The corrosion protective property of modified iron oxide pigments was investigated by impedance measurements, corrosion weight loss tests, and IR absorption spectrum analyses. Pigments were calcined in three mixture ratios of metal oxide (MO, M=Mg, Ca, Zn) and iron oxide (α-Fe₂O₃). Namely the mole compounding ratios of MO and α-Fe₂O₃ are 3:7, 5:5, 7:3. From the impedance measurements of paint films composed of boiled linseed oil and these pigments, the paint film containing pigment of ZnO+ZnO·Fe₂O₃ indicated a high film resistance (R_f) of about 10⁷Ω·cm². In the weight loss test, the steel was inhibited in the extracted solution. So it was found that the pigment was good corrosion protective pigment. But the pigment containing too much Mg or Ca led the paint film to the deterioration. The deterioration of paint film containing pigment of MgO+MgO·Fe₂O₃ did not depend on pigment concentration, and it is suggested that the decrease of adhesion at the paint film/substrate interface is based on the excess formation of metal soaps. From the values of R_f, the pigments used in this work were superior to simply mixed powder in the same composition.

View full abstract

Electrochemical voltametric scans and slow-strain rate tests have been used to characterize the stress corrosion cracking behavior of carbon steel in diethanolamine (DEA) and monoethanolamine (MEA) solutions. Pure DEA and MEA solutions show a weak electrochemical reactivity toward carbon steel and do not promote cracking. However, solutions of these aminoalcohols saturated with CO₂ show considerable electrochemical reactivity and a strong tendency to cause stress corrosion cracking in the potential range -0.8 to -0.6V (SCE). In CO₂ saturated MEA solutions cracking was intergranular with a minor tendency for transgranular cracking only at lower potentials. In CO₂ saturated DEA solutions only transgranular cracking was observed in the whole potential range of cracking. The mechanistic significance is discussed.

View full abstract

Stress corrosion cracking of aluminum alloy 5052-H 34 in 0.82kmol·m^-3 aqueous chloride solution at 353K was investigated as functions of strain rate and pH by using slow strain rate technique (SSRT) and scanning electron microscope. In this study, argon gas was used as a standard environment, not distilled water, since thick oxide film was easily formed on the surface in distilled water and affected stress-strain curves. It was found that oxide film affected stress-strain curves in pH range of 1.0 to 12.0 at strain rate of above 3.90×10^-6s^-1 like in distilled water, and SCC appeared to occur at slower strain rates. In acidic (<pH 1.0) and alkaline (> pH 12.0) solutions, 5052 alloy showed SCC at a strain rate of below (6.51×10^-5s^-1. These results were also supported by the observation of surface appearances and fracture appearances.

View full abstract

Stress corrosion cracking susceptibility of 13Cr and 17Cr martensitic stainless steels was examined as a function of applied potential under slow strain rate test conditions in 1N-H₂SO₄ and neutral chloride solutions. The steels tempered at 550°C (sensitized) exhibit active path type stress corrosion cracking in the transition potential region betweem dissolution and passivation of Cr depleted zone in 1N-H₂SO₄ solution at room temperature. On the other hand, in 20-20, 000ppm chloride solution at 10-80°C the same steel shows active path type stress corrosion cracking independent of applied potential. Stress corrosion cracking occurs only in the environment in which the potential of the bottom of the localized corrosion attack is steadily kept in the above transition potential region, while in a mild environment the steel is repassivated and in an aggressive environment it shows pitting and crevice corrosion, thus being unable to keep the potential in the above cracking region. The steels tempered at the temperature other than sensitizing one do not show active path type stress corrosion cracking at the entire potential region tested (-0.6-+0.4V vs. SCE). Hydrogen embrittlement occurs at the cathodic potential and stress corrosion cracking susceptibility in neutral chloride solutions increases with increasing temperature and chloride concentration. Consequently the localized corrosion and stress corrosion cracking susceptible regions are plotted in the temperature-chloride concentration diagram.

View full abstract

Chemical plant equipments are used in much corrosive environment and have a close contact with chemical process. Even if the corrosive environment condition is severe to the material, they can be used by improving the structure. The fundamental concepts are as follows. 1) Reduction of load. 2) Simplification of structure. 3) Suitable arrangement. Many of these practical ideas are made from the field experience.

View full abstract

The ion beam mixing and dynamic mixing methods produce films with several advantages; (1) a good adhesion between the coating films and the substrates (2) shorter preparation time than for the case of ion implantation (3) the formation of thick coating filmes (4) easy control of the film composition at low temperature (5) the preferred orientation of thin films.

View full abstract