Preparation and electrochemical characterization of activated carbons by chemical-physical activation

A process was proposed based on the combination of chemical and physical activation for the production of activated carbons used as the electrode material for electric double layer capacitor (EDLC). By material characterization and electrochemical methods, the influences of the activitation process on the specific surface area, pore structure and electrochemical properties of the activated carbons were investigated. The results show that specific surface area, the mesopore volume, and the specific capacitance increase with the increase of the mass ratio of KOH to char (m(KOH)/m(char)) and the activation time, respectively. When m(KOH)/m(char) is 4.0, the specific surface area and the mesopore volume reach the maximum values, i.e. 1 960 m²/g and 0.308 4 cm³/g, and the specific capacitance is 120.7 F/g synchronously. Compared with the chemical activation, the activated carbons prepared by chemical-physical activation show a larger mesopore volume, a higher ratio of mesopore and a larger specific capacitance. Foundation item: Project(2007BAE12B01) supported by the National Key Technology Research and Development Program of China     

Hydrogen sorption properties of nanocrystalline Mg2FeH6-based complex and catalytic effect of TiO2

The diversities of hydrogen sorption properties of Mg₂FeH₆-based complexes with and without TiO₂ were investigated. Mg₂FeH₆-based complexes with and without TiO₂ were synthesized respectively by reactive mechanical alloying, and hydrogen sorption properties of the complexes were examined by Sieverts-type apparatus. The results show that the sample without TiO₂ releases 4.43 % (mass fraction) hydrogen in 1.5 ks at 653 K under 0.1 MPa H₂ pressure and absorbs 90% of the total 4.43 % (mass fraction) hydrogen absorbed in 85 s at 623 K under 4.0 MPa H₂ pressure. But for the sample with TiO₂ addition under the same condition, it only needs 400 s to release all of the stored hydrogen and 60 s to absorb 90% of the total hydrogen absorbed. The activation energies for desorption process of the samples with and without TiO₂ are determined to be 71.2 and 80.3 kJ/(mol·K), respectively. The improvement in hydrogen sorption rate and and reduction in activation energy can be attributed to the addition of TiO₂.     

一种新的混沌神经网络及其应用

提出一种新的混沌神经元模型,该神经元的激励函数由复合正弦函数和Sigmoid函数构成,通过分叉图及Lyapunov指数的计算,分析了其动力学特征.基于该模型构造了一种新的暂态混沌特征神经网络,并将其应用于组合优化问题.仿真实验结果表明了该算法的有效性与可行性.     

激活能测试装置设计及微晶硅薄膜激活能测试

为了分析微晶硅薄膜的本征特性,设计了激活能测试装置。测试装置包括测试平台、真空系统和加热控制系统。同时给出激活能计算方法,并对不同电压、不同取点个数对激活能测试的影响进行分析。分析结果表明,不同测试电压对激活能测试结果影响很小,不同取点个数计算的激活能差别也很小。     

一种新的盲源分离拟开关算法

针对电子战中各种信号混叠严重难以分离的现象,在盲源分离开关算法基础上提出一种新的盲信源分离拟开关算法.该算法引入单位对称加权滑动向量来加权每次迭代所得的分离信号作为源信号,用峭度取代原算法的峭度符号位作为判断函数来自适应选择加权相应激活函数,以此优化学习算法,结合信号分选的具体应用,给出了迭代结束的评判方法.计算机仿真实验表明,在强噪声背景影响下,该算法能够更加有效地分离空间未知多源线性混叠信号,且在分离效果、稳定性、处理速度和抗噪性能上都比原算法有较大改进.     

Thermal activation and radiation quenching characteristics and their application to the pre-dose dating of porcelain

The pre-dose technique is important for thermoluminescence (TL) dating of porcelain. The principle of pre-dose dating is based on two characteristics: thermal activation and radiation quenching of the porcelain. Based on these principles, two measurement methods, "the activation method" and "the quenching method", respectively, have been developed for evaluation of the porcelain paleodose. The paleodose values obtained are the same for the ages in the range of 100―1000 a BP for porcelains measured by these two methods. But for dating at lower age limits (less than 100 a BP), the activation method is more accurate; conversely, at higher age limits (greater than 1000 a BP) the quenching method is more accurate. In addition, two specific calculating methods are described for a few porce-lains having anomalous activation and quenching characteristics that make these two methods invalid.     

Discrimination for ablative control mechanism in solid-propellant rocket nozzle

The ablation in solid-propellant rocket nozzle is a coupling process resulted by chemistry, heat and mass transfer. Based on the heat and mass transfer theory, the aero-thermo-dynamic, and thermo-chemical kinetics, the thermal-chemical ablation model is established. Simulations are completed on the heat flow field and chemical ablation in the nozzle with different concentrations, frequency factors and activation energy of H2. The calculation results show that the concentration and the activation energy of H...     

Investigation of conductivity characteristics of nitrile butadiene rubber vulcanizates filled with semiconducting carbide ceramic

SiC‐ and B₄C‐filled NBR rubber composites were prepared with various volume fractions of filler by a conventional roll‐mill method. The morphological structures of the NBR–SiC and NBR–B₄C composites were analyzed by scanning electron microscopy. The dependence of room‐temperature volume resistivity (ρ_v) on the concentration of filler in the two systems was studied. In addition, variation in the number of current carriers (n), mobility carriers (μ), dielectric constant (ε), and dielectric loss factor (tan δ) on filler concentration in the two systems were investigated in detail. The applicability of composites as negative temperature coefficient (NTCR) linear thermistors was studied by the dependence of volume resistivity on temperature. The resistivity showed negative temperature dependence and changed linearly with temperature parallel. The conduction mechanism of the conductivity of the two composites was analyzed in terms of the computed activation energy and hopping energy. Change in volume resistivity as a function of frequency for the two systems was also investigated. Finally, the dependence of volume resistivity on applied pressure and possible real applications of these composites as transducers in pressure sensors were also studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2158–2165, 2007     

Cobalt-Molybdenum Sulfide Catalysts Prepared by In Situ Activation of Bimetallic (Co-Mo) Alkylthiomolybdates

Unsupported cobalt-molybdenum sulfide catalysts were prepared from bimetallic CoMo alkyl precursors by in situ activation during the hydrodesulfurization (HDS) of dibenzothiophene (DBT). The bimetallic CoMo precursors were prepared by reaction of tetraalkylammonium thiomolybdate salts, (R₄N)₂MoS₄ (where R = H, methyl, butyl, pentyl or hexyl), with CoCl₂ in water at a Co/Mo molar ratio of 0.3. These catalysts exhibit a Swiss-cheese-like morphology, high surface areas (from 52 up to 320 m²/g), high content of carbon (C/Mo = 2.2-3.3) and type IV adsorption-desorption isotherms of nitrogen. The in situ activation of these tetraalkylammonium thiobimetalate precursors leads to a mesoporous structure with pore size ranging from 2 to 4.5 nm. X-ray diffraction showed that the structure of unsupported cobalt-molybdenum sulfide catalysts corresponds to a poorly crystalline structure characteristic of 2H-MoS₂ with low-stacked layers. The nature of the alkyl group strongly affects both the surface area and the HDS activity. The catalytic activity is strongly enhanced when using carbon-containing precursors; the CoMo catalysts prepared by in situ activation of Co/[N(C₄H₉)₄]₂MoS₄ presents the highest HDS activity. The highest surface area of the catalysts was observed for the CoMo catalyst formed from Co/[N(C₆H₁₃)₄N]₂MoS₄.     

CORRELATION OF DIFFUSION COEFFICIENTS FOR LIQUIDS AND DENSE FLUIDS WITH TEMPERATURE AND PRESSURE

On the basis of the free volume theory and activation energy concept,a fundamental equation whichtakes into account the effects of temperature and pressure has been developed.By introducing differentexpressions for the free volume and activation energy,several equations for fluid diffusion coefficients were derivedaccordingly.With the van der Waals free volume and intermal energy formula,a three-parameter model for fluiddiffusion coeffficients at moderate pressure was obtained.The grand average absolute deviation percent of 345data points (44 systems)for self-and infinite dilute inter-diffusivities is 2.32,against the results of the model ofCohen and Turnbull,4.13.In particular,by means of the modified Carnahan-Starling free volume equation,afour-parameter model with average abosolute deviation percent 2.64(30 systems,644 data points)for theestimation of dense fluid inter-and self-diffusivities at high pressures and in supercritical conditions was derived.The derived model is superior to the method of L