Corrosion-resistant nickel thin films by electroless deposition in foam of electrolyte
- PDF / 556,550 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 85 Downloads / 223 Views
Research Letter
Corrosion-resistant nickel thin films by electroless deposition in foam of electrolyte Takahiro Furuhashi, and Yoshiyasu Yamada, Yamada Co. Ltd., Ryouke, Naka-ku, Hamamatsu, Shizuoka 430-0852, Japan Masato Hayashi, Shoji Ichihara, and Hiroaki Usui, Division of Applied Chemistry, Institute of Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588, Japan Address all correspondence to Hiroaki Usui at [email protected] (Received 3 September 2018; accepted 17 December 2018)
Abstract Nickel thin films were prepared by electroless plating in a foam of electrolyte generated by bubbling nitrogen into a hypophosphite-based electroless plating solution added with surfactants of sulfuric acid monododecyl ester sodium salt and ammonium pentadecafluorooctanoate (APFO). Ferroxyl test revealed that the films deposited in foam had substantially higher corrosion resistance than those deposited in liquid. Even with a film thickness of only 1.5 µm, the fraction of corroded area was as small as 0.002% when the film was deposited in the foam. The notable improvement in the corrosion resistance was made possible by adding APFO as the surfactant.
Introduction Electroless nickel plating has wide applicability in industry owing to such unique features as high uniformity in film thickness, high hardness, and superior corrosion resistance compared with the films deposited by electroplating. However, there still exist unsolved issues such as generation of hydrogen bubbles in the deposition process. The hydrogen gas, which is generated by a side reaction during the reduction of metal ions, causes such a problem as pinhole defects that deteriorate the corrosion resistance of the films. In general, corrosion of a metal surface is enhanced by microscopic imperfections in crystal structure such as grain boundary. On the other hand, the plated metal films include substantial amount of macroscopic defects, and the chemical degradation proceeds primarily through the pinholes by corroding the substrate instead of the film material itself. This is the reason why protective nickel films require thicknesses larger than 15 µm in spite of the chemical inertness of nickel itself.[1] The pinholes cause a crucial problem also in the electroplating process. Recently, several unique electroplating methods have been proposed to solve this issue by using unconventional plating media such as supercritical carbon dioxide.[2] We found that electroplating in a foam of electrolyte is effective in reducing the number of pits and pinholes.[3] It is considered that the foam can remove hydrogen bubbles efficiently from the cathode surface.[4] A small hydrogen bubble generated on the surface has higher inner pressure than that in a larger bubble consisting the foam, because the inner pressure is inversely proportional to the bubble diameter according to the Young– Laplace equation. As a consequence, the small hydrogen bubble that came in contact with the bubble in the foam
collapses promptly to merge into the foam. Th
Data Loading...
