The corrosion of iron plate was inhibited in 0.01-20% sodium chloride aqueous solutions with magnetic field. The corrosion was inhibited with increasing of magnetic flux density. Magnetic field accelerated the dissolution rate and solubility of oxygen gas. Magnetic field had some accelerated the catholic reaction (O2+4H++4Fe2+→4Fe3++2H2O), however magnetic field had more inhibited the anodic reaction (Fe→Fe2++2e-). Reactions (Fe2++8γ-FeOOH+ 2e-→3Fe3O4+4H2O and Fe2++OH-→FeOH+→Fe3O4) were activated with magnetic field. The white sediment on iron plate was changed to Fe3O4. A Fe3O4 was attracted by a magnetic force, and was deposited on surface. The corrosion was inhibited as the surface of iron was passivity. It was concluded that the attraction effect of Fe3O4 by a magnet and the increasing of formation rate of Fe3O4 were main effects with magnetic field in initial period.
The corrosion damages of separators after 1754h operation has been studied, and the effect of Cr content and carburization on the corrosion has been discussed. The obtained results are as follows; 1) The separator materials are carburized. The carburization of separator is especially remarkable at the anode side. 2) The increase of Cr content improves the corrosion resistance in the anode side condition. 3) The carburization reduces the corrosion resistance and that effect is especially severe in the anode side condition.
Nondestructive exploratory tests of corrosion of steels embedded in water, rubber, cement and soil were carried out by microwave radar measurement. The possibility of these tests was investigated by its simulation (theoretical analysis). The time at first peak of reflection wave (tp) of corroded steel delayed in comparison with that of uncorroded one. The experimental data of tp and its delay time (Δt) corresponded to the calculated ones by simulation. It is thought that from the embeding conditions of steels, i.e., 1) ε, 2) tan δ and 3) thickness of media and 4) ε and 5) tan δ of corrosion layers, and the relation with Δt and thickness of corrosion layer, the degree of corrosion of embedded steels can be predictable by measurements of Δt.
The embritllement during the electrolytic hydrogen charging at 25-80°C and its recovery during hydrogen outgassing at 65-110°C after the charging were examined on Alloy 800 in some details with regard to tensile properties, fracture surface, and X-ray diffraction. A thin layer of hydride formed on the surface during the charging. It was unstable and disappeared after outgassing, leaving local lattice strain in the underlying metal. Many cracks on the specimen surface were observed along (111) or (110) traces on grains and grain boundaries. Brittle fracture always occurred at grain boundaries in tensile test. Tensile strength and strain at fracture decreased with the increases in charging time and temperature. There was a relation of h∝t1/2 between the depth of brittle layer (h) and charging time (t). The activation energy for the diffusion of hydrogen atoms obtained from the temperature dependence of h vs. t1/2 was estimated to be 11.0kcal/mol. On the other hand, activation energy for recovery process was calculated from Arrhenius plot of the reciprocal of the time to 50% recovery of the strain at fracture to be 12.2kcal/mol. A linear relation was held between the mean depth of brittle layer and tensile strength, and also between the depth and strain at fracture, regardless of charging and outgassing. These results show that the both processes of embrittlement and its recovery are rate-determined by the diffusion of hydrogen atoms in the metal.
The aspects of surface analytical techniques by detecting outcoming electrons from samples were summarized to get acquainted to the fundamental knowledge of typical electron microscopes-scanning electron microscope, scanning transmission electron microscope, transmission electron microscope, spin polarized scanning electron microscope, analytical electron microscope and scanning tunneling microscope-, electron spectrometry-electron energy loss spectrometry, high resolution electron energy loss spectrometry, Auger electron spectrometry, X ray photoelectron spectrometry (X ray electron spectrometry, electron spectrometry for chemical analysis), conversion electron Mossbauer spectrometry- and electron diffractometry-low energy electron diffractometry, reflection high energy electron diffractometry-. Electron or photon induced current methods for analysing n-p junction, and positron annihilation technique for analysing atomic vacancy type defects were also mentioned.
This paper summarizes recent trends in seawater-resistant stainless steels. These steels can be classified into 4 types; ferritic stainless steels which contain more than 25%Cr-3%Mo, austenitic stainless steels which contain more than 20%Cr-24%Ni-5%Mo, N-bearing austenitic stainless steels which contain more than 20%Cr-17%Ni-4%Mo-0.1%N, and duplex stainless steels which contain more than 25%Cr-6%Ni-3%Mo-0.1%N. The high-alloy ferritic stainless steels exhibit the best corrosion resistance to seawater among these types of steels. The superiority of the ferritic stainless steels is attributable to the difference in the effect of Cr on respective anodic polarization behavior of ferritic and austenitic stainless steels. At present, the ferritic stainless steels are mainly used in the condenser tubes of power plants, and the N-bearing austenitic stainless steels mainly in the pipe work of offshore platforms. Ultra-high nitrogen containing austenitic stainless steels, high-alloy duplex stainless steels manufactured by the powder metallurgical process, and anodic and catholic chromating stainless steels have also been studied as new seawater-resistant stainless steels.