The atom-probe was used to examine the local compositional fluctuation and the Passivated surface of type 316 stainless steel. The analysis of the field evaporated clean surface shows the presence of compositional fluctuation in a few nanometer size region. Immersion of the clean surfaces in nitric acid results in the formation of passive film which is at most 4 monolayers thick and consists mainly of Cr-compounds. The alloying elements, Cr and Ni, are enriched in the film, while Mo is enriched at the film-metal interface. Furthermore it should be noted that variations in thickness and composition of the passive film are shown in a few nanometer size region. This may be resulted from the compositional fluctuation in the stainless steel.

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Progressive penetration for crevice corrosion of high purity 18Cr-14Ni steel under glass was measured in-situ in 3% NaCl solution at 80°C using developed moire system. Generalized time variation of penetration depth for growing picture elements, PE(II), consisted of three stages, which were stage I, transient stage and stationary growing stage, stage II, with dissolution rate V_II. Repassivating picture elements, PE(IR), passed similar stage I with the same dissolution rate V_I as PE(II) and then resulted in repassivation. V_I was always larger than V_II and did not depend on electrode potential, while V_II depended highly on it. Penetration depths attained at the end of stage I were h*₂ of 30-40μm for PE(II) and h*_RL of 15-20μm or h*_RU of 30-35μm for PE(IR). With increasing electrode potential above repassivation potential for crevice corrosion, E_R, increasing number of PE(II) and PE(IR) reached h*₂ and h*_RU, respectively, which were numerically equal to each other. This penetration depth, h*₂≅h*_RU, should be called a critical depth for growing crevice because for PE(II) to exceed it means to continue to grow and for PE(IR) not to exceed it does to repassivate. Based on the fact that density of PE(II) depended on position inside the crevice, it seemed to need conjoint action of adjacent picture elements for a certain picture element to exceed the critical depth and continue to grow.

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In order to make clear the effect of volcanic environment on the corrosion of metals, corrosion tests where heating and cooling are repeated between 40°C and 20°C in SO₂ gas atmosphere (150-200ppm) were carried out on the specimens, carbon steel (SS 41), copper, aluminium, and zinc-plated steel which were covered with volcanic ash on the surfaces. The corrosion phenomena were investigated by means of the measurement of mass loss for corrosion and electron probe microanalysis. For SS 41, aluminium, and zinc-plated steel, the corrosion is greatly accelerated by volcanic ash when it accumulate thick on the surface. The copper specimen corrodes faster in the case of no volcanic ash, while under the presence of volcanic ash the corrosion is greatly accelerated as volcanic ash layer becomes thicker. These effects of volcanic ash on the corrosion are attributed to capillary condensation and water-retaining effects of volcanic ash layer.

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The effect of various oxidation conditions on metal release of SUS 304L stainless steels in deaerated pure water at 488K was investigated. The behavior of metal release was also discussed in relation to the surface films which were formed by various oxidation treatments. The results obtained are as follows: (1) The oxidation treatment in high purity argon gas at high temperatures for short time such as 1273K-2min (120S) was effective to decrease the metal dissolution, and the oxide films primarily consisted of spinel type double oxide layer containing high concentration of Mn and Cr. (2) The oxidation treatments in non-deaerated pure water at 561K for 24-336h (86.4-1209.6ks) were furthermore effective to decrease the metal dissolution. (3) It may be concluded that the key factors controlling the metal release are thickness, structure and compactness together with compositions of surface oxide films.

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Zinc-aluminium alloys are known as a die casting alloy and a superplastic alloy. Recently, many zinc-aluminium alloys have been developed for hot dip galvanizing. In this paper, the corrosion behaviour of these alloys is discussed. It is shown how the corrosion behaviour of zinc-aluminium alloys depends on the aluminium content and microstructure of the alloy.

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