The electropolishing behavior of Nb in a 30 wt％ sulfuric acid solution was investigated by controlling the potential of Nb using a three-electrode cell. The Electropolishing was performed with various combinations of cathodic pulse potential （E_c） and anodic one （E_a）. Almost completely mirrored surface was obtained after 120 minutes under the condition of E_c＝－3.0 V and E_a＝＋10 V with both pulse periods of 2.0 ms. The mirrored surface was also obtained within 60 minutes by shortening anodic pulse time （t_a） to 1.0 ms at E_c＝－3.0 V and E_a＝＋10 V. This is due to the fact that anodic current decays so quickly at E_a＝＋10 V that anodic pulse time can be shortened to 0.25 ms with no change in anodic charge in one pulse. Thus the total number of cycles in a given time can be increased by shortening t_a, which leads to faster electropolising rate: 0.92μm min^－1 at t_a＝2.0 ms and 1.52μm min^－1 at t_a＝0.25 ms.

The electrochemical impedance spectroscopy （EIS） was examined as the method for analyzing the film formation of an amine cured epoxy paint applied in a wet surface. The impedance characteristics of the models with the epoxy resin and amine curing agent which different affinity for water were analyzed. It was found that the hydrophobic paint film was less affected by the wet environment than the hydrophilic paint film, and the resistance develops in a short time. In addition, from the results of adhesive strength, it was estimated that the water film at the substrate/coating film interface was eliminated in the very early stage. The EIS method was found to be useful for analyzing the coating film formation process in a wet surface.

In order to verify the applicability of glass-fiber reinforced plastics with an unsaturated polyester matrix in manhole environments, degradation characteristics in a weak alkaline aqueous solution were evaluated based on solution immersion test. The decrease in flexural strength after immersion test at 313 K fitted well to the logarithmic approximation. Based on Arrhenius equation, we estimated the deterioration behavior under 288 K conditions, which corresponded to a manhole environment. However, since a problem in applying the logarithmic approximation became clear, a more appropriate estimation method is required.

The new evaluation test method, CCS （Continuous Current Step） method, for crevice corrosion propagation of stainless steels was proposed. This CCS method is based on the crevice corrosion propagation mechanism of stainless steels in natural seawater. The steady state potential （E_OUT） is measured galvanostatically on CCS test. The data sets of E_OUT－i were obtained for various stainless steels. It was considered that this E_OUT reflected the state of active corrosion in anolyte of inside crevice under the constant current density.

The E_OUT－i data was analyzed by the exponential decay curve. When the current density i was under 1× 10^－5 A cm^－2（ ≈0.1 mm/y）, the obtained potential E_OUT was considered as the repassivation potential called E_R（CCS） in this test. The crevice corrosion propagation was regarded as stop at less noble potential of E_R（CCS）.

The effects of Cr, Ni, Mo and Cu on the E_OUT－i relations were tested in artificial seawater. E_R（CCS） related to the metal composition and was described as one equation by using the new index, CCR（Crevice Corrosion Propagation Resistance Index）.

CCR＝[Cr]＋0.95[Ni]＋0.74[Mo]＋2.03[Cu]

E_R（CCS）＝－317＋13.75 CCR（mV vs.SHE）

This new index, CCR, succeeded in unification of the crevice corrosion propagation （E_R（CCS）） for various stainless steels.

The corrosion resistance of the δ₁ phase （Zn-Fe compound） coated on galvannealed steel sheets （GA） and the Γ phase （Zn-Fe compound）, α solid solution （Fe-Zn solid solution）, which were formed by heating GA, was investigated using combined cyclic corrosion test, polarization measurements and structure analyses. The results suggest that the α solid solution, Γ and δ₁ phases have relatively good corrosion resistance in order, and these coating phases have sacrificial corrosion protection against base steel. It was also considered that the corrosion prevention of α solid solution will decrease when the exposed area of the base steel becomes large.