OS2-7
ジルコニウム融体の表面張力解析を利用した酸素量推算：
国際宇宙ステーションでの静電浮遊実験促進のために
Estimating Oxygen for Enhanced Utilization of theElectrostatic Levitation Furnace on the International
Space Station via Surface Tension Analysis
小澤俊平 1, 清宮優作 2, 白鳥英 3，小畠秀和 4，杉岡健一 5, 石川毅彦 6
Shumpei OZAWA1, Yusaku SEIMIYA 2, Suguru SHIRATORI 3，Hidekazu KOBATAKE 4，Ken-Ichi
SUGIOKA5, and Takehiko ISHIKAWA 6
千葉工業大学，Chiba Institute of Technology,千葉工業大学附属研究所，Research Liaison Centre
3 東京都市大学，Tokyo City University
4 同志社大学，Doshisha University
5 富山県立大学，Toyama Prefectural University
6 宇宙航空研究開発機構宇宙化学研究所，Institute of Astronautical Science, JAXA121.

Introduction
The lectrostatic Levitation Furnace (ELF) aboard the KIBO at the International Space Station (ISS) provides

an ideal environment, free of the effects of gravity, for precise measurements of the thermophysical propertiesof high-temperature melt and for studying the metastable solidification of deep undercooled melts1). Given its
high oxygen solubility, liquid zirconium is typically maintained at elevated temperatures for extended
durations prior to the main experiments to lower the oxygen partial pressure (Po2) in the ELF chamber. The
dissolution of oxygen into the sample and its oxidation affect the investigation of solidification behavior andthermophysical properties, particularly surface tension. However, the effects of Po2 in the ELF chamber havenot been quantitatively evaluated in these space missions because the ELF does not include an oxygen sensor
due to spatial constraints of the ISS.
As part of a broader initiative by JAXA to use the ELF for fundamental materials research, we have proposed
to estimate the oxygen partial pressure in the ELF chamber. This will involve analyzing the relationshipbetween the surface tension of liquid zirconium, its temperature, and the concentration of dissolved oxygen
within the sample. In this presentation, we will outline the rationale, objectives, and current preparation statusof our proposal.

2.

Estimating Po2 in the ELF chamber
The surface tension of liquid zirconium is affected by the amount of dissolved oxygen and temperature,
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since oxygen acts as a potent surfactant2). We have measured the surface tension of liquid zirconium as afunction of temperature and dissolved oxygen concentration using the oscillating droplet method withelectromagnetic levitation (EML) technique on Earth. For example, in a typical experiment conducted at 1900
K, we observed that an increase in the concentration of dissolved oxygen from the measurement atmospherecorrelates with a decrease in surface tension, as depicted in Figure 12-4). By establishing a precise relationshipbetween surface tension, temperature, and oxygen concentration, we can estimate the concentration ofdissolved oxygen in liquid zirconium maintained within the ELF by analyzing the corresponding temperatureand surface tension data. This estimation allows for the calculation of the corresponding Po2 in the ELF
chamber based on the amount of oxygen dissolved from the measurement atmosphere.
Additionally, to validate the accuracy of this approach, especially in correcting for the effects of gravitational
acceleration on surface tension measurements with EML, we plan to compare surface tension data of liquid
platinum — which is unaffected by oxygen — measured using the EML on Earth with those obtained in theELF. Notably, previous measurements of the surface tension of liquid platinum on Earth, utilizing both EML
and ESL techniques, have demonstrated comparatively good agreement, thereby implying the reliability ofthese methods5).

Figure 1 Surface tension of liquid zirconium as a function of oxygen content at around 1900 K measured
using EML2) with comparative literature data from Allen3) and Ohishi et al4).

Acknowledgements
This research was partially funded by the Japan Society for the Promotion of Science (JSPS) KAKENHI
under Grant No. P20H02453, and by the Grant-in-Aid for Front Loading Research, which is supported by theAdvisory Committee for Space Utilization Research in the Institute of Space and Astronautical Science, Japan
Aerospace Exploration Agency (ISAS/JAXA).
References
1)

2)

3)

T. Ishikawa, C. Koyama, H. Oda, H. Saruwatari, and P-F. Paradis: Status of the Electrostatic Levitation Furnace inthe ISS -Surface Tension and Viscosity Measurements. Int. J. Microgravity Sci. Appl., 39 (2022) 390101, DOI:
10.15011/jasma.39.390101.
Y. Seimiya, R. Shinazawa, T. Katsumi, and S. Ozawa,: Surface Tension of Liquid Zirconium Considering Effect ofOxygen Dissolution from Measurement Atmosphere. Int. J. Microgravity Sci. Appl., 41 (2024) 410102, DOI:
10.15011/jasma.41.410102.
B. C. Allen: The surface tension of liquid transition metals at their melting points. Trans. AIME., 227 (1963) 1175
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Y. Ohishi, T. Kondo, T. Ishikawa, J. Okada, Y. Watanabe, H. Muta, K. Kurosaki, and S. Yamanaka: Thermophysical
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