Znめっき皮膜およびZn-Fe合金めっき皮膜上の初期酸化皮膜解析

抄録

Initial oxide films formed on electrodeposited zinc (EG) and zinc-iron alloy (Zn-7 mass% Fe) coatings and zinc-iron alloy coating produced by thermal alloying of zinc electroplated steel (EGA) were analyzed using AES, XPS and TEM in order to elucidate electrochemical behavior of the zinc and zinc-iron alloy coatings. The outmost layer of oxide film for EG and EGA was composed of Zn(OH)₂ and adsorbed H₂O, and that for Zn-7 mass% Fe of Zn(OH)₂, a small amount of Fe and adsorbed H₂O. The inner layer of oxide film was composed of the following; predominantly ZnO for EG, predominantly amorphous Zn-(OH)₂ and a small amount of Fe for Zn-7 mass% Fe, and predominantly ZnO and a small amount of Fe for EGA. The chemical state of Fe in the film could not be determined, but Fe is presumably oxidized. The suppression of oxygen reduction reaction on Zn-7 mass% Fe coating was considered to result from barrier effect against electron transfer in insulating Zn(OH)₂ uniformly formed on the coating. The suppression action does not occur on EG and EGA coatings because of the formation of n-type semiconductive ZnO on the coatings.