My primary interests are in the fields of corrosion and micro-electrochemistry. I have focused on passivation, localized corrosion, and surface finishing of metals and semiconductors for development of functional materials. Main works currency undertaken are the followings.
Visualization of distribution in electrochemical reactivity on electrode surface and in-situ investigation of local corrosion on passive metals using scanning electrochemical microscopy (SECM)
SECM was invented by Prof. Allen J. Bard and his coworkers several years ago. It is capable of characterizing and modifying solid/liquid or liquid/liquid interface at mezzo-scopic resolution. A micro-electrode, diameter of which is less than some 10 um, held precisely in three dimensions and immersed in electrolyte containing redox species as well as specimen, counter, and reference electrodes plays a 'probe' in SECM. The current passing through the probe electrode reflects to interelectrode-distance and electrochemical activity of specimen surface, due to deformation of hemispherical diffusion layer on the probe electrode (Fig. 1).
Figure 1. Probe current depends on electric properties of specimen surface and inter-electrode distance.
As the probe scans to parallel for the specimen surface, therefore, a image shown electrochemical active sites of the specimen can obtain from probe currents (Fig. 2).
Figure 2. Line scan of SECM probe reveals electric property distribution of specimen surface.
- Application -
Figure 3. Probe current image for Fe(II) dissolution from FeAlCr alloy in sulfuric acid. Reactivity depends on metallugical structure of the specimen; {110} < {111} < {100} < grain boundary < triple point.
Mechano-electrochemistry of passive metal surface using micro-indentation technique
Passive film is a thin protective product on metal or alloy. It has a self-healing ability and plays an important rule of corrosion protection in corrosive media. When it is ruptured (depassivation), the substrate metal or alloy is sustainable for a long time if the film repairs immediately (repassivation). Micro-indentation technique invented is possible to depassivate the passive surface mechanically by loading/unloading micro-indenter in solution and to monitor the response of surface-transformation and electrochemistry including current and electrode potential. This technique is effective for well understanding the mechanism of depassivation-repassivation as well as its kinetics (Fig. 4).
Figure 4. Current transients from passivated surface during the downward and upward drives of micro-indenter.
Hydrodynamic micro-electrochemistry using flowing electrolyte-type scanning droplet cell
Scanning droplet cell (SDC), in which the electrolyte droplet contacted to the specimen surface with a tip of the capillary is employed as a working electrode with a micrometer size, is used to investigate the microelectrochemistry on the materials surface. However it is relatively difficult for the conventional SDC to avoid electrolyte contamination or easy scanning with a stabilized droplet when SDC is used for electrodeposition or electrodissolution of metals. A flowing electrolyte-type SDC developed by our labo. overcomes these difficulties and it is used as a new microelectrochemical method (Fig. 5).
Figure 5. Half cross-sectional distributions of velocity and concentration in flowing-electrolyte micro droplet cell.
Last Updated: Sep. 18, 2008
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