The electrodeposition of Zn-Cr alloys from sulfate baths was conducted to investigate the codeposition mechanism of Cr with Zn. Results are as follows:
(1) Cr was codeposited with Zn at high current densities in both polyethylene glycol (PEG)-free and PEG-containing baths. However, PEG made it possible to reduce Cr³⁺ to metallic state and Cr existed in the form of Cr³⁺ hydroxide in the deposits obtained in PEG-free bath.
(2) Partial polarization curves of Zn shifted when PEG was added to the baths.
(3) The pH in the cathode layer was found to rise from bulk pH 2.0 to about 4. Zn and Cr hydroxides seemed to form simultaneously in the cathode layer.
(4) It was estimated that alloys were electrodeposited from the composite Zn and Cr oxides formed due to the pH rise in the cathode layer and that the PEG acted as a polarizer to shift the cathode potential toward the reduction potential of Cr.

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The electrodeposition of Zn-Cr alloys from sulfate solutions was conducted using rectangular pulsed current. Changes in the current efficiency and the Cr content in the deposits with varying values for the average current density showed similar results as seen in direct current plating. Cr in the deposits existed in both its metallic and trivalent states in the pulsed current plating, while no metallic Cr was observed in the deposits in direct current plating. Results thus indicated that the use of pulsed current increased the limiting current of Zn to attain the deposition potential of Cr. The superimposition of direct current on pulsed current allowed a significant increase in the content of metallic Cr in the deposits, suggesting that the superimposition of direct current prevented the reoxidation of Cr in the deposits during the off-time period of pulse plating. Varying the plating conditions resulted in the cathode being polarized to an extremely negative region where mass transport became predominant. At that point, the deposits contained a considerable amount of trivalent Cr, which was the product of hydrolysis resulting from the accelerated decomposition of water.

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Zinc coating by electrodeposition has been utilized in the production of corrosion-resistant steel sheets. In addition, binary Zn alloys such as Zn-iron-group metal, Zn-Mn and Zn-Cr electrodeposited from the sulfate type baths provide excellent corrosion-resistant coatings for the steel sheets used especially as automotive body panels. In the sulfate type baths, single Zn and Zn alloys can be deposited at higher current densities than the critical one. In this paper, based on that hydrogen does not evolve at its equilibrium potential, the electrochemical meaning of the critical current density is discussed. The anomalous deposition behavior of Zn-iron group metal alloys, in which electrochemically less noble Zn is deposited preferentially, is explained according to the hydroxide suppression mechanism. Further, the characteristic deposition behavior of Zn-Mn and Zn-Cr alloys is also referred briefly.

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Zn-Cr electrodeposition behavior was studied in the sulfate solutions containing acyclic polymer additives such as gelatin and polyethylene glycol (PEG) at 2kA/m². The electroreduction of Cr ions into metal was promoted by the addition of gelatin as well as PEG to the solution, and the deposits contained Cr in both trivalent and metallic states. The ratio of metallic Cr to total Cr changed depending on the molecular weight and the concentration of gelatin and PEG added to the electrolytic solution. Further, the cathode potential shifted to the less noble direction with increasing molecular weight or concentration of these additives. The ratio of metallic Cr in deposits showed a close relation with the cathode potential, and reached a maximum value at approximately −1.2V (vs. NHE). At potentials less noble than −1.2V, the deposits contained a considerable amount of trivalent Cr, which was the product of hydrolysis resulting from the accelerated hydrogen evolution by both the decomposition of water and the decrease in overpotential for hydrogen due to increase in Cr content in deposits.

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国際人間工学連合の改訂コア・コンピテンシーや，本学会から提言された持続可能な人間工学目標などにおいて，ステークホルダ協働を新たな学術研究課題として認識することが提言されている．本リサーチ・イシューでは，ステークホルダのウェルビーイングに配慮しながら人間工学知見を活用してチーム・ビルディングを行うための要素を「束ねる科学を実践するための7つの人間工学Tips」として紹介し研究課題として提言する．人間工学専門家には人々の暮らしが良くなるような選択をナッジするアーキテクチャであり，ステークホルダの相互作用をデザインし，社会課題を解決するアントレプレナーとしての役割が求められている．

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