Electrochemical measurement methods under thin electrolyte films are described and the applications to atmospheric corrosion studies are introduced. Firstly, oxygen reduction mechanism under a thin solution film is provided on the basis of cathodic polarization curves obtained under electrolyte films of various thicknesses. Dependencies of corrosion rates for carbon steel, stainless steel and copper on the thickness of the solution film are also discussed on the obtained EIS under thin films. Secondly, corrosion monitoring results of carbon steel and stainless steel exposed to cyclic wet and dry conditions are presented and their corrosion mechanisms are briefly described. Finally, atmospheric corrosion monitoring in actual atmospheric environments is introduced and the relation between atmospheric corrosion rate and environmental factors such as relative humidity and airborne sea salt is discussed.
In order to investigate the effect of boiling under reduced pressure on corrosion of stainless steel in the nitric acid solution, the corrosion tests simulating the high-level radioactive liquid waste evaporator were performed. The results of immersion tests of stainless steels in the solution with and without boiling showed that the corrosion rates in boiling solution were larger than those in not boiling solution in case of same temperature of solution. Moreover, the cathode polarization curves showed that the corrosion potential of stainless steel in boiling solutions were shifted nobler, and the current intensity became larger than that in not boiling solutions. According to these results, it can be concluded that boiling of solution under reduced pressure accelerate the corrosion rates.
A simple test method is proposed for reproducing stress corrosion cracking of pure copper in ammoniacal environment. A test tube of ammonia aqueous solution and C-ring specimens sampled from a pure copper tube were put in a 500mL polypropylene bottle for three weeks under room temperature. The pure copper tubes used in this work were high phosphorous deoxidized copper tube containing 0.028% P, low phosphorous deoxidized copper tube containing 0.007% P and oxygen-free copper tube without P. Tempers of these tubes were H, 1/2H and O defined in JIS H0500. Intergranular corrosion or intergranular cracking was occurred on the surface of P-deoxidized 1/2H and O copper tubes under gas-phase ammonia derived from 1 to 9% ammonia water, while intergranular corrosion was not observed in the oxygen-free copper and all H-tempered copper tubes. It was found that no stress corrosion cracking occurs in the pure copper tubes without phosphorous or with small crystal grains by work hardening.
It is very important to clarify the initiation and propagation behavior of crevice corrosion of stainless steel in natural seawater. Dynamical observation of crevice corrosion behavior of SUS304 stainless steel with the metal/quartz glass crevice in natural seawater was carried out for 764h. The corrosion potential of the specimen was continuously measured throughout the test duration. After the immersion test, the corrosion depth profile of the specimen was measured. The results were as follows. (1) The corrosion potential gradually increased up to about 600mV vs. SHE by the bio-film formation and dropped at 331.5h immersion resulting from the initiation of crevice corrosion near the crevice mouth. (2) The crevice corrosion spread throughout the crevice as two-dimensional propagation, though the corrosion depth was very small. The propagation behavior of crevice corrosion after 100h from the initiation of crevice corrosion changed from two-dimensional propagation to three-dimensional one, namely toward thickness. (3) Average current through the immersion test was 74.5μA calculated from the crevice corrosion volume that was measured after the immersion test.
In a previous study, self-healing polyurethane coatings with microcapsules containing the high reactive liquid phase have been developed for the protection of metal from corrosion for long periods. In this study, we examine the effect of the amount of glycerol added in the microcapsule formation process on the shape of capsules and the self-healing ability of coatings with microcapsules. The capsule formation with large amounts of glycerol gave rise to clusters of capsules, while with small amounts of glycerol, the capsules were mainly independent ones. The self-healing property of the coatings was more remarkable with decreasing the amount of glycerol in the capsule formation process.
The corrosion behavior of STPG 370 carbon steel piping were studied in order to acquire the key knowledge for discussing the integrity of the cooling water cleanup system piping of the spent fuel pool of the Fukushima Daiichi Nuclear Power Station Units 1 to 4. A series of recirculation pipe tests were carried out in simulated spent fuel pool environments for 6068 h at the longest. The Sch.40 200A pipe was observed to be self-passivated in the test solution of the Larson-Skold index (LSI) = 0.10. The Sch.40 150A pipe was self-passivated in the test solution of LSI = 0.44 as well as that of LSI = 0.10. The test results suggest that the STPG 370 carbon steel piping tends to be self-passivated and consequently tends to suffer localized corrosion damage in actual spent fuel pool environments. In the water chemistry of the current situation for the Fukushima Daiichi nuclear power station of Units 1 to 3, the localized corrosion on the piping of the cooling water purification system made by carbon steel was considered to be likely to occur.
The diagnosis method for corrosion of copper in the fresh water was proposed by combining the potentiodynamic polarization curve measurement and the galvanostatic polarization measurement. The procedure for diagnosis of corrosion of copper in the various concentrations of test solution is described below: The potentiodynamic polarization curve measurement of copper → The galvanostatic polarization measurement at 500 μA cm-2 for 10 min → The diagnosis of corrosion morphology of copper based on the potential changes of copper during the galvanostatic polarization. A corrosion map 3D was developed by the results of diagnosis of corrosion of copper. The axes of corrosion map 3D were the potential after 10 min of galvanostatic polarization at 500 μA cm-2, the current density of potentiodynamic polarization curve of copper at 0.2 V vs. SSE and pH of the test solution. This diagram demonstrated that the corrosion morphology of copper in the various concentrations of test solution could be divided into four corrosion categories (general dissolution, general micropit, pitting corrosion, no corrosion) precisely.