Low-Temperature Catalytic Synthesis of Boron Nitride Nanotubes by Alkali Metal Ferrites
Mustafa Baysal
MAT, PhD Dissertation, 2018
Thesis Jury
Prof. Dr. Yuda Yürüm (Thesis Advisor), Prof. Dr. Melih Papila, Assoc. Prof. Selmiye Alkan Gürsel, Prof. Dr. Fatma Yüksel, Prof. Dr. Emin Arca
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Date & Time: 3th January, 2018 – 10.00 AM
Place: Fens L-065
Keywords : BNNT, Catalytic CVD, Thermal CVD, Catalyst, KFeO2, Alkali Metal Ferrites, Nanostructure growth
Abstract
Chemical Vapor Deposition (CVD) is an advantageous technique that allows synthesis of boron nitride nanotubes (BNNT) of high purity in large volumes. The product quality and energy efficiency of the CVD processes are mainly governed by appropriate choice of catalyst. In this study, we achieved BNNT growth by alkali metal ferrites with thermal CVD (TCVD) method. Three steps were applied through the whole research. i) Before proposed new catalyst for BNNT synthesis, conventional catalyst system (MgO and Fe2O3) was utilized for BNNT production between 1000 oC and 1200 oC with TCVD growth vapor trap (GVT) approach. Moreover, CVD system parameters were investigated. The temperature was found to be the most crucial factor to BNNTs to form. ii) To reduce BNNT synthesis temperature, we report the use of a novel alkali based catalyst, KFeO2, to trigger the BNNT formation by TCVD. When KFeO2 was replaced with the conventional catalyst, BNNT synthesis temperature was reduced to 750 oC – 800 oC, which is significantly lower than the typical temperatures of TCVD reported in the literature (1100 oC -1300 oC). Growth mechanism and effect of alkali metal were investigated. iii) To support the idea of alkali assisted BNNT synthesis, other alkali metal ferrites from Cs to Li were used in the BNNT synthesis with TCVD. It was proved that without alkali metal catalyst in the growth vapor BNNT synthesis was not possible at temperatures below 1000 oC. Moreover, synthesis temperature and final morphology changed depending on the alkali metal used as in ferrite form.