利用水热合成方法制备正交氮化硼微晶

利用水热方法制备了正交氮化硼微晶, 于400 ℃时制备的氮化硼结晶质量较高, 主要物相为正交氮化硼(oBN). 在反应原料中加入水合肼和氯化铵都有利于样品结晶质量的改善和产率的提高. 在合成氮化硼反应过程中, 适当减慢反应体系的升温速率有利于提高oBN的结晶质量和产率, 但是当升温速率过慢时, oBN的稳定性有所降低, 立方氮化硼(cBN)的稳定性则在一定程度上得到提高. 此外, 反应过程中的原料配比对样品的物相及其结晶质量也有很大影响.     

Effect of pH on the Hydrothermal Synthesis of BN Nanocrystals

Boron nitride (BN) has been synthesized using hydrothermal synthesis method. The experimental results showed that the pH value of the reaction solution has an important effect on the yield and phases of BN samples. As the pH value decreased, the content of cBN increased and the yield improved. The increase in cBN content is resulted from the conversion of oBN into cBN under hydrothermal condition, and the growth of cBN nanocrystals may due to the decrease in the reaction speed, thus the crystalline perfection of BN improved when the pH value decreased.     

Low-temperature solid state synthesis and in situ phase transformation to prepare nearly pure cBN

Cubic boron nitride (cBN) is synthesized by a low-temperature solid state synthesis and in situ phase transformation route with NH(4)BF(4), B, NaBH(4) and KBH(4) as the boron sources and NaN(3) as the nitrogen source. Furthermore, two new strategies are developed, i.e., applying pressure on the reactants during the reaction process and introducing the structural induction effect. These results reveal that the relative contents of cBN are greatly increased by applying these new strategies. Finally, almost pure cBN (～90%) crystals are obtained by reacting NH(4)BF(4) and NaN(3) at 250 °C and 450 MPa for 24 h, with NaF as the structural induction material. The heterogeneous nucleation mechanism can commendably illuminate the structure induction effect of NaF with face center cubic structure. In addition, the induction effect results in the cBN nanocrystals presenting obvious oriented growth of {111} planes.     

Phase transformation of boron nitride under hypothermal conditions

Phase transformation among different boron nitride (BN) phases in hydrothermal solution was investigated. It was found that hexagonal boron nitride (hBN) firstly formed in the solution at relatively low temperature (i.e., 220 °C). After that, a spot of hBN began to transform into wurtzite boron nitride (wBN) and cubic boron nitride (cBN) at 230 °C. More and more hBN converted into wBN and cBN with the increase in temperature, and this transformation process completed at 300 °C. In this paper, we have explained the mechanism of the above phase transformation by using a reported “puckering mechanism”.     

高温高压Li3N-hBN体系cBN转变的热力学分析

以经典热力学第二定律ΔG<0为依据,分析了静态高温高压触媒法合成立方氮化硼(cBN)过程中发生的可能反应.考虑温度和压强对反应物相体积的影响,计算了六方氮化硼(Li3N-hBN)体系中hBN+Li3N→Li3BN2,h BN→cBN及Li3BN2→Li3N+cBN反应在高温高压条件下的ΔG.结果证实,Li3BN2由Li3N与hBN在高温高压(T>1300 K,P>3.0 GPa)条件下反应得到,在cBN的合成(T=1600～1800 K,P=4.6～6.0 GPa)条件下,hBN和Li3BN2都有向cBN转化的倾向,但由hBN向cBN直接转变的反应自由能比Li3BN2分解生成cBN的反应自由能更负,反应的可能性更大.探讨了高温高压条件下立方氮化硼的转变机理。     

Multi-step Reaction Route Developed for Improving Crystallinity of Boron Nitride Nanoparticles

A multi-step reaction route was developed to synthesize boron nitride(BN) nanoparticles via the reaction between NaN₃ and BCl₃ in a benzene-thermal solution. By means of this route, the crystallinity of BN nanoparticles was improved via increasing the reaction steps. Meanwhile, a phase transformation from hexagonal BN(hBN) or turbostratic BN(tBN) to cubic BN(cBN) occurred, resulting in the increase of cBN content. Moreover, the content of cBN also slightly increased when the temperature was elevated from 265 ℃ to 280 ℃.     

Studying the growth of cubic boron nitride on amorphous tetrahedral carbon interlayers

The growth of cubic boron nitride (cBN) films on bare silicon and amorphous tetrahedral carbon (ta-C) layers prepared on silicon substrates was studied. The cBN films were prepared by radio frequency magnetron sputter deposition at approximately 870 degrees C. The original ta-C interlayers were graphitized and restructured under high temperature and possibly under ion bombardment during BN deposition. The majority of graphitic basal planes were nearly perpendicular to the surface of silicon substrates. The BN films grown on these restructured carbon layers were deposited with higher content of cubic phase and did not show delamination signs. Turbostratic BN (tBN) basal planes extended carbon basal planes and their edges served as cBN nucleation sites. The cBN films grown on textured ta-C interlayers were insensitive to the ambient environment. The residual sp(3)-bonded carbon phase confined in the interlayers probably acts as a diffusion barrier preventing the oxidation of dangling bonds near BN interface and thus precludes weakening the interface as a result of volume expansion. The carbon interlayers also improve the crystallinity of the oriented tBN because they are continuation of carbon graphitic basal planes so that the volume fraction of nitrogen-void (N-void) defects in the sp(2)-bonded BN intermediate layers is reduced. The strong sp(3)-bonded carbon matrix could thereto withstand large compressive stress and facilitates deposition of thicker cBN films.     

Thermal stability of cubic boron nitride films deposited by chemical vapor deposition

Thermal stability of well-crystallized cubic boron nitride (cBN) films grown by chemical vapor deposition has been investigated by cathodoluminescence (CL), Raman spectroscopy, and scanning electron microscopy (SEM) with the cBN films annealed at various temperatures up to 1,300 degrees C. The crystallinity of the cBN films further improves, as indicated by a reduction of the relevant Raman line width, when the annealing temperature exceeds 1,100 degrees C. Structural damage or amorphization was observed on the grain boundaries of the cBN crystals when annealing temperature reaches 1,300 degrees C. The CL spectra are found to be unchanged up to 1,100 degrees C after annealing at 500 degrees C, showing the stability of the cBN films in electronic properties up to this temperature. New features were observed in the CL spectra when annealing temperature reaches 1,200-1,300 degrees C.     

Comparison of Different Crucible Materials for the Growth of AlN Crystals

Choice of crucible material is a key issue during the growth of AlN crystal. The stabilities at high temperature and life-spans of boron nitride (BN) crucible,tantalum (Ta) crucible and tungsten (W) crucible were compared. Tantalum crucible behaved worse at high temperature and life-span was shortened as compared with the other two crucible materials. It was very crisp and easy to crack. In contrast,self-seeded AlN crystals with different morphologies could be obtained at different high temperatures using BN crucible. The boron nitride crucible was stable below 2200 ℃,above which it would decompose. Thus it was unsuitable for the bulky AlN crystal growth. Tungsten crucible could endure the temperatures higher than 2200℃. Unfortunately we could only get AlN polycrystallines using tungsten crucible. After 50～100 hours’ run,the crucible was destroyed completely due to the multiple deep cracks. XRD results of destroyed tungsten crucible indicated that the main phases are tungsten carbide and tungsten nitride.     

Interfacial study of cubic boron nitride films deposited on diamond

We have studied the nucleation and growth of cubic boron nitride (cBN) films deposited on silicon and diamond-coated silicon substrates using fluorine-assisted chemical vapor deposition (CVD). These comparative studies substantiate that the incubation amorphous/turbostratic BN layers, essential for the cBN nucleation on silicon, are not vital precursors for cBN nucleation on diamond, and they are inherently eliminated. At vastly reduced critical bias voltage, down to -10 V, cBN growth is still maintained on diamond surfaces, and cBN and underlying diamond crystallites exhibit an epitaxial relationship. However, the epitaxial growth is associated with stress in the cBN-diamond interfacial region. In addition, some twinning of crystallites and small-angle grain boundaries are observed between the cBN and diamond crystallites because of the slight lattice mismatch of 1.36%. The small-angle grain boundaries could be eliminated by imposing a little higher bias voltage during the initial growth stage. The heteroepitaxial growth of cBN films on different substrate materials are discussed in the view of lattice matching, surface-energy compatibility, and stability of the substrate against ion irradiation.     

Effects of boron nitride nanopowder on thermal,chemical and gas barrier properties of starch

Starch/boron nitride （starch/BN） bionanocomposites were prepared with the reinforcement of boron nitride nano powder by solution technique. The dispersion of BN in the starch was achieved by a continuous sonication process. The interaction between starch and boron nitride nanopowder was investigated by Fourier transform infrared （FTIR） spectroscopy. The structural properties of starch/BN bionanocomposites was studied by X-ray diffraction （XRD）. The high resolution transmission electron microscopy （HRTEM） was used for the study of dispersion of boron nitride in starch matrix and diffraction patterns were studied by selected area electron diffraction （SAED）. Thermal stability of the starch was increased with rising concentrations of boron nitride due to incorporation of rigid nano BN with starch matrix. The substantial reduction in oxygen permeability was obtained by increasing the concentration of BN. The biodegradability of synthesized bionanocomposites was measured by using activated sludge water. Further, it was noticed that, starch/BN bionanocomposites are resistant towards inorganic acids and bases. The tensile strength of starch/BN bionanocomposites was increased whereas; the water resistance property of the materials was decreased with increasing BN loading.     

Prepared Low Stress Cubic Boron Nitride Film by Physical Vapor Deposition

We present low stress cubic boron nitride (cBN) films with a transition layer deposited on the metal alloy substrates by tuned substrate radio-frequency magnetron sputtering. The films were characterized by Fourier transform infrared spectroscopy and transmission electron microscopy (TEM). The IR peak position of cubic boron nitride at 1006.3 cm⁻¹, which is close to the stressless state, indicates that the film has very low internal stress. The TEM image shows that pure CBN phase exists on the surface of the film. Several phases of boron nitride were found at the medium implantation dose. It is believed that the transition from the low ordered phases to cBN phase occurred during implantation.     

Hydrogenation of fragment cations produced by femtosecond laser ablation of boron nitride

Cations (positive ions) produced by laser ablation of boron nitride (BN) have been mass analyzed and the size-dependent hydrogenation reactivity is revealed for the first time. The main product cations determined by femtosecond laser ablation (fsLA) were a series of B(BN)(n)(+), with much lesser production of B(2)(BN)(k)(+) and N(BN)(m)O(+) series cations. Least-squares fitting of the relative yields of hydrogenated cations indicates that the yield of B(BN)(n)H(+) almost diminishes for n ≥ 5 and that of B(BN)(n)H(2)(+) increases as n increases. Based on the different n-dependence and electronic structures of B(BN)(n) and B(BN)(n)(+), B(BN)(n) is likely to be the precursor of B(BN)(n)H(+), and B(BN)(n)(+) that of B(BN)(n)H(2)(+). In contrast to fsLA, the production of H(+) by nanosecond laser ablation is not observed and the production of various cationic species makes it difficult to identify either the fragment species or their hydrogenated products. This observation highlights the significant efficiency of fsLA in producing H(+) (and presumably H) from the surface adsorbates.     

First-principles study of interaction between H2 molecules and BN nanotubes with BN divacancies

The interaction between H(2) molecules and boron nitride (BN) single-walled nanotubes with BN divacancies is investigated with density-functional theory. Our calculations reveal that H(2) molecules adsorb physically outside defective BN nanotubes, and cannot enter into BN nanotubes through bare BN divacancies because the energy barrier is as high as 4.62 eV. After the defects are saturated by hydrogen atoms, the physisorption behavior of H(2) molecules is not changed, but the energy barrier of H(2) molecules entering into BN nanotubes through the defects is reduced to 0.58 eV. This phenomenon is ascribed to hydrogen saturation induced reduction of electrostatic potential around the defects.     

毛刺状竹节结构氮化硼纳米管的合成与生长机理

以非晶硼和氧化镍纳米颗粒为原料,在氨气中1100℃下合成了毛刺状竹节结构的氮化硼纳米管. 利用X射线衍射和透射电镜研究了氮化硼纳米管的结构和形貌. 竹节结构纳米管表面的毛刺是六方氮化硼的纳米薄片. 提出了一种基于固态硼和气态二氧化硼扩散的毛刺形貌生长机理.     

Preparation and characterization of SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Na<Subscript>2</Subscript>O glass coated cBN abrasive particles via sol–gel route

SiO₂–Al₂O₃–Na₂O glass coated cubic boron nitride (cBN) abrasive particles were prepared by sol–gel technique. The results indicated that SiO₂–Al₂O₃–Na₂O glass was excellent material for oxidation protection of cBN abrasive grains because coefficient of thermal expansion of this glass closely matched that of cBN materials. The single particle compressive strength and impact toughness of this glass coated cBN abrasive particles were significantly increased. For the application of glass coated cBN abrasives to vitrified grinding wheels, it was evident that the glass coating provided high bonding strength between cBN abrasive grains and vitrified bond system.     

不同浓度KCl和NH4Cl溶液中H3BO3介稳区的性质

测定了H3BO3在0~25 ℃内于不同浓度KCl和NH4Cl溶液中的溶解度和超溶解度, 得到了H3BO3的介稳区宽度, 并推算出表观成核级数m, 给出了成核速率方程. 研究了KCl和NH4Cl对H3BO3介稳区性质的影响, 并对影响的机理进行了探讨. 结果表明, KCl使H3BO3介稳区向低温方向移动; NH4Cl使H3BO3介稳区向高温方向移动; 根据所得结论分析了KCl和NH4Cl在柴达木西部油田水析硼过程中的影响, 认为KCl和NH4Cl在蒸发过程中浓度的变化是造成硼分散析出而不能富集的因素之一.     

Synthesis of high quality inorganic fullerene-like BN hollow spheres via a simple chemical route

High quality inorganic fullerene-like boron nitride hollow spheres (100-200 nm) have been successfully synthesized via a simple chemical route with a 30-40% yield of BN hollow spheres.     

Synthesis of BN coatings on carbon fiber by dip coating

BN coatings were deposited on carbon fibers by dip coating method. The deposited coatings were characterized by scanning electron microscopy, Fourier‐transformed infrared spectroscopy, X‐ray photoelectron spectroscopy and X‐ray diffraction. The influence of temperature on composition and structure of the coatings was investigated. Composition and structure examinations revealed that the crystallinity of the coatings increased with the increasing temperature, and the coating is a mixture of little oxides, turbostratic boron nitride and hexagonal boron nitride. Furthermore, experiments were also conducted in order to describe the growth mechanism, thus forming the basis of future growth of BN coating on fibers by dip coating. Copyright © 2016 John Wiley & Sons, Ltd.     

不同处理方法对氮化硼负载铁基催化剂费托合成性能的影响

采用等体积浸渍法制备了三种氮化硼(BN)负载的铁基催化剂,将其用于费托合成反应中;结合XRD、TEM、FT-IR和H2-TPR等表征手段,研究了催化剂的物相结构、形貌特征、还原性能以及F-T合成反应性能。结果表明,Cu助剂加入不会破坏载体BN的物相结构,而硼砂的加入会提高载体BN的结晶度; Cu助剂和硼砂加入对催化剂形貌的影响不明显,但都会使所制备的负载型铁基催化剂还原温度降低。在n(H2_)/n(CO)=2.0、340℃、2 MPa和GHSV=1500 h~(-1)的条件下,三种催化剂Fe/BN、Fe/BNM和Fe-Cu/BN上的CO的转化率分别为12.3%、36.2%和31.6%,产物中甲烷选择性为57.9%、26.8%和44.7%。Fe-Cu/BN和Fe/BNM两种催化剂活性均比Fe/BN催化剂有所提高,表明BN负载的铁基催化剂可以通过加入助剂以及改善载体与活性组分之间的相互作用来提升其对F-T合成反应的催化活性。相关结果可为探索制备高活性的氮化硼基FT合成催化剂提供思路。