拡散支配条件下からの亜鉛めっきにおける陰極電位の復極現象とめっき亜鉛の {1120} 面優先配向についての研究

抄録

The effects of brighteners on zinc electroplating from alkaline zincate baths have been investigated by electrochemical methods, scanning electron microscopy and X-ray diffraction. Bright zinc electrodeposits obtained under diffusion-controlled zinc electroplating exhibited the preferred {1120} orientation parallel to the surface of the substrate. These results were interpreted in the light of deformation twinning on the basal plane, which caused the basal plane platelets to be aligned perpendicular to the substrate. Brightener was adsorbed on the electrode preferentially by shifting the impressed potential in the less noble direction. This resulted in strongly preferred {1120} oriented deposits at higher overpotential, and the range of bright electroplating extended even to electrolysis under diffusion-controlled zinc electroplating. It was also found that the overpotential for hydrogen evolution reaction on the zinc deposit with preferred {1120} orientation was smaller than that of other crystal facets of deposits. The strongly preferred {1120} oriented deposition caused the cathode potential to reduce the extent of polarization by accelerating the hydrogen evolution reaction. The Tafel slope of hydrogen evolution during zinc electroplating changed from 40 to 50mV/decade at lower overpotential to 130 to 140mV/decade at higher overpotential.