We examined the diffusion behavior of hydrogen dissolved in palladium film electroplated on copper. The diffusion coefficient of hydrogen DH in the palladium film was determined to be 2.6×10-11m2/s at 298K by using the electrochemical stripping method. This value of DH is smaller than the value of DH in the bulk of palladium reported in the literature. When the palladium electroplated specimens were heat-treated at temperatures higher than 873K, DH was nearly equal to that for the bulk of palladium. These results can be explained on the basis of the trapping effect by the lattice defects such as dislocations and grain boundaries.
In this study, Ni2+ removal from electroless nickel plating wastewater (A. co., Ltd.) by reduction crystallization was investigated, to make clear the effect of seeds specific surface area on the Ni2+ removal characteristics. Although the main reaction in this research is the same as the one in electroless nickel plating, the authors have proposed reduction crystallization in which wastewater from electroless nickel plating contacts with suspended nickel powder, to remove and recover Ni2+. The results could be obtained on the relationship between the pH change profile and recovery efficiency in the reaction process, in which nickel powders having various specific surface area were used as seeds. Experimental results were discussed, considering surface conditions of grown nickel and the behavior of produced fines. With a constant 10% NaOH solution feed rate, the pH profile changed in the process of Ni2+ reduction, by changing the specific surface area of seeds, which means that Ni2+ removal efficiency was affected by the specific surface area of seeds. When constant pH7 was maintained, higher removal efficiency (0.99; Ni2+ concentration in the treated water 2.5×10-2g·dm-3) could be obtained, although the specific surface area of Ni seed powder varied. Specific surface of seeds, based on the roughness of seed crystal, was suggested to be an effective factor on the Ni metal coating behavior on the seed surface and also the phenomena of fines production in the process of Ni deposition.
We have studied electrochemical pulse etching of NiTi shape memory alloy (SMA) sheet for a micromachining application. The effects of pattern width, etching depth and pulse duty ratio on etch rate and side etching have been studied in comparison with DC etching. Etch factor (=etching depth/side etching width) tended to be lower at narrow and deep etched grooves in the case of the DC etching, however, the factor was not influenced by the pattern width in the case of the pulse etching. The etch factor of the pulse etching increased with increasing the etched depth, contrary to the DC etching, because reaction products could be diffused out of the etched groove while the pulse voltage was turned off. The pulse etching is more suitable for narrow and deep micromachining than the DC etching. When the pulse duty ratio was below 50%, the etching rate was proportional to the duty ratio, therefore, the etch rate could be controlled by the duty ratio. When the duty ratio was over 50%, the etch rate did not increase any more, because the diffusion of the reaction products was not sufficient and the electrolytic current decayed during the ON-time of the pulse. In the decayed current region, mirror-like flat etched surface was obtained because of the electrolytic polishing effect. Through etching could be carried out successfully by using a dummy Ni layer on the backside of the sheet; therefore, micro actuators could be fabricated from an SMA sheet by using the electrochemical pulse etching.
Rotational bending fatigue tests were carried out on SAE 1547 steel modified by a fine particle bombarding, with special attention focused on the effect of the processing condition on the fatigue properties. The air pressure strongly affects the stability of the compressive residual stress and the fatigue strength of the specimen treated by high air pressure is slightly higher than that of the low air pressure specimens. The specimen treated with small particles show significantly higher fatigue strength compared to those treated by large particles. This is because the compressive residual stress remained after stress cycling at the surface of the specimens treated with small particles. In addition, the surface hollows formed by impingement of the particles were smaller than those treated by large particles.