Kinetics of electrical conductivity of TATB detonation products as an indicator of growth of carbon nanoparticles

Two stages of growth of electrical conductivity of detonation products of plastic-bonded TATB are registered: a fast stage with a characteristic time of 0.1 μsec, which is commensurable with the time of chemical reactions, and a subsequent slow stage, which lasts for 0.5–1.0 μsec until specimen unloading begins. Under the assumption of the thermal mechanism of conductivity emergence, the second stage could be caused by an increase in temperature due to slow energy release in the course of growth of carbon nanoparticles in explosion products. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 92–98, January–February, 2007.     

Carbon Cloth Reinforced Carbon Aerogel Films Derived from Resorcinol Formaldehyde

Carbon cloth reinforced RF (Resorcinol Formaldehyde) aerogel films have been produced with extremely high RC ratio (molar ratio of resorcinol to catalyst) or with no catalyst at all. The gels were subcritically dried. Carbon aerogel films were obtained by pyrolysis of the RF aerogel films. The structure of the composite porous films was investigated using infrared spectrometer, optical and electron scanning microscope. The IR measurements indicated that the bottom surface reflectance of the films is higher than the top surface. The microscopical pictures revealed that the bottom surface of the films has a denser structure than the top surface, and the presence of carbon cloth in the sol-gel process strongly influences the structure of the films. The carbon cloth fibers act as catalytic sites. The particles are more likely to form around the fibers instead of within the sol. This leads to a somewhat reduced specific surface area as was shown via N₂ sorption and BET analysis.Using the 4-probe method the electrical conductivity of the carbon cloth reinforced carbon films was found to be higher than that of pure carbon aerogel films.     

Enhanced electrical conductivity in graphene-filled polycarbonate nanocomposites by microcellular foaming with sc-CO2

Electrically conductive polycarbonate (PC) foams containing a low concentration of graphene nanoplatelets (0.5 wt.%) were produced with variable range of expansion ratio by applying a high-pressure batch foaming process using sc-CO₂. The structure of the foams was assessed by means of SEM, AFM and WAXS, and the electrical conductivity was measured in the foam growing direction. Results showed that electrical conductivity of PC composite foams remarkably increased when compared to that of non-foamed PC composite, with both the electrical conductivity and the main cell size of the foams being directly affected by the resultant expansion ratio of the foam. This interesting result could be explained by the development of an interconnected graphene nanoparticle network composed by increasingly well-dispersed and reoriented graphene nanoplatelets, which was developed into the solid fraction of the foam upon foaming by sudden depressurising of the plasticised CO₂-saturated PC preform. Some evidences of morphological changes in the graphene nanoplatelets after foaming were obtained by analysing variations in graphene’s (0?0?2) diffraction plane, whose intensity decreased with foaming. A reduction of the average number of layers in the graphene nanoplatelets was also measured, both evidences indicating that improved dispersion of graphene nanoparticles existed in the PC composite foams. As a result, foams with a proper combination of low density and enhanced electrical conductivity could be produced, enabling them to be used in applications such as electromagnetic interference shielding.     

合成工艺对聚吡咯电导率及可溶性的影响

研究了聚吡咯(PPy)的化学氧化合成，制得了粉末状的聚吡咯样品，并对样品进行了表征。讨论了合成温度、添加剂、氧气对聚吡咯电导率的影响以及聚吡咯的可溶性问题。实验表明：低温、无氧气存在和加入聚乙二醇(PEG)等合成条件有利于电导率的提高；在有十二烷基苯磺酸(DBSA)存在的情况下，聚吡咯可溶于间甲酚。     

On minimum mass transfer at a sintered metal electrode

Limiting diffusion currents were measured at the inner surface of sintered nickel electrodes sheets and a model adapted from heterogeneous catalysis was used to quantify the minimum mass transfer within the porous material. External mass transport from the bulk electrolyte was induced by rotating a disc facing the sintered nickel disc electrode located at the bottom of a cylinder. Values of the volumetric mass transfer coefficient at two sintered materials were thus obtained. The method and its limitations are discussed.     

导电硅橡胶导电性和电热性的研究

对乙炔炭黑作导电填料的导电硅橡胶的导电性和电热性进行了研究。结果表明，由乙炔炭黑用量和渗滤阈可以预测和控制导电硅橡胶的体积电阻率；导电硅橡胶的电阻－温度变化规律符合隧道效应理论模型，导电硅橡胶的电压－电流特性呈非线性欧姆性，且乙炔炭黑用量越大，电压－电流特性的非线性欧姆性越显著；发热量与热损耗量达到平衡时，导电硅橡胶的表面温度可维持140℃，导电硅橡胶可作面状发热体使用；在满足导电性能的前提下，为保证导电硅橡胶良好的物理性能，应控制乙炔炭黑用量。     

导电炭黑/氯化丁基橡胶力学和电性能的研究

通过共混法制备了导电炭黑/氯化丁基橡胶复合材料,研究了复合材料的拉伸性能与导电、介电性能。研究发现,随着导电炭黑和硫化剂含量的增加,拉伸强度先出现一个极大值随后下降,在炭黑用量为5%,硫化剂用量为3%时,拉伸强度最大,为9.1 MPa;而断裂伸长率一直下降。当导电炭黑超过5%以后,电导率迅速增加,出现渗流现象。介电常数实部ε′和介电损耗因子tanδ随导电炭黑用量的增加而增大,但当导电炭黑用量较高(20%)时,在高频时,ε′和tanδ都下降。     

Copper-doped mesoporous activated carbons as electrode material for electrochemical capacitors

Cu-doped activated carbon composites were prepared from phenolic resins by a doping method. The structure and specific capacitance of Cu-doped activated carbon composites were investigated using nitrogen gas adsorption and constant current cycling (CCC) methods. The pore size distributions of activated carbon-Cu series indicated that the doped Cu had no drastic effect on the structure of ACs. The percentage of copper in the composite electrode was less than 1 wt. %. It was found that the AC-Cu series had higher capacitance than that of activated carbons; even though their BET surface area was not larger than that of the AC ones. The Cu-doped activated carbon composite prepared by activating at 800 °C for 2 h had high capacitance (120 F g⁻¹) which was more than 25% than that of the ACs. XRD and TEM showed that copper existed in the form of oxidation state and the diameter of particles was under 100 nm.     

Preparation of polyaniline and studying its electrical conductivity

Polyaniline was prepared by chemical methods. Its electrical conductivity was measured. The electrical conductivity of polyaniline salt and polyaniline base were compared with composites prepared by the hot press of polyaniline base with KBr, Co(CH₃COO)₂, and picric acid. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1658–1665, 2000     

Bubble shape,gas flow and gas–liquid mass transfer in pulp fibre suspensions

Gas–liquid mass transfer in pulp fibre suspensions in a batch‐operated bubble column is explained by observations of bubble size and shape made in a 2D column. Two pulp fibre suspensions (hardwood and softwood kraft) were studied over a range of suspension mass concentrations and gas flow rates. For a given gas flow rate, bubble size was found to increase as suspension concentration increased, moving from smaller spherical/elliptical bubbles to larger spherical‐capped/dimpled‐elliptical bubbles. At relatively low mass concentrations (C_m = 2–3% for the softwood and C_m ? 7% for the hardwood pulp) distinct bubbles were no longer observed in the suspension. Instead, a network of channels formed through which gas flowed. In the bubble column, the volumetric gas–liquid mass transfer rate, k_La, decreased with increasing suspension concentration. From the 2D studies, this occurred as bubble size and rise velocity increased, which would decrease overall bubble surface area and gas holdup in the column. A minimum in k_La occurred between C_m = 2% and 4% which depended on pulp type and was reached near the mass concentration where the flow channels first formed.     

Evaluation of electrical conductivity models for conductive polymer composites

The electrical conductivity of polymeric materials can be increased by the addition of carbon fillers, such as carbon fibers and graphite. The resulting composites could be used in applications such as interference shielding and electrostatic dissipation. Electrical conductivity models are often proposed to predict the conductivity behavior of these materials in order to achieve more efficient material design that could reduce costly experimental work. The electrical conductivity of carbon‐filled polymers was studied by adding four single fillers to nylon 6,6 and polycarbonate in increasing concentrations. The fillers used in this project include chopped and milled forms of polyacrylonitrile (PAN) carbon fiber, Thermocarb^TM Specialty Graphite, and Ni‐coated PAN carbon fiber. Material was extruded and injection‐molded into test specimens, and then the electrical conductivity was measured. Data analysis included a comparison of the results to existing conductivity models. The results show that the model proposed by Mamunya, which takes into account the filler aspect ratio and the surface energy of the filler and polymer, most closely matched the conductivity data. This information will then be used in the development of improved conductivity models. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1341–1356, 2002     

环氧树脂/玻璃布/BN导热复合材料的制备与性能研究

采用高温模压成型法制备环氧树脂(EP)/玻璃布/氮化硼(BN)导热复合材料。探讨了BN用量和偶联剂处理对复合材料力学性能、导热性能和介电性能等影响。结果表明:当w(BN)=15%时,复合材料的冲击强度较高;导热性能随着BN用量的增加而增大;当w(BN)=25%时,改性复合材料的热导率为0.901 2 W/(m.K),此时复合材料仍保持较低的介电常数和介电损耗。当BN用量相同时,偶联剂表面处理可有效改善复合材料的力学性能和导热性能。     

微通道反应器的一维放大及气液传质特性

微通道反应器能有效增强气液间传质,但处理能力受限。为了提高微通道的处理量,对微通道反应器的一维放大及气-液传质特性进行了研究。以乙醇胺（MEA）和甲基二乙醇胺（MDEA）混合水溶液吸收CO₂为研究物系,在通道深度恒定时,考察了微通道宽度、气液流速对传质特性的影响。结果表明,传质系数和体积传质系数均随通道宽度先增大后缓慢减小,在通道宽度为1000 μm时达到最大值。比表面积随通道宽度的增大而降低。因此,合理增大微通道宽度,可在提高处理能力的同时,仍然保持良好的传质特性。     

在搅拌槽中含惰性颗粒的液液固三相体系的液液传质特性

在化工、石油、冶金等工业中普遍涉及多相体系,近年来新的化学反应不断应用于工业生产,出现不少新的复杂多相体系,如液液固、气液液等．在己内酰胺生产、浸取一萃取耦合操作、纳米颗粒制备等过程中都涉及液液固体系,但有关的化学工程研究似乎仍是空白．     

Polyaniline/polyimide blends as gas sensors and electrical conductivity response to CO–N2 mixtures

The effects of dopant type, doping level, polyimide (PI) content and temperature on electrical conductivity response of polyaniline (PANI) and polyaniline/polyimide (PANI/PI) blends to CO–N₂ gas mixtures were systematically investigated. At the same doping level, HNO₃‐doped PANI has a greater electrical conductivity response and sensitivity towards CO than that of camphor sulfonic acid (CSA)‐doped PANI because the former has a more ordered structure. The interaction mechanism between CO and PANI is proposed to occur at the attack site, ? N?H? or the amine nitrogen where CO withdraws an electron. Addition of PI causes a small change in electrical conductivity under atmospheric conditions when PI content is below the percolation threshold value of 55 wt%. Addition of PI reduces brittleness and improves electrical conductivity sensitivity towards CO; the effect is more pronounced at higher temperatures. Copyright © 2005 Society of Chemical Industry     

Investigation of the reaction zone in heterogeneous explosives substances using an electrical conductivity method

A technique for measuring the electrical conductivity profile behind a detonation wave front with a resolution of about 0.1 mm was used to analyze the reaction zone in heterogeneous explosives. TNT-RDX mixtures, RDX with additives of water, NaCl, and a saturated aqueous solution of NaCl, and pure RDX of low density were studied. It was shown that the particle size of the explosive can have a significant effect on the structure of the reaction zone. The most narrow conducting zone (0.22 mm) was observed in fine RDX of density 1.2 g/cm³. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 2, pp. 109–115, March–April, 2008.     

A new equation for predicting electrical conductivity of carbon‐filled polymer composites used for bipolar plates of fuel cells

In this article, a statistical‐thermodynamic formula based on a new approach has been developed to predict electrical conductivity of carbon‐filled composites used for bipolar plate of proton exchange membrane fuel cell. In this model, based on percolation threshold phenomenon, it is assumed that the relationship between electrical conductivity of composite and filler volume fraction follows a sigmoidal equation. Afterwards, the four effective factors on composite conductivity including filler electrical conductivity, filler aspect ratio, wettability, as well as interface contact resistance are replaced upon constant parameters of sigmoidal function. In order to test the model, some single‐filler composites have been manufactured by using the phenolic resin as binder and graphite (G), expanded graphite (EG), and carbon fiber (CF) as fillers. The fitting quality is measured by R‐square, adjusted R‐square, SSE, and RMSE parameters. The results showed that there is a noteworthy agreement between the model and the experimental data. Compared to the other models, this model can be used for more types of fillers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of mineral fillers addition and preparation method on the morphology and electrical conductivity of epoxy/multiwalled carbon nanotube nanocomposites

This study investigated the correlation between the electrical conductivity and the micro and nanomorphology of multiwalled carbon nanotubes (MWCNTs)/epoxy nanocomposites with and without the inorganic fillers montmorillonite (MMT), sepiolite and calcium carbonate (CaCO₃). The nanocomposites were prepared by dispersing the MWCNT and fillers through ultrasonication directly in the resin or solvent. For nanocomposites without fillers, the compositions prepared with solvent demonstrated higher electrical conductivities, which correlate with a microscale morphology formed by networks of highly interconnected MWCNT agglomerates. The addition of MMT induced a deleterious effect on the electrical conductivity of the nanocomposites since this filler hinders the formation of MWCNT agglomerate networks. The effect of sepiolite on electrical conductivity is also negative, but in this case, nonmorphological effects are likely of greater importance. The addition of CaCO₃ improved the electrical conductivity of the binary nanocomposites under specific conditions. For this filler, a synergic effect was achieved for the composition prepared with solvent, which resulted in an approximately sixfold increase in electrical conductivity relative to the nanocomposite without filler.