Papers by Keyword: Boron Nitride

Abstract: Boron nitride (BN) coatings were deposited on carbon substrates by low pressure chemical vapor deposition (LPCVD) in a large temperature range of 650~1200 °C, employing BCl3-NH3-H2 reaction system. The effects of depositing temperature on the yield, control step of deposition progress (deposition mechanism), microstructure, and crystallization degree of BN coating were investigated. Results show that BN deposition rate first increases and then decreases as the rising temperature and the maximum deposition rate occurs at 900~1000 °C. By the determination of the Arrenius relationship, there are three temperature regions with different active energies and controlled by different deposition mechanisms, i.e. chemical reaction, mass transport and depletion of reactants. Through the surface morphology observation by scanning electron microscopy (SEM), chemical composition analyses by energy dispersion spectroscopy (EDS) and crystallization degree and grain size comparison by Raman spectroscopy, it can be drawn that interphase-used BN is suitable to be deposited at 1000 °C.

Abstract: We reported on a convenient route to synthesize rhombohedra boron nitride (r-BN) micro-rod using urea (CO(NH₂)₂) and sodium borohydride (NaBH₄) through thermal treatment at 1300 °C. The structure, morphology, and chemical composition of the obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). In order to determine the phase composition and abundance of the as-synthsized simples, Rietveld refinement has been performed to analyze the XRD data using the Rietan-2000 program. The results show that the abundance of r-BN is about 90.6 wt % and h-BN is 9.4 wt % deduced from Reitveld refinement.

Abstract: In this paper, we report the structural and optical properties of bamboo-like silicon-doped boron nitride nanotubes. The morphologies and structures of the nanotubes were characterized using electron microscopy and FTIR spectroscopy. Three strong broad peaks centered at 1.76ev, 2.20ev, 2.40ev were observed from the room-temperature PL spectrum of the nanotubes. The spectrum suggested the existence of multifold energy levels within the band gap.

Abstract: This paper reports on two examples of biomedical applications of ceramic nanoparticles. Thanks to their physical and chemical inertia, barium titanate nanoparticles and boron nitride nanotubes have been proved to have an optimal in vitro biocompatibility, even at high concentrations. Barium titanate nanoparticles-doxorubicin composites are successfully internalized by cancer cells, and allow for a considerable enhancement of drug up-take. Conversely, boron nitride nanotubes are explored as “nanotransducers”, thanks to their excellent piezoelectric properties. These two examples encourage further investigations and applications in biology and medicine of ceramic nanomaterials, that exhibit interesting advantages respect to traditional materials.

Abstract: A new kind of thermally conductive composites reinforced by glass fibers with boron nitride (BN) as thermally conductive filler was prepared in heat press molding. Thermal conductivity of the composites was found to increase with increasing in filler content. But impact strength and flexural strength reach the top point, 385.05KJ/m² and 912.6481MPa, with content of 50wt% and 20wt% respectively. The thermal conductivity of 0.8385 W/mK was obtained at 50wt% filler content. Experimental dates show that mixed matrix of epoxy (EP) and polyimide (PI) displays high thermal stability and can improve thermal stability compared to pure epoxy obviously at 50wt% PI content. Additionally, the obtained composites possess high surface resistivity and volume resistivity, which are suitable for substrate materials.

Abstract: The barium-excessive BaTiO₃ ceramics with BN addition for laminated positive temperature coefficient (PTC)thermistors are fabricated. The tape casting technique and reduction/reoxidation process are employed into the fabricating procedure. The influences of BN additive on ceramic characteristics are discussed. The addition over 5% leads to rectangular and abnormal large grains. The 5% BN-doped ceramics shows a resistivity of 233 Ω•cm and PTC jump of 3.4 orders of magnitude. The charge carrier density in grain bulk and acceptor state density at grain boundaries are evaluated. The correlation of BN doping amount with room temperature resistivity, PTC jump, reoxidation effect as well as charge carrier and acceptor state density are investigated.

Abstract: In this study, aluminum nitride, boron nitride, copper, aluminum, with aluminum extruded heat sink as a cooling way of thermoelectric chip. Heat sink temperature change observed and measured the thermoelectric chip output voltage and current. The results showed that with the aluminum extrusion heat sink will increase the efficiency of thermoelectric chip. Copper + aluminum extrusion heat sink, the average electric power increased 173.93%, while the aluminum + aluminum extruded heat sink mean power increased 212.25 %, while the AlN + aluminum extrusion heat sink fins as mean power increased 197.5 %, And the BN + aluminum extrusion heat sink as a heat sink, the average electric power increased 266.17 %.

Abstract: In contemporary electronic technology era, the volume of electronic equipment and printed circuit board reduced so dramatically that the requirements of heat dissipation and insulation increase thereafter. In this research, γ-aminopropyltriethoxysilane (KH550)-treated boron nitride (BN) powder was used as a filler to modify epoxy composites. Effects of the BN particle size and concentration on the thermal conductivity of composites were investigated. SEM image showed the treated BN filler dispersed well in the composite matrix. Moreover, the thermal conductivity was enhanced as the BN concentration was increased. Similar phenomenon was also observed when the filler particle size was reduced. Results indicated that with increasing amount of BN addition, the composites’ thermal conductivity showed a nearly linear increase. When the mass fraction of BN was 30% and its particle size was 220 nm, the thermal conductivity reached 3.4 W/(m•k), which was 17 times as high as that of pure EP resin.

Abstract: The oxidation kinetics of SiC fiber-reinforced SiC matrix composites with a BN interphase (SiC/BN/SiC) and the constituent fibers was characterized by thermogravimetric analysis and microstructural characterization at temperatures (816-1538°C) and oxygen partial pressures (0.1% to 5% O₂) relevant to the hypersonic flight and re-entry environments. TGA of the SiC fibers showed that oxidation of the thin BN surface layer led to initially rapid oxidation kinetics and formation of a relatively thick silica scale at very short times under most test conditions. At longer times the fiber oxidation kinetics were representative of silica formation on pure SiC. Oxidation of the composites was conducted on coupons with the SiC seal coat removed on one edge to simulate damage to the composite, allowing ingress of oxygen to the fiber tows. Microscopy was conducted to determine the distance of oxygen ingress into the coupon. At the lower temperatures and oxygen partial pressures the exposed edge did not seal off by silica formation, yet the BN interphase areas were only minimally oxidized. At the intermediate temperatures silica formed at the exposed surface limiting further oxidation of the exposed fibers and BN interphase areas. Finally at the highest temperature and lowest oxygen partial pressure, active oxidation of SiC occurred for both the fibers and coupons resulting in irregular material attack. Implications for use of SiC/BN/SiC materials for hypersonic vehicle thermal protection systems are summarized.

Abstract: Four types of boron nitride (BN) nanotubes are selectively synthesized by annealing porous precursor in flowing NH3 and NH3/H2 atmosphere at temperature ranging from 1000 to 1200°C in a vertical furnace. The as-synthesized BN nanotubes, including cylinder, wave, bamboo and bubble-chain, are characterized by scanning and transmission electron microscopy. Selectivity of BN nanotubes is estimated as approximately 80 to 95%. The porous precursor B31Fe17(MgO)27 prepared by self-propagation high-temperature synthesis (SHS) method plays a key role in controllable synthesis of the as-grown BN nanotubes. The chemical reaction and annealing mechanism are also discussed.