An example of evaluating such important parameters in cathodic protection （CP） as protection potential, protection current density and time variation in cathodic polarization characteristic, was elucidated for carbon steels in seawater as a typical case of diffusion-control of dissolved oxygen. Following the analyses of cathodic polarization characteristic with time, behavior of the galvanic CP using Al-alloy anode was simulated by using the proper ties of potentiostatic CP.
The examples for the measurement using electrochemical technique in seawater environment are described in this article, especially in the natural seawater which contains the microorganisms. The noticeable feature of the electrochemical behavior of stainless steels in the natural seawater is the ennoblement of open circuit potential （Ecorr）, and this ennoblement can be considered as the fundamentals of Microbiologically Influenced Corrosion （MIC） of stainless steels in natural seawater.
In order to clarify the relationship between the anode buried depth and the interference effect in a cathodic protection of impressed current system, evaluation by field tests and the finite element analysis were carried out. Evaluation parameters of the interference effect were the ground surface potential distribution formed by an anode and a cathode, and the internal current in a simulated underground metallic utility. Changes of these parameters were measured and observed by change of the buried depth of the anode. As a result, when protection current was small and the distance between the underground metallic utility and the cathode was 1 m, it showed that interference effect did not depend on anode buried depth.
In this study, the influence of chemical factors of anticorrosion paint blended with blast furnace slag mixed cement on rust prevention effect was evaluated electrochemically. The blast furnace slag mixed cement provides an alkali atmosphere in the rust preventive layer and protects steel from invasion of corrosive agents. The rust preventive effect is emphasized when used in combination with nitrite. As a condition for nitrite to exhibit rust prevention effect, strong alkali and nitrite / chloride concentration ratio of ［NO2－］/［Cl－］≧1 are necessary. Sulfate ions required smaller amount of nitrite ions than chloride ions.
The rusting of stainless steel in an atmospheric environment is mainly caused by dew droplets. However, the dew behaviors such as dew forming and drying that lead to rusting have not been fully clarified yet. In this study, the dew behaviors were precisely analyzed by the in-situ microscopic observation under the atmospheric condition simulating real environment.
The dew forming process progresses with 2 phenomena: the growth of the single droplet and the coalescence with another one. The mass of the sea salt in a single droplet increases by these phenomena.
The dew drying process is divided into three stages: the pinning stage when the contact angle of the droplet decreases, the de-pinning stage when the contact area of the droplet decreases, and the self-pinning stage when the contact angle decreases furthermore. At the self-pinning stage, the salt starts to precipitate and the rust forms under and beside the precipitation.
It is considered that those behaviors of dew forming and drying cause the formation of the rusting pattern on the stainless steel; a number of small rusted points are distributed uniformly.
Inhibition mechanisms of many corrosion inhibitors in deaerated acid and oxygenated neutral solutions have been discussed on the basis of the hard and soft acids and bases principle （HSAB principle）. However, inhibition effects of precipitation inhibitors such as propargyl alcohol CH≡CCH2OH, bismuth （III） ion, Bi3＋ and benzylthiocyanate, C6H5CH2SCN, which are effective for corrosion of metals in the acid solutions have not been described. In this paper, the inhibition mechanisms of these precipitation inhibitors in aqueous acid solutions are discussed based on the HSAB principle.