In this paper, Kelvin method, which can be utilized to measure a contact potential difference between two dissimilar metals, is introduced. A basic principle of Kelvin method for the measurements of the contact potential differences is described. Some measured results in some corrosion systems are also explained.
Corrosion behavior under thin water film like atmospheric corrosion is different from underwater environment. Conventional electrochemical techniques can not be applied to such corrosion in a non-submerged environment, and galvanic couples have been applied conventionally. These are commonly referenced as ACM. The authors have tried to evaluate the corrosion of each environment mainly by applying the ACM type corrosion sensors consisting of Fe/Ag couples, exposing them to various environment. In this paper, the electrochemical properties of the ACM sensor were discussed.
Electrochemical quartz crystal microbalance （EQCM） is a method to determine a mass change related to electrode reactions by measuring a change in the resonance frequency of the quartz. Because the EQCM can detect a nano-scale mass change, it is a powerful tool for analysis of electrode reactions. This article provides an introduction of the EQCM principle, applications of the EQCM to corrosion studies, and problems for measurements.
In absorption refrigeration systems, molybdate is used as a key inhibitor against corrosion of steel, although it is liable to precipitate because of its limited solubility in a concentrated LiBr solution. In this research, the use of sulfite is proposed as a precipitation inhibitor for molybdate and its effect on the passivation of iron is examined. The effect of the stronger passivator of nitrate on the actions of sulfite is also investigated. The results show that sulfite decreases the amount of corrosion of iron and promotes the formation of the oxide layer （MoO2, Fe3O4） on the surface of iron irrespective of presence of nitrate. Thus, sulfite is concluded as an effective additive in an absorption refrigerator for better control of molybdate concentration and corrosion of iron.
C-ring stress corrosion tests under three conditions were carried out to investigate the effect of humidity and oxygen concentration on stress corrosion cracking of phosphorous deoxidized copper tubes. Three conditions were high humidity, low humidity and low oxygen conditions. The relative humidity and oxygen concentration were 100％ and about 20％ respectively in the high humidity condition. The air in the container with desiccant agent stored at a relative humidity of 90 to 95％ in the low humidity condition. In the low oxygen condition, the air in the container was replaced by the nitrogen gas and kept the concentration of oxygen less than 5％ during the exposure test. Although stress corrosion cracks occurred in the specimens exposed under both high humidity and low oxygen conditions, the time to occurrence of SCC under the low oxygen condition was longer than that under the high humidity condition. No SCC and intergranular corrosion developed in the specimen exposed under the low humidity condition for one week. It was found that lowering the humidity has an inhibitive effect on the SCC of the phosphorous deoxidized copper tube.
Corrosion rate and diffusible hydrogen content of high tensile steel under constant load testing （CLT） in pH2 corrosive solution were investigated using electrochemical impedance spectroscopy （EIS） and thermal desorption spectroscopy （TDS）. Rp－1 which is an index of corrosion rate increased as stress increased, which was correlated with the result of corrosion weight loss. This considered to be due to an increase in active nascent surfaces with increasing stress. Diffusible hydrogen content increased with stress, in particular by plastic deformation. The latter was more affected by the effect of corrosion rate and diffusible hydrogen content on stress. In other words, we have concluded that diffusible hydrogen content which related to hydrogen embrittlement was more affected by defects in steels by deformation than hydrogen entry from surface corrosion reaction in corrosion environment.
An example of Al corrosion in organic solvent is shown here. Severe Al corrosion occurred in a short time in Polypropylene Glycol Monobutyl Ether （PGME） including about 2％ of N-Phenyl-1-Naphtylamine at a temperature of 110℃. An investigation showed that the corrosive medium of Al was PGME itself, the principal component of the solvent. Al is replaced with H of OH group, a component of PGME, to form an organic Al compound, dissolving in PGME, while H separated from PGME changed into hydrogen gas. Here we show the corrosion status, the procedure and results of the investigation, and the results of the corrosion reproduction test.