Pengyuan Zhang,Zhengyi Xu,Bo Zhang,Bing Lei,Zhiyuan Feng,Guozhe Meng,Yanqiu Wang,Junyi Wang,Fuhui Wang
In our previous work, we found that hydrogen permeation can be noticeably reduced during Ni–Cu electroplating by the addition of Ce salt to the plating solution. The mechanism of hydrogen permeation inhibition via Ce salt was further studied in the present work. Through the Iver–Pickering–Zamenzadeh (IPZ) model fitting of the kinetic of hydrogen evolution reaction , we found that the trace Ce salt that precipitated during electroplating could improve Tafel reaction kinetic parameters and reduce the strength of the Ni–H and Cu–H bonds due to its abundant d/f electrons and enough d/f orbitals. Meanwhile, Ce can provide electrons for the Heyrovsky reaction. These effects promoted surface electron migration and thus led to the desorption of adsorbed hydrogen atoms (H ads ) and the decreased diffusion of H ads into the Ni–Cu coatings. The accuracy of the IPZ model fitting results was verified by hydrogen evolution rate experiments during the electroplating process. Hence, Ce salt can effectively inhibit hydrogen permeation and reduce the dehydrogenation annealing time, thereby showing great potential for energy saving and emission reduction in the electroplating industry.
To prepare an environmentally friendly and corrosion-resistant chemical conversion film on a steel substrate, cerium salt, titanium salt, and the organic additives 2-mercaptobenzimidazole (2-MBI) and polyethylene glycol (PEG) were introduced into oxalic acid (OA) to form an oxalate composite chemical conversion film. The composite chemical conversion film is composed of large-sized FeC 2 O 4 ·2H 2 O rectangular crystal grains and long aspect ratio FeC 2 O 4 ·2H 2 O nanorods interspersed among the grains. A large number of nanoscales FeC 2 O 4 ·2H 2 O grains help to disperse the corrosion current, preventing localized corrosion, and the fitted polarization resistance reaches 7203.7ohm cm 2 . 2-MBI complexes with metal ions, participating in the formation of the double electric layer. Titanium salt participates in film formation in the form of titanium oxide, while PEG and OA enhance the bonding strength and density of the film-forming materials in the layer by coating titanium oxide, acting as dispersants and wetting agents. As Fe 2+ generated from corrosion at the interface between the steel substrate and the working liquid combines with oxalic acid to form insoluble ferrous oxalate, the carbon chain migrates outward to the surface of the conversion film. The stronger bond energies of C = O, C O-Fe, and Fe-O facilitate the inward movement of self-assembly behaviour, which significantly increases the carbon content on the film surface and reducing the surface energy in contact with air. After soaking in a 5 wt.% sodium chloride solution, sodium-containing compounds formed on the surface of the conversion film, hindering chloride corrosion. The large number of nanoscale ultrafine dihydrate ferrous oxalate grains in the film effectively suppresses localized corrosion. During the corrosion process, 2-MBI moves to the film surface through complexes formed with titanium oxide via Ti-N bonds, thereby obstructing the intrusion of corrosion liquid ions and enhancing the corrosion resistance of the film layer, endowing it with a certain degree of self-healing capability. Cerium salt participates in film formation as a non-stoichiometric compound with an ambiguous valence state, and the transformation of the cerium element's valence state is another reason for the self-healing property of the conversion film.
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