than 10ppm accelerate the corrosion of carbon steel covered with mill scale. Besides, the bicarbonate ions whose concentration is 100ppm stabilize the mill scale. In neutral solution, the dissolved silica accelerates the anode reaction of carbon steel. Contrary to this in alkaline solution, the dissolved silica gives the corrosion resistance to the carbon steel with covered with mill scale.
Fracture dynamics of atmospheric rusts were studied by Lamb-wave acoustic emission (AE) analysis. Fracture parameters of the rust were estimated by the waveform matching of the S0-mode packet of Lamb AEs monitored during tensile- and compressive-bending of steel plates with atmospheric rust produced by out-door exposure for 500 days. Generation times of rust fractures are estimated to be less than 1μs, however, the crack volumes are several hundred to thousand times larger those of the delayed fractures. Next we monitored water-born longitudinal AEs from rust fracture on the bottom plate of the water-storage cylindrical tanks using the sensors mounted on the side-wall, and estimated their source locations. AEs were monitored by the AE system with 20dB amplification, however, their source location accuracy was poor due to the low S/N ratio.
A new method was proposed of analyzing the double layers structures of calcareous deposit films formed on the surface of steel cathodically polarized in seawater. The method was based on the assumption that pore-water in the deposits should be distributed between the layers according to the difference of their water-affinities. From the assumption, various structural factors concerning the double layers in the deposits were derived. In order to examine the validity of the theoretical model for analyzing the double layers structures, calcareous deposit films with various Ca/Mg compositions was prepared through either varying hydrodynamic state of seawater around the cathode or diluting seawater under a constant cathodic current density and temperature. The application of the above model to these deposits proved the validity of the model to analyze the double layers structures.