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At the moment, two synthesis mechanisms have been suggested: the base growth mechanism and the tip growth mechanisms [ 19 , 25 — 26 ]. The linear BNNTs are obtained with the base growth mechanism [ 19 ]. In the tip growth mechanism, the catalyst is located on the tip of growing BNNTs [ 26 ]. Thus, the BNNTs are generally formed in bamboo-like structures. To the best of our knowledge, unprocessed colemanite has not previously been used as a precursor for the BNNT synthesis.

In this study, we demonstrate the synthesis of BNNTs from unprocessed colemanite. The reaction parameters such as the amount of colemanite, the type and amount of catalyst, the reaction temperature and duration were studied and optimized. Finally, the formation mechanism of BNNTs was elucidated. With this method, randomly oriented BNNTs with 10—30 nm size ranges in high yields can be easily synthesized directly from colemanite. In recent studies, particularly amorphous boron has been preferred as the precursor boron compound to synthesize high-yield BNNTs [ 5 , 27 — 28 ]. Colemanite as the most important of boron ores can be used for the synthesis of BNNTs since it contains B 2 O 3 in its structure.

In this study, the influence of temperature, type of catalyst, and reaction time on the BNNT yield and the structure were investigated. The most important factor in BNNT synthesis is the proper selection of the catalyst.

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This may be due to the catalysis of Mg or other metal oxide impurities in the colemanite sample. For the initiation of the synthesis reaction the catalyst in the reaction mixture must be as close as possible to the reaction mixture surface to interact with NH 3 gas. Since these metal oxides stay buried under the colemanite due to the density difference, they do not effectively interact with NH 3 gas. Therefore, no BNNT formation was observed.

However, when iron oxides were used as catalysts, the formation of BNNTs was dramatically improved.


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When Fe 3 O 4 was used, the diameter of the BNNTs was dramatically increased and zigzag structures with shorter length were observed as seen in Fig. This clearly indicates that the mechanisms of the two different iron oxide catalysts, Fe 3 O 4 or Fe 2 O 3 , are rather different. Only the use of Fe 2 O 3 resulted in high yield BNNTs, so that the reaction conditions in the presence of this catalyst were further optimized.

Next, the reaction time on the yield and the size composition of BNNTs were investigated. The reaction was set to 30, 60, and min. No BNNTs synthesis was observed at 30 min. As the reaction time increased from 30 to , the formation of BNNTs was more complete. The BNNTs formed at 60 min were shorter.

When the time was increased to min, a high yield of the BNNTs was observed. Further increase of the time to min did not alter the yield. It was found that when the reaction time was increased, the length of the formed BNNTs was increased. We concluded that the ideal reaction time for high yield BNNT formation was min. With a ratio of at a 30 min, and b 60 min. At min with a ratio of c d and e Some BN structures were clustered when the ratio was data not shown. Finally, an ratio of the catalyst caused the formation of BNNTs with a large diameter ,which were thick and had a zigzag structure Fig.

The SEM images presented in Fig.

B-C-N Nanotubes and Related Nanostructures : Yoke Khin Yap :

Our observations suggest that the BNNT synthesis consists of the clustered structures composed of boron nitride BN and iron atoms. The initial BN-Fe complex shown with arrows in Fig. Based on our observations we propose a similar growth mechanism for the formation of BNNTs from colemanite.

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Another important point in the synthesis of BNNTs is the reaction termination temperature i. As seen in the TEM images in Fig. We propose that the BNNTs are synthesized according to the base growth mechanism. In this mechanism, metallic Fe in a certain size forms from the Fe 2 O 3 catalyst. This initial step of metallic catalyst formation is the most important step in the synthesis of BNNTs. When a higher amount of Fe 2 O 3 is used at the beginning of the synthesis, the formed metallic Fe can form aggregates. The second step is the formation of the BN initial complex on the surface of already formed Fe metallic catalyst.

This initial complex including metallic Fe catalyst is shown with arrows in Fig. When B and N are super-saturated, the BN core begins to grow on the surface of the metallic Fe surface. For instance, Yu et al.

B-C-N Nanotubes and Related Nanostructures

Zhong et al. Okan et al. In another study, Singhal et al. Wang et al.


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  • The BNNT synthesis and growth mechanism depend on the reaction parameters such as substrate, catalyst and temperature but the mechanism has not been elucidated yet. According to the nucleation theory, the formation of a core depends on surface energy, supersaturation, vapor pressure, temperature and binding energy [ 23 — 24 ].

    Nanoscale Photonics and Optoelectronics Lecture Notes in Nanoscale Science and Technology

    To synthesize unique, high yield and large scale BNNTs, the synthesis mechanism has to be clearly understood. At the moment, two synthesis mechanisms have been suggested: the base growth mechanism and the tip growth mechanisms [ 19 , 25 — 26 ]. The linear BNNTs are obtained with the base growth mechanism [ 19 ]. In the tip growth mechanism, the catalyst is located on the tip of growing BNNTs [ 26 ].

    Thus, the BNNTs are generally formed in bamboo-like structures. To the best of our knowledge, unprocessed colemanite has not previously been used as a precursor for the BNNT synthesis. In this study, we demonstrate the synthesis of BNNTs from unprocessed colemanite. The reaction parameters such as the amount of colemanite, the type and amount of catalyst, the reaction temperature and duration were studied and optimized. Finally, the formation mechanism of BNNTs was elucidated. With this method, randomly oriented BNNTs with 10—30 nm size ranges in high yields can be easily synthesized directly from colemanite.

    In recent studies, particularly amorphous boron has been preferred as the precursor boron compound to synthesize high-yield BNNTs [ 5 , 27 — 28 ]. Colemanite as the most important of boron ores can be used for the synthesis of BNNTs since it contains B 2 O 3 in its structure. In this study, the influence of temperature, type of catalyst, and reaction time on the BNNT yield and the structure were investigated.

    The most important factor in BNNT synthesis is the proper selection of the catalyst.

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    This may be due to the catalysis of Mg or other metal oxide impurities in the colemanite sample. For the initiation of the synthesis reaction the catalyst in the reaction mixture must be as close as possible to the reaction mixture surface to interact with NH 3 gas. Since these metal oxides stay buried under the colemanite due to the density difference, they do not effectively interact with NH 3 gas.