氮化硼/碳纤维复合织物的性能研究

将氮化硼粉末负载于碳纤维织物上,用扫描电镜和紫外分光光度计观察和测试了氮化硼/碳纤维复合织物的表面形貌和紫外漫反射性能。结果显示:有大量氮化硼负载于碳纤维织物上;在250～600 nm波长范围,氮化硼/碳纤维复合织物的紫外漫反射性能比纯碳纤维织物的更好。用网络分析仪测试了氮化硼/碳纤维复合织物的电磁屏蔽性能,发现负载了氮化硼的碳纤维织物的电磁屏蔽性能略弱于纯碳纤维织物。     

Synthesis of Boron Nitride Coating on Carbon Nanotubes

A method to synthesize boron nitride coating on the surface of carbon nanotubes (nanofibers) without damaging the tube walls has been developed. A reaction between boric acid and ammonia was performed at moderate temperatures on the surface of carbon nanotubes to form boron nitride (BN) coatings. The surface structure of the carbon nanotubes significantly influences the morphology of the boron nitride coating. If the surface of the tubes is free of defects, highly crystallized insulating BN nanotubes can encapsulate carbon nanotubes. On the surface of carbon nanotubes with disordered wall structure, a polycrystalline BN sheath was produced.     

Influence of the thermal process of carbon template removal in the mesoporous boron nitride synthesis

Influence of the thermal process involved in the carbon template elimination during the synthesis of mesoporous boron nitride by using nanocasting process of a mesoporous CMK-3 carbon with a borazinic precursor is presented. The borazinic precursor, the tri(methylamino)borazine (MAB), is converted to boron nitride (BN) inside the mesopores of a CMK-3 mesoporous carbon template by ceramization under nitrogen or under ammonia. The carbon template elimination is carried out by thermal treatment under air or under ammonia. The X-ray diffraction, TEM and pore size analysis are used to study the texture of the boron nitride synthesized from the carbon template. A template elimination performed by hydrogenation with an ammonia treatment allows to obtain an organized porous structure, which is not possible by using an oxidation treatment. In order to preserve the mesoporous organization of boron nitride, a two steps procedure (ceramization followed with template elimination by hydrogenation) is more efficient than a one step procedure (ceramization and template hydrogenation simultaneously).     

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.     

The tribological performance of BCN films under ionic liquids lubrication

Boron carbon nitride films were deposited onto silicon substrates by medium frequency magnetron sputtering from graphite and boron targets with Ar and N₂ as feedstock. The three elements of B, C and N were bonded to each other and an atomic-level hybridized B–C–N had been formed in the films. The tribological performances of the boron carbon nitride film with 1-butyl, 3-methylimidazolium tetrafluoroborate ionic liquid as lubricant and the electrochemical corrosive behaviors of the BCN film were investigated. The boron carbon nitride film demonstrated excellent tribological properties and corrosion resistance as compared with diamond like carbon film. An extensive discussion of the effect of film intrinsically structure on both lubrication and corrosion under ionic liquid condition is given. In addition, the interrelation between the tribological properties and corrosion resistance is illustrated.     

有机前驱体法制备氮化硼纤维的研究进展

氮化硼纤维作为正在发展中的一种重要的高性能无机纤维,具有优异的耐高温和透波性能。目前高性能氮化硼纤维的制备主要采用类似于碳纤维生产的有机前驱体转化法。介绍了国内外合成氮化硼纤维前驱体的各种合成方法以及各种合成产物制备氮化硼纤维路线的优缺点,并对氮化硼纤维研究的发展趋势进行了展望。     

Ion implantation induced phase transformation in carbon and boron nitride thin films

The mechanism behind energetic ion impact induced stress reduction in highly stressed tetrahedral amorphous carbon and cubic boron nitride thin films is investigated by real time in situ spectroscopic ellipsometry and ex situ electron microscopy. Highly stressed carbon and boron nitride films were grown by filtered cathodic vacuum arc and RF magnetron sputtering, respectively. The films were then implanted by 5–10 keV argon ions and the film optical properties and thickness monitored in situ by spectroscopic ellipsometry. In both cases the films were observed to expand due to a reduction in the density of the ion-modified layer. Cross-sectional transmission electron microscopy and electron energy loss spectroscopy of the carbon films showed that this reduction in density is associated with a conversion of diamond-like bonding to graphite-like bonding. In situ stress measurements performed on the boron nitride films revealed a simultaneous reduction in stress with expansion of the material.     

Thermal properties and formation mechanism of h‐BN nanoneedles synthesized via carbothermic reduction reaction

Hexagonal boron nitride (BN) was synthesized through the carbothermic reduction reaction (CRR) of boric acid using lactose as a carbon source under the nitrogen atmosphere at 1500^°C for 3 hours. The boron/carbon (B/C) molar ratio was controlled during the CRR, and the produced samples were investigated by XRD diffraction pattern, FTIR analysis, and Raman spectra. Boron carbide (B₄C) was formed in samples that have a higher carbon content, in addition to boron nitride. While boron nitride pure sample was produced from lower carbon content samples. Formation of B₄C was found to depend on the B/C molar ratio. The morphology of the produced powder was also investigated by SEM and TEM, which revealed that the samples consist of nanoneedles of BN and hexagonal particles of B₄C. The vapor‐solid (VS) reaction mechanism was processed greatly with increasing boron amount, producing boron nitride nanoneedles, which compete with the liquid‐solid (LS) reaction mechanism. The physicochemical properties of the produced samples were studied by DTA, UV, PL, and AC impedance measurements, and revealed that the samples are promising to many proper applications.     

High density carbon fiber/boron nitride matrix composites: Fabrication of composites with exceptional wear resistance

This paper describes the fabrication of high density (ρ ∼ 1.75 g/cc) composites containing a hybrid (carbon and boron nitride), or complete boron nitride matrix. The composites were reinforced with either chopped or 3D needled carbon fibers. The boron nitride was introduced via liquid infiltration of a borazine oligomer that can exhibit liquid crystallinity. The processing scheme was developed for the chopped carbon fiber/boron nitride matrix composites (C/BN) and later applied to the 3D carbon fiber reinforced/boron nitride matrix composites (3D C/BN). The hybrid matrix composites were produced by infiltrating the borazine oligomer into a low density 3D needled C/C composite to yield 3D C/C-BN. In addition to achieving high densities, the processing scheme yielded d₀₀₂ spacings of 3.35 Å, which afforded boron nitride with excellent hydrolytic stability. The friction and wear properties of the composites were explored over the entire energy spectrum for aircraft braking using an inertial brake dynamometer. The C/BN composites outperformed both the previously reported C/C-BN and chopped fiber reinforced C/C. The high density 3D C/BN performed as well as both the 3D C/C and the C/BN. The 3D C/C-BN provided outstanding wear resistance, incurring nearly zero wear across the entire testing spectrum. The coefficient of friction was relatively stable with respect to energy level, varying from 0.2 to 0.3.     

High pressure synthesis of new heterodiamond phase

New heterodiamond phase (structure type of cubic boron nitride) with boron and nitrogen atoms partially substituted by carbon has been synthesized by using high pressure-high temperature treatment of the mixture of boron and C₃N₄ carbon nitride powders. This phase consisted of up to 5 micron-sized individual crystals. The composition of new phase was established with the help of microanalysis and structure refinement.     

Preparation and Use of a Boron Nitride Precursor as Binder for the Densification of Boron Nitride

A precursor of boron nitride was prepared through the partial condensation of 2,4,6-trichloroborazine and bis-(trimethylsilyl)acetylene. This reaction was conducted at 100°C and is catalyzed by AlCl₃. The condensation product pyrolyzed at 800°C, producing trimethylsilyl chloride as a volatile product and a boron nitride rich residue containing 54 wt% of the initial weight. Mixtures of the precursor and commercial boron nitride were made and hot-pressed at 800°C and 27.6 MPa. A maximum density of 1.84 g/cm³ is reached at a loading corresponding to the deposition of 13 wt% residue derived from the precursor. Examination by analytical electron microscopy, including X-ray energy dispersive spectroscopy and electron energy loss spectroscopy analyses, revealed the location of material derived from the precursor in BN-binder composites through the presence of residual aluminum, silicon, and carbon. Crystallization of boron nitride from the precursor appears to have taken place, as deduced from the morphology of the phases observed and association with residual elements present in the binder.     

Desintering Process in the Gas-Pressure Sintering of Silicon Nitride

A unique desintering phenomenon has been observed in gas-pressure sintering of silicon nitrides with additives of yttria and alumina. The desintering phenomenon occurred, simultaneous with weight increase, only when a boron nitride crucible was used in combination with the application of high nitrogen pressure (5 MPa). When the nitrogen pressure was low (0.5 MPa), or when the boron nitride crucible was replaced by a graphite crucible, this desintering phenomenon was not observed. These results could be rationalized by the chemical dissolution of nitrogen into the oxynitride melts and the resultant evolution of carbon monoxide. This indicates that the high nitrogen overpressure employed in gas-pressure sintering of silicon nitride ceramics is not always beneficial.     

Ultrasound exfoliation of inorganic analogues of graphene

High-intensity ultrasound exfoliation of a bulk-layered material is an attractive route for large-scale preparation of monolayers. The monolayer slices could potentially be prepared with a high yield (up to 100%) in a few minutes. Exfoliation of natural minerals (such as tungstenite and molybdenite) or bulk synthetic materials (including hexagonal boron nitride (h-BN), hexagonal boron carbon nitride (h-BCN), and graphitic carbon nitride (g-C₃N₄)) in liquids leads to the breakdown of the 3D graphitic structure into a 2D structure; the efficiency of this process is highly dependent upon the physical effects of the ultrasound. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) were employed to verify the quality of the exfoliation. Herein, this new method of exfoliation with ultrasound assistance for application to mono- and bilayered materials in hydrophobic and hydrophilic environments is presented.     

Role of the particle size of graphite-like boron nitride in nucleation of cubic boron nitride

The influence of the reduced radius of grains of the graphite-like hexagonal boron nitride (h-BN) on the nucleation of the cubic boron nitride (c-BN) during synthesis from an initiator solution at a high pressure is analyzed. The colloidal mechanism of nucleation is confirmed experimentally. It is shown that there is a correlation between the nucleus sizes of the hexagonal boron nitride and the pressure of the onset of nucleation of the cubic boron nitride. The effect of these sizes of the hexagonal boron nitride on the concentration of crystal nuclei of the cubic boron nitride is studied. The kinetic nucleation curves are obtained. It is demonstrated that the concentration of crystallization centers depends on the thermodynamic and kinetic parameters, as well as on the particle size of the graphite-like hexagonal boron nitride. Original Russian Text ? S.P. Bogdanov, 2008, published in Fizika i Khimiya Stekla.     

Effect of Interfacial Interaction on Morphology and Properties of Polyethylene/Boron Nitride Thermally Conductive Composites

In this study, polyethylene-g-maleic anhydride was utilized to enhance interfacial interaction between boron nitride and polyethylene. Moreover, KH550 was used as a surface treatment agent to improve interfacial interaction between boron nitride and polyethylene. It was found that surface functionalization of boron nitride particles and the addition of polyethylene-g-maleic anhydride can promote dispersion of boron nitride particles with reduced aggregation, resulting in the improvement of both tensile and impact strength of polyethylene/boron nitride composites. Compared to surface functionalization of boron nitride particles, the addition of polyethylene-g-maleic anhydride was much effective to enhance thermal conductivity of polyethylene/boron nitride composites and drop effectively rheological percolation threshold and gel point of polyethylene/boron nitride composites.     

氮化硼陶瓷纤维的制备与应用

氮化硼陶瓷纤维是一种正在发展的新型高性能材料,然而传统的高温法很难制备高质量的氮化硼陶瓷纤维材料,只能通过前驱体转化法实现。概述了氮化硼陶瓷纤维的合成路线以及各种前驱体制备氮化硼陶瓷纤维的优缺点,并对前驱体法制备氮化硼陶瓷纤维的发展趋势做了展望。     

Carbothermic formation of boron nitride

Formation of boron nitride by reaction of boric oxide with carbon and nitrogen was studied. It was found from the results of experiments conducted by holding B₂O₃-activated C mixtures under a flowing nitrogen atmosphere that formation of boron nitride was complete in 120 min at 1500 °C. After cleaning the reaction product from the ash of the activated carbon and from the unreacted B₂O₃ pure BN powder was obtained. B₄C was found to exist as an intermediate species in the reaction products of the experiments in which BN formation was not complete. The results of experiments conducted with the objective of gaining an insight into the reaction mechanism by using different geometrical arrangements show that liquid B₂O₃ and solid carbon need not be in contact in the formation of BN from B₂O₃, C and N₂ and indicate that the reaction proceeds through a gaseous boron containing species which is most probably B₂O₃(g).     

Excellent electrical conductivity of the exfoliated and fluorinated hexagonal boron nitride nanosheets

The insulator characteristic of hexagonal boron nitride limits its applications in microelectronics. In this paper, the fluorinated hexagonal boron nitride nanosheets were prepared by doping fluorine into the boron nitride nanosheets exfoliated from the bulk boron nitride in isopropanol via a facile chemical solution method with fluoboric acid; interestingly, these boron nitride nanosheets demonstrate a typical semiconductor characteristic which were studied on a new scanning tunneling microscope-transmission electron microscope holder. Since this property changes from an insulator to a semiconductor of the boron nitride, these nanosheets will be able to extend their applications in designing and fabricating electronic nanodevices.     

Polymeric Cyanoborane, (CNBH2)n: Single Source for Chemical Vapor Deposition of Boron Nitride Films

Polymeric cyanoborane, (CNBH₂) _n , is a material readily prepared by passing hydrogen chloride through an ether suspension of sodium cyanotrihydroborate. This polymeric material was volatilized in a CVD reactor to produce, at 600°C, amorphous films containing boron, nitrogen, and carbon. Residual carbon present in the films was removed by ammonia treatment at 800°C, producing nearly stoichiometric boron nitride films that were adherent to a variety of substrates including silicon.     

Reversed texture in nanometric carbon/boron nitride multilayers

A structure-controlled series of carbon/boron nitride multilayers, with bilayer thicknesses from 1.25 to 160 nm has been grown by sequential evaporation of carbon and boron assisted with nitrogen ions. The minimum bilayer thickness for a stable stack is 2.9 nm. A turbostratic texture of the carbon and BN phases is evidenced even for small periods of the bilayers. Interestingly, BN and C basal planes of adjacent sub-layers exhibit perpendicular alignment between them: along the growth direction for h-BN rich layers, and parallel to the surface for the C rich ones.