Boron nitride nanotubes filled with zirconium oxide nanorods
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Boron nitride nanotubes (BNNTs) filled with zirconium oxide (ZrO2) nanorods were synthesized by the improved solid-gas multiphase reaction method. The structure of ZrO2 nanorods was monoclinic single crystal or multi-twin crystal. The diameters of ZrO2 nanorods varied from 20 to 40 nm. The inner diameters of BNNTs were similar to those of corresponding ZrO2 nanorods. The BNNTs exhibited open end, closed end, or an end connected with a short tube grown from the tip of the ZrO2 nanorod. No preferred orientation was observed for the growth of ZrO2 nanorods. The discovery of carbon nanotubes1 has stimulated a great interest in the study of filled carbon nanotubes (CNTs). Many metals or metal carbides and oxides have been encapsulated in CNTs by various methods, e.g., heating the metals with open-ended nanotubes,2–4 chemical treatment,5–7 arc discharge,8–10 catalyzed hydrocarbon pyrolysis,11–13 and electrochemical techniques.14–16 The introduction of different materials into multiwalled carbon nanotubes may significantly alter their conducting, electronic, and mechanical properties, arising from the internal framework within the structure. Because of the uniform conducting property17 and relatively high thermal and chemical stability of hexagonal boron nitride (h-BN) and BN nanotubes, it has been expected that the filled BN nanotubes would have more applications in nanoscaled electronic devices and preparation of nanostructured ceramic materials. Recently, Zhang et al. have reported the synthesis of coaxial nanocable based on (BN)xCy nanotubes filled with coaxial SiC and SiO2 cores by the laser ablation method.18 Han et al. have successfully synthesized (BN)xCy or BN nanotubes filled with BmC19 and SinC20 cores by CNT-confined reaction and substitution reaction. However, both methods involved carbon or carbon nanotubes and resulted in (BN)xCy nanotubes or carbide cores. Pure BN nanotubes filled with metals or metal oxides have not been synthesized so far. In this work, we report synthesis of multiwalled BN nanotubes filled with zirconium oxide (ZrO2) nanorods by the improved solid-gas multiphase reaction method. Their structure and morphology were studied by transmission electron microscopy (TEM). Zirconium diboride (ZrB2) powder in an aluminum oxide (Al2O3) crucible was placed in the center of a long quartz reactor. Solid NH4Cl in the front section of the reactor was used as reactive nitrogen source. Nitrogen a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 17, No. 11, Nov 2002
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gas (N2) was used as the carrier. The reactor was heated up to 1200 °C. A gaseous mixture of nitrogen and ammonia from decomposed NH4Cl flowed over the crucible. After the reaction, the white powder that formed on the up surface of ZrB2 powder was collected for TEM observation. The TEM specimen was prepared by ultrasonic dispersion of the powder in ethanol and deposited on a standard, holey-carbon-film-covered copper grid. TEM and high-resolution TEM
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