Investigation into Local Electrochemical Behavior of Metals with 3D Printed Solution Flow-Type Micro Droplet Cell
Authors: Sakata Kei , Muhammad Bilal , Sakairi Masatoshi 
Published: December 2020

In recent years, metallic materials have shown to exhibit advanced properties, such as high strength, high corrosion resistance and flatness. Non-uniformity of metallic materials plays an significant role in these properties. In order to investigate the non-uniformity of metals, it is necessary to carry out a higher resolution analysis. Therefore, electrochemical technology in small area is required. One of the techniques is an electrochemical microdroplet cell. The electrochemical micro-cell has received attention as a measurement method to investigate local electrochemical behaviors. There are tow types of electrochemical microdroplet cells; a meniscus type and a gasket type. The classification is based on the difference in the structure between the capillary tip and sample surface.1),2) Independent of structure of the cell, the microdroplet cells have enabled us to investigate small surface areas. However, because of a concentration gradient in the solution inside the capillary, appropriate measurement and chemical reaction cannot be performed. To avoid this problem, a gasket-type electrochemical microdroplet cell with a θ-shaped glass capillary was developed.3) Solution supply and ejection could be performed using two channels. A dual capillary solution flow-type microdroplet cell (Sf-MDC) was also developed.4) This Sf-MDC has a co-axial double tube structure which has two capillaries with different diameters; the solution is supplied from the inner capillary and collected by the outer capillary. This Sf-MDC was applied to form porous-type aluminum anodic oxide locally5)-7) and to investigate SCC mechanism near fusion line.8) This Sf-MDC is very useful for local electrochemical measurement and mask-less local surface treatments. However, the structures of previous Sf-MDC are very complex and difficult to fabricate. Therefore, 3D printing was applied to fabricate Sf-MDC and local electrochemical measurements were carried out by fabricated Sf-MDC.
Sf-MDC was designed using computer-aided design software and fabricated by 3D printer. A Pt wire and an Ag / AgCl wire were inserted inside the cell as counter and reference electrodes. Fig. 1 shows the 3D printed Sf-MDC is attached to a microscope. Using optical microscope, it is possible to control measuring position precisely and carry out electrochemical measurement locally.
The surface states before and after the electrochemical measurements were observed. The immersion potential measurements and the potentio-dynamic polarization measurements were carried out using 10 mM NaCl. Both the immersion potentials and the polarization curves of aluminum alloys were different by measuring locations.
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Fig. 1 Optical images of local electrochemical measurement by Sf-MDC fabricated by 3D printer.

Figure 1