The amount of bound water in the passive film formed on AISI type 304 and 316 stainless steels under potentiostatic conditions was determined by a coulometric titration method, in which an analysis train specially designed for precise determination of very small content of water was used. From the measurements it was found that the passive films on AISI type 304 stainless steel passivated at +0.20 and +0.60V (SCE) had the bound water of 0.102 and 0.076μg/cm² respectively. This passivation-potential dependence of the amount of bound water was in agreement with that already obtained by using a tritium tracer technique. In the case of the film passivated at elevated temperatures, the amount of bound water decreased with the rise of the passivation temperature. Furthermore, it was found that the dehydration process at 120° and 350°C was markedly different between the specimens passivated at +0.20 and +0.60V; the dehydration of the film on the +0.60V passivated specimen proceeded with intermittent release of the water, while such an intermittent dehydration behavior was not observed for the +0.20V passivated one. In the case of AISI type 316 stainless steel the amount of bound water in the passive film was in the range from 0.04 to 0.06μg/cm² independent of the passivation potentials (+0.20, +0.40, and +0.60V). The dehydration of the passive films on 316 stainless steel was easily completed in a short time and the process was scarcely affected by the passivation potentials.

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In the conventional electrochemical method determining hydrogen content in iron and steel, a thin palladium layer is electrodeposited on the one side of specimen in order to prevent the passivation of steel and to promote ionization reaction of hydrogen. However, it is very difficult to obtain a uniform deposition layer of palladium and the undeposited or bare part of the surface requires the passivation current of order of 1-2μa/cm², reducing the accuracy of hydrogen measurement. Nickel deposition was found to be much advantageous and its passivation current was less than 0.1μa/cm². The suitable thickness of electrodeposited nickel was 500-1000Å. The range of electrode potential for ionizing hydrogen was found to be -0.1-0.3 volt vs. SCE in 1N NaOH solution. In this potential region, the surface of electrodeposited nickel layer is probably covered by Ni₃O₄ or Ni₂O₃ through which however hydrogen atoms can permeate.

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A number of studies have been reported to clarify the corrosion mechanism and the structure of precipitated film (rust layer) in slightly acidified solution (pH>3.0). Usually, the structure of precipitated film are apparently affected by the physical conditions of environment such as fluid velocity and the chemical composition of materials and corrodents. Many of studies have been carried out on the effect of chemical composition of materials upon the precipitated film, but there seems to be a few study on the effect of internal structures induced by plastic deformation on the corrosion behaviour in slightly acidified solution. The present work has been carried out in order to study the relationships between the internal structure of cold-drawn mild steels and the corrosion behaviour in slightly acidified and neutral solutions. Results obtained are summarized as follows: 1) Effect of fluid velocity on the corrosion rate was studied in pH 4.0 hydrochloric and nitric acid solution. It was found that the dissolution rate of iron as ion increased in proportion to Re^0.6 in the turbulent flow, but in the laminar flow the rate was constant and equal to that observed in the stagnant solution. The rate of increase of iron in the precipitated film was proportional to Re^0.067 throughout the laminar and turbulent flow region. 2) The total corrosion rate of cold-drawn mild steel was higher than that of annealed steel in slightly acidified solution. This is mainly due to an increase of the amount of magnetite in the rust layer. Although the amount of total iron increased linearly with time of corrosion, the variation of structure of the precipitated film with time in slightly acidified solution differed in chloride and nitric solutions. Some considerations were made on the corrosion mechanism based on the above mentioned facts. 3) The precipitated film was observed preferentially on the pearlite grains and grain boundaries. Preferential attack of cementite and micro-pitting in the pearlite grains were observed under the rust layer. Relationships between the increased precipitation of magnetite and the preferential dissolution (or decomposition) of cementite was discussed. 4) Studies were also made on the corrosion in the neutral tap water. At the higher fluid velocity in the turbulent flow, specimens remained bright after long duration test and no effect of plastic deformation was observed. On the other hand, with decreasing fluid velocity the corrosion rate increased. In the stagnant solution, the amount of precipitated oxide of cold-drawn mild steel was larger than those of annealed one. The structure of rust layer and the attacked surface were investigated.

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The corrosion behaviors of potential metallic materials for the liquid metal fast breeder reactor (LMFBR) and the controlled thermonuclear reactor (CTR) in liquid alkali metals have been reviewed. Emphasis is given to the corrosion behaviors above 500°C in the primary alkali metal systems. The solubilities of metals in liquid sodium and lithium, which have a great effect on the corrosion and mass transfer of metals under large temperature gradients, are shown. Analyses are given to the thermodynamic aspects of nonmetallic elements (oxygen, nitrogen, carbon and hydrogen) for metal-sodium and metal-lithium systems of interest, which are related with the types of interactions (embrittlement, compound formation, reduction in strength, and alkali metal penetration of the metals). The monitoring and controlling of nonmetallic elements at low levels in sodium and lithium are described. The recent experimental result and the model on the corrosion and mass transfer of austenitic stainless steels in flowing sodium and the recent experimental results on the corrosion of vanadium base alloys in sodium are shown and discussed. Also, the influence of nonmetallic elements on the compatibility of potential containment materials for CTR application with liquid lithium is described.

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This review discusses the nature of passivity of iron and iron-base alloys. It assesses the current state of understanding, defines the areas of agreement and of disagreement in the field, and poses the questions that must be answered to further our understanding.

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