Spectral properties of spherical boron nitride prepared using carbon spheres as template

Spherical boron nitride nanoparticles have been successfully fabricated by temperature-controlled pyrolysis procedure in a N₂ atmosphere, using boron acid and urea as the precursors. The carbon spheres were prepared from glucose (C₆H₁₂O₆) by a hydrothermal method as a template to be used. Comprehensive scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier infrared spectrum (IR) characterizations all confirm that the obtained products are spherical boron nitride. The amount of C₆H₁₂O₆ and reaction time were found to affect the morphology and structure of the as-prepared products. The average diameter of the spherical boron nitride nanoparticles synthesized with the addition of C₆H₁₂O₆ is about 0.3–1 µm. The spherical boron nitride has a high surface area of 176.78 m²g⁻¹ and ~3.5 nm pore size. The as-synthesized nanospheres also exhibit strong photoluminescence (PL) bands at 436, 454, 486, and 616 nm under 312 nm excitation, indicating that they could have potential application in novel optical devices.     

Template synthesis of large pore ordered mesoporous carbon

Nanocast carbon (NCC-1) with large pores and ordered structure was synthesized via a nanocasting process using aluminum-containing SBA-15 as template and furfuryl alcohol (FA) as carbon precursor. This carbon has several interesting features, such as two steps with distinguished hystereses in the nitrogen sorption isotherm, high surface area of 2000 m²/g and large pore volumes of 3.0 cm³/g. It was found that the key factors in the synthesis of such carbons are the aging temperature of the SBA-15 template, the concentration of furfuryl alcohol (dissolved in trimethylbenzene), and the carbonization temperature. The optimal conditions for materials with high surface area and pore volumes are SBA-15 starting materials aged at 140 °C, 25 vol% of FA solution and 850–1100 °C carbonization temperatures. Moreover, it has been demonstrated that such nanocast carbon can be synthesized in a more facile way than previously reported. Purely siliceous SBA-15 without the need of Al³⁺-incorporation can be directly used as template. In this case, the polymerization catalyst—oxalic acid and FA were simultaneously introduced into the pore space of SBA-15.     

Urchin-like boron nitride hierarchical structure assembled by nanotubes-nanosheets for effective removal of heavy metal ions

Water pollution has become a serious global issue owing to the large amounts of contaminants generated from industrial and agricultural development. Recently, various boron nitride-based micro/nano-materials have exhibited efficient sorption capacity for contaminants from water. Herein, novel urchin-like boron nitride hierarchical structure assembled by free-growing boron nitride nanotubes and crapy boron nitride nanosheets is firstly fabricated via a sample two-step approach, including the synthesis of analogous "core-shell" structured boron-containing precursor and thermal catalytic chemical vapor deposition. A combined growth mechanism of vapor-liquid-solid and vapor-solid is proposed to control the formation of BN hierarchical structure. The unique structure exhibits superior removal capacity of 115.07?mg?g^?1 and 92.85?mg?g^?1 for Pb²⁺ and Cu²⁺ in water solution, respectively. The excellent adsorption performance of the product mainly derives from the vast lattice imperfections, the high-density edge active sites, the expanded interplanar spacing, as well as the unique structural characteristics. They are beneficial for structural stability and enough space for accommodating the adsorbed heavy metal ions. These results indicate that the urchin-like boron nitride hierarchical structure is a promising adsorption material for water treatment.     

Anchoring carbon nanotubes to boron nitride microrods for enhancing the thermal conductivity of polystyrene

The development of high-performance thermally conductive fillers is crucial for the thermal management of polymer-based composites. Herein, a facile precursor pyrolysis strategy was adopted to fabricate boron nitride@multiwalled carbon nanotubes (BN@MWCNTs) fillers, wherein uniformly distributed MWCNTs were firmly anchored on BN microrods. Benefiting from the unique structure, the BN@MWCNTs act as fillers in the design of polystyrene (PS)/BN@MWCNTs composites via in situ polymerization. As a result, a 7.74-fold higher thermal conductivity (TC) (9.55 W/m·K) was achieved for the 10 wt% BN@MWCNTs, as compared to native PS/BN/MWCNTs prepared by the conventional melt-mixing method. More importantly, the PS/BN@MWCNTs composites exhibited satisfactory electrical insulation owing to the isolation effect of BN. Overall, this work provides a promising frontier for the design of polymer-based thermally conducting materials for applications in thermal management.     

The influence of carbon source on the wall structure of ordered mesoporous carbons

A series of ordered mesoporous carbons (OMCs) have been synthesized by filling the pores of siliceous SBA-15 hard template with various carbon precursors including sucrose, furfuryl alcohol, naphthalene and anthracene, followed by carbonization and silica dissolution. The carbon replicas have been characterized by powder XRD, TEM and N₂ adsorption techniques. Their electrochemical performance used as electric double-layer capacitors (EDLCs) were also conducted with cyclic voltammetry and charge-discharge cycling tests. The results show that highly ordered 2D hexagonal mesostructures were replicated by using all these four carbon sources under the optimal operation conditions. Physical properties such as mesoscopic ordering, surface areas, pore volumes, graphitic degrees, and functional groups are related to the precursors, but pore sizes are shown minor relationship with them. The sources, which display high yields to carbons, for example, furfuryl alcohol and anthracene are favorable to construct highly ordered mesostructures even at high temperatures (1300 °C). OMCs prepared from non-graphitizable sources such as sucrose and furfuryl alcohol display amorphous pore walls, and large surface areas and pore volumes. The functional groups in the precursors like sucrose and furfuryl alcohol can be preserved on carbon surfaces after the carbonization at low temperatures but would be removed at high temperatures. The graphitizable precursors with nearly parallel blocks and weak cross-linkage between them like anthracene are suitable for deriving the OMCs with graphitic walls. Therefore, the OMCs originated from sucrose and furfuryl alcohol behave the highest capacitances at a carbonization of 700 °C among the four carbons due to the high surface areas and plenty of functional groups, and a declination at high temperatures possibly attribute to the depletion of functional groups. Anthracene derived OMCs has the lowest capacitance carbonized at 700 °C, and a steady enhancement when heated at high temperatures, which is attributed to the graphitization. The OMCs derived from naphthalene have the stable properties such as relatively high surface areas, few electroactive groups and limited graphitizable properties, and in turn medium but almost constant capacitances.     

Combustion synthesis of hexagonal boron nitride nanoplates with high aspect ratio

High crystalline hexagonal boron nitride nanoplates with high aspect ratio of ~400 have been synthesized by combustion synthesis method through magnesiothermic reduction reaction between B₂O₃ and Mg in N₂ pressure. The synthesized hexagonal boron nitride nanoplates were about 50 nm in thickness and larger than 20 μm in lateral size. The six-fold symmetric spots electron diffraction pattern of transmission electron microscopy shows that the nanoplate is well crystallized. Hexagonal boron nitride nanoplates grow via an Oswald ripening process and have larger lateral size when it was prepared with larger magnesium particles. High temperature liquid magnesium provides an important environment for the growth and crystallization of boron nitride. This work provides an effective way to achieve low-cost and large-scale preparation of high-quality boron nitride nanoplates.     

Scalable production of boron nitride nanosheets in ionic liquids by shear-assisted thermal treatment

Due to their intriguing properties, boron nitride nanosheets (BNNSs) with large lateral size and high crystallinity have great promise for many applications. However, the quantitative exfoliation of hexagonal boron nitride (h-BN) into good quality BNNSs still remains a key challenge. Herein, we report a scalable method to exfoliate BNNSs in ionic liquids (ILs) via shear-assisted thermal treatment. Few-layer BNNSs with well-preserved structural integrity are successfully prepared by this method. The synergistic effects of strong physical adsorption and intercalation of IL molecules, chemical interactions between hydrogen fluoride (HF) and h-BN, activation energy provided by heat treatment, and shear forces generated by repetitive stirring effect contribute to the exfoliation of BNNSs.     

Silica, carbon and boron nitride monoliths with hierarchical porosity prepared by spark plasma sintering process

Silica SBA-15, carbon CMK-3, boron nitride (BN), the latter synthesized from the first two compounds as templates, are mesoporous materials in the form of powders. They have a high specific surface area and an important mesoporous volume. The porosity is organized with the hexagonal symmetric space group p6mm. For selected applications, it could be interesting to preserve these characteristics with materials in a well-defined shape at a macroscopic scale (few millimeters to centimeter). Spark plasma sintering (SPS) is a well-known technique which allows to prepare monoliths with relatively mild conditions. The SPS technique has been used on these mesoporous powders without charge or with a uniaxial charge and at temperatures of 600 °C, 800 °C for silica, 1100 °C, 1300 °C for carbon and 1600 °C, 1700 °C for boron nitride during 1–5 min. The nitrogen adsorption/desorption isotherms reveal that the obtained monoliths present high specific surface area (300–500 m²/g) and important mesoporous volume. The coexistence of interconnected mesoporosity and macroporosity (with volume’s close value) was observed by SEM and TEM, while the XRD and TEM characterization show that the mesoporosity organization is partially preserved.     

A mesoporous composite template composed of self-assembled silica nanotube and multi-walled carbon nanotube

The multi-walled carbon nanotubes (MWNTs) were successfully embedded in the hexagonally-arranged silica tubular structure by the self-organization of two surfactant systems providing a MWNT-incorporated silica nancomposite template. The anionic surfactant (sodium dodecyl sulfate, SDS) adsorbed on the MWNT surfaces allowed the MWNTs to interact with the outer surface of the self-assembled non-ionic surfactant, poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer. Due to the hydrophilic–hydrophilic interaction between the PEO blocks and the sulfate group of SDS, the MWNTs were most possibly surrounded by the outer wall of the SBA-15 hexagonal tubes aligning in the longitudinal and transverse directions to the silica tube direction. According to the interplanar distances, electron microscopy images, and N₂ adsorption–desorption isotherms, the synthesized SBA-15/MWNT system exhibited the structural integrity of silica-tube arrangement and structural characteristics of MWNTs in terms of BET surface area and micropore volume. This work made it clear that the developed SBA-15/MWNT template could be used to synthesize various MWNT-incorporated 2-D replicas.     

Formation of thin boron nitride coating on multiwall carbon nanotube surfaces

Thin boron nitride films were deposited onto outer surfaces of multiwall carbon nanotubes (MWCNTs) by dip coating, which involves infiltration by boric acid solutions and subsequent nitridation of the boron oxide in ammonia flow at 1050 °C. The overall composition of the samples was determined by electron energy loss (EELS) and X-ray photoelectron spectroscopy (XPS), the surface composition and chemical structure of the BN coatings by XPS, the morphology of the BN/MWCNT composites by scanning and transmission electron microscopy (SEM, TEM), and the resistance against oxidation at elevated temperatures by thermal analysis (TGA). It was proved that single and multilayer BN coverage were achieved at the applied experimental conditions, and the coated samples showed significantly increased oxidation resistance compared to the uncoated MWCNTs.     

Fabrication and mechanical properties of boron nitride nanotube reinforced silicon nitride ceramics

In this study, silicon nitride (Si₃N₄) ceramics added with and without boron nitride nanotubes (BNNTs) were fabricated by hot-pressing method. The influence of sintering temperature and BNNTs content on the microstructures and mechanical properties of Si₃N₄ ceramics were investigated. It was found that both flexural strength and fracture toughness of Si₃N₄ were improved when sintering temperature increases. Moreover, α-Si₃N₄ phase could transform into β-Si₃N₄ phase completely when sintering temperature rises to 1800 °C and above. BNNTs can enhance the fracture toughness of Si₃N₄ dramatically, which increases from 7.2 MPa m^1/2 (no BNNTs) to 10.4 MPa m^1/2 (0.8 wt% BNNTs). However, excessive addition of BNNTs would reduce the fracture toughness of Si₃N₄. Meanwhile, the flexural strength and relative density of Si₃N₄ decreased slightly when BNNTs were added. The related toughening mechanism was also discussed.     

添加物对氮化硼材料性能的影响

研究了引入锆英石和氧化铝等添加物的热压氮化硼材料的抗氧化性、热震稳定性及力学性能。结果表明，向氮化硼中引入锆英石和氧化铝后，虽然未能按预期设想生成莫来石，但却对提高氮化硼材料的抗氧化性、热震稳定性及力学性能有利。     

Surface-diffusion mechanism for synthesis of substrate-free and catalyst-free boron nitride nanosheets

This study presents an innovative surface-diffusion mechanism for the growth of substrate-free and catalyst-free boron nitride nanosheets (BNNSs) by annealing an ammonium borate hydroxide hydrate precursor in a NH₃ chemical vapor deposition system. At elevated temperatures, part of NH₄B₅O₈ slowly decomposes and forms B₂O₃, and flowing NH₃ gradually diffuses to the B₂O₃ surface to form vertically aligned BNNSs. The lateral dimension and crystallinity of the BNNSs increase, while their thickness decreases with the continuous surface-diffusion reaction. The residual NH₄B₅O₈ and B₂O₃ absorbs moisture in the air to constitute NH₄B₅O₈·4H₂O and H₃BO₃ substrates. With increasing annealing temperature and soaking time (at 1400 °C for 7 h), all NH₄B₅O₈ decomposes and the surface-diffusion reaction between B₂O₃ and NH₃ completely occurs, forming substrate-free BNNSs with a lateral dimension of 1 μm and a thickness of 10 nm. This reliable approach for synthesizing BNNSs paves the way for future applications in advanced ceramic composites.     

Effect of activation on boron nitride coating on carbon fiber

Boron nitride (BN) thin coating has been formed on the surface of chemically activated polyacrylonitrile (PAN) carbon fibers by dip coating method. The chemical activation of PAN fibers was carried out by two different chemicals, i.e. nitric acid (HNO₃) and silver nitrate (AgNO₃) solution. The chemical activation changes the surface properties, e.g. surface area and surface microstructure of the carbon fibers. These surface modifications ultimately influence properties of boron nitride coating on carbon fibers. The boron nitride coating on carbon fibers showed better crystallinity, strength and oxidation resistance when carbon fibers were activated by HNO₃. This improvement in strength and oxidation resistance is attributed to better crystallinity of boron nitride coating on HNO₃ activated PAN fibers.     

Synthesis of mesoporous alumina by using a cost-effective template

A salt of stearic acid, i.e., magnesium stearate [(C₁₇H₃₅COO)₂Mg], can be used as a chemical template for the formation of mesoporous alumina, and is a less expensive reagent than stearic acid. Mesoporous alumina prepared using this cost-effective surfactant shows similar pore properties with respect to pore size (3.5 nm) and surface area (above 300 m²Vg) to that prepared using stearic acid. In addition, textural porosity, arising from non-crystalline intraaggregate voids and spaces, was effectively removed by the addition of magnesium nitrate. The entire transformation from aluminum hydroxide to active alumina was performed at 550 °C, and the crystallinity of the product was confirmed by powder XRD analysis.²⁷A1 MAS NMR result shows the phase of mesoporous alumina is the γ-alumina form.     

Template-directed synthesis of boron nitride nanotube arrays by microwave plasma chemical reaction

Highly-ordered boron nitride (BN) nanotube arrays have been synthesized by microwave plasma-enhanced chemical vapor deposition (MW-PECVD) below 520 °C under the confinement of anodic aluminum oxide (AAO) template with borane/argon and ammonia/nitrogen as precursors. The low growth temperature and aligned arrangement of the BN nanotubes are beneficial to practical applications despite of the amorphous nature of the product. Novel morphology of Y-branching and dendriform BN nanotubes were also observed when the branching AAO template was used.     

Preparation of boron nitride-based coatings through thermal diffusion process

ABSTRACT

Preparation of boron nitride (BN)-based coatings for friction and corrosion conditions has been proposed and made through the thermal diffusion process following chemical vapour deposition principles. It includes the formation of gaseous B- and N-based species due to high-temperature reactions (decomposition) in the B- and N-rich powders with consequent deposition of B and N onto the heated substrate and their diffusion into the substrate with formation and consolidation of a thin BN layer. The proposed process can be used for complex-shape components employing simple production equipment.     

Room temperature synthesis of boron nitride thin films by dual-ion beam sputtering deposition

Boron nitride (BN) films are prepared by dual-ion beam sputtering deposition at room temperature (~25 °C). An assisting argon/nitrogen ion beam (ion energy E_i=0–300 eV) directly bombards the substrate surface to modify the properties of the BN films. The effects of assisting ion beam energy on the characteristics of BN films were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Raman spectra, atomic force microscopy, and optical transmittance. The density of the B–N bond in the film increased with the increase in assisting ion beam energy. The highest transmittance of more than 95% in the visible region was obtained under the assisting ion beam energy of 300 eV. The band gap of BN films increased from 5.54 eV to 6.13 eV when the assisted ion-beam energy increased from 0 eV to 300 eV.     

A simple,low cost,and template-free method for synthesis of boron nitride using different precursors

In this research, hexagonal boron nitride (h-BN) was synthesized using a simple, low cost, and template-free method with urea-boric acid (UB), melamine-boric acid (MB), and melamine-urea and boric acid (MUB) precursors, followed by the pyrolysis and heat treatment in a nitrogen atmosphere at 1050 °C. Samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Raman Spectroscopy, Fourier transform IR (FT-IR), and Brunauer–Emmett–Teller (BET) techniques. The specific surface areas obtained for h-BN synthesized by UB, MB, and MUB precursors were 87.43, 573.07, and 1005.7 m²/g, respectively. The average diameters of the pores using the Barrett, Joyner, and Halenda (BJH) model were 37.78, 3.68, and 2.13 nm, respectively. A thermogravimetric analysis showed a wider range of decomposition temperatures after using three precursors for synthesizing h-BN. Crumpled, whisker, and flower-like morphologies for UB, MB, and MUB precursors were respectively found using FESEM investigations. The formation of h-BN within the MUB sample was confirmed using the XPS analysis with measured peaks of 398.5 and 190.6 eV belonging to N 1s and B 1s, respectively. Raman spectroscopy revealed a high-intensity peak in 1366 cm^?1 related to the E_2g mode for h-BN synthesized with MUB. Therefore, the results demonstrate that the employed method can increase the potential of using the h-BN porous powder with a high specific surface area as a lubricant, thermal insulation filler, anti-corrosion filler in paint coatings, adsorption of various gas and hydrocarbon molecules as well as its application in drug-delivery nanocarriers.     

Influence of boron nitride nanotubes on the damage evolution of SiCf/SiC composites

As-grown and BN-coated boron nitride nanotubes (BNNTs) were incorporated into SiC_f/SiC composites to produce nanotube-based hierarchical composites. In-depth studies on damage evolution reveal that early damage development are delayed owing to the restriction effects on crack propagations from as-grown and BN-coated BNNTs. Moreover, this delay effect is more pronounced from BN-coated BNNTs because BN-coated BNNTs/matrix interfacial bonding strength is low. Final failure of composites with as-grown BNNTs still comes much earlier compared with virgin composite due to strong fibers/matrix bonding enhanced by as-grown BNNTs. This premature final failure is remedied in large part in composites with BN-coated BNNTs because fibers/matrix bonding enhanced by as-grown BNNTs is weaken after the deposition of an interphase on nanotube surface. Additionally, the type, the number and the released energy level of damage mechanisms during the whole damage evolution after the incorporation of as-grown and BN-coated BNNTs were also discussed elaborately compared with virgin composite.