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Sang-hyon Chu

Publications and source records attributed to Sang-hyon Chu.

14 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2022

Liquid crystals of neat boron nitride nanotubes and their assembly into ordered macroscopic materials

Boron nitride nanotubes (BNNTs) have attracted attention for their predicted extraordinary properties; yet, challenges in synthesis and processing have stifled progress on macroscopic materials. Recent advances have led to the production of highly pure BNNTs. Here we report that neat BNNTs dissolve in chlorosulfonic acid (CSA) and form birefringent liquid crystal domains at concentrations above 170 ppmw. These tactoidal domains merge into millimeter- sized regions upon light sonication in capillaries. Cryogenic electron microscopy directly shows nematic alignment of BNNTs in solution. BNNT liquid crystals can be processed into aligned films and extruded into neat BNNT fibers. This study of nematic liquid crystals of BNNTs demonstrates their ability to form macroscopic materials to be used in high- performance applications.

Cedric J. Simonsen Ginestra↗
NASA NTRS2019

Exceptional Thermal Properties of Polymer-Derived Ceramic Composites Reinforced with High Volume Fractions of Boron Nitride Nanotube at Elevated Temperature

We report for the first time the synthesis of boron nitride nanotube (BNNT) reinforced ceramic composites using the polymer derived ceramic (PDC) processing route. The nanocomposites had a BNNT loading of up to 35.4 vol.%. TGA results showed that the nanocomposites have good thermal stability up to 900 oC in air. BNNTs in the nanocomposites survived in an oxidizing environment up to 900 oC, revealing that the nanocomposites can be used for high temperature applications. Thermal conductivity of PDC reinforced with 35.4 vol.% BNNT was measured as 4.123 W/(m·K) at room temperature, which is a 2100 % increase compared to that of pristine PDC. The thermal conductivity value increases with the increase of BNNT content. A thermal conductivity percolation phenomenon appeared when the BNNT content increased to 36±5 vol.%. The results of this study showed that BNNTs could effectively improve the thermal conductivity of PDC materials. BNNT reinforced PDC could be used as thermal structural materials in a harsh environment at the temperature up to 900 deg C.

Yujun Jia↗
NASA NTRSDate not supplied

Multifunctional Surface Treatment for Self-Sterilization and CO2 Sequestration for Sustainable Space Exploration

A long-term human space presence is dependent on maintaining a safe living environment. Disinfecting surfaces is essential to protecting astronauts from potential pathogens, as well as structural components of the habitat from damaging biofilms. Developing a surface coating that utilizes readily available light has the potential to provide sterilization with additional functionality. Titanium dioxide (TiO2) is a commonly used photocatalyst owing to its efficiency, economic feasibility, and safety to humans. TiO2 photocatalyst modified with other metals such as copper or iron could allow for self-sterilization, photocatalytic memory, and photoreduction of carbon dioxide (CO2) to fuels on Mars. Sustainable design of the photocatalyst should account for the resources available, specifically within the Martian and Lunar regolith. This project reviews the current technologies to design a TiO2 photocatalyst which can be incorporated into a space habitat’s inner lining.

Human Space Exploration↗