A sensor probe involving a copper reference electrode was developed for copper corrosion diagnosis（CCD）in fresh water. Electrochemical measurements are often employed for CCD in three-electrode system. In such cases, commercial glass reference electrodes are used for electrochemical measurements. Because the repeated use of commercial glass reference electrodes in fresh water with different compositions degrades the reference electrode, a maintenance-free reference electrode is necessary for fieldwork involving CCD. In this study, a copper tube was selected as the reference electrode for electrochemical measurements. Our newly developed sensor probe for CCD comprises three copper tubes as the working electrode, counter electrode, and reference electrode. Each 1.6-mm-diameter copper tube was covered with a polyvinyl chloride insulator and was arranged as parallel with the others, with 1.6 mm spacing. Because these copper tubes can be cut off easily after electrochemical measurements, the maintenance-free reference electrode can be used for each electrochemical measurement. Potentiostatic polarization and galvanostatic polarization were conducted using the sensor probe. Then the obtained values（current and potential）and pH of the test solution were applied to the three-dimensional diagram, designated as corrosion map 3D, for CCD. Results confirmed that the corrosion diagnosis in corrosion map 3D can be categorized as having no corrosion, pitting corrosion, or general dissolution. Moreover, results obtained using the sensor probe showed good agreement with results obtained using the three-electrode system involving the commercial glass reference electrode.

Many studies have investigated Ni-Sn alloy because it has good luster and excellent corrosion resistance. Electroplating methods have already reached a practical level of applicability, but electroless plating methods have not reached such a degree of utility because they present difficulties such as insufficient film thickness and low Sn content in the deposited film. Therefore, we fixed the bath temperature and stirring under the operating conditions and studied details of the plating bath composition to deposit a film with a high Sn content of 50 wt% or more using electroless plating.

Results confirmed that the Sn contents in the deposited films differed depending on the complexing agent concentration, metal ratio, bath pH, and especially the metal source. Citric acid and sodium gluconate were suitable as complexing agents for each metal source. In the plating bath using Ni（OH）₂ as the Ni metal source, high contents of Sn were co-deposited stably. Moreover, Sn^4＋ was more suitable than Sn^2＋ as the Sn metal source. Because Sn^4＋ formed stable complex ions, the plating bath was stabilized. A film with high Sn content was deposited. Therefore, films with 50 wt% or more Sn contents were obtained even when using electroless plating.