Preparation of self-supporting nickel targets from Ni, Ni and Ni

The investigation of the distribution of the fusion-barrier height by heavy-ion collisions requires thin self-supporting targets. To increase the accuracy of the measurement the thickness and homogeneity has to be known as precisely as possible.We prepared the self-supporting nickel foils out of the isotopes ⁵⁸Ni, ⁶⁰Ni and ⁶¹Ni. The resulting targets were between 75 and 105 μg/cm^² thick. The foils were produced on copper backing by electron-beam gun evaporation and by extracted ion-beam sputtering, both in high vacuum. To obtain self-supporting nickel foils the copper was removed by etching. We will discuss and compare both methods.     

Facile synthesis of cubic boron nitride nanoparticles from amorphous boron by triple thermal plasma jets at atmospheric pressure

Cubic boron nitride (c-BN) is a superhard material, with hardness value comparable to that of diamond. c-BN is used in a wide range of industrial applications, including tool, abrasives, and refractory. The hardness of c-BN can be improved by decreasing the particle size to the nanoscale; however, the simultaneous application of high pressure (～8 GPa) and temperature (>2,500 K) is required to synthesize the c-BN crystal structure. In this study, we effectively synthesized c-BN nanoparticles from amorphous boron using a triple direct current (DC) thermal plasma jet system at atmospheric pressure. The injection of nitrogen as plasma forming gas generated reactive nitridation species. The average particle size of the synthesized c-BN was 22 nm, and the major crystal structure is the (1 1 1) cubic phase. We carried out a numerical simulation for a thermal fluid, to confirm the high temperature and velocity fields of the plasma jets that formed inside the reactor as the flow rate of plasma forming gas was adjusted. A high production yield of 51% was achieved using amorphous boron at a feed rate of 190 mg/min and the c-BN nanoparticles exhibited high crystallinity without requiring pre-and post-processing.     

Bio-inspired structured boron carbide-boron nitride composite by reactive spark plasma sintering

Nature creates composite materials with complex hierarchical structures that possess impressive mechanical properties enhancement capabilities. An approach to improve mechanical properties of conventional composites is to mimic the biological material structured ‘hard’ core and ‘soft’ matrix system. This would allow the efficient transfer of load stress, dissipation of energy and resistance to cracking in the composite. In the current study, reactive spark plasma sintering (SPS) of boron carbide B₄C was carried out in a nitrogen N₂ gas environment. The process created a unique core-shell structured material with the potential to form a high impact-resistant composite. Transmission electron microscopy observation of nitrided-B₄C revealed the encapsulation of B₄C grains by nano-layers of hexagonal-boron nitride (h-BN). The effect of the h-BN contents on hardness were measured using micro- and nano-indentation. Commercially available h-BN was also mechanically mixed and sintered with B₄C to compare the effectiveness of nitrided B₄C. Results have shown that nitrided B₄C has a higher hardness value and the optimum content of h-BN from nitridation was 0.4%wt with the highest nano-indentation hardness of 56.7 GPa. The high hardness was attributed to the h-BN matrix situated between the B₄C grain boundaries which provided a transitional region for effective redistribution of the stress in the material.     

Preparation of Pa targets

²³¹Pa is an alpha-emitter belonging to the actinide group. Because it is both toxic and highly radioactive, it requires special precautions during target fabrication. The isotopic material was available in the chemical form of dried nitrate. It had to be converted to Pa-oxide, which is our most favourable source material for the preparation of actinide targets. Targets in the thickness range between 70 and 100 μg/cm² were produced by cold crucible electron beam evaporation–condensation on different backings and target frames.     

海水淡化反渗透膜脱硼性能的研究

采用小型反渗透装置,研究各因素对海水反渗透膜(SWRO)脱硼性能的影响.结果表明:试验用海水膜脱硼性能优于苦咸水膜和FILMTEC海水膜;不调节pH下脱硼率为60％～80％,调节pH脱硼率可高达98％以上;pH≤8.0条件下,脱硼率随进水压力增大显著提高,当pH≥9.5则影响减小;此外,海水膜的脱硼率基本不受元件回收率和进水硼浓度的影响.因此,提高pH和进水压力能有效改善反渗透脱硼性能.     

Recent progress in boron nanomaterials

Abstract

Various types of zero, one, and two-dimensional boron nanomaterials such as nanoclusters, nanowires, nanotubes, nanobelts, nanoribbons, nanosheets, and monolayer crystalline sheets named borophene have been experimentally synthesized and identified in the last 20 years. Owing to their low dimensionality, boron nanomaterials have different bonding configurations from those of three-dimensional bulk boron crystals composed of icosahedra or icosahedral fragments. The resulting intriguing physical and chemical properties of boron nanomaterials are fascinating from the viewpoint of material science. Moreover, the wide variety of boron nanomaterials themselves could be the building blocks for combining with other existing nanomaterials, molecules, atoms, and/or ions to design and create materials with new functionalities and properties. Here, the progress of the boron nanomaterials is reviewed and perspectives and future directions are described.     

超细高能燃料无定形硼粉的自蔓延制备与表征

采用自蔓延高温合成(SHS)法,用高活性金属Mg粉还原B2O3粉,通过镁热还原反应B2O3 3Mg→2B 3MgO制备出超细高能燃料无定形硼粉,研究镁热还原工艺对还原产物的影响.采用X射线衍射仪对盐酸溶浸后的还原产物进行物相分析.结果表明:还原过程中生成的酸不溶物MgB6、BxO、Mg2SiO4、FeB49是影响硼粉纯度的主要杂质.利用费歇尔粒度测试仪(F.S.S.S)检测无定形硼粉的平均粒径和比表面积.通过优化制备工艺,在B2O3/Mg(质量分数,%)为3.0、反应体系温度为850℃的条件下,可制备出纯度高于94%、比表面平均粒径为0.5～0.7μm、比表面积达4～6m2/g的超细无定形硼粉.     

碳化硼材料研究进展

碳化硼陶瓷具有高硬度、高熔点和低密度的特点，是优异的结构陶瓷，在民用、宇航和军事等领域都得到了重要应用。研究了碳化硼结构陶瓷的优异性能和制备新工艺，综述了碳化硼材料的发展和研究现状，着重阐述了碳化硼陶瓷烧结的主要难点－致密化和韧化机理，提出利用原位自生法和前驱体热解法等新工艺制备纳米颗粒增强的碳化硼复合材料，是制备高性能碳化硼复合材料发展的新方向。     

聚苯胺膜的制备研究

为了得到性能优异的高分子导电材料,利用乳液聚合法制备了聚苯胺。系统地研究了各影响因素对聚苯胺电导率的影响。测试结果显示最佳制备条件为：过硫酸铵16．42g,盐酸12mL,十二烷基苯磺酸钠0．21g。聚苯胺的电导率可达0．78S／cm。以三氯甲烷做溶剂,以聚苯乙烯为成膜物可以制备导电聚苯胺的自支撑膜,通过扫描电镜分析表明聚苯胺粒度较为均匀。     

Investigation of Ti coatings on cubic boron nitride (cBN) grits by discharge treatment in spark plasma sintering system

The Ti coatings on cubic boron nitride (cBN) grits were prepared by discharge treatment on a mixture of Ti powders and cBN grits in spark plasma sintering system. The uniform and full coatings with a thickness of ～1.2 μm were prepared at 850 °C for 60 min, which were constituted with TiB₂, TiN, and Ti phases. The compressive fracture strength and toughness impact of the Ti-coated cBN grits were 11.6% and 7.4% higher than the cases of the pristine ones, respectively. With the aid of Ti coatings, the interface bonding strength between cBN grits and Fe-based matrix was improved by 335 MPa in the Fe-based matrix/cBN composites.     

Mechanism of nucleation and growth of cubic boron nitride thin films

The mechanism and the crystallography of the nucleation and growth of cubic boron nitride (c-BN) films deposited on 〈100〉-oriented silicon substrate by RF bias sputtering have been studied by means of cross-sectional high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Both methods provide experimental information showing no sp²-bonded BN layer formation in the subsurface region of c-BN phase. This is clear evidence for layer-by-layer homoepitaxial growth of cubic boron nitride without graphitic monolayers in the near-surface region of the film. The turbostratic boron nitride (t-BN) consists of thin sub-layers, 0.5–2 nm thick, growing in such a way that a sub-layer normal is almost parallel to the growth direction. t-BN also comprises a large volume fraction of the grain boundaries with high interface energies. The present result and the finding by Shtansky et al. [Acta Mater. 48, 3745 (2000)], who showed that an individual sub-layer consists of parallel lamellae in both the hexagonal +h-BN) and rhombohedral (r-BN) configurations, demonstrate that high intrinsic stress in the films is due to the complex structure of sp²-bonded BN. The crystallography of c-BN films indicates heteroepitaxial nucleation of cubic phase on the graphitic BN structural precursor. The present results are consistent with stress-induced c-BN formation.     

Mechanism of nucleation and growth of cubic boron nitride thin films

The mechanism and the crystallography of the nucleation and growth of cubic boron nitride (c-BN) films deposited on 100-oriented silicon substrate by RF bias sputtering have been studied by means of cross-sectional high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Both methods provide experimental information showing no sp²-bonded BN layer formation in the subsurface region of c-BN phase. This is clear evidence for layer-by-layer homoepitaxial growth of cubic boron nitride without graphitic monolayers in the near-surface region of the film. The turbostratic boron nitride (t-BN) consists of thin sub-layers, 0.5–2 nm thick, growing in such a way that a sub-layer normal is almost parallel to the growth direction. t-BN also comprises a large volume fraction of the grain boundaries with high interface energies. The present result and the finding by Shtansky et al. [Acta Mater. 48, 3745 (2000)], who showed that an individual sub-layer consists of parallel lamellae in both the hexagonal (h-BN) and rhombohedral (r-BN) configurations, demonstrate that high intrinsic stress in the films is due to the complex structure of sp²-bonded BN. The crystallography of c-BN films indicates heteroepitaxial nucleation of cubic phase on the graphitic BN structural precursor. The present results are consistent with stress-induced c-BN formation.     

先驱体法合成氮化硼研究进展

综述了无氧有机先驱体法合成氮化硼的研究进展 ,系统介绍了由硼烷、硼吖嗪、卤化硼合成氮化硼的工艺条件 ,及由这些化合物制备聚合物先驱体的合成途径及其陶瓷转化 ,概述了先驱体法待研究的问题 .     

Synthesis of an orthorhombic high pressure boron phase

The densest boron phase (2.52 g cm^-3) was produced as a result of the synthesis under pressures above 9 GPa and temperatures up to ∼1800 °C. The x-ray powder diffraction pattern and the Raman spectra of the new material do not correspond to those of any known boron phases. A new high-pressure high-temperature boron phase was defined to have an orthorhombic symmetry (Pnnm (No. 58)) and 28 atoms per unit cell.     

Synthesis of an orthorhombic high pressure boron phase

Abstract

The densest boron phase (2.52 g cm^-3) was produced as a result of the synthesis under pressures above 9 GPa and temperatures up to ～1800 °C. The x-ray powder diffraction pattern and the Raman spectra of the new material do not correspond to those of any known boron phases. A new high-pressure high-temperature boron phase was defined to have an orthorhombic symmetry (Pnnm (No. 58)) and 28 atoms per unit cell.     

碳化硼的热电性能

介绍了由Peltier效应和Seebeck效应发展起来的半导体热电材料的原理及其应用。碳化硼是最具港力的高温热电材料之一。本文总结了碳化硼热电性能的最新研究成果，提出了其作为高温热电材料应用的限制因素以及解决的可能途径。     

Molecular dynamics study of deposition mechanism of cubic boron nitride

We have performed molecular dynamics simulations of bombardment of graphitic boron nitride (gBN) by energetic boron and nitrogen particles in order to examine the roles of ion bombardment in ion/plasma-assisted deposition of cubic boron nitride (cBN) thin films. We have found that the interaction of the energetic particles with gBN creates four-fold coordinated local structures (sp³-formation) inside gBN. We have also found that clusters of sp³-formations are created as a result of successive bombardment, some of which have cBN-like structures. On the basis of these results, we propose an atomic-scale model of cBN nucleation in which successive sp³-formation converts gBN into cBN.     

Thin films of boron nitride grown by CVD

For the first time, thin films of boron nitride were deposited by chemical vapour deposition on to polished silicon and other metal substrates using the inorganic compound H₃BNH₃ (aminodiborane) and ammonia as carrier gas. The substrate temperature was varied from 400 to 600°C. The films were chemically inert and adherent to the substrates. The FTIR spectrum of the film showed B-N-B absorption at 800 cm⁻¹, B-N stretching at 1056 cm⁻¹, and also a weak absorption at 1340cm⁻¹ corresponding to B-N-B bending vibration. Deposited films also exhibited X-ray diffraction pattern with interplanar spacing with (002) plane of hexagonal boron nitride.     

氮化硼纳米管的研究现状

详细介绍了氮化硼纳米管自发现以来的研究情况,阐述了氮化硼纳米管的结构与性质,对目前已有的合成方法进行了归类与总结,同时分析了各自的优缺点,概述了其应用研究的进展情况,并提出了今后研究和应用的发展方向.     

On the strength of polycrystals of boron nitride dense modifications

An analytical algorithm for the calculation of stresses in polycrystals of boron nitride dense modifications has been described. The relations established between the tensile and compression strength have been based on the Griffith fracture hypothesis for a biaxial stressed state. The effect has been taken into account of technological residual thermal stresses, which are formed in wurtzitic boron nitride (wBN) grains in sintering at the stage of cooling because of the thermal expansion anisotropy, on the strength of wBN.