コアシェル窒化鉄ナノ粒子の合成・分散と磁性材料への応用

内容の要旨 , 審査の要旨広島大学(Hiroshima University)博士(工学)Doctor of Engineeringdoctora

Porous activated carbon particles from rice straw waste and their adsorption properties

The purpose of this research was to synthesize porous activated carbon particles from rice straw waste and investigate their adsorption properties. Production of porous carbon particles involved several steps: (i) burning rice straw waste; (ii) ball-mill process; and (iii) the activation treatment. To achieve the optimum process in the activation treatment, the concentration of activating agent (i.e. potassium hydroxide) was varied. Experimental results showed that this method is effective to create porous carbon particles. Control of the porosity is also possible by managing the amount of activation agent (i.e. potassium hydroxide). The higher concentration of activation agent has a direct correlation to produce more cavities in the material. The study also confirms that the change in porosity has a direct impact to the ability of the product for adsorbing molecules. Since the present method is converting rice straw waste into useful and valuable porous carbon particles, further development of this study would give a positive impact for the reduction of rice straw waste emission

Low-Energy Bead-Mill Dispersion of Agglomerated Core–Shell α‑Fe/Al₂O₃ and α″-Fe₁₆N₂/Al₂O₃ Ferromagnetic Nanoparticles in Toluene

Magnetic materials such as α″-Fe₁₆N₂ and α-Fe, which have the largest magnetic moment as hard and soft magnetic materials, are difficult to produce as single domain magnetic nanoparticles (MNPs) because of quasistable state and high reactivity, respectively. The present work reports dispersion of agglomerated plasma-synthesized core–shell α″-Fe₁₆N₂/Al₂O₃ and α-Fe/Al₂O₃ in toluene by a new bead-mill with very fine beads to prepare single domain MNPs. As a result, optimization of the experimental conditions (bead size, rotation speed, and dispersion time) enables the break-up of agglomerated particles into primary particles without destroying the particle structure. Slight deviation from the optimum conditions, i.e., lower or higher dispersion energy, gives undispersed or broken particles due to fragile core–shell structure against stress or impact force of beads. The dispersibility of α″-Fe₁₆N₂/Al₂O₃ is more restricted than that of α-Fe/Al₂O₃, because of the preparation conditions. Especially for α″-Fe₁₆N₂/Al₂O₃, no change on crystallinity (98% α″-Fe₁₆N₂) or magnetization saturation after dispersion was observed, showing that this method is appropriate to disperse α″-Fe₁₆N₂/Al₂O₃ MNPs. A different magnetic hysteresis behavior is observed for well-dispersed α″-Fe₁₆N₂/Al₂O₃ MNPs, and the magnetic coercivity of these NPs is constricted when the magnetic field close to zero due to magnetic dipole coupling among dispersed α″-Fe₁₆N₂ MNPs