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Oral presentation

Thermoelectric properties of soil clay minerals treated by molten salt electrolysis

Honda, Mitsunori; Kaneta, Yui; Muraguchi, Masakazu*; Hayakawa, Kosetsu*; Oda, Masato*; Iino, Chiaki*; Ishii, Hiroyuki*; Goto, Takuya*; Yaita, Tsuyoshi

no journal, , 

Ten years have passed since the earthquake and nuclear power plant accident at 1F that occurred in 2011, and the contaminated soil generated in Fukushima Prefecture is now being managed as removed soil at intermediate storage facilities. In the course of developing technology to remove cesium from the removed soil, we have focused on the functionality of crystalline minerals after removal of cesium, and have been investigating their potential as thermoelectric materials. In this study, we report on the evaluation of thermoelectric properties (electrical conductivity, thermal diffusivity, and Seebeck coefficient) and structural analysis of crystalline minerals.

Oral presentation

Evaluation of thermoelectric properties of soil clay minerals towards fabrication of thermoelectric material

Honda, Mitsunori; Kaneta, Yui; Muraguchi, Masakazu*; Hayakawa, Kosetsu*; Oda, Masato*; Iino, Chiaki*; Ishii, Hiroyuki*; Goto, Takuya*; Yaita, Tsuyoshi

no journal, , 

Ten years have passed since the Great East Japan Earthquake and the accident at the Fukushima Daiichi Nuclear Power Plant, and the contaminated soil generated in Fukushima Prefecture has been decontaminated and managed as removal soil. We have been conducting research on the volume reduction and recycling of Fukushima weathered biotite, which is known to be a strong adsorbent of radioactive Cs contained in the removed soil. In this study, thermoelectric properties (Seebeck coefficient, electrical conductivity, and thermal diffusivity) of soil clay minerals and molten salt-electrolyzed soil clay minerals were evaluated in order to clarify their properties as thermoelectric materials.

Oral presentation

Investigation of the influence of measurement terminals on thermoelectric property measurements by heat transfer simulation

Wako, Toshinobu*; Hayakawa, Kosetsu*; Matsumura, Hiroshi*; Muraguchi, Masakazu*; Oda, Masato*; Iino, Chiaki*; Ishii, Hiroyuki*; Honda, Mitsunori

no journal, , 

This report investigates the effect of heat transfer due to contact with measurement terminals on the measurement results of thermoelectric material properties using heat transfer simulation. In thermoelectric conversion technology, miniaturization and thinning of elements are being studied for their compatibility with compact power supplies for the IoT, etc. In order to achieve this, it is necessary to accurately measure thermoelectric properties of minute materials, and it is essential to evaluate the results in the entire measurement system.

Oral presentation

Measurement of thermal conductivity of soil clay minerals treated by molten salt electrolysis

Hayakawa, Kosetsu*; Matsumura, Hiroshi*; Wako, Toshinobu*; Muraguchi, Masakazu*; Oda, Masato*; Iino, Chiaki*; Ishii, Hiroyuki*; Honda, Mitsunori

no journal, , 

We have been developing new thermoelectric materials from soil clay minerals treated by molten salt electrolysis, and have been evaluating their basic properties. In this study, we report the results of the measurement of thermal conductivity of soil clay minerals, which is essential for the determination of thermoelectric performance index.

Oral presentation

Development of thermoelectric conversion materials from weathered biotite using molten salt treatment

Honda, Mitsunori; Kaneta, Yui; Muraguchi, Masakazu*; Hayakawa, Kosetsu*; Oda, Masato*; Iino, Chiaki*; Ishii, Hiroyuki*; Goto, Takuya*; Yaita, Tsuyoshi

no journal, , 

Twelve years have passed since the 1F accident that occurred in 2011, and contaminated soil generated in Fukushima Prefecture is being managed as removed soil. We have focused on the functionality of several crystalline minerals obtained in the process of developing a technology to remove Cs from the removed soil, and are examining their potential as thermoelectric conversion materials. In this study, we report on the evaluation of thermoelectric properties (electrical conductivity, thermal diffusivity, and Seebeck coefficient) of the crystalline minerals.

Oral presentation

Thermoelectric properties of Fukushima weathered biotite for thermoelectric conversion materials

Honda, Mitsunori; Kaneta, Yui; Hayakawa, Kosetsu*; Muraguchi, Masakazu*; Iino, Chiaki*; Oda, Masato*; Ishii, Hiroyuki*; Goto, Takuya*; Yaita, Tsuyoshi

no journal, , 

In this study, thermoelectric properties (electrical conductivity, Seebeck coefficient, and thermal diffusivity) were evaluated (OZMA-1-S1) for polycrystalline minerals obtained by systematically changing the conditions of WB and the molten treatment. The Seebeck coefficient and thermal diffusivity were evaluated on the same sample. Macroscopic and microscopic structures were identified by various X-ray analyses and first-principles calculations. As for the electrical conductivity results of WB, the biotite material is usually known as an electrical insulator at room temperature, but after grinding, classification, molten salt treatment, and sintering, it was found to have electrical conductivity on the order of 1.49 $$times$$10$$^{-4}$$ ($$mu$$V/K) in the temperature range 650-850$$^{circ}$$C, indicating that it has semiconducting electrical conductivity properties. Seebeck coefficient measurements in the same temperature range showed a high value of -2.0$$times$$10$$^{5}$$ ($$mu$$V/K). Calculating the dimensionless performance index ${it ZT}$ from the obtained results, ${it ZT}$=0.29 was obtained. Regarding the thermoelectric property evaluation results for the molten salt treated polycrystalline minerals, higher electrical conductivity properties than WB were obtained for the same temperature range. These results suggest that WB can be used to show useful thermoelectric properties in the high temperature region above 650$$^{circ}$$C.

Oral presentation

Thermal conductivities and structures of Fukushima weathered biotite

Hayakawa, Kosetsu; Muraguchi, Masakazu*; Oda, Masato*; Iino, Chiaki*; Ishii, Hiroyuki*; Honda, Mitsunori

no journal, , 

Oral presentation

First-principles calculations to elucidate the molten salt reaction mechanism of cesium adsorbed weathered biotite.

Iino, Chiaki*; Okumoto, Shunsuke*; Oda, Masato*; Nara, Jun*; Muraguchi, Masakazu*; Ishii, Hiroyuki*; Honda, Mitsunori

no journal, , 

Weathered Biotite (WB) with Cs adsorbed on it is removed of less than 99.9999% of Cs by the molten salt method, and crystalline minerals such as Augite and Wadalite are synthesized. In order to elucidate the reaction mechanism of the synthesis of Wadalite, a comparative study of chemical potentials was conducted to investigate the stable structures and electronic properties of WB and Wadalite before and after the reaction, using first-principles calculations.

Oral presentation

Reaction mechanism of Wadalite formation process in molten salt treatment

Okumoto, Shunsuke*; Iino, Chiaki*; Oda, Masato*; Muraguchi, Masakazu*; Hayakawa, Kosetsu*; Ishii, Hiroyuki*; Honda, Mitsunori

no journal, , 

As part of research and development for environmental restoration of Fukushima, we have conducted study on Cs removal from weathered biotite using molten salt method. 99.9999% or less of Cs removal and formation of crystalline minerals such as ordinary Augite and wadalite were confirmed, but the atomic-level reaction mechanism of the reaction process and products is necessary. In this study, the stable structure of wadalite was investigated using first-principles calculations, and the reaction mechanism was investigated using the obtained stable structure.

Oral presentation

Estimation of heating element cooling and power generation using peltier module

Tanima, Shin*; Nakamura, Hayato*; Oda, Masato*; Iino, Chiaki*; Ishii, Hiroyuki*; Honda, Mitsunori; Muraguchi, Masakazu*

no journal, , 

Using the thermal network method, the internal temperature distribution of a thermoelectric power generation module during operation was modeled by incorporating the contact resistance with the heat source and the contact thermal resistance inside the module. By varying the value of contact thermal resistance and evaluating the temperature difference between the top and bottom of the thermoelectric element, a simple estimate of the actual electromotive force inside the power generation module was shown. These results lead to the establishment of a method to evaluate the actual amount of electricity generated by thermoelectric power generation modules installed under various conditions. In the future, we plan to further model the thermoelectric modules for conditions closer to reality and utilize the results in the design of highly efficient thermoelectric modules.

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