Graduate School of Engineering
Department of Materials Science

Materials Electrochemistry (Prof. Muto, Asst. Prof. Nishimoto)

Summary of the Research

The goal of our research is to provide a molecular-level understanding of electrochemical reactions on metal surfaces and to utilize the knowledge to prevent corrosion and to modify surface properties of materials. Corrosion is irreversible interfacial reactions of materials and their environments. Unfortunately, almost all environments, such as seawater, soil and humidified air, can cause corrosion of metals. Corrosion prevention is important due to its impact on public safety, environmental protection, and cost-effective operations of equipment. Corrosion processes are complex and electrochemical in nature. We develop experimental techniques and devices for micro/nano-electrochemistry, fluorescence chemical imaging, and real-time in situ observation of corrosion and electrochemical processes. Topics include: 1) mechanism and prevention of localized corrosion of metals, 2) environmentally-friendly coatings and inhibitors, 3) hydrogen embrittlement of steels, 4) performance and durability of fuel cell catalysts, and 5) application of scanning probe microscopy to electrochemistry.

Fig. 1

Research Highlight

Micro-electrochemical approach

We have developed a micro-electrochemical system for in situ high-resolution optical microscopy [1]. The real-time observations of pit initiation at MnS inclusion in type 304 stainless steel in NaCl solutions were performed, and the pitting of stainless steels was initiated at MnS/steel boundaries [2, 3]. In our laboratory, the micro-scale polarization technique was also applied for investigating localized corrosion behavior of carbon steels, aluminum alloys, 55mass%Al-Zn-Mg coated steels, and so on [4-7].

Fig. 2

Chemical imaging of solution/metal interfaces

A sensing plate for the simultaneous measurements of pH and Cl− concentration was fabricated. Terbium–dipicolinic acid complex and quinine sulfate were used to measure the pH and Cl− concentration, respectively. The pH and Cl− distributions inside the crevice of stainless steel were visualized [8, 9]. In addition, electrochromic devices of WO3 were developed for hydrogen detection in metals [10].

Fig. 2
References

[1] Aya Chiba, Izumi Muto, Yu Sugawara, and Nobuyoshi Hara, “A Microelectrochemical System for In Situ High-Resolution Optical Microscopy: Morphological Characteristics of Pitting at MnS Inclusion in Stainless Steel”, Journal of The Electrochemical Society, 159 (2012), C341-C350.

[2] Aya Chiba, Izumi Muto, Yu Sugawara, and Nobuyoshi Hara, “Pit Initiation Mechanism at MnS Inclusions in Stainless Steel: Synergistic Effect of Elemental Sulfur and Chloride Ions”, Journal of The Electrochemical Society, 160 (2013), C511-C520.

[3] Masashi Nishimoto, Izumi Muto, Yu Sugawara, and Nobuyoshi Hara, “Micro-Electrochemical Properties of CeS Inclusions in Stainless Steel and Inhibiting Effects of Ce3+ Ions on Pitting”, Journal of The Electrochemical Society, 164 (2017), C901-C910.

[4] Mariko Kadowaki, Izumi Muto, Yu Sugawara, Takashi Doi, Kaori Kawano, and Nobuyoshi Hara, “Improving Pitting Corrosion Resistance at Inclusions and Ductility of a Martensitic Medium-Carbon Steel: Effectiveness of Short-Time Tempering”, Journal of The Electrochemical Society, 165 (2018), C711-C721.

[5] Hiroshi Kakinuma, Izumi Muto, Yoshiyuki Oya, Yoshihiko Kyo, Yu Sugawara, and Nobuyoshi Hara, “Mechanism for the Morphological Change from Trenching to Pitting around Intermetallic Particles in AA1050 Aluminum”, Journal of The Electrochemical Society, 166 (2019), C19-C32.

[6] Shimpei Tokuda, Izumi Muto, Yu Sugawara, Michiyasu Takahashi, Masamitsu Matsumoto, Nobuyoshi Hara, “Micro-electrochemical investigation on the role of Mg in sacrificial corrosion protection of 55mass%Al-Zn-Mg coated steel”, Corrosion Science, 129 (2017), 126-135.

[7] Yu Sugawara, Waka Inoue, Izumi Muto, and Nobuyoshi Hara, “Methodology for Fabrication of Highly Pitting Corrosion-Resistant Type 304 Stainless Steel by Plasma Carburizing and Post-Pickling Treatment”, Journal of The Electrochemical Society, 165 (2018), C441-C449.

[8] Takefumi Kaji, Toshiya Sekiai, Izumi Muto, Yu Sugawara, and Nobuyoshi Hara, “Visualization of pH and pCl Distributions: Initiation and Propagation Criteria for Crevice Corrosion of Stainless Steel”, Journal of The Electrochemical Society, 159 (2012), C289-C297.

[9] Masashi Nishimoto, Junichiro Ogawa, Izumi Muto, Yu Sugawara, Nobuyoshi Hara, “Simultaneous visualization of pH and Cl− distributions inside the crevice of stainless steel”, Corrosion Science, 106 (2016), 298-302.

[10] Yu Sugawara, Yuto Sakaizawa, Akihiro Shibata, Izumi Muto, Nobuyoshi Hara, “Detection of Hydrogen Distribution in Pure Iron Using WO3 Thin Film”, ISIJ International, 58 (2018), 1860-1867.