Ignition of fuel/air mixtures by radiatively heated particles

The current work examines the ignition of fuel/air mixtures by particles which have been heated up rapidly by intense electromagnetic radiation from an infrared laser source. Experiments have been conducted at relatively large beam sizes, where ignition times are a function of the irradiance. Particles in the form of fine powders were placed into a chamber filled with ignitable butane/air mixtures. Possible ignition is shown for a range of carbon based materials including different carbon blacks, graphite, the C₆₀ fullerene and diamond powder, as well as for non-reactive powders such as silicon carbide, iron-, copper- and silicon oxides. The irradiance was varied independently and results are shown to become independent of the size of the irradiated area if a sufficiently large area is illuminated. The particle size was found to have a significant impact on the time to ignition. Specifically, finer particles lead to shorter ignition times due to the higher surface area to volume ratio which reduces both particle and gas heating times. Ignition could be achieved across the whole flammability range of butane/air using carbon black and silicon carbide particles, although, near the rich flammability no ignition could be obtained with carbon black.     

导电炭黑微观结构及其应用性能

以乙炔炭黑、副产炭黑和炉法导电炭黑为研究对象,较为系统地分析了与导电炭黑应用性能密切相关的微晶结构、表面性质、颗粒形貌和粒度分布特征,探讨了导电炭黑微观结构对应用性能的影响。研究结果表明,导电炭黑的微观结构决定了其应用性能,而决定应用性能的关键在于其与基体材料的匹配性。副产炭黑在橡胶和塑料中导电性能较好,乙炔炭黑在锂离子电极材料中的导电性能较好。     

A positron annihilation study of carbon black and carbon-black-filled polybutadiene

Studies have been made on positron lifetimes in carbon blacks and carbon black filled polybutadiene. The results for the carbon blacks can be interpreted with the aid of the theoretical results of Brandt and Paulin: Phys. Rev. B5, 2430 (1972) and show that while positron annihilation occurs principally from a bound state, diffusion in the carbon black is extremely small. A numerical upper limit on the diffusion coefficient has been obtained. The data from the rubber is discussed with the aid of a specially developed extension of the previous theory. Here one finds that whereas the variations in the long-component intensity with carbon black loading can be very satisfactorily explained, there is again no evidence for any diffusion effects in the rubber, and an upper limit can be placed on the diffusion coefficient here also. Indeed the variation in the long-component intensity with particle size goes the opposite way to what one would expect if diffusion were dominant. This effect is attributed to the increase in the amount of bound rubber as the particle size is reduced, and the consequent increase in the number of annihilation sites.     

Solid-state NMR investigation on mica-filled rubber composites

Rubber composites filled with carbon black and mica flakes were investigated by solid-state NMR and dynamic mechanical measurements. The results show that in rubber (butyl, EPDM, and chloroprene) and rubber composites filled with mica flakes there exists an interphase of considerable fraction with a different T₁ρ value from the matrix. The hindered segmental motion in this interphase appears in the dynamic mechanical measurement with a high and broad tan δ and a high loss modulus E". The value of E" increases with increasing percentage of mica.     

Simulation of Electrical Resistivity of Carbon Black Filled Rubber under Elongation

It has been known that the carbon black (CB) network is responsible for the electrical and mechanical behaviors of filled rubber. Due to the complexity involved in the filled rubber in relation to the conductive mechanism of the CB network, there has been little work concerned with simulation of the electrical behavior at large strains. Based upon an infinite circuit model, the electrical resistivity of CB filled rubber under elongation is simulated. For CB (N330) filled natural rubber with volume fraction of 27.5%, the simulated electrical resistivity increases with elongation at small stains, corresponding to the breakup of the agglomerates. The reduction in resistivity at larger strains corresponds to the decrease of the junction width, which results in a decrease of the contact resistance. Good agreement is found between the simulations and the experimental data available in the literature. The simulated results confirm the effects of the breakdown of the CB network and the alignment of CB aggregates under strain on the electrical resistivity.     

Actuation behavior of waterborne polyurethane/conductive filler nanocomposite electrode

This study dealt with the Maxwell stress effect of waterborne polyurethane (WPU)/conductive filler nanocomposite, which was a promising candidate for a material to be used in a dielectric elastomer actuator electrode. Conductive nanocomposites were produced by using three types of conductive filler: carbon black (CB), vapor grown carbon fiber (VGCF), and silver powder (Ag). Among them, conductive nanocomposite containing VGCF exhibited the lowest threshold concentration; and the mixture of CB and VGCF (CB/VGCF) filler had a synergistic effect to electrical conductivity. Actuation test revealed that CB/VGCF nanocomposite electrode had the largest displacement. Then it could be stated that the improvement of the displacement in CB/VGCF nanocomposite electrode originated from the increase in relative dielectric constant. In addition, a unique feature for the hysteresis of bending deformation was observed. This feature is that the prior application of an electric field significantly improves the bending speed in the successive application. Also, the effect of electrode thickness on the displacement and breakdown strength was examined.     

Static and dynamic non-linear behaviors of carbon particle filled polymers with positive thermal coefficient

Polymers filled with conductive particles like carbon black, short carbon fibers or microbeads, may exhibit a very large positive thermal coefficient of the electrical resistance when they are heated above room temperature. Such a behavior is particularly useful in industrial applications for producing electrical safety devices. We present a comprehensive study of the electrical properties of epoxies filled with carbon microbeads when heating is achieved by the Joule effect. In that case, the electrical responses up to a large enough electrical excitation must be non-linear as a result of progressive heating of the material. As expected, we have found that it depends on both the 'intrinsic' properties of the sample (essentially a function of the composition) and the extent of thermal coupling between the investigated sample and the external thermal bath (variable heat leak). We have particularly studied the stationary states under constant applied voltage and the transients following a step like time dependent voltage. Most of our findings agree with the general results of percolation theory combined with theoretical models of rupture on a random fuse network and with a simple model of heat flow through the sample and from the sample to the thermal bath.     

Effect of Compression Pressure on the Ethylene Propylene Diene Terpolymer (EPDM)/Acrylonitrile Butadiene Copolymer (NBR) Rubber Blends Filled with Different Types of Carbon Black

Blends of ethylene-propylene diene terpolymer/acrylonitrile butadiene copolymer (EPDM/NBR) loaded with different types [(N326-HAF) and (N774-SRF)] and ratios of carbon black (CB) fillers were prepared. The mechanical properties of the EPDM/NBR rubber blends unloaded and loaded with different ratios of CB were investigated. Among the blends, the one with 75% EPDM and 25% NBR, both loaded and unloaded with CB, were found to exhibit the highest tensile strength and elongation at break. The observed changes in the mechanical properties of the blends were correlated to the morphology as observed by scanning electron microscopy. The changes of the electrical resistivity of the rubber blend composites during compression were investigated. The experimental results were explained from the position that an external pressure induces either an increase or decrease of the resistivity of the blend composites according to whether annihilation or creation of effective conductive paths occurs, respectively.     

Effect of carbon source on the carbothermal reduction for the fabrication of ZnO nanostructure

Surface area effect of carbon source on the carbothermal reduction for the fabrication of ZnO nanostructure was investigated. For a systematic comparison, graphite and three kinds of carbon black powder were used as source materials for the carbothermal reduction. Depending on the surface area, the carbothermal reduction at 800 °C for 30 min resulted in Zn-silicate island or ZnO nanorod at the same experimental condition. These structures were characterized with a scanning electron microscopy, a transmission electron microscopy, an energy dispersive spectroscopy and an X-ray photoelectron spectroscopy. The results show that the reducing power of ZnO_(s) source into Zn_(g) vapor is strongly dependent on the surface area of carbon source, and that the fabrication of ZnO nanostructure can be performed more efficiently by using carbon source with large surface area.     

Effect of Carbon Black Nature on Vulcanization and Mechanical Properties of Rubber

The influence of the basic properties of carbon black, such as structure, panicle size, and surface activity on the vulcanization and mechanical properties of filled natural rubber compounds was investigated in detail. This is important for a better understanding of the rubber performance and the mechanism of reinforcement. In particular, the effect of carbon black surface activity, which was changed by introducing one kind of hindered amine light stabilizer on rubber reinforcement is emphasized.     

Effect of mesoporous carbon containing binary conductive additives in lithium ion batteries on the electrochemical performance of the LiCoO2 composite cathodes

Binary conductive additives (BCA), formed by sonication of mesoporous carbon (MC) and acetylene black (AB), were used as conductive additives to improve the electrochemical performance of a LiCoO₂ composite cathode. The electrochemical performance of the LiCoO₂ composite cathode dispersed with BCA was investigated. The results showed that the electrochemical performance (including the discharge capacity, the discharge voltage and the total internal resistance) of a BCA loaded LiCoO₂ composite cathode was better than that of a cathode loaded with AB. The possible mechanism is that the MC in BCA can adsorb and retain electrolyte solution, which allows an intimate contact between the lithium ions and the cathode active material LiCoO₂ due to its large mesopore specific surface area. A simplified model was also proposed.     

Synthesis of carbon black/polystyrene conductive nanocomposite. Pickering emulsion effect characterized by TEM

In this study, carbon black/polystyrene electrically conductive composites were obtained by suspension polymerization technique. The composite was characterized using transmission electron microscopy, which indicated two outstanding features concerning to the carbon black; first, that the carbon particles were adsorbed onto the surface of the polystyrene particles, similarly as in the Pickering emulsion phenomenon and second, that the primary aggregate structure of the carbon black was significantly affected by the dispersion process. On the other hand, the composite resistivity was in the order of 200 Ωcm, which was attributed to the direct contact of primary carbon black particles (percolation) and not to the tunneling effect. The obtained composite was evaluated as the electrically conductive element in SBR matrix.     

Dielectric Spectroscopy of Anisotropic Polypropylene/Nylon‐66 Blends Containing Carbon Black

The relationships of the dielectric properties and structure of polypropylene (PP)/nylon (Ny) blends containing carbon black (CB) were studied. Dielectric anisotropy was found in blends exhibiting an oriented fibrillar Ny network covered by CB particles. In the Ny fibril direction the composites are conductive, while in the perpendicular direction they are insulating, as indicated by the different frequency dependence of the AC conductivity in the two orthogonal directions. However, once CB is located within both the Ny and the PP the dielectric behavior is isotropic. This was further confirmed by Cole‐Cole plots, which, for the first time, were found to fit numerical predictions of the “resistor‐capacitor” (RC) model. The CB network formed upon the surface of the Ny fibrils is denser and/or better structured than that formed within the Ny phase. Thus, the former can be envisioned as a 2D system, as suggested by the values of the scaling exponents of the AC conductivity and permittivity with frequency, which have a lower activation energy for charge transport. The dielectric measurements were found helpful in elucidating the CB network structure.     

Effects of the Synergy of Hardness and Resilience on the Akron Abrasion Properties of SBR Vulcanizates

The hardness (H) and resilience (R) of rubber vulcanizates were combined together in this paper, named as hardness–resilience product (H⁴R), and its relationship with the Akron abrasion loss was investigated using various styrene-butadiene rubber (SBR) vulcanizates possessing specific hardness and resilience characteristics as samples. For the unfilled SBR vulcanizates with different chain microstructure, possessing high elastic resilience and low hardness, the results showed that their Akron abrasion loss had a good linear relationship with the log(H⁴100R). This linear relationship also occurred when these SBRs were filled with 50 phr carbon black. For two particular types of SBR, after being filled with different fractions of carbon black and aged for different times, all their Akron abrasion losses (including unaged, aged for 24 h, and aged for 48 h) also had a good linear relationship with the log(H⁴100R). However, this linear relationship weakened for one of the SBRs after being aged for 48 h. In the high H⁴R region (the carbon black fractions being 60 and 70 phr), the data obviously deviated from the fitting curve due to the high hardness of the aged vulcanizates. However, after being filled with 50 phr of various kinds of carbon blacks, the relationships between abrasion loss and log(H⁴100R) were also approximately linear, with the correlation coefficient of the fitting curves being 0.99966 and 0.99878, respectively, for the two types of SBR.     

Characterization of Nano‐Particles Using Laser‐Induced Incandescence

Laser‐induced incandescence (LII) is introduced as a valuable tool for the characterization of nanoparticles. This optical measurement technique is based on the heating of the particles by a short laser pulse and the subsequent detection of the thermal radiation. It has been applied successfully for the investigation of soot in different fields of application, which is described here in the form of an overview with a focus on work done at the LTT‐Erlangen during the last 10 years. In laboratory flames the soot primary particle size, volume concentration, and relative aggregate size have been determined in combination with the number density of primary particles. Furthermore, the primary particle sizes of carbon blacks have been measured in situ and online under laboratory conditions and also in production reactors. Measurements with different types of commercially available carbon black powders, which were dispersed in a measurement chamber yielded a good correlation between LII results and the specified product properties. Particle diameters determined by LII in a furnace black reactor correlate very well with the CTAB‐absorption number, which is a measure for the specific surface area. It turned out that the LII method is not affected by variations of the aggregate structure of the investigated carbon blacks. The LII signal also contains information on the primary particle size distribution, which can be reconstructed by the evaluation of the signal decay time at, at least, two different time intervals. Additionally, soot mass concentrations have been determined inside diesel engines and online measurements were performed in the exhaust gas of such engines for various engine conditions simultaneously providing information about primary particle size, soot volume, and number concentration. The LII results exhibit good correlation with traditional measurement techniques, e.g., filter smoke number measurements. In addition to the soot measurements, primarily tests with other nanoparticles like TiO₂ or metal particles are encouraging regarding the applicability of the technique for the characterization of such different types of nanoparticles.     

微纳混合结构黑硅的制备及其关键工艺技术讨论

黑硅是一种能大幅提高器件光电转换效率的新型电子材料,微纳混合结构黑硅是一种比普通黑硅材料更高效的新型黑硅材料,如何制备出大面积、形貌特征好、表面洁净度高的黑硅材料是制备高效的黑硅太阳能电池的前提。首先,利用湿法腐蚀方法,通过设计合适的反应固体装置和良好的工艺控制手段,在金字塔硅表面制备了大面积的微纳混合结构黑硅;然后,对其制备的关键工艺技术进行了研究讨论。实验结果表明,该方法制备的微纳混合结构黑硅具有形貌特征好、表面洁净度高和低表面反射率等特征。有效去除表面银沉积物后,该黑硅在300~1 100 nm范围内的加权平均反射率低至4.06%。该制备工艺方法适用于大面积高效微纳混合结构黑硅的规模制备,在高效黑硅太阳能电池领域具有重要的应用价值。     

倾斜直流场下的介质板击穿统计分析

传统分析介质板次级电子倍增问题的粒子追踪算法方法存在运算耗时长、运算量大等缺点,为此采用统计方法实现了倾斜强直流场下介质击穿过程中次级电子倍增效应的数值模拟,给出了击穿过程中电子数量,电子渡越时间等关键参数的时间图像,同时研究了倾斜角、介质表面光滑度和次级电子产生率对次级电子倍增效应的影响。研究结果表明:强直流场下的次级电子倍增效应存在倾斜角的区域,倾斜角太大或者太小,都可能不会发生次级电子倍增效应,如果倾斜角位于区域内,则饱和状态时电子数目随着倾斜角度的变大而变小;选取光滑系数和次级电子产生系数越小的介质材料,抑制次级电子倍增效应的效果越好。     

Hollow Silica Spheres Embedded in a Porous Carbon Matrix and Its Superior Performance as the Anode for Lithium‐Ion Batteries

Silica (SiO₂) is regarded as one of the most promising anode materials for lithium‐ion batteries due to the high theoretical specific capacity and extremely low cost. However, the low intrinsic electrical conductivity and the big volume change during charge/discharge cycles result in a poor electrochemical performance. Here, hollow silica spheres embedded in porous carbon (HSS–C) composites are synthesized and investigated as an anode material for lithium‐ion batteries. The HSS–C composites demonstrate a high specific capacity of about 910 mA h g^?1 at a rate of 200 mA g^?1 after 150 cycles and exhibit good rate capability. The porous carbon with a large surface area and void space filled both inside and outside of the hollow silica spheres acts as an excellent conductive layer to enhance the overall conductivity of the electrode, shortens the diffusion path length for the transport of lithium ions, and also buffers the volume change accompanied with lithium‐ion insertion/extraction processes.     

Influence of filler type on wet skid resistance of SSBR/BR composites: Effects from roughness and micro-hardness of rubber surface

The wet skid resistance (WSR) of SSBR/BR(solution styrene-butadiene rubber/butadiene rubber) composites filled with carbon black, silica, and nano-diamond partly replacing carbon black or silica, respectively, was measured with a portable British Pendulum Skid Tester (BPST). A dynamic mechanical thermal analyzer was used to obtain the viscoelasticity of the composites. A 3D scanning white-light interfering profilometer was used and the scratch test performed to characterize surface roughness and micro-roughness, respectively, of the composites. WSR of the silica-filled composite was better than that of the carbon black-filled one, and further enhancement of WSR was obtained by replacing silica with nano-diamond. Tan δ of the composites at 0 °C, 10 Hz, and tensile strain of 2% did not show good correlation with WSR. The surface roughness of the composites had effects on WSR. The scratch test indicated that the higher the hardness of the filler in the composite, the higher the micro-hardness and the better the WSR. Therefore, the surface micro-hardness of the composites is an important factor affecting WSR, besides viscoelasticity and surface roughness.     

Carbon sphere as a black pigment for an electronic paper

Carbon black, a black material popular for use in electronic paper, could limit the performance of the electronic paper due to its non-uniform structure. Carbon spheres, with spherical shape and relatively narrow size distribution, are expected to overcome this limitation and substitute for carbon black in the electronic paper. Carbon spheres were synthesized through a hydrothermal reaction using glucose as a raw material. By controlling reaction time and glucose concentration, appropriate non-agglomerated carbon spheres with an average diameter of 202.26 (±26.15) nm were fabricated. To increase their dispersibility in dielectric fluid, p-(2-ethylhexyl acrylate) was grafted onto the surface of the carbon spheres. Then, acid and base charge control agents were mixed with the carbon spheres to produce a pigment with higher mobility in the dielectric fluid. The optimized combination of pigment, charge control agent and solvent reveals reasonably fast switching time of about 540 ms.