The inhibiting function of propargyl alcohol in nickel electrodeposition was studied by observing the cathodic polarization curves on nickel RDE in nickel sulfamate baths. The behavior of propargyl alcohol inhibiting the electrodeposition was analyzed based on the diffusion-adsorption-reduction model. The variations of the diffusion rate, the interfacial concentration and the coverage of propargyl alcohol with the electrode potential were simulated based on the reduction rate estimated from the model and the experimental results. The results of the simulation explained the experimental results well. Such a simulation gives useful information on the investigation of the additive behavior and the current distribution in the electrodeposition onto a micropatterned substrate.
The shape control function of propargyl alcohol (PA) in the electrodeposition of nickel onto a micropatterned substrate was simulated under the condition that the rate of PA reduction was equal to the rate of PA diffusion at every point of the cathode surface, the concept of which was derived from the results obtained in the previous paper. The function of PA was related to higher diffusion rate and higher interfacial concentration, and consequently higher surface coverage of PA at the edge of the cathode surface, as compared with those at the center of the surface. The simulation showed that the function of PA was active in the initial stage of electrodeposition; it was more effective at less negative potentials, for example at -0.80V vs. Ag/AgCl, and less effective at more negative potentials, for example at -0.85V. The simulation also showed, however, that the function became ineffective as the deposit grew, showing that the diffusion rate and the interfacial concentration tended to be uniform on the grown surface. These results of the simulation explained the experimental results well, and showed this simulation method to be useful for the investigation of the behavior of additives.
The molten carbonate fuel cell (MCFC) which possesses a high conversion efficiency, is expected to be a future energy conversion device. However, the MCFC operates at a high temperature, and therefore, the battery materials corrode. This has been a serious problem in realizing the high-performance of the MCFC. In this study, the corrosion behavior of Fe metal and Fe-Ni alloy, which are used as separators, in 46mol% Li2CO3-54mol% Na2CO3 (46/54melt), 52mol% Li2CO3-48mol% Na2CO3 (52/48melt), and 58mol% Li2CO3-42mol% Na2CO3 (58/42melt) systems have been focused on. From the results of the SEM observation and XRD measurement, the corrosion of Fe metal was restrained effectively in the 52/48melt. LiFeO2, which made the substrate surface stronger against corrosion, was formed densely on the surface of substrates immersed in the 52/48melt. On the other hand, when the substrates were immersed in the other melts, LiFeO2 did not exist on the surface. LiFe5O8, which could not make the substrate surface stronger against corrosion, existed on the surface and the layer was formed coarsely. Moreover, the Fe-Ni alloy substrate restrained the spreading of corrosion compared to the Fe metal substrate. GD-OES depth profiles of Fe-Ni alloy indicated that the Ni metal layer, which is formed in the corrosion surface layer, suppressed the spreading of corrosion. The corrosion of Fe-Ni was also restrained effectively in the 52/48melt. It is considered that the double layer of LiFeO2 and Ni metal effectively inhibited the spreading of corrosion on Fe-Ni alloy.
This study reports on conditions of D. C. plasma nitriding with nitrogen and hydrogen mixed gas in order to get a smooth and clean surface without compound layers after nitriding steel. Tool steels of SKH 51, SKD 11 and SKD 61 were D. C. plasma nitrified at 773K for 3600sec in a nitrogen and hydrogen mixed gas atmosphere of 532Pa. The composition of nitrogen in the nitriding gas was changed from 10 to 90vol%. The steels were nitrided and hardened by a nitrogen diffusion layer both with and without compound layers in the steels. The surfaces of the plasma nitrified steels kept metallic brightness and smoothness like a mirror without compound layers when they were nitrided with less then 20vol% nitrogen gas. In 30 to 90vol% nitrogen gas, the tool steels were nitrided with compound layer and their surfaces lost brightness and smoothness because they became rough and changed to a gray color. SEM micrographs showed some differences between the shapes of the surfaces of the tool steels after the plasma nitriding. The surface roughnesses of plasma nitrided tool steels were unrelated to the thickness of compound layers. The tool steels were plasma bright nitrided with less then 20vol% nitrogen gas. In this study of the tool steels, SKH 51 was the most suitable steel for plasma bright nitriding.
The time-variation of hydrogen gas quantity evolved during zinc electroplating from an alkaline zincate bath containing additives was evaluated using an electronic balance, since the hydrogen gas caused buoyancy to the working electrode arranged in the parallel to the solution surface. The ease of hydrogen evolution on metal electrodes in alkaline zincate bath was order of nickel≥SUS304> iron>copper, which was also the decreasing order of hydrogen-overpotential of these electrodes. At the beginning of electroplating, there was remarkable hydrogen evolution and retardation of zinc deposition on the iron electrode. On the other hand, zinc deposition promptly started on the copper electrode, for which hydrogenoverpotential was greater than that of the iron electrode, which resulted in the suppression of hydrogen evolution.