Metallic corrosion and semiconductor corrosion are both subject to the local cell model, in which the energy levels of electrons and holes are determinant in the corrosion. In metals available electrons and holes locate at the same level of electrode potential: whereas, in semiconductors they locate at their respective levels different from the electrode potential. Electron-associated corrosion and hole-associated one are indistinguishable with metals but take place in different ways with semiconductors depending on whether of p-type or n-type. Photo-effects on corrosion are negligible with metals but are significant with semiconductors. The corrosion of metals may be inhibited in contact with n-type semiconductors, while it may be accelerated with p-type semiconductors.
SUS304, SUS316 and SUS329J4L specimens with and without crevice are exposed in a river for up to 18 months with three conditions; in fresh water, brackish water areas and in the mud in order to investigate the relation between corrosion behavior and environmental factors of river, such as micro organisms and barnacles. Corrosion potential of the specimen was monitored continuously and specimens were collected successively to reveal the change of corrosion morphology including attachment of aquatic organisms. The results obtained are as follows. (1) Corrosion potential of all specimens immersed in fresh water or brackish water are ennobled up to about 500mV vs. SHE. (2) In brackish water, crevice corrosion occurred beneath barnacle on the specimens of SUS304 and SUS316. However, frequency of crevice corrosion to the number of barnacles attached is at most 3 to 4%. (3) The density of attached sulfate-reducing bacteria (SRB) increases under barnacle much more than on barnacle. (4) Corrosion of several forms occurs to specimens positioned in mud which reason may be due to SRB.
Topographic measurements of rusted, pretreated and several coated steel surfaces were done employing non-contact 3D optical surface profiler. A laser displacement sensor technique was applied in this technique. This method efficiently and quantitatively evaluated surface topographies and curves of cross-sections of pretreated and anticorrosive coated surfaces. The results indicated that pit formed during SST (Salt Spray Test) was grown as a result of initiation and then further blistering upon exposure to SST. The area ratio of these blisters were successfully measured by 3D topographic study without any inference from surface outflow rust. It was found that the blistering area ratio depends on various factors like coating condition, nature of paint, coating thickness etc.
We performed the electrochemical experiments, such as measurements of polarization curves, corrosion potentials and constant-potential holding tests, using copper tubes with/without residual carbon film under water with/without nitrite inhibitor taken from the heat storage plants working in Tokyo. The polarization curve under the water with nitrite inhibitor shows the passivation from -950mV to 120mV (Ag/AgCl), while the one under the water without inhibitor does not show the passivation. The passive current density of the copper tube with residual carbon film is higher than that of the copper tube without carbon film. In the constant-potential holding test at 200mV for 168h, the current density at 168h was 20μA/cm2 under the water without inhibitor and 0μA/cm2 with inhibitor. After the constant-potential holding test, the surface of specimens in the water without inhibitor were covered with the oxide films and patinas. The surface of specimens in the water with inhibitor remained the bright metallic color and had spottily some patinas. Under these patinas, the pitting corrosion has slightly occurred.