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Takayuki Watanabe

Professor
Department of Chemical Engineering
Kyushu University

Field of study : Plasma Chemistry, Energy Engineering
Key words : Plasma Processing, Modeling of Plasma Flow, Nanomaterials, Waste Treatment, Lunar Resource Utilization

http://www.chem-eng.kyushu-u.ac.jp/lab5/index-e.html/

• November 13, 2023: Prof. Watanabe was awarded Plasma Innovation Award, Asia-Pacific Physical Societies, The Division of Plasma Physics.
• May 21-26, 2023: 25th International Symposium on Plasma Chemsitry (ISPC25, Kyoto, Japan), Chair: Prof. Watanabe, Download here
• May 20-21, 2023: IPCS Summer School (Kyoto, Japan), Chair: Prof. Watanabe and Tanaka.
• December, 2021: Prof. Tanaka was promoted to Associate Professor.
• September, 2020: Prof. Tanaka was selected as Trainees of SENTAN-Q (Diversity and Super Global Training Program).
• September 9, 2019: "Kunming University of Science and Technoglogy - Kyushu University Joint Research Center on Plasma Metallurgy Materials" was opened in Kunming, China.
• July 2, 2019: Our paper on The Astrophysical Journal Letters was picked by Physics Today, Making Cosmic Dust in The Lab
• June 11, 2019: Our research about plasma waste treatment was televised on TV program.
• October 12, 2018: Our research about plasma waste treatment was televised on TV program.
• January 1, 2018: The Board of Directors of the International Plasma Chemistry Society.
• September 17, 2017: Our research about plasma waste treatment was televised on TV program.
• April 22, 2016: Our research about plasma waste treatment was televised on TV program.
• November 9, 2014: Our research about plasma waste treatment was televised on TV program. See YouTube
• October 2014: Prof. Watanabe was awarded Plasma Materials Science Awards, Japan Society for Promotion of Sciences, 153rd Committee on Plasma Materials Science.
• March 5, 2012: Our research about plasma waste treatment was televised on Discovery Channel "Rebuilding Japan".
• May 30, 2009: The Prime Minister Observes Advanced Environment-Friendly and Energy-Saving Technology Facilities.

Waste Treatment by Atmospheric Pressure Plasmas can be downloaded from here.

Thermal plasmas have simply been used as a high temperature source. This indicates that thermal plasmas may have more capabilities in material processing, especially production of high-quality and high-performance materials, if thermal plasmas are utilized effectively as chemically reactive gases. Therefore we developed the numerical analysis to investigate non-equilibrium characteristics in thermal plasmas. These results can be utilized for the nano-material synthesis as well as waste treatment using thermal plasmas.

2 Related recent research topics

Modeling of Reactive Plasma Flows

The induction thermal plasma approach has been applied for many fields, including treatment of harmful waste materials, recovery of useful material from waste, and production of high-quality and high-performance materials, such as synthesis of nanoparticles, deposition of thin films, and plasma spraying. Induction thermal plasmas offer unique advantages including high enthalpy to enhance reaction kinetics, high chemical reactivity, oxidation and reduction atmospheres in accordance with required chemical reactions, and rapid quenching. These advantages increase the advances and demands in plasma chemistry and plasma processing.

However, thermal plasmas have been simply used as high-temperature source, because argon is typically used as the plasma gas. In some applications such as reactive plasma spraying, material synthesis, and waste treatment, thermal plasmas with adding reactive gas are desirable to enhance the chemical reactivity of the plasma.

Thermal plasmas have been mainly treated as equilibrium conditions even though sophisticated modeling considering chemical reactions has been required for industrial applications. In previous works, estimation of thermodynamic and transport properties was oversimplified, therefore, more sophisticated models are required. The oversimplified estimation, such as use of equilibrium properties and use of the first-order approximation of Chapman-Enskog method, would cause errors in the numerical results.

In order to improve the accuracy of thermodynamic and transport properties, higher-order approximation of Chapman-Enskog method was applied for estimation of the transport properties of induction thermal plasmas. The thermal conductivity and the electrical conductivity by higher-order approximation differ from those of the first-order approximation especially over 10000 K.

In this study, a non-equilibrium modeling of induction thermal plasmas was developed without chemical equilibrium assumptions. This formulation including the finite-rates of dissociation and ionization is presented using higher-order approximation of Chapman-Enskog method for estimation of the transport properties.

Development of Innovative In-Flight Glass Melting Technology for Energy Conservation

We developed innovative in-flight glass melting technology under the support of New Energy and Industrial Technology Development Organization (NEDO) project in Japan from 2005 until 2012. The granulated raw material with small diameter is dispersed in thermal plasmas and the powders contact fully with the plasma and burner flame. The high heat-transfer and temperatures of the plasma will melt the raw material quickly. In addition, the decomposed gas of carbonates is removed during the in-flight treatment to reduce the fining time considerably. Compared with the traditional glass production, the total vitrification time is evaluated only 2-3 h in the same productivity as the fuel-fired melter. A multiphase AC arc was developed for the application of glass melting technology. The large volume discharge produced by a stable multiphase AC arc is preferable to melt the granulated glass materials. The discharge behavior and the high-temperature region of the plasma can be controlled by the electrode configurations.

The most important invention is the development of multiphase AC arc. The large volume discharge produced by a stable multiphase AC arc is preferable to melt the granulated glass materials. The discharge behavior and the high temperature region of the plasma can be controlled by the electrode configurations. The spatial characteristics of the arc discharge were examined by image analysis of high-speed camera. Results show arc existence area is related with electrode configuration. This study provides the useful information of efficient particle treatment in the preferred electrode configuration.

Generation of Water Plasmas under Atmospheric Pressure

Preparation of Functional Nanoparticles by Thermal Plasmas

Functional nanoparticles of silicide and boride were prepared by induction thermal plasmas. Silicide and rare-earth boride are attractive materials because of their high melting temperature, high electrical conductivity and low work function. Therefore these nanoparticles would be applied for electromagnetic shielding, and solar control windows with interaction with IR and UV light.

For the preparation of silicide, Si powder premixed with metal powder (Mo, Ti, Co, Fe, Cr, or Mn) was injected into the plasma. For the preparation of rare-earth boride, premixed powders of rare-earth oxide, B and C were introduced into the thermal plasma. In the thermal plasma, the injected powders were evaporated and reacted with boron. After the evaporation and reaction, the vapor was rapidly cooled after the plasma flame. The nanoparticles were prepared on condition that the vapor was quickly quenched by the water-cooled copper coil.

We developed transparent radiation shield by making the shield materials into nanoparticles, and we conducted the collaborative project with Japan Atomic Energy Agency (JAEA).

Recently, We developed nanoparticle synthesis for cathode, anode, and electrolyte of lithium-ion secondary battery. These nanoparticles leads to the development of all solid-state lithium-ion battery improvement with high energy density.

We actively extended the research to the investigation of interplanetary dust particles contain glass with embedded metals and sulfides (GEMS) grains, which are considered to be among the building blocks of the solar system. GEMS grains formed either in the local environment of our protoplanetary disk considering the nucleation and growth of solids from high-temperature gas during cooling.

Another purpose is to investigate the condensation mechanism of mixture vapor of feed powders in thermal plasmas. The characteristics of the prepared nanoparticles are affected by the vapor pressure ratio of the constituent materials. Investigation of physical and chemical processes in thermal plasma processing is indispensable for Nanoparticle synthesis.

Waste Treatment by Reactive Thermal Plasmas

Attractive thermal plasma processes have been proposed especially for waste treatment, because engineering advantages such as smaller reactor, lower capital cost, portability allowing on-site destruction, rapid start-up and shutdown offer efficient destruction of hazardous and waste materials.

Waste material can be efficiently degraded by thermal plasmas under reducing or oxidizing conditions. However, thermal plasmas have been mainly used as a high temperature source. This indicates that thermal plasmas may have more capability for waste treatment, if thermal plasmas are utilized effectively as chemically reactive gas.

In this research, application for destruction of hazardous and waste materials by thermal plasmas is developed. Radioactive waste treatment by thermal plasmas is an active research field, therefore plasma treatments of low-level radioactive wastes (LLW) as well as ion-exchange resin are investigated.

Moreover, reactive thermal plasma for halogenated hydrocarbon decomposition is developed. For halogenated hydrocarbon decomposition, the stable generation of DC steam plasmas is the important factor for industrial application. Steam plasmas are suitable for halogenated hydrocarbon decomposition because hydrogen and oxygen combine with the liberated halogen and carbon atoms to prevent recombination reactions that result in the reformation of halogenated hydrocarbons.

Development of Material Processing by Non-Equilibrium Atmospheric Plasmas

Atmospheric pressure plasma has been studied for the application of material surface cleaning, preparation of surface coating, and modification of polymer film. In this study, the atmospheric non-thermal plasmas ere applied to surface cleaning of waste plastic.

The paint attached to waste plastic surface causes low quality of recycled plastic. The paint removable is difficult by the conventional dry cleaning process, therefore new cleaning technology for waste-plastic recycle has been required.

The mechanism of the cleaning with atmospheric plasmas was investigated from the measurements of optical emission spectroscopy, the atomic concentrations of plastics surface were measured with electron spectroscopy for chemical analysis.

Furthermore, a kinetic model is developed to investigate ozone and oxygen radical production in dry air treated by a non-thermal plasma jet at atmospheric pressure.

Lunar Resources Utilization

Ground-engineering work on experimental missions for lunar resource utilization has been conducted. The goal of the research program is to conceptually design an experiment system for unmanned water production on the Moon, and to define essential technological breakthroughs.

As part of the research program, an experimental study on hydrogen reduction of lunar soil has been performed to design a chemical reactor of the water production. A fixed-bed reduction reactor and lunar soil simulants were prepared for our water-production experiments.

Over 20 processes of oxygen production on the moon have been proposed. Among these processes, oxygen production employing hydrogen reduction is the most feasible process. In this process, ilmenite contained in lunar soil is reduced with hydrogen producing water. Oxygen is subsequently produced by electrolysis. Hydrogen produced in reaction can be recycled.

Understanding the hydrogen reduction mechanism of ilmenite is important for the mission of utilizing lunar soil. The purpose of this work is to discuss the possibility and the mechanism of water production.