Graduate School of Engineering
Department of Metallurgy
Advanced Materials Physical Chemistry
Materials Physical Chemistry (Prof. Zhu)
A. Molten Salt Electrochemistry
Molten salts are an excellent medium that have wide electrochemical windows and enable many processings involving the reduction of reactive metals such as lithium and rare earth metals. We study a production of reactive metals (electrowinning), surface modification of refractory materials with electroplating, and recycling of reactive metals (electrorefining) by utilizing molten salt electrochemistry. For instance, we succeeded in the electrochemical formation of oxidation resistant MoSi2 film on the surface of Ni based superalloy used as a turbine blade material. We currently develop an innovative refractory material by siliciding the surface of C/C composite that has ultra-lightweight and high-strength even at high temperature.
B. High Temperature Chemical Process
High temperature chemical processing is essential for the productions of reactive metals and functional materials and for the recycling of metals and waste treatment. For instance, we developed recycling process for rare earth permanent magnet alloys (Nd-Fe-B system) by using molten fluoride. In general, the magnet alloy scraps are heavily contaminated by oxygen, and they can’t be recycled as it is. We deoxidized the scraps by remelting with fluoride and obtained magnet alloys with low oxygen concentration (under 200 mass-ppm O). Oxygen concentration of virgin material of magnet alloy is approximately 500 mass-ppm, and the developed process has enough deoxidation capability for practical application in principle.
C. Thermophysical Properties of High Temperature Melts
Thermophysical properties of high temperature melts (molten metals, molten salts, molten slag etc.) such as viscosity, density, surface tension and electrical conductivity are very important to study the liquid structure at the atomic level, to design the metallurgical apparatus and to simulate the industrial process. We study the essential behavior of melt by determining the accurate properties. For instance, we developed a new rotating crucible viscometer and succeeded in accurate determination of viscosity of molten silicate containing fluoride. We currently develop a viscometer that can accurately determine several mPa·s of viscosity for revealing viscosity behavior in wide composition range.