Electrodeposition of metal ions, Mz+, on foreign metal substrate, M', at potentials more positive than the reversible potential of the Mz+/M electrode is termed “underpotential deposition (UPD)”. The general feature of UPD was described, laying emphasis on the width of UPD potential window being to proportional to the difference in work function between two metals, M' and M. The effects of UPD on electrode reactions such as oxygen reduction, hydrogen evolution and metallic corrosion were reviewed and the discussion was made on the roles of UPD in the mechanism of electrode reactions. Particularly, the effect of Pb-UPD on corrosion of Ni was explained in detail with relation to the Pb-induced stress corrosion cracking (Pb-SCC) of Ni base alloys. Moreover, the structural change from UPD adsorption layer to surface alloy and the co-adsorption structure of electrolyte anions and of UPD metal atoms were exemplified and the importance of in-situ analysis of the electrode interface was pointed out to clarify the roles of UPD in reaction mechanism.
This study was carried out to clarify the electrochemical characteristics of Alloy 182 Weld and Low Alloy Steel in high temperature and high pressure water from 25°C to 288°C. The specimen was obtained from Alloy 182 overlaid weld and low alloy steel. Corrosion potential of each metals and galvanic current between the metals in 5.0×10−3 M H2SO4 and 4.5×10−3 M Na2SO4 aqueous solution were measured in an autoclave. The temperature of the autoclave was raised from 25°C to 288°C at a rate of 5°C/min. As the results of these tests, temperature range was observed in which alloy 182 has possibility to dissolve, i.e., corrosion potential of Alloy 182 was less noble than low alloy steel between 170°C and 220°C.
Strauss test, Coriou test and Huey test were conducted on a Type 316L austenitic stainless steel. Improvement in grain boundary corrosion resistance was verified after raising low Σ coincidence site lattice (CSL) grain boundary (GB) frequency by controlling grain boundary character distribution (GBCD). During crevice corrosion test under gamma-ray irradiation, initiation frequency of GB corrosion after GBCD controlled specimens decreased to 1/10 of GBCD uncontrolled counterpart along with lower depth of corrosion. Stress corrosion cracking (SCC) propagation rate of GBCD controlled specimen decreased to less than 1/2 of GBCD uncontrolled specimen in high temperature and high pressure water. Based on these results, we expect that GBCD control will improve corrosion resistance of austenitic material in a wide range of application and environment.