The influence of the pyrolysis process on mechanical parameters and tightness of the black glasses layers on titanium substrates

Black glasses are amorphous materials in which structure Si–O bonds coexist with Si–C bonds. The substitution of divalent oxygen ions by tetravalent carbon ions causes the change of properties, especially mechanical ones. The materials were obtained from the sol-gel synthesized ladder-like polysilsesquioxane organosilicon precursors. After deposition on titanium substrates and ceramization, continuous and hermetic layers were obtained. Adhesion, Young's modulus, hardness, roughness and corrosion resistance were examined as the most relevant mechanical properties of the obtained layers. Nanoindentation, surface mapping, electrochemical, SEM and confocal microscope measurements results are discussed in relation to the pyrolysis temperature of the black glasses layers.     

Effect of Carbon Containing Materials on Pure Carbon Reaction-bonded SiC

Petroleum coke, graphite, gas carbon and lower sulfur carbon black were used to prepare reaction-bonded silicon carbide. The influences of different carbon containing materials on properties of carbonaceous precursors, sintering process, and microstructure of the prepared SiC were researched. The results show that ： （ 1 ） With the density of carbon containing materials increasing, the porosity of carbonaceous precursors decreases and the infiltrating process of liquid silicon is more difficult. （2） The reaction between carbon containing materials and liquid silicon, the volume effect is more obvious with the density of carbon containing materials increasing. （3） As the carbon containing materials density decreasing, residual carbon in reaction bonded SiC also decreases.     

Improving of Micro Porous Layer based on Advanced Carbon Materials for High Temperature Proton Exchange Membrane Fuel Cell Electrodes

This work reports the study of four different carbon materials for their application as carbon material in microporous layers for high temperature proton exchange membrane fuel cells electrodes. The microporous layers were prepared with carbon black (a commercial one, Vulcan XC72), two different carbon nanofibers, CNF, (Ribbon and Platelet structure) and carbon nanospheres, all of them prepared in our lab. The microporous layers were characterized by XRD. The hydrophobicity, electrical conductivity, and permeability to different gases were also evaluated. The stability is an important issue to be overcome in the field of proton exchange membrane fuel cells. Thus, accelerated thermal and electrochemical degradation tests in phosphoric acid media were carried out to evaluate the stability of the different advanced materials tested under the same conditions. From all the performed essays, the carbon nanospheres were the best nano‐carbon materials because of the lower degradation degree shown by the microporous layer prepared with them and the good conductivity and permeability achieved, whereas CNF with a Platelet structure showed a low electrochemical stability due to their greater edge plane exposure which favors their corrosion.     

Effect of dopant precursors on the optical properties of rare-earths doped oxyfluoride glass-ceramics

The crystallization of fluoride nanocrystals (NCs) in chemically and mechanically stable aluminosilicate glasses has shown interesting optical properties even for small crystal fractions (10-15 wt%). When rare-earth (RE) ions are used as dopants, crystal-like features can be reproduced and an increase in the emission and/or energy transfer processes, with respect to the starting glasses, is observed. A crucial point for these materials is the study of the local surrounding of RE ions and their incorporation in the NCs. In fact, the effective concentration in the NCs can be much higher than the nominal concentration, up to one order of magnitude or even higher. The knowledge of RE ions incorporation in the NCs permits choosing proper doping levels to optimize both linear and nonlinear optical properties. In this work, transparent oxyfluoride glass-ceramics with LaF₃ NCs, doped with Nd³⁺ and Er³⁺ using oxide and fluoride precursors, were prepared using the melt-quenching method and controlled crystallization. The local surrounding of the RE ions was studied using X-ray absorption spectroscopy, electron paramagnetic resonance and photoluminiscence. The results show that most RE ions are already in a fluorine-rich amorphous environment even in the initial glass. The crystallization process provokes the RE ion redistribution and incorporation in the fluoride NCs. The different RE precursors, used as oxides or fluorides, have an influence on the incorporation of the RE in the NCs and, as a consequence, on the final optical properties.     

Mechanical behavior of two-dimensional carbon/carbon composites with interfacial carbon layers

Effect of interfacial carbon layers on the mechanical properties and fracture behavior of two-dimensional carbon fiber fabrics reinforced carbon matrix composites were investigated. Phenolic resin reinforced with two-dimensional plain woven carbon fiber fabrics was used as starting materials for carbon/carbon composites and was prepared using vacuum bag hot pressing technique. In order to study the effect of interfacial bonding, a carbon layer was applied to the carbon fabrics in advance. The carbon layers were prepared using petroleum pitch with different concentrations as precursors. The experimental results indicate that the carbon/carbon composites with interfacial carbon layers possess higher fracture energy than that without carbon layers after carbonization at 1000°C. For a pitch concentration of 0.15 g/ml, the carbon/carbon composites have both higher flexural strength and fracture energy than composites without carbon layers. Both flexural strength and fracture energy increased for composites with and without carbon layers after graphitization. The amount of increase in fracture energy was more significant for composites with interfacial carbon layers. Results indicate that a suitable pitch concentration should be used in order to tailor the mechanical behavior of carbon/carbon composites with interfacial carbon layers.     

Electrochemical properties of graphene nanosheet/carbon black composites as electrodes for supercapacitors

Graphene nanosheet/carbon black composites were prepared by the ultrasonication and in situ reduction methods. Microstructure measurements show that most carbon black particles deposit on the edge surfaces of nanosheets by the ultrasonication method, and on the basal surfaces of nanosheets by in situ reduction method. The electrochemical performances of hybrid materials are superior to pure graphene material, demonstrating that carbon black particles as spacers ensured the high electrochemical utilization of graphene layers as well as the open nano-channels provided by three-dimensional graphene nanosheet/carbon black hybrid material. Therefore, the resulting composite is a promising carbon material for supercapacitors.     

掺杂和密闭透窗对炸药激光起爆感度的影响

用Bruccton法测定了掺杂碳黑和碳纳米管的RDX和PETN炸药的起爆阈值,同时比较了K9玻璃和蓝宝石两种玻璃透窗下激光起爆感度的区别,以及自由振荡和调Q两种激光模式对RDX和PETN起爆感度的影响.结果表明,掺杂碳黑和碳纳米管均可提高RDX和PETN的感度,碳黑的掺杂效果好于碳纳米管,其中掺杂质量分数1%碳黑的RD...     

Nanostructural Characterization of Silicon Oxycarbide Glasses and Glass-Ceramics

Silicon oxycarbide glasses were synthesized by the sol-gel process using precursors such as methyl-, propyl-, and phenyltrimethoxysilanes. The final products contained 14–38 wt% carbon. A TEM study on the nanometer scale revealed that all of the materials were amorphous and monophasic, and that it was not possible to detect any crystalline or otherwise distinct carbon phases. Hot-pressing the glasses led to the crystallization of graphite and silicon carbide within the amorphous matrix. X-ray and electron diffraction showed increasing crystallinity at the higher hot-pressing temperatures. Hot pressing at 1400°C resulted in the appearance of fine-grained silicon carbide, whereas at the highest temperature (1650°C), graphite and both hexagonal and cubic silicon carbide were produced. Subsequent heat treatment of the hot-pressed glasses under an argon atmosphere at 1400°C resulted in the formation of cristobalite. The glass-ceramics produced at the highest hot-pressing temperatures were more resistant to the crystallization of cristobalite during subsequent heat treatments.     

The influence of carbon atom distribution in precursors with 1:1 carbon to silicon atoms ratio on structure and thermal evolution of obtained silicon oxycarbide based materials

In this work, a number of precursors with 1:1 silicon to carbon atoms ratio and various carbon atom distributions were synthesized and pyrolyzed in order to obtain silicon oxycarbide based materials. The different carbon atom distributions were obtained using both simple monomers with only one silicon atom, as well as large monomers containing either four or sixteen silicon atoms with predefined carbon atom positions. The silicon oxycarbide based materials were investigated using IR, XRD, ²⁹Si MAS NMR and elemental analysis after annealing at various temperatures, as well as TG. The research shows that carbon atom distribution has great impact on the structure of final material and can be used to tailor the material for its projected uses.     

Surface behaviour of high MgO-containing glasses of the Si–Ca–P–Mg system in a synthetic physiological fluid

Two glasses of the Si–Ca–P–Mg system with low SiO₂ content (25 and 29 mol%) and high MgO contents (31 and 36 mol%, respectively) have been immersed in a Kokubo’s synthetic physiological solution for different times up to 30 days. The surface modifications of the glasses were observed by SEM and the changes in the surface composition followed by EDS. ICP was used to assess the evolution of ionic concentrations in the solution, namely Ca and P.It was observed that both glasses induced the precipitation of Ca–P rich layers on their surfaces, although these were poorly attached to the glass substrate. Ca and P ions required for the apatite formation were mainly provided by the composition of the glass, which was severely dissolved in the solution.The observed apatite-forming ability of these glasses, notwithstanding their high MgO content, suggests that further improvements at the surface and in the glasses can lead to attractive potentially bioactive materials.     

纳米炭黑填充Lyocell基碳纤维的结构与性能

采用纳米炭黑填充Lyocell纤维制备碳纤维,并对纤维的结构与性能进行了分析。结果表明:经过不同温度预氧化处理后和最终得到的碳纤维的X射线衍射图谱中都保留着纳米炭黑的特征衍射峰;填充纳米炭黑的Lyocell基碳纤维的力学性能显著提高,填充质量分数10%纳米炭黑的Lyocell基碳纤维强度和模量分别比未填充的提高45%和56%;纳米炭黑填充的Lyocell基碳纤维结构致密、表面光洁,没有明显的裂纹和缺陷。     

Influence of carbon on the synthesis of AlN powder from combustion synthesis precursors

AlN powders were synthesized by carbothermal reduction of combustion synthesis precursors. Water-soluble organics and carbon black were used as carbon sources. The effects of carbon on the synthesis of AlN powders were studied. Results showed that AlN powders were synthesized directly from γ-Al₂O₃ without γ-Al₂O₃ to α-Al₂O₃ phase transition when water-soluble organics were used as carbon sources, and the nitridation of the precursors could be completed at 1400 °C. However, AlN powders were synthesized from the nitridation of α-Al₂O₃ when carbon black was used as carbon source, and the reaction temperature for a complete conversion increased to 1500 °C. The particles of AlN powders synthesized with water-soluble organics was smaller than the particles of AlN powders synthesized with carbon black and their particle size distribution was sharper. The specific surface area of synthesized AlN powders increased with the increase of carbon content in the precursors.     

Nanodiamond nucleation below 2273 K at 15 GPa from carbons with different structural organizations

Five precursors covering the whole range of carbon structural organization, i.e. a quasi-amorphous soot (QAS), a raw carbon black (CB), a carbon black heat-treated at 2600 °C (HTCB), a polycrystalline graphite (PCG) and a highly oriented pyrolytic-graphite (HOPG) were run at 15 GPa in the 1500-1900 °C range between 15 and 60 min. Full transformation into nano-diamonds was not always achieved and the corresponding run products preserved the tracks of the transformation mechanisms which led to diamond formation. These mechanisms and their kinetics were characterized combining X-ray powder diffraction, Raman micro-spectroscopy and high-resolution TEM. Globally, the disordered precursors react faster than the crystalline ones: they achieve higher transformation rates and become transparent more easily. For the spherical CB particles, nano-diamond preferentially nucleates in their centre. The graphitic layers in the QAS directly transform into diamond without any prior graphitization. The crystalline organization is even found to decrease for the graphitized precursors (HTCB and PCG) as evidenced by HRTEM images showing graphite delamination. These precursors mostly evolve according to a diffusion-limited reconstructive mechanism which initiates at the precursor structural defects. HOPG behaves differently since it mostly transforms into lonsdaleite rather than cubic diamond.     

不同炭黑对聚丙烯／炭黑复合材料导电性能的影响

研究了四种不同的导电炭黑与聚丙烯复合制得的复合材料的体积电阻率与炭黑含量的关系，确定了复合体系中炭黑的渗滤阈值。用扫描电镜(SEM)观察了不同炭黑含量的复合材料的断面形貌，用透射电镜(TEM)观察分析了四种炭黑的结构及粒径，并对其比表面积进行了测定。结果表明：炭黑不同，得到的复合材料的渗滤阈值有很大差别。炭黑结构性越高，比表面积越大，粒径越小，其导电性能越好，得到的渗滤阈值越低。特别是具有空壳结构的炭黑，其渗滤阈值明显低于其他三种炭黑。     

生物质基碳气凝胶的研究进展

碳气凝胶是一种新型的纳米多孔碳材料,具有孔隙率高、比表面积大、导电性能优良、耐高温等优点,在催化剂载体、电容器及吸附材料等领域具有广阔的应用前景。与传统的碳气凝胶相比,生物质基碳气凝胶具有前驱体环保可再生的优势,可为生物质高值化、功能化利用提供新思路。本文在简单介绍生物质基碳气凝胶制备过程（包括溶胶-凝胶化、干燥、炭化）的基础上,重点介绍了3类来自不同生物质前驱体（植物纤维素、细菌纤维素和具有三维多孔结构的植物本身）碳气凝胶的制备方法,并对碳气凝胶及其复合材料在催化剂载体、吸附材料、超级电容器、锂离子电池方面的应用进行了综述,最后对生物质基碳气凝胶的研究方向和发展前景进行总结和展望。     

Growth of carbon nanotubes on natural organic precursors by chemical vapor deposition

Some plant tissues are rich in transition metal Fe. So, we explored the use of black jew’s-ear fungus and black sesame seeds as catalyst precursors to prepare carbon nanotubes by chemical vapor deposition. Each catalyst particle arises from the metal content of a single cell of the precursor, hence the distribution of catalyst particles is uniform. Their size and composition are almost identical. Carbon nanotube arrays can grow when black sesame seeds are used as catalyst precursors. Carbon nanotubes with diameters 80 nm and length greater than 100 μm can grow when black jew’s-ear fungus are used.     

Hydration and reaction mechanisms on sodium silicate glass surfaces from molecular dynamics simulations with reactive force fields

Recent development of reactive force fields have enabled molecular dynamics simulations of interactions between silicate glasses and water at the atomistic scale. While multicomponent silicate glasses encompass a wide variety of compositions and properties, one common structural feature in these glasses is the combination of the network structure that is made up of silica tetrahedra linked through corner sharing interspersed with network modifiers like alkali and alkaline-earth ions that break up the Si–O–Si linkages by forming nonbridging oxygen. In reactions with water, ion exchange between alkali ions in the glass and proton or hydronium in the solution, as well as hydrolysis reaction of the Si–O–Si linkages and subsequent silanol formation, is observed and well documented. We have used a set of recently developed reactive force field to investigate the reactions between water and the surfaces of silica and sodium silicate glasses of different compositions for reactions up to 8 nanoseconds. Our results indicate sodium leaching into water and diffusion of water molecules up to 25 Å into the glass surface. We examined the structural and compositional changes inside the glass and around the diffused ions and use these to explain the rates of silanol formation at the surface. We also observed proton transport in the glass which has an indirect influence on the silanol formation rates. While the surface of the glass was rough to start with, it undergoes further modification into a hydrated gel-like structure in the glass for up to 5 Å in the higher alkali containing glasses. It was found that the leached sodium ions remain close to the interface and that fragments of silicate network from the surface is capable of dislodging from the bulk glass and enter the aqueous solution. These simulations thus provide insights into the formation and structure of an alteration layers commonly observed in multicomponent silicate glasses corroded in aqueous solutions.     

电容器电极用新型炭材料的研究进展

综述了活性炭电极材料的性质与电容器性能的关系,介绍了不同原料制备的活性炭、改性活性炭、活性炭纤维、炭纳米管及炭黑等用于电容器电极材料的研究进展。最后,阐述了电容器电极用炭材料的发展趋势。     

填料对硅橡胶包覆层耐烧蚀性能的影响

利用田口方法中的望小特性研究了４种填料对硅橡胶包覆层耐烧蚀性能的影响。结果表明：白炭黑对线烧蚀率影响高度显著,随着白炭黑添加量的增加,硅橡胶耐烧蚀性能变差;三氧化二铁加入量增加能提高硅橡胶耐烧蚀性能。     

硫掺杂炭材料的制备与应用

杂原子掺杂可以改变炭材料的表面化学结构,从而带来材料性能的变化。研究人员通过选择不同的碳源、开发新的制备技术等手段,相继制备了多种结构独特、性能优异的硫掺杂炭材料。本文基于硫掺杂炭材料国内外的最新研究进展,总结了以不同碳前体制备硫掺杂炭材料的研究工作,评述了不同前体及制备工艺对硫掺杂炭材料组成、结构的影响;并简要介绍了硫原子掺杂对炭材料在超级电容器、电催化等方面应用性能的影响。有关硫掺杂炭材料的研究还是一个全新的课题,尽管研究人员已经做了大量努力,但如何控制材料的结构仍然是一个具有挑战性的课题,利用富碳前体做原料来控制制备硫掺杂炭材料对于规模化应用更具实际意义。