P17
無容器浮遊法で作成した Fe 系酸化物の磁性
Magnetic properties of Fe-based oxides prepared bycontainerless method
石塚美里 1, 佐藤令奈 1 , 高橋圭太 1 , 渡邉匡人 1, 石川毅彦 2 , 小山千尋 2 , 織田裕久 2 , 伊藤剛 2
Misato ISHIZUKA1, Reina SATO1, Keita TAKAHASHI1, Masahito WATANABE1,Takehiko ISHIKAWA2, Chihiro KOYAMA2, Hirohisa ODA2 and Takeshi ITO2
1 学習院大学理学部, Faculty of Science, Gakushuin University
2 宇宙航空研究開発機構，JAXA
1.

Introduction

We have performed using an electrostatic levitation furnace installed in ISS an investigation of thethermophysical properties of the molten SiO2-CaO-FeO system which is the basis for the steel-making slags.
Since the oxide system includes Fe ions, it is interested in magnetic properties for the solidified oxide systems.
The magnetic properties of the oxide system including Fe ions would depend on the atmospheric oxygen
conditions because of the reaction for 4Fe3+ + 2O2- ⇄ 4Fe2+ + O2 at the interface between liquid and atmosphericgas state. Since under microgravity conditions the atmospheric gas around molten oxide has no convections, thedifference in the magnetic properties of the oxides solidified on the ground is expected. From the background, weinvestigate the magnetic properties of the SiO2-CaO-FeO oxide system solidified under microgravity and on theground using the magnetization curve and its temperature dependence.
2. Experiments
2.1. Preparation of solidification samples of SiO2-CaO-FeO system under microgravity and on the ground
Master samples of SiO2:CaO:FeO = 20:20:60 mass% (Ox2) and SiO2:CaO:FeO = 40:40:20 mass% (Ox6) wereprepared from reagent grade SiO2, CaO and FeO powders. Master samples were prepared by drying SiO2,CaO, and FeO powders at 300°C for 14 hours and evaporating the H 2O contained in the raw powder. Aweighed mixed oxides were placed in a cooled copper crucible, sintered by CO 2 laser irradiation at 1000°C in
dry air, and prepared by the aerodynamic levitation (ADL) method. A sintered sample of approximately 2mmin diameter was levitated using an aerodynamic nozzle, and containerless melting and solidification wasperformed. After these procedures, selected samples without voids and air bubbles by X-ray radiographchecking were installed in ISS. These samples were levitated and melted in the dried air (N 2/O2 mixture gas)
atmosphere by the electrostatic levitation furnace (ELF) in ISS 1) for the density measurements of the molten
state and then they were solidified by stopping the irradiation of heating laser of 980nm wavelength withnatural cooling. On the other hand, on the ground samples were levitated and melted in the air atmosphere
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by an aerodynamic levitation system with a CO2 laser of 10.6μm-wavelength and after completely melting
solidified by stopping the irradiation of the CO2 laser.
Sample temperature was monitored by a monochromatic pyrometer with an emissivity of 1 both in ELF andon the ground. After measurements, we corrected the temperature emissivity of 1 to real temperature using
the emissivity of the molten SiO2-CaO-FeO measured by our proposed methods 2). Figure 1 shows an exampleof temperature profiles during melting and solidification. As a result, the recalescence phenomenon, in which
crystallization occurs due to the release of latent heat of solidification from the supercooled melt in both theaerodynamic levitation and the ELF was observed for Ox2, but not for Ox6. Therefore, Ox2 was found to be
crystalline state, while Ox6 was glass state with an amorphous structure.

(b)

(a)

Figure1.

Temperature profiles during cooling in ADL and ELF for (a) Ox2 and (b) Ox6 samples.

2.2. Magnetic property measurement from the magnetization curve by VSM method
The oxide samples using the above procedure in the ELF and on the ground were investigated for theirmagnetic properties. The magnetic properties investigations were performed using a vibrating samplemagnetometer (VSM) from room temperature to 1200℃. From the VSM measurements, we obtained themagnetization curve in which the magnetization of samples is changed with the external magnetic fields. Fromthe magnetization curve and its temperature dependence, we can identify the type of magnetic properties andthe origin of magnetic properties. Moreover, the sample surfaces and inside were observed by scanningelectron microscopy (SEM) with energy-dispersed X-ray analysis (EDX) for investigation of morphology andsegregation of ions.
3. Result and discussion
Figure 2 shows the sample surface morphorogy by SEM observations. The appearance of the sample
surface differs depending on the composition, with Ox2 showing crystals precipitated on the surface. On theother hand, the surface of Ox6 is quite uniform, and this image confirms that it is formed of glass state. Figure
3 shows the magnetization curve by VSM measurements of Ox2 and Ox6 samples made by the ADL method
and the ELF onboard the ISS. The results show that both samples of Ox2 have ferromagnetic properties. Onthe other hand, Ox6 does not have ferromagnetic properties, it can be confirmed that the magnetizationslightly changes with the value of the magnetic field, and in particular, the ELF sample has a paramagnetic
behavior in which the magnetization is proportional to the applied magnetic field. In addition, a comparisonof the Ox2 magnetization of the ELF sample with that of the ADL sample showed that the saturation
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magnetization of the ELF sample was smaller than that of the ADL sample. The reason for this is thought tobe that the ELF and ADL methods both melted in air composition gas, but in ELF no gas convection conditions
around the molten samples, and the different atmosphere around the sample would result in a difference inthe presence of Fe3+ state in the sample3,4).

(a)

(b)

Figure2. SEM images of samples solidified in ELF under microgravity for (a) Ox2 and (b) Ox6 compositions.

(b)

(a)

Figure 3. Magnetization curve using VSM at room temperature of samples solidified by the ADL
method and ELF for (a) Ox2 and (b) Ox6 compositions.

4. Conclusion
SiO₂-CaO-FeO oxides were solidified using the aerodynamic levitation method on the ground and ELF
under microgravity, and the magnetic properties were compared ADL samples with those of an ELF sampleof the same composition. Both samples exhibited magnetization with hysteresis loops depending oncomposition. The comparison revealed a significant difference in the magnitude of magnetization between theADL sample and the ELF sample, with the ELF sample being smaller. The cause of this difference is thought
to be the difference in the presence of Fe3+ state that causes the magnetism, but the details are not yet known.
We will investigate the details of the origin of the magnetization of the oxide system through temperaturedependence of magnetization-curve and compositional analysis in the future.
References
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© 2023 by the authors. Submitted for possible open access publication under theterms and conditions of the Creative Commons Attribution (CC BY) license(http://creativecommons.org/li censes/by/4.0/).

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