Developing new technique is essential for acquiring new knowledge in corrosion study. One of the most powerful non-electrochemical techniques that have been developed recently is the scanning probe microscopy (STM, AFM, KFM, SNOM and etc.). Beside this technique, QCM, SECM, SVET are often used in corrosion study. In present paper, the problems when we use STM, AFM, KFM, QCM and SECM are mainly discussed.
Corrosion of stainless steels, SUS304L, SUS310S, and Ni-based alloy, HastelloyC-276, covered with/without Fe2O3, FeCl2 or FeCl3 powder was investigated for 5 days in O2-H2O-HCl atmospheres at 160-210°C under heat transfer conditions. Corrosion rate of SUS304L and SUS310S was much higher than that of HastelloyC-276, and was enhanced considerably by covering with FeCl3. The enhanced corrosion rate on the FeCl3-covered specimen was due to the formation of concentrated FeCl3/HCl solution by absorbing H2O and HCl into FeCl3. Corrosion mechanisms of stainless steels are discussed thermodynamically in terms of oxychlorination of iron.
A photon rupture technique was used to investigate abrupt destruction and repair of passive oxide films on A-9 mass% Si coated steels. Specimens covered by anodic oxide films were irradiated with a focused pulse of a pulsed Nd-YAG laser beam at a constant potential in 0.1kmol/m3 Na2B4O7, pH=9.2, with and without Cl- and SO42- ions while monitoring the current transients. Irradiation with a focused pulse of a pulsed laser beam in the solutions causes abrupt removal of the anodic oxide film at the irradiated area. Without aggressive anions and also with aggressive anions at low potential, oxide films were reformed after the laser irradiation. With increasing the potential, the current increased in the solutions with aggressive anions. This behavior can be explained by a preferential dissolution of the metal substrate, which is enhanced at higher potentials. It may be concluded that localized corrosion of Al-Si coated layers occurs at high potentials while film repair occurs at low potentials in solutions with aggressive anions.
The fouling of material surface through the adhesion of marine organisms such as mussels and barnacles is a serious problem for facilities that involve the use of seawater. The use of copper alloys to avoid such fouling is promising because they release copper ions that inhibit the growth of marine organisms. However, the release of copper ions leads to the deterioration of the alloy through corrosion. Thus, these two conflicting characteristics makes the use of such alloys questionable. We describe here, however, a copper alloy that has excellent anti-fouling characteristics and is also satisfactory resistant to corrosion. The effect of two types of alloying elements, namely Ni and Be, on the corrosion of a copper alloy was examined. The former would be expected to promote corrosion resistance, and the latter to serve as an anti-fouling agent. Corrosion tests were carried out in a jet-in-slit apparatus in which so-called erosion-corrosion as well as the flow velocity difference-induced corrosion can be rapidly reproduced. As expected, an increase in Ni content leads to an increase in the corrosion resistance of the copper alloy. Too high content of Ni, however, causes pitting corrosion. Contrary to expectations, the addition of Be decreased the depth of corrosion.
It is important to examine the effect of corrosion products on the corrosion rate of carbon steel overpack container for the geological disposal of radioactive wastes. In order to understand the influence of Fe3O4 film as the corrosion product, the corrosion behavior of carbon steel with and without Fe3O4 film produced by oxidization in a concentrated alkali solution was examined. The result of immersion corrosion tests in compressed bentonite containing water showed that the corrosion of carbon steel was promoted by the self-reduction reaction of Fe3O4 film, and that the most stable corrosion product in the test environment was a mixture of FeCO3 and Fe2(OH)2CO3. Then, to reveal the effect of alloying elements on the corrosion of the steel in the test environment, several kinds of low alloy steel were prepared by adding various metallic elements to the steel. The corrosion resistance of the low alloy steels with and without Fe3O4 film was examined. The result showed the corrosion of the steels was suppressed by the addition of Cu, Ti, and Cr, independently of the existence of Fe3O4 film. Among them, Cu showed the highest suppression effect.
By using the humped specimen, which is processed by the humped die, in the slow strain rate technique (SSRT) test, fracture facet due to stress corrosion cracking (SCC) can be observed in relatively short duration. Although the cold work and concentrated stress and strain caused by the characteristic shape of the specimen accelerate the SCC, to date these acceleration effects have not been examined quantitatively. In the present study, the acceleration effects of the humped specimen were examined through experiments and finite element analyses (FEA). The experiments investigated the SCC of alloy 600 in the primary water environment of a pressurized water reactor. SSRT tests were conducted using two kinds of humped specimen: one was annealed after hump processing in order to eliminate the cold work, and the other was hump processed after the annealing treatment. The work ratio caused by the hump processing and stress/strain conditions during SSRT test were evaluated by FEA. It was found that maximum work ratio of 30% is introduced by the hump processing and that the distribution of the work ratio is not uniform. Furthermore, the work ratio is influenced by the friction between the specimen and dies as well as by the shape of dies. It was revealed that not only the cold work but also the concentrated stress and strain during SSRT test accelerate the crack initiation and growth of the SCC.