Kazuki Morita | The University of Tokyo (original) (raw)

Papers by Kazuki Morita

Crystal Growth & Design, Mar 11, 2022

Materials Science in Semiconductor Processing, Dec 1, 2018

Hf, Zr, or Ti was employed as additive to enhance removal of the main impurities from metallurgic... more Hf, Zr, or Ti was employed as additive to enhance removal of the main impurities from metallurgical-grade Si (MG-Si) during the Si-Sn alloy refining process. The microstructure of Si-Sn alloy without/with Zr, Hf, or Ti was observed and analyzed by electron probe microanalysis (EPMA) to investigate the distribution of impurities. Compositions of intermetallic phases precipitated in Sn or among the grain boundaries of Si were quantitatively analyzed using EPMA. The mechanisms of their formation and the removal of impurities are discussed. The results of Si refining showed that the addition of Hf or Zr slightly enhanced the removal of Al. The high refining temperature in the Si-Sn alloy refining process was responsible for the low extraction of B. Most of Zr, Hf, or Ti was removed simultaneously with other impurities during the Si-Sn alloy refining process.

Industrial & Engineering Chemistry Research, Feb 28, 2022

材料とプロセス : 日本鉄鋼協会講演論文集 = Current advances in materials and processes : report of the ISIJ meeting, Sep 1, 2002

Materials transactions, 2021

CoCrCuFeNi high-entropy alloys (HEAs) have high ductility owing to their unique two-phase microst... more CoCrCuFeNi high-entropy alloys (HEAs) have high ductility owing to their unique two-phase microstructure. Phase relations and microstructure evolution were investigated by scanning electron microscopy coupled with energy dispersive spectrometry and differential thermal analysis. These results contributed to clarifying the formation mechanism of the HEA microstructures. The effects of Mg addition as an alloying element in HEAs were also studied, with respect to precipitation hardening, thereby aiming to obtain strength-ductility balanced HEAs.

Separation and Purification Technology, Dec 1, 2021

Abstract A novel approach is proposed to prepare high-purity Si by enhancing B removal from metal... more Abstract A novel approach is proposed to prepare high-purity Si by enhancing B removal from metallurgical-grade Si with high-entropy alloys as solvents. CrMnFeNiM (M = Al, Co, Ti, and Cu) alloy is melted with metallurgical-grade Si at 1773K. After a period of holding time, the recrystallization of high-purity Si is realized by electromagnetic directional solidification. High-purity Si enrich in the upper region of the sample, and impurities precipitate in the bottom Si-based alloy. The enrichment percentage of Si is more than 92.9%, up to 97.4%. The maximum distribution ratio and minimum segregation coefficient of B are obtained in Si-CrMnFeNiAl solvent, which are 19.9 and 0.036, respectively. The primary cause why Si-20 at. %CrMnFeNiAl solvent stands out is that the activity coefficients of metals and B in the melt are large, which makes the formation of boride easier. This method provides a potential possibility for improving the B removal effect and reducing the cost to prepare high-purity Si.

Elsevier eBooks, 2014

Thermodynamic Aspects of Process Metallurgy. Introduction to Thermodynamics of Metallurgical Proc... more Thermodynamic Aspects of Process Metallurgy. Introduction to Thermodynamics of Metallurgical Processes

Proceedings of SPIE - The International Society for Optical Engineering, 1990

Molecular dispersions of amorphous siliceous materials doped with organic molecules, TPPS, were p... more Molecular dispersions of amorphous siliceous materials doped with organic molecules, TPPS, were prepared by a sol-gel process in which Si(0C2H5)4 was hydrolyzed in neutral solution. An amorphous silica which was doped with TPPS on the order of 1x105 mol/mol Si02 showed photochemical hole burning at 4 K. The TPPS/a-Si02 was heat-treated at various temperatures and the change of optical spectrum were observed as a function of temperature. It was found that the sample was comparatively stable upto 200 °C.

Materials Science & Technology Conference and Exhibition, 2014

Proceedings of SPIE, Oct 13, 1994

Tetraphenylporphinetetrasulfonic acid (TPPS), which is known as a photo-chemical holeburning (PHB... more Tetraphenylporphinetetrasulfonic acid (TPPS), which is known as a photo-chemical holeburning (PHB) dye, was incorporated in silica gels obtained by the sol-gel process from tetraethoxysilane (TEOS). The form of TPPS must be free-base (H 2P), which exists in basic condition, to be active in PHB. In this study to obtain transparent and dense silica gels doped with free-base TPPS, a two-step hydrolysis process using solutions containing NaOH or using ammonia were developed. In the first step we used acidic catalyst to get denser and transparent gels and in the second step basic catalyst was adopted to obtain free-base TPPS. Monolithic silica gels can be obtained by this two-step process from the hydrolysis of TEOS. By the spectroscopic analysis of TPPS incorporated in the gels, it is found that the free base form of TPPS is retained at the molar ratio of NaOH/TEOS above 10-3. The spectra of monocation are observed at the molar ratio of NaOH/TEOS below 10-3. And the dimerization of TPPS incorporated in the TEOS gels does not occur at higher NaOH concentration than that in the TMOS gels.

Materials transactions, 2017

We propose a process for the direct synthesis of solar grade Si from a metallurgical Si wafer foc... more We propose a process for the direct synthesis of solar grade Si from a metallurgical Si wafer focusing on the fact that its microstructure is composed of almost pure Si grains and grain boundaries enriched with impurities. Principally, heating a metallurgical grade Si wafer above its eutectic temperature and applying a temperature gradient allows the grain boundaries to be melted and causes them to migrate to the high-temperature direction. The liquid phases are nally terminated at the end surface, resulting in the upgrading of the Si and making it more favorable for solar cells. In the present paper, to determine the puri cation effect during the liquid phase migration process, thermodynamic assessment was performed using CALPHAD method. Liquid phase migration experiments were also conducted using synthetic MG-Si (Si-Fe alloy) to determine the reaction time for the process. A maximum migration velocity of 8.17 × 10 −7 m/s was obtained at 1623 K, which allows the migration process to be accomplished within 3 min for a 150-μm wafer.

Tetsu To Hagane-journal of The Iron and Steel Institute of Japan, 1988

Separation and Purification Technology, Nov 1, 2021

Abstract Si recycling from Si powder waste is of great significance to the production profits and... more Abstract Si recycling from Si powder waste is of great significance to the production profits and alleviate hazardous effects on the ecological environment. Solvent refining is an effective way to reproduce solar-grade silicon (SoG–Si) by recycling and reusing the Si powder waste. Herein, a Si–Sn–Cu ternary solvent with Zr-assisted refining method was proposed to make full use of the high activity coefficients of B and the strong B affinity of Zr. The activity coefficients of B at the different compositions of the Si–Sn–Cu ternary solvent were firstly measured, which provided guidance on the solvent optimization to improve the B removal efficiency. The precise temperature control enabled the obtainment of large-area bulk Si from Si–Sn–Cu solvent, and the enrichment percentage of the obtained bulk Si from ternary Si–Sn–Cu solvent was 99.2%. Moreover, compared to the binary solvents, the absolute B content in primary Si further decreased to 4.7 ppmw after directional solidification, showing a better B removal fraction (95.3%). It provides a new scientific insight and an experimental evidence for the effective separation and purification of primary Si crystals from Si-based multicomponent solvents.

Journal of Non-crystalline Solids, 2020

Here, we demonstrate an extensive theoretical analysis of the free energy of mixing of liquid tra... more Here, we demonstrate an extensive theoretical analysis of the free energy of mixing of liquid transition-metal alloys. The interatomic interaction is modeled by a semi-empirical potential, where the contributions from nearly-free and tight-binding electrons are described by the pseudopotential perturbation theory and the bondorder tight-binding potential, respectively. The liquid structure and the structure-dependent part of the free energy are calculated through the Weeks-Chandler-Anderson (WCA) approach with the non-additive hardsphere reference system. The calculated free energy of mixing values shows reasonable agreement with experimental values, especially for alloys with small differences in group numbers for their components.

Journal of Mining and Metallurgy, Section B, 2015

In order to optimize the removal of boron during the refining of slag to obtain solar grade silic... more In order to optimize the removal of boron during the refining of slag to obtain solar grade silicon, the density of molten slag was measured by an improved Archimedean method within a temperature range from 1073 to 1373 K. It was found that the density of molten slag at 1723 K can be deduced by linear fitting, and that the slag density decreases with increasing temperature. However, a reduction in slag density occurs with decreasing CaO concentration. An increase in the molar volume of slag was also observed with increasing temperature.

Proceedings of SPIE, Dec 7, 1992

Amorphous siliceous materials with molecular dispersions of organic molecules, TPPS, TMPyP and DA... more Amorphous siliceous materials with molecular dispersions of organic molecules, TPPS, TMPyP and DAQ were prepared by a sol-gel process in which Si(OC2H5)4 was hydrolyzed in weak acid solution. Effect of ultrasonic irradiation on the sol-gel process was studied for the TPPS/a-SiO2 system in order to attain the further molecular dispersions and shorten the sol-gel reactions. Optical properties of TMPyP doped sol-gel thin films were observed. An amorphous silica thin film which was doped with TMPyP on the order of 1 X 10-3 mol/mol SiO2 showed photochemical hole burning at 20 K. the TMPyP/a-SiO2 was heat-treated at various temperatures and the changes of optical spectrum were observed as a function of temperature. It was found that the sample was comparatively stable up to 200 degree(s)C. Apparent quantum yields of PHB of porphines and quinizarin in polymer or sol-gel film and bulk were discussed.

Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science, Mar 19, 2018

We developed a kinetic model that considers both silicon loss and boron removal in a metallurgica... more We developed a kinetic model that considers both silicon loss and boron removal in a metallurgical grade silicon refining process. This model was based on the hypotheses of reversible reactions. The reaction rate coefficient kept the same form but error of terminal boron concentration could be introduced when relating irreversible reactions. Experimental data from published studies were used to develop a model that fit the existing data. At 1500°C, our kinetic analysis suggested that refining silicon in a moist hydrogen atmosphere generates several primary volatile species, including SiO, SiH, HBO, and HBO 2. Using the experimental data and the kinetic analysis of volatile species, we developed a model that predicts a linear relationship between the reaction rate coefficient k and both the quadratic function of p(H 2 O) and the square root of p(H 2). Moreover, the model predicted the partial pressure values for the predominant volatile species and the prediction was confirmed by the thermodynamic calculations, indicating the reliability of the model. We believe this model provides a foundation for designing a silicon refining process with a fast boron removal rate and low silicon loss.