Ultrathin (less than 5.4 nm), ordered (self-assembly), and highly interconnected (one- and two-dimensional polymers) protective films were prepared on a passivated iron electrode by chemical modification of a carboxylate self-assembled monolayer with alkyltriethoxysilanes. Prevention of passive film breakdown by coverage of the passivated electrode with the films was examined by anodic polarization measurements in a borate buffer containing 0.1 M Cl-. Complete protection of the passive film against breakdown was observed over the passive and transpassive regions.
Many steel structures built in marine environment were mainly protected by organic coatings. For saving the life cycle cost (LCC) of these structures, it is very important to predict the lifetime of those. About 25 kinds (n=2) of organic coated steel pipes were exposed at seashore at Miyakojima Island in OKINAWA for 20 years and were evaluated the degradation of coated materials. The obtained results are as follows: 1) Some monitoring techniques measured at exposure site were not effective for predicting the degradation of organic coating materials. A new monitoring technique to evaluate degradation will be expected. 2) A correspondence between the exposure results and laboratory acceleration test results was examined. It is shown that the rusted area spread from scratched portion exposed at splash zone correlates the rust width in SST, and also changes in adhesion strength of the tidal and submerged zone correlate with those of rotating immersion test. So, the preferable acceleration test can predict the degradation of organic coatings, in the case of having the similar environmental condition. 3) Maximum corrosion depth under the defect portion of organic coating was measured after removal the coating and rust. The maximum depth of submerged zone was deeper than those of tidal and splash zone. These phenomena were affected by macro cell formation, which consisted of sound coating as cathode and defect part as anode. The degradation of organic coated steel in marine environment should be considered the effect of macro cell formation.
In the secondary systems of pressurized water reactors (PWRs), all volatile treatment (AVT) is applied. Hydrazine is added as an oxygen scavenger. The authors hypothesized that carbohydrazide would be a harmless alternative to hydrazine. In the present study, the thermal decomposition and corrosion suppression effects on carbon steel of carbohydrazide were evaluated in comparison with those of hydrazine. The rate constant of the thermal decomposition of carbohydrazide was evaluated. The oxygen-scavenging efficiency of carbohydrazide is slightly lower than that of hydrazine. However, it has been confirmed that corrosion of carbon steel is suppressed more in carbohydrazide solution than in hydrazine solution at 423 K. It is considered that carbohydrazide is less reducing at 423 K than hydrazine, and that carbohydrazide suppresses reductive dissolution of iron oxides. It can be concluded that carbohydrazide is a promising alternative to hydrazine in the secondary systems of PWRs.
The high-temperature oxidation behavior of intermetallic compound TiAl was investigated in oxygen containing trace amounts of halide vapor as NaCl, NaBr or NaF at 1323 K. Mass gain due to oxidation for the TiAl specimen was large in pure oxygen without any halide vapors. In this case, a thick scale consisting mostly of TiO2 was formed on the specimen. In the oxygen containing trace amounts of halide vapor, on the contrary, a small mass gain was observed, not depending on the kind of halide. The result corresponded to the formation of a thin scale consisting of α-Al2O3. Consequently, it was found that a protective alumina scale was preferentially formed on the TiAl in the oxygen containing trace amounts of halide vapor, leading to an improvement in the oxidation resistance of the TiAl in this atmosphere. The reason for the preferential formation of alumina scale was discussed from the standpoint of thermodynamics. A model for the alumina scale formation was proposed that it was caused by a repetition of the halogenating of aluminum at the scale/substrate interface and the oxidation of the aluminum halide in the scale.