Casey Smith

Advisor: Prof. Will Gutekunst

will defend a doctoral thesis entitled,

Processing and Properties of High-Performance BNNT Fibers and Other Macrostructures

On

Wednesday, December 4 at 1:00 pm

Closed Defense

Committee

            Prof. Will Gutekunst – School of Chemistry and Biochemistry (advisor)

            Prof. Jud Ready – School of Materials Science and Engineering

            Prof. John Reynolds – School of Chemistry and Biochemistry

      Prof. Jason Azoulay – School of Chemistry and Biochemistry

            Dr. Amjad Almansour – NASA Glenn Research Center

Abstract

In the last two decades, key innovations have been made in the synthesis and applications for boron nitride nanotubes (BNNTs). BNNTs are electrical insulators with a band gap of 5-6 eV, but also possess resistance to significant oxidation up to 900 °C, low-κ dielectric properties, high thermal conductivity, and high strength. This combination of properties makes BNNTs good candidates for applications requiring one or more of these attributes. Formation of BNNT fibers has been reported in the literature by two methods: wet spinning from BNNTs in a superacid solution and direct assembly from the as-grown BNNT material upon synthesis in the reactor. The wet spinning method to produce BNNT fiber involves a process of forming a liquid crystalline phase of BNNT in a superacid and produces moderately aligned BNNT fibers. To date, these literature-reported fibers have a tensile strength of 10-16 MPa and a modulus of 0.5-1.5 GPa. A new method to process BNNT fibers with a high degree of alignment, high modulus, and good tensile strength is presented in this thesis. The processing-structure-property relationship for these BNNT fibers is examined. Also, new state-of-the-art tensile properties are achieved for BNNT fibers: tensile modulus of 396 GPa and strength of 500 MPa. Additionally, a new method is reported to disperse and process BNNTs using alcohols and glycerol. BNNT films from alcohol dispersions show thermal conductivity as high as 44 W/mK, dielectric breakdown strengths up to 160 kV/mm, and dielectric constants of 2.0-7.0 at 1-100 MHz. Factorial experimental design is used to study the impact of processing parameters on these properties. This work represents significant progress towards producing BNNT fibers and films with improved structure and properties.